Classifications

• • 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
  • H10D84/0144—Manufacturing their gate insulating layers
• • 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
• • 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
• • 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
  • H10D84/80—Integrated devices formed in or on semiconductor substrates that comprise only semiconducting layers, e.g. on Si wafers or on GaAs-on-Si wafers characterised by the integration of at least one component covered by groups H10D12/00 or H10D30/00, e.g. integration of IGFETs
  • H10D84/82—Integrated devices formed in or on semiconductor substrates that comprise only semiconducting layers, e.g. on Si wafers or on GaAs-on-Si wafers characterised by the integration of at least one component covered by groups H10D12/00 or H10D30/00, e.g. integration of IGFETs of only field-effect components
  • H10D84/83—Integrated devices formed in or on semiconductor substrates that comprise only semiconducting layers, e.g. on Si wafers or on GaAs-on-Si wafers characterised by the integration of at least one component covered by groups H10D12/00 or H10D30/00, e.g. integration of IGFETs of only field-effect components of only insulated-gate FETs [IGFET]
  • H10D84/85—Complementary IGFETs, e.g. CMOS

Definitions

• This invention relates generally to semiconductor fabrication technology, and, more particularly, to a method of making transistors with gate insulation layers of differing thickness.
• Figure 1 depicts an example of an illustrative transistor 10 fabricated on a wafer or substrate 11.
• the transistor 10 is comprised of a gate insulation layer 14, a gate electrode 16, sidewall spacers 19 and source/drain regions 18.
• the gate electrode 16 has a critical dimension (gate length) 16 A.
• Trench isolation regions 17 are also formed in the substrate 11.
• Also depicted in Figure 1 are a plurality of conductive contacts 15 formed in a layer of insulating material 21. The conductive contacts 15 provide electrical connection to the source/drain regions 18.
• the transistor 10 defines a channel region 12 in the substrate 11 beneath the gate insulation layer 14.
• the substrate 11 is normally doped with an appropriate dopant material, e.g., a P-type dopant such as boron or boron difluoride for NMOS devices, or an N-type dopant such as arsenic or phosphorous for PMOS devices.
• a P-type dopant such as boron or boron difluoride for NMOS devices
• an N-type dopant such as arsenic or phosphorous for PMOS devices.
• the gate insulation layer 14 which is typically comprised of silicon dioxide, may be formed as thin as 2.0-2.5 nm (20-25 A), and further reductions are planned in the future.
• the thin gate insulation layer 14 enables higher transistor drive currents and faster transistor switching speeds.
• reducing the thickness of the gate insulation layer 14 to the levels described above may also lead to other problems.
• a gate current i.e., a current between the substrate 11 and the gate electrode 16 may be established.
• Such a gate current is due, in part, to the reduced thickness of the gate insulation layer 14, which tends to limit its ability to perform its intended ' function of electrically isolating the gate electrode 16.
• This gate current can be problematic in many respects in that it may increase power consumption and off-state leakage currents for the transistor 10.
• transistors with different gate insulation thicknesses for various circuits within the integrated circuit device, i.e., so-called dual gate oxide circuits, triple gate oxide circuits. That is, for at least some circuits, the gate insulation layer 14 for certain transistors 10 is formed to a very thin thickness, whereas other transistors in less critical circuits of the integrated circuit device have a thicker gate insulation layer 14.
• a first transistor 22 has a relatively thick gate insulation layer 22A
• a second transistor 24 has a relatively thin gate insulation layer 24 A.
• the relative thicknesses of the gate insulation layers 22A, 24 A depicted in Figure 2 are exaggerated for purposes of clarity and explanation.
• the transistor 24 may form part of a critical path of the integrated circuit device in terms of performance, whereas the transistor 22 may not be in such a critical path, or it may otherwise be important to provide a relatively thick gate insulation layer 22A for the transistor 22, i.e., it may be part of the input/output circuitry for the integrated circuit product.
• One illustrative process flow for forming the transistors 22, 24 depicted in Figure 2 is as follows. Initially, the trench isolation regions 17 are formed in the substrate 11. Thereafter, a sacrificial oxide layer (not shown) may be deposited or thermally grown above the surface of the substrate 11. Next, a patterned layer of photoresist (not shown) is formed above the substrate 11. The patterned layer of photoresist is used to expose selected portions of the substrate 11 where it is desired to form transistors having an increased gate insulation thickness, such as the transistor 22 depicted in Figure 2. After the masking layer is formed, an ion implant process is performed to implant fluorine atoms through the sacrificial oxide layer into the portions of the substrate 11 exposed by the patterned masking layer.
• a wet etching process typically a wet etching process using HF acid, is used to remove the sacrificial oxide layer and to generally clean the substrate 11 prior to the formation of the gate insulation layers 22A, 24A for the transistor devices 22, 24.
• a thermal oxidation process is performed to form the gate insulation layers 22A, 24A depicted in Figure 2.
• the gate insulation layers formed in areas where fluorine is implanted into the substrate 11 are thicker because the implanted fluorine atoms enhance the oxidation rate of the silicon substrate 11.
• traditional processing operations may be continued to form the transistors 22, 24.
• the aforementioned process flow is not without problems.
• the trench isolation regions 17 that were previously exposed to the fluorine implant process tend to etch at a faster rate than that of trench isolation regions 17 not exposed to the fluorine implant process.
• the isolation regions 17 implanted with fluorine i.e., the insulation regions associated with the transistor 22, tend to be over-etched during the wet etching process used to remove the sacrificial oxide layer.
• portions 23 of the substrate 11 adjacent the affected isolation regions 17 may be exposed.
• the exposed portions of the substrate 11 may be problematic in many respects, e.g., it may lead to reduced device performance.
• the present invention is directed to a method that may solve, or at least reduce, some or all of the aforementioned problems.
• the present invention is generally directed to a method of making transistors with differing gate insulation thickness.
• the method comprises forming a sacrificial layer of material above a substrate comprised of silicon, performing a wet etching process to remove the sacrificial layer, implanting fluorine atoms into selected portions of the substrate after the sacrificial layer is removed, and performing a thermal oxidation process to form a plurality of gate insulation layers above the substrate, the gate insulation layers formed above the fluorine implanted selected portions of the substrate having a thickness that is greater than a thickness of the gate insulation layers formed above portions of the substrate not implanted with fluorine.
• Figure 1 is a cross-sectional view of an illustrative prior art semiconductor device formed above a substrate
• Figure 2 is a cross-sectional view of an illustrative substrate having a plurality of transistors with gate insulation layers of differing thickness formed in accordance with one illustrative prior art technique;
• Figures 3A-3F are various cross-sectional views of a method in accordance with one illustrative embodiment of the present invention.
• Figures 4A-4B are plots of various test data indicating the effectiveness of the present invention.
• the present invention is directed to a method of making transistors with gate insulation layers of differing thickness.
• the present invention will be initially disclosed in the context of the formation of an illustrative NMOS transistor, those skilled in the art will understand after a complete reading of the present application that the present invention is not so limited. More particularly, the present invention may be employed with respect to a variety of technologies, e.g., NMOS, PMOS, CMOS, etc., and it may be employed with a variety of different type devices, e.g., memory devices, microprocessors, logic devices, etc. The present invention may also be employed in the context of forming integrated circuit devices above silicon-on-insulator (SOI) substrates and the like.
• SOI silicon-on-insulator
• a plurality of isolation regions 32 are formed in a semiconducting substrate 30, and a sacrificial layer 34 is formed above the surface 36 of the substrate 30.
• various well implants and anneal processes may be performed to form the desired wells (if any) within the substrate 30 for forming NMOS and PMOS devices, i.e., a CMOS application.
• the isolation regions 32 may be formed by a variety of known techniques. For example, a plurality of trenches may be formed in the substrate 30 and subsequently filled with an insulating material, such as silicon dioxide.
• the sacrificial layer 34 may be comprised of, for example, silicon dioxide, it may have a thickness of approximately 10-20 nm (100- 200 A), and it may be formed by a plurality of techniques, i.e., deposition, thermal growth, etc.
• a wet etching process is performed to remove the sacrificial layer 34 and clean the surface 36 of the substrate 30 prior to the formation of the gate insulation layers for the completed device.
• This wet etching process may be performed using, for example, a dilute HF acid at a concentration of approximately 10:1.
• a patterned layer of photoresist 38 (positive or negative material) is formed above the surface 36 of the substrate 30.
• the patterned layer of photoresist 38 has a plurality of openings 39 through which areas of the substrate 30 are exposed for further processing.
• An ion implantation process is then performed to implant fluorine atoms into the portions of the substrate 30 exposed by the patterned masking layer 38.
• the implant dose of the fluorine atoms will vary depending upon the desired thickness of the gate insulation layers to be formed above the substrate 30 in the regions where the fluorine atoms are implanted.
• the ion implant process 40 may be performed using an implant dose of approximately 5E 14 -5E 15 ions/cm 2 .
• This ion implant process results in the implantation of fluorine atoms into the substrate 30, as indicated by a region 33. Note that this ion implant process 40 is performed after the sacrificial layer 34 has been removed by performing a wet etching or stripping process, e.g., a dilute HF acid etch process.
• the patterned layer of photoresist 38 is removed and the surface 36 of the substrate 30 is cleaned.
• the removal of the photoresist material may be accomplished by a variety of techniques, e.g., by performing an oxygen (0 2 ) plasma ashing process, followed by a dilute sulfuric acid wet rinse process.
• the sacrificial layer 34 is removed prior to the fluorine implant step 40 wherein fluorine atoms are implanted into the exposed portions of the substrate 30 and the exposed isolation structures 32.
• the present invention may be used to reduce or eliminate the exposed portions 23 of the substrate, as depicted in Figure 2.
• a thermal oxidation process is performed at a temperature of approximately 600-1000°C to form gate insulation layers 42, 44 depicted in Figure 3E.
• the gate insulation layer 42 has a thickness that is approximately 0.1-1.0 nm (1-10 A) thicker than the gate insulation layer 44.
• the increased thickness of the gate insulation layer 42 is due to the presence of the fluorine atoms implanted during the implant process 40 described above.
• the difference in the thickness of the insulation layers 42, 44 may be controlled based upon the amount of fluorine implanted into the substrate 30. In general, the more fluorine implanted into the substrate 30 during the implant process 40, the greater than the thickness differential between the gate insulation layer 42 and the gate insulation layer 44.
• the gate insulation layer 42 may have a thickness of approximately 2.1-3.0 nm (21-30 A), whereas the gate insulation layer 44 may • have a thickness of approximately 2.0-2.5 nm (20-25 A).
• Such processing includes formation of the gate electrode, sidewall spacers and source/drain regions.
• the integrity of the isolation regions adjacent the area of the substrate 30 implanted with fluorine atoms is maintained. That is, due to the fact that the sacrificial layer 34 is removed prior to the fluorine implant process 40, the etching rate of the isolation regions is not enhanced by implanting fluorine into the isolation regions prior to the isolation regions being exposed to the relatively aggressive wet etch process, e.g., HF acid etching process, that is used to remove the sacrificial layer 34. As a result, the integrity of the isolation regions remains intact.
• the relatively aggressive wet etch process e.g., HF acid etching process
• Figures 4 A and 4B are plots of various test data demonstrating the effectiveness of the present invention.
• Figure 4A is a plot of the parasitic field transistor threshold voltage.
• Figure 4B is a plot of the gate current for the active/STI edge gate oxide capacitors. In both plots, three lines are identified.
• Line 50 represents data for devices formed in accordance with the prior art techniques described in the background section of the application. That is, line 50 is representative of devices wherein the isolation regions are exposed to a fluorine implant process and thereafter exposed to an etching process.
• Line 52 corresponds to devices made in accordance with the inventive methods disclosed herein.
• Line 54 is representative of devices where no fluorine implant is performed at all.
• the median value 56 of the threshold voltage for the sampled universe is approximately 9.2 volts for the devices made in accordance with the prior art techniques (plot 50); approximately 10.8 volts for the devices made in accordance with the present invention (plot 52); and approximately 11.2 volts for devices wherein no dual gate oxide implantation step is performed (plot 54).
• the relatively higher threshold voltage exhibited by plot 52 (present invention) as compared to plot 50 (prior art) means that, through use of the present invention, there is less consumption or erosion of the isolation regions using the processes disclosed herein for dual gate formation.
• the median value 56 for the gate current of the active/STI edge intensive gate oxide capacitors is lower for devices formed in accordance with the present invention as compared to devices formed in accordance with the prior art process flow. That is, as shown in Figure 4B, the median value 56 for the gate current of the devices formed in accordance with the present invention (plot 52) is approximately le "4 amps/cm 2 , whereas the gate current for the prior art process (plot 50) is approximately 0.13 amps/cm 2 . The gate current for non-dual gate devices (plot 54) is shown to be slightly less than le "3 amps/cm 2 .
• the undesirable gate current for the active/STI edge capacitors is lower than the gate current of devices made in accordance with the prior art process flow. This is the result of the reduced erosion of the isolation regions using the inventive process disclosed herein for forming dual gate oxides.
• the present invention is generally directed to a method of making transistors with gate insulation layers of differing thickness.
• the method comprises forming a sacrificial layer of material above a substrate comprised of silicon, performing a wet etching process to remove the sacrificial layer, implanting fluorine atoms into selected portions of the substrate after the sacrificial layer is removed, and performing a thermal oxidation process to form a plurality of gate insulation layers above the substrate, the gate insulation layers formed above the fluorine implanted selected portions of the substrate having a thickness that is greater than a thickness of the gate insulation layers formed above portions of the substrate not implanted with fluorine.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Manufacturing & Machinery (AREA)
• Computer Hardware Design (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Power Engineering (AREA)
• Metal-Oxide And Bipolar Metal-Oxide Semiconductor Integrated Circuits (AREA)
• Insulated Gate Type Field-Effect Transistor (AREA)
• Formation Of Insulating Films (AREA)
• Semiconductor Memories (AREA)

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• 2002
  • 2002-05-14 US US10/145,519 patent/US6541321B1/en not_active Expired - Lifetime
  • 2002-12-17 CN CNB02828948XA patent/CN1310314C/zh not_active Expired - Fee Related
  • 2002-12-17 WO PCT/US2002/040500 patent/WO2003098685A1/en not_active Ceased
  • 2002-12-17 EP EP02790146A patent/EP1504470A1/en not_active Withdrawn
  • 2002-12-17 JP JP2004506080A patent/JP2005526399A/ja active Pending
  • 2002-12-17 AU AU2002353166A patent/AU2002353166A1/en not_active Abandoned
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