Contact structures for semiconductor devices and method for their manufacture

Abstract: A contact structure and a method for fabrication is disclosed for a semiconductor device that includes a plurality of semiconductor regions along the surface of the device, each region having a top surface and at least a sidewall surface, where a first part of the semiconductor regions are of a first conductivity type and a second part of semiconductor regions are of a second conductivity type. Select dielectric spacers are formed along the sidewalls of the select semiconductor regions of first conductivity type while a refractory metal such as titanium, molybdenum or tungsten is used to form contact on the sidewalls of the semiconductor regions of second conductivity type. This structure is most advantageous in bipolar, CMOS and BiCMOS transistor structures as it allows the formation of the sidewall spacers on emitter/gate contacts while having local metal interconnects with the reactive metal on the sidewall of the select base/source/drain contacts.

Description: The present invention relates generally to integrated circuits and their fabrication, and in particular, to a device with selective spacer formation on a first type of conductive material and local silicide interconnect formation on a second type of conductive material. The use of a polysilicon layer for local interconnect has been reported in the literature for both bipolar and field effect (otherwise known as metal oxide semiconductor or "MOS") technologies. In bipolar processes, a polysilicon layer can be used to electrically contact base, collector, and emitter regions of bipolar transistors. In MOS technologies, a polysilicon layer can be used to electrically contact the source-drain regions of the MOS transistors and form the gates of MOS transistors. By suitable patterning of the polysilicon layer forming the buried contacts, a local interconnect may be formed. Global interconnects are then formed by contacting the polysilicon layer using conventional metal interconnects. Since the number of metal layers which may be formed on a given portion of a wafer is limited, the use of a polysilicon layer for local interconnect allows a metal layer that was formerly used for local interconnect to be employed as an additional global interconnect layer. In addition to the advantages in layout provided by an additional global interconnect layer, the use of a polysilicon layer to form device contacts also results in an improvement in transistor performance through reduction in device parasitic areas (e.g., the extrinsic base area in bipolar transistors). It also results in simplification of contact etch technology for shallow junctions where very high etch selectivity to the substrate is required. This is particularly important in processes where dielectric planarization is performed before contact etch, because the thickness nonuniformity of the dielectric creates a substantial risk of etching into the shallow junction. By using a polysilicon layer to contact the shallow junction, metal contacts may be made to the polysilicon layer rather than the shallow junction, and the risk of overetching is reduced. Recent processes also provide for fabricating metal silicide layers on desired components of bipolar circuits by a process that is self-aligned to the components. These processes have been modified to limit dopant movement from polysilicon into the silicide, to eliminate metallic contaminants from the surface of the field oxide surrounding active device areas, and to eliminate the need for masking/etching the metal silicide. One process utilizing some of the above techniques is taught by Koh et al . in U.S. Patent No. 4,609,568. Advanced complementary MOS (CMOS), bipolar/CMOS (BiCMOS), MOS, and bipolar devices have very high packing densities. The formation of spacers on the sidewalls of, for example, emitter/gate polysilicon regions on a substrate are essential in order to isolate these regions. Some processes form spacers on the sidewalls of the emitter/gate polysilicon patterns by depositing a uniform oxide where vertical polysilicon sidewalls have been created. A plasma etch is then performed to selectively remove oxide from horizontal surfaces of the polysilicon, but not the vertical sidewalls. This step may be followed by formation of metal silicide contacts. While meeting with some success, the above processes have met with certain limitations. For example, contact resistance is often increased because only the top portion of the polysilicon is provided with a silicide region. From the above, it is seen that an improved device with sidewall spacers and a method of fabrication thereof is desired. The independant claims define the present invention. The present invention offers a method of forming sidewall oxide on selected vertical sidewalls of a polysilicon layer. In some embodiments the process does not require a masking step to remove the spacer oxide from other vertical sidewalls. In one embodiment, oxide is removed from the sidewall of p-type polysilicon while maintaining oxide on the sidewalls of n-type polysilicon sidewalls. The invention provides for differential oxide growth on n-type polysilicon as compared to p-type polysilicon. The process reduces the need to control oxide uniformity and comformality, while resulting in a local interconnect with silicided sidewalls on selected polysilicon sidewalls. According to the embodiments of the invention, a contact structure for a semiconductor device is fabricated that includes a plurality of semiconductor regions along the surface of the device, each region having a top surface and at least a sidewall surface, where some of the semiconductor regions are intrinsic or of a first conductivity type and the remaining semiconductor regions are of a second conductivity type. Dielectric spacers are maintained along the sidewalls of the semiconductor regions of first conductivity type, but not along regions of the second conductivity type. A refractory metal, such as titanium, molybdenum or tungsten, is used in some embodiments to form contacts on the sidewalls of the semiconductor regions of second conductivity type. The structure provided herein will have applications in bipolar, MOS, and BiCMOS transistor structures, for example, as it allows the formation of the sidewall spacers on selected polysilicon contacts, gates, emitters and the like without the need for additional masking steps. This process avoids a subsequent masking step to selectively remove any excess dielectric material to form the desired sidewall spacers. Also according to this invention, a method is disclosed for fabricating a spacer structure that includes the steps of forming a first region of a semiconductor material with a first conductivity type that has a top surface and a sidewall, forming a second region of a semiconductor material of second conductivity type that has a top surface and a sidewall, forming a dielectric layer on the device, including the first and second regions, and then removing the excess dielectric layer from the device except where on sidewalls of the first region. One specific embodiment of this invention forms the spacer structure in a method that allows the subsequent metal interconnect to be self-aligned. This method further includes the steps of depositing a metal on the device and reacting the metal with the semiconductor material desired, and then removing the excess metal in some embodiments. In one embodiment, these steps are part of the overall process used to fabricate bipolar, field effect, CMOS and/or BiCMOS based integrated circuit devices. An important advantage of the present invention is the reduction of base contact resistance in bipolar devices and source/drain contact resistance in MOS devices with the use of self aligned silicide formation. Since the spacer is formed only around the emitter/gate of a transistor, silicide forms on the sidewall of, for example, the base contact, source contact, or drain contact polysilicon. This reduces the resistance and required overlap of the base/source/drain polysilicon contacts onto the active region and results in smaller device areas. Further device performance improvements are obtained by way of silicide formation along horizontal surfaces of an active area of a device such as a base, source, or drain of a transistor. It is another advantage of the present invention to eliminate the spacer on silicided polysilicon used for local interconnect which increases the area which becomes silicided. This results in a reduction of the resistance in the interconnect and is particularly significant for sub-micron geometries. It is another advantage of the present invention to improve device performance by reducing the critical feature size below that defined by photolithography as the thermal oxide spacer encroaches on the emitter/gate. Other advantages of the present invention will become apparent after having read the following detailed description of the preferred embodiments which are illustrated by the various figures. Figs. 1a to 1j illustrate the steps of forming a combination bipolar/CMOS device according to a particular embodiment of the present invention; and Fig. 2 is a cross-sectional view of a completed BiCMOS integrated circuit structure. The description which follows is directed to one particular embodiment of the present invention suitable for a BiCMOS process. It should be understood however, that the present invention is not limited thereto and may be employed in any semiconductor fabrication process where low contact series resistance and sidewall spacer formation are desired. Fig. 1a shows a silicon substrate 2 after having undergone preliminary processing. For example, silicon substrate 2 has been processed to form an bipolar NPN region, an NMOS region, and a PMOS region, including p+ channel stop 6 and a p+ buried layer 8 in NMOS region. The NPN region is intended to be used for forming an NPN bipolar transistor, whereas the NMOS region is intended to be used for forming an N channel MOS device, and the PMOS region is intended to be used for forming a P channel MOS device. If desired, the bipolar region may be used to form a PNP device by interchanging the conductivity type of the substrate dopants. Other possible applications include, for example, the formation of P-N junction diodes. Silicon substrate 2 is formed of a p-type material. Consequently, NPN bipolar region and PMOS region have formed therein arsenic doped n+ buried layers 12 and 14, respectively. N+ buried layers 12 and 14 may be formed, for example, by the process disclosed in U.S. Patent No. 3,648,125 to Douglas L. Peltzer which is incorporated herein by reference for all purposes. An epitaxial silicon layer 15 having a thickness of about 1 µm is grown on the substrate. The epitaxial layer includes N wells 20 and 22, respectively, formed by diffusion of an appropriate n-type impurity, such as phosphorous, into epi region 15 according to well known techniques. N+ buried regions 12 and 14 typically have an impurity concentration of approximately 1 x 10 20 atoms/cm 3 and are approximately 1 µm thick, whereas N regions 20 and 22 typically have an impurity concentration of approximately 1 x 10 16 atoms/cm 3 and a thickness of approximately 0.8 µm. Isolation between the devices is provided by oxide regions 24, 26, 28, 30 and 32. The oxide regions are formed by means well known to those of skill in the art. For example, a silicon dioxide layer may be thermally grown on the surface of the substrate 2 by placing substrate 2 in a steam environment after masking with an oxide/nitride sandwich at a temperature of approximately 900°C for 30 minutes. As a result, NPN region is electrically isolated from NMOS region by field oxide region 28, and NMOS region is electrically isolated from PMOS region by field oxide region 30. Field oxide region 26 separates NPN region into a collector contact region 34 and a base/emitter region 36. Alternatively, the field oxide regions are formed by the well known LOCOS process. A grown screen oxide layer having a thickness of about 250 Å (1nm=10Å) is then formed on the device surface and a mask is formed, exposing only the sink region 34. A sink implant using an implant energy of between about 100 and 190 keV with a dose of between about 1x10 14 and 1x10 16 using phosphorus as a dopant. The resulting dopant concentration in the sink region 34 is between about 1x10 19 and 1x10 20 /cm 3 . The screen mask is then removed and a separate mask/ion implantation is performed to dope the channel (well) region of the PMOS transistor to a concentration of between about 2x10 16 and 5x10 16 and using phosphorus as a dopant. In preferred embodiments, the implant energy used for the PMOS region is between about 50 and 150 keV with energy of between about 50 and 100 keV preferred. The resulting net dopant concentration in the epitaxial channel region of the n-well 22 is between about 2x10 16 and 5x10 16 /cm 3 . The sink region 34 and n-well 22 are then annealed and driven in by heating with a conventional thermocycle in nitrogen. A mask is then formed on the surface of the device which exposes only the NMOS and PMOS transistor regions. This mask is used for threshold voltage implant. The implant is used to adjust the threshold voltage of the NMOS and PMOS transistors as necessary, typically to between about ±0.6 and 1.0 volts. In preferred embodiments, the threshold voltage implant is an implant of boron at a dose of between about 1x10 13 to 5x10 13 and preferably at 50 KeV. The threshold voltage implant sets the threshold of the NMOS and PMOS transistors. In preferred embodiments, the threshold voltage implant ultimately provides transistors with threshold voltages of about 0.75 v for NMOS and -0.85 v for PMOS. The screen oxide is stripped and a thin layer of silicon dioxide is formed on the exposed surfaces of substrate 2. The silicon dioxide layer is used to form the gate oxide 37 for the MOS devices. In this embodiment, it has a thickness in the range of from approximately 150 Å to 300 Å, although the thickness range may vary depending on the desired operating characteristics of the MOS devices. The gate oxide layer is then masked and etched for formation of the gate oxide regions on the NMOS and PMOS transistors. Polycrystalline silicon layer 48 is deposited as a blanket coating by CVD over the remaining portions of gate oxide 37 and the exposed areas of silicon substrate 2. Polycrystalline silicon layer 48 preferably has a thickness of from approximately 2000 Å to 4000 Å. A mask is formed exposing the base regions of the bipolar transistor and a p-type implant is performed. Dopants from the poly are then diffused into the underlying monocrystalline silicon to form the base region of the bipolar transistor. Thereafter, a mask is formed which exposes selected regions which will eventually be a portion of the resistor 50, the base contacts 52, 54, and well tap contact 56. The regions are preferably doped p+ to a concentration of between about 1x10 19 and 1x10 20 using boron. Next, the p+ mask is removed and an n+ mask is formed to expose openings to define emitter contact 58, collector contact 60, NMOS gate 62, and PMOS contact 64. Polycrystalline silicon layer 48 then is implanted with an n-type impurity, such as arsenic, and the ions are implanted with sufficient implant energy and dose to provide a concentration of from approximately 1x10 19 and 1x10 20 . As shown in Fig. 1b, the remaining portions of the mask are removed, and a layer of silicon nitride 66 having a thickness of between about 1,000 Å and 2,000 Å is deposited across the entire upper surface to provide an oxidation mask. The structure is then annealed at a temperature of from approximately 900°C to 950°C for approximately 30 minutes in a nitrogen atmosphere to diffuse the dopants through the implanted portion of polycrystalline silicon layer 48. Thereafter in Fig. 1c, a mask is formed over nitride layer 66 to protect the contact of the base 52, 54, emitter contact 58, and collector 60 of the bipolar transistor, and the source contacts 56, 64, gates 68, 70 and drain contacts 62, 56 of the NMOS and PMOS transistors, respectively. The device is plasma etched and the exposed portions of polysilicon then are over-etched until they are removed. Next, the mask is removed, and another photoresist mask is formed to expose the source and drain of the NMOS transistor. Then, an n-type lightly doped drain (LDD) implant is performed with phosphorous ions on the exposed regions with an implantation energy of 40 KeV to a concentration of from approximately 1x10 17 to 1x10 19. This forms N implant areas 72 and 74 and diffuses buried contacts 76, 78 in the NMOS region. Next, as shown in Fig. 1d, the mask is removed, and a photoresist mask is deposited over substrate 2 forming openings over base/emitter region 36 and PMOS region. Then, a p-type implant is performed for PMOS region and the link implant for base/emitter region 36, preferably with boron difluoride at an implantation energy of 50 KeV to a concentration of from approximately 1x10 17 to 1x10 19 . This forms P implant areas 80 and 82 in the base region of the bipolar transistor and P implant areas 84, 86 in the PMOS region. The n-type emitter 88 is diffused from the overlying emitter contact. Thereafter, the mask is removed. Next, as shown in Fig. 1e, a conformal silicon dioxide layer 90 is grown using steam between about 800 and 900°C, and preferably about 800°C, to grow a thickness of oxide from approximately 1,000 to 3,000 Å, preferably 2,000 Å. As shown in the figure, oxide covers the sidewalls of the base contacts, the collector contact, and the emitter contact, as well as the exposed horizontal upper portion of the base in the bipolar transistor. A small amount of additional oxide growth may also occur on the upper surface of the field oxide region. In the MOS device, oxide covers the sidewalls of the source and drain contacts as well as the exposed upper portion of the source and drain regions. Heavily doped n+ type silicon grows an oxide up to eight times as thick as that on P doped polysilicon or single crystal silicon. This phenomenon is used to form selective spacers on the sidewalls of n+ emitter contact 58 and gate contacts 68, 70, and polysilicon, but not on the sidewall of the P doped base contact 52, source contact 54 or drain contact 46 polysilicon. Thick oxide is also formed on n+ collector contact 60, as well as MOS contacts 62 and 64. An oxide etch in hydrofluoric acid removes substantially all of the undesired oxide on the p+ doped polysilicon and contacts 52, 54, 56 as well as the horizontal upper portion of the epi-layer in the extrinsic base region and source and drain regions of the MOS transistors. While hydrofluoric acid is used to etch the oxide in preferred embodiments, isotropic plasma etch chemistries and the like may also be used with beneficial results. The etch is timed to remove oxide on p doped poly while leaving oxide on n+ type poly. The time required for oxidation of the oxide will vary depending upon the oxide thickness, but may readily be determined by those of skill in the art. As seen in Fig. 1f, the remaining oxide 90 forms the spacer sidewalls 92, 94, 96, 98, 100 and 102 of emitter contact 58, collector contact 60, gates 68, 70 and NMOS drain 62 and PMOS source 64, respectively. These spacer sidewalls 92, 94, 96, 98, 100 and 102 will eventually separate the emitter/gate silicide from the base/drain/source silicide. The remaining oxide on the sidewalls of n+ has a thickness of between 750 Å and 2,500 Å, with a thickness of about 1,500 Å preferred. This process avoids an extra process step of using a mask to selectively remove polysilicon sidewall spacers. This elimination of the spacer on the soon to be silicided polysilicon used for local interconnect increases the area which becomes silicided, resulting in a reduction of the resistance. This also significantly reduces the required size of the individual transistor, thus allowing greater density. Finally, the thermal oxide sidewalls 92, 96 and 98 encroach on the emitter 88 and gates 104, 106 thereby reducing the critical feature size below that defined by photolithography, thereby further improving device performance. In the next step, shown in Fig. 1g, a mask is formed to exposed source/drain region of the NMOS transistor. An n-type ion implant then is performed, preferably with arsenic, at an implantation energy of, about 20 to 40 KeV to a concentration of approximately 10 18 atoms/cm 2 to heavily dope N implant areas 72 and 74 for forming the source 108 and drain 110 of the NMOS device, and to form a heavily doped N implant area in the collector contact 60 of the bipolar device. Afterwards, substrate 2 is optionally annealed to form an n+ collector contact junction 112 in bipolar region, and a contiguous n+ source 108 and n+ drain 110 in NMOS region. Similarly, as shown in Fig. 1h, a mask is formed to expose openings over the PMOS region and the base of the bipolar transistor. A p-type ion implant is performed to provide a concentration of approximately 10 17 to 10 19 atoms/cm 2 to heavily dope P implant areas 80 and 82 for creating the source 114 and drain 116 of the PMOS device. Substrate 2 is then annealed at a temperature of 900° for approximately 15 minutes to form a contiguous base 120 in NPN region, a p+ source 108 in NMOS region, and a p+ drain 116 in PMOS region. Next, a layer of refractory metal such as titanium, molybdenum, tantalum, tungsten or the like, is deposited across the surface of the device. Using means well known to those of skill in the art, the layer is heated to form metal silicide in regions where the deposited metal is in contact with polysilicon. Remaining unreacted metal is then etched away from the device, leaving a structure as shown in Fig. 1i. As shown therein, bipolar polysilicon base contacts 52, 54 are covered with silicide metallic (i.e., containing metal) regions 112 such as metal silicide regions across their horizontal upper surfaces and along their vertical side walls. In addition, silicide 122 extends from the base contact sidewall along the surface of the monocrystalline base 120 up to the emitter sidewall oxide 92. The n+ emitter 58 and collector 60 contacts, however, are covered only on the top surface of the contact extending to the side wall oxide 92, 94, respectively. The silicide 124 on the NMOS polysilicon drain contact 62 and gate contacts 68,70 also are covered only on the top surface up to the sidewall oxides 100, 96, 98, respectively. Silicide 124 is also formed on the monocrystalline source 110 between the sidewall oxide spacers 100 and 96 of the source 110 and the gate 104, respectively. The polysilicon well tap 56 also is covered with silicide 126 which covers both the vertical sidewalls and horizontal upper surface of contact 56. Additionally, silicide 126 extends across the upper surface of the NMOS and PMOS transistors up to the of the transistor gates sidewall oxide 96, 98. The PMOS source contact 64 includes silicide 128 across its horizontal upper surface to its vertical sidewall oxide 102 and across the horizontal surface of source 114 up to the gate sidewall oxide 98. Also included is silicide 130 on resistor contact 50. The structure may be subjected to further well-known integrated circuit processes to create additional layers of interconnections. For example, as illustrated in Fig. 1j, passivating material 132 may be deposited across the entire upper surface of the integrated circuit, openings formed therein, and a layer of metal deposited thereon to provide connections 134 to the silicide regions shown. An example of a completed structure according to the invention is illustrated in Fig. 2. The foregoing has been a description of the preferred embodiment. For example, the dopant types of the various devices could readily be reversed. Still further, although specific times, temperatures, thicknesses, dopant types, and materials have been described for purposes of illustrating the invention, these are set forward to enable a full understanding of the invention, and are not intended to limit the invention. The scope of the invention may be ascertained from the appended claims.

Claims: A contact structure (122 - 130) for a semiconductor device having active regions in a substrate (2), the structure comprising: a) a plurality of separated semiconductor regions (50 - 64) arranged horizontally along a surface and extending from the substrate, said semiconductor regions each having a top surface vertically displaced from said active regions and at least one sidewall surface, a first group (58, 60, 62, 64, 68, 70) of said semiconductor regions having a first conductivity type (n), and a second group (52, 54, 56) of said semiconductor regions having a second conductivity type (p); b) dielectric regions (92 - 102) along said sidewalls of the first group of semiconductor regions; and c) reacted metal contacts (122, 126) formed along said sidewalls of said second group of the semiconductor regions. A contact structure as in claim 1 wherein said contacts (122, 126) extend along said top surface of said semiconductor regions of second conductivity type. A contact structure as in claim 1 wherein said first conductivity type is n-type and said second conductivity type is p-type. A contact structure as in claim 1 wherein said device is a bipolar transistor. A contact structure as in claim 4 wherein a group (58) of said semiconductor regions of first conductivity type are bipolar emitter contacts. A contact structure as in claim 4 wherein a group (60) of said semiconductor regions of first conductivity type are bipolar collector contacts. A contact structure as in claim 4 wherein a group (52, 54) of said semiconductor regions of second conductivity type are bipolar base contacts. A contact structure as in claim 1 wherein said device is a field effect device. A contact structure as in claim 8 wherein a group of said semiconductor regions of first conductivity type are gate regions (68, 70). A contact structure as in claim 8 wherein a group of said semiconductor regions of second conductivity type are source contact regions (56). A contact structure as in claim 8 wherein a group of said semiconductor regions of second conductivity type are drain contact regions. A contact structure as in claim 1 further including a plurality of active regions selectively interspaced between said semiconductor regions. A contact structure as in claim 12 wherein said reacted metal sidewall contacts (122, 126) further extend across said active regions. A contact structure as in claim 7 wherein said reacted metal sidewall contacts (122) further extend across said base regions. A contact structure as in claim 10 wherein said reacted metal sidewall contacts (126) further extend across said source regions. A contact structure as in claim 11 wherein said reacted metal sidewall contacts (126) further extend across said drain regions. A contact structure as in claim 1 wherein said semiconductor regions of second conductivity type include reacted metal top contacts. A contact structure as in claim 17 wherein said reacted metal top contacts on said regions of second conductivity type extend up to said sidewalls of said first group of semiconductor regions. A contact structure as in claim 12 wherein said active regions are formed of an epitaxial layer (15). A contact structure as in claim 1 wherein said device is a BiCMOS device. A contact structure as in claim 1 wherein said first group of semiconductor regions has reacted metal top contacts (124, 128). A contact structure as in claim 21 wherein said reacted metal top contacts on said regions of first conductivity type extend up to said sidewalls of said first regions. A BiCMOS device as in claim 20, comprising: a) an npn bipolar transistor; b) a CMOS device, said CMOS device comprising an NMOS transistor and a PMOS transistor; and c) a polysilicon contact layer (48) for said BiCMOS device comprising: i) a p-type polysilicon base contact (52, 54) for said bipolar transistor, said base contact further comprising a silicide layer (122) on a top surface and a sidewall thereof, said silicide layer further extending along a base region (120) of said bipolar transistor; ii) an n-type polysilicon emitter contact (58) for said bipolar transistor, said emitter contact comprising oxide sidewalls (92), said silicide on said bipolar base region extending up to and contacting said oxide sidewalls, said emitter contact further comprising silicide (122) extending along an upper surface of said emitter contact between said oxide sidewalls; iii) an n-type collector contact (60) for said bipolar transistor, said collector contact comprising oxide sidewalls (94) and silicide (122) extending along an upper surface of said collector contact between said sidewalls; iv) n-type gates (68, 70) for said NMOS and PMOS transistors, said n-type gates further comprising oxide sidewalls (96, 98) and silicide (124) extending along an upper surface thereof between said oxide sidewalls; v) at least one n-type contact (62, 64) to each of said NMOS and PMOS transistors, said at least one n-type contact comprising oxide sidewalls (100, 102) and silicide (124, 128) along an upper surface thereof; and vi) a p-type well (56) for said NMOS and PMOS transistors, said p-type well comprising silicide (126) along an upper surface thereof and along a sidewall thereof, said silicide further extending along an active region of said NMOS and PMOS transistors up to said oxide sidewalls on said n-type contacts to each of said NMOS and PMOS transistors. Ä method of fabricating a spacer structure on a semiconductor device having active regions in a substrate (2), the method comprising the steps of: a) forming a first plurality of separated semiconductor regions (58, 60, 62, 64, 68, 70) of a first conductivity type (n) arranged horizontally along a surface of the structure with said regions each having a top surface vertically displaced from said active regions and at least a first sidewall: b) forming a second plurality of separated semiconductor regions (52, 54, 56) of a second conductivity type (p) arranged horizontally along the surface of the substrate with said regions having a top surface vertically displaced from said active regions and at least a first sidewall; c) forming a dielectric layer (90) on said device, including said semiconductor regions of first conductivity type and semiconductor regions of second conductivity type; and d) removing the dielectric layer from said sidewalls of said regions of second conductivity type, a portion (92 - 102) of said dielectric layer remaining on said sidewalls of said semiconductor regions of first conductivity type. The method according to claim 24 wherein reacted metal (122- 130) is formed on selected portions of the sidewall regions of second conductivity type further comprising the steps of: a) depositing a metal on the device; b) performing a first reaction of the metal with the semiconductor regions; and c) removing unreacted metal. The method according to claim 25 further comprising a second reaction of said metal with said regions. The method according to claim 25 or 26 wherein said reacted metal is formed on the top surface of the selected portions of regions of second conductivity type. The method according to claim 25 or 26 wherein said reacted metal is formed on selected portions of the top surfaces of regions of first conductivity type. The method according to claim 25 wherein said metal is from a group consisting of titanium, tungsten, cobalt, chromium, nickel, palladium, platinum, tantalum, vanadium, and molybdenum. The method according to claim 24 wherein said first conductivity type is n-type and second conductivity type is p-type. A method of constructing a first level contact structure on a semiconductor device as defined in one of the claims 24 to 30 comprising the steps of: a) masking and implanting a polysilicon layer (48) with a first conductivity type dopant; b) masking and implanting said polysilicon with a second conductivity type dopant; c) depositing a nitride layer on said poly layer; d) etching the polysilicon layer for forming a plurality of openings; e) forming a thermal oxide layer (90) across the surface of said structure, said thermal oxide layer being thicker on said polysilicon of said first conductivity type than on said polysilicon of said second conductivity type; and f) etching said oxide so that said oxide on sidewalls of said polysilicon of said second conductivity type is substantially removed while leaving an effective amount of oxide on sidewalls of said polysilicon of said first conductivity type for isolation of said sidewalls of said polysilicon of said first conductivity type. The method according to claim 31 wherein said oxide forming step (e) is an oxidation of about 800°C in steam. The method according to claim 31 wherein said etching step (f) is performed using hydrofluoric acid.

Inventors: SOLHEIM ALAN G, SOLHEIM, ALAN G., Solheim, Alan G., c/o A.N. Solheim
Applicants: NAT SEMICONDUCTOR CORP, NATIONAL SEMICONDUCTOR CORPORATION
Application year: 1991
Main classification: H01L29
IPC codes: H01L29, H01L27, H01L21