CN110942986A - Method for removing oxide film formed on surface of silicon wafer - Google Patents
Method for removing oxide film formed on surface of silicon wafer Download PDFInfo
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- CN110942986A CN110942986A CN201811106595.3A CN201811106595A CN110942986A CN 110942986 A CN110942986 A CN 110942986A CN 201811106595 A CN201811106595 A CN 201811106595A CN 110942986 A CN110942986 A CN 110942986A
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
- H01L21/3105—After-treatment
- H01L21/311—Etching the insulating layers by chemical or physical means
- H01L21/31105—Etching inorganic layers
- H01L21/31111—Etching inorganic layers by chemical means
- H01L21/31116—Etching inorganic layers by chemical means by dry-etching
Abstract
The method comprises the following steps: preparing a silicon wafer on which an oxide film is formed; disposing a disk-shaped wafer mounting table, which is formed of an acid-resistant resin layer in a portion in contact with the oxide film, in a reaction vessel of a vapor phase etching apparatus; placing the silicon wafer on a placing table such that the center of the wafer coincides with the central axis of the placing table; and a step of removing an oxide film to a desired interval a from an interface between the chamfered surface and the lower surface of the wafer toward the inner side of the wafer by flowing a gas containing hydrogen fluoride into the reaction container; the desired distance a is adjusted by changing the table diameter of the mounting table.
Description
Technical Field
The present invention relates to an oxide film removal method for removing an excess oxide film formed on the outer peripheral portion of a wafer by a vapor phase etching method when forming an oxide film on the surface of a silicon wafer as a protective film for preventing autodoping during epitaxial layer growth, for example. More specifically, the present invention relates to an oxide film removing method capable of removing an excess oxide film formed on a chamfered surface and an end surface of a wafer, accurately removing the oxide film formed on a lower surface of the wafer with a desired edge relief width, and greatly reducing a spot area generated in the vicinity of an outer edge of the oxide film on the lower surface of the wafer.
Background
Leading edgeIn LSI (Large Scale Integration), p and p are used, which are adjusted to a predetermined resistivity by adding a dopant such as boron+、p++Epitaxial wafer, for example, p/p epitaxial wafer, in which low-resistance semiconductor wafer such as a silicon wafer is used as a substrate and an epitaxial layer having higher resistance than the resistivity of the wafer substrate is formed on the surface of the wafer substrate+Epitaxial wafers, and the like.
However, one of the problems in the production of an epitaxial wafer is a so-called self-doping phenomenon in which a dopant such as boron added to a wafer substrate diffuses from the wafer substrate to the outside during a high-temperature process for forming an epitaxial layer on the wafer substrate and contaminates the epitaxial layer as a device formation region.
In order to solve such a problem of self-doping, it has been conventionally common to form an oxide film in advance as a protective film for preventing external diffusion of a dopant on the back surface of a silicon wafer before formation of an epitaxial layer. The oxide film is usually formed by a CVD (Chemical Vapor Deposition) method or the like, but in this case, the oxide film is formed not only on the lower surface of the silicon wafer but also partially on the end surface and chamfered surface of the wafer and the edge of the upper surface of the wafer which is a formation region of the epitaxial layer. When the epitaxial layer is formed in a state where an excess oxide film is formed on the edge of the upper surface of the wafer, the epitaxial layer comes into contact with the oxide film at that position, and there arises a problem that granular Si particles called nodules are generated at that position.
The nodules cause particle generation in the device process, and therefore, it is necessary to avoid contact between the epitaxial layer and the oxide film at the edge of the upper surface of the wafer as described above. Therefore, after the process of forming the oxide film on the lower surface of the wafer, a process of removing an excess oxide film formed on the outer peripheral portion of the wafer is performed before the epitaxial layer is formed. In general, as shown in fig. 9, while removing an excess oxide film formed on the chamfer surface and the end surface of the wafer, the oxide film is removed to form a region (edge relief width) where the oxide film 32 is removed from the interface between the chamfer surface and the lower surface of the wafer toward the inner side of the wafer up to a desired interval a. In the present specification, the wafer outer peripheral portion refers to a portion of the edge of the wafer upper surface, the chamfered surface, the edge of the end surface, and the edge of the lower surface, on which an excess oxide film is formed on the surface of the silicon wafer.
Conventionally, as a method for removing an excess oxide film on the outer peripheral portion of a wafer, a chemical method, a mechanical method such as a polishing process, in which the outer peripheral portion of the wafer is brought into contact with an etching solution having a dissolving action on the oxide film to remove the excess oxide film, has been generally used. As a method for removing an oxide film by a mechanical method, there is disclosed a method for removing an oxide film on the outer periphery of a wafer by pressing a nonwoven fabric impregnated with an etching solution to the outer periphery of the wafer and rotating the wafer (see, for example, patent document 1). However, in this method, the etching liquid is dropped on the lower surface side of the wafer, and uniform etching along the outer peripheral direction of the wafer is difficult, and there is a problem that the interface between the region where the oxide film (protective film) is formed on the lower surface of the wafer and the region where the oxide film on the lower surface of the wafer is removed is likely to become uneven.
Further, a method of polishing a silicon wafer is disclosed, which is characterized in that an oxide film on the outer peripheral portion of the back surface of the wafer is polished so that the thickness of the oxide film becomes thinner from the inner side to the outer side of at least 2mm from the outermost peripheral portion of the back surface of the wafer while removing the oxide film on the chamfered portion of the wafer (for example, refer to patent document 2). In this method, particles can be prevented from adhering to the surface after the operation, and a silicon wafer whose resistivity is not lowered by the self-doping can be provided. However, in the oxide film removal method using the mechanical method, although the oxide film removal accuracy is excellent, only the single wafer processing is performed to polish the outer peripheral portion of the wafer, and there are problems that the productivity is poor, the apparatus configuration is large, and the cost is high.
On the other hand, as a method for analyzing metal impurities present on a silicon surface, an impurity analysis method using a method for removing an oxide film by a vapor phase etching method is disclosed (for example, see patent document 3). In this method, after an oxide film is formed on the surface of the upper surface of a silicon wafer to be analyzed, the wafer on which the oxide film is formed is placed on a stage provided in a chamber of a vapor phase etching apparatus so as to face upward. Next, vapor or the like containing hydrofluoric acid and hydrogen peroxide water is supplied into the chamber, and the oxide film on the wafer surface is dissolved and removed. Then, the droplets are supplied to the surface of the wafer from which the oxide film has been removed, and the impurities in the collected droplets are analyzed.
Documents of the prior art
Patent document
Patent document 1: japanese laid-open patent publication No. S62-128520 (page 3, line 3 from the bottom left to the bottom right, line 6, FIG. 3)
Patent document 2: japanese patent laid-open No. 2006-186174 (claim 1, paragraph [0010 ])
Patent document 3: japanese patent laid-open No. 2005-265718 (claim 1).
Disclosure of Invention
Problems to be solved by the invention
The present inventors have paid attention to the application of the vapor phase etching technique employed in the analysis method disclosed in patent document 3 to the removal of the excess oxide film formed on the outer peripheral portion of the wafer. However, the present inventors have conducted various experiments and obtained the following findings.
It is known that although the excess oxide film formed on the upper surface, chamfer surface, end surface, and the like of the wafer can be removed by using the vapor phase etching method, it is difficult to control the oxide film formed on the lower surface of the wafer to a desired edge relief width (interval a). In particular, in the case of manufacturing a silicon wafer having a wide edge relief width by increasing the removal width of the peripheral edge of the oxide film on the lower surface of the wafer, it was confirmed that there is a limit in widening the removal width of the peripheral edge of the oxide film even if the processing time in the vapor phase etching is extended.
Further, it was confirmed that, in the case of performing epitaxial growth on a silicon wafer from which an oxide film on the outer peripheral portion of the wafer was removed by the vapor phase etching method, a defect was generated in which an oxide film removal unevenness region (hereinafter referred to as a "scar region 33") having different oxide film thicknesses as shown in fig. 10 was formed in a wide range in the vicinity of the outer peripheral edge of the oxide film formed on the lower surface of the wafer.
Although the occurrence of the scar region has little direct influence on the quality of the wafer, if the width of the scar region is increased to a certain extent, the product is difficult to be shipped as an appearance defective product. In this case, it is necessary to remove all the oxide film once, regenerate the oxide film, and then perform vapor phase etching, which causes a problem of an increase in manufacturing cost. In addition, since the oxide film is formed to be very thin in the scar region, nodules may occur in the scar region during the epitaxial growth. Further, when the width of the scar region is large, the dopant in the silicon wafer may diffuse to the outside through the site where the scar region is generated with a small thickness of the oxide film. Therefore, when removing the excess oxide film formed on the outer peripheral portion of the wafer by the vapor etching method, it is effective to reduce the generation of the scar region.
An object of the present invention is to provide an oxide film removing method capable of removing an excess oxide film formed on a chamfered surface and an end surface of a wafer, accurately removing the oxide film formed on a lower surface of the wafer with a desired edge relief width, and greatly reducing an oxide film removal unevenness region (a scar region) in which oxide films having different thicknesses are generated in the vicinity of an outer edge of the oxide film on the lower surface of the wafer.
Means for solving the problems
The invention of claim 1 is a method for removing an oxide film formed on a surface of a silicon wafer, comprising: preparing a silicon wafer having an upper surface, a lower surface, a chamfered surface, and an end surface, and having an oxide film formed on at least the entire lower surface of the silicon wafer; disposing 1 or 2 or more disk-shaped wafer-mounting tables each having an acid-resistant resin layer at least in a portion thereof in contact with the oxide film in a reaction vessel of a vapor phase etching apparatus; placing the silicon wafer on the placing table such that a center of the wafer coincides with a central axis of the placing table with a lower surface of the silicon wafer facing an upper surface of the placing table; and a step of removing an oxide film to a desired distance a from an interface between the chamfered surface and the lower surface of the wafer toward the inner side of the wafer by flowing a gas containing hydrogen fluoride into the reaction container; the desired distance a is adjusted by changing the table diameter of the mounting table.
An aspect 2 of the present invention is the invention according to the aspect 1, further characterized in that a surface roughness Ra of a portion of the mounting stage, which is in contact with the oxide film, is 0.5 μm or less.
In accordance with a 3 rd aspect of the present invention, which is the invention according to the 2 nd aspect, further, a surface roughness Ra of a portion of the mounting stage which is in contact with the oxide film is 0.4 μm or less.
An aspect 4 of the present invention is the invention according to the aspect 1, wherein the mounting base is made of any one of polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, and polytetrafluoroethylene.
In accordance with a 5 th aspect of the present invention, which is the invention according to the 1 st aspect, the mounting table is further characterized in that a surface of the mounting table is covered with a resin film having a surface roughness Ra of 0.5 μm or less.
The invention according to claim 6 is the invention according to claim 5, further characterized in that the resin film has a surface roughness Ra of 0.4 or less.
The invention according to claim 7 is the invention according to claim 5, further characterized in that the resin film is formed of any one of polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, and polytetrafluoroethylene.
An aspect 8 of the present invention is the invention according to the aspect 1, and further characterized in that a table having a concave portion formed in a central portion of a mounting surface is used as the mounting table.
An aspect 9 of the present invention is an epitaxial wafer obtained by performing an epitaxial growth process on an upper surface of a silicon wafer from which an oxide film has been removed by the method of aspect 1.
Effects of the invention
In the oxide film removing method according to claim 1 of the present invention, the removal width of the outer peripheral edge of the oxide film on the lower surface of the wafer, that is, the edge relief width (interval a) can be arbitrarily adjusted by changing the stage diameter of the mounting stage.
In the oxide film removing method according to claim 2 or 3 of the present invention, a surface roughness Ra of a portion of the mounting stage in contact with the oxide film is set to be lower than a predetermined value. This improves the adhesion force between the surface of the mounting stage and the oxide film formed on the lower surface of the silicon wafer, and can significantly reduce the number of the mura areas.
In the method for removing an oxide film according to claim 4 of the present invention, the mounting base is made of any one of polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, and polytetrafluoroethylene. These materials have excellent acid resistance, and can provide an effect of preventing the occurrence of damage when the wafer is mounted.
In the method for removing an oxide film according to claim 5 or 6 of the present invention, the surface of the mounting stage is covered with a resin film having a desired surface roughness. In this manner, if a resin film having a desired surface roughness is used, the surface of the stage can be easily made to have a desired surface roughness without significantly modifying the conventional apparatus.
In the method according to claim 7 of the present invention, the resin film is formed of any one of polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, and polytetrafluoroethylene. These materials have excellent acid resistance, and can provide an effect of preventing the occurrence of damage when the wafer is mounted.
In the method according to claim 8 of the present invention, since the stage having the recessed portion formed in the central portion of the mounting surface is used as the mounting stage, the adhesion force between the mounting stage surface and the oxide film formed on the lower surface of the wafer is improved in the vapor phase etching, and the number of the spot areas can be further reduced.
The epitaxial wafer according to claim 9 of the present invention is obtained by removing an excess oxide film by the method of the present invention and performing an epitaxial growth process on the upper surface of the wafer. The epitaxial wafer is obtained by performing an epitaxial process on a silicon wafer having a small number of spot areas from which an excess oxide film is removed by the method of the present invention. Therefore, the generation of nodules due to the scar region does not occur during the epitaxial process, and the generation of self-doping can be reliably prevented.
Drawings
Fig. 1 is a schematic cross-sectional view showing an example of a vapor phase etching apparatus used in the method according to the embodiment of the present invention.
Fig. 2 is an enlarged cross-sectional view of a key part showing a state in which a silicon wafer before and after a vapor phase etching process is placed on a placing stage according to an embodiment of the present invention.
Fig. 3 is an enlarged cross-sectional view of a key part showing a state where a silicon wafer before a vapor etching process is placed on a placing stage having a surface covered with a resin film according to the embodiment of the present invention.
Fig. 4 is a key part enlarged cross-sectional view showing an example of a mounting stage having a surface covered with a resin film, which is different from the example shown in fig. 3.
FIG. 5 is a graph showing the relationship between the treatment time and the interval a when the vapor phase etching treatment was performed using the mounting stage having a stage diameter of 210mm in example 1.
FIG. 6 is a graph showing the relationship between the treatment time and the interval a when the vapor phase etching treatment was performed using the mounting stage having a stage diameter of 198mm in example 1.
FIG. 7 is a graph showing the relationship between the treatment time and the interval a when the vapor phase etching treatment was performed using the mounting stage having a stage diameter of 195mm in example 1.
Fig. 8 is a graph showing the measurement result of the width of the scar region in example 2.
Fig. 9 is a cross-sectional view of a conventional silicon wafer formed with a prescribed edge relief width.
Fig. 10 is an enlarged cross-sectional view of a critical part showing a state of a silicon wafer in which a scar region is generated.
Detailed Description
Next, a mode for carrying out the present invention will be described based on the drawings.
An example of a gas phase etching apparatus used in the method for removing an oxide film according to the present invention will be described with reference to fig. 1. As shown in fig. 1, the vapor phase etching apparatus 10 includes a reaction chamber 11 that accommodates a silicon wafer 31 therein and is supplied with an etching gas 14. The reaction vessel 11 is sealed by the upper lid 12, and the temperature and pressure inside the reaction vessel are kept constant, so that the supplied etching gas 14 can stay inside the reaction vessel. In addition, the reaction container 11 is provided with 1 or 2 or more stages 13 for placing silicon wafers 31 held horizontally in the reaction container 11 during the vapor phase etching. Fig. 1 shows an example in which 2 stations are provided.
A gas supply pipe 16 is provided in the reaction vessel 11, and N is blown into an aqueous solution 18 such as a hydrofluoric acid aqueous solution2The etching gas 14 generated by bubbling the carrier gas 20 is supplied into the reaction container 11 through the gas supply port 16 a. The supplied etching gas 14 is supplied to the removal of the oxide film 32, and is then exhausted to the outside of the system through a gas exhaust pipe not shown.
Next, a method of removing the oxide film 32 formed on the outer peripheral portion of the silicon wafer 31 according to the present invention will be described using the gas phase etching apparatus 10 shown in fig. 1. The method for removing the oxide film of the present invention is not limited to the method using the apparatus.
First, a silicon wafer having an upper surface, a lower surface, a chamfered surface, and an end surface, and an oxide film formed on at least the lower surface, the chamfered surface, and the end surface by, for example, a CVD method, is prepared. The silicon wafer 31 is obtained by subjecting a wafer obtained by slicing and slicing a silicon single crystal ingot grown by, for example, a Czochralski method (hereinafter, referred to as a CZ method) to a conventional processing such as chamfering, mechanical polishing (lapping), etching, and mirror polishing, and then subjecting the wafer to a cleaning step. Here, in order to obtain a p-type silicon wafer having a resistivity of, for example, 0.01 Ω, seeds or trees to 0.1 Ω, seeds or trees, when a silicon single crystal is pulled by the CZ method, boron or the like having a resistivity within the above range is previously added as a dopant to a crucible filled with high-purity silicon polycrystal as a silicon source material in a pulling apparatus. p is a radical of+Adding boron and p with the amount of about 10m omega, seeds and cm to 20m omega, and the amount of the seeds and the seeds with the resistivity of about 10m omega, seeds and cm to 20m omega into a type silicon wafer++And adding boron with the resistivity of 1m omega, seeds and cm-10 m omega, and seeds and cm or so into the type silicon wafer.
The oxide film is formed by CVD method by using a vapor phase etching apparatus, and for example, if the diameter of the wafer is 300mm, the oxide film is formed to a film thickness of about 2000 to 9000 angstroms.
Then, the silicon wafer 31 on which the oxide film 32 is formed is removed as shown in fig. 2(a) and 2(b)The excess oxide film 32 formed on the outer peripheral portion thereof is subjected to a vapor etching process. In this vapor etching, the oxide film 32 is removed from the interface between the chamfered surface and the lower surface of the wafer to the inside to the range of the desired gap a so as to achieve the desired edge relief width. At this time, the desired interval a shown in fig. 2(b) is set according to the resistivity of the wafer. For example, p++Since a dopant such as boron is added in a large amount to a silicon wafer having a very low resistivity, such as a type silicon wafer, the amount of dopant diffused outside increases in a high temperature process such as epitaxial growth, and the desired interval a is set to be relatively small.
In the method for removing an oxide film according to the present invention, the removal width of the outer peripheral edge of the oxide film on the lower surface of the wafer can be accurately adjusted by adjusting the diameter of the mounting stage in the vapor phase etching in accordance with the desired target interval a, and the edge relief width can be arbitrarily adjusted. Thus, a silicon wafer with an oxide film having a desired edge relief width can be accurately formed.
The surface roughness Ra of the portion of the mounting stage 13 in contact with the oxide film is preferably 0.5 μm or less. This can provide an effect on the placement stage surface. When the surface roughness Ra is 0.5 μm or less, the adhesion between the surface of the mounting stage and the oxide film formed on the lower surface of the wafer can be improved. Thus, the number of the spot regions generated by the etching gas entering the gap between the surface of the mounting stage and the oxide film formed on the lower surface of the wafer can be reduced. If the thickness is larger than 0.5 μm, the etching gas may enter a gap between the surface of the mounting stage and the oxide film formed on the lower surface of the wafer during the vapor phase etching, and the width of the scar region may become large, which is not preferable. Among them, the surface roughness Ra is particularly preferably 0.4 μm or less. In the present specification, the surface roughness Ra means a value represented by a center line average roughness (Ra value) defined in JIS B0601 (2011). The placing table 13 is not limited to a structure in which the entire surface is formed flat and is in contact with the entire oxide film formed on the lower surface of the wafer, and may be a structure in which a concave portion is provided in the center portion of the surface of the placing table 13, and the wafer is supported by the contact portion in a ring-like contact with the periphery of the lower surface of the wafer as shown in fig. 2(a) and 2 (b). Thus, the adhesion force between the surface of the mounting stage and the oxide film formed on the lower surface of the wafer can be improved, and the number of the spot areas can be reduced. In this case, it is more preferable that the surface of the portion other than the concave portion which is in contact with the oxide film is formed in advance so as to have the desired surface roughness.
It is preferable that at least the surface of the mounting table 13 which is in contact with the oxide film formed on the lower surface of the wafer is formed of any one of polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, and polytetrafluoroethylene. If the mounting table is formed of the above-mentioned material, the acid resistance is excellent as compared with the case of using a mounting table made of another material, and the effect that the wafer is less likely to be damaged when it is set can be obtained.
Examples of the method for making the surface of the mounting table 13 have the desired roughness include: a method of forming the mounting table itself from the polyvinyl chloride or the like and polishing the surface; and a method of applying a material such as polyvinyl chloride to a portion of the surface of the mounting stage made of another material, which portion is in contact with the oxide film, by blowing and polishing the surface to have a desired surface roughness.
As shown in fig. 3, the resin film 13a having a surface roughness Ra of 0.5 μm or less, and more preferably 0.4 μm or less may be coated on the surface of the mounting table 13 to obtain a desired surface roughness. For the above reasons, it is preferable to use a resin film made of any one of polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, and polytetrafluoroethylene. In this method, the surface of the mesa can be easily made to have a desired surface roughness in a conventional apparatus without significantly modifying the apparatus.
Further, if the number of times of the vapor etching treatment is increased, the surface roughness of the mesa surface also gradually deviates from the set value due to the deterioration of the apparatus with time. Therefore, it is necessary to perform a regeneration process such as a polishing process on the surface of the stage, but if the method is a method of covering a detachable resin film having a desired surface roughness, the surface of the stage can be restored to the desired surface roughness by an easy method of replacing with a new resin film.
In the method of covering the resin film, as shown in fig. 4, even if the mounting table has a large diameter, the present invention can be easily implemented without changing the diameter of the mounting table 13 itself. That is, the diameter of the resin film is set to be smaller than the diameter of the mounting table so as to obtain the desired gap a, and the resin film is covered on the surface of the mounting table provided in the conventional apparatus. In this case, if the thickness of the resin film is too thin, the distance between the oxide film and the surface of the stage becomes narrow, and as a result, the effect of the present invention described above is difficult to obtain. The thickness of the resin film in the case of the method shown in FIG. 4 is preferably set to be in the range of 5 to 100 μm.
Next, the silicon wafer 31 on which the oxide film 32 is formed is transported into the reaction container 11 of the gas phase etching apparatus 10. The silicon wafer 31 transported into the reaction container 11 is placed on the placing table 13 such that the lower surface of the wafer on which the oxide film 32 is formed faces the upper surface of the placing table 13, and the center of the wafer coincides with the central axis of the placing table 13 as shown in fig. 2(a) or 4. The reaction container 11 in which the silicon wafer 31 is transported is sealed and sealed by the upper lid 12.
Then, a hydrogen fluoride gas is generated as the etching gas 14 by a gas supply source provided outside the reaction container 11 shown in fig. 1. The hydrogen fluoride gas can be produced by storing an aqueous solution 18 such as an aqueous hydrofluoric acid solution in a container 19 and blowing N into the aqueous solution 18 in the container 192The carrier gas 20 is uniformly bubbled until a saturated state is reached, thereby generating. The generated hydrogen fluoride gas flows into the reaction container 11 through a gas supply port 16a as an etching gas 14 via a gas supply pipe 16 connecting the container and the reaction container 11.
The hydrogen fluoride gas flowing into the reaction container 11 is brought into contact with an excess oxide film formed on the outer peripheral portion of the wafer not in contact with the mounting stage, thereby etching and removing the oxide film. In the vapor phase etching, the mounting table may be rotated, but in order to avoid the occurrence of etching unevenness due to the gas flow, it is desirable that the mounting table is not rotated and is performed in a standing state.
Examples
Next, examples of the present invention will be described in detail together with comparative examples.
< example 1 >
First, a boron-doped p-type silicon wafer having a diameter of 200mm, a chamfer width of 0.3mm, and a resistivity of 0.01 Ω & cm was prepared, and an oxide film having a film thickness of 5000 angstroms was formed on the lower surface of the silicon wafer by a CVD method. At this time, an oxide film is inevitably formed on the chamfered surface and the end surface except the lower surface of the wafer.
Next, a polyvinyl chloride-made mounting table 13 having a surface roughness Ra of 0.5 μm and a recess at the center as shown in fig. 2(a) was provided in the reaction vessel 11 of the vapor phase etching apparatus 10 shown in fig. 1.
Next, as shown in fig. 1, the silicon wafer 31 on which the oxide film is formed is transported into the reaction container 11 of the vapor phase etching apparatus 10. Further, as shown in fig. 2(a), the transported silicon wafer 31 is placed on the placing table 13 such that the lower surface of the wafer faces the upper surface of the placing table 13 and the center of the wafer coincides with the central axis of the placing table 13.
Next, as shown in FIG. 1, the inside of the reaction vessel 11 was sealed with the upper lid 12, and N as a carrier gas was blown into the vessel 19 storing the hydrofluoric acid aqueous solution2Hydrogen fluoride gas is generated by bubbling the hydrofluoric acid aqueous solution. The hydrogen fluoride gas flows as an etching gas 14 into the reaction chamber 11 from a gas supply port 16a of a gas supply pipe 16. Then, by bringing the oxide film 32 into contact with hydrogen fluoride gas, as shown in fig. 2(b), the excess oxide film 32 formed on the outer peripheral portion of the wafer is removed by vapor etching.
In this example, the diameter of the mounting table 13 provided in the reaction vessel 11 was set to 3 levels of 210mm phi, 198mm phi and 195mm phi, and the removal width (interval a) of the oxide film outer peripheral edge of the lower surface of the wafer when the etching treatment time was changed was measured. The results are shown in FIGS. 5 to 7. The value of the interval a in fig. 5 to 7 is calculated by subtracting the value of the chamfer width from the measured length from the wafer end face to the oxide film on the wafer lower surface.
As is clear from fig. 5 to 7, when etching was performed using a stage having a stage diameter of 210mm phi, the interval a was controlled to 0.70mm even when the etching treatment time was increased to 1200 seconds, whereas 1.50mm was used in the case of the stage having a diameter of 198mm phi and 3.10mm was used in the case of the stage having a diameter of 195mm phi, and it was found that the width of the interval a could be increased as the stage diameter became smaller. Thus, it was confirmed that there was a correlation between the diameter of the used mounting table and the width of the gap a, and it was found that the gap a could be controlled to a desired width by adjusting the table diameter.
< example 2 >
The relationship between the surface roughness of the surface of the mounting stage 13 and the width of the spot generation region was examined by changing the surface roughness as in test examples 1 to 5 below.
(test example 1)
The extra oxide film 32 formed on the outer peripheral portion of the wafer was removed by vapor etching in the same manner as in example 1, using a mounting stage 13 having a stage diameter of 198mm phi and a surface roughness Ra of 0.5 μm, with an etching treatment time of 600 seconds.
(test example 2)
The excess oxide film 32 formed on the outer peripheral portion of the wafer was removed by vapor etching in the same manner as in test example 1 except that the mounting stage 13 having a surface roughness Ra of 0.4 μm was used.
(test example 3)
The excess oxide film 32 formed on the outer peripheral portion of the wafer was removed by vapor etching in the same manner as in test example 1 except that the mounting stage 13 having a surface roughness Ra of 0.3 μm was used.
(test example 4)
The excess oxide film 32 formed on the outer peripheral portion of the wafer was removed by vapor etching in the same manner as in test example 1 except that the mounting stage 13 having a surface roughness Ra of 6.5 μm was used and the mounting stage 13 having a surface covered with a resin film made of polyvinylidene chloride having a surface roughness Ra of 0.05 μm was used.
(test example 5)
An excess oxide film 32 formed on the outer peripheral portion of the wafer was removed by vapor etching in the same manner as in test example 1 except that the mounting stage 13 having a surface roughness Ra of 6.5 μm was used.
< comparative test and evaluation 1 >
In each of test examples 1 to 5, the width of the spot area was measured by performing the vapor phase etching under the same conditions for 5 times in total. The width of the scar region was measured using an optical microscope. The results are shown in FIG. 8.
As is clear from fig. 8, in test examples 1 to 4, the width of the spot area was very small. In particular, it is found that the width of the spot area is as small as 0.5mm or less in all the results of the tests 2 to 4.
< example 3 >
For each test example, 5 pieces of silicon wafers subjected to vapor phase etching in each of test examples 1 to 5 of example 2 were collected. An epitaxial film was formed on the surface of each wafer on the upper surface side of the wafer on which the oxide film was not formed, and the presence or absence of nodules in the scribe areas on the lower surface of the wafer was confirmed by visual inspection.
The epitaxial film was formed using a single wafer type epitaxial apparatus, and a p-type silicon epitaxial film having a thickness of 2 μm was formed on the surface of a silicon wafer by supplying a trichlorosilane gas as a source gas and a diborane gas as a dopant gas at a temperature of 1150 ℃.
As a result, it was confirmed that a few nodules were generated in the spot region in 1 wafer among the wafers having the epitaxial films formed on the silicon wafers obtained in test example 5. On the other hand, the wafers having the epitaxial films formed on the silicon wafers obtained in test examples 1 to 4 had no nodules in the spot areas.
Description of the reference numerals
10 gas phase etching device
11 reaction vessel
12 upper cover
13 stage for placing
14 etching gas
16 gas supply pipe
31 silicon wafer
32 oxidation film.
Claims (9)
1. A method for removing an oxide film formed on a surface of a silicon wafer, comprising:
preparing a silicon wafer having an upper surface, a lower surface, a chamfered surface, and an end surface, and having an oxide film formed on at least the entire lower surface of the silicon wafer;
disposing 1 or 2 or more disk-shaped wafer-mounting tables each having an acid-resistant resin layer at least in a portion thereof in contact with the oxide film in a reaction vessel of a vapor phase etching apparatus;
placing the silicon wafer on the placing table such that a wafer center of the silicon wafer is aligned with a central axis of the placing table with a lower surface of the silicon wafer facing an upper surface of the placing table; and
a step of removing an oxide film to a desired distance a from an interface between the chamfered surface and the lower surface of the wafer toward the inner side of the wafer by flowing a gas containing hydrogen fluoride into the reaction container;
the desired distance a is adjusted by changing the table diameter of the mounting table.
2. The method for removing an oxide film according to claim 1, wherein a surface roughness Ra of a portion of the mounting stage which is in contact with the oxide film is 0.5 μm or less.
3. The method for removing an oxide film according to claim 2, wherein a surface roughness Ra of a portion of the mounting stage which is in contact with the oxide film is 0.4 μm or less.
4. The method for removing an oxide film according to claim 1, wherein the acid-resistant resin layer is formed of any one of polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, and polytetrafluoroethylene.
5. The method for removing an oxide film according to claim 1, wherein the acid-resistant resin layer comprises a detachable resin film having a surface roughness Ra of 0.5 μm or less.
6. The method for removing an oxide film according to claim 5, wherein the resin film has a surface roughness Ra of 0.4 μm or less.
7. The method for removing an oxide film according to claim 5, wherein the resin film is formed of any one of polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, and polytetrafluoroethylene.
8. The method for removing an oxide film according to claim 1, wherein a stage having a recess formed in a central portion of a mounting surface is used as the mounting stage.
9. An epitaxial wafer obtained by performing an epitaxial growth process on the upper surface of a silicon wafer from which an oxide film has been removed by the method according to claim 1.
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