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    • 专利摘要:
    Abstract. A silicon carbide semiconductor device having a JFET or a MOSFETincludes a semiconductor substrate (5), a trench (6), a channel layer (7),and a second gate region (8). The semiconductor substrate (5) has asilicon carbide substrate (1), a drift layer (2) Von the silicon carbidesubstrate (1), a first gate region (3) on the drift layer (2), and a sourceregion (4) on the first gate region (3). The trench (6) has a strip shapewith a longitudinai direction and reaches the drift layer (2) by penetratingthe source region (4) and the firstgate region (3). The channel layer (7)is formed on an inner wall of the trench (6). The second gate region (8)formed on the channel layer (7). The source region (4) is not located atan end portion of the trench (6) in the longitudinai direction. i l-28-
    公开号:SE1051367A1
    申请号:SE1051367
    申请日:2010-12-22
    公开日:2011-06-26
    发明作者:Yuuichi Takeuchi；Rajesh Kumar Malhan；Naohiro Sugiyama
    申请人:Denso Corp；
    IPC主号:
    专利说明:

    v30SILICON CARBIDE SEMICONDUCTOR DEVICE AND METHOD OFMANUFACTURING THE SAMEDescriptionThe. present invention relates to a g silicon carbide (SiC)semiconductor device having a junction field-effect transistor (JFET) or ametal-oxide semiconductor field-effect transistor (MOSFET) with a trenchstructure and also relates to a method of manufacturing the SiCsemiconductor device. iA SiC semiconductor device having a JFET with a trench structurehas been disciosed, for example, in JP 2003-69041 'A or US 2005/0233539corresponding to JP 2005-328014 A. FIGS. 7A-7C iilustrates such aconventional SiC semiconductor device. FIG. 7A is a plan view of theconventional SiC semiconductor device, FIG. 7B is a cross-sectional viewtaken along the line VIIB-VIIB in FIG. 7A,5and FIG. 7C is a cross-sectionalview taken along the line VIIC-VIIC in FIG. 7A. gAs shown in FIGS. 7A-7C, after a n"-type drift layer J2, a p+-typefirst gate region J3, a n+-type source region J4 are formed, in turn, on an*-type SiC substrate J1, atrench J5 penetrating these is formed. Then,an n'-type channel layer J6 and a p+-type second gate region J7 areformed in the trench J5. Although not shown in the drawings, a gatevoltage applied to a gate electrode electrically connected to the secondgate region J7 is controlled so that a drain current can flow between asource electrodeelectrícally connected to the n+-type source region J4and a drain electrode electrically connected to the n+-type SiC substrateJ1. i In the above-described conventional SiC semiconductor device, asshown in FIG. 7A, each trench J5 has a strip shape, and the trenches J5are laid out in a stripe pattern. However, it has been confirmed that whenthe trenches J5 has a strip shape, an excessive drain current flows. FIG.8 is a characteristicdiagram obtained when a drain current characteristici with respect to a gate voltage of the SiC semiconductor device is_1_measured. As can be understood from FIG. 8, when the gate voltageapproaches a threshold for driving the JFET, the drain current starts toflow before the gate voltage exceeds the threshold. Due to the drain. current occurring near the threshold, an ideal JFET characteristic, in whichthe drain current does not start to flow until the gate voltage reaches thethreshold,_cannot be obtained. iIt has been confirmed that such a problem can occur not only in aJFET, but also in an accumulation mode MOSFET.
    In view of the above, it is an object of the present invention to _provide a SiC. semiconductor device having .a JFET or a MOSFET with atrench structure for reducing an excessive drain current occurring when agatevoltage approaches a threshold. It is another object of the presentinvention to provide a method of manufacturing the SiC semiconductordevice. I I IAccording to a first aspect of the present invention, a siliconcarbide semiconductor device having a JFET includes a semiconductorsubstrate including a first conductivity type silicon carbide substrate, a“ first conductivity type drift layer formed on the first conductivity type isilicon carbide substrate by epitaxial growth, a second conductivity typefirst gate region formed on the drift layer by epitaxial growth, and a firstconductivity type source region formed. on the first gate region byepitaxial growth or ion implantation. The silicon carbide semiconductordevice further includes a trench, a first conductivity type channel layer,and a second conductivity type second gate region. The trench has astrip shape with a longitudinal direction and reaches the drift layer bypenetrating the source region and the first gate region. The channellayer is formed on an inner wall of the trench by epitaxial growth. Thesecond gate region is formed on the channel layer. The source region isnot formed at an end portion of the trench in the longitudinal direction.The source region can be formed at a long side portion of the trench.According to a second aspect of the present invention, a silicon_2_2_5carbide semiconductor device having a MOSFET includes a semiconductorsubstrate including a first conductivity type silicon carbide substrate, afirst conductivity type drift layer formed on the first conductivity typesilicon carbide substrate by epitaxial growth, a second conductivity typebase layer formed on the drift -layer by epitaxial growth, and a firstconductivity type source region formed on the base layer by epitaxialgrowth or ion implantation. The silicon carbide semiconductor devicefurther includes a trench, a first conductivity type channel layer, a gateinsulation layer, and a gate electrode. The trenchhas a strip shape witha longitudinal direction and reaches the drift layer by penetrating thesource region and the base layer. The channel layer is formed on an innerwall of the trench by epitaxial growth. _ The gate insulation layer is formedon the channel layer. The .gate electrode is formed on a surface of thegate insulation layer in the trench. Thesource region is not formed at anend portion of the trench in the longitudinal direction. The source regioncan be formed at a long side portion of the trench.
    According to a third aspect of the present invention, a method ofe manufacturing a silicon carbide semiconductordevice having a JFET ~includes preparing a semiconductor substrate including a firstconductivity type silicon carbide substrate, a first conductivity type driftlayer formed on the first conductivity type silicon carbide substrate byepitaxial growth, a second conductivity type first gate region formed onthe drift layer by epitaxial growth, and a first conductivity type source iregion formed on the first gate region by epitaxial growth or ionimplantation. The method further includes forming a strip-shaped trenchhaving a longitudinal direction and reaching the drift layer by penetratingthe source region and the gate region, forming a first conductivity type-channel layer on an inner wall of the trench by epitaxial growth, forming asecond conductivity type second gate region on the channel layer,planarizing the channel layer and the second gate regionluntil the source~ region is exposed, and removing the source region, the channel layer, andthe second gate region at least at an end portion of the trench in the_3_'30longitudinal direction by performing selective etching after the planarizingso that the end portion of the trench has a recess shape with a depthgreater than a thickness of the source region. Instead of the removingi step, the method can include forming a second conductivity region havinga depth greater than a thickness of the source region at an end portion ofthe trench in the longitudinal direction after the planarizing in such amanner that the source region located at least at the end portion of thetrench is covered with the second conductivity region. ,According to a fourth aspect of the present invention, a method ofmanufacturing a silicon carbide semiconductor device having a MOSFETincludes preparing a semiconductor I substrate including a firstconductivity type silicon carbide substrate, a first conductivity type driftlayer formed on the first conductivity type silicon carbide substrate by Iepitaxial growth, a second conductivity type base layer formed on the driftlayer_ by epitaxial growth, and a first conductivity type source regioni formed on the base layer by epitaxial growth or ion implantation. Themethod further includes forming a strip-shaped trench having alongitudinal direction and reaching the drift layer by penetrating thesource region and the base layer, forming a first conductivity type channellayer on an inner wall of the trench by epitaxial growth, forming agateinsulation layer on the channel layer, forming a gate electrode on a surfaceof the gate insulation layer in the trench, planarizing the gate electrode,the gate insulation layer, and the channel layer until the source region isexposed, removing the source region, the channel layer, and the secondgate region at least at an end portion of the trench in the longitudinaldirection by performing selective etching after the planarizing so that theend portion of the trench has a recess shape with a depth greater than athickness of the source region. Instead of the removing step, the methodcan include forming a second conductivity region having a depth greaterthan a, thickness of the source region at an end portion of the trench in thelongitudinal direction after the planarizing in such a manner that thesource region located at least at the end portion of the trench is covered_4_zhowith the second conductivity region. iAccording to a fifth embodiment of the present invention, a methodof manufacturing a silicon carbide semiconductor device having a JFET'includes preparing a semiconductor substrate including a firstconductivity type silicon carbide substrate, a 'first conductivity type driftlayer formed on the first conductivity type silicon carbide substrate byepitaxial growth, a second conductivity type first gate region formed on'the drift layer by epitaxial growth, anda first conductivity type sourceregion formed on the first gate region by epitaxial growth or ionimplantation. The method further includes forming a strip-shaped trench.having a longitudinal direction and reachíng the drift layer by penetratingthe source region and the gate region, forming a first conductivity typechannel layer on an inner wall of the trench by epitaxial growth, andforming a second conductivity type second gate region on the channellayer. The preparing step includes forming the source region on the firstgate region by ion implantation in such “a manner that the source region is .formed at a long side portion of the trench and is not formed at an endportion of the trench in the longitudinal direction.According to a sixth embodimentof the present invention, amethod of manufacturing a silicon carbide semiconductor device having a vMOSFET includes preparing a semiconductor substrate including a firstconductivity type silicon carbide substrate, a first conductivity type driftlayer formed on the first conductivity type silicon carbide substrate byepitaxial growth, a second conductivity type base layer formed on the driftlayer by epitaxial growth, and a first conductivity type source regionformed on the base layer by epitaxial growth or ion implantation. Themethod further includes forming a strip-shaped trench having alongitudinal direction and reachíng the drift layer by penetrating thesource region and the base layer, forming a first conductivity type channel i, layer on an inner wall of the trench by epitaxial growth, forming a gateinsulation layer on the channel layer, and forming a gate electrode on asurface of the gate insulation layer in the trench. The preparing step_5-15.
    G20includes forming the source region on the base layer by ion implantationin such a manner that the sourceregion is formed at a long side portion ofthe trench and is not formed at an end portion of the trench in thelongitudinal direction.
    The above and other objectives, features and advantages of thepresent invention will become more apparent from the following detaileddescription made with' check to the accompanying drawings. In thedrawings: I iFIG. 1A is a diagram illustrating a plan view of a SiC semiconductordevice according to a first embodiment of the present invention, FIG. 1B isa diagram illustrating' a cross-sectional view taken along the line IB-IB inFIG. 1A, FIG. IC is a diagram illustratinga cross-sectional view takenalongthe line IC-IC in FIG. 1A, and FIG. 1D is a diagram illustrating across-sectional view taken along the line ID-ID in FIG. 1A;FIG. 2 is a diagram illustrating a result of a measurement of acharacteristic of a* drain current with respect to a gate voltage for aconventional structure and a structure according to the first embodiment;FIGS. 3A-3F are diagrams illustrating cross-sectional views of amethod of manufacturing the SiC semiconductor device of FIGS. 1A-1D;FIG. 4A is a diagram illustrating a plan view of a SiC semiconductordevice according to a second embodiment of the present invention, FIG.4B is a diagram illustrating a cross-sectional view taken along the lineIVB-IVB in FIG. 4A, and FIG. 4C is a diagram illustrating a cross-sectionalview taken along the line IVC-IVC in FIG. 4A; iFIGS. 5A and SB are diagrams illustrating cross-sectional views of.a method of manufacturing the SiC semiconductor device of FIGS. 4A-4C;FIG. 6A is a diagramillustrating a plan view of a SiC semiconductordevice according to a third embodiment of the present invention, FIG. 6Bis a diagram illustrating a cross-sectional view taken along the lineVIB-VIB in FIG. 5A, and FIG. 6C is a diagram illustrating a cross-sectionalview taken along the line VIC-VIC in FIG. 5A; VFIG. 7A is a diagram illustrating a plan view of a conventional SiC-5-125semiconductor device, FIG. 7B is a diagram illustrating a cross-sectionalview taken along the line VIIB-VIIB in FIG. 7A, and FIG. 7C is a diagramillustrating a cross-sectional view taken along the line VIIC-VIIC in FIG.7A; c iFIG. 8 is a diagram illustrating a result of a measurement of acharacteristic of a drain current with respect to a gate voltage for theconventional SiC semiconductor device; kFIGS. 9A-9C are plan views of an end portion of av trench of theconventional SiC semiconductor device;FIG. 10 is a diagram illustrating a measurement of a difference inthe amount of growth between an n"-type channel layer formed at a longside portion of theltrench and an n'-type channel layer formed at the endportion of the trench of the conventional SiC semiconductor device; andFIG. 11 is a diagram illustrating a result of a measurement of acharacteristic of a drain current with respect, to a gate voltage for eachi case of FIGS. 9A-9C.
    The present inventors have studied the above problem deeply andfound out that a JFET formed at an end portion of the trench J5 causes theproblem. That is, when the trench J5 has a strip shape, a JFET is« basically constructed with a long side portion of the trench J5. In thiscase, since the n+-type source region J4 is formed by epitaxial growth, the inI-type source region J4 is formed over the entire substrate so that the 1JFET can be formed not only at the long side portion of the trench J5 butalso at the end portion of the trench J5. A threshold of the JFET formedat the end portion of the trench J5 is different from ha threshold of the JFETformed at the long side portion of the trench J5. The present inventorshave concluded that the threshold difference can cause the aboveproblem.
    The present inventors have conducted an experiment to confirmthe conclusion by changing the width of the trench J5. FIGS. 9A-9C areplan views of the end portion of the trench J5. As can be seen from FIGS._7_15.2_59A-9C, when the width of the trench J5 is changed to 1.2pm, 1.7_um, and2.1um, the thickness of the n'-type channel layer J6 grown at the endportion of the trench J5 becomes 0,.8um, O.6um, and O.5um, respectively.Such a phenomenon occurs due to dependency of migration at the time offorming the n'-type channel layer Jo on the width of the trench J5.Specifically, due to capillary action, as the width of the trench J5 becomessmaller, migration to the end portion of the trench J5 becomes larger. Asa reference, the present inventors have measured a difference in “theamount of growth between the n'-type channel layer J6 formed at the longside portion of the trench J5 and the n'-type channel layer J6 formed atthe end portion of the trench J5. FIG. 10 shows the result of themeasurement. As shown in FIG. 10, the difference in the amount ofgrowth decreases with an increase in the width of the trench J5 andincreases with a decrease in the width of the trench J5.
    Further, the present inventors have measured a characteristic of a idrain current Id with respect to a gate voltage Vg for each case shown inFIGS. 9A-9C. FIG. 11 shows a result of the measurement. It is notedthat “W” in FIG. _11 depicts the width of the trench J5.
    A broken line in FIG. 11 represents an ideal characteristic in whichthe drain current Id 'does not flow until the gate voltage Vg reaches thethreshold. In the case of the conventional SiC semiconductor device, acharacteristic of the drain current Id with respect to the gate voltage Vgdeviates from theideal characteristic. The characteristic deviation variesdepending on the thickness of the nFtype channel layer J6 formed at theend portion of the trench J5. Specifically, the characteristic deviationincreases with the thickness of the n'-type channel layer J6. This isbecause thethreshold decreases with the increase in the thickness of then'-type channel layer J6. As the thickness of the n'-type channel layer J6at the end portion of the trench J5 becomes larger with a decrease in thewidth of the trench JS, the characteristic deviation becomes larger due tothe effect of the threshold of the JFET structure formed at the end portionof the trench J5. i Therefore, the above problem can be solved by_8_15Apreventing the JFET structure from being formed at the end portion of thetrench J5.
    Embodíments of the present invention based on the above studiesare described below with reference to the drawings. Throughouttheembodiments, the same symbols are given to the same or correspondingparts in the' drawings. i(First embodiment)A SiC semiconductor device according to a first embodiment of thepresent invention is described below with reference to FIGS. 1A-1D. FIG.1A is a plan view of .the SiC semiconductor device, AFIG. 1B is across-sectional view taken along the line IB-IB in FIG. 1A, FIG. 1C is across-sectional view taken along the line IC-ICin FIG. 1A, and FIG. 1D isa cross-sectional view taken along the line ID-IDin FIG. 1A.
    The SiC semiconductor device illustrated in FIGS .1A-1D is formedby using an nT-type SiC substrate 1. For* example, an off-substrate canbe used as the n+-type SiC substrate. 1. Since a layout of a cell of a JFETformed in the n'*-type SiC substrate 1 is independent of an off-direction,there is no need that the cell of the JFET is laid out according to theoff-direction. i iA basic structure of the JFET is described below with reference toFIG. 1B. As shown in FIG. 1B, a trench 6 is formed in a semiconductorsubstrate 5. The semiconductor substrate 5 includes an nT-type SiCsubstrate 1, an n'-type drift layer 2 on the n+-type SiC substrate 1, ap+-type first gate region 3 on the n'-type drift layer 2, and an n+-typesource region 4 on the p+-type first gate region 3. An n'-vtype channellayer 7 is formed on an inner wall of the trench 6. The n'-type channellayer 7 extends to a' surface of the semiconductor substrate 5. A p+-typesecond gate region 8 is formed on a surface of the n'-type channel layer 7to completely fill the trench 6. gate electrode 9 is formed on a surfaceof the second' gate region 8, and a source electrode 11 is formed on thegate electrode 9 through an interlayer dielectric layer 10. The sourceelectrode 11 is electrically connected to the n*-type source region 4 via a_19-.20contact hole formed in the interlayer dielectric layer 10. Further, a drainelectrode 12 is formed on a back surface of the n+-type SiC substrate 1and electrically connected to the n+-type SiC substrate 1 serving as adrain region. The JFET has such a basic structure.
    Further, as shown in FIG. 1A, an opening of the trench 6 has a stripshape with a iongitudinal direction. Multiple trenches 6, each of whichhas such an opening shape, are arranged in parallel to form a stripepattern. As shown in FIGS. 1C, 1D, the n+-type source region 4 on anouter edge of the n+-type SiC substrate 1, including a region around anend portion of the trench 6 in the iongitudinal direction, is removed toform a mesa structure. Further, the n'-type channel layer 7 and thesecond gate region 8 at the end portion of the trench 6 are removed toform a recess shape. Therefore, the n+-type source region 4 remainsonly at a position" adjacent to a long side of each trench 6 so that a JFETcan be formed only at the position adjacent to the long side of each trench6. “ gIn the case of the SiC semiconductor device having such astructure, even if the n'-type channel layer 7 is thicker at the end portionof the trench 6 than at the long side portion of the trench 6, it is less likelythat a JFET is formedat the end portion of the trench 6. Therefore, unlikethe conventional structure in which theJFET is formed at the endportionof the trench 6, there is no effect caused by a deviation of a threshold ofa JFET formed at the end portion of the trench 6 from a threshold of a JFETformed at the long side portionof the trench 6. Thus, the structure of theSiC semiconductor device according to the first embodiment can reducean excessive drain current occurring when a gate voltage approaches athreshold. ,It is preferable that the recess shape be formed by removing then'-type channel layer 7 at the end portion of the trench 6 in such a mannerthat the n'-type channel layer 7 becomes thinner at the end portion of thetrench 6 than at the long side portion of the trench 6 and by removing then'-type channel layer 7 at the end portion of the trench 6 by a thickness-10- 1greater than the thickness of the first gate region 3. In other words, it ispreferable that the depth of the recess shape is greater than the thicknessof the first gate region 3 to remove a thicker portion of the n'-type channellayer 7 at the end portion of the trench 6 than the n'-type channel layer 7at the long side portion of the trench 6. In such an approach, thedistance between the n'-type channel layer 7 at the end portion of thetrench 6 and the n+-type source region 4 becomes greater than a channellength. Therefore, the drain "current does not flow even when the gatevoltage is close to the threshold. Thus, the excessive drain current canbe prevented.
    FIG. 2 is a diagram illustrating a result of a measurement of acharacteristic of a drain current (A) with respect to a gate voltage (V) fora conventional structure in which the n+-type source region 4 at the endportion of the trench 6 remains and for the recess shape structure of the ipresentembodiment in which the n+-type source region 4 at the endportion of the trench 6 is removed. As can be seen from FIG. 2, unlikethe conventional-structure, the recess-shape structure of the present'embodimentprevents the drain current from flowing until the gatevoltage reaches the threshold so that the drain current cannot flow even.when the gate voltage approaches the threshold. The measurementresult shown in FIG. 2 indicates y that the structure of the SiCsemiconductor device according to the present embodiment can reducethe excessive drain current occurring when the gate voltage approachesthe threshold.
    Next, a method of manufacturing the SiC semiconductor deviceaccording to the first embodiment is described below with reference toFIGS. 3A-3F. FIGS. 3A-3F are cross-sectional views illustrating themethod of manufacturing the SiC semiconductor device. FIGS. 3A, 3C,and 3E correspond to FIG. 1B. FIGS. 3B, 3D, and 3F correspond to FIG.1D. FIGS. 3A and 3B illustrate the same process. FIGS. 3C and 3D,illustrate the sameprocess. FIGS. 3E and 3F illustrate the same process.Firstly, in a process shown in FIGS. 3A and 3B, the n'-type drift-11- I15' ilayer 2, the p+-type first gate region 3, and the n+-type source region 4are epitaxially grown, in turn, on the surface of the n*-type SiC substrate1 to form the semiconductor substrate 5.
    ! Next, in a process shown in FIGS. 3C and 3D, after a mask havingan opening corresponding to the trench 6 is placed on the semiconductor”substrate 5, anisotropic etchingsuch as reactive ion etching (RIE) isperformed so that the trench 6 can be formed in the semiconductorsubstrate 5. Then, the n'-type channel layer 7 is formed on thesemiconductor substrate 5, including the inside. of the trench 6, byepitaxial growth. At this time, due to migration of the n'-type channellayer 7, the n"-type channel layer 7 becomes thicker at a bottom portionand the end portion of the trench 6 than at the long side portion of thetrench 6.
    Then, ina process shown in FIGS. 3E and 3F, after the p+-typesecond gate region 8 is formed on the surface of the n'-type channel layer7, the second gate region 8 and the n'-type channel layer 7 are planarizedby chemical mechanical polishing (CMP) or thelike until the n+~typesource region 4 is exposed. As a result, the second gate region 8 and then'-type channel layer 7 "can remain onlyin the trench 6.
    Then, the nT-type source region 4 on the outer edge of thesemiconductor substrate 5 is removed to form a mesa structure. - At thesame time, the n+~type source region 4, the n'-type channel layer 7, andthe second gate region 8 near the end portion of the trench 6 are partiallyremoved to form a recess shape. Specifically, after a mask having anopening corresponding to the outer edge of the semiconductor substrate 5and an opening corresponding to the n"-type source region 4, the n'-typechannel layer 7, and the second gate region 8 to be partially removed isplaced on the semiconductor substrate 5, an anisotropic etching such asRIE is performed so that parts corresponding to the openings of the maskare removed. Thus, in addition to the n+-type source region 4 on the“outer edge of the semiconductor substrate 5, the n*-type source region 4,the n'-type channel layer 7, and the second gate region 8 at the end_12-20'_25portion of the trench 6 are partially removed so that the recess shape canbe formed. Then, although not shown in the drawings, a process offorming the gate electrode 9, a process of forming the interlayer dielectriclayer 10, a process of forming the contact hole, a process of forming thesource electrode 11, and a process of forming the drain electrode 12 areperformed in a conventional manner so that the SiC semiconductor deviceshown in FIG. 1 can be manufactured.
    (Second embodiment)A SiC semiconductor device according to a second embodiment ofthe present invention is described below with reference to FIGS. 4A-4C.The second embodiment prevents a JFET from being formed at the endportion of the trench 6 in a way different from that of the first embodiment.
    A difference between the first and second embodiments is as follows.
    FIGS. 4A-4C are diagrams illustrating the SiC semiconductordevice according to the second embodiment. FIG. 4A is a plan view ofthe SiC semiconductor device, FIG. 4B is a cross-sectional view takenalong the line IVB-IVB in FIG. 4A, “and FIG. 4C is a cross-sectional viewtaken along the line Ivc-Ivc in FIG. 4A.
    As shown in FIGS. 4A-4C, according to the second embodiment,unlike the first embodiment in which the nT-type source region 4, then'-type channel layer 7, and the second gate region 8 near the end portionof the trench 6 are partially removed, p-type impurities are ion-implantedinto a region near the end portion of the trench 6 to form a p+-type region20. Specifically, as shown in FIG. 4A, the p+-type region 20 is laid out to_ form a strip» shape (rectangular shape) that completely covers the endportion of each trench 6. The p+-type region 20 is shallower than the firstgate region 3 or the second gate region 8 and deeper than the n+-typesource region 4. The n'-type channel layer 7 located between then*-type source region 4 and the second gate region 8 at least at the endportion of the trench 6 is completely covered with the pT-type region 20 toprevent the JFET from being formed at the end portion of the trench 6.As described above, according to the second embodiment, the_13-region near the end portion of the trench 6 is completely covered with the "p*-type region 20. Therefore, the JFET formed at the end portion of thetrench 6 can be prevented so that the same advantage as the firstembodiment can be obtained.
    Next, a method of manufacturing the SiC semiconductor deviceaccording to the second embodiment is described below with reference toFIGS. 5A-5D. FIGS. 5A-5D are cross-sectional views iilustrating themethod of manufacturing the SiC semiconductor device. FIGS. 5A and5C correspond to FIG. 1B. FIGS. 5B and 5D correspond to FIG. 1D.FIGS. 5A and 5B illustrate the same process. FIGS. 5C and 5D illustratethe same process.
    Firstly, the processes shown in' FIGS. 3A-3F are performed so thatthe semiconductor substrate 5 having a structure shown "in FIGS. 5A andi 5B can be formed. Then, although not shown in the drawings, ha mask,such as LTO, havingan opening corresponding to the p+-type region 20 isplaced on the semiconductor substrate 5. Then, p-type impurities areion impianted into the region of the semiconductor substrate 5 near theend portion of the trench 6 by using the mask. Then, the impiantedp-type impurities are activated by annealing treatment so that the .* structure shown in FIGS. 5C and 5D can be formed. Then, although notshown in the drawings, a process of forming a mesa structure byremoving the n+-type source region 4 on the outer edge of thesemiconductor substrate 5, a process of forming the gate electrode 9, aprocess of forming the interlayer dielectric layer 10, a process of formingthe contact hole, and a process of forming the source electrode 11, and aprocess of forming the drain electrode 12 are performed in a conventionalmanner so thatthe SiC semiconductor device shown in FIGS. 4A-4C canbe manufactured.
    As described above, the method of manufacturing the SiCsemiconductor device according to the second embodiment is basicallythe same as the method of manufacturing the SiCsemiconductor deviceaccording to the first embodiment except that the process of forming the_14-p““-type region 20 is performed and that the nïtypesource region 4, then'-type channel layer 7, and the second gate region 8 atthe end portion ofthe trench 6 are not partially removed att the time of forming the me-sastructure.
    (Third embodiment)A SiC semiconductor device according to a third embodiment ofthepresent invention is described below with reference to FIGS. 6A-6C. Thethird embodiment prevents a JFET from being formed at the end portion ofthe trench 6 in a way different from that of the first embodiment. Adifference between the first and third embodiments is as follows.
    FIGS. 6A-6C are diagrams illustrating the SiC semiconductor,deviceaccording to the third embodiment. FIG. 6A is a plan view of theSiC semiconductor device, FIG. 6B is a cross-sectional view taken alongthe line VIB-VIB in FIG. 6A, and FIG. 6C is a cross-sectional view takenalong the line 1vc-v1c in FIG. 6A. iAs shown in FIGS. 6A-6C, according to the present embodiment,unlike the first embodiment in which the n+-type source region 4, theni-type channel layer 7, and the second gate region 8 near the end portionof the trench 6 are partially removed, the 'n+-type source region 4 isformed by selective ion implantation in such a manner that the n+-type ysource region 4 is not formed in a region near the end portion of the trench6. Specifically, as shown in FIG. 6A, n-type impurities are ion implantedinto a region adjacent to the long side portion of each trench 6 so that then+-type source region 4 can be formed at the long side portion of eachtrench 6. Further, as shown in FIGS. 6A-6C, the first gate region 3 iselongated to the level of the surface of the second gate region 8 near the _end portion of the trench 6 to preventthe n+-type source region 4 frombeing formed at the end portion of the trench 6.As described above, according to the third embodiment, then*~type source region 4 is formed by selective ion implantation to preventthe n+-type source region 4 from being formed at the end portion of thetrench 6. Therefore, the JFET formed at the end portion of the trench 6_15-.1015-.30can be prevented so that the same advantage as the first embodiment canbe obtained. _The method of manufacturing the SiC semiconductor deviceaccording to the third embodiment is basically the same as the method ofmanufacturing the SiC semiconductor device according to the firstembodiment except that the process of forming the n+-type source region4 is performed by ion implantation.
    (Modifications)The embodiments described above can be modified in various ways,for example, as follows. JIn the embodiments, the SiC semiconductor device has a JFET.Ålternatively, the SiC semiconductor device can have a MOSFET by.forming a gate insulation layer instead of the second gate region 8 on asurface of the n'-type channel layer 7 and by forming a gate electrode ona surface of the gate insulation layer. In such an approach, a MOSFETformed at the end portion of the trench 6 can be prevented so that theI same advantage as the embodiments can be obtained.
    A method of manufacturing the SiC semiconductor device having aMOSFET is basically the same as the method of manufacturing the SiCsemiconductor device having a JFET except that a process of forming agate insulation layer by thermal oxidation is performed after forming then'-type channel layer 7, that a process of forming the gate electrode onthe surface of the gate electrode is performed, and that a process ofplanarizing the gate electrode, the gate insulation layer, andthe nf'-typeéchannel layer 7 are performed until a base region corresponding to thefirst gate region 3 is exposed.
    In the first embodiment, the recess shape is formed over arelatively wide region near the end portion of the trench 6 is formed. Inthe second embodiment, the pI-type region 20 is formed over a relativelywide region near the endportion of the trench 6. It is noted that theseare only examples. k It does not matter how to form the recess shape, aslong as the nI-type source region 4 is removed to prevent the JFET from_16-10'A15620A25being formed at the end portion of the trench 6. It does not matter howto form the pI-type region 20, as long as the n+-type source region 4 isy inverted to p-type to prevent the JFET from being formed at the endportion of the trench 6. It is preferable that.the recess shape be formedby completely removing a thicker portion of the n'-type channel layer 7 atthe end portion of the trench 6 than the n"-type channel layer 7 at the longside portion of the trench 6. Likewise, it is preferable that the pI-typeregion 20 be formed to completely cover the thicker portion of then-typechannel layer 7. In such an approach, even when the mask used to formthe recess shape or the pI-type region 20 becomes misaligned, it is less 'likely that the JFET or the MOSFET is formed at the end portion of thetrench 6. _ ' _I In the embodiments, the JFET and the MOSFET are n-channeltypes in which a channel region is formed in the ni-type channel layer 7.Ålternativelyythe JFET and the MOSFET can be p-channel types.
    In the embodiments, *the nI-type source region 4 isformed byepitaxial growth. Alternatively, the n+-type source region 4 can beformed by ion ímplantation of n-ltype impurities into the first gate region3. yi In the embodiments, the trench 6 has a strip shape with alongitudinal direction. The strip shape is not limited to a rectangle. Forexample,'the strip shape can be a parallelogram or a hexagon in which thecenter of the endportion of the trench -6 is sharpened(e.g., a shapeformed by elongating two opposing sides of a regular hexagon). ' iSuch changes and modifications are to be understood as being iwithin the scope of the present invention as defined by the appended'claims._17-
    权利要求:
    Claims (19)
    [1] Claims:i 1. A silicon carbide semiconductor device having a JFETcomprising: i a semiconductor substrate (5) including a first conductivity typesilicon carbide substrate (1), a first conductivity type drift layer (2) formedon the first conductivity type silicon carbide substrate (1) by epitaxiaigrowth, a second conductivity type first gate region (3) formed on thedrift layer (2) by epitaxiai growth, and a first conductivity type sourceregion (4) formed on the first gate region (3) byepitaxial growth or ionimplantation; a strip-shaped trench (6) having a longitudinal direction andreaching the drift layer (2) by penetrating the source region (4) and thefirst gate region (3); i a first conductivity type channel layer (7) formed on an inner wallofthe trench (6) by epitaxiai growth; and_ a second conductivity type second gate region (8) formed on thechannel layer (7), wherein , the source region (4) is not formed at an end portion of the trench(6) in thelongitudinal direction.
    [2] 2. A silicon carbidesemiconductor device having a MOSFET I comprising: a semiconductor substrate (5) including a first conductivity type ' silicon carbide substrate (1), a first conductivity type drift layer (2) formedon the first conductivity type silicon carbide substrate (1) by epitaxiaigrowth, a secondconductivity type 'base layer (3) formed on the drift layer(2) by epitaxiai growth, and a first conductivity type source region (4)formed on the base layer (3) by epitaxiai growth or ion implantation; a strip-shaped trench (6) having a longitudinal direction andreaching the drift layer (2) by penetrating the source region (4) and thebase layer (3); sig- a first conductivity type channel layer (7) formed on an inner wall of the trench (6) by epitaxial growth; a gate insulation layer formed on the channel layer (7); and a gate electrode formed on a surface of the gate insulation layer inthe trench (6), wherein i i i the source region (4) is not formed at an end portion of the trench(6) in the longitudinal direction.
    [3] 3. The silicon carbide semiconductor device according to claim 1or 2, wherein the end portion of the trench (6) has a recess shape with a depthgreater than a thickness of the source region (4) to remove at least thesource region (4) at the end portion of the trench (6).
    [4] 4. The silicon carbide semiconductor device according to claim 3,wherein (i the depth of the» recess shape is greater than a thickness of the firstgate region (3) to remove a thicker portion of the n'-type channel layer 7at the end portion of the trench 6 than the n'-type channel layer 7 at thelong side portion of the trench 6.
    [5] 5. The silicon carbide semiconductor device according to claim 3or 4,! wherein the trench (6) comprises a plurality of trenches that are arrangedparallel in a stripe pattern, and the end portion of the plurality of trenches is continuously removedto form the recess shape. ( i
    [6] 6. The silicon carbide semiconductor device according to claim 1or 2, further comprising:a second conductivity region (20) formed at the end portion of the _19- trench (6) and having a depth greater than a thickness of the sourceregion (4), wherein k at least the source region (4) and the channel region (7) that arelocated at the end portion of the trench (6) is covered with the secondconductivity region (20). i
    [7] 7. The silicon carbide semiconductor device according to claim 6, i wherein the trench (6) comprises a plurality of trenches that are .arrangedparallel in a stripe pattern, and the second conductivity region (20) continuously covers the endportion of the plurality of trenches.
    [8] 8. A silicon carbide semiconductor device having a JFET ^ comprising: a semiconductor substrate (5)inc|uding a first conductivity typesilicon carbide substrate (1), a first conductivity type drift layer (2) formedon the first conductivity type silicon carbide substrate (1) by epitaxialgrowth, a second conductivity type first gate region (3) formed onthedrift layer (2) by epitaxial growth, and a first conductivity type sourceregion (4) formed on the first gate region (3) by ion implantation; a strip-shaped trench (6) having a longitudinal direction and reaching the drift layer (2) by penetrating the source region (4) and the gate region (3) ; a first conductivity type channel layer (7) formed on an inner wall V of the trench (6) by epitaxial growth; and a second conductivity type second gate region (8) formed on thechannel layer (7), wherein __ the source region (4) is formed at a long side portion of the trench(6) and is not formed at an end portion of the trench (6) in the longitudinal direction. _20-
    [9] 9. A silicon carbide semiconductor device having a MOSFETcomprising: _ _ a semiconductor substrate (5) including a first conductivity typesilicon carbide substrate (1), a first conductivity type drift layer (2) formedon the first conductivity type silicon carbide substrate (1) by epitaxialgrowth, a second conductivity type base layer (3) formed on the drift layer(2) by epitaxial growth, and a first conductivity type source region (4)formed on the base layer (3) by epitaxial growth or ion implantation; a strip-shaped, trench (6) having a longitudinal direction andreaching the drift layer (2) by penetrating the source region (4) and thebase layer (3); i a first conductivity type channel layer (7) formed on an inner wallof the trench (6) by-epitaxial growth; * a gate insulation layer formed on the channel layer (7); and a gate electrode formed on a surface of thegate insulation layer inthetrench (6), wherein _ i the source region (4) is formed at a long side portion of the trench(6) and is not formed at an end portion of the trench (6) in the longitudinaldirection. i
    [10] 10. A method of manufacturing a silicon carbide semiconductordevice having a JFET comprising: i preparing a semiconductor substrate (5) including a firstconductivity type silicon carbide substrate (1), a first conductivity typedrift-layer (2) formed on the first conductivity type silicon carbidesubstrate (1) by epitaxial growth, a second conductivity type first gateregion (3) formed on the drift layer (2) by epitaxial growth, and a firstconductivity type source region (4) formed on the first gate region (3) byepitaxial growth for ion implantation; y forming a strip-shaped trench (6) having a longitudinal direction l-21-» and reaching the drift layer (2) by penetrating the source region (4) andthe gate region (3); A i forming a first conductivity type channel layer (7) on an inner wallof the trench (6) by epitaxial growth; i forming a second conductivity type second gate region (8) on thechannel layer (7); t planarizing the channel layer (7) and the second gate region (8)until the source region (4) is exposed; and i removing the source region (4), thechannel layer (7), and thesecond gate region (8) at least lat an end portion of the trench (6) in thelongitudinal direction by performing selective etching after the planarizingso that the end .portion of the trench (6) has a recess shape with a depthgreater than a thickness of the source region (4).
    [11] 11. A method of manufacturing a silicon carbide semiconductor ~ device having a MOSFET comprising:preparing a semiconductor substrate (5) including a firstconductivity type silicon carbide substrate '(1), a first conductivity type drift layer (2) formed on the first conductivity type silicon carbide substrate (1) by epitaxial growth, a second conductivity type base layer-(3) formed on the drift layer (2) by epitaxial growth, and a firstconductivity type source region (4) formed on the base layer (3) byepitaxial growth or ion implantation; forming a strip-shaped trench (6) having a longitudinal directionand reaching the drift layer (2) by penetrating the source region (4) andthe base layer (3); forming a first conductivity type channel layer (7) on an inner wall of the trench (6) by epitaxial growth;forming a gate insulation layer on the channel layer (7); andv forming a gate electrode on a surface of thegate insulation layer inthe trench (6); i _22- planarizing the gate electrode, the gate insulation layer, and thechannel layer (7) until the source region (4) is exposed; and removing the source region (4), the channel layer (7), and thesecond gate region (8) at least at an end portion of the trench (6) in thelongitudinal direction by performing selective etching after the planarizingso that the end portion of the trench (6) has a recess shape with a depthgreater than a thickness of the source region (4).
    [12] 12. The method accordingto claím 10 or 11, wherein the» removing includes removing a thicker portion of the n'-type'channel layer (7) at the end portion of the trench (6) than the n'-typechannel layer (7) at a long side portion of the trench (6).
    [13] 13. The method according to claim 12, whereins the forming the trench (6) includes arranging a plurality of trenches (6) in parallel to form a stripe pattern, and the removing includes continuously removing the end portion ofthe plurality of trenches to form the recess shape. s
    [14] 14. A method of manufacturing a silicon carbidesemiconductordevice having a JFET comprising: i V! preparing a semiconductor substrate (5) including a firstconductivity type silicon carbide substrate (1), a first conductivity typedrift layer (2) formed on the first conductivity type silicon carbidesubstrate (1) by epitaxial growth, a second conductivity type first gateregion (3) formed on the drift layer (2) by epitaxial growth, and a firstconductivity type source region (4) formed on the first gate region (3) byepitaxial growth or ion implantation; _ forming a strip-shaped trench (6)'having a longitudinal directionand reaching the drift layer (2) by penetrating the source region (4) andthe gate region (3); V _23- forming a first conductivity type channel layer (7) on an inner wallof the trench (6) by epitaxial growth;forming a second conductivity type second gate region (8) on the channel layer (7); planarizíng the channel layer (7) and the second gate region (8) until the source region (4) is exposed; and _ forming a second conductivity region (20) having a depth greaterthan a thickness of the source region (4) at an end portion of the trench(6) in the longitudinal direction after the planarizíng in such a manner thatthe source region (4) located at least at the end portion of the trench (6)is covered with the second conductivity region (20).
    [15] 15. A method of manufacturing a silicon carbide-semiconductordevice having a MOSFET comprising: ( _ preparing a semiconductor substrate (5) including a firstconductivity type silicon carbide substrate (1), a first conductivity typedrift layer (2) formed on the first conductivity tYDe silicon carbidesubstrate (1) by epitaxial growth, a second conductivity type base layer(3) formed on the drift layer (2) by epitaxial growth, and a firstconductivity type source region (4) formed on the base layer (3) byepitaxial growth or ion implantation; forming a strip-shaped trench (6) having a longitudinal directionand reaching the drift layer (2) by penetrating the source region (4) andthebase layer (3); forming a first conductivity type channel layer (7) on an inner wall ' of the trench (6) by epitaxial growth; forming a gate insulation layer on the channel layer (7); and forming a gate electrode on a surface of the gate insulation layer inthe trench (6); planarizíng the gate electrode, the gate insulation layer, and thechannel layer (7) until the source region (4) is exposed; and _24- forminga second conductivity region (20) having a depth greaterthan a thickness of the source region (4) at an end portion of the trench(6) in the iongitudinal direction after the planarizing in such a manner that the source region (4) located at least at the end portion of the trench (6) __ v is covered with the second conductivity region (20).
    [16] 16. The method according to claim 14 or 15, whereintheforming the trench (6) includes arranging a' plurality of i trenches (6) in parallel to form a stripe pattern, and the forming the second conductivity region (20) includescontinuously covering the end portion of the plurality of trenches with thesecond conductivity region (20).
    [17] 17. A method of manufacturing a silicon carbide semiconductor device having a JFET comprising: preparing a s semiconductor substrate (5) including a firstconductivity type silicon carbide substrate (1), a first conductivity typedrift layer (2) formed on the first conductivity type silicon carbidesubstrate (1) by epitaxial growth, a second conductivity type first gateregion (3) formed on the drift layer (2) by epitaxial growth, and a flrstconductivity type source region (4) formed on the first gate region (3) byepitaxial growth or ion implantation; i forming a strip-shaped trench(6) having a iongitudinal directionand reaching the drift layer (2) by penetrating the source region (4) andthe gate region (3); ' V) forming a first conductivity type channel layer (7) on an inner wallof the trench (6) by epitaxial growth; and V forming a second conductivity type second gate region (8) on thechannel layer (7), wherein 'g the preparing the semiconductor substrate (5) includes formingthe source region (4) on the first gate region (3) by ion implantation in -25- such a manner that the source region (4) is formedat a long side portion of the trench (6) and is not formed at an end portion of the trench (6) in i the longitudinal direction.
    [18] 18. A method of manufacturing a silicon carbide semiconductordevicelhaving a MOSFET comprising; V preparing a semiconductor substrate »(5) including a firstconductivity type silicon carbide substrate (1), a first conductivity typedrift layer (2) formed on the firstconductivity type silicon carbidesubstrate (1) by epitaxial growth, a second conductivity type base layer(3) formed on the drift layer (2) by epitaxial growth, and a firstconductivity type source region (4) formed on .the base layer (3) byepitaxial growth or ion implantation; i h* i forming a strip-shaped trench (6) having a longitudinal directionand reaching the drift layer '(2) by penetrating the source region (4) and (the base layer (3); forming a first conductivity type channel layer (7) on an inner wallof the trench (6) by epitaxial growth;forming a gate insulation layer on the channel layer (7); and forming a gate electrode on a surface of the gate insulation layer in ~ the trench (6), wherein the preparing the semiconductor substrate (5) includes formingthe source region (4) on the base layer (3) by ion implantation in such amanner that the source region (4) is formed at a long side portion of thetrench (6) and is not formed at an end portion of the trench (6) in thelongitudinal direction. V h
    [19] 19. The method according to claim 17 or 18, wherein. the preparing the semiconductor substrate (5) includes formingthe source region (4) by ion implantation in such a manner that the sourceregion (4) is not formed at a deeper portion of the channel layer (7) at the _26- end portion of the trench (6) than the Channel layer (7) at the long side portion of the trench (6). _27..
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    法律状态:
    2019-07-30| NUG| Patent has lapsed|
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    JP2009294799A|JP5170074B2|2009-12-25|2009-12-25|Silicon carbide semiconductor device and manufacturing method thereof|
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