GB2355851A - Short gate/channel MOSFET - Google Patents
Short gate/channel MOSFET Download PDFInfo
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- GB2355851A GB2355851A GB0015499A GB0015499A GB2355851A GB 2355851 A GB2355851 A GB 2355851A GB 0015499 A GB0015499 A GB 0015499A GB 0015499 A GB0015499 A GB 0015499A GB 2355851 A GB2355851 A GB 2355851A
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/43—Electrodes ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/49—Metal-insulator-semiconductor electrodes, e.g. gates of MOSFET
- H01L29/51—Insulating materials associated therewith
- H01L29/511—Insulating materials associated therewith with a compositional variation, e.g. multilayer structures
- H01L29/513—Insulating materials associated therewith with a compositional variation, e.g. multilayer structures the variation being perpendicular to the channel plane
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/02—Elements
- C30B29/06—Silicon
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B33/00—After-treatment of single crystals or homogeneous polycrystalline material with defined structure
- C30B33/005—Oxydation
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- 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
- H01L21/02104—Forming layers
- H01L21/02107—Forming insulating materials on a substrate
- H01L21/02225—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer
- H01L21/02227—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a process other than a deposition process
- H01L21/0223—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a process other than a deposition process formation by oxidation, e.g. oxidation of the substrate
- H01L21/02233—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a process other than a deposition process formation by oxidation, e.g. oxidation of the substrate of the semiconductor substrate or a semiconductor layer
- H01L21/02236—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a process other than a deposition process formation by oxidation, e.g. oxidation of the substrate of the semiconductor substrate or a semiconductor layer group IV semiconductor
- H01L21/02238—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a process other than a deposition process formation by oxidation, e.g. oxidation of the substrate of the semiconductor substrate or a semiconductor layer group IV semiconductor silicon in uncombined form, i.e. pure silicon
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- 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
- H01L21/28—Manufacture of electrodes on semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/268
- H01L21/28008—Making conductor-insulator-semiconductor electrodes
- H01L21/28017—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon
- H01L21/28158—Making the insulator
- H01L21/28167—Making the insulator on single crystalline silicon, e.g. using a liquid, i.e. chemical oxidation
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- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/401—Multistep manufacturing processes
- H01L29/4011—Multistep manufacturing processes for data storage electrodes
- H01L29/40114—Multistep manufacturing processes for data storage electrodes the electrodes comprising a conductor-insulator-conductor-insulator-semiconductor structure
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- H—ELECTRICITY
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/43—Electrodes ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/49—Metal-insulator-semiconductor electrodes, e.g. gates of MOSFET
- H01L29/51—Insulating materials associated therewith
- H01L29/517—Insulating materials associated therewith the insulating material comprising a metallic compound, e.g. metal oxide, metal silicate
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- 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
- H01L21/28—Manufacture of electrodes on semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/268
- H01L21/28008—Making conductor-insulator-semiconductor electrodes
- H01L21/28017—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon
- H01L21/28158—Making the insulator
- H01L21/28167—Making the insulator on single crystalline silicon, e.g. using a liquid, i.e. chemical oxidation
- H01L21/28194—Making the insulator on single crystalline silicon, e.g. using a liquid, i.e. chemical oxidation by deposition, e.g. evaporation, ALD, CVD, sputtering, laser deposition
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- Insulated Gate Type Field-Effect Transistor (AREA)
Abstract
The device 10 has a gate length of 0.05-1.25 microns where the short channel effect is prevented by halo or pocket implantation regions 13 formed in the channel rather than by lightly doped drain or source regions. The thin gate oxide 16 comprises upper and lower portions 17 and 18, and is substantially stress free and planar with respect to the substrate 12.
Description
2355851 MOS TRANSISTOR AND METHOD OF MANUFACTURE
Field of the Invention
The present invention relates integrated circuits generally, and particularly to a MOS transistor and its method of manufacture.
Background of the Invention
As integrated circuit (IQ complexity increases, the size of devices within the IC must decrease. To decrease the size of a device, the various elements (features) of a device must be reduced proportionately. This is known as device scaling. One common device in integrated circuits is the metal oxide semiconductor field effect transistor (MOSFET). In a MOSFET, device scaling requires a reduction gate and channel lengths. As gate and channel lengths are reduced, a number of effects can result in unacceptable reliability and performance in the MOSFET. These effects are commonly referred to as short-channel effects and are particularly problematic in devices-having channel lengths of approximately 1.25 gin or less.
One effect of the reduced channel length devices is increased horizontal and vertical electric field components, particularly in the drain region. This increase in the electric field can cause inversion-layer carriers to be accelerated (or become "hot") to an extent that they may cause a number of harmful device phenomena, commonly referred to as hot carrier effects. Ultimately, these phenomena can adversely impact device reliability and perforTnance.
One way to overcome hot carrier effects is through the use of a lightly doped drain (LDD) structure. In an LDD structure, the source and drain have graded doping profiles. In the source and drain regions nearest the channel, the doping level is lower, relative to the more highly doped source and drain regions farther from the channel. The lightly doped source and drain regions serve to reduce the electric field strength in the regions of the channel near the source and drain. This reduced electric field strength has been somewhat successftil in reducing hot carrier generation, and thereby hot carrier effects.
While the LDD structure has been useful in reducing short channel effects such as hot carrier effects, there are certain drawbacks to its use. One such drawback is an increase in series resistance between the source and the drain (referred to -2as series source-drain resistance (R,d)). This is due to the reduced doping level at the lightly doped source and drain region. This increased resistance results in a reduction in the saturation current (also referred to as drive current Id,al or "on" current I.). A reduction in Ion may result in a reduction in device switching speed. A MOSFET being used as a switch may be thought of as a device for charging and discharging a capacitor. The time required to charge the capacitor is directly related to the current. As such, if the current is reduced, the switching speed is, reduced. Accordingly, this increase in Rd in conventional devices incorporating an LDD is undesirable.
Another drawback to the LDD structure is the complexity of its fabrication. In order to fabricate this structure, there are many additional processing steps that must be added to the process flow in MOSFET fabrication. These include additional photolithographic masking levels, LDD implantation and the formation of a dielectric spacer.
Accordingly, what is needed is a device that overcomes the above illustrated drawbacks of LDD MOSFET devices.
Summary of-the Invention
The present invention relates to a reduced feature size MOS transistor that has improved short channel effects but does not include an LDD structure. In an illustrative embodiment, a MOS transistor has a gate length of 1.25 irn or less.
Moreover, by eliminating the use of the LDD structure, series sourcedrain resistance is reduced resulting in improved drive current and switching speed.
In another embodiment, a technique for fabricating a MOS transistor is disclosed. Illustratively, a gate structure having a length of 1.25 [trn or less is formed over a substrate. Thereafter, a source and a drain are formed without lightly doped regions.
Brief Description of the Drawings
The invention is best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
Figure I is a cross-sectional view of an exemplary embodiment of the present invention.
Figures 2-4 are cross-sectional views of an illustrative fabrication sequence according to an exemplary embodiment of the present invention.
Figure 5 is a graphical representation of time versus substrate current indicative of hot carrier aging (HCA) according to an exemplary embodiment of the 5 present invention and for a conventional device.
Figure 6 is a graphical representation of drive gate length versus drive current for conventional devices which use an LDD structure and for exemplary devices of the present invention.
Detailed Description
The present invention will now be described more fully with reference to the accompanying drawing figures, in which exemplary embodiments of the present invention are shown. Referring to Fig. 1, a MOS transistor 10 in accordance with an exemplary embodiment of the present invention is first described. Illustratively, the transistor 10 includes a gate structure 11 disposed over a substrate 12. A channel 13 is disposed between a source 14 and a drain 15. The gate structure I I includes an oxide layer 16, which includes a first oxide portion 17 and a second oxide portion 18. The second oxide portion 18 forms an interface 19 with the substrate 12. The oxide layer may have a layer of material 20 disposed between it and a conductive layer 2 1.
For purposes of illustration, the transistor 10 is an NMOS device. As such, the source 14 and drain 15 are d6ped n+, while the substrate is ptype. Of course, the present invention may be used in other devices including PMOS and complementary MOS (CMOS) devices. The substrate 12 is illustratively silicon; it may be monocrystalline or polycrystalline silicon. Most generally it is oxidizable silicon. Layer 20 may be a highk material, including but not limited to tantalum pentoxide, barium-strontium titanate, and silicate dielectric materials. Additionally, other materials may be disposed between the conductive layer 21 and the oxide layer 16 to achieve a variety of results as would be appreciated by the artisan of ordinary skill.
The MOS field effect transistor of the exemplary embodiment of Figure 1, does not incorporate a lightly doped drain or a lightly doped source. This is in clear contrast to conventional devices having gate lengths of approximately 1. 25 Rni or less which employ an LDD structure to mitigate hot carrier effects. In the exemplary embodiment shown in Fig. I the device 10 may have a gate length (and thus a channel -4length), L, on the order of approximately 1.25 Vtm or less. Moreover, sub-Micron devices may incorporate the present invention. It is anticipated that t he gate lengths may be in the range of approximately 0. 25 trri to approximately 0.05 tm. Finally, as is well known in the art, device scaling mandates that the gate length and other device features must be proportional according to scaling rules. Thus, the oxide layer 16 has a thickness that is scaled to the gate length chosen. Accordingly, in the illustrative embodiment, gate lengths in the range of approximately 1.25 irn to approximately 0.05 trn corresponds to the oxide layer I I having a thickness in the range of approximately 20.0 mu to approximately 1.5 nm, respectively.
The oxide/substrate interface 19 is substantially stress-free and planar.
Moreover, oxide layer 16 has a reduced number of interface traps (Nit) and a reduced defect density (D,,) compared to conventional oxides. These and other characteristics of the oxide layer 16 are useful in achieving the inv ention of the present disclosure. As discussed in more detail below, the device of the present invention has certain advantageous characteristics over conventional devices. These characteristics include an improvement in drive current and switching. speed. Moreover, this increase in drive current may be realised even though the channel may require an increased doping level used to curb an undesired short channel effect known as punchthrough (discussed more fully herein). Additionally, the effects of hot carriers, which can result in a degradation in device reliability, can be minimized in devices using the present invention. Finally, the present invention is advantageous because it reduces the complexity of fabrication. To this end, the relatively complex processing sequences needed to form LDD structures, which are considered a necessary trade-off in conventional short channel length devices, are unnecessary in the present invention.
25. Turning now to Figs.2-4, an illustrative fabrication sequence is described.
Figure 2 is the oxide growth sequence used in the formation of oxide layer 16 over the substrate 13, resulting the formation of a substantially stress free and planar interface 19. Thereafter, as shown in Fig. 3, the gate structure 11 is completed via conventional processing schemes which may include: deposition of a high-k layer; amorphous silicon or polycrystalline silicon deposition, gate impla ntation and gate masking steps.
As shown in Fig. 3), after the gate structure 11 is completed, the channel 0 is formed. This may be carried out by standard implantation techniques. The channel doping is raised via tilted "halo" or "pocket" implants 30 of the same conductivity type as the channel. For the exemplary NMOS device, an implant such as boron in the energy range of 5-40keV, a dose in the range of approximately 5x 1011 to rD approximately 5x 1013 /cm', at an implant tilt angle in the range of 7- 45' (with respect to a normal to the substrate) may be used. Similarly, for a PMOS device a phosphorus implant in the energy range of 20-120keV, a dose in the range of approximately 5x 10 to approximately 5x 1013 /CM2, at an implant tilt angle in the range of 7- 45' may be used.
The illustrative channel doping concentration is now in the range of approximately I X 1016 to approximately I X 10 19 /CM3. This channel doping step serves to reduce punclithrough and thus short channel effects in the devices.
As shown in Fig. 4, after the halo implantation, the source 14 and drain are formed. In the exemplary NMOS device, this is carried out by implanting arsenic in the energy range of 5-50keV, a dose in the range of approximately 5x 1014 to approximately 5x 1015 /CM2, and an implant tilt angle in the range of 0- 7'. Similarly, for the PMOS device the source and drain is formed via a boron implant in the energy range of 0.5-10keV, a dose in the range of approximately 5x 10 14 to approximately 5xlO 15 /CM2, and a implant tiltangle in the range of 0-7. Alternatively, a BF2 implant in the energy range of 5-50keV, a dose range of approximately 5x 1014 to approximately 5xlO'5 /CM2, and a implant tilt angle in the range of 0-7'. The resulting doping levels in the source and drain are in the range of approximately 1 X 1020 /CM3 to approximately 5x 1020 /CM3. In clear contrast to the prior art LDD devices, the source 14 and drain 15 in the illustrative embodiment of Figs. I and 4 are substantially uniformly doped, and do not include a lightly doped region.
Through a review of Figs. 2-4, the relative ease of fabrication of the illustrative embodiment may be appreciated. The process needed to fabricate conventional short channel devices includes the fabrication of an LDD. At minimum, this adds a mask formation step so that a first implantation could be carried out. This is needed to form the lightly doped source and drain regions. Thereafter, a spacer must be deposited and etched. In conventional LDD devices, the spacer is needed in the fabrication of the more heavily doped regions of the source and drain. In addition to adding to the complexity of fabrication, the added implants and spacer may have deleterious effects on the resultant device. These include, for example increased series -6source/drain resistance, R,d, and thus reduced saturated drive current Idsat and switching speed.
As mentioned previously, hot carrier effects can adversely impact device reliability. In MOS transistors having gate lengths of approximately 1.25 microns or less, hot carrier effects result from increased horizontal and vertical components of the electric field in the reduced length channel. This causes inversion-layer charges to be accelerated (or heated) to an extent that they may cause a number of harmful device phenomena, commonly referred to as hot carrier effects. Hot carrier effects can ultimately degrade the reliability of the device. This is commonly referred to as hot carrier aging (HCA).
Hot carrier aging is believed to be due to interface trap generation or the breaking of passivated dangling bonds by hot carriers. Dangling bonds in the siliconsilicon dioxide interface are conventionally passivated in a hydrogen ambient, thereby reducing the number of interface traps. While this passivation technique has met with some success in conventional devices, hot carriers can readily break silicon-hydrogen bonds, thereby re-establishing the previously passivated interface traps. The traps in the interface act as scattering centers, thereby reducing the mobility of carriers within the channel.
As is known, the drive current, 1,,, (or saturation current, Id,at), and the transconductance, g,,, are directly proportional to the mobility of the carriers in the channel. Accordingly, as the scattering centers become more abundant due to hot carrier effects, the mobility of carriers in the channel is reduced, and the drive current and transconductance are reduced. Thus, the number of interface traps can cause the device to degrade (age) due to drift in device parameters such as drive current and transconductance. This degradation has a deleterious impact on device reliability.
The oxide layer 16 has a reduced incidence of dangling silicon bonds, and thereby a reduced number of interface traps. Applicants theorize that this is a result of a more complete oxidation process and because the interface is substantially stressfree and planar. Moreover, since there are fewer interface traps in the oxide of the present invention, there are fewer traps to be pa ssivated with hydrogen. It is anticipated that there will be less device drift due to hydrogen release in devices which incorporate the oxide of the present invention. Finally, while the LDD structure has helped to -7reduce hot carrier effects in short channel devices, the illustrative embodiment of the present invention results in a greater reduction in hot carrier effects The resulting improvement in hot carrier aging can be seen clearly in the graphical representation of Fig. 5. The hot carrier aging criterion by convention is a 15% change in transconductance. The plot labeled 51 is for a device according to an illustrative embodiment of the present invention incorporating a 0.24 gm gate length with an oxide layer having a thickness of 5 rim (50A). The plot labeled 50 is for a conventional device having the same gate length, which incorporates an LDD structure to reduce the ill-effects of hot carriers. As is evident from Fig. 5, the substrate current limit of I iA/Vtm is achieved at 100 hours in a conventional LDD MOSFET; and in an exemplary device of the present invention this is limit achieved at 400 hours. As will be readily appreciated to those of ordinary skill in the art, in devices having comparable gate lengths, hot carrier aging is improved by a factor of four by the present invention when compared to conventional devices, which require the LDD structure.
In addition to improvements in reliability through reduced HCA, the device of the present invention also has increased drive current as a result of both increased carrier mobility and reduced source-drain resistance. The increased mobility is a result of the reduction in scattering centers, as discussed above. The reduction in Rsd is a direct benefit of the elimination of the lightly doped source and drain regions used in conventional LDD structures. To this end, because the incidence of hot carriers is reduced by means other than the LDD structure, it is not needed in the exemplary device of the present invention. Accordingly, the source and drain doping levels of the present invention are substantially uniform being in the range of approximately I X 1020 to approximately 5x 1020/CM3. This results in a source-drain sheet resistance in the range of approximately 50 to approximately 150 ohms/sq. This translates directly into Rsd Of approximately 2 5 to approximately 100 ohms per pm. of gate width in an exemplary device of the present invention. (It is of interest to note that by convention, gate width is measured along the z- direction in the coordinate axis shown in Fig. 1). In contrast, the lightly doped regions of a conventional lightly doped source and lightly doped drain are 1019/CM3 on the orderof IxIO19 to 5x. The corresponding source/drain sheet resistance of a conventional LDD is in the range 500-1500 ohms/sq. This results in Rsd, Of 100200 ohms per tm of gate width in such conventional devices.
As a result of the reduction in the series source drain resistance by virtue of the present invention, the drive current is improved. Turning to Figure 6, a graphical representation of gate length versus drive current is shown. Plot 60 is a graph of the drive current of exemplary devices of the present invention. Plot 61 is for conventional devices which use an LDD structure. Clearly, an improvement in transistor drive current. Idsatis measured in illustrative devices of the present invention when compared to conventional device having similar feature sizes, and which incorporate an LDD structure.
As alluded to above, the increased drive current results in a faster switching speed. Again, a MOSFET being used as a switch may be thought of as a device that charges and discharges a capacitor. These capacitors are intrinsic parts of CMOS circuits arising from such elements as MOS gate capacitance, source/drain junction capacitance, and metal interconnect capacitance. The time required to charge the capacitor is directly related to the current. As such, if the drive current is increased, the switching speed is increased. Having improved drive current levels results in a ring oscillator circuit using exemplary MOSFETs of the present invention having switching speeds on the order of 25% greater than conventional LDD MOS transistors Moreover, this increase in the drive current in the exemplary device of the present invention is realized even though the threshold voltage Vt may be slightly increased. To this end. one phenomena that may occur in reduced channel length devices is known as punch-through. Punch through is normally observed when the applied gate voltage is well below Vt. Punch-through occurs when the drain depletion region widens when the reverse bias on the drain is increased. When this depletion region width is great enough, the source and drain depletion regions may meet and an unacceptable level of carrier flow may occur. This results in poor charge control, and is manifest in unacceptable off current levels. While the LDD structure, having reduced doping levels at the source and drain regions nearest the channel may reduce the effects of punch through, often this must be mitigated by increasing the doping level of the channel to reduce the drain/source depletion region width. However, the increased channel doping concentration can increase the threshold voltage as a greater voltage is required to create inversion for conduction in the channel. The increased threshold voltage may cause a reduction in the drive current. Thus, the trade-off to the reduction in punch through via increased channel doping is often a reduction in drive current in conventional LDD devices.
Applicants have found that the exemplary device of the present invention maintains an increase in the drive current in spite of the increase in threshold voltage.
Illustratively, in a 0.24 pm feature size device. the drive current increased 20% over a similar conventional LDD device having similar device feature sizes. This was in spite of a 50 mV increase in the threshold voltage. Applicants attribute this to the reduction in the series source-drain resistance realized through the invention of the present disclosure.
The invention having been described in detail, it is clear that various modification and variations of the embodiments disclosed above may be readily apparent to one having ordinary skill in the art having had the benefit of the present disclosure without departing from the scope of the invention as claimed.
Claims (25)
1. A semiconductor device, comprising:
a substrate having a source, a drain and a channel between said source and said drain; and a gate structure disposed over said channel, said gate structure having a length of 1.25 Lrn or less and wherein the device does not include a lightly doped drain region.
2. A semiconductor device as recited in claim 1, wherein said gate structure includes an oxide layer and said oxide layer has a thickness in the range of approximately 1.5 mn to approximately 20.0 nm.
3. A semiconductor device as recited in claim 2, wherein said oxide layer and said substrate form an interface and said interface is substantially planar and stress-free.
4. A semiconductor device, said device being a field effect transistor, comprising:
substrate having a source, a drain and a channel between said source and said drain; gate structure including an oxide, which forms an interface with said substrate, wherein said gate structure has a length in the range of approximately 0.05 [tm to approximately 0.25 4m and the transistor does not include a lightly doped drain region.
5. A semiconductor device as recited in claim 4, wherein said oxide layer has a thickness in the range of approximately 1.5 rim. to approximately 20.0 run.
6. A semiconductor device as recited in claim I or claim 4, wherein said channel has a length in the range of approximately 0.05 Lm to approximately 0.25 Rm.
7. A semiconductor device as recited in claim claim I or claim 4, wherein a series source/drain resistance exists in the transistor, and said series - I I source/drain resistance is in the range of approximately 20 0 to approximately 100 Q per pm of gate width.
8. A semiconductor device as recited in claim I or claim 4, wherein the device is an NMOSFET.
9. A semiconductor device as recited in claim 8, wherein said source and said drain are doped n+ and said substrate is p-type.
10. A semiconductor device as recited in claim 1 or claim 4, wherein said source and drain have a doping concentration in the range of approximately I X 1020 atoMS/CM3 to approximately 5x 1020 atoMS/CM3.
11. A semiconductor device as recited in claim I or claim 4, wherein the device is PMOSFET.
12. A semiconductor device as recited in claim 11, wherein said source and said drain are doped p+ and said substrate is n-type.
I I A semiconductor device as recited in claim 4, wherein said interface is substantially planar and stress-free.
14. A semiconductor device as recited in claim I or claim 4, wherein said channel has a doping concentration of approximately IXIO I 6/CM3 to approximately I X 10 19/CM3.
15. A process for fabricating an integrated circuit, comprising:
20. forming a gate structure over a substrate, said gate structure having a length of approximately 1.25 pin or less; and forming a source and a drain, said source and said drain not having lightly doped regions.
16. A process as recited in claim 15, wherein said process further comprises forming a channel before forming said source and said drain.
17. A process as recited in claim 15, wherein said forming said gate structure further comprises:
forming an oxide layer over said substrate; and forming a conductive layer over said oxide layer.
18. A process for fabricating an integrated circuit, comprising:
forming an oxide layer over a substrate; forming a conductive layer over said oxide layer, said oxide layer and said conductive layer forming a gate having a length of 1.25 gm. or less; forming a channel in said substrate; and forming a source and a drain, said source and said drain not having lightly doped regions.
19. A process as recited in claim 16 or claim 18, wherein said channel is doped by a halo implantation.
20. A process as recited in claim 15 or claim 18, wherein said length is in the range of approximately 0.25 gm to approximately 0.05 Lrn.
2 1. A process as recited in claim 17 or claim 18, wherein said oxide layer has a first oxide portion and a second oxide portion.
22. A process as recited in claim 15 or claim 18, wherein a spacer is not formed adjacent said gate structure.
23. A process as recited in claim 17 or claim 18, wherein said oxide layer has a thickness in the range of approximately 1.5 nm to approximately 20.0 nm.
24. A process as recited in claim 15 or claim 18, wherein said source an& said drain having doping levels in the range of approximately I X 1020/CM3 to approximately 5x 1020/CM3.
25. A process as recited in claim 16 or claim 18, wherein said channel has a doping level in the range of approximately I X 10 16/CM3 to approximately 1xlO 19/CM3.
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US14090999P | 1999-06-24 | 1999-06-24 | |
US16803699P | 1999-11-30 | 1999-11-30 | |
US09/597,076 US6551946B1 (en) | 1999-06-24 | 2000-06-20 | Two-step oxidation process for oxidizing a silicon substrate wherein the first step is carried out at a temperature below the viscoelastic temperature of silicon dioxide and the second step is carried out at a temperature above the viscoelastic temperature |
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US6521496B1 (en) | 1999-06-24 | 2003-02-18 | Lucent Technologies Inc. | Non-volatile memory semiconductor device including a graded, grown, high quality control gate oxide layer and associated methods |
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