US20170243749A1 - Method of forming oxide layer - Google Patents

Method of forming oxide layer Download PDF

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US20170243749A1
US20170243749A1 US15/049,152 US201615049152A US2017243749A1 US 20170243749 A1 US20170243749 A1 US 20170243749A1 US 201615049152 A US201615049152 A US 201615049152A US 2017243749 A1 US2017243749 A1 US 2017243749A1
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oxide layer
area
forming
quality enhancement
mixture
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US9741572B1 (en
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Chueh-Yang Liu
Chun-Wei Yu
Yu-Ying Lin
Yu-Ren Wang
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United Microelectronics Corp
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United Microelectronics Corp
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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 at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System 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
    • H01L21/28185—Making the insulator on single crystalline silicon, e.g. using a liquid, i.e. chemical oxidation with a treatment, e.g. annealing, after the formation of the gate insulator and before the formation of the definitive gate conductor
    • 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 at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System 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
    • 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
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/77—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate
    • H01L21/78—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices
    • H01L21/82—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices to produce devices, e.g. integrated circuits, each consisting of a plurality of components
    • H01L21/822—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices to produce devices, e.g. integrated circuits, each consisting of a plurality of components the substrate being a semiconductor, using silicon technology
    • H01L21/8232—Field-effect technology
    • H01L21/8234—MIS technology, i.e. integration processes of field effect transistors of the conductor-insulator-semiconductor type
    • H01L21/823462—MIS technology, i.e. integration processes of field effect transistors of the conductor-insulator-semiconductor type with a particular manufacturing method of the gate insulating layers, e.g. different gate insulating layer thicknesses, particular gate insulator materials or particular gate insulator implants
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/66007—Multistep manufacturing processes
    • H01L29/66075—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials
    • H01L29/66227—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
    • H01L29/66409—Unipolar field-effect transistors
    • H01L29/66477—Unipolar field-effect transistors with an insulated gate, i.e. MISFET
    • H01L29/66545—Unipolar field-effect transistors with an insulated gate, i.e. MISFET using a dummy, i.e. replacement gate in a process wherein at least a part of the final gate is self aligned to the dummy gate
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/66007—Multistep manufacturing processes
    • H01L29/66075—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials
    • H01L29/66227—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
    • H01L29/66409—Unipolar field-effect transistors
    • H01L29/66477—Unipolar field-effect transistors with an insulated gate, i.e. MISFET
    • H01L29/66787—Unipolar field-effect transistors with an insulated gate, i.e. MISFET with a gate at the side of the channel
    • H01L29/66795—Unipolar field-effect transistors with an insulated gate, i.e. MISFET with a gate at the side of the channel with a horizontal current flow in a vertical sidewall of a semiconductor body, e.g. FinFET, MuGFET

Definitions

  • the present invention relates to a method of forming an oxide layer, and more particularly, to a method including a quality enhancement process to etch the oxide layer and densify the oxide layer at the same time for reducing the thickness of the oxide film and enhancing the quality of the oxide film at the same time.
  • the sizes of the semiconductor devices become smaller for increasing the integrity of the integrated circuit.
  • the thickness control of layers in the semiconductor device becomes more and more critical.
  • MOSFET metal-oxide-semiconductor field effect transistor
  • the traditional gate oxide and polysilicon gate electrode are replaced by a high dielectric constant (high-k) gate dielectric and a metal gate electrode.
  • high-k gate stacks the interfacial layer (IL) underlying the high-k dielectric layer plays a critical role in the performance of the.
  • the thickness and the quality of the IL may be influenced by subsequent thermal processes, and the performance of the MOSFET device will be affected accordingly.
  • different circuit modules and/or transistors and other devices in the same chip may operate indifferent voltage regimes.
  • an integrated switching-mode power supply which may include a power transistor and a control circuit for switching the power transistor ON and OFF to convert a supply voltage into a desired output voltage
  • the power transistor may have an operating voltage much higher than an operating voltage of transistors constituting the control circuit.
  • gate insulation layers with different thicknesses are required.
  • a quality enhancement process using a mixture of dilute hydrofluoric acid (DHF) and hydrogen peroxide (H 2 O 2 ) is performed to etch the oxide layer and densify the oxide layer at the same time.
  • the thickness of the oxide layer may be reduced and well controlled, and the quality of the oxide layer may be enhanced by the quality enhancement process without damaging a surface of a semiconductor substrate.
  • a method of forming an oxide layer is provided in an embodiment of the present invention.
  • the method includes the following steps.
  • a first oxide layer is formed on a semiconductor substrate, and a quality enhancement process is then performed to etch the first oxide layer and densify the first oxide layer at the same time for forming a second oxide layer.
  • the first oxide layer is etched and densified at the same time by a mixture of dilute hydrofluoric acid (DHF) and hydrogen peroxide (H 2 O 2 ) in the quality enhancement process.
  • DHF dilute hydrofluoric acid
  • H 2 O 2 hydrogen peroxide
  • FIG. 1 is a flow chart illustrating a method of forming an oxide layer according to a first embodiment of the present invention.
  • FIGS. 2-6 are schematic drawings illustrating the method of forming the oxide layer according to the embodiment of the present invention, wherein
  • FIG. 3 is a schematic drawing in a step subsequent to FIG. 2 .
  • FIG. 4 is a schematic drawing in a step subsequent to FIG. 3 .
  • FIG. 5 is a schematic drawing in a step subsequent to FIG. 4 .
  • FIG. 6 is a schematic drawing in a step subsequent to FIG. 5 .
  • FIG. 7 is a flowchart illustrating a method of forming an oxide layer according to a second embodiment of the present invention.
  • FIG. 1 is a flowchart illustrating a method of forming an oxide layer according to a first embodiment of the present invention.
  • FIGS. 2-6 are schematic drawings illustrating the method of forming the oxide layer in this embodiment.
  • the method of forming the oxide layer in this embodiment includes the following steps.
  • a semiconductor substrate 10 is provided.
  • the semiconductor substrate 10 may include a silicon substrate, an epitaxial silicon substrate, a silicon germanium substrate, a silicon carbide substrate, or a silicon-on-insulator (SOI) substrate, but not limited thereto.
  • SOI silicon-on-insulator
  • the semiconductor substrate 10 may include a plurality of fin structures (not shown) and a shallow trench isolation (STI, not shown) may be formed between the fin structures, but not limited thereto.
  • the semiconductor substrate 10 may include a first area R 1 and a second area R 2 separated from each other by the STI.
  • the first area R 1 may be an area requiring a relatively thicker oxide layer
  • the second area R 2 may be an area requiring a relatively thinner oxide layer.
  • the first area R 1 may be an input/output area and the second area R 2 may be a logic area, but the present invention is not limited to this.
  • a third oxide layer 20 is formed on the semiconductor substrate 10 .
  • the third oxide layer 20 is formed on the first area R 1 and the second area R 2 of the semiconductor substrate 10 .
  • the third oxide layer 20 maybe formed by a thermal oxidation process.
  • the third gate oxide layer 20 may be formed by an in-situ steam generation (ISSG) process, which may utilize imported hydrogen gas and oxygen gas, but this is not limited thereto.
  • ISSG in-situ steam generation
  • a dummy material layer 30 such as an amorphous silicon layer, maybe formed on the third oxide layer 20 , and the dummy material layer 30 and the third oxide layer 20 may be patterned to form a plurality of dummy gates 30 P and a patterned third oxide layer 20 P.
  • the patterned third oxide layer 20 P is disposed between each of the dummy gates 30 P and the semiconductor substrate 10 , and the dummy gates 30 P may be formed on the first area R 1 and the second area R 2 of the semiconductor substrate 10 .
  • Sidewall spacers 40 may be formed on the side walls of the dummy gates 30 P and the patterned third oxide layer 20 P.
  • An interlayer dielectric 50 may be formed to cover the dummy gates 30 P and the semiconductor substrate 10 , and a chemical mechanical polish (CMP) process may then be performed to expose the dummy gate 30 P.
  • CMP chemical mechanical polish
  • a patterned resist 60 maybe formed to cover the dummy gate 30 P on the first area R 1 , and the dummy gate 30 P on the second area R 2 may be removed by an etching process.
  • the third oxide layer 20 on the second area R 2 is then removed.
  • the third oxide layer 20 on the second area R 2 may be removed by dilute hydrofluoric acid (DHF).
  • DHF dilute hydrofluoric acid
  • a wet etching process using an etchant of DHF may be performed to remove the third oxide layer 20 on the second area R 2 , but not limited thereto.
  • the third oxide layer 20 on the second area R 2 may also be removed by other processes and/or other chemicals. Accordingly, a first trench T 1 may then be formed on the second area R 2 and expose a part of the semiconductor substrate 10 .
  • a first oxide layer 71 is formed on the second area R 2 of the semiconductor substrate 10 .
  • the third oxide layer 20 is formed on the first area R 1 and the second area R 2 of the semiconductor substrate 10 before the step of forming the first oxide layer 20 , and the third oxide layer 20 on the second area R 2 is removed before the step of forming the first oxide layer 71 .
  • the first oxide layer 71 may include a chemical silicon oxide layer formed by a sulfuric acid peroxide mixture (SPM) treatment, and the first oxide layer 71 is formed on the semiconductor substrate 10 exposed by the first trench T 1 on the second area R 2 .
  • the first oxide layer 71 may also be formed by other appropriate processes and/or chemicals.
  • the patterned resist covering the first area R 1 may be removed by the SPM treatment also, but not limited thereto.
  • the treatment time of the SPM treatment may range between 40 seconds and 120 seconds, and the treatment time may be about 60 seconds for example, but not limited thereto.
  • a thickness of the first oxide layer 71 (such as a first thickness TK 1 shown in FIG. 4 ) is less than a thickness of the third oxide layer 20 (such as a third thickness TK 3 shown in FIG. 4 ) preferably, but not limited thereto.
  • a quality enhancement process 90 is then performed to etch the first oxide layer 71 and densify the first oxide layer 71 at the same time for forming a second oxide layer 72 .
  • the first oxide layer 71 is etched and densified at the same time by a mixture of dilute hydrofluoric acid (DHF) and hydrogen peroxide (H 2 O 2 ) in the quality enhancement process 90 .
  • the DHF in the mixture is configured to etch the first oxide layer 71
  • the hydrogen peroxide in the mixture is configured to oxidize the etched first oxide layer 71 and form the second oxide layer 72 with better quality.
  • a thickness of the second oxide layer 72 (such as a second thickness shown in FIG. 5 ) is less than the first thickness TK 1 of the first oxide layer 71 preferably so as to form the thinner second oxide layer 72 .
  • the first thickness TK 1 of the first oxide layer 71 is about 5.74 angstroms
  • the second thickness of the second oxide layer 72 after the quality enhancement process 90 may be about 5 . 14 angstroms.
  • the second thickness TK 2 of the second oxide layer 72 is less than the third thickness TK 3 of the third oxide layer 20 .
  • the thickness of the second oxide layer 72 may be well controlled by the process time of the quality enhancement process 90 and/or the ratio of DHF in the mixture used in the quality enhancement process 90 .
  • a ratio between hydrofluoric acid and hydrogen peroxide may range between 1:30 and 1:60, but not limited thereto.
  • a ratio of hydrofluoric acid, hydrogen peroxide, and water in the mixture may range between 1:30:465 and 1:60:435.
  • the etching rate of the mixture of DHF and hydrogen peroxide may be controlled to be relatively low for controlling the second thickness TK 2 of the second oxide layer more precisely and uniformly.
  • the quality enhancement process 90 may be performed at room temperature, but not limited thereto.
  • the relatively loose structure in the first oxide layer 71 (such as SiOx) tends to be removed by DHF in the mixture used in the quality enhancement process 90 , and the regrowth part of the second oxide layer 72 may contain more relatively dense structure (such as silicon dioxide). Therefore, a silicon dioxide (SiO 2 ) concentration of the second oxide layer 72 may be higher than a silicon dioxide concentration of the first oxide layer 20 because of the densify performance of the quality enhancement process 90 .
  • the quench time (Q-time) of the second oxide layer 72 may be increased without thickness increase because the second oxide layer 72 is densified by the quality enhancement process 90 .
  • chemical oxide with hydrogen-termination may be removed by DHF in the quality enhancement process 90 , and the surface of the second oxide layer 72 may be hydrophilic accordingly.
  • the semiconductor substrate 10 will not be damaged by the quality enhancement process 90 because there is no ammonium hydroxide (NH 4 OH) used in the quality enhancement process 90 .
  • the dummy gate 30 P on the first area R 1 may be removed for forming a second trench T 2 on the first area R 1 and exposing the third oxide layer 20 on the first area R 1 .
  • a high dielectric constant (high-k) dielectric layer 80 may then be formed on the second oxide layer 72 .
  • the high-k dielectric layer 80 may be formed conformally on the interlayer dielectric 50 , the inner surface of the first trench T 1 , the inner surface of the second trench T 2 , the third oxide layer 20 , and the second oxide layer 72 .
  • the high-k dielectric layer 80 may include material selected from the group consisting of hafnium oxide (HfO 2 ), hafnium silicon oxide (HfSiO 4 ), hafnium silicon oxynitride (HfSiON), aluminum oxide (Al 2 O 3 ), lanthanum oxide (La 2 O 3 ), tantalum oxide (Ta 2 O 5 ), yttrium oxide (Y 2 O 3 ), zirconium oxide (ZrO 2 ), strontium titanate oxide (SrTiO 3 ), zirconium silicon oxide (ZrSiO 4 ), hafnium zirconium oxide (HfZrO 4 ), strontium bismuth tantalate, (SrBi 2 Ta 2 O 9 , SBT), lead zirconate titanate (PbZr x Ti 1 ⁇ x O 3 , PZT), and barium strontium titanate (Ba x Sr 1 ⁇ x TiO 3 , BST).
  • hafnium oxide
  • a barrier layer (not shown), a work function layer (not shown), and a metal conductive material (not shown) maybe formed in the first trench T 1 and the second trench T 2 so as to form metal gate structures on the first area R 1 and the second area R 2 respectively. Therefore, the second oxide layer 72 may be an interfacial layer of a transistor subsequently formed on the second area R 2 , and the third oxide layer 20 may be an interfacial layer of a transistor subsequently formed on the first area R 1 .
  • the relatively thicker third oxide layer 20 may be formed for the high voltage device on the input/output area, and the relatively thinner second oxide layer 72 may be formed for the low voltage device on the logic area.
  • the film quality of the second oxide layer 72 may be enhanced by the quality enhancement process using the mixture of DHF and hydrogen peroxide, and electrically performance of the semiconductor device including the second oxide layer 72 may be improved accordingly.
  • the method of forming the oxide layer in the present invention is not limited to form the interfacial layer of a metal oxide semiconductor (MOS) transistor as the embodiment described above.
  • the method of forming the oxide layer may also be used to form a high quality and extremely thin oxide layer for other devices, such as an oxide layer of a charge trapping structure in a memory device, but not limited thereto.
  • FIG. 7 is a flow chart illustrating a method of forming an oxide layer according to a second embodiment of the present invention.
  • step S 21 may be executed after the step S 12 and before the step S 13
  • step S 22 may be executed after the step S 13 and before the step S 14 .
  • another DHF treatment for about 10 seconds may be performed to remove native oxide before forming the first oxide layer.
  • a clean process may be performed to remove particles after the SPM treatment described above and before the quality enhancement process in the step S 14 .
  • the clean process may include a standard clean 1 (SC1) clean process or other appropriate clean processes.
  • SC1 standard clean 1
  • the quality enhancement process using the mixture of dilute hydrofluoric acid (DHF) and hydrogen peroxide (H 2 O 2 ) is performed to etch the oxide layer and densify the oxide layer at the same time.
  • the thickness of the oxide layer may be reduced and well controlled, and the quality of the oxide layer may be enhanced by the quality enhancement process.

Abstract

A method of forming an oxide layer is provided in the present invention. The method includes the following steps. A first oxide layer is formed on a semiconductor substrate, and a quality enhancement process is then performed to etch the first oxide layer and densify the first oxide layer at the same time for forming a second oxide layer. The first oxide layer is etched and densified at the same time by a mixture of dilute hydrofluoric acid (DHF) and hydrogen peroxide (H2O2) in the quality enhancement process. The thickness of the second oxide layer may be reduced and the quality of the second oxide layer may be enhanced by the quality enhancement process at the same time.

Description

    BACKGROUND OF THE INVENTION
  • 1. Field of the Invention
  • The present invention relates to a method of forming an oxide layer, and more particularly, to a method including a quality enhancement process to etch the oxide layer and densify the oxide layer at the same time for reducing the thickness of the oxide film and enhancing the quality of the oxide film at the same time.
  • 2. Description of the Prior Art
  • In the continuously improved semiconductor integrated circuit technology, the sizes of the semiconductor devices become smaller for increasing the integrity of the integrated circuit. In the scaling down process, the thickness control of layers in the semiconductor device becomes more and more critical. For improving the metal-oxide-semiconductor field effect transistor (MOSFET) device performance as feature sizes continue to decrease, the traditional gate oxide and polysilicon gate electrode are replaced by a high dielectric constant (high-k) gate dielectric and a metal gate electrode. In high-k gate stacks, the interfacial layer (IL) underlying the high-k dielectric layer plays a critical role in the performance of the. However, the thickness and the quality of the IL may be influenced by subsequent thermal processes, and the performance of the MOSFET device will be affected accordingly.
  • In an integrated circuit, different circuit modules and/or transistors and other devices in the same chip may operate indifferent voltage regimes. In an integrated switching-mode power supply, which may include a power transistor and a control circuit for switching the power transistor ON and OFF to convert a supply voltage into a desired output voltage, the power transistor may have an operating voltage much higher than an operating voltage of transistors constituting the control circuit. In order to have an area-efficient high voltage device with low voltage control devices fabricated on a same die, gate insulation layers with different thicknesses are required. When the high-voltage driving elements and the low-voltage driving elements are embodied simultaneously, a thick gate oxide film for high voltage and a thin gate oxide film for low voltage are required.
    • SUMMARY OF THE INVENTION
  • It is one of the objectives of the present invention to provide a method of forming an oxide layer. In the method of forming the oxide layer of the present invention, a quality enhancement process using a mixture of dilute hydrofluoric acid (DHF) and hydrogen peroxide (H2O2) is performed to etch the oxide layer and densify the oxide layer at the same time. The thickness of the oxide layer may be reduced and well controlled, and the quality of the oxide layer may be enhanced by the quality enhancement process without damaging a surface of a semiconductor substrate.
  • A method of forming an oxide layer is provided in an embodiment of the present invention. The method includes the following steps. A first oxide layer is formed on a semiconductor substrate, and a quality enhancement process is then performed to etch the first oxide layer and densify the first oxide layer at the same time for forming a second oxide layer. The first oxide layer is etched and densified at the same time by a mixture of dilute hydrofluoric acid (DHF) and hydrogen peroxide (H2O2) in the quality enhancement process.
  • These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
    • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 is a flow chart illustrating a method of forming an oxide layer according to a first embodiment of the present invention.
  • FIGS. 2-6 are schematic drawings illustrating the method of forming the oxide layer according to the embodiment of the present invention, wherein
  • FIG. 3 is a schematic drawing in a step subsequent to FIG. 2,
  • FIG. 4 is a schematic drawing in a step subsequent to FIG. 3,
  • FIG. 5 is a schematic drawing in a step subsequent to FIG. 4, and
  • FIG. 6 is a schematic drawing in a step subsequent to FIG. 5.
  • FIG. 7 is a flowchart illustrating a method of forming an oxide layer according to a second embodiment of the present invention.
    •  DETAILED DESCRIPTION
  • Please refer to FIGS. 1-6. FIG. 1 is a flowchart illustrating a method of forming an oxide layer according to a first embodiment of the present invention. FIGS. 2-6 are schematic drawings illustrating the method of forming the oxide layer in this embodiment. The method of forming the oxide layer in this embodiment includes the following steps. As shown in FIG. 1 and FIG. 2, a semiconductor substrate 10 is provided. The semiconductor substrate 10 may include a silicon substrate, an epitaxial silicon substrate, a silicon germanium substrate, a silicon carbide substrate, or a silicon-on-insulator (SOI) substrate, but not limited thereto. The semiconductor substrate 10 may include a plurality of fin structures (not shown) and a shallow trench isolation (STI, not shown) may be formed between the fin structures, but not limited thereto. In this embodiment, the semiconductor substrate 10 may include a first area R1 and a second area R2 separated from each other by the STI. The first area R1 may be an area requiring a relatively thicker oxide layer, and the second area R2 may be an area requiring a relatively thinner oxide layer. For example, the first area R1 may be an input/output area and the second area R2 may be a logic area, but the present invention is not limited to this. In step S11, a third oxide layer 20 is formed on the semiconductor substrate 10. Specifically, the third oxide layer 20 is formed on the first area R1 and the second area R2 of the semiconductor substrate 10. The third oxide layer 20 maybe formed by a thermal oxidation process. Preferably, the third gate oxide layer 20 may be formed by an in-situ steam generation (ISSG) process, which may utilize imported hydrogen gas and oxygen gas, but this is not limited thereto.
  • In the method of this embodiment, for a replacement metal gate (RMG) process, a dummy material layer 30, such as an amorphous silicon layer, maybe formed on the third oxide layer 20, and the dummy material layer 30 and the third oxide layer 20 may be patterned to form a plurality of dummy gates 30P and a patterned third oxide layer 20P. The patterned third oxide layer 20P is disposed between each of the dummy gates 30P and the semiconductor substrate 10, and the dummy gates 30P may be formed on the first area R1 and the second area R2 of the semiconductor substrate 10. Sidewall spacers 40 may be formed on the side walls of the dummy gates 30P and the patterned third oxide layer 20P. An interlayer dielectric 50 may be formed to cover the dummy gates 30P and the semiconductor substrate 10, and a chemical mechanical polish (CMP) process may then be performed to expose the dummy gate 30P.
  • As shown in FIG. 3, a patterned resist 60 maybe formed to cover the dummy gate 30P on the first area R1, and the dummy gate 30P on the second area R2 may be removed by an etching process. As shown in FIG. 1 and FIG. 3, in step S12, the third oxide layer 20 on the second area R2 is then removed. In this embodiment, the third oxide layer 20 on the second area R2 may be removed by dilute hydrofluoric acid (DHF). Specifically, a wet etching process using an etchant of DHF may be performed to remove the third oxide layer 20 on the second area R2, but not limited thereto. In other embodiment of the present invention, the third oxide layer 20 on the second area R2 may also be removed by other processes and/or other chemicals. Accordingly, a first trench T1 may then be formed on the second area R2 and expose a part of the semiconductor substrate 10.
  • As shown in FIG. 1 and FIG. 4, in step S13, a first oxide layer 71 is formed on the second area R2 of the semiconductor substrate 10. In other words, the third oxide layer 20 is formed on the first area R1 and the second area R2 of the semiconductor substrate 10 before the step of forming the first oxide layer 20, and the third oxide layer 20 on the second area R2 is removed before the step of forming the first oxide layer 71. Specifically, the first oxide layer 71 may include a chemical silicon oxide layer formed by a sulfuric acid peroxide mixture (SPM) treatment, and the first oxide layer 71 is formed on the semiconductor substrate 10 exposed by the first trench T1 on the second area R2. However, in other embodiments of the present invention, the first oxide layer 71 may also be formed by other appropriate processes and/or chemicals. In addition, the patterned resist covering the first area R1 may be removed by the SPM treatment also, but not limited thereto. The treatment time of the SPM treatment may range between 40 seconds and 120 seconds, and the treatment time may be about 60 seconds for example, but not limited thereto. A thickness of the first oxide layer 71 (such as a first thickness TK1 shown in FIG. 4) is less than a thickness of the third oxide layer 20 (such as a third thickness TK3 shown in FIG. 4) preferably, but not limited thereto.
  • As shown in FIG. 1, FIG. 4, and FIG. 5, in step S14, a quality enhancement process 90 is then performed to etch the first oxide layer 71 and densify the first oxide layer 71 at the same time for forming a second oxide layer 72. The first oxide layer 71 is etched and densified at the same time by a mixture of dilute hydrofluoric acid (DHF) and hydrogen peroxide (H2O2) in the quality enhancement process 90. The DHF in the mixture is configured to etch the first oxide layer 71, and the hydrogen peroxide in the mixture is configured to oxidize the etched first oxide layer 71 and form the second oxide layer 72 with better quality. In addition, a thickness of the second oxide layer 72 (such as a second thickness shown in FIG. 5) is less than the first thickness TK1 of the first oxide layer 71 preferably so as to form the thinner second oxide layer 72. For example, when the first thickness TK1 of the first oxide layer 71 is about 5.74 angstroms, the second thickness of the second oxide layer 72 after the quality enhancement process 90 may be about 5.14 angstroms. Accordingly, the second thickness TK2 of the second oxide layer 72 is less than the third thickness TK3 of the third oxide layer 20. The thickness of the second oxide layer 72 may be well controlled by the process time of the quality enhancement process 90 and/or the ratio of DHF in the mixture used in the quality enhancement process 90. For example, in the mixture of DHF and hydrogen peroxide, a ratio between hydrofluoric acid and hydrogen peroxide may range between 1:30 and 1:60, but not limited thereto. Additionally, a ratio of hydrofluoric acid, hydrogen peroxide, and water in the mixture may range between 1:30:465 and 1:60:435. In other words, the etching rate of the mixture of DHF and hydrogen peroxide may be controlled to be relatively low for controlling the second thickness TK2 of the second oxide layer more precisely and uniformly. In addition, the quality enhancement process 90 may be performed at room temperature, but not limited thereto. The relatively loose structure in the first oxide layer 71 (such as SiOx) tends to be removed by DHF in the mixture used in the quality enhancement process 90, and the regrowth part of the second oxide layer 72 may contain more relatively dense structure (such as silicon dioxide). Therefore, a silicon dioxide (SiO2) concentration of the second oxide layer 72 may be higher than a silicon dioxide concentration of the first oxide layer 20 because of the densify performance of the quality enhancement process 90. The quench time (Q-time) of the second oxide layer 72 may be increased without thickness increase because the second oxide layer 72 is densified by the quality enhancement process 90. Additionally, chemical oxide with hydrogen-termination may be removed by DHF in the quality enhancement process 90, and the surface of the second oxide layer 72 may be hydrophilic accordingly. The semiconductor substrate 10 will not be damaged by the quality enhancement process 90 because there is no ammonium hydroxide (NH4OH) used in the quality enhancement process 90.
  • As shown in FIG. 5 and FIG. 6, the dummy gate 30P on the first area R1 may be removed for forming a second trench T2 on the first area R1 and exposing the third oxide layer 20 on the first area R1. A high dielectric constant (high-k) dielectric layer 80 may then be formed on the second oxide layer 72. Specifically, the high-k dielectric layer 80 may be formed conformally on the interlayer dielectric 50, the inner surface of the first trench T1, the inner surface of the second trench T2, the third oxide layer 20, and the second oxide layer 72. The high-k dielectric layer 80 may include material selected from the group consisting of hafnium oxide (HfO2), hafnium silicon oxide (HfSiO4), hafnium silicon oxynitride (HfSiON), aluminum oxide (Al2O3), lanthanum oxide (La2O3), tantalum oxide (Ta2O5), yttrium oxide (Y2O3), zirconium oxide (ZrO2), strontium titanate oxide (SrTiO3), zirconium silicon oxide (ZrSiO4), hafnium zirconium oxide (HfZrO4), strontium bismuth tantalate, (SrBi2Ta2O9, SBT), lead zirconate titanate (PbZrxTi1−xO3, PZT), and barium strontium titanate (BaxSr1−xTiO3, BST). A barrier layer (not shown), a work function layer (not shown), and a metal conductive material (not shown) maybe formed in the first trench T1 and the second trench T2 so as to form metal gate structures on the first area R1 and the second area R2 respectively. Therefore, the second oxide layer 72 may be an interfacial layer of a transistor subsequently formed on the second area R2, and the third oxide layer 20 may be an interfacial layer of a transistor subsequently formed on the first area R1. By the method of the present embodiment described above, the relatively thicker third oxide layer 20 may be formed for the high voltage device on the input/output area, and the relatively thinner second oxide layer 72 may be formed for the low voltage device on the logic area. The film quality of the second oxide layer 72 may be enhanced by the quality enhancement process using the mixture of DHF and hydrogen peroxide, and electrically performance of the semiconductor device including the second oxide layer 72 may be improved accordingly.
  • It is worth noting that the method of forming the oxide layer in the present invention is not limited to form the interfacial layer of a metal oxide semiconductor (MOS) transistor as the embodiment described above. In other embodiments of the present invention, the method of forming the oxide layer may also be used to form a high quality and extremely thin oxide layer for other devices, such as an oxide layer of a charge trapping structure in a memory device, but not limited thereto.
  • Please refer to FIG. 7. FIG. 7 is a flow chart illustrating a method of forming an oxide layer according to a second embodiment of the present invention. As shown in FIG. 7, the difference between the method in this embodiment and the method in the first embodiment is that step S21 may be executed after the step S12 and before the step S13, and step S22 may be executed after the step S13 and before the step S14. Specifically, in the step S21, another DHF treatment for about 10 seconds may be performed to remove native oxide before forming the first oxide layer. In the step S22, a clean process may be performed to remove particles after the SPM treatment described above and before the quality enhancement process in the step S14. The clean process may include a standard clean 1 (SC1) clean process or other appropriate clean processes.
  • To summarize the above descriptions, according to the method of forming the oxide layer in the present invention, the quality enhancement process using the mixture of dilute hydrofluoric acid (DHF) and hydrogen peroxide (H2O2) is performed to etch the oxide layer and densify the oxide layer at the same time. The thickness of the oxide layer may be reduced and well controlled, and the quality of the oxide layer may be enhanced by the quality enhancement process.
  • Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

Claims (14)

1. A method of forming an oxide layer comprising:
forming a first oxide layer on a semiconductor substrate, wherein the semiconductor substrate comprises a first area and a second area;
performing a quality enhancement process to etch the first oxide layer and densify the first oxide layer at the same time for forming a second oxide layer, wherein the first oxide layer is etched and densified at the same time by a mixture of dilute hydrofluoric acid (DHF) and hydrogen peroxide (H2O2) in the quality enhancement process, wherein the DHF in the mixture is configured to etch the first oxide layer, the hydrogen peroxide in the mixture is configured to oxidize the etched first oxide layer for densifying the first oxide layer, and the second oxide layer comprises the oxidized first oxide layer;
forming a third oxide layer on the first area and the second area of the semiconductor substrate before the step of forming the first oxide layer; and
removing the third oxide layer on the second area before the step of forming the first oxide layer, wherein the first oxide layer is formed on the second area of the semiconductor substrate.
2. The method of claim 1, wherein a ratio between hydrofluoric acid and hydrogen peroxide in the mixture ranges between 1:30 and 1:60.
3. (canceled)
4. The method of claim 1, wherein the quality enhancement process is performed at room temperature.
5. (canceled)
6. The method of claim 1, wherein the third oxide layer on the second area is removed by dilute hydrofluoric acid.
7. The method of claim 1, wherein the third oxide layer is formed by a thermal oxidation process.
8. The method of claim 7, wherein the thermal oxidation process comprises an in-situ steam generation (ISSG) process.
9. The method of claim 1, wherein the first area is an input/output area and the second area is a logic area.
10. The method of claim 1, wherein a thickness of the second oxide layer is less than a thickness of the third oxide layer.
11. The method of claim 1, wherein the first oxide layer comprises a chemical silicon oxide layer formed by a sulfuric acid peroxide mixture (SPM) treatment.
12. The method of claim 11, further comprising:
performing a clean process to remove particles after the SPM treatment and before the quality enhancement process.
13. The method of claim 12, wherein the clean process comprises a standard clean 1 (SC1) clean process.
14. The method of claim 1, further comprising:
forming a high dielectric constant (high-k) dielectric layer on the second oxide layer.
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