US20070111548A1 - Plasma doping method and plasma doping apparatus - Google Patents

Plasma doping method and plasma doping apparatus Download PDF

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US20070111548A1
US20070111548A1 US11/647,235 US64723506A US2007111548A1 US 20070111548 A1 US20070111548 A1 US 20070111548A1 US 64723506 A US64723506 A US 64723506A US 2007111548 A1 US2007111548 A1 US 2007111548A1
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impurity
plasma
plasma doping
vacuum chamber
film
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Yuichiro Sasaki
Katsumi Okashita
Hiroyuki Ito
Bunji Mizuno
Tomohiro Okumura
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Panasonic Corp
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Matsushita Electric Industrial Co Ltd
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Priority to US11/730,244 priority Critical patent/US20070176124A1/en
Priority to US11/748,607 priority patent/US7358511B2/en
Publication of US20070111548A1 publication Critical patent/US20070111548A1/en
Assigned to MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD. reassignment MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: OKUMURA, TOMOHIRO, ITO, HIROYUKI, MIZUNO, BUNJI, OKASHITA, KATSUMI, SASAKI, YUICHIRO
Assigned to PANASONIC CORPORATION reassignment PANASONIC CORPORATION CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
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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
    • H01L21/26—Bombardment with radiation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/22—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions; Interactions between two or more impurities; Redistribution of impurities
    • H01L21/223—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions; Interactions between two or more impurities; Redistribution of impurities using diffusion into or out of a solid from or into a gaseous phase
    • H01L21/2236—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions; Interactions between two or more impurities; Redistribution of impurities using diffusion into or out of a solid from or into a gaseous phase from or into a plasma phase
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/48—Ion implantation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/32—Gas-filled discharge tubes
    • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
    • H01J37/32412—Plasma immersion ion implantation

Definitions

  • the present invention relates to a plasma doping method, a plasma doping apparatus used therefor, and a silicon substrate formed using the same.
  • the invention relates to a method of performing plasma doping that dopes an impurity into a surface of a solid sample, such as a semiconductor substrate or the like.
  • a plasma doping (PD) method that ionizes the impurity and dopes the ionized impurity into a solid at low energy (for example, see Patent Document 1).
  • Non-Patent Document 1 the plasma doping method is also described in ITRS2003 as a next-generation technology of ion implantation.
  • the plasma doping method is different from the ion implantation method.
  • the apparatus includes an ion source that generates plasma from gas, an analysis magnet that performs mass separation in order to select desired ions among ions extracted from the ion source, an electrode that accelerates the desired ions, and a process chamber that implants the accelerated desired ions into a silicon substrate.
  • an ion source that generates plasma from gas
  • an analysis magnet that performs mass separation in order to select desired ions among ions extracted from the ion source
  • an electrode that accelerates the desired ions
  • a process chamber that implants the accelerated desired ions into a silicon substrate.
  • the extraction energy when the extraction energy is set small, the number of ions to be extracted is decreased.
  • the acceleration energy when the acceleration energy is set small, while an ion beam is transported from the ion source to a wafer, a beam diameter is widened due to a repulsive force by charges between the ions. Accordingly, the ion beam may collide against the inner wall of a beam line, and thus a large number of ions may be lost. For this reason, throughput of an implantation processing may be lowered.
  • B+ ions when B+ ions are implanted, if the acceleration energy becomes 2 keV or less, the throughput starts to be lowered. Then, if the acceleration energy becomes 0.5 keV or less, the beam transportation itself may be difficult. Further, even though the acceleration energy is lowered to 0.5 keV, the B ions may be implanted at a depth of approximately 20 nm. That is, in case of forming an extension electrode having a thinner thickness, productivity may be lowered drastically.
  • the apparatus includes a plasma generation source that induces plasma into a cylindrical vacuum chamber, in which a silicon substrate can be disposed, a bias electrode, on which the silicon substrate is disposed, and a bias power supply that adjusts a potential of the bias electrode. That is, the apparatus has the configuration, in which the analysis magnet and the acceleration electrode are not provided, different from the apparatus used in the ion implantation.
  • the bias electrode that serves as a plasma source and a wafer holder is provided in the vacuum chamber. Then, the ions are accelerated and introduced by a potential to be generated between the plasma and the wafer.
  • Non-Patent Document 2 a process technology that forms a source-to-drain extension electrode having a very small thickness and low resistance. This new process technology is known as a process technology that has particular effects (Non-Patent Document 2).
  • doping material gas such as B 2 H 6
  • boron ions in plasma are supplied to a surface of a sample by a high-frequency power supply.
  • a dose (impurity doping amount) determines low resistance that is one of important elements in determining element characteristics. Accordingly, the control of the dose is very important.
  • the source-to-drain extension electrode having a very small thickness and low resistance can be formed.
  • a control method of the dose for controlling the element characteristics has not been developed yet. Up to now, a method that changes the dose by changing a plasma doping time has been tested, but this method does not obtain sufficient control precision and thus is unpractical.
  • B 2 H 6 gas as a material containing an impurity to be doped is diluted with He gas having small ionization energy, then He plasma is generated earlier, and subsequently B 2 H 6 is discharged (Patent Document 2).
  • the concentration of B 2 H 6 gas is preferably less than 0.05%.
  • the dose is changed by changing the time while the gas concentration is kept constant. That is, when the B 2 H 6 gas concentration is low, the change in the dose is small with respect to the change in time, and thus the dose is easily controlled.
  • the control precision of the dose is increased.
  • the dose may be changed each time plasma is irradiated onto the silicon substrate, regardless of the same plasma condition, and reproducibility may be degraded.
  • the state in the vacuum chamber is changed for each time accordingly. Accordingly, it is difficult to adjust the dose with good reproducibility.
  • the state in the vacuum chamber is changed for each time, it is difficult to keep an in-plane dose of the silicon substrate uniformly.
  • the dose can be made uniform by adjusting possible parameters or the shape of the apparatus, but the uniform dose cannot be repeatedly reproduced.
  • Patent Document 1 U.S. Pat. No. 4,912,065
  • Patent Document 2 JP-A-2004-179592
  • Patent Document 3 Japanese Patent No. 3340318
  • Non-Patent Document 1 Column of Shallow Junction Ion Doping of FIG. 30 of Front End Process in International Technology Roadmap for Semiconductors 2001 Edition (ITRS2001)
  • Non-Patent Document 2 Y. Sasaki, et al., Symp. on VLSI Tech. p180 (2004)
  • Non-Patent Document 3 B. Mizuno et al., Plasma Doping into the side-wall of a sub-0.5 ⁇ m width Trench, Ext. Abs. of International Conference on SSDM, p. 317 (1987)
  • Non-Patent Document 4 B. Mizuno, et al., Plasma Doping for silicon, Surface Coating tech., 85, 51 (1996)
  • Non-Patent Document 5 B. Mizuno, et al., Plasma Doping of Boron for Fabricating the Surface Channel Sub-quarter micron PMOSFET, symp. VLSI Tech, p. 66 (1996)
  • the inventors have focused that a film is formed on an inner wall of a vacuum chamber as a plasma chamber and the state of the film is changed. Specifically, if a plasma doping treatment is repeated using mixture gas plasma of B 2 H 6 gas and helium gas, the color concentration of the film and the formation area of the film are changed. That is, the inventors have focused that the thickness of the film becomes larger and the formation area of the film is increased. The invention has been finalized from this viewpoint.
  • the inventors have supposed that the plasma concentration of the surface of the sample is changed when the film containing the impurity fixed to the inner wall of the vacuum chamber is attacked (sputtered) by ions in plasma or the variation is changed by the thickness of the film and the formation area of the film. In addition, the inventors have supposed that the change depends on the density of the impurity contained in a unit volume of the film.
  • the dose of the impurity that is doped into the surface of the silicon substrate from a film containing the impurity fixed to the inner wall of the vacuum chamber is changed for each time.
  • the invention has been finalized in consideration of the above problems, and it is an object of the invention to provide a plasma doping method that can make a dose from a film to a silicon substrate for each time uniform even though a plasma processing is repeated.
  • the invention performs dose control and in-plane uniformity on the basis of a technical spirit that reverse the common knowledge of plasma doping up to now.
  • the impurity is doped from ions, gas, radicals in plasma, and the material is supplied from a gas pipe connected to the vacuum chamber as gas. That is, the amount of the impurity contained in gas, the gas concentration or pressure, a mixture ratio of gas, and the like, determines the amount of the impurity doped into the surface of the semiconductor substrate. Accordingly, it is designed such that a plasma density or gas flow and a pressure distribution are made uniform on the surface of the semiconductor substrate.
  • the adjustment of the dose is performed by adjusting the concentration of the impurity contained in gas to be supplied so as to adjust the concentration of the impurity contained in plasma or by adjusting an irradiation time of plasma.
  • the impurity doped into the film once is discharged in plasma again, and the discharged impurity is doped into the surface of the semiconductor substrate.
  • the inventors have thought that a more accurate determination of the ratio of the factors relative to the dose requires future studies, and depends on the condition of plasma doping, but it is important to reduce the ratio of the dose from plasma that is considered as the principal factor in the related art. As considered in the related art, even though the parameters of plasma are adjusted, it can be seen that it is impossible to control the dose, stably keep repetitive uniformity, and perform a process with good reproducibility.
  • a plasma doping method that places a sample on a sample electrode in a vacuum chamber, generates plasma in the vacuum chamber, and causes impurity ions in the plasma to collide against a surface of the sample so as to form an impurity doped layer in the surface of the sample.
  • the plasma doping method includes a maintenance step of preparing the vacuum chamber having a film containing an impurity formed on an inner wall thereof such that, when the film containing the impurity fixed to the inner wall of the vacuum chamber is attacked by ions in the plasma, the amount of an impurity to be doped into the surface of the sample by sputtering is not changed even though the plasma containing the impurity ions is repeatedly generated in the vacuum chamber, a step of placing the sample on the sample electrode, and a step of irradiating the plasma containing the impurity ions so as to implant the impurity ions into the sample, and doping the impurity into the sample by sputtering from the film containing the impurity fixed to the inner wall of the vacuum chamber.
  • the film is formed on the inner wall of the vacuum chamber such that the amount of the impurity to be doped into the sample by sputtering from the film containing the impurity of the inner wall of the vacuum chamber is not changed and then plasma doping is performed. Therefore, impurity doping can be stably performed with good reproducibility.
  • the maintenance step may include, before forming the film containing the impurity, a substep of removing the film containing the impurity fixed to the inner wall of the vacuum chamber.
  • the sample may be a silicon substrate, and the film containing the impurity fixed to the inner wall of the vacuum chamber may be formed such that, when a dose of the impurity is the same level with a tolerance of ⁇ 10% even though the plasma containing the impurity ions is repeatedly generated in the vacuum chamber, the dose is made uniform in a surface of the silicon substrate.
  • the plasma doping method according to the aspect of the invention may further include a step of adjusting the shape of the inner wall of the vacuum chamber such that the amount of an impurity to be stuck to the inner wall of the vacuum chamber has a desired value.
  • the shape of the inner wall of the vacuum chamber is adjusted such that, when the formation of the film is completed, the total distribution of the distribution of the impurity to be doped from the plasma containing the impurity ions and the distribution of the impurity to be doped by sputtering from the film containing the impurity fixed to the inner wall of the vacuum chamber is made uniform in the surface of the silicon substrate. It is important and more preferable to perform the adjustment such that the concentration is made uniform when the formation of the film is completed. In such a manner, uniform plasma doping can be realized with good repeatability.
  • the plasma doping method according to the aspect of the invention may further include a step of adjusting a gas supply method such that the amount of an impurity to be stuck to the inner wall of the vacuum chamber has a desired value.
  • in-plane uniformity of the dose can be improved by adjusting the gas jetting port and the semiconductor substrate.
  • in-plane uniformity can be improved by moving, for example, rotating the semiconductor substrate with respect to the gas jetting port.
  • the maintenance step may include a substep of providing the vacuum chamber, from which the film containing the impurity is removed, in a plasma doping apparatus and then generating the plasma containing the impurity ions in the vacuum chamber so as to form the film containing the impurity ions.
  • the step of forming the film containing the impurity ions may provide the vacuum chamber, from which the film containing the impurity is removed in the maintenance step, in a plasma doping apparatus separately provided in order to form the film and may generate the plasma containing the impurity ions in the vacuum chamber so as to form the film containing the impurity ions.
  • the plasma doping method according to the aspect of the invention may further include a step of doping the impurity into the sample by sputtering from the film containing the impurity fixed to the inner wall of the vacuum chamber while measuring and managing a temperature of the inner wall of the vacuum chamber.
  • the amount of the impurity to be doped from the film containing the impurity into the semiconductor substrate is changed by the temperature of the inner wall of the vacuum chamber. Accordingly, in order to keep the amount of the impurity constant, it is preferable to keep the temperature of the inner wall of the vacuum chamber constant. Further, in order to set the amount of the impurity to be doped from the film to a desired value, it is preferable to adjust the temperature of the inner wall of the vacuum chamber to a desired temperature.
  • a dummy chamber may be disposed in the vacuum chamber to cover the inner wall, and a film may be formed on the inner wall of the vacuum chamber.
  • the dummy chamber In vacuum equipment, there are many cases where the dummy chamber is called an inner chamber.
  • the formation of the film on the inner wall of the vacuum chamber, the studies of the shape of the inner wall, or the management of the temperature has been described.
  • the inner chamber the same effects can be obtained through the same studies. Therefore, the inner chamber still falls within the scope of the invention.
  • the inner chamber does not have a function of holding the vacuum state, but can be simply detached, easily cleaned, and used as consumption goods. Accordingly, when the inner chamber is provided, it is desirable in that, instead of detaching and cleaning an expensive vacuum chamber, only the inner chamber can be detached and cleaned.
  • the plasma may be plasma of gas containing boron.
  • the boron film can be formed on the inner wall of the vacuum chamber.
  • it is configured such that, when the film containing the impurity fixed to the inner wall of the vacuum chamber is attacked by the ions in the plasma, the amount of the impurity to be doped into the surface of the sample by sputtering is not changed even though the plasma containing the impurity ions are repeatedly generated in the vacuum chamber. Therefore, a high-accurate impurity profile can be obtained with good controllability, together with the impurity by sputtering.
  • the gas containing boron may be gas of molecules having boron and hydrogen.
  • BF 3 or the like may be used, but, since F has a high sputter rate, it is difficult form a stable film.
  • gas having an atom having a low sputter rate is preferably used.
  • the sputter rate is high, the surface of the silicon substrate may be chipped off during the plasma doping treatment, a device cannot be manufactured according to design. Further, since the surface of the silicon substrate doped with the impurity is chipped off, impurity doping itself may not be performed with good controllability. Since hydrogen has a sputter rate less than F, if the gas of molecules having boron and hydrogen is used, a high-accurate impurity profile can be obtained with good controllability.
  • the gas containing boron may be diborane (B 2 H 6 ).
  • B 2 H 6 is industrially cheap, and is filled in a gas tank to be then transported and preserved in a gas state, which results in ease of handling.
  • a sputter rate is low, and thus a high-accurate impurity profile can be obtained with good controllability.
  • the plasma may be plasma of gas that is obtained by diluting gas of molecules having boron and hydrogen with rare gas.
  • the film may be easily separated. If the film is separated, particles may be generated to cause degradation of yield in manufacturing a semiconductor, which causes an inconvenience. Accordingly, if the gas concentration is lowered through the dilution with a different gas, a film that is rarely separated can be formed.
  • the dilution gas rare gas having chemical stability is preferably used.
  • the rare gas may be an atom having an atomic weight equal to or less than neon.
  • rare gas having a large atomic weight has a high sputter rate, and thus it is difficult to form a stable film. Further, it may chip off the surface of the silicon substrate. Therefore, the rare gas having an atomic weight smaller than neon is preferably used.
  • the rare gas may be helium.
  • helium has the smallest atomic weight and the lowest sputter rate among the rare gases. Therefore, a stable film is easily formed, and chipping of the silicon substrate can be suppressed to the minimum.
  • the plasma may be plasma of gas that is obtained by diluting diborane (B 2 H 6 ) with helium.
  • an implantation depth of boron may be in a range of 7.5 mm to 15.5 mm.
  • an implantation depth of boron may be equal to or less than 10 nm.
  • the plasma may use continuous plasma.
  • uniformity of 1.5% or less can be realized by adjusting the PD time using the continuous plasma.
  • plasma doping there are developed a technology using continuous plasma and a technology using pulse plasma.
  • pulse plasma it has been reported that, in an implantation technology for a deep region more than approximately 20 nm, not the implantation to a shallow region as intended in the invention, uniformity and reproducibility are secured by plasma doping.
  • uniformity and reproducibility are insufficient.
  • uniformity and reproducibility can be secured.
  • a plasma doping apparatus that performs the above-described plasma doping method includes a vacuum chamber, a sample electrode, a gas supply device that supplies gas into the vacuum chamber, an exhaust device that exhausts the vacuum chamber, a pressure control device that controls a pressure in the vacuum chamber, and a power supply for a sample electrode that supplies power to the sample electrode.
  • the plasma doping apparatus may further include a plasma generation device that forms the film containing the impurity.
  • the plasma doping apparatus may further include a mechanism that adjusts a flow distribution of the gas to be supplied to the vacuum chamber such that the flow distribution of the gas can be adjusted after the film containing the impurity is formed, without exposing the inner wall of the vacuum chamber to atmosphere.
  • the plasma doping apparatus may further include a mechanism that adjusts a temperature of the inner wall of the vacuum chamber to a desired temperature.
  • the temperature control of the inner wall of the vacuum chamber can be realized by measuring the temperature using a temperature sensor and heating the inner wall using a heater. According to the experiment of the inventors, if the experiment is performed with no temperature control, the temperature of the inner wall of the vacuum chamber is initially at a room temperature, but it is increased to 40° C. to 90° C. when the plasma doping treatment is repeated. The increased temperature depends on the number of processing times or the conditions. Then, if the plasma doping treatment ends, the temperature is gradually decreased to the room temperature. That is, the temperature varies when the plasma doping treatment starts and when the plasma doping treatment is repeated. In addition, the temperature of the inner wall of the vacuum chamber is affected by a difference from an external temperature.
  • the temperature of the inner wall it is preferable to adjust the temperature of the inner wall to a temperature that the inner wall naturally reaches when the plasma doping treatment is repeated, for example, a desired temperature of 40° C. to 90° C. Therefore, the amount of the impurity to be doped from the film can be adjusted to a desired value. Further, it is more preferable to adjust the temperature of the inner wall to a desired temperature 50° C. to 70° C. As a result, since the adjustment to a temperature that the inner wall naturally reaches under more plasma doping conditions can be performed, good repeatability can be obtained.
  • a silicon substrate that has a diameter 300 mm and into a surface of which boron is doped by plasma doping using continuous plasma containing boron.
  • a profile of doped boron has a depth ranging 7 nm to 15.5 nm with a boron concentration of 5 ⁇ 10 18 cm 3
  • steepness of the depth profile of boron is in a range of 1.5 nm/dec 3 nm/dec upon evaluation at a distance where the boron concentration is lowered from 1 ⁇ 10 19 cm ⁇ 3 to 1 ⁇ 10 18 cm ⁇ 3
  • a dose of boron has a standard deviation of 2% or less at a surface excluding an end 3 mm of the silicon substrate.
  • the above-described substrate when the above-described substrate is manufactured, the following marked effects can be obtained. If boron is doped at the depth of the above range, a very fine source-to-drain extension electrode of a MOSFET of a 65 nm node to 22 nm node can be formed. Further, when boron is doped at the steepness of the above range, a very fin drain current of the MOSFET can be increased. When boron is doped by plasma doping, the very fine electrode of the MOSFET can be produced with good productivity. In addition, since in-plane uniformity of the dose can be improved by the 300 mm substrate, productivity and yield can be improved.
  • a germanium substrate or a strained silicon substrate may be used since an atom used in the germanium substrate or the strained silicon substrate has an atomic weight not different only negligibly from the silicon atom and thus it can be supposed that the same effects are obtained.
  • FIG. 1 is a diagram showing the relationship between the number of substrates subjected to plasma doping and sheet resistance
  • FIG. 2 is a diagram showing repetitive reproducibility of sheet resistance (a ratio of sheet resistance ranges from 0.5 to 4.0);
  • FIG. 3 is a diagram showing repetitive reproducibility of sheet resistance (a ratio of sheet resistance ranges from 0.8 to 1.2);
  • FIG. 4 is a diagram showing repetitive reproducibility of in-plane uniformity
  • FIG. 5 is a diagram showing repetitive reproducibility of in-plane uniformity
  • FIG. 6 is a diagram showing the relationship between the number of substrates subjected to plasma doping and sheet resistance
  • FIG. 7 is a diagram showing repetitive reproducibility of sheet resistance
  • FIG. 8 is a diagram showing repetitive reproducibility of in-plane uniformity
  • FIG. 9 is a diagram showing the relationship between a plasma doping time, and dose and in-plane uniformity
  • FIG. 10 is a diagram showing a SIMS profile of boron immediately after plasma doping
  • FIG. 11 is a diagram showing the comparison result between uniformity of a plasma doping region obtained by an example of the invention and uniformity of a plasma doping region obtained by a comparative example;
  • FIG. 12 is a diagram showing the comparison result between uniformity of a plasma doping region obtained by an example of the invention and uniformity of a plasma doping region obtained by a comparative example;
  • FIG. 13 is a diagram showing the comparison result between uniformity of a plasma doping region obtained by an example of the invention and uniformity of a plasma doping region obtained by a comparative example;
  • FIG. 14 is a diagram showing a plasma doping apparatus according to a first embodiment of the invention.
  • FIG. 15 is a diagram showing a chamber provided in a vacuum chamber and a cover closing an opening for a transfer arm according to the invention.
  • FIG. 16 is a diagram showing a plasma doping apparatus used for comparison of uniformity in the first embodiment of the invention.
  • FIG. 14 is a cross-sectional view of a plasma doping apparatus that is used in the embodiment of the invention.
  • the plasma doping apparatus includes a vacuum chamber 15 that has a film containing an impurity formed on an inner wall thereof, a turbo molecular pump 6 that serves as an exhaust device for exhausting the vacuum chamber 15 , a pressure regulating valve 7 that serves as a pressure control device for controlling a pressure in the vacuum chamber 15 , a coil and antenna 3 that serves as a plasma source provided in the vicinity of a dielectric window facing a lower electrode 14 , a high-frequency power supply 12 that supplies high-frequency power of 13.56 MHz to the coil and antenna 3 , and a high-frequency power supply 1 that serves as a voltage source for supplying a voltage to the lower electrode 14 .
  • a substrate to be processed (substrate) 13 is placed on the lower electrode 14 serving as a sample table, and plasma irradiation is performed onto the substrate 13 .
  • a high frequency is supplied from the coil and antenna 3 through the high-frequency power supply 1 for generating plasma and the matching box 2 for adjusting the discharge.
  • Required gas is supplied through the mass flow controllers (MFC) 4 and 5 .
  • a degree of vacuum in the vacuum chamber 15 is controlled by the mass flow controllers 4 and 5 , the turbo molecular pump 6 , the pressure regulating valve 7 , and the dry pump 8 .
  • Power is supplied to the vacuum chamber 15 from the high-frequency power supply 12 through the matching box 11 .
  • the substrate 13 to be processed that is provided in the vacuum chamber 15 is placed on the sample table 14 , and then the power is supplied.
  • a predetermined gas is introduced from the gas supply device into the vacuum chamber 15 of the process chamber through the mass flow controllers 4 and 5 , while gas exhaust is performed by the turbo molecular pump 6 as an exhaust device. Further, the vacuum chamber 15 is kept at a predetermined pressure by the pressure regulating valve 7 as a pressure control device. Then, high-frequency power of 13.56 MHz is supplied from the high-frequency power supply 1 to the coil 3 as a plasma source, such that inductively coupled plasma is generated in the vacuum chamber 15 . In this state, the silicon substrate 13 as a sample is placed on the lower electrode 14 . Further, high-frequency power is supplied by the high-frequency power supply 12 , and then the potential of the lower electrode 14 can be controlled such that the silicon substrate (the substrate to be processed) 13 as a sample has a negative potential with respect to plasma.
  • plasma of gas containing an impurity is generated in the vacuum chamber so as to form a film.
  • plasma doping may be repeatedly performed on a dummy substrate under a constant plasma doping condition.
  • the film is attacked by ions in the plasma, and the amount of an impurity to be doped into the surface of the silicon substrate by sputtering is increased.
  • the increase reaches the saturation before long, and, under the constant plasma doping condition, a dose of the impurity to be doped by the plasma doping treatment one time is made uniform even when plasma doping is repeated. For example, if doping is performed on the silicon substrate multiple times under the constant plasma doping condition, and the dose into the silicon substrate is made uniform, it can be seen that the formation of the film is completed. If the first dose to the substrate tends to be smaller the final dose to the substrate, the formation of the film is not completed, and thus the formation of the film is continued.
  • the shape of the inner wall of the vacuum chamber is adjusted such that, when the formation of the film is completed, the total distribution of the distribution of the impurity to be doped from the plasma containing the impurity ions and the distribution of the impurity to be doped by sputtering from the film containing the impurity fixed to the inner wall of the vacuum chamber is made uniform in the surface of the silicon substrate.
  • the silicon substrate 13 is placed on the sample table 14 as the lower electrode, while the vacuum chamber 15 is exhausted, helium gas is supplied into the vacuum chamber 15 by the mass flow controller 4 and diborane (B 2 H 6 ) gas as doping material gas is supplied into the vacuum chamber 15 by the mass flow controller 5 .
  • the pressure regulating valve 7 is controlled such that the pressure of the vacuum chamber 15 is kept at 0.9 Pa.
  • high-frequency power 1500 W is supplied to the coil 3 as a plasma source so as to generate plasma in the vacuum chamber 15 .
  • high-frequency power 200 W is supplied to the lower electrode 14 such that boron is implanted in the vicinity of the surface of the silicon substrate 13 .
  • plasma that is exposed to the silicon substrate 13 is mixture gas plasma of B 2 H 6 and He (B 2 H 6 /He plasma).
  • the mixture ratio of B 2 H 6 and He can be changed by changing a ratio of flow rates of He gas and B 2 H 6 gas flowing in the mass flow controllers 4 and 5 .
  • a bias is applied by irradiating the mixture gas plasma of B 2 H 6 and He (B 2 H 6 /He plasma) onto the silicon substrate, there is a time when doping and sputtering of boron to the silicon substrate are saturated (balanced). That is, if plasma irradiation starts, the dose is initially increased, and thereafter, a time when the dose is substantially uniform without depending on the time variation is continued. Accordingly, the dose can be accurately controlled through a process window of the time when the dose is made substantially uniform without depending on the time variation. Further, in-plane uniformity can be obtained by previously measuring, in the surface of the silicon substrate, the time when the dose is made uniform and setting the doping time according to the latest start time.
  • the film containing the impurity may be formed after the vacuum chamber is mounted after the maintenance of the plasma doping apparatus. After the film is formed, the impurity is doped under an actual plasma doping condition. In such a manner, a process can be performed while the formed film is not exposed to atmosphere. In case of the boron film, boron tends to act with moisture. Accordingly, it is preferable to use the above-described configuration since, according to the above-described configuration, the film can be formed without acting with moisture and then used in the process.
  • the film containing the impurity may be formed by providing a vacuum chamber, from which the film containing the impurity is removed through a maintenance step, in a plasma generation device separately prepared in order to form the film, and generating the plasma containing the impurity ions in the vacuum chamber. If a plurality of vacuum chambers are prepared, the vacuum chamber to which the film is attached in advance may be provided in the plasma doping apparatus, thereby performing the plasma doping treatment, while the film is being attached by the plasma generation device separately prepared. Accordingly, while the film is being attached to the inner wall of the vacuum chamber, the plasma doping treatment can be performed on the silicon substrate, thereby improving productivity.
  • Example 1 of the invention will be described. Moreover, when there is not particular description, the following experiment method is common to the individual examples.
  • the plasma doping apparatus shown in FIG. 14 is an apparatus that is typically used.
  • the gas mixture ratios of B 2 H 6 and He are 0.05% and 99.95%
  • source power is 1500 W
  • bias power is 135 W
  • a pressure is 0.9 Pa.
  • a plasma doping time when a bias is applied is 60 seconds. Under the constant conditions, plasma doping is performed on a substrate having a diameter 300 mm in the vacuum chamber immediately after the maintenance.
  • a heat treatment is performed on the first, 25-th, 75-th, 125-th, 250-th, and 500-th processed silicon substrates at 1075° C. for 20 seconds.
  • sheet resistance at 121 places excluding an end 3 mm of the substrate are measured by a four-probe method, and a standard deviation with respect to the average value of sheet resistance is calculated. In-plane uniformity is represented by the standard deviation (1 ⁇ ) of sheet resistance.
  • the reason why the heat treatment is not performed on the second to 24-th substrates is that the treatment is performed using a dummy silicon substrate.
  • the dummy silicon substrate means that, an actual silicon substrate is used, but a new substrate is not used for each PD treatment and the PD treatment is repeatedly performed on the same silicon substrate approximately one hundred times. This is a measure that saves consumption of the silicon substrate without having an affect on the experiment for forming the film containing boron on the inner wall of the vacuum chamber.
  • FIG. 1 shows the relationship between the number of substrates subjected to the plasma doping treatment and sheet resistance. Even though the treatment is performed under the same condition, sheet resistance is initially high and then gradually decreased as the number of processed substrates increases. As the analysis result of the film formed on the inner wall of the vacuum chamber after the experiment, it can be seen that boron is contained in the film. It is considered that the film is formed while the PD treatment is repeated and then sheet resistance is decreased.
  • FIGS. 2 and 3 are diagrams having a ratio of sheet resistance when 236.1 ohm/sq is substituted with ‘1’ as a vertical axis and the number of substrates subjected to the PD treatment as a horizontal axis.
  • FIG. 3 shows the ratio of sheet resistance ranging from 0.8 to 1.2. Referring to FIG. 3 , the decrease of sheet resistance is not saturated, that is, the formation of the film is not saturated, in case of the 25-th processed substrate.
  • sheet resistance of the first substrate subjected to the PD treatment is approximately 3.2 times as much as average sheet resistance (236.1 ohm/sq) of the 75-th substrate and later. It is possible to consider that the dose is substantially in proportion to sheet resistance. Accordingly, it means that the dose to the first substrate is only approximately 30% of the dose to the 75-th substrate or later.
  • a factor that boron is doped entirely depends on B 2 H 6 gas plasma introduced in forms of gas, ions, and radicals through the plarmization of boron contained in B 2 H 6 gas introduced from the gas introduction port. At this time, since the film containing boron is not formed, the dose from the film is zero.
  • a factor depends on the film containing boron formed on the inner wall of the vacuum chamber, in addition to the B 2 H 6 gas plasma. Since the PD condition is unchanged for the first substrate or the 75-th substrate, the dose from the B 2 H 6 gas plasma is not changed. The changed is the dose from the film. Table 1 shows the dose of the first substrate and the 75-th substrate and later by factors. It can be seen that, after the 75-th substrate and later, the dose from the film containing boron becomes a principal factor at approximately 70%. The dose from the B 2 H 6 gas plasma occupies only approximately 30%. This is a new fact that reverses the concept of plasma doping in the related art.
  • FIG. 4 shows the relationship between the number of substrates subjected to the plasma doping treatment and in-plane uniformity of sheet resistance. It can be seen that the in-plane uniformity is improved from 5.28% in the first substrate to a range of 2% to 3% in the 25-th substrate and later. This is because the shape of the inner wall of the vacuum chamber is adjusted such that the in-plane uniformity is improved when the formation of the film is completed. In the related art, the shape of the vacuum chamber or the position of the coil is adjusted so as to make the plasma or gas distribution uniform. This corresponds to a case where the maximum in-plane uniformity is obtained in the first substrate.
  • the in-plane uniformity is neglected since the film is not completely formed, and the shape of the inner wall of the vacuum chamber is adjusted while focusing on the state when the formation of the film is completed.
  • the 25-th substrate and later when the film is being formed has in-plane uniformity superior to the first substrate.
  • markedly improved in-plane uniformity with respect to the first substrate can be continuously realized with good repetitive reproducibility.
  • the plasma doping apparatus in which the shape of the inner wall of the vacuum chamber after the maintenance is adjusted in advance such that in-plane uniformity is improved when the formation of the film is completed, is prepared, and plasma doping is performed.
  • a chamber serving as an inner wall is provided in the vacuum chamber. This chamber cannot be kept in a vacuum state. This chamber is used to form a film on its surface. With this chamber, it is unnecessary to clean the entire vacuum chamber upon the maintenance, and only the above-described chamber may be removed and cleaned.
  • the above-described chamber does not have a vacuum keeping capability compared with the vacuum chamber, and thus the structure can be simplified, and cleaning can be easily performed.
  • the shape of the chamber has been studied as follows.
  • the chamber is substantially symmetric as viewed from the center of the silicon substrate.
  • it is necessary to form an opening, through which a transfer arm for transferring the silicon substrate into the vacuum chamber enters and leaves the vacuum chamber.
  • symmetry is drastically lacking.
  • the inventors have studied for making the area of the opening as small as possible to an extent such that the silicon substrate and the transfer arm get therethrough.
  • FIG. 5 in the PD treatment of the 100-th substrate and later when the formation of the film is completed, very good uniformity of 2% or less is obtained.
  • FIG. 15 ( a ) is a diagram showing when a semiconductor substrate is transferred.
  • FIG. 15 ( b ) is a diagram showing a state where plasma doping is performed.
  • a plasma doping apparatus in which a gas supply method is adjusted in advance immediately after the maintenance, is prepared, and plasma doping is performed.
  • a head plate is disposed to the silicon substrate, 18 holes are opened in the head plate like a shower head, and gas is supplied from the holes into the vacuum chamber. Then, the positions of the holes are adjusted such that the in-plane uniformity is improved when the formation of the film is completed.
  • the plasma doping apparatus used herein is shown in FIG. 16 .
  • a predetermined gas is introduced from a gas supply device 102 into a vacuum chamber 101 while gas exhaust is performed by a turbo molecular pump 103 as an exhaust device.
  • the vacuum chamber 101 can be kept at a predetermined pressure by the pressure regulating valve 4 .
  • high-frequency power of 13.56 MHz is supplied to a coil 108 provided in the vicinity of a dielectric window 107 facing a sample electrode 106 by a high-frequency power supply 105 , such that inductively coupled plasma can be generated in the vacuum chamber 101 .
  • a silicon substrate 109 as a sample is placed on the sample electrode 106 .
  • a high-frequency power supply 110 that supplies high-frequency power to the sample electrode 106 is provided.
  • the high-frequency power supply 110 functions as a voltage source for controlling the potential of the sample electrode 106 such that the substrate 109 as the sample has a negative potential with respect to the plasma. In such a manner, ions in the plasma are accelerated and collide against the surface of the sample, such that the impurity can be doped into the surface of the sample. Moreover, the gas supplied from the gas supply device 102 is exhausted from an exhaust port 111 to the pump 103 .
  • a flow rate of gas containing impurity material gas is controlled to a desired value by a flow rate control device (mass flow controller) provided in the gas supply device 102 .
  • a flow rate control device mass flow controller
  • gas obtained by diluting the impurity material gas with helium for example, gas obtained by diluting diborane (B 2 H 6 ) with helium (He) at 0.5% is used as impurity material gas, and the flow rate of the impurity material gas is controlled by a first mass flow controller. Further, the flow rate of helium is controlled by a second mass flow controller.
  • the gases whose flow rates are controlled by the first and second mass flow controllers are mixed in the gas supply device 102 , and then introduced to a gas main path 114 through a pipe (gas introduction path) 113 . Subsequently, the mixture gas is introduced into the vacuum chamber 101 by gas outlet ports 115 through a plurality of holes connected to the gas main path.
  • the plurality of gas outlet ports 115 are configured to blow off the gas from a surface facing the sample 109 toward the sample 109 .
  • the gas outlet ports 115 are substantially provided symmetrically with respect to the center of the dielectric window 107 .
  • the gas outlet ports 115 have a structure to substantially isotropically blow off the gas toward the sample. That is, 24 gas outlet ports 115 are substantially isotropically arranged.
  • Reference numeral 116 denotes a matching box, and reference numeral 117 denotes a V DC monitor.
  • FIG. 7 is a diagram showing repetitive reproducibility of sheet resistance. Here, a ratio of sheet resistance ranging from 0.8 to 1.2 is shown. In the 375-th substrate and later, sheet resistance is converged on a variation within a tolerance ⁇ 5% from the average value, and a decrease of sheet resistance is saturated. That is, it can be understood that the formation of the film is saturated by the PD treatment around the 375-th substrate. After the formation of the film is completed, while sheet resistance varies around the average value within a small range, the PD treatment can be performed continuously many times.
  • FIG. 8 is a diagram showing repetitive reproducibility of in-plane uniformity.
  • the gas supply method is adjusted immediately after the maintenance.
  • very good uniformity of 1.85% or less is obtained.
  • the PD time means a time when a bias is applied by irradiating plasma.
  • the PD time is changed to 14 seconds, 45 seconds, and 100 seconds.
  • the PD time is 60 seconds.
  • data for the treatment of the 1375-th substrate closest to the 1350-th substrate is referred to.
  • FIG. 9 shows the relationship between the PD time and the dose.
  • FIG. 9 also shows a change in in-plane uniformity.
  • the dose is initially increased, and then the dose is increased such that 1.7E15 cm ⁇ 2 becomes an asymptotic line. It is recognized that there is a time when the change of the dose is very small without depending on the time variation. Through a process window of the time, the dose can be accurately controlled. It is more preferable to set a time when the dose occupies 70% or more of the asymptotic line. Accordingly, the in-plane uniformity can be further improved. It is still more preferable to set a time when the dose is closer to the asymptotic line. Therefore, the optimum in-plane uniformity can be obtained. Actually, when the PD time is 100 seconds, the in-plane uniformity of 1.34% at 1 ⁇ can be realized, regardless of the same condition, excluding the shape of the chamber, the gas supply method, and the PD time.
  • FIGS. 11 to 14 are diagrams showing in-plane uniformity of the samples of the first substrate in the comparative example, the 1000-th substrate in the example, and the 1375-th substrate in the example, respectively.
  • FIGS. 12 ( a ) to 12 ( b ) are diagrams showing in-plane uniformity of the samples of the first substrate and the 125-th substrate in the comparative example, respectively.
  • FIGS. 13 ( a ) to 13 ( c ) are diagrams showing the results after 14 seconds in the comparative example, after 60 seconds in the example, and after 100 seconds in the example.
  • an implantation depth of boron is 9.4 nm (see FIG. 10 ). This means that implantation energy of boron is very low. Low energy corresponding to the implantation depth of 10 nm or less is widely industrially used in the related art. However, even in the ion implantation method capable of realizing excellent uniformity, it is not easy to realize uniformity of 2% or less over the entire surface excluding an end 3 mm of the 300 mm substrate. Further, in a plasma doping method that is known to have a difficulty in realizing uniformity, a degree of difficulty is still more severe.
  • uniformity of 2% or less can be realized over the entire surface excluding the end 3 mm of the 300 mm substrate at the implantation depth of 10 nm or less.
  • uniformity of 1.5% or less can be realized.
  • FIG. 10 shows a SIMS profile when a bias voltage in the plasma doping apparatus used in the invention is changed.
  • the implantation depth of boron can be changed in a range of 7.5 nm to 15.5 nm. If an implantation energy range corresponds to at least the above-described implantation depth, the film containing boron can be formed on the inner wall of the vacuum chamber so as to saturate sheet resistance. Further, the shape of the inner wall of the vacuum chamber can be adjusted in advance such that the in-plane uniformity is improved when the formation of the film is completed. That is, through the same experiment, the fact that the method according to the invention can be used similarly and validity are confirmed.
  • the PD condition that is actually used after the film formation is repeated.
  • the film may be formed a different condition from the PD condition to be actually used.
  • the gas mixture ratios of B 2 H 6 and He are 0.05% and 0.95% in the example, the gas mixture ratios may be 0.1% and 99.9%. It is preferable in that, if the B 2 H 6 concentration is higher, the film can be formed in a short time. However, if the B 2 H 6 concentration is increased to 5%, it is known that the film is not stabilized, and sheet resistance and in-plane uniformity are also unstable.
  • the film can be formed in a short time. After the film is formed in such a manner, from a practical viewpoint, it is preferable to adjust the B 2 H 6 concentration such that the dose has a desired value, and immediately perform actual plasma doping.
  • the optimum B 2 H 6 concentration upon the film formation will be studied in future, but it belongs to a typical design item that still falls within the scope of the invention.
  • the dummy silicon substrate may be disposed on the sample electrode. After the formation of the film is completed, preferably, the dummy substrate is removed from the sample electrode, and then a substrate to be processed is placed and an actual treatment starts. Accordingly, an extra substrate for the formation of the film is not used. From this viewpoint, it is efficient.
  • Comparative Example 1 will be described with reference to FIG. 4 .
  • the plasma condition, the gas supply method, and the shape of the inner wall of the vacuum chamber are adjusted such that in-plane uniformity of the dose is improved.
  • a concept of the dose from the film is unconscious.
  • This approach does not have the maintenance step of preparing the vacuum chamber having the film containing the impurity on the inner wall thereof such that, when the film containing the impurity fixed to the inner wall of the vacuum chamber is attacked by ions in plasma, the amount of the impurity to be doped into the surface of the sample by sputtering is not changed even though plasma containing the impurity ions is repeatedly generated in the vacuum chamber.
  • a known approach that adopts in order to improve repeatability and in-plane uniformity with plasma doping almost corresponds to the above-described case.
  • in-plane uniformity of 1.5% can be realized by the treatment of the first substrate.
  • Sheet resistance is 455 ohm/sq.
  • Comparative Example 1 in a state before the film is formed immediately after the maintenance, the shape of the inner wall of the vacuum chamber or the gas supply method is adjusted such that the in-plane uniformity is improved.
  • the film containing boron is formed on the inner wall of the vacuum chamber by plasma doping, and the state is changed. Accordingly, good in-plane uniformity cannot be repeatedly and stably obtained, and the same sheet resistance cannot be repeatedly obtained.
  • the maintenance step that prepares the vacuum chamber having the film containing the impurity on the inner wall such that the dose from the film is not changed even though the plasma is repeatedly generated.
  • the shape of the inner wall of the vacuum chamber or the gas supply method is adjusted.
  • the following marked effects can be obtained. That is, even though production is repeated for a long time, in-plane uniformity can be kept to a stable and good level. Further, sheet resistance is stabilized and thus the same sheet resistance can be obtained.
  • Comparative Example 2 not immediately after the maintenance, when the film is being formed, which is not intended for convenience of the experiment, the gas supply method and the shape of the inner wall of the vacuum chamber may be adjusted such that the in-plane uniformity is improved.
  • An experiment of repeatability of sheet resistance may start.
  • gas plasma containing an impurity for plasma doping
  • mixture gas plasma of B 2 H 6 and He for example, when mixture gas plasma of B 2 H 6 and He is used, a film is naturally formed even though an experimenter does not intend to form the film.
  • Comparative Example 2 corresponds to a case where an experimenter who makes an experiment on a depth control of an impurity upon plasma doping starts an experiment on in-plane uniformity or repeatability without performing the maintenance of the vacuum chamber for convenience for the experiment.
  • Comparative Example 2 there may be a case where the formation of the film is unintentionally completed.
  • it is difficult to increase repetitive stability of sheet resistance and in-plane uniformity to a reliable level.
  • it is very difficult to increase repeatability of in-plane uniformity.
  • the shape of the inner wall of the vacuum chamber and the gas supply method are adjusted by exposing the vacuum chamber to atmosphere, with no mechanical movement.
  • the generation frequency of the particles clearly becomes high compared with a case where production can be performed with no exposure to atmosphere after the formation of the film.
  • the film containing boron it is particularly difficult. From the experiment result, it is known that the film containing boron is likely to act with moisture. For this reason, upon the exposure to atmosphere, the film acts with moisture in atmosphere, the quality of the film is changed. Accordingly, even though the vacuum chamber is vacuumized and the adjustment is performed for plasma doping, performance of the film before the exposure to atmosphere is not obtained. Accordingly, in the case of the film containing boron, it is impossible to adjust the shape of the inner wall of the vacuum chamber and the gas supply method by exposing the vacuum chamber to atmosphere after the film is formed.
  • the vacuum chamber cannot be exposed to atmosphere. Accordingly, in the comparative example, it is more difficult to adjust in-plane uniformity. Therefore, the effects of the example more markedly exhibit. As such, like the example, it is preferable to adjust the shape of the inner wall of the vacuum chamber and the gas supply method in advance before the film is formed such that in-plane uniformity is improved after the film is formed.
  • Patent Document 3 There is disclosed a technology that causes sputtering gas to collide against a solid target containing an impurity in a plasma state so as to fly the impurity out of the target, and dopes the flown impurity into the surface of the sample.
  • a microwave of 1 GHz or more is introduced into a vacuum chamber.
  • a material forming the target is a metal. Accordingly, in a parallel flat-plate type plasma generation device not having a plasma generation unit, such as ECR or the like, plasma is also generated.
  • ECR18 is provided so as to introduce a microwave of 1 GHz or more into the vacuum chamber.
  • the microwave of 1 GHz or more is introduced into the vacuum chamber, high-density plasma of 1000 times as much as plasma in the parallel flat-plate type plasma generation device is generated.
  • the impurity such as boron or the like, can be implanted into the surface of the silicon substrate in a short time. For this reason, the temperature of the silicon substrate is not increased to 300° C. or more, and thus it is possible to prevent a resist pattern formed on the silicon substrate from being burned.
  • the solid target containing the impurity is prepared and placed in the vacuum chamber.
  • the maintenance that forms the film containing the impurity such that the amount of an impurity to be doped into the surface of the sample by sputtering is not changed even though the plasma containing the impurity ions is repeatedly generated in the vacuum chamber is not performed. Accordingly, it is difficult to obtain in-plane uniformity or repeatability. The reason will be described. Even though the solid target is disposed in the vacuum chamber, if the plasma containing the impurity used in the example (boron in the example) is repeatedly excited in the vacuum chamber, a film containing boron is being formed in the surface of the solid target.
  • the film containing boron is formed on the surface of the inner wall at a portion of the inner wall of the vacuum chamber that is not covered with the solid target. Then, repetitive excitation is performed, and the formation of the film is saturated and completed after the excitation for a certain time. Accordingly, only by disposing the solid target in the vacuum chamber, the maintenance step that prepares the vacuum chamber having the film containing the impurity on the inner wall such that dose from the film is not changed even though the plasma is repeatedly generated in the vacuum chamber is not provided. As a result, it is difficult to obtain repeatability of sheet resistance.
  • a method of creating a target is not clearly described, in general, it is considered that the target is not created in the vacuum chamber, and the externally created target is provided in the vacuum chamber.
  • a solid containing an impurity is necessarily exposed to atmosphere one time. Accordingly, the solid may act with oxygen in atmosphere, and an oxide film may be formed in the surface of the film. Further, the solid may act with moisture in atmosphere, and the quality of the film may be changed. The oxidization of the film or the action with moisture in atmosphere has a large affect on the dose of the impurity after plasma doping and uniformity.
  • the film containing the impurity is formed on the inner wall such that the dose from the film containing the impurity fixed to the inner wall of the vacuum chamber is not changed even though the plasma is repeatedly generated. Accordingly, the marked effects, for example, repetitive reproduction of the dose, can be obtained.
  • the film containing the impurity fixed to the inner wall of the vacuum chamber is formed such that, when a dose of the impurity is the same level with a tolerance of ⁇ 10% even though the plasma containing the impurity ions is repeatedly generated in the vacuum chamber, the dose is made uniform in a surface of the silicon substrate. Accordingly, while good in-plane uniformity of the dose is kept, repetitive reproducibility can be obtained.
  • the step of forming the film containing the impurity is performed by providing the vacuum chamber, from which the film containing the impurity is removed in the maintenance step, in the plasma doping apparatus and generating the plasma containing the impurity ions in the vacuum chamber. Accordingly, the film containing the impurity can be used for plasma doping with no exposure to atmosphere. Therefore, there is no affect of atmospheric humidity or temperature, and repetitive reproducibility can be secured over the entire surface of the 300 mm substrate excluding the end 3 mm. In addition, very uniform plasma doping of the impurity can be performed with the standard deviation of 1.7%, and, if the PD time is adjusted, 1.5% or less.
  • Plasma doping has attracted attention for 20 years since a group including one of the inventors had stated an impurity implantation method to a silicon trench in 1986 to 1987 (Non-Patent Document 3). Thereafter, in a technical field for forming a shallow junction, a MOS device fabricated using plasma doping had stated in 1996 (Non Patent Documents 4 and 5). For 10 years since then, plasma doping has attracted attention and would be expected to be put to practical use. However, plasma doping has been yet far from practical use.
  • One of the problems as the obstruction to practical use was repetitive stability of the dose and in-plane uniformity. The invention is to solve this problem.
  • the plasma doping method of the invention it is possible to realize a plasma doping method that can control an impurity concentration profile with high accuracy and can form a shallow impurity diffusion region.
  • the plasma doping method of the invention can be applied to the use, such as an impurity doping process of a semiconductor or manufacturing of a thin film transistor used in liquid crystal or the like.

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