WO2013105179A1 - シリコン単結晶ウェーハの製造方法及び電子デバイス - Google Patents
シリコン単結晶ウェーハの製造方法及び電子デバイス Download PDFInfo
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- WO2013105179A1 WO2013105179A1 PCT/JP2012/008002 JP2012008002W WO2013105179A1 WO 2013105179 A1 WO2013105179 A1 WO 2013105179A1 JP 2012008002 W JP2012008002 W JP 2012008002W WO 2013105179 A1 WO2013105179 A1 WO 2013105179A1
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- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 111
- 239000010703 silicon Substances 0.000 title claims abstract description 111
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims abstract description 109
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- 238000004519 manufacturing process Methods 0.000 title claims abstract description 27
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 417
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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
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/322—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to modify their internal properties, e.g. to produce internal imperfections
- H01L21/3221—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to modify their internal properties, e.g. to produce internal imperfections of silicon bodies, e.g. for gettering
- H01L21/3225—Thermally inducing defects using oxygen present in the silicon body for intrinsic gettering
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/12—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/16—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, only elements of Group IV of the Periodic Table
Definitions
- the present invention relates to a method for manufacturing a silicon single crystal wafer suitable for manufacturing an image sensor device or a memory device, and an electronic device using the same.
- a silicon single crystal wafer used for a semiconductor device is generally cut out from a silicon single crystal ingot grown by the Czochralski method (hereinafter referred to as [CZ method]) and manufactured through a process such as polishing.
- the required items required for this silicon single crystal wafer are incorporated in the formation of a surface defect-free layer (hereinafter referred to as “DZ layer”), the control of the dissolved oxygen concentration affecting the mechanical strength, and the device process.
- This is control of oxygen precipitates (Bulk Micro Defect: hereinafter referred to as [BMD]) formed inside the wafer in order to remove the metal contamination elements from the surface layer of the wafer (referred to as gettering).
- COP Crystal Originated Particle
- OSF Oxidation Induced Stacking Fault nuclei (small defects that cause OSF)
- N nitrogen
- Patent Document 1 a nitrogen (N) -added wafer subjected to high-temperature annealing in an Ar atmosphere has been proposed as a method for forming a high-quality DZ layer by eliminating the glow-in defects on the wafer surface layer.
- Patent Document 2 a method for growing a silicon single crystal (hereinafter referred to as a complete crystal) in which the growth conditions of the CZ method are controlled and grow-in defects such as COP and OSF nuclei do not exist has been proposed (for example, Patent Document 2).
- Patent Document 2 a method for performing epitaxial growth on a silicon single crystal wafer and using the epitaxial layer as a DZ layer.
- BMD control is important for all devices, but is particularly important for solid-state imaging devices.
- a solid-state imaging device which is a photoelectric conversion device, generates charges according to the intensity of light hitting the imaging surface and converts the light into an electrical signal. Therefore, it is desirable that the charge amount on the imaging surface when light is blocked, that is, when no light is applied, is “zero”.
- the amount of charge is measured as a current, and it is desirable that the current during light shielding, that is, the dark current, be as small as possible.
- a deep level is formed in the forbidden band of the semiconductor. As a result, electric charges are generated through defects even in a state where no light is applied. This is known as generation / recombination current, and deteriorates the dark current characteristics, that is, the electrical characteristics of the solid-state imaging device.
- the BMD removes (getters) the metal contamination element from the wafer surface layer portion. Deterioration of electrical characteristics can be prevented.
- gettering it is desirable that the total volume of BMD (which is proportional to the density ⁇ BMD size per one) is large, and the BMD is formed as close as possible to the device formation region (proximity gettering). It is desirable. The reason is that in order to getter contaminant elements such as metals, it is necessary for the contaminant elements to diffuse to the position of the BMD, which is the getter site, during heat treatment. This is because the diffusion distance of the contaminating elements tends to be shortened.
- the BMD size is too large, the BMD itself becomes a dislocation generation source, the wafer is deformed by the heat treatment in the device manufacturing process, and the adverse effect that the alignment accuracy of the device pattern is lowered in the photolithography process and the yield is lowered.
- the size needs to be kept below a predetermined size. Thus, it is necessary to control the density and size of the BMD within a certain range. The same applies to memory devices.
- An intrinsic gettering method in which oxygen precipitation heat treatment is performed before epitaxial growth or the like to form BMD in bulk can be applied to a silicon single crystal wafer used for a solid-state imaging device.
- IG method Intrinsic Gettering: hereinafter referred to as “IG method”
- the IG method requires heat treatment for a long time at a high temperature, there is a concern in terms of cost, metal contamination is likely to occur during the heat treatment, or slip occurs due to the heat treatment. For this reason, in recent years, many wafers in which an epitaxial layer is formed on a wafer cut from a crystal doped with carbon (C) at the stage of growing a silicon single crystal by the CZ method have been adopted.
- C crystal doped with carbon
- the wafer has no BMD formed at the shipment stage, but carbon is present in the wafer, so oxygen is likely to precipitate even at a relatively low temperature of 400-800 ° C., and BMD is easy even in the heat treatment of the solid-state imaging device manufacturing process. It is characterized by being formed.
- JP 2002-353225 A Japanese Patent Laid-Open No. 08-330316 US2001 / 0055689 Japanese Patent Laid-Open No. 11-116390 Japanese Patent No. 3763629 JP 2010-40587 A JP 2009-170656 A JP 2001-203210 A JP 2003-297839 A WO2010 / 119614
- the thickness of the epitaxial layer tends to be thin.
- the thickness of the epitaxial layer is sometimes 5 ⁇ m or less. As the epitaxial layer becomes thinner, the following new problems have emerged.
- a silicon single crystal wafer for forming an epitaxial layer is cut out from a silicon single crystal grown by the CZ method, and the silicon single crystal pulled by the CZ method pulling furnace depends on the temperature fluctuation of the silicon melt surface, Concentrations of oxygen, carbon, and a dopant element (for example, phosphorus (P)) have concentric shades in the wafer surface. This density is called striation.
- a dopant element for example, phosphorus (P)
- the problem is oxygen striation that forms precipitates and has a large diffusion constant.
- the BMD formed by the BMD forming heat treatment is formed using the oxygen striation as a template, and therefore appears in the wafer as BMD shading.
- the formed BMD is effective as a gettering source for removing metal contamination from the surface layer.
- a defect level is formed, so that the diffusion current which is a dark current is increased.
- the epitaxial layer is thick, the distance between the BMD and the device formation region is large, so diffusion current is not a problem. However, when the epitaxial layer is thin, this effect cannot be ignored and has become a problem.
- the BMD that adversely affects the characteristics of the solid-state imaging device is the BMD that occurs closest to the device formation region, that is, the BMD generated immediately below the DZ layer. It is thought that there is.
- the wafer oxygen may be diffused into the DZ layer or the epitaxial layer by the heat treatment in the device process to form minute oxygen precipitates or oxygen donors in the epitaxial layer or the DZ layer. All of these appear as shades using oxygen striation as a template, and when the epitaxial layer is thinned, the amount of oxygen diffusing up to the surface layer of the epitaxial layer, which is a device formation region, increases, and its influence becomes large. As a result, when the epitaxial layer is thinned, these effects become obvious, and in a solid-state imaging device, it appears as striped image noise using a striation as a template, resulting in a large quality deterioration.
- Patent Document 4 As a method for improving the striation of oxygen, there has been proposed a method of improving the structure of the heater in the furnace of the CZ method apparatus by reducing temperature fluctuations on the surface of the silicon melt (Patent Document 4). However, this method is not sufficient because striation cannot be completely eliminated. Further, there still remains a problem that oxygen may diffuse into the DZ layer or the epitaxial layer during the heat treatment in the device process to form a minute BMD or oxygen donor.
- COP exists in a silicon single crystal wafer used as a substrate of an epitaxial wafer for an image sensor.
- Patent Document 5 describes that in the case of epitaxial growth under normal pressure, the disappearance of COP occurs on the surface of the epitaxial layer unless the thickness of the epitaxial layer is 2 ⁇ m or more.
- Patent Document 6 proposes a method of performing RTA treatment at 1300 ° C. or higher and 1380 ° C. or lower in an oxygen atmosphere.
- COP can be extinguished and oxygen can be diffused inward in the surface layer.
- oxygen diffused inward by the RTA treatment is not treated by the subsequent heat treatment.
- oxygen incorporated into the bulk of the silicon single crystal wafer in the CZ growth stage diffuses to the surface as usual.
- Both the oxygen diffused and the oxygen taken into the bulk of the silicon single crystal wafer during the CZ growth stage diffuse into the DZ layer and the epitaxial layer during the device heat treatment.
- more oxygen is taken into the device formation region than the silicon single crystal wafer not subjected to RTA treatment, and more donors and precipitates are likely to be generated in the device formation region.
- the present invention has been made in view of the above problems, and an object thereof is to provide a method capable of manufacturing a silicon single crystal wafer on which a good gettering layer close to a device formation region is formed.
- the present invention provides a method for producing a silicon single crystal wafer, wherein a first heat treatment temperature is applied to the silicon single crystal wafer in an oxygen-containing atmosphere by using a rapid heating / cooling device.
- the first heat treatment is performed for 1 to 60 seconds and then cooled to 800 ° C. or lower at a temperature drop rate of 1 to 100 ° C./second, so that oxygen is diffused inward and the oxygen concentration is near the surface of the silicon single crystal wafer.
- a method for producing a silicon single crystal wafer is provided, wherein a peak region is formed and then a second heat treatment is performed to agglomerate oxygen in the silicon single crystal wafer into the oxygen concentration peak region.
- oxygen is diffused inward into the surface layer of the silicon single crystal wafer by the first heat treatment, and the second heat treatment is performed to agglomerate the oxygen inside the wafer in the oxygen concentration peak region.
- a concentration oxygen concentration peak region can be formed. For this reason, a silicon single crystal wafer on which a uniform gettering layer close to the device formation region is formed can be manufactured.
- the oxygen concentration of the silicon single crystal wafer subjected to the first and second heat treatments is 4 ⁇ 10 17 atoms / cm 3 (ASTM'79) or more and 16 ⁇ 10 17 atoms / cm 3 (ASTM'79) or less. It is preferable that With a silicon single crystal wafer having such an oxygen concentration, an oxygen concentration peak region having a sufficient peak concentration can be efficiently formed by the first and second heat treatments.
- the conditions of the first and second heat treatments are set in advance as follows: a silicon single crystal wafer after the first heat treatment; a silicon single crystal wafer after the first and second heat treatment; or after the first and second heat treatments.
- the oxygen concentration profile of the silicon single crystal wafer subjected to the oxygen precipitate revealing heat treatment is measured, and the silicon single crystal wafer after the first and second heat treatment or the oxygen precipitate revealing heat treatment is performed after the first and second heat treatment.
- the half-value width of the oxygen concentration profile of the silicon single crystal wafer is determined to be a condition smaller than the half-value width of the oxygen concentration profile of the silicon single crystal wafer after the first heat treatment, and the first and first conditions are determined under the determined condition. 2 It is preferable to perform heat treatment.
- the first and second heat treatments ensure an oxygen concentration peak region having a uniform in-plane oxygen concentration in the vicinity of the wafer surface. Can be formed.
- the conditions of the first and second heat treatments are determined as conditions under which oxygen precipitation defects are not formed on the surface of the silicon single crystal wafer after the first and second heat treatments, and the first conditions are determined under the determined conditions. It is preferable to perform the second heat treatment.
- a higher quality silicon single crystal wafer in which no defects are generated on the wafer surface by the first and second heat treatments. Can be manufactured.
- the first heat treatment is preferably performed at a first heat treatment temperature of 1320 ° C. or higher and a melting point of silicon or lower in an atmosphere containing 20% or more of oxygen.
- the first heat treatment is preferably performed at a first heat treatment temperature of 1290 ° C. or higher and lower than the melting point of silicon in an atmosphere containing oxygen of 0.01% or more and less than 20%.
- the second heat treatment it is preferable to perform a precipitation nucleus growth heat treatment at 800 to 1200 ° C. for 1 hour or longer after the precipitation nucleus formation heat treatment.
- a precipitation nucleus growth heat treatment it is preferable to perform a precipitation nucleus growth heat treatment at 800 to 1200 ° C. for 1 hour or longer after the precipitation nucleus formation heat treatment.
- an epitaxial layer is formed on the surface of the silicon single crystal wafer after the first and second heat treatments.
- the present invention also provides an electronic device characterized in that it is formed on the surface of the epitaxial layer of a silicon single crystal wafer manufactured by the method for manufacturing a silicon single crystal wafer of the present invention.
- Such an electronic device is a high-quality electronic device having no defect in the device formation region and having a good gettering layer formed directly therebelow.
- a uniform and high concentration oxygen concentration peak region can be formed in the vicinity of the surface of the silicon single crystal wafer. Therefore, a good gettering layer close to the device formation region is formed, and the device formation region is not adversely affected.
- FIG. 6 shows the oxygen-fixing heat treatment temperature dependence of the peak height of the oxygen concentration of Sample 3 (after performing rapid heating / rapid cooling heat treatment, oxygen fixing heat treatment, and oxygen precipitate revealing heat treatment) in Example 1 and Comparative Example 1; It is a graph.
- the present inventors diligently studied a method for forming a high concentration oxygen concentration peak region near the wafer surface.
- oxygen was introduced into the silicon single crystal wafer by rapid thermal annealing (RTA: Rapid Thermal Anneal) in an oxygen-containing atmosphere, and then heat treatment was performed in various temperature regions, and then the oxygen concentration profile and BMD were evaluated.
- RTA Rapid Thermal Anneal
- the present inventors confirmed that the oxygen concentration profile of as RTA (after RTA treatment) in an oxygen-containing atmosphere has a peak at a depth of about 1 ⁇ m to 3 ⁇ m as a result of the above-described oxygen concentration profile and BMD evaluation. did. However, when heat treatment is subsequently performed at a temperature below a certain temperature, the width becomes narrower than the oxygen concentration profile of as RTA, the oxygen concentration profile becomes steeper, and the peak oxygen concentration becomes high. The present invention was completed by finding a negative diffusion phenomenon in which oxygen diffuses at a high peak position.
- Sample A which was made into a silicon single crystal wafer having a peak oxygen concentration of 1.28 ⁇ 10 18 / cm 3 at a depth of about 2 ⁇ m from the wafer surface by RTA treatment in an oxygen-containing atmosphere, and then heat-treated at 600 ° C. for 4 hours.
- Sample B which was heat treated at 800 ° C. for 4 hours was prepared. Thereafter, both samples were heat-treated at 800 ° C. for 4 hours and then heat-treated at 1000 ° C. for 16 hours, and the BMD in the cross section was etched and observed.
- the profile of the oxygen concentration in the depth direction was measured by SIMS (Secondary Ion Mass Spectrometer).
- the solid solution concentration of oxygen at a temperature of 600 ° C. is 1.5 ⁇ 10 14 / cm 3 .
- the oxygen precipitation reaction is 2Si + 2O + V ⁇ SiO 2 + ISi (1) It is believed that.
- Si silicon
- O oxygen
- V vacancies
- ISi interstitial silicon
- the precipitation reaction rate that is, the precipitation nucleation rate is increased.
- the oxygen concentration in the surrounding area decreases, so locally oxygen diffuses toward the precipitation nuclei and is consumed by the precipitates to grow the precipitation nuclei.
- oxygen diffuses outward from the surface during the heat treatment so that the oxygen concentration on the surface decreases, and oxygen diffuses toward the surface.
- the density of the precipitation nuclei When the density of the precipitation nuclei is small, the amount of oxygen that contributes to the growth of the precipitation nuclei is relatively small, and most of the oxygen is diffused toward the surface having a low concentration and released from the surface.
- the degree of supersaturation exceeds a certain value, it is considered that oxygen undergoes a phase change to a precipitation layer before diffusing.
- a high concentration oxygen precipitation layer hereinafter referred to as HD-BMD layer
- the amount of oxygen consumed by the growth of the precipitate increases, and the concentration difference around the precipitate generated by the growth of the precipitate becomes larger than the concentration difference generated by the outward diffusion between the surface and the bulk. No longer spreads.
- the outward diffusion becomes extremely small, most of the oxygen diffuses toward the precipitate, and oxygen is fixed (consumed) to the oxygen precipitate.
- oxygen in the wafer aggregates (reversely diffuses) in the concentration peak position, that is, the HD-BMD layer.
- This phenomenon is considered to be proportional to the ease of oxygen precipitation. Since the ease of oxygen precipitation is proportional to the degree of oxygen supersaturation or the vacancy concentration at a certain heat treatment temperature, it is considered that the same effect occurs when the vacancy concentration is high even if the degree of supersaturation is small.
- a silicon single crystal wafer is held at a first heat treatment temperature for 1 to 60 seconds in an oxygen-containing atmosphere using a rapid heating / rapid cooling device, and then at a temperature decreasing rate of 1 to 100 ° C./second.
- a first heat treatment that cools to below °C
- oxygen is diffused inward to form an oxygen concentration peak region near the surface of the silicon single crystal wafer, and then a second heat treatment is performed to obtain a silicon single crystal wafer.
- This is a method for producing a silicon single crystal wafer, characterized by aggregating oxygen in the oxygen concentration peak region.
- each step will be described in detail.
- a silicon single crystal wafer to be heat-treated in the present invention a silicon single crystal wafer produced from a silicon single crystal ingot grown by a CZ method or an FZ method, or an epitaxial layer on the silicon single crystal wafer It can be set as the epitaxial wafer which formed.
- a single-side polished wafer hereinafter referred to as an SSP wafer obtained by slicing a silicon single crystal ingot grown by the CZ method into a wafer and then mirror-polishing one surface of the wafer after chamfering, lapping, and etching.
- a double-side polished wafer Double Side Polish wafer, hereinafter referred to as a DSP wafer
- a wafer that has been subjected to the double-side polishing in the manufacturing process and has not been subjected to the final mirror polishing process (hereinafter referred to as a DSP wafer before final polishing) can also be used.
- the oxygen concentration of the silicon single crystal wafer subjected to the first and second heat treatment in the present invention is preferably 4 ⁇ 10 17 atoms / cm 3 (ASTM'79) or more, more preferably 8 ⁇ 10 17 atoms / cm 3 (ASTM'79)) or more, and preferably 16 ⁇ 10 17 atoms / cm 3 (ASTM'79) or less.
- a silicon single crystal wafer as described above is held at a first heat treatment temperature in an oxygen-containing atmosphere for 1 to 60 seconds using a rapid heating / rapid cooling device, and then at a temperature decreasing rate of 1 to 100 ° C./second to 800 ° C.
- oxygen is diffused inward to form an oxygen concentration peak region in the vicinity of the surface of the silicon single crystal wafer.
- oxygen diffuses inward from the wafer surface to the oxygen solid solution concentration at the heat-treatment temperature during the heat treatment, and from the surface to the depth direction.
- An oxygen concentration distribution having a simple decay profile according to the diffusion constant of oxygen is formed.
- oxygen is diffused outward from the surface while the temperature is rapidly lowered to 800 ° C. or lower at a temperature lowering rate of 1 ° C./second or more and 100 ° C./second or less, so that the oxygen concentration on the surface side decreases.
- a profile (oxygen concentration peak region) having an oxygen concentration peak at a certain depth can be formed.
- the peak concentration and peak position can be controlled by the heat treatment holding temperature, time, temperature drop rate, and wafer oxygen concentration.
- the temperature lowering rate is 1 ° C./second or more from the viewpoint of productivity, and if it exceeds 100 ° C./second, there is a possibility that slip occurs.
- Such first heat treatment will be described in more detail below.
- Fig. 1 (a) shows the case where oxygen is diffused inward from the wafer surface by using a high oxygen concentration silicon single crystal wafer and a low oxygen concentration silicon single crystal wafer and heating and holding in a rare gas atmosphere containing oxygen.
- the conceptual diagram of is shown.
- the solid line and the dotted line are the oxygen concentration distributions before the oxygen inward diffusion heat treatment of the low oxygen concentration wafer and the high oxygen concentration wafer, respectively.
- 2 shows an oxygen concentration distribution which diffuses inward during holding at the first heat treatment temperature of the high oxygen concentration wafer.
- the first heat treatment (oxygen inward diffusion heat treatment) is held for 1 to 60 seconds in oxygen gas or a rare gas containing oxygen (eg, Ar, N 2 ). During this holding, oxygen diffuses inward according to the diffusion constant of oxygen at the holding temperature in a state where the oxygen concentration on the surface of the silicon single crystal wafer is maintained at the solid solution concentration C 0 given by the following equation (2) (FIG. 1 (a) one-dot broken line and two-dot broken line).
- C 0 9 ⁇ 10 22 ⁇ Exp ( ⁇ 1.52 / kT) (2)
- k Boltzmann constant
- T absolute temperature (K).
- the obtained oxygen concentration profile is a function of the heat treatment temperature, the oxygen concentration of the wafer, and the heat treatment time.
- the oxygen concentration profile has a shape having a peak at a certain depth from the surface layer (one-dot broken line and two-dot broken line in FIG. 1B). That is, an oxygen concentration peak region is formed.
- the peak concentration and its position can be controlled by the first heat treatment temperature (oxygen inward diffusion heat treatment temperature), the holding time, the oxygen concentration of the wafer, and the temperature lowering rate, and are determined appropriately so as to obtain a desired profile. can do.
- RTA treatment temperature is, for example, 1320 ° C. or higher
- COP can be extinguished and at the same time glow-in oxygen precipitates can be completely extinguished (eg, Patent Document 10). reference). Therefore, even if a wafer having a glow-in defect is used, a DZ layer can be formed on the surface layer by the first heat treatment, and the cost of the crystal can be reduced.
- the first heat treatment can be performed in an atmosphere containing 20% or more of oxygen at a first heat treatment temperature of 1320 ° C. or higher and lower than the melting point of silicon (about 1410 ° C.).
- a first heat treatment temperature 1320 ° C. or higher and lower than the melting point of silicon (about 1410 ° C.).
- the present inventors have found a phenomenon in which subsequent oxygen precipitation is promoted when the treatment temperature is 1320 ° C. or higher even in the RTA treatment in an atmosphere containing 20% or more of oxygen. The reason for this is not clear, but it is considered that vacancies are injected in the RTA treatment at 1320 ° C. or higher.
- the HD-BMD layer is more easily formed, which is advantageous.
- the RTA treatment is performed at a high temperature of 1320 ° C. or higher, an oxygen concentration profile having a peak concentration of 9 ⁇ 10 17 atoms / cm 3 or higher can be obtained. Therefore, in the second heat treatment, for example, by performing the heat treatment at a temperature of 400 ° C. to 700 ° C. at which oxygen precipitation nuclei are most easily formed, a sufficient degree of oxygen supersaturation can be obtained, and an HD-BMD layer can be formed effectively.
- the first heat treatment can also be performed at a first heat treatment temperature of 1290 ° C. or higher and lower than the melting point of silicon in an atmosphere containing oxygen of 0.01% or more and less than 20%.
- a rare gas atmosphere for example, Ar
- oxygen precipitation is promoted thereafter even at a lower temperature of 1290 ° C. than in the case of 100% oxygen. That is, since vacancies are effectively injected at a lower RTA temperature than in the case of 100% oxygen atmosphere, the same oxygen precipitation as in the case of a 100% oxygen and higher RTA temperature can be obtained at a lower RTA temperature. This makes it possible to reduce the process temperature.
- a single wafer type or batch type RTA apparatus can be used, and a commercially available RTA apparatus (for example, Helios manufactured by Matson Corporation) can be used.
- (C) Second heat treatment oxygen fixing heat treatment step
- oxygen in the silicon single crystal wafer is aggregated in the oxygen concentration peak region.
- oxygen is aggregated in the oxygen concentration peak region to form and grow oxygen precipitation nuclei, thereby forming a high concentration oxygen precipitation layer (HD-BMD layer) in the vicinity of the wafer surface.
- HD-BMD layer high concentration oxygen precipitation layer
- this second heat treatment it is preferable to perform a precipitation nucleus formation heat treatment at 400 to 700 ° C. for 2 to 20 hours.
- a precipitation nucleus formation heat treatment it is possible to form precipitation nuclei so that the oxygen concentration peak in the vicinity of the surface does not disappear, and to effectively aggregate oxygen in the oxygen concentration peak region.
- a precipitation nucleation growth heat treatment is preferably performed at 800 to 1200 ° C. for 1 hour or longer. In this way, by performing a higher temperature precipitation nucleus growth heat treatment after the precipitation nucleus formation heat treatment, oxygen can be efficiently aggregated in the oxygen concentration peak region, so the precipitation nuclei formed in the bulk can be grown. Can be stabilized.
- the heat treatment can be performed using a commercially available vertical heat treatment apparatus or horizontal heat treatment apparatus.
- As the atmospheric gas O 2 , N 2 , Ar, a mixed gas thereof, or H 2 gas may be used.
- the oxygen precipitation phenomenon is an extremely complicated phenomenon determined by the degree of supersaturation of oxygen, the concentration of point defects, and the concentration of impurities such as C and N, and the conditions for forming the HD-BMD layer described above are functions of all these factors. It is impossible to uniquely determine the condition.
- vacancies are known to promote the formation of oxygen precipitates, and the vacancy concentration varies greatly depending on the atmosphere and temperature of the RTA treatment.
- vacancies are injected in an RTA process in an NH 3 atmosphere, and the concentration of injected vacancies increases as the maximum temperature of the RTA process increases, and increases as the temperature decrease rate increases (for example, Patent Document 8).
- the present invention it is preferable to investigate in advance preliminary conditions for the formation of the oxygen concentration peak region and the aggregation of oxygen in the region for the first heat treatment and the second heat treatment as follows. For example, by preparing a wafer with varying oxygen concentration and changing the first heat treatment conditions (atmosphere gas, temperature, holding time, temperature drop rate) and performing the heat treatment, and the first heat treatment performed on the sample 1, Sample 2 subjected to heat treatment under different second heat treatment conditions (temperature and time) is prepared.
- the above-described precipitation nucleus formation heat treatment and precipitation nucleus growth heat treatment may be performed in two stages, or another heat treatment may be performed.
- the oxygen diffusion distance is too small and it is difficult to find the difference.
- the oxygen precipitate is made visible by heating the sample 2 under the heat treatment conditions, for example, by holding at 800 ° C. for 4 hours, then raising the temperature to 1000 ° C. and holding at 1000 ° C. for 16 hours. It is desirable to prepare Sample 3 that has been subjected to heat treatment for revealing oxygen precipitates.
- the oxygen concentration profile in the depth direction of each sample is measured, and a first region where the oxygen concentration profile increases from the value on the main surface and a second region where the oxygen concentration profile decreases from the maximum value of the first region are measured.
- the width (half-value width) between the positions where the oxygen concentration in the first region and the second region is 1 ⁇ 2 of the maximum value is obtained.
- a combination of the first heat treatment condition and the second heat treatment condition is obtained such that the half width of the sample 2 or the sample 3 is smaller than the half width of the sample 1, and the first heat treatment and the second heat treatment are performed under the combination condition. Is preferred.
- the sample 2 (which has been subjected to the first heat treatment and the second heat treatment) is selectively etched to obtain a combination of the first heat treatment condition and the second heat treatment condition so that no defects appear on the surface. It is preferable to perform the first heat treatment and the second heat treatment.
- the first heat treatment condition may be determined by performing a preliminary experiment using the second heat treatment condition as the heat treatment condition of the device process.
- the second heat treatment is omitted, and only the first heat treatment is performed before shipment, thereby forming a high-density and uniform HD-BMD layer at a depth of about 1 ⁇ m from the wafer surface layer by the heat treatment in the device process. it can.
- the outward diffusion of oxygen from the wafer can be extremely suppressed on the surface side of the HD-BMD layer, so that the desired quality can be ensured and at the same time the heat treatment cost can be greatly suppressed. is there.
- the present invention can also perform the heat treatment of the present invention on the wafer after epitaxial growth as described above, but as a silicon single crystal wafer to be heat-treated in the present invention in the step (a), other than the epitaxial wafer is prepared, An epitaxial layer can also be formed on the surface of the wafer after the heat treatment of the present invention in which the steps (b) to (d) are performed. Thereby, generation of defects in the epitaxial layer is suppressed, and an epitaxial wafer in which a high-density and uniform HD-BMD layer is formed at a depth of about 1 ⁇ m below the epitaxial layer can be manufactured. If a DSP wafer before final polishing is used as a starting material, a step of final mirror polishing of one main surface may be performed before the epitaxial growth step as necessary.
- an epitaxial layer on the surface of a silicon single crystal wafer having a resistivity of 5 m ⁇ cm or less.
- the dopant concentration of such a resistivity wafer is as extremely high as about 1 ⁇ 10 19 / cm 3 or more.
- a dopant having an ion radius larger than Si, such as P (phosphorus) is contained in a high concentration.
- the lattice constant of the wafer becomes larger than that of the epitaxial layer. For this reason, misfit dislocations easily occur due to lattice mismatch.
- a silicon single crystal wafer in which an HD-BMD layer is formed on the surface layer by heat treatment as in the present invention is generated during epitaxial growth because BMD existing at a high density on the surface layer relieves stress caused by a difference in lattice constant. Generation of misfit dislocations can be suppressed.
- a shallow DZ layer can be formed on the surface layer, and at the same time, a steep and high-density BMD can be formed directly below the DZ layer with a narrow width of about 2 ⁇ m.
- This BMD density is higher than the BMD formed in the bulk by oxygen taken in during the growth of the silicon single crystal, and is formed between the bulk BMD and the device formation region. For this reason, it is possible to shield the influence on the device of the BMD density distribution having a nonuniform in-plane stripe pattern using bulk oxygen striation as a template, and it becomes possible to manufacture a device having in-plane uniform characteristics.
- the BMD when high-density BMD is formed on the entire bulk, precipitates become excessive and cause warping of the wafer.
- the BMD has a high density but a small formation layer width. By forming the layer, the total amount of precipitates in the entire wafer is reduced, and there is an advantage that generation of warp due to excessive precipitation can be suppressed.
- the steep BMD formed immediately below the DZ layer or the epitaxial layer can relieve stress at the bottom of the STI used for device element isolation and suppress the occurrence of slip.
- Example 1 A silicon single crystal ingot having a p-type, oxygen concentration of 6.5 ⁇ 10 17 atoms / cm 3 and a resistivity of 20 ⁇ cm is grown by the CZ method, sliced into a wafer, chamfered, lapped, etched, and then the front and back surfaces of the wafer Both main surfaces were polished, and one main surface was subjected to final mirror polishing. Thereby, a double-sided polished wafer (DSP wafer) having a diameter of 12 inches (300 mm) and a thickness of 775 ⁇ m was prepared.
- DSP wafer double-sided polished wafer having a diameter of 12 inches (300 mm) and a thickness of 775 ⁇ m was prepared.
- the temperature of the DSP wafer is increased from room temperature to 1350 ° C. at a heating rate of 50 ° C./second in a 100% oxygen atmosphere. After holding for 10 seconds, the temperature was lowered to 800 ° C. at a rate of 30 ° C./second and subjected to rapid heating / cooling heat treatment (RTA treatment), that is, oxygen in-diffusion heat treatment. .
- RTA treatment rapid heating / cooling heat treatment
- a commercially available vertical furnace (VERTEX-III manufactured by Kokusai Electric Co., Ltd.) is used to make the inside of the furnace an N 2 gas atmosphere with an oxygen concentration of 5%.
- the heat treatment temperature was varied at 400 ° C., 500 ° C., 600 ° C., 700 ° C., and 800 ° C., and each two sheets were held for 4 hours (oxygen fixing heat treatment) and then taken out.
- Sample 2 was the first of the two. The second piece was put into a furnace maintained at 600 ° C.
- sample 2 was selectively etched to examine the presence or absence of surface defects, but no surface defects were detected in all the samples.
- Sample 1 measures the depth distribution of the oxygen concentration by SIMS
- sample 3 measures the depth distribution of the oxygen concentration by SIMS, and further observes the distribution of the BMD in the depth direction by selective etching of the cross section. went.
- FIG. 2 is a depth profile of the oxygen concentration of Sample 1 (after oxygen inward diffusion heat treatment by rapid heating / cooling heat treatment). A distribution having a peak concentration at a depth of about 1 ⁇ m from the surface is shown, the peak concentration is 1.28 ⁇ 10 18 atoms / cm 3 , and the peak concentration height (A in the figure) is halved. The value width (B in the figure) is 2.90 ⁇ m.
- FIG. 3 is a depth profile of the oxygen concentration of Sample 3 (after performing rapid heating / rapid cooling heat treatment, oxygen fixing heat treatment, and oxygen precipitate clarification heat treatment).
- the oxygen fixing heat treatment temperature is 400 ° C. to 700 ° C.
- a distribution having a clear oxygen concentration peak at a depth of about 2 ⁇ m is obtained.
- the half width at which the height of the peak oxygen concentration is halved is 1.1 ⁇ m, 1.5 ⁇ m, 1.0 ⁇ m and 1.1 ⁇ m at 400 ° C., 500 ° C., 600 ° C. and 700 ° C., respectively.
- the full width at half maximum of sample 1 of as RTA is narrower than 2.90 ⁇ m.
- BMD is proportional to the oxygen concentration distribution, and when oxygen fixing heat treatment is performed at 400 ° C., 500 ° C., 600 ° C., and 700 ° C., the oxygen concentration has a steep peak portion, whereas 800 ° C. It can be seen that when the oxygen fixing heat treatment is performed, the oxygen concentration gradually increases in the depth direction, and the BMD distribution also changes gently and has no peak portion.
- FIG. 4 shows the temperature dependency of the peak height of the oxygen concentration of sample 3 on the oxygen fixing heat treatment temperature.
- the temperature of the precipitation nucleation step in the oxygen fixing heat treatment is a temperature of 300 ° C. or higher and 750 ° C. or lower, an oxygen concentration peak appears, which is the second heat treatment condition of the present invention.
- the temperature of the precipitation nucleus forming step of the oxygen fixing heat treatment is more preferably 400 ° C. or higher and 700 ° C. or lower.
- Example 2 comparative example 2
- a CZ method is used to grow a p-type silicon single crystal ingot having an oxygen concentration of 6.5 ⁇ 10 17 atoms / cm 3 and a resistivity of 20 ⁇ cm, slicing it into a wafer, chamfering, lapping, and etching. Both sides of the back surface were polished, and one main surface was finally mirror-polished. Thereby, a double-sided polished wafer (DSP wafer) having a diameter of 12 inches (300 mm) and a thickness of 775 ⁇ m was prepared.
- DSP wafer double-sided polished wafer
- the plurality of DSP wafers are heated from room temperature to X ° C. at a heating rate of 50 ° C./second in a 100% oxygen atmosphere and held for 10 seconds. Thereafter, the temperature was lowered to 800 ° C. at a rate of 30 ° C./second to perform rapid heating / cooling heat treatment (RTA treatment), that is, oxygen inward diffusion heat treatment.
- RTA treatment rapid heating / cooling heat treatment
- X degreeC they were 1300 degreeC, 1320 degreeC, 1330 degreeC, and 1350 degreeC.
- One of the wafers subjected to oxygen inward diffusion heat treatment at each temperature was extracted and used as sample 1.
- a commercially available vertical furnace (VERTEX-III manufactured by Kokusai Electric Co., Ltd.) was used in the furnace to increase the N concentration of 5%.
- the sample was taken out after being kept in a 2- gas atmosphere at 450 ° C. for 4 hours (oxygen fixing heat treatment). The first one was designated as sample 2.
- the second piece was put into a furnace maintained at 600 ° C. in an N 2 gas atmosphere with an oxygen concentration of 5% using a commercially available vertical furnace (VERTEX-III manufactured by Kokusai Electric Inc.) at 5 ° C./min.
- sample 2 was selectively etched to examine the presence or absence of surface defects, but no surface defects were detected in all the samples.
- Sample 1 measures the depth distribution of the oxygen concentration by SIMS
- sample 3 measures the depth distribution of the oxygen concentration by SIMS, and further observes the distribution of the BMD in the depth direction by selective etching of the cross section. went.
- FIG. 5 is a depth profile of the oxygen concentration of Sample 1 (after rapid heating and rapid cooling heat treatment). Each shows a distribution having a peak concentration at a depth of about 1 ⁇ m from the wafer surface.
- FIG. 6 is a profile in the depth direction of the oxygen concentration of Sample 3 (after performing rapid heating / rapid cooling heat treatment, oxygen fixing heat treatment, and heat treatment for revealing oxygen precipitates). When the oxygen inward diffusion temperature is 1320 ° C. or higher, an oxygen concentration peak appears.
- FIG. 7 shows the result of selective etching of the cross section of Sample 3 when the oxygen indiffusion temperature is 1350 ° C.
- a high-concentration BMD layer is formed in a narrow region having a width of several ⁇ m and a depth of 2 ⁇ m from the surface.
- a similar high density BMD layer was observed when oxygen in-diffusion heat treatment was performed at 1320 ° C. or higher, but not at 1300 ° C.
- FIG. 8 shows the BMD density of sample 3 at a depth of 100 ⁇ m.
- the BMD density at a depth of 100 ⁇ m indicates whether or not oxygen originally present in the bulk formed BMD, not oxygen in the high concentration oxygen layer diffused in the surface layer by RTA treatment (oxygen inward diffusion heat treatment).
- FIG. 8 also shows the BMD density of samples subjected to RTA treatment (oxygen inward diffusion heat treatment) at 1200 ° C., 1250 ° C., and 1280 ° C. for reference.
- the BMD density decreases as the temperature increases up to a treatment temperature of 1300 ° C.
- the first heat treatment is an RTA treatment (oxygen inward diffusion heat treatment) at 1320 ° C. or higher, the oxygen concentration injected by inward diffusion increases, and vacancies are also injected.
- Subsequent oxygen fixing heat treatment brings about a synergistic effect that the degree of oxygen saturation becomes extremely high, and further, precipitation becomes easier due to the influence of vacancies.
- the plurality of DSP wafers were heated from room temperature to X ° C. at a temperature rising rate of 50 ° C./second in an Ar gas atmosphere having an oxygen concentration of 19%. Then, after holding for 10 seconds, the temperature was lowered to 800 ° C. at a rate of 30 ° C./second to perform rapid heating / cooling heat treatment (RTA treatment), that is, oxygen inward diffusion heat treatment.
- RTA treatment rapid heating / cooling heat treatment
- X degreeC they were 1250 degreeC, 1270 degreeC, 1290 degreeC, and 1310 degreeC.
- One of the wafers subjected to oxygen inward diffusion heat treatment was extracted and used as sample 1.
- a commercially available vertical furnace (VERTEX-III manufactured by Kokusai Electric Co., Ltd.) was used in the furnace to increase the N concentration of 5%. It was taken out after being kept in a two- gas atmosphere at 450 ° C. for 4 hours (oxygen fixing heat treatment). The first one was sample 2, and the second one was kept at 600 ° C. in an N 2 gas atmosphere with an oxygen concentration of 5% using a commercially available vertical furnace (VERTEX-III manufactured by Kokusai Electric). Add to the furnace, heat treatment up to 800 ° C. at 5 ° C./min, hold at 800 ° C.
- Sample 2 was selectively etched to examine the presence or absence of surface defects, but no surface defects were detected in all the samples.
- Sample 1 measures the depth distribution of oxygen concentration by SIMS
- Sample 3 measures the depth distribution of oxygen concentration by SIMS, and further observes the distribution of BMD in the depth direction by selective etching of the cross section. It was.
- the RTA temperature (temperature of the oxygen inward diffusion heat treatment) is a high temperature of 1290 ° C. or higher, the oxygen concentration profile has a peak in sample 3, and the half width is smaller than that in sample 1. It turns out that it corresponds to the heat processing conditions of this invention. On the other hand, when the temperature is lower than 1290 ° C., the peak disappears in the oxygen concentration profile in sample 3, and the oxygen concentration distribution follows normal oxygen outward diffusion, and does not correspond to the heat treatment condition of the present invention.
- FIG. 9 shows the BMD density and RTA temperature of the sample 3 at a depth of 100 ⁇ m.
- the BMD density decreases as the temperature increases until the RTA temperature reaches 1270 ° C. It is considered that oxygen precipitation is suppressed by injecting.
- the temperature exceeded 1270 ° C. BMD turned around and showed an increasing tendency.
- Examples 4 and 5 Comparative Example 4-6
- a CZ method is used to grow a p-type silicon single crystal ingot having an oxygen concentration of 6.5 ⁇ 10 17 atoms / cm 3 and a resistivity of 20 ⁇ cm, slicing it into a wafer, chamfering, lapping, and etching.
- the back surface was double-side polished, and one main surface was final mirror-polished. Thereby, a double-sided polished wafer (DSP wafer) having a diameter of 12 inches (300 mm) and a thickness of 775 ⁇ m was prepared.
- DSP wafer double-sided polished wafer having a diameter of 12 inches (300 mm) and a thickness of 775 ⁇ m was prepared.
- the temperature of the plurality of DSP wafers is raised from room temperature to 1350 ° C. at a heating rate of 50 ° C./second in a 100% oxygen atmosphere. After holding for 10 seconds, the temperature was lowered to 800 ° C. at a rate of 30 ° C./second to perform rapid heating / cooling heat treatment (RTA treatment), that is, oxygen inward diffusion heat treatment.
- RTA treatment rapid heating / cooling heat treatment
- One of them was extracted as sample 1, and the oxygen concentration profile was measured by SIMS.
- the measured oxygen concentration had a peak concentration of 1.2 ⁇ 10 18 atoms / cm 3 and a half-value width of the peak concentration of 2.90 ⁇ m.
- FIG. 10 shows SIMS profiles of the oxygen concentrations of Samples 2 of Examples 4 and 5 and Comparative Examples 4 to 6.
- a clear oxygen concentration peak appears in Example 4.
- the half-value width of the peak oxygen concentration is narrower than the half-value width of 2.90 ⁇ m of the sample 1 before the oxygen fixing heat treatment, which indicates that the heat treatment conditions of the present invention are satisfied.
- Example 4 no surface layer defect occurred.
- Example 5 a clear peak of oxygen concentration appears, and the half-value width of the peak oxygen concentration is narrower than the half-value width of sample 1 before the oxygen fixing heat treatment. Applicable.
- the surface layer defect has generate
- Comparative Examples 4 to 6 do not correspond to the heat treatment conditions of the present invention because no peak of oxygen concentration appears.
- Example 4 of the present invention the oxygen concentration in the range from the surface to 8 ⁇ m, that is, the oxygen concentration in the epitaxial layer, is high, as in Comparative Example 4 and Comparative Example 6, before the additional heat treatment.
- the amount of oxygen diffused in the wafer during the RTA process oxygen inward diffusion heat treatment
- the oxygen diffused inward uniformly in the plane by the RTA treatment is diffused in the epitaxial layer
- the distribution of oxygen in the epitaxial layer is uniform in the plane. Furthermore, in the case of Example 4, as clearly shown in FIG.
- FIG. 11 is an oxygen concentration profile after performing heat treatment at 1000 ° C. for 8 hours as an additional heat treatment on Sample 2 (after formation of the epitaxial layer) of Examples 4 and 5 and Comparative Examples 4 to 6.
- the oxygen concentration in the epitaxial layer after the additional heat treatment is lower than that in Comparative Example 6.
- oxygen that originally exists in the bulk forms in-plane striped (concentric pattern) shades called striations, and if diffused into the epitaxial layer as it is, the shades are used as a template for the epitaxial layer.
- Oxygen diffused in it also forms a striped shade.
- oxygen diffused in the epitaxial layer during device heat treatment becomes donors or precipitates are formed, these also have a striped distribution, so that the device characteristics also appear as striped characteristic unevenness.
- the diffusion of oxygen originally present in the bulk into the epitaxial layer can be suppressed as in the present invention, the above-described problems can be prevented.
- the oxygen concentration immediately below the epitaxial layer is remarkably increased by the additional heat treatment, and a steep and high-density BMD layer having the same shape as the oxygen concentration distribution is formed in this region.
- This high-concentration BMD layer is a layer in which in-plane uniform oxygen precipitation nuclei formed from oxygen diffused inward uniformly by RTA treatment are grown, and since BMD is uniformly formed in the plane, Thus, the stripe-like BMD density due to the bulk oxygen striation is not obtained.
- the heat treatment temperature in the precipitation nucleus forming step of the oxygen fixing heat treatment is 800 ° C., and the HD-BMD layer is not formed at this stage.
- Temporal heat treatment is performed (Table 2). For this reason, oxygen diffuses outward in accordance with normal diffusion, and the oxygen concentration on the surface is significantly reduced. As a result, less oxygen diffuses into the epitaxial layer even during the subsequent epitaxial growth and additional heat treatment after the epitaxial growth.
- a high-density BMD cannot be formed directly under the epitaxial layer, and the effect of proximity gettering cannot be expected.
- the BMD formed at a position distant from the epitaxial layer is the one in which oxygen originally present in the wafer is manifested as BMD, and there is a problem that stripe-like BMD shading due to striation is formed. is there. Further, the in-plane distribution of oxygen diffused into the epitaxial layer also has a problem that it becomes a striped distribution due to oxygen striation.
- Comparative Example 5 is a wafer epitaxially grown by performing only the RTA process (oxygen inward diffusion heat treatment) and not performing the oxygen fixing heat treatment (Table 2).
- the oxygen fixing heat treatment since the oxygen fixing heat treatment is not performed, the HD-BMD layer is not formed.
- AsEpi after epitaxial growth
- the sample subjected to additional heat treatment after epitaxial growth have the maximum amount of oxygen diffused in the epitaxial layer (FIGS. 10 and 11). This is a result equivalent to simply increasing the oxygen concentration of the wafer.
- Comparative Example 6 is a normal epitaxial wafer in which neither oxygen inward diffusion heat treatment nor oxygen fixing heat treatment is performed (Table 2).
- the oxygen originally present in the wafer is merely diffused according to normal outward diffusion, and has no effect of suppressing the diffusion of oxygen to the epitaxial layer. Therefore, in the epitaxial layer after the additional heat treatment after the epitaxial growth ( The oxygen concentration at a depth of 0 to about 8 ⁇ m in FIG. 11 is higher than that in Example 4.
- Comparative Examples 4 to 6 since the oxygen concentration profile gradually increases from the surface toward the bulk, and the BMD profile has the same distribution as this, the high density BMD is formed in a steep and narrow region immediately below the epitaxial layer. Can not form. Further, in Comparative Examples 4 to 6, the distribution of oxygen concentration diffused in the formed BMD and the epitaxial layer was a non-uniform distribution using striation as a template.
- the present invention is not limited to the above embodiment.
- the above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.
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Abstract
Description
その他、シリコン単結晶ウェーハ上にエピタキシャル成長を行い、エピタキシャル層をDZ層として用いる方法がある。
ゲッタリングのためには、BMDの総体積(密度×1個当たりのBMDサイズに比例する)が大きいことが望ましく、しかも、デバイス形成領域のなるべく近傍にBMDが形成されている(近接ゲッタリング)ことが望ましい。その理由は、金属等の汚染元素をゲッタリングするためには、熱処理中に汚染元素がゲッターサイトであるBMDの位置まで拡散する必要があるが、近年のデバイス工程の低温化・短時間化に伴い、汚染元素の拡散距離は短くなる傾向にあるためである。
すなわち、ウェーハのバルクからエピタキシャル層やDZ層への酸素の拡散はできる限り小さいことが望ましい。あるいは、ウェーハの酸素ストリーエーションは小さいことが望ましい。
この方法ではCOPは消滅させることができ、かつ表層に酸素を内方拡散させることができるが、RTA処理後の熱処理についての記載がなく、RTA処理で内方拡散した酸素は、その後の熱処理で通常の外方拡散に従い、また、CZ育成段階でシリコン単結晶ウェーハのバルクに取り込まれた酸素も通常どおり表面まで拡散してしまうため、ストリエーションの影響を排除できないばかりでなく、RTA処理で内方拡散した酸素とCZ育成段階でシリコン単結晶ウェーハのバルクに取り込まれた酸素の両者が、デバイス熱処理中にDZ層やエピタキシャル層へ拡散してしまう。これにより、RTA処理していないシリコン単結晶ウェーハよりも多くの酸素がデバイス形成領域に取り込まれてしまい、より多くのドナーや析出物がデバイス形成領域に発生しやすいという問題点がある。
このような酸素濃度のシリコン単結晶ウェーハであれば、第1及び第2熱処理によって十分なピーク濃度の酸素濃度ピーク領域を効率的に形成できる。
このように第1及び第2熱処理の条件を決定して、当該条件で熱処理を行うことで、第1及び第2熱処理によって、ウェーハ表面近傍に面内均一な酸素濃度の酸素濃度ピーク領域を確実に形成することができる。
このように第1及び第2熱処理の条件を決定して、当該条件で熱処理を行うことで、第1及び第2熱処理によって、ウェーハ表面に欠陥が生じていない、より高品質なシリコン単結晶ウェーハを製造できる。
このように第1熱処理を行うことで、ウェーハ表層に酸素を効率的に内方拡散させることができる。
このように第1熱処理を行うことで、比較的低い温度でもウェーハ表層に酸素を効率的に内方拡散させることができる。
このような第2熱処理を行うことで、高密度の析出核の形成が効果的に実施できる。
このような第2熱処理を行うことで、高密度に形成した析出核を成長させて効果的に安定化することができる。
このようにエピタキシャルウェーハを作製することで、エピタキシャル層の直下に高密度の酸素濃度ピーク領域を有し、エピタキシャル層には酸素析出欠陥が形成されないウェーハを製造できる。
このような電子デバイスであれば、デバイス形成領域に欠陥を有さず、その直下に良好なゲッタリング層が形成された高品質の電子デバイスとなる。
まず、酸素含有雰囲気の急速熱処理(RTA:Rapid Thermal Anneal)によりシリコン単結晶ウェーハ内に酸素を導入し、その後様々な温度領域で熱処理を行った後、酸素濃度プロファイルとBMDの評価を実施した。
また、その後の熱処理により酸素は外方拡散して、表層の酸素濃度は再び低下するため、表層20μmまでBMDが存在しないDZ層が形成されると記載されている。この点は特許文献6も同様であり、基本的に酸素は通常の拡散挙動を示している。
これに関して本発明者らは、上記酸素濃度プロファイルとBMDの評価の結果、酸素含有雰囲気下のas RTA(RTA処理後)の酸素濃度プロファイルは深さが1μmから3μm程度にピークを持つことを確認した。しかしながら、その後ある温度以下で熱処理した場合に、as RTAの酸素濃度プロファイルより幅が狭くなって、酸素濃度プロファイルが急峻になり、ピーク酸素濃度が高くなる、すなわち見かけ上、ウェーハ内で、濃度の高いピーク位置に酸素が拡散してくるという負の拡散現象を見出し本発明を完成させた。
酸素含有雰囲気のRTA処理によって、ウェーハ表面から約2μmの深さ位置に1.28×1018/cm3のピーク酸素濃度を有するシリコン単結晶ウェーハにした後、600℃で4時間熱処理したサンプルAと800℃で4時間熱処理したサンプルBを準備した。その後、両サンプルを800℃で4時間熱処理後に1000℃で16時間熱処理を実施し、その断面のBMDをエッチングして観察した。同時に、酸素濃度の深さ方向のプロファイルをSIMS(Secondary Ion Mass Spectrometer)で測定した。
他方サンプルBの場合は、as RTAのウェーハで見られた酸素濃度のピークは消滅しており、一般的な酸素の拡散に従った酸素濃度プロファイルとなっていた。また表面から深さ2μmの位置には、BMDは形成されていなかった。
600℃の温度における酸素の固溶濃度は、1.5×1014/cm3である。他方as RTAのウェーハの酸素ピーク濃度は1.28×1018/cm3であり、過飽和度(=ピーク濃度/固溶濃度)は約8500倍となる条件で析出熱処理が実行されたことになる。
2Si+2O+V→SiO2+ISi・・・(1)
と考えられている。ここでSi:シリコン、O:酸素、V:空孔、ISi:格子間シリコンである。
析出核(あるいは析出物)が形成されると、この周辺の酸素濃度が低下するため、局所的には周辺の酸素は析出核に向かって拡散し、析出物で消費されて析出核を成長させる。同時に、熱処理中に酸素は表面から外方拡散するため表面の酸素濃度が低下し、酸素は表面に向かって拡散する。析出核の密度が小さい場合は、析出核の成長に寄与する酸素量は相対的に小さく、大部分の酸素は消費されずに、濃度の低い表面に向かって拡散し、表面から放出される。しかしながら過飽和度がある値以上になると、酸素は拡散する前に析出層へと相変化すると考えられる。その結果、高濃度酸素析出層(以下HD-BMD層という)が形成される。これにより、析出物の成長によって消費される酸素量が大きくなり、表面とバルクの外方拡散で生じる濃度差よりも、析出物の成長により生じる析出物周辺の濃度差が大きくなり、酸素は外方拡散しなくなる。あるいは外方拡散が極めて小さくなり、大部分の酸素は析出物に向かって拡散するようになって、酸素は酸素析出物に固着(消費)されるようになる。その結果、ウェーハ内の酸素は濃度のピーク位置、すなわちHD-BMD層に凝集(逆拡散)するようになると考えられる。この現象は、酸素析出のし易さに比例すると考えられる。酸素析出のし易さは、ある熱処理温度における酸素の過飽和度あるいは空孔濃度に比例するため、過飽和度が小さくても空孔濃度が高い場合は同様な効果が生じると考えられる。
本発明は、シリコン単結晶ウェーハに対して、急速加熱・急速冷却装置を用いて、酸素含有雰囲気下、第1熱処理温度で1~60秒保持した後1~100℃/秒の降温速度で800℃以下まで冷却する第1熱処理を行うことによって、酸素を内方拡散させてシリコン単結晶ウェーハの表面近傍に酸素濃度ピーク領域を形成し、その後、第2熱処理を行うことによって、シリコン単結晶ウェーハ内の酸素を前記酸素濃度ピーク領域に凝集させることを特徴とするシリコン単結晶ウェーハの製造方法である。以下、各工程について詳細に説明する。
本発明で熱処理を行うシリコン単結晶ウェーハとしては、CZ法又はFZ法で育成されたシリコン単結晶インゴットから作製されたシリコン単結晶ウェーハ又は、該シリコン単結晶ウェーハ上にエピタキシャル層を形成したエピタキシャルウェーハとすることができる。
例えば、CZ法で育成したシリコン単結晶インゴットをスライスしてウェーハとした後に、面取り、ラッピング、エッチング後にウェーハの一方の表面を鏡面研磨した片面ポリッシュドウェーハ(Single Side Polishウェーハ、以下SSPウェーハという)又は、ウェーハの表裏面に対して両面研磨を行った後に一主表面を最終の鏡面研磨した両面研磨ウェーハ(Double Side Polishウェーハ、以下DSPウェーハという)を用いることができる。または、上記製作工程の両面研磨までを行って、最終の鏡面研磨工程を行っていないウェーハ(以下、最終研磨前DSPウェーハという)を用いることもできる。
このような酸素濃度のシリコン単結晶ウェーハであれば、熱処理によってより高濃度の酸素濃度ピーク領域を形成でき、また、表面への欠陥発生も効果的に防止できる。
上記のようなシリコン単結晶ウェーハに対して、急速加熱・急速冷却装置を用いて、酸素含有雰囲気下、第1熱処理温度で1~60秒保持した後1~100℃/秒の降温速度で800℃以下まで冷却する第1熱処理を行うことによって、酸素を内方拡散させてシリコン単結晶ウェーハの表面近傍に酸素濃度ピーク領域を形成する。
このような第1熱処理について、以下より詳細に説明する。
C0=9×1022×Exp(-1.52/kT)・・・(2)
ここで、k:ボルツマン定数、T:絶対温度(K)である。
1~100℃/秒と速い降温速度であれば、ウェーハ表面からの酸素の外方拡散による酸素量の低下を小さくできるとともに、より多くの空孔(高濃度)をバルク中に凍結(=注入)させることができるので、酸素析出を促進できるという利点が生じる。
従来、酸素を20%以上含有する雰囲気下のRTA処理では、ウェーハに格子間シリコンが注入されるため、酸素析出は抑制され、HD-BMD層は形成されにくくなると考えられていた。しかしながら、本発明者らは、酸素を20%以上含有する雰囲気のRTA処理においても処理温度が1320℃以上になると、その後の酸素析出が促進されるという現象を見出した。この理由は明確ではないが、1320℃以上のRTA処理では空孔が注入されるようになるためと考えられる。このように空孔注入により、その後の析出が促進されると、HD-BMD層がより形成しやすくなり有利である。また、1320℃以上の高温でRTA処理した場合は、9×1017atoms/cm3以上のピーク濃度を有する酸素濃度プロファイルを得ることができる。このため、第2熱処理において、例えば最も酸素析出核を形成しやすい400℃~700℃の温度で熱処理を行うことで、十分な酸素の過飽和度となり、効果的にHD-BMD層を形成できる。
酸素濃度が0.01%以上20%未満の希ガス雰囲気(例えばAr)を用いると、酸素100%の場合に比べてより低温である1290℃でも、その後酸素析出が促進されるようになる。すなわち、酸素100%の雰囲気の場合よりも低温のRTA温度で効果的に空孔注入されるため、より低温のRTA温度で100%酸素で高温のRTA温度の場合と同様な酸素析出を得ることができるようになり、プロセスの低温化が実現できる。
第1熱処理の後、第2熱処理を行うことによって、シリコン単結晶ウェーハ内の酸素を酸素濃度ピーク領域に凝集させる。
このように酸素を酸素濃度ピーク領域に凝集させて酸素析出核を形成、成長させることで、ウェーハ表面近傍に高濃度酸素析出層(HD-BMD層)が形成される。
このような温度、時間で析出核形成熱処理を行うことで、表面近傍の酸素濃度ピークを消滅しないように析出核を形成して、酸素濃度ピーク領域に酸素を効果的に凝集させることができる。
このように、析出核形成熱処理後に、より高温の析出核成長熱処理を行うことで、酸素濃度ピーク領域により効率的に酸素を凝集させることができるため、バルク内に形成した析出核を成長させて安定化させることができる。
例えばNH3雰囲気のRTA処理では空孔が注入され、しかも注入される空孔濃度は、RTA処理の最高温度が高いほど高くなり、また降温速度が大きいほど高くなる(例えば特許文献8)。逆にO2雰囲気のRTA処理では酸素析出を抑制する格子間シリコンが注入されることが報告されている(例えば特許文献9)。
例えば、酸素濃度を振ったウェーハを準備し、第1熱処理条件(雰囲気ガス、温度、保持時間、降温速度)を変えて熱処理を行ったサンプル1と、サンプル1に行った第1熱処理にさらに、第2熱処理条件(温度と時間)を変えて熱処理を行ったサンプル2を準備する。この場合、第2熱処理は上記した析出核形成熱処理と析出核成長熱処理を2段階で行ってもよいし、さらに別の熱処理を行ってもよい。
このようにして決定した条件で第1熱処理と第2熱処理を実施すれば、表面は欠陥がなく、しかも表層から1μm程度の深さに高密度で均一なHD-BMD層が形成でき、しかもHD-BMD層より表面側にはウェーハからの酸素の外方拡散が極めて抑制されたシリコン単結晶ウェーハを製作することが可能となる。
第2熱処理(第2熱処理を割愛する場合は第1熱処理)後、ウェーハ表面と裏面に形成された酸化膜を除去するため、例えば、市販されているウエット洗浄装置を用いて、5%の濃度のHF水溶液を満たした洗浄槽にウェーハを浸漬させ、酸化膜を除去する。その後、連続して所謂RCA洗浄(SC1洗浄槽、SC2洗浄槽の順にウェーハを浸漬させる)を行えばよい。
なお、出発材料として、最終研磨前DSPウェーハを用いた場合は、必要に応じてエピタキシャル成長工程前に、一主表面を最終の鏡面研磨する工程を実施しても良い。
このような抵抗率のウェーハのドーパント濃度はおよそ1×1019/cm3以上と極めて高い。その上に通常抵抗率5Ωcm程度(ドーパント濃度がおよそ1×1016/cm3)のエピタキシャル層を成長させる場合、例えばP(リン)のようなイオン半径がSiより大きなドーパントが高濃度に含有されたウェーハの格子定数は、エピタキシャル層の格子定数より大きくなる。このため、格子不整合によりミスフィット転位が発生しやすくなる。しかしながら、本発明のように熱処理によりHD-BMD層を表層に形成したシリコン単結晶ウェーハは、表層に高密度に存在するBMDが格子定数の差により生じる応力を緩和するため、エピタキシャル成長中に発生するミスフィット転位の発生を抑制することができる。
しかも、バルク全体に高密度のBMDを形成させた場合は、析出物が過剰となりウェーハのソリを誘発する原因になるが、本発明のように、高密度であるが形成層の幅が小さいBMD層を形成することで、ウェーハ全体に占める析出物の総量が小さくなり、析出過多によるソリの発生を抑制できるという利点もある。
(実施例1,比較例1)
CZ法でp型、酸素濃度6.5×1017atoms/cm3、抵抗率20Ωcmのシリコン単結晶インゴットを育成し、スライスしてウェーハ状に切り出し、面取り、ラッピング、エッチング後に、ウェーハの表裏面に対して両面研磨し、一主表面を最終の鏡面研磨した。これにより、直径が12インチ(300mm)で厚さが775μmの両面研磨ウェーハ(DSPウェーハ)を準備した。
また、サンプル1はSIMSで酸素濃度の深さ方向分布を測定し、サンプル3はSIMSで酸素濃度の深さ方向分布を測定し、さらに断面の選択エッチングによりBMDの深さ方向の分布の観察を行った。
一般的にBMDは酸素濃度分布に比例し、400℃、500℃、600℃、700℃で酸素固着熱処理した場合は、酸素濃度が急峻なピーク部分を有しているのに対して、800℃で酸素固着熱処理をした場合には、深さ方向になだらかに酸素濃度は増加しており、BMD分布もなだらかな変化をしてピーク部分を有さないことが分かる。
CZ法で、p型、酸素濃度6.5×1017atoms/cm3、抵抗率20Ωcmのシリコン単結晶インゴットを育成し、スライスしてウェーハ状に切り出し、面取り、ラッピング、エッチング後に、ウェーハの表裏面に対して両面研磨し、一主表面を最終の鏡面研磨した。これにより、直径が12インチ(300mm)で厚さが775μmの両面研磨ウェーハ(DSPウェーハ)を準備した。
また、サンプル1はSIMSで酸素濃度の深さ方向分布を測定し、サンプル3はSIMSで酸素濃度の深さ方向分布を測定し、さらに断面の選択エッチングによりBMDの深さ方向の分布の観察を行った。
図6は、サンプル3(急速加熱・急速冷却熱処理、酸素固着熱処理、酸素析出物の顕在化熱処理を実施後)の酸素濃度の深さ方向プロファイルである。酸素内方拡散温度が1320℃以上の場合は、酸素濃度のピークが出現している。ピーク濃度の半値幅をサンプル1と比較すると、酸素内方拡散熱処理温度が1320℃の場合は2.2μmから0.27μm、1330℃の場合は2.4μmから0.86μm、1350℃の場合は2.9μmから1.6μmと減少していた。他方、酸素内方拡散温度が1300℃の場合はピーク濃度は消滅しており、所謂外方拡散に従ったプロファイルとなっている。
図8から明確なように、100%酸素雰囲気でRTA処理(酸素内方拡散熱処理)したサンプルの場合は、処理温度が1300℃までは温度が高くなるほどBMD密度は減少しており、従来の知見が再現されている。すなわち、酸素雰囲気のRTA処理では表面から格子間シリコンが注入されることにより、酸素析出が抑制されたと考えられる。他方、1300℃を超えるとこれまでの知見とは異なり、BMDは一転して増加傾向を示した。この理由は明確ではないが、1300℃より高温では空孔注入が発生したため酸素析出がエンハンスされたと考えられる。
CZ法で、p型、酸素濃度6.5×1017atoms/cm3、抵抗率20Ωcmのシリコン単結晶インゴットを育成し、スライスしてウェーハ状に切り出し、面取り、ラッピング、エッチング後に、ウェーハの表裏面に対して両面研磨し、一主表面を最終の鏡面研磨した。これにより、直径が12インチ(300mm)で厚さが775μmの両面研磨ウェーハ(DSPウェーハ)を準備した。
サンプル1は、SIMSで酸素濃度の深さ方向分布を測定し、サンプル3はSIMSで酸素濃度の深さ方向分布を測定し、さらに断面の選択エッチングによりBMDの深さ方向の分布の観察を行った。
図9から明確なように、酸素濃度19%のArガス雰囲気でRTA処理したサンプルの場合は、RTA温度が1270℃までは温度が高くなるほどBMD密度は減少しているため、表面から格子間シリコンが注入されることにより、酸素析出が抑制されると考えられる。他方1270℃を超えると、BMDは一転して増加傾向を示した。
CZ法で、p型、酸素濃度6.5×1017atoms/cm3、抵抗率20Ωcmのシリコン単結晶インゴットを育成し、スライスしてウェーハ状に切り出し、面取り、ラッピング、エッチング後に、ウェーハの表裏面を両面研磨し、一主表面を最終の鏡面研磨した。これにより、直径が12インチ(300mm)で厚さが775μmの両面研磨ウェーハ(DSPウェーハ)を準備した。
これらのウェーハに対して、市販の縦型炉(国際電気社製 VERTEX-III)を用いて、炉内を酸素濃度5%のN2ガス雰囲気で酸素固着熱処理(析出核形成ステップ後に連続して析出核成長ステップを実施)を実施した。表2に、実施例4、5と比較例4、5の酸素固着熱処理条件を示す。
サンプル2の酸素濃度プロファイルをSIMSを用いて測定し、選択エッチングで表面の欠陥の有無を評価した。サンプル2の酸素濃度プロファイルにおける酸素濃度ピークの有無、および、酸素濃度ピークが出現した場合は、酸素濃度プロファイルから求めた半値幅を調べた。これらの結果を表2に示す。
一方、比較例4~6は酸素濃度のピークが出現していないことから本発明の熱処理条件には該当しない。
しかしながら、RTA処理で面内均一に内方拡散した酸素が、エピタキシャル層中に拡散したものであるため、エピタキシャル層中の酸素の分布は面内均一である。さらに、実施例4の場合は、図10から明確なように、酸素固着熱処理により、エピタキシャル層直下に高密度のHD-BMD層が形成されているため、その後、追加熱処理を行った場合でも、バルクから拡散してきた酸素は、このHD-BMD層で酸素析出物を成長させるために消費されてしまい、エピタキシャル層中への拡散が抑制されることになる。
このため、酸素は通常の拡散に従って外方拡散して、表面の酸素濃度が著しく低下している。これにより、その後のエピタキシャル成長中およびエピタキシャル成長後の追加熱処理でも、エピタキシャル層中に拡散する酸素が少ない。しかし、エピタキシャル層直下に高密度のBMDを形成することはできず、近接ゲッタリングの効果を期待できない。さらには、エピタキシャル層から離れた位置に形成されるBMDは、もともとウェーハ中に存在した酸素がBMDとして顕在化したものであり、ストリエーションによる縞状のBMD濃淡を形成してしまうという問題点がある。さらに、エピタキシャル層中に拡散した酸素の面内分布は、やはり酸素ストリエーションによる縞状の分布になってしまうという問題点がある。
この場合、酸素固着熱処理を実施していないため、HD-BMD層が形成されていない。このため、エピタキシャル成長や追加熱処理の際に、酸素は通常の外方拡散で表面に向かって拡散するが、もともとウェーハに存在していた酸素とRTA処理で内方拡散した酸素の両者が外方拡散するため、AsEpi(エピタキシャル成長後)およびエピタキシャル成長後に追加熱処理したサンプルのいずれも、エピタキシャル層中に拡散した酸素量は最大になっている(図10,11)。これは、単純にウェーハの酸素濃度を高くした場合と等価な結果である。
この場合、もともとウェーハ内に存在した酸素が通常の外方拡散に従って拡散しただけであり、エピタキシャル層への酸素の拡散を抑制する効果がないため、エピタキシャル成長後に追加熱処理をした後のエピタキシャル層中(図11の深さ0~約8μm)の酸素濃度は、実施例4よりも多くなっている。
Claims (10)
- シリコン単結晶ウェーハの製造方法であって、
シリコン単結晶ウェーハに対して、急速加熱・急速冷却装置を用いて、酸素含有雰囲気下、第1熱処理温度で1~60秒保持した後1~100℃/秒の降温速度で800℃以下まで冷却する第1熱処理を行うことによって、酸素を内方拡散させて前記シリコン単結晶ウェーハの表面近傍に酸素濃度ピーク領域を形成し、その後、第2熱処理を行うことによって、前記シリコン単結晶ウェーハ内の酸素を前記酸素濃度ピーク領域に凝集させることを特徴とするシリコン単結晶ウェーハの製造方法。 - 前記第1及び第2熱処理を行うシリコン単結晶ウェーハの酸素濃度を、4×1017atoms/cm3(ASTM‘79)以上、16×1017atoms/cm3(ASTM‘79)以下とすることを特徴とする請求項1に記載のシリコン単結晶ウェーハの製造方法。
- 前記第1及び第2熱処理の条件を、予め、前記第1熱処理後のシリコン単結晶ウェーハと、前記第1及び第2熱処理後のシリコン単結晶ウェーハあるいは前記第1及び第2熱処理後に酸素析出物顕在化熱処理を行ったシリコン単結晶ウェーハの酸素濃度プロファイルを測定し、前記第1及び第2熱処理後のシリコン単結晶ウェーハあるいは第1及び第2熱処理後に酸素析出物顕在化熱処理を行ったシリコン単結晶ウェーハの酸素濃度プロファイルの半値幅が、前記第1熱処理後のシリコン単結晶ウェーハの酸素濃度プロファイルの半値幅より小さくなる条件に決定して、該決定した条件で前記第1及び第2熱処理を行うことを特徴とする請求項1又は請求項2に記載のシリコン単結晶ウェーハの製造方法。
- 前記第1及び第2熱処理の条件を、前記第1及び第2熱処理後のシリコン単結晶ウェーハの表面に酸素析出欠陥が形成されない条件に決定して、該決定した条件で前記第1及び第2熱処理を行うことを特徴とする請求項1乃至請求項3のいずれか一項に記載のシリコン単結晶ウェーハの製造方法。
- 前記第1熱処理を、酸素を20%以上含有する雰囲気下、1320℃以上でシリコンの融点以下の第1熱処理温度で行うことを特徴とする請求項1乃至請求項4のいずれか一項に記載のシリコン単結晶ウェーハの製造方法。
- 前記第1熱処理を、酸素を0.01%以上20%未満含有する雰囲気下、1290℃以上でシリコンの融点以下の第1熱処理温度で行うことを特徴とする請求項1乃至請求項4のいずれか一項に記載のシリコン単結晶ウェーハの製造方法。
- 前記第2熱処理において、400~700℃で2~20時間の析出核形成熱処理を行うことを特徴とする請求項1乃至請求項6のいずれか一項に記載のシリコン単結晶ウェーハの製造方法。
- 前記第2熱処理において、前記析出核形成熱処理後、800~1200℃で1時間以上の析出核成長熱処理を行うことを特徴とする請求項7に記載のシリコン単結晶ウェーハの製造方法。
- 前記第1及び第2熱処理後に、前記シリコン単結晶ウェーハの表面にエピタキシャル層を形成することを特徴とする請求項1乃至請求項8のいずれか一項に記載のシリコン単結晶ウェーハの製造方法。
- 請求項9に記載のシリコン単結晶ウェーハの製造方法で製造したシリコン単結晶ウェーハの前記エピタキシャル層表面に形成されたものであることを特徴とする電子デバイス。
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