Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/34—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies not provided for in groups H01L21/18, H10D48/04 and H10D48/07, with or without impurities, e.g. doping materials
  • H01L21/38—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions
  • H01L21/385—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions using diffusion into or out of a solid from or into a solid phase, e.g. a doped oxide layer
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D30/00—Field-effect transistors [FET]
  • H10D30/01—Manufacture or treatment
  • H10D30/021—Manufacture or treatment of FETs having insulated gates [IGFET]
  • H10D30/0223—Manufacture or treatment of FETs having insulated gates [IGFET] having source and drain regions or source and drain extensions self-aligned to sides of the gate
  • H10D30/0227—Manufacture or treatment of FETs having insulated gates [IGFET] having source and drain regions or source and drain extensions self-aligned to sides of the gate having both lightly-doped source and drain extensions and source and drain regions self-aligned to the sides of the gate, e.g. lightly-doped drain [LDD] MOSFET or double-diffused drain [DDD] MOSFET
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
  • H01L21/22—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions; Interactions between two or more impurities; Redistribution of impurities
  • H01L21/225—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions; Interactions between two or more impurities; Redistribution of impurities using diffusion into or out of a solid from or into a solid phase, e.g. a doped oxide layer
  • H01L21/2251—Diffusion into or out of group IV semiconductors
  • H01L21/2254—Diffusion into or out of group IV semiconductors from or through or into an applied layer, e.g. photoresist, nitrides
  • H01L21/2255—Diffusion into or out of group IV semiconductors from or through or into an applied layer, e.g. photoresist, nitrides the applied layer comprising oxides only, e.g. P2O5, PSG, H3BO3, doped oxides
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D64/00—Electrodes of devices having potential barriers
  • H10D64/01—Manufacture or treatment
  • H10D64/021—Manufacture or treatment using multiple gate spacer layers, e.g. bilayered sidewall spacers
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D84/00—Integrated devices formed in or on semiconductor substrates that comprise only semiconducting layers, e.g. on Si wafers or on GaAs-on-Si wafers
  • H10D84/01—Manufacture or treatment
  • H10D84/0123—Integrating together multiple components covered by H10D12/00 or H10D30/00, e.g. integrating multiple IGBTs
  • H10D84/0126—Integrating together multiple components covered by H10D12/00 or H10D30/00, e.g. integrating multiple IGBTs the components including insulated gates, e.g. IGFETs
  • H10D84/0165—Integrating together multiple components covered by H10D12/00 or H10D30/00, e.g. integrating multiple IGBTs the components including insulated gates, e.g. IGFETs the components including complementary IGFETs, e.g. CMOS devices
  • H10D84/017—Manufacturing their source or drain regions, e.g. silicided source or drain regions
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D84/00—Integrated devices formed in or on semiconductor substrates that comprise only semiconducting layers, e.g. on Si wafers or on GaAs-on-Si wafers
  • H10D84/01—Manufacture or treatment
  • H10D84/02—Manufacture or treatment characterised by using material-based technologies
  • H10D84/03—Manufacture or treatment characterised by using material-based technologies using Group IV technology, e.g. silicon technology or silicon-carbide [SiC] technology
  • H10D84/038—Manufacture or treatment characterised by using material-based technologies using Group IV technology, e.g. silicon technology or silicon-carbide [SiC] technology using silicon technology, e.g. SiGe

Definitions

• the invention relates to the field of forming self-aligned source and drain regions for field-effect transistors.
• ion implantation is used to align a source and drain region with a gate (and/or with gate spacers in some processes).
• the ion implantation damages the crystalline structure of the silicon substrate necessitating thermal annealing.
• the implanted dopant diffuses thereby deepening the source and drain regions. These deeper regions make it difficult to control the adverse effects of short channels.
• the source and drain extension regions should be extremely shallow and heavily doped (e.g., 0.05 to 0.1 um versus 0.2 to 0.4 um for 0.2 to 0.5 um channel length transistors).
• Scaling implanted p+ junctions is particularly difficult since the light boron (B 11 ) ions channel during implantation and secondly, since the ions damage the silicon bonds causing point defects. These point defects significantly increase the diffusion of the boron atoms (up to 1000 times) during subsequent thermal annealing. Thus, even for light ions, such as B11 , and low energy implants, the implant damage results in enhanced diffusion.
• Another technique for solving this problem is to diffuse the portion of the source and drain regions adjacent to the gate (tip or tip region) from doped spacers and to form the more heavily doped main portions of the source and drain regions by ion implantation.
• This provides some advantage over the ion implantation of both the tip region and main portion of the source and drain regions but implant damage from the source/drain implant still affects the depth of the diffused tip region resulting in degraded short channel effects. Short channel effects are discussed in numerous publications such as Silicon Processing forthe VLSI Era. Vol. 2, by S. Wolf, published by Lattice press, see Section 5.5, beginning at page 338.
• the present invention permits the simultaneous formation of both an ultra shallow heavily doped source and drain extension region, main portions of the source and drain regions and doping of the polysilicon gate without ion implantation.
• a method for fabricating field-effect transistors on a substrate where the source and drain regions are formed in alignment with a gate is described.
• a source of dopant is used having (i) a more lightly doped region which is formed directly adjacent to the gate and (ii) a more heavily doped region spaced apart from the gate.
• This dopant source is formed on the suiface of the substrate.
• the dopant is diffused from the source of dopant in a heating step simultaneously forming both the lightly doped source and drain tip region and the main portion of the source and drain regions. This diffusion is done in an ambient that may include oxygen or ammonia.
• boron is diffused from two different layers of borosilicate glass (BSG).
• BSG borosilicate glass
• Spacers are formed adjacent to the gate by anisotropically etching a silicon nitride layer which overlies a 2% BSG layer. Then a 6% BSG layer is formed over the spacers and 2% BSG layer to supply the dopant for the more heavily doped main portion of the source and drain regions.
• Both BSG layers are annealed prior to being pattemed to prevent the formation of an unstable boron compound that would otherwise adversely effect diffusion. Rapid thermal processing is used to diffuse the dopant into the substrate from both BSG layers.
• the substrate surface is first damaged by a heavy neutral species such as silicon or implanted with a neutral species -3- such as carbon which can be used to increase or decrease the diffusion of boron in the substrate before the doped glass is deposited on the substrate.
• a chemically formed oxide of 5-20A is formed over the substrate prior to formation of the doped glass.
• Figure 1 is a cross sectional elevation view of a section of a substrate showing an n-well isolated from a p-well. Polysilicon gates and a first glass layer are also shown.
• Figure 2 illustrates the substrate of Figure 1 after a first photoresist layer has been masked and etching, and during an ion implantation step used to form the tip regions for the n-channel transistor.
• Figure 3 illustrates the substrate of Figure 2 after the formation of a TEOS layer and a silicon nitride layer.
• Figure 4 illustrates the substrate of Figure 3 after the silicon nitride layer has been anisotropically etched to form spacers and after the substrate has been covered with a second glass layer.
• Figure 5 illustrates the substrate of Figure 4 after the masking and etching of a photoresist layer and during an ion implantation step used to form the main portion of the source and drain regions for the n-channel transistor.
• Figure 6 illustrates the substrate of Figure 5 after diffusion of the boron dopant from the glass layers to form the source and drain regions for the p-channel transistor.
• Figure 7 illustrates the substrate of Figure 4 for an alternate embodiment where the n-type dopant is diffused from a glass layer.
• Figure 8 illustrates a preliminary processing step for the substrate of Figure 1 prior to the formation of the first glass layer.
• Figure 9 illustrates another preliminary step for the substrate of Figure 1 prior to the formation of the first glass layer.
• a method and structure for forming low damage, shallow source and drain regions in alignment with a gate for a field-effect transistor is described.
• numerous well-known steps such as masking and etching steps are not discussed in detail in order not to obscure the present invention.
• specific details are set forth such as specific boron dopant concentrations in order to provide a thorough understanding of the present invention.
• While the present invention is not Iimited to any particular geometry in one embodiment, it is used for the fabrication of transistors having a channel length of approximately 0.1 um with transistors that operate from a 1.8 volt supply.
• a section of a monocrystalline silicon substrate 15 is illustrated having a well doped within an n-type conductivity dopant (n well 21 ) and a region or well doped with a p-type conductivity dopant (p well).
• n well 21 an n-type conductivity dopant
• p well a region or well doped with a p-type conductivity dopant
• an n well may be used for p-channel transistors with the n-channel transistors being formed directly in a p-type substrate.
• n and p well of Figure 1 are isolated from one another by a recessed isolation region specifically, trench 10. Additionally, within the n well 21 there are other isolation trenches 12 for isolating from one another p-channel transistors formed within the n well. Likewise, there are isolation trenches 13 formed within the p well to isolate n-channel transistors formed in the p well from one another.
• the isolation trenches may be formed using well-known technology. Other isolation technologies such as local oxidation of silicon (LOCOS) may be used instead of trenches
• LOC local oxidation of silicon
• a gate insulative layer (such as a high quality, thermally grown oxide to insulate the gate from the substrate) is formed over the substrate.
• a polycrystalline silicon (polysilicon) layer is deposited and the gates for the field-effect transistors are fabricated using ordinary photolithographic and etching techniques. Two such gates insulated from the substrate are shown in Figure 1. Gate 11 , formed above the n well, as will be seen, is used for a p-channel transistor; the other gate 14, formed above the p well, is used for an n-channel transistor. Numerous steps typically used before the fabrication of the gates are not illustrated, such as cleaning steps, ion implantation steps to adjust threshold voltage, etc. Additionally, other processing steps for reducing the amount of diffusion are discussed later in conjunction with Figures 8 and 9.
• a conformal layer 16 of borosilicate glass (BSG) is deposited over the entire substrate.
• This layer may be 10 ⁇ A-30 ⁇ A thick.
• the layer in one embodiment has a 2% functional description concentration of a p-type conductivity dopant (boron). This layer is referred to hereinafter as 2% BSG layer.
• TEOS or silane based chemistry is used to deposit the 2% BSG layer.
• This layer is formed in one embodiment at a temperature of 400-600°C.
• the p-channel transistor is formed using the present invention while the n-channel transistor is formed using well-known ion implantation.
• the formation of the n-channel transistor is described nonetheless since the masking steps for the n-type implants are used to diffuse the p-type dopant sources.
• Figure 2 illustrates the first of two ion implantation step used in the formation of the n-channel transistor.
• a photoresist layer 17 is formed over the substrate 15. This layer is masked exposed and developed by well-known techniques to reveal the substrate regions where the source and drains are formed for the n-channel transistors and additionally, regions where an n-type dopant is used for well tap 20. This is shown in Figure 2 where the photoresist members 17 protect predetermined areas of the substrate while leaving exposed other areas.
• the exposed portions of glass layer 16 are etched in alignment with the photoresist members 17. This etching step uses a hydrogen fluoride (HF) based solution.
• HF hydrogen fluoride
• the substrate is then subjected to ion implantation of an arsenic dopant as shown by the arrows 18. This forms the regions 19 in alignment with the gate 14 and a region 20 between the trenches 12.
• This arsenic doping implant is relatively light and is used for forming the tip regions of the source and drain regions for the n-channel transistor.
• the main portions of the source and drain regions for this n- channel transistor are subsequently formed with the second ion implantation step.
• a conformal layer of undoped silicon dioxide is formed from tetraethyl orthosilicate (TEOS) by low pressure chemical vapor deposition layer 30 or other undoped LPCVD oxide film is formed over the substrate using well-known processing.
• This layer provides an etchant stop for the spacers formed for the n-channel transistor.
• the TEOS layer may be 5 ⁇ A-30 ⁇ A thick.
• a conformal layer 31 of silicon nitride is formed over the TEOS layer 30.
• This silicon nitride layer is approximately 80 ⁇ A thick in one embodiment.
• Well-known type, i.e., sufficient selectively anisotropic etching is used to etch the silicon nitride layer to form spacers 31 shown on opposite sides of gates 11 and 14 of Figure 4.
• the TEOS layer acts as an etchant step to protect the silicon.
• the TEOS and BSG regions not covered by the nitride spacers are then etched away. A wet etchant may be used for this purpose.
• a thin layer of silicon dioxide (5-20A of chemically grown oxide) may now be formed so that there is an ultra thin uniform oxide on the exposed silicon prior to formation of the second glass layer.
• This oxide is discussed in conjunction with Figure 8.
• a second layer 35 of BSG is formed over the substrate. This time, however, the layer has a 6% concentration of boron (6% BSG).
• This layer in one embodiment is approximately 20 ⁇ A-60 ⁇ A thick and is deposited using a TEOS or silane based chemistries at a temperature of 400-600°C in one embodiment.
• This second glass layer is annealed prior to patterning in an RTA step in the same manner and for the same reason as the first glass layer as discussed above.
• a photoresist layer 40 is masked, exposed and developed to expose generally the same areas that were exposed in Figure 2. Specifically, gate 12, the areas adjacent to gate 12 (source and drain regions) and region 20; the remainder of the substrate shown in Figure 5 is protected by the photoresist members 40.
• the cap layer over the glass layer 35 (if used) and the 6% BSG layer 35 are then etched in alignment with the photoresist members 40. This is done by HF based chemistry.
• the second n-type ion implantation step is now used to implant the arsenic dopant into the regions of the substrate not protected by the photoresist layer 40, spacers 31 , or gate 12.
• the arrows 41 illustrate the implantation of this arsenic dopant.
• This dopant is used to form the main portions N+ of the 45 source and drain regions for the n-channel transistors. Note that since the spacers 31 are in place, the dopant is implanted in alignment with the spacers and not in alignment with the gate.
• this drive step employs rapid thermal processing. Specifically, driving at 1000°C to 1040°C for 10-20 seconds with ramping up to and down from this temperature at 70°C per second. A standard Halogen lamp band rapid thermal reactor is used.
• the depth of these regions can be made even more shallow or intentionally made deeper by diffusing the dopant in an ambient that alters the diffusing in silicon.
• ambients are ones that includes oxygen or ammonia. For instance, if the diffusion takes place in an ambient of 10% oxygen and 90% nitrogen the junction depth is reduced by approximately 20% compared to diffusion in an ambient of 100% nitrogen, in general, the oxygen atoms displace silicon atoms in the silicon lattice thereby slowing the diffusion of the boron in silicon.
• Other annealing ambients or compounds that provide this function may be used.
• Glass layers 16 and 35 may remain in place for the remainder of the processing and may stay in the completed integrated circuit.
• Glass layer 35 may be removed to facilitate a subsequent selective TiSi or CoSi2 layer on gates 1 1 and 12 and regions 41 and 45.
• Figure 8 shows one additional processing step which may be used prior to the deposition of the first glass layer shown in Figure 1.
• the substrate of Figure 1 is again shown prior to the deposition of the 2% glass layer.
• an ultra thin layer 60 of silicon dioxide (5-20A thick) is first formed on the substrate.
• This layer may be a chemically grown oxide layer.
• the glass layer is then formed on the silicon dioxide layer.
• This oxide layer is no thicker than a typical native oxide layer, however, it is intentionally grown to assure its uniformity across the wafer. This is in contrast to a native oxide layer which may not be uniform across the wafer because of, for example, water drops on the wafer. This oxide strongly affects indiffusion of the boron from the glass.
• the ultra thin oxide layer provides a uniform interface and thereby assures more predictable diffusion of the boron into the substrate. As mentioned earlier, this oxide is also formed prior to the deposition of the second glass layer.
• FIG 9 another processing step which may be used to modulate the diffusion rate of the indiffused boron dopant is shown.
• a heavy neutral species such as silicon or implanted with a neutral species such as carbon which alters the boron diffusing in silicon.
• Other heavy or neutral atoms may be used such as arsenic, antimony, indium, nitrogen, fluorine, etc. While in Figure 9 this implantation is shown prior to the formation of the glass layer, the implantation may occur after the formation of the glass layer, that is through the glass layer. The damaging of the substrate surface or presence of neutral species in the substrate surface in this manner can be used to slow the rate of diffusion creating a shallower junction. Silicon damage above 3e14 dose reduces the boron diffusion.
• the various techniques for reducing the diffusion or controlling it such as the growing of the 5-20A of silicon dioxide, the damaging of the upper surface of the substrate, implantation of a neutral species of diffusion in the ambient of oxygen, etc., and the densification of the glass layers prior to their patterning may be used in combination or alone for improving the reliability and performance of the resultant transistors.
• the result of the processing described above is a source and drain region for the p-type transistor having a tip region 40 adjacent to the gate (from the dopant diffused into the substrate from the 2% BSG layer 16) and a more highly doped main portion of the source and drain regions 41 spaced apart from the gate (from the dopant diffused from the 6% BSG layer 35).
• the p-type tip region has a dopant concentration of 1-5x10 19 cr ⁇ r 3 while the main portion of the source and drain region has a dopant concentration of 2-5x10 20 cn ⁇ 3 .
• concentrations of dopants in the glass may be used.
• layer 16 may have a dopant concentration between 1 to 4% and layer 35 may have a dopant concentration between 6 to 12%.
• the ultra-shallow p+ regions formed with the described invention, as illustrated in the figures has shown to provide substantial improvement over prior art fabrication where the p-channel source and drain regions are formed with a tip implant in alignment with the gate followed by implantation of the main portion of source and drain regions in alignment with a spacer.
• Transistors made with the low damage doped source and drain regions of the present invention have shown in one benchmark to have a 25% improved gate delay when operated at 1.8v even when compared to a prior art transistor operated at 2.5v.
• the present invention as described above, two masking steps are saved when compared to the prior art technique of forming the p- channel device through two implantation steps, one for the tip implant and the other for the main portion of the source and drain regions. Note that with the present invention, the two masking steps used to expose those areas of the substrate which are doped with the n-type dopant for the n- channel transistor source and drain region are also used to etch the BSG layers 16 and 35. In the prior art, two additional masking steps are needed to protect the n-channel device when the p-channel device are implanted.
• the glass layer 35 is etched in alignment with the photoresist members 40 prior to the implantation illustrated by lines 41. It may be desirable in some processes to leave the 6% BSG layer in piace.
• the second ion implantation step used to form the N+ source and drain regions for the n-channel transistor is then done through this glass layer.
• the counter doping effect of the boron dopant in the n- type source and drain regions in general will not present a problem.
• the arsenic dopant level of the source and drain region for the n-channel transistor is high and consequently, not significantly affected by the introduction of the boron atoms. Leaving Iayer 35 in place saves the step used to remove this Iayer from the areas not protected by the photoresist members.
• the p-channel transistor is shown fabricated with the present invention and the n-channel transistor is fabricated using conventional ion implantation, the n-channel transistor may likewise be fabricated using one or two layers of glass phosphorous or arsenic doped glass.
• the dopant for the p-channel transistor was obtained from a glass, specifically BSG, other materials may be used as a source of the dopant such as polysilicon or germanium-silicon.
• Figure 7 illustrates altemate processing where a single glass Iayer doped with an n-type dopant is used.
• an additional glass Iayer 50 doped with the n-type dopant e.g., 6% PSG
• the glass Iayer 50 is formed over the structure shown in Figure 5 without the photoresist Iayer 40.
• the n-channel transistor is simultaneously formed.
• Dopant from Iayer 50 forms the main source/drain regions of the n-channel transistor. Note the dopant from Iayer 50 does not diffuse into the Iayer 35. This dopant also diffused under the spacers on gate 12 to form more lightly doped tip regions for the n-channel transistor.
• the gate 12 is doped with the n-type dopant from Iayer 50.
• the glass Iayer 16 need not be used to form the p- channel transistor. That is, as in the case of the n-channel transistor described in conjunction with Figure 7, the dopant may be driving under the spacer from the 6% glass Iayer to form the tip source/drain regions. This permits the doping of source/drain for both n-channel and p-channel transistors with a single masking step.

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• 1996
  • 1996-10-03 AU AU72574/96A patent/AU7257496A/en not_active Abandoned
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