METHOD FOR MAKING DMOS DEVICES INCLUDING A SUPERLATTICE AND FIELD PLATE FOR DRIFT REGION DIFFUSION

Abstract

A method for making a double-diffused MOS (DMOS) device may include forming a semiconductor layer having a first conductivity type, forming a drift region of a second conductivity type in the semiconductor substrate, forming spaced-apart source and drain regions in the semiconductor layer, and forming a first superlattice on the semiconductor layer. The first superlattice may include a plurality of stacked groups of layers, each group of layers including a plurality of stacked base semiconductor monolayers defining a base semiconductor portion, and at least one non-semiconductor monolayer constrained within a crystal lattice of adjacent base semiconductor portions. The method may also include forming a gate above the first superlattice, and a forming field plate layer adjacent the drift region and configured to deplete the drift region.

Claims

1-24. (canceled)

25. A method for making a semiconductor device comprising: forming a semiconductor layer having a drift region therein; forming a first superlattice on the semiconductor layer, the first superlattice comprising a plurality of stacked groups of layers, each group of layers comprising a plurality of stacked base semiconductor monolayers defining a base semiconductor portion, and at least one non-semiconductor monolayer constrained within a crystal lattice of adjacent base semiconductor portions; forming a gate above the first superlattice; forming a field plate adjacent the gate and configured to deplete the drift region; and forming a second superlattice in the semiconductor layer beneath the drift region, the second superlattice comprising a plurality of stacked groups of layers, each group of layers comprising a plurality of stacked base semiconductor monolayers defining a base semiconductor portion, and at least one non-semiconductor monolayer constrained within a crystal lattice of adjacent base semiconductor portions.

26. The method of claim 25 comprising forming spaced-apart source and drain regions in the semiconductor layer.

27. The method of claim 26 wherein forming the field plate comprises forming the field plate to be electrically coupled with the source region.

28. The method of claim 26 comprising forming a body implant in the semiconductor layer adjacent the source region.

29. The method of claim 25 comprising forming at least one resurf region below the second superlattice.

30. The method of claim 29 wherein the at least one resurf region comprises a lower resurf region, and an upper resurf region between the lower resurf region and the second superlattice.

31. The method of claim 25 further comprising forming a semiconductor cap layer on the first superlattice and defining a channel beneath the gate.

32. The method of claim 25 wherein forming the gate comprises forming a gate dielectric layer on the semiconductor layer and gate electrode layer on the gate dielectric layer.

33. The method of claim 32 wherein the gate dielectric layer has first and second portions, with the second portion being thicker than the first portion.

34. The method of claim 25 wherein the base semiconductor monolayers comprise silicon.

35. The method of claim 25 wherein the non-semiconductor monolayers comprise oxygen.

36. A method for making a semiconductor device comprising: forming a semiconductor layer having a drift region therein; forming a first superlattice on the semiconductor layer, the first superlattice comprising a plurality of stacked groups of layers, each group of layers comprising a plurality of stacked base silicon monolayers defining a base silicon portion, and at least one oxygen monolayer constrained within a crystal lattice of adjacent base silicon portions; forming a gate above the first superlattice; forming a field plate adjacent the gate and configured to deplete the drift region; and forming a second superlattice in the semiconductor layer beneath the drift region, the second superlattice comprising a plurality of stacked groups of layers, each group of layers comprising a plurality of stacked base semiconductor monolayers defining a base semiconductor portion, and at least one non-semiconductor monolayer constrained within a crystal lattice of adjacent base semiconductor portions.

37. The method of claim 36 comprising forming spaced-apart source and drain regions in the semiconductor layer.

38. The method of claim 37 wherein forming the field plate comprises forming the field plate to be electrically coupled with the source region.

39. The method of claim 37 comprising forming a body implant in the semiconductor layer adjacent the source region.

40. The method of claim 36 comprising forming at least one resurf region below the second superlattice.

41. The method of claim 36 further comprising forming a semiconductor cap layer on the first superlattice and defining a channel beneath the gate.

42. The method of claim 36 wherein forming the gate comprises forming a gate dielectric layer on the semiconductor layer and gate electrode layer on the gate dielectric layer.

43. The method of claim 42 wherein the gate dielectric layer has first and second portions, with the second portion being thicker than the first portion.

44. A method for making a semiconductor device comprising: forming a semiconductor layer having a drift region therein; forming a first superlattice on the semiconductor layer, the first superlattice comprising a plurality of stacked groups of layers, each group of layers comprising a plurality of stacked base semiconductor monolayers defining a base semiconductor portion, and at least one non-semiconductor monolayer constrained within a crystal lattice of adjacent base portions; forming a gate above the first superlattice; forming a field plate adjacent the gate and configured to deplete the drift region; and forming a second superlattice in the semiconductor layer beneath the drift region, the second superlattice comprising a plurality of stacked groups of layers, each group of layers comprising a plurality of stacked base silicon monolayers defining a base silicon portion, and at least one oxygen monolayer constrained within a crystal lattice of adjacent base silicon portions.

45. The method of claim 44 comprising forming spaced-apart source and drain regions in the semiconductor layer.

46. The method of claim 45 wherein forming the field plate comprises forming the field plate to be electrically coupled with the source region.

47. The method of claim 45 comprising forming a body implant in the semiconductor layer adjacent the source region.

48. The method of claim 44 comprising forming at least one resurf region below the second superlattice.

49. The method of claim 44 further comprising forming a semiconductor cap layer on the first superlattice and defining a channel beneath the gate.

50. The method of claim 44 wherein forming the gate comprises forming a gate dielectric layer on the semiconductor layer and gate electrode layer on the gate dielectric layer.

51. The method of claim 50 wherein the gate dielectric layer has first and second portions, with the second portion being thicker than the first portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a greatly enlarged schematic cross-sectional view of a superlattice for use in a semiconductor device in accordance with an example embodiment.

[0017] FIG. 2 is a perspective schematic atomic diagram of a portion of the superlattice shown in FIG. 1.

[0018] FIG. 3 is a greatly enlarged schematic cross-sectional view of another embodiment of a superlattice in accordance with an example embodiment.

[0019] FIGS. 4-7 are schematic cross-sectional diagrams of various DMOS devices including one or more superlattice layers in different example embodiments.

[0020] FIG. 8 is a process flow diagram illustrating method aspects associated with the fabrication of the DMOS devices of FIGS. 5-8.

[0021] FIG. 9A is a schematic cross-sectional diagram of an alternative embodiment of the DMOS device of FIG. 4 including a field plate for drift region depletion.

[0022] FIG. 9B is a doping profile graph illustrating dopant concentration vs. depth for an example implementation of the DMOS device of FIG. 9A, as well as for a similar device without a superlattice layer.

[0023] FIG. 10 is schematic cross-sectional diagram of an alternative embodiment of the DMOS device of FIG. 6 including a field plate for drift region depletion.

[0024] FIG. 11 is schematic cross-sectional diagram of an alternative embodiment of the DMOS device of FIG. 7 including a field plate for drift region depletion.

DETAILED DESCRIPTION

[0025] Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which the example embodiments are shown. The embodiments may, however, be implemented in many different forms and should not be construed as limited to the specific examples set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in different embodiments.

[0026] Generally speaking, the present disclosure relates to semiconductor devices having an enhanced semiconductor superlattice therein to provide performance enhancement characteristics. The enhanced semiconductor superlattice may also be referred to as an MST layer or MST technology in this disclosure.

[0027] More particularly, the MST technology relates to advanced semiconductor materials such as the superlattice 25 described further below. In prior work, Applicant theorized that certain superlattices as described herein reduce the effective mass of charge carriers and that this thereby leads to higher charge carrier mobility. See, e.g., U.S. Pat. No. 6,897,472, which is hereby incorporate herein in its entirety by reference.

[0028] Further development by Applicant has established that the presence of MST layers may advantageously improve the mobility of free carriers in semiconductor materials, e.g., at interfaces between silicon and insulators like SiO.sub.2 or HfO.sub.2. Applicant theorizes, without wishing to be bound thereto, that this may occur due to various mechanisms. One mechanism is by reducing the concentration of charged impurities proximate to the interface, by reducing the diffusion of these impurities, and/or by trapping the impurities so they do not reach the interface proximity. Charged impurities cause Coulomb scattering, which reduces mobility. Another mechanism is by improving the quality of the interface. For example, oxygen emitted from an MST film may provide oxygen to a SiSiO.sub.2 interface, reducing the presence of sub-stoichiometric SiOx. Alternately, the trapping of interstitials by MST layers may reduce the concentration of interstitial silicon proximate to the SiSiO.sub.2 interface, reducing the tendency to form sub-stoichiometric SiOx. Sub-stoichiometric SiOx at the SiSiO.sub.2 interface is known to exhibit inferior insulating properties relative to stoichiometric SiO.sub.2. Reducing the amount of sub-stoichiometric SiOx at the interface may more effectively confine free carriers (electrons or holes) in the silicon, and thus improve the mobility of these carriers due to electric fields applied parallel to the interface, as is standard practice in field-effect-transistor (FET) structures. Scattering due to the direct influence of the interface is called surface-roughness scattering, which may advantageously be reduced by the proximity of MST layers followed by anneals or during thermal oxidation.

[0029] In addition to the enhanced mobility characteristics of MST structures, they may also be formed or used in such a manner that they provide piezoelectric, pyroelectric, and/or ferroelectric properties that are advantageous for use in a variety of different types of devices, as will be discussed further below.

[0030] Referring now to FIGS. 1 and 2, the materials or structures are in the form of a superlattice 25 whose structure is controlled at the atomic or molecular level and may be formed using known techniques of atomic or molecular layer deposition. The superlattice 25 includes a plurality of layer groups 45a-45n arranged in stacked relation, as perhaps best understood with specific reference to the schematic cross-sectional view of FIG. 1.

[0031] Each group of layers 45a-45n of the superlattice 25 illustratively includes a plurality of stacked base semiconductor monolayers 46 defining a respective base semiconductor portion 46a-46n and a non-semiconductor monolayer(s) 50 thereon. The non-semiconductor monolayers 50 are indicated by stippling in FIG. 1 for clarity of illustration.

[0032] The non-semiconductor monolayer 50 illustratively includes one non-semiconductor monolayer constrained within a crystal lattice of adjacent base semiconductor portions. By constrained within a crystal lattice of adjacent base semiconductor portions it is meant that at least some semiconductor atoms from opposing base semiconductor portions 46a-46n are chemically bound together through the non-semiconductor monolayer 50 therebetween, as seen in FIG. 2. Generally speaking, this configuration is made possible by controlling the amount of non-semiconductor material that is deposited on semiconductor portions 46a-46n through atomic layer deposition techniques so that not all (i.e., less than full or 100% coverage) of the available semiconductor bonding sites are populated with bonds to non-semiconductor atoms, as will be discussed further below. Thus, as further monolayers 46 of semiconductor material are deposited on or over a non-semiconductor monolayer 50, the newly deposited semiconductor atoms will populate the remaining vacant bonding sites of the semiconductor atoms below the non-semiconductor monolayer.

[0033] In other embodiments, more than one such non-semiconductor monolayer may be possible. It should be noted that reference herein to a non-semiconductor or semiconductor monolayer means that the material used for the monolayer would be a non-semiconductor or semiconductor if formed in bulk. That is, a single monolayer of a material, such as silicon, may not necessarily exhibit the same properties that it would if formed in bulk or in a relatively thick layer, as will be appreciated by those skilled in the art.

[0034] Applicant theorizes without wishing to be bound thereto that non-semiconductor monolayers 50 and adjacent base semiconductor portions 46a-46n cause the superlattice 25 to have a lower appropriate conductivity effective mass for the charge carriers in the parallel layer direction than would otherwise be present. Considered another way, this parallel direction is orthogonal to the stacking direction. The band modifying layers 50 may also cause the superlattice 25 to have a common energy band structure, while also advantageously functioning as an insulator between layers or regions vertically above and below the superlattice.

[0035] Moreover, this superlattice structure may also advantageously act as a barrier to dopant and/or material diffusion between layers vertically above and below the superlattice 25. These properties may thus advantageously allow the superlattice 25 to provide an interface for high-K dielectrics which not only reduces diffusion of the high-K material into the channel region, but which may also advantageously reduce unwanted scattering effects and improve device mobility, as will be appreciated by those skilled in the art.

[0036] It is also theorized that semiconductor devices including the superlattice 25 may enjoy a higher charge carrier mobility based upon the lower conductivity effective mass than would otherwise be present. In some embodiments, and as a result of the band engineering achieved by the present embodiments, the superlattice 25 may further have a substantially direct energy bandgap that may be particularly advantageous for opto-electronic devices, for example.

[0037] The superlattice 25 also illustratively includes a cap layer 52 on an upper layer group 45n. The cap layer 52 may comprise a plurality of base semiconductor monolayers 46. The cap layer 52 may have between 2 to 100 monolayers of the base semiconductor, and, more preferably between 10 to 50 monolayers.

[0038] Each base semiconductor portion 46a-46n may comprise a base semiconductor selected from the group consisting of Group IV semiconductors, Group III-V semiconductors, and Group II-VI semiconductors. Of course, the term Group IV semiconductors also includes Group IV-IV semiconductors, as will be appreciated by those skilled in the art. More particularly, the base semiconductor may comprise at least one of silicon and germanium, for example.

[0039] Each non-semiconductor monolayer 50 may comprise a non-semiconductor selected from the group consisting of oxygen, nitrogen, fluorine, carbon and carbon-oxygen, for example. The non-semiconductor is also desirably thermally stable through deposition of a next layer to thereby facilitate manufacturing. In other embodiments, the non-semiconductor may be another inorganic or organic element or compound that is compatible with the given semiconductor processing as will be appreciated by those skilled in the art. More particularly, the base semiconductor may comprise at least one of silicon and germanium, for example.

[0040] It should be noted that the term monolayer is meant to include a single atomic layer and also a single molecular layer. It is also noted that the non-semiconductor monolayer 50 provided by a single monolayer is also meant to include a monolayer wherein not all of the possible sites are occupied (i.e., there is less than full or 100% coverage). For example, with particular reference to the atomic diagram of FIG. 2, a 4/1 repeating structure is illustrated for silicon as the base semiconductor material, and oxygen as the energy band-modifying material. Only half of the possible sites for oxygen are occupied in the illustrated example.

[0041] In other embodiments and/or with different materials this one-half occupation would not necessarily be the case as will be appreciated by those skilled in the art. Indeed, it can be seen even in this schematic diagram, that individual atoms of oxygen in a given monolayer are not precisely aligned along a flat plane as will also be appreciated by those of skill in the art of atomic deposition. By way of example, a preferred occupation range is from about one-eighth to one-half of the possible oxygen sites being full, although other numbers may be used in certain embodiments.

[0042] Silicon and oxygen are currently widely used in conventional semiconductor processing, and, hence, manufacturers will be readily able to use these materials as described herein. Atomic or monolayer deposition is also now widely used. Accordingly, semiconductor devices incorporating the superlattice 25 in accordance with the embodiments may be readily adopted and implemented, as will be appreciated by those skilled in the art.

[0043] Referring now additionally to FIG. 3, another embodiment of a superlattice 25 in accordance with the embodiments having different properties is now described. In this embodiment, a repeating pattern of 3/1/5/1 is illustrated. More particularly, the lowest base semiconductor portion 46a has three monolayers, and the second lowest base semiconductor portion 46b has five monolayers. This pattern repeats throughout the superlattice 25. The non-semiconductor monolayers 50 may each include a single monolayer. For such a superlattice 25 including Si/O, the enhancement of charge carrier mobility is independent of orientation in the plane of the layers. Those other elements of FIG. 3 not specifically mentioned are similar to those discussed above with reference to FIG. 1 and need no further discussion herein.

[0044] In some device embodiments, all of the base semiconductor portions of a superlattice may be a same number of monolayers thick. In other embodiments, at least some of the base semiconductor portions may be a different number of monolayers thick. In still other embodiments, all of the base semiconductor portions may be a different number of monolayers thick.

[0045] Turning to FIG. 4, an example double-diffused MOS (DMOS) device 100 which incorporates the above-described MST technology is now described. The DMOS 100 illustratively includes a substrate 101, in which shallow P and N regions 102, 103 are formed, as well as source and drain implants 104, 105, respectively. An MST film 125 is formed on the upper surface of the substrate 101, along with a cap layer 152 which may define the channel of the device beneath a gate 106. In some embodiments, the channel may also extend into the MST film 125. By way of example, the cap layer 152 may have a thickness in a range of 5 nm to 100 nm, and the shallow N region 103 may have a thickness in a range of 100 nm to 1000 nm, although other dimensions may be used in different embodiments.

[0046] As previously noted, the above-described MST films may advantageously provide intrinsic mobility in certain configurations via the energy band-modifying effect. However, in the present application the improved performance of the DMOS device 100 is achieved as a result of the modified doping profile that is achievable because of the presence of the MST film 125. This leads to increased mobility due to lower surface roughness scattering, lower coulombic scattering, and increased conduction in the near surface region 117. In other words, this technical advantage may be achieved irrespective of, and is not reliant upon, the energy band-modifying capabilities of MST films.

[0047] Referring now to FIG. 5, in an alternative embodiment of the DMOS device 101 the MST layer 125 is buried in the substrate 101, as opposed to being on the surface of the substrate as in the DMOS device 100 described above. In still another example embodiment of the DMOS device 101 illustrated in FIG. 6, a dual-layer MST configuration is provided which includes both a buried (lower) MST layer 125a and a surface (upper) MST layer 125b.

[0048] Referring to FIG. 7, still another dual-layer MST DMOS device 100 includes double resurf N and P regions 107, 108. This configuration provides for a thinner drift enabled by the double resurf and double MST layer 125a, 125b configuration. Furthermore, the MST layer 125a advantageously reduces compensation of the drift region by the resurf doping, as will be appreciated by those skilled in the art. In some embodiments, the N and P resurf implants 107, 108 may be implemented using the same mask as the drift mask to advantageously reduce cost. The resurf N region 107 may be connected to the drain region 105.

[0049] An example approach for fabricating the above-noted DMOS devices 100-100 is now described with reference to the process flow diagram 800 of FIG. 8. The lot starts with a laser processing module 801. If either of the dual MST layer DMOS devices 100 or 100 is to be formed, then a low temperature (LT) shallow trench isolation (STI) module 802 is performed. Otherwise, the process proceeds to a pad oxidation module 803, followed by a nitride hard mask module 804 and an active area mask module 805. A shallow trench isolation (STI) module 806 is then performed.

[0050] If one of the DMOS devices 100, 100, or 100 is being fabricated, then a buried MST epitaxial module 807 is performed after the STI module 206. Otherwise, processing proceeds to the shallow P and N mask/implant modules 808, 809, respectively, and a well rapid thermal anneal (RTA) module 810. If one of the DMOS devices 100, 100, or 100 is being fabricated, then a surface MST epitaxial module 811 is performed after the well RTA module 810. The process continues with an RTA oxidation module 812, thick chemical vapor deposition (CVD) oxide module 813, and thick oxide mask/etch module 814. Gate formation includes a gate oxidation module 815, gate polysilicon deposition module 816, a poly mask/etch module 817, and a poly reoxidation module 818. The method further illustratively includes a lightly doped drain (LDD)/halo mask/implant module 819, LDD RTA module 820, nitride spacer module 821, and/or other LDD RTA module 822, spacer formation module 823, N+/P+ mask/implant module 824, and source/drain RTA module 825.

[0051] In the above described DMOS devices with a surface MST layer, the MST surface layer enables a retrograde profile near the surface of the substrate, resulting in higher mobility (lower coulomb scattering). Furthermore, the MST surface layers improve mobility below/near gate oxide interface due to lower Surface Roughness Scattering (SRS). Another technical advantage is that the MST layers enable tailoring of doping profiles to direct current flow away from the drift region interface in case of high interface charge. Furthermore, the MST layers advantageously enable preventing compensation of the drift region by resurf region doping, resulting in higher bulk mobility. This allows for a thinner drift region as compared to conventional devices.

[0052] Turning now to FIG. 9A, another example DMOS device 200 is described. The DMOS 200 is similar to the DMOS device 100 and illustratively includes a substrate 201, in which shallow P (body) region 202 and shallow N (drift) region 203 are formed, as well as source and drain implants 204, 205, respectively. An MST film 225 is formed on the upper surface of the substrate 201, along with a cap layer 252 which may define the channel of the device beneath a gate 206. Here, the gate has a stepped gate oxide layer 230 with a thinner first portion and a thicker second portion, and a gate electrode layer 231 on the stepped gate oxide layer. As noted above, in some embodiments the channel may also extend into the MST film 225. The cap layer 252 and drift region 203 may have similar dimensions to those described above.

[0053] This configuration provides numerous technical advantages. In particular, the dopant retention characteristics of the MST film 225 enable a steeper doping profile concentrated in the drift region as compared to a similar device without such an MST layer, as seen in the plot lines 236 and 237 of the graph 235 of FIG. 9A. The resulting doping profile advantageously provides a relatively low drift resistance path, as will be appreciated by those skilled in the art.

[0054] The DMOS 200 also illustratively includes a conductive field plate 240 (e.g., a tungsten plug field plate) over the gate 206 adjacent to the drift region 203. This provides another significant technical advantage, in that it allows the drain-source breakdown voltage BVdss to remain unaffected. This is because the drift region is fully depleted from the top by the field plate 240, which is grounded along with the source region 204 and body implant region 202. Moreover, the drift region may also be depleted from the bottom by the P-RESURF implant as well.

[0055] Referring now to FIG. 10, in an alternative embodiment of the DMOS device 201, a dual-layer MST configuration is provided which includes both a buried (lower) MST layer 225a and a surface (upper) MST layer 225b, as similarly described with reference to FIG. 6 above. This embodiment also provides a technical advantage of Ron resistance reduction, as the lower MST layer 225a helps prevent intermixing of N-drift and P-RESURF dopants. In some embodiments, only the buried MST layer 225a may be present (similar to the embodiment described with reference to FIG. 7 above).

[0056] Referring to FIG. 11, still another dual-layer MST DMOS device 200 includes double resurf N and P regions 207, 208. As discussed above with reference to FIG. 7, this provides for a thinner drift region 203 enabled by the double resurf and double MST layer 225a, 125b configuration. Furthermore, the MST layer 125a advantageously reduces compensation of the drift region by the resurf doping, as will be appreciated by those skilled in the art. Here again, in some embodiments the N and P resurf implants 207, 208 may be implemented using the same mask as the drift mask to advantageously reduce cost, and resurf N region 207 may be connected to the drain region 205. This configuration also provides for significant Ron and BVdss improvement. That is, the MST-enabled PN super junction RESURF configuration allows lower Ron and higher BV due to a reduction of dopant intermixing, as well as a larger vertical depletion region, as will be appreciated by those skilled in the art.

[0057] Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.