METHOD FOR DETERMINING THE CONDITIONS FOR THE FORMATION OF AN OXIDE FILM, METHOD FOR THE FORMATION OF AN OXIDE FILM AND METHOD FOR THE PRODUCTION OF A WAFER

Abstract

A method for determining oxide film formation comprises: forming a first oxide film on a first wafer using a first shell body; determining a correlation between at least one configuration requirement of grooves and a contact section of the shell body and a film thickness distribution of the oxide film; determining a target film thickness distribution of the oxide film; and determining, based on the film thickness distribution of the first oxide film and the correlation, the at least one configuration requirement that enables the formation of the oxide film with the target film thickness distribution as an application requirement.

Description

TECHNICAL AREA The present invention relates to a method for determining an oxide film formation condition, a method for forming an oxide film and a method for producing a wafer. STATE OF THE ART A process is known in which an oxide film is formed on a wafer by heating a film formation tray and supplying a starting gas to the wafer mounted on the film formation tray (see, for example, patent literature 1). The film-forming shell described in patent literature 1 comprises a support element that supports an outer circumference of the wafer and a shell body that supports the support element. Patent literature 1 describes how the film thickness distribution of the oxide film on the wafer can be made more uniform by reducing the contact area between the support element and the shell body. QUOTE LIST PATENT LITERATURE Patent literature 1: Republishing of the international PCT publication 2011 / 070741 SUMMARY OF THE INVENTION TASK(S) THAT THE INVENTION IS / ARE INTENDED TO SOLVE However, in recent years, with the increasing need for greater uniformity of the film thickness distribution, variations in the film thickness distribution among a large number of film forming devices have become a problem. One object of the invention is to provide a method for determining an oxide film formation condition that enables the formation of an oxide film with a desired film thickness distribution on a wafer, a method for forming an oxide film and a method for producing a wafer. MEANS OF SOLVING THE TASK(S) A method for determining an oxide film formation condition according to one aspect of the invention is a method for determining an oxide film formation condition for forming an oxide film on a wafer using a film-forming device, wherein the film-forming device is configured to form the oxide film on the wafer using a film-forming shell comprising: a support element supporting an outer circumference of the wafer, and a shell body supporting the support element by heating the film-forming shell and supplying a starting gas to the wafer, wherein the support element comprises an annular placement section on which the wafer is placed and a leg extending downward from the placement section, wherein the shell body comprises: a cylindrical recess in which the support element is housed; a plurality of grooves along an outer edge of a bottom surface of the recess;and a contact section provided between a pair of adjacent slots and supporting the leg of the support element, wherein the wafer comprises a first wafer, the shell body comprises a first shell body, the oxide film comprises a first oxide film, the method comprising: forming the first oxide film on the first wafer using the first shell body; recognizing a correlation between at least one configuration requirement of the slots and the contact section and a film thickness distribution of the oxide film; recognizing a target film thickness distribution of the oxide film; and determining, based on the film thickness distribution of the first oxide film and the correlation, the at least one configuration requirement that enables the formation of the oxide film with the target film thickness distribution as an application requirement. In the method for determining the oxide film formation condition according to the aspect of the invention, the correlation preferably includes a first correlation between at least a part of a width in a circumferential direction of each of the grooves and a thickness of the oxide film in a region adjacent to the at least a part in the outer circumference of the wafer. In the method for determining the oxide film formation condition according to the aspect of the invention, it is preferred that the film formation tray comprises a plurality of film formation trays, the tray body comprises a plurality of tray bodies, the film formation device is configured to form the oxide film on the wafer, which is supported by each of the film formation trays, while the plurality of film formation trays, which are provided with the tray bodies and arranged in the feed direction, are conveyed in a feed direction, and the correlation comprises a second correlation between a contact area between the leg and the contact section at a location in a conveying width direction orthogonal to the feed direction of the tray body and a thickness of the oxide film in a region adjacent to the location in the outer circumference of the wafer. In the method for determining the oxide film formation condition according to the aspect of the invention, the second correlation is preferably a correlation in which, if the contact area at the point in the conveying width direction is larger, the oxide film in the area next to the point is thinner. In the method for determining the oxide film formation condition according to the aspect of the invention, it is preferred that the film formation shell comprises a plurality of film formation shells, the shell body comprises a plurality of shell bodies, the film formation device is configured to form the oxide film on the wafer, which is supported by each of the film formation shells, while the plurality of film formation shells, which are provided with the shell bodies and arranged in the feed direction, are conveyed in a feed direction, the contact section comprises a plurality of contact sections, and the correlation includes a third correlation between a contact area between the leg and the contact sections at locations in the feed direction of the shell body and in a direction opposite to the feed direction, and a thickness of the oxide film in areas adjacent to the locations on the outer circumference of the wafer. In the method for determining the oxide film formation condition according to the aspect of the invention, the third correlation is preferably a correlation in which, if the contact area is larger at the locations in the feed direction and in the opposite direction to the feed direction, the oxide film is thicker in the areas next to the locations. A method for forming an oxide film according to a further aspect of the invention comprises: carrying out the method for determining the oxide film formation condition according to the above aspect of the invention; and forming a second oxide film on a second wafer using a second tray body that meets the application requirement, wherein the oxide film includes the second oxide film, the wafer includes the second wafer, and the tray body includes the second tray body. In the method for forming the oxide film according to a further aspect of the invention, it is preferred that the shell body comprises a plurality of types of shell bodies which differ from one another in at least one configuration requirement, wherein the method further comprises preparing the plurality of types of shell bodies which differ from one another in at least one configuration requirement, wherein in the formation of the second oxide film the second oxide film is formed using the second shell body by selecting the second shell body which meets the at least one configuration requirement for any one of the plurality of types of shell bodies. A method for producing a wafer according to yet another aspect of the invention includes forming the oxide film on the second wafer by the method for forming the oxide film according to the further aspect of the invention. BRIEF EXPLANATION OF THE DRAWINGS Fig. 1 schematically illustrates a configuration of a film-forming device according to a related technique of the invention. Fig. 2A is a top view illustrating a configuration of a film-forming dish according to the related technique and experimental examples 1 and 2. Fig. 2B is a sectional view along line IIB-IIB in Fig. 2A illustrating the configuration of the film-forming dish according to the related technique and experimental examples 1 and 2. Fig. 2C is a sectional view along line IIC-IIC in Fig. 2A illustrating the configuration of the film-forming dish according to the related technique and experimental examples 1 and 2. Fig. 3A is a top view illustrating a dish body according to experimental example 3. Fig. 3B is a top view illustrating a dish body according to experimental example 4.Figure 4A schematically illustrates a central area contained within a film thickness evaluation area used to investigate a correlation between the configuration requirements of grooves and contact sections of the shell body and the film thickness distribution of an oxide film. Figure 4B schematically illustrates an outer circumferential area contained within the evaluation area. Figure 4C schematically illustrates conveying width direction areas contained within the evaluation area. Figure 4D schematically illustrates conveying direction areas contained within the evaluation area. Figure 5 is a flowchart illustrating a method for producing a wafer according to an exemplary embodiment of the invention. Figure 6 is a flowchart illustrating an oxide film formation process according to the exemplary embodiment. DESCRIPTION OF THE FORM(S) Related technology Before describing an exemplary embodiment of the invention, a configuration of a film-forming device used in the exemplary embodiment will first be explained. Fig. 1 schematically illustrates a configuration of a film-forming device according to a related technique of the invention. A film-forming device 1, illustrated in Fig. 1, forms an oxide film on a wafer W. The film-forming device 1 includes a plurality of film-forming trays 2, a circulation unit 3, and a film-forming unit 4. The wafer W can be made of materials such as silicon, germanium, gallium arsenide, gallium phosphide, or indium phosphide. The film formation tray 2 holds the wafer W. Details of the configuration of the film formation tray 2 will be described later. The circulation unit 3 circulates a predetermined number of film-forming trays 2 within the film-forming device 1. The circulation unit 3 includes a first lifting unit 31, a film-forming conveying unit 32, a second lifting unit 33, and a return conveying unit 34. The first lifting unit 31 comprises a first lift 311, on which the film-forming tray 2 is placed, and a first lift driver 312, which raises and lowers the first lift 311. In a state where the first lift 311 is in a raised position, the wafer W is transferred into the film-forming tray 2 by a transfer unit (not illustrated) prior to film formation, and this film-forming tray 2 is fed to the film-forming conveying unit 32. The structure for feeding the film-forming tray 2 from the first lift 311 to the film-forming conveying unit 32 is not particularly restricted, and any known structure can be used. The film-forming conveying unit 32 comprises a pair of conveying rollers 321 and a conveyor belt 322 stretched over the pair of conveying rollers 321. The film-forming conveying unit 32 conveys the plurality of film-forming shells 2 in a state of contact with one another to the film-forming unit 4 by rotating the conveyor belt 322 in a clockwise direction as shown in Fig. 1. Exemplary configurations in which the film-forming shells 2 are conveyed by the conveyor belt 322 include one in which projections provided on the conveyor belt 322 are fitted into locating grooves formed in a lower surface of a shell body 22 to perform the conveying. The direction in which the film-forming conveying unit 32 conveys the film-forming shells 2 can be referred to as the “feed direction”.Additionally, a direction orthogonal to the feed direction and a vertical direction can be referred to as the "conveying width direction". The second lifting unit 33 comprises a second lift 331, on which the film-forming tray 2 is placed, and a second lift driver 332, which raises and lowers the second lift 331. In a state where the second lift 331 is in a raised position, the film-forming tray 2, which receives the wafer W after film formation, is fed to the second lift 331 by the feed roller 321. In a state where the second lift 331 is in a lowered position, the film-forming tray 2, which receives the wafer W after film formation, is fed from the second lift 331 to the return conveying unit 34. The structure for feeding the film formation tray 2 from the conveyor roller 321 to the second stroke 331 and the structure for feeding the film formation tray 2 from the second stroke 331 to the return conveying unit 34 are not particularly restricted, and any known structure can be used. The return feeder 34 conveys the film-forming tray 2, which receives the wafer W after film formation, in a direction opposite to the feed direction. The film-forming tray 2, conveyed by the return feeder 34, is fed to the first lift 311, which is located in a lowered position. The structure for feeding the film-forming tray 2 from the return feeder 34 to the first lift 311 is not particularly restricted, and any known structure can be used. The direction in which the return feeder 34 conveys the film-forming tray 2 can be referred to as the "return direction". When the film-forming tray 2 is fed from the return conveying unit 34 to the first stroke 311 at the lowered position, the first stroke 311 rises to the raised position. In a state where the first stroke 311 is at the raised position, the wafer W, after film formation, is transferred by the transfer unit from the film-forming tray 2 to a wafer storage area (not illustrated). Subsequently, as described above, the wafer W is transferred by the transfer unit (not illustrated) into the film-forming tray 2 before film formation, and this film-forming tray 2 is fed to the film-forming conveying unit 32. The film formation unit 4 forms an oxide film on the wafer W in the film formation tray 2, which is conveyed by the film formation conveying unit 32. The film formation unit 4 includes a preheater 41, a heater 42, an outlet gas supply device 43, a pair of barrier gas supply devices 44, and a pair of outlet devices 45. The preheater 41 and the heater 42 are, for example, arranged in a space surrounded by the conveyor belt 322. The heater 42 is arranged downstream of the preheater 41 in the feed direction. The wafer W in the film-forming tray 2 is initially heated by the preheater 41 to a temperature lower than the film-forming temperature and is then heated by the heater 42 to the film-forming temperature. The output gas supply unit 43 is arranged above the heater 42. The output gas supply unit 43 discharges an output gas G1 downwards and directs it onto the wafer W. An oxide film is formed by reaction on the heated wafer W. Examples of the output gas include a mixture of monosilane (SiH4) and oxygen (O2) and a mixture of tetraethoxysilane (TEOS, chemical formula: Si(OC2H5)4) and ozone (O3). The barrier gas supply devices 44 are arranged on the feed direction side and on the return direction side relative to the outlet gas supply device 43 above the heater 42. Each of the barrier gas supply devices 44 discharges a barrier gas G2 downwards to prevent the outlet gas G1 from escaping beyond the film-forming unit 4 in both the feed and return directions. Examples of the barrier gas G2 include nitrogen gas. The outlet devices 45 are positioned between the outlet gas supply device 43 and the respective barrier gas supply devices 44 on the feed and return directions. Each outlet device 45 discharges the barrier gas G2 and the outlet gas G1, which are not used for film formation, from a space between the outlet gas supply device 43 and the film formation trays 2, beyond the outlet gas supply device 43. Next, a configuration of the film-forming tray 2 is described in detail. Fig. 2A is a top view illustrating the configuration of the film-forming tray. Fig. 2B is a sectional view along line IIB-IIB in Fig. 2A. Fig. 2C is a sectional view along line IIC-IIC in Fig. 2A. As illustrated in Figs. 2A to 2C, the film formation shell 2 includes a support element 21 and a shell body 22. The support element 21 and the shell body 22 are made of SiC, for example. The support element 21 supports an outer circumference of the wafer W. The support element 21 includes a placement section 211 and a leg 212. The placement section 211 is formed in a ring shape. The wafer W is placed on the placement section 211. The leg 212 is formed such that it extends cylindrically downwards from the entire outer edge of the placement section 211. The shell body 22 is formed in a rectangular parallelepiped shape. In a top view illustrated in Fig. 2A, side surfaces of the shell body 22 corresponding to the long sides of the rectangle form opposite surfaces 22A, which, as illustrated in Fig. 1, face adjacent film-forming shells 2 when conveyed by the film-forming conveying unit 32 of the film-forming device 1. Side surfaces of the shell body 22 corresponding to the short sides of the rectangle form non-opposite surfaces 22B, which do not face adjacent film-forming shells 2 when conveyed by the film-forming conveying unit 32 of the film-forming device 1. A recess 221 with a cylindrically recessed shape is formed in a central section of the shell body 22. A plurality of arcuate grooves 222 are formed along an outer edge of the bottom surface of the recess 221. A point between a pair of adjacent grooves 222 forms a contact section 223 that supports the leg 212 of the support element 21. Background leading to the invention Next, a backstory leading up to the invention will be described. An experiment was conducted to investigate a correlation between configuration requirements of the grooves 222 and the contact sections 223 provided for the shell body 22 of the film formation shell 2 and a film thickness distribution of the oxide film on the wafer W. Fig. 3A is a top view illustrating a shell body according to experimental example 3. Fig. 3B is a top view illustrating a shell body according to experimental example 4. Fig. 4A schematically illustrates a central region contained within a film thickness evaluation area used to investigate the correlation between the oxide film thickness distribution and the configuration requirements of the grooves and contact sections of the shell body. Fig. 4B schematically illustrates an outer circumferential region contained within the evaluation area. Fig. 4C schematically illustrates a conveying width direction region contained within the evaluation area. Fig. 4D schematically illustrates a conveying direction region contained within the evaluation area. Procedures for preparing evaluation samples First, four types of shell bodies 22 were prepared, differing from one another in at least one configuration requirement of the grooves 222 and the contact sections 223, such as number, shape, or position. Specifically, shell bodies 23, 24, 25, and 26 were prepared according to experimental examples 1, 2, 3, and 4, respectively. It should be noted that in shell bodies 23, 24, 25, and 26, any configuration that is the same as that of shell body 22 in the related technique described above, or that is the same among shell bodies 23, 24, 25, and 26, is designated by the same name and reference numeral. The shell body 23 of experimental example 1 has the configuration illustrated in Figs. 2A to 2C. Six grooves 232 of the same shape are formed in a bottom surface of the recess 221 of the shell body 23. Each groove 232 is formed such that it has a circumferential length of L1. As shown in Table 1 below, the groove 232 is formed such that it satisfies a ratio “J1:J0 = 4:1”, where J1 denotes the width of the groove 232 and J0 denotes the width (thickness) of the leg 212 of the support element 21. The grooves 232 are formed at equal intervals so that six first contact sections 233 of the same shape are provided. The circumferential length of each of the first contact sections 233 thus provided is M1, as shown in Table 1. Experimental Example 1J1(J1:J0 = 4:1)606 Experimental Example 2J2(J2:J0 = 6:1)606 Experimental example 3J1224 Experimental example 4J1022 The shell body 24 of experimental example 2 has the configuration illustrated in Figs. 2A to 2C. Six grooves 242 of the same shape are formed in a bottom surface of the recess 221 of the shell body 24. The length of each groove 242 is the same L1 as the length of groove 232 in experimental example 1. As shown in Table 1, each groove 242 is formed such that it satisfies a relationship “J2:J0 = 6:1”, where J2 denotes the width of the groove 242. The grooves 242 are formed at equal intervals, so that the length of each of the first contact sections 243 becomes the same M1 as the length of the first contact section 233 in experimental example 1. The shell body 25 of experimental example 3 has a configuration illustrated in Fig. 3A. In a bottom surface of the recess 221 of the shell body 25, four grooves 252 of the same shape are formed. The length of each groove 252 is L2, which is longer than the length of the groove 232 of experimental example 1. The width of each groove 252 is the same J1 as the width of the groove 232 of experimental example 1. The grooves 252 are formed such that two first contact sections 233 and two second contact sections 254 are provided in the circumferential direction. The first contact sections 233 and the second contact sections 254 are arranged alternately. Each of the second contact sections 254 is formed such that it satisfies a relationship "M2:M1 = 52:1", where M2 denotes the length of the second contact section 254. The length M2 of the second contact section 254 is shorter than a length obtained by adding the lengths M1 of the two first contact sections 233 and the length L1 of the groove 232 adjacent to these first contact sections 233 in the shell body 23 of experimental example 1.The grooves 252 are formed in the recess 221 such that the center in a longitudinal direction of each of the first contact sections 233 is positioned at a location closest to one of the non-opposite surfaces 22B, and the center in a longitudinal direction of each of the second contact sections 254 is positioned at a location closest to one of the opposite surfaces 22A. That is, the grooves 252 are formed such that a first contact section 233 is positioned on each side in the conveying width direction, and a second contact section 254 is positioned on the feed direction side and one on the return direction side. The shell body 26 of experimental example 4 has a configuration illustrated in Fig. 3B. In a bottom surface of the recess 221 of the shell body 26, two grooves 262 of the same shape are formed. The length of each groove 262 is L3, which is longer than the length of the groove 252 of experimental example 3. The width of each groove 262 is the same J1 as the width of the groove 232 of experimental example 1. The grooves 262 are formed such that two second contact sections 254 are positioned at the same locations as the second contact sections 254 of experimental example 3. That is, the grooves 262 are formed such that one second contact section 254 is positioned on the feed direction side and one on the return direction side. In addition, ten wafers W with a diameter of 300 mm were prepared. Seven film-forming shells 2, each containing the shell body 23 of experimental example 1, one film-forming shell 2 containing the shell body 24 of experimental example 2, one film-forming shell 2 containing the shell body 25 of experimental example 3, and one film-forming shell 2 containing the shell body 26 of experimental example 4, were then arranged in the circulation unit 3 of the film-forming device 1. Using four film-forming shells 2, each containing one of the shell bodies 23, 24, 25, and 26 of experimental examples 1, 2, 3, and 4, an oxide film was then formed on a corresponding wafer W in each of the four film-forming shells 2. The target thickness of the oxide film is 350 nm.In the following, the wafers W, which were subjected to film formation using the film-forming shells 2, which are equipped with the shell bodies 23, 24, 25 and 26 of experimental examples 1, 2, 3 and 4, can be referred to as wafers W1, W2, W3 and W4 of experimental examples 1, 2, 3 and 4. Method for investigating the correlation between configuration requirements of grooves and contact sections of the shell body and the film thickness distribution of the oxide film 1. Correlation between grooves of the shell body and the film thickness distribution of the oxide film For each of the wafers W1 and W2 of experimental examples 1 and 2, the oxide film thickness distribution was measured. Then, for each of the wafers W1 and W2, the average oxide film thickness was calculated in a central region A1, illustrated in Fig. 4A, and in an outer circumferential region A2, illustrated in Fig. 4B. The central region A1 is a circular area with a diameter of 60 mm, with the center of wafer W as its center. The outer circumferential region A2 is an annular area within 30 mm of an outer edge of wafer W. The width of the outer circumferential region A2 is greater than J2, which is the width of the grooves 242 of experimental example 2. Next, an initial film thickness ratio was calculated for each of wafer W1 of experimental example 1 and wafer W2 of experimental example 2 based on the following equation (1). Then, an initial effect assessment score was calculated to evaluate the effect of the groove width based on the following equation (2). The results of the calculations for equations (1) and (2) are given in Table 2. First film thickness ratio 1.030 1.015 First effect rating value 0.985 As shown in Table 2, the first effect assessment value was less than 1. This shows that the width of the grooves 222 and the film thickness distribution of the oxide film exhibit such a correlation that, as the width of the grooves 222 increases, the oxide film becomes thinner in the outer circumference of the wafer W than in the central section. The inventors derived the reason for such a correlation as follows. As the width of the groove 222 increases, the distance from an inner edge of the groove 222 (an edge on the recess center side in a top view) to the leg 212 of the support element 21 becomes longer, and the amount of heat transferred from the inner edge of the groove 222 via the leg 212 to the outer circumference of the wafer W decreases. When the amount of heat transferred to the outer circumference W of the wafer decreases, the temperature of the outer circumference becomes lower, and the oxide film on the outer circumference becomes thinner. From the conclusion described above, it is also assumed that if the width of the groove 222 decreases, the oxide film in the outer circumference of the wafer W becomes thicker than in the central section. Furthermore, it is assumed that by making a part of the groove 222 wider or narrower in the circumferential direction than the remaining section, the oxide film can be made thinner or thicker at a location next to this part than at a location next to the remaining section. This means that it was confirmed that at least a portion of the width in the circumferential direction of the groove 222 and the ratio of the oxide film thickness in a region adjacent to at least a portion in the outer circumference of the wafer W to the oxide film thickness in the central section of the wafer W exhibit a correlation (which can be referred to below as the "first correlation"). The first correlation can also be described as a correlation between at least a portion of the width in the circumferential direction of the groove 222 and the oxide film thickness in a region adjacent to at least a portion in the outer circumference of the wafer W. 2. Correlation between the presence or absence of contact sections in the conveying width direction of the shell body and the film thickness distribution of the oxide film. The oxide film thickness distribution was measured for each wafer W3 of experimental example 3 and wafer W4 of experimental example 4. Then, for each wafer W3 and W4, the average oxide film thickness was calculated in two conveying width direction regions A3, illustrated in Fig. 4C, and in the central region A1. Each conveying width direction region A3 is a substantially semicircular region at each end in the conveying width direction of wafer W. The circumferential length of the conveying width direction region A3 is 60 mm, which is greater than M1, the length of the first contact section 233 of experimental example 3. The radial length of the conveying width direction region A3 is 30 mm. Next, a second film thickness ratio was calculated for each of wafer W3 of experimental example 3 and wafer W4 of experimental example 4 based on the following equation (3). The calculation results are given in Table 3 below. Then a second effect score was calculated to assess the effect of the presence or absence of contact sections in the conveying width direction based on the following equation (4). The results of the calculations for equations (3) and (4) are given in Table 3. Second film thickness ratio 1.018 1.113 Second Effect Rating Value 0.915 As shown in Table 3, the second effect assessment value was less than 1. This shows that the presence or absence of the contact sections 223 in the transport width direction and the film thickness distribution of the oxide film exhibit such a correlation that, compared to a case in which no contact sections 223 are provided at locations in the transport width direction of the tray body 22, in a case in which the contact sections 223 are provided at locations in the transport width direction of the tray body 22, the oxide film becomes thinner in areas adjacent to these locations on the outer circumference of the wafer W than in the central section. As shown in Fig.As illustrated in Figure 3A, the locations in the conveying width direction of the shell body 22, where the contact sections 223 are provided, are within sectors, each of which includes a center 221C of the recess 221, is symmetrical with respect to a reference line T1 parallel to the conveying width direction, and has a central angle θ1 of 60 degrees. Typically, in a plan view, the center 221C of the recess 221 coincides with a center Wc of the wafer W, which is supported by the support element 21. The inventors derived the reason for such a correlation as follows. While the oxide film on the wafer W is formed in one of the film-forming shells 2, film-forming shells 2 are present on both the feed-direction side and the return-direction side of the film-forming shell 2 for which the oxide film formation is carried out (hereinafter, the feed-direction side and the return-direction side can be collectively referred to as "both sides in the conveying direction"), but no film-forming shells 2 are present on both sides in the conveying width direction. Thus, the temperature on both sides in the conveying width direction of the shell body 22 is lower than that on both sides in the conveying direction.Therefore, heat is dissipated on both sides in the transport width direction of the placement section 211 of the support element 21 through the leg 212 and the contact sections 223 on both sides in the transport width direction into the shell body 22. As a result, the temperature on both sides in the transport width direction of the wafer W decreases, and the oxide film on both sides in the transport width direction becomes thinner. From the conclusion described above, it is also assumed that, compared to a case in which the contact sections 223 are provided at locations in the transport width direction of the shell body 22, in a case in which no contact sections 223 are provided at locations in the transport width direction of the shell body 22, the oxide film in areas next to these locations on the outer circumference of the wafer W becomes thicker than in the central section. Furthermore, it is assumed as follows: If the contact sections 223 are provided at locations in the transport width direction of the tray body 22, heat near these locations in the transport width direction of the tray body 22 is dissipated more easily as the length of the contact sections 223 increases. Thus, as the contact sections 223 become longer and the contact area between the contact sections 223 and the leg 212 increases, the oxide film in areas adjacent to these locations in the transport width direction on the outer circumference of the wafer W becomes thinner than in the central section. This means that it was confirmed that the contact area between the contact sections 223 and the leg 212 at locations in the conveying width direction of the tray body 22 and the ratio of the oxide film thickness in areas adjacent to these locations on the outer circumference of the wafer W to the oxide film thickness in the central section of the wafer W exhibit a correlation (which can be referred to below as the "second correlation"). The second correlation can also be described as the correlation between the contact area between the leg 212 and the contact sections 223 at locations in the conveying width direction of the tray body 22 and the oxide film thickness in areas adjacent to these locations on the outer circumference of the wafer W. 3. Correlation between contact area between contact sections and legs in the conveying direction of the shell body and film thickness distribution of the oxide film For the wafers W of experimental examples 1 and 3, the average film thickness of the oxide film in the central region A1 and in two conveying direction regions A4, illustrated in Fig. 4D, was calculated. The conveying direction regions A4 are essentially arc-shaped regions on both sides in the conveying direction of the wafer W. The circumferential length of the conveying direction region A4 is 220 mm, which is longer than the length of the arc-shaped region including the two first contact sections 233 with the groove 232 arranged between them in experimental example 1 and the length of a second contact section 254 in experimental example 3. The width (radial length) of the conveying direction region A4 is 30 mm. Next, a third film thickness ratio was calculated for each of wafer W1 of experimental example 1 and wafer W3 of experimental example 3 based on the following equation (5). Then a third effect assessment value was calculated to evaluate the effect of the contact area between the contact sections and the leg in the direction of transport based on the following equation (6). The results of the calculations for equations (5) and (6) are given in Table 4. Third film thickness ratio 1.038 1.060 Third Effect Valuation Value 1.021 As shown in Table 4, the third effect rating was greater than 1. Here, the contact area between leg 212 and a second contact section 254 of experimental example 3, which is located next to the radially outer side of each conveying direction region A4 during film formation, is larger than the contact area between leg 212 and the two first contact sections 233 of experimental example 1. This shows that the contact area between the leg 212 and the contact sections 223 in the conveying direction and the film thickness distribution of the oxide film exhibit such a correlation that, as the contact area increases at locations in the conveying direction of the tray body 22, the oxide film becomes thicker in areas adjacent to these locations on the outer circumference of the wafer W than in the central section. As illustrated in Fig. 3B, the locations in the conveying direction of the tray body 22 where the contact sections 223 are provided are within sectors, each of which includes the center 221C of the recess 221, is symmetrical with respect to a reference line T2 parallel to the conveying direction, and has a central angle θ2 of 90 degrees. Each conveying direction region A4 is a region within the sector illustrated in Fig. 3B. The inventors derived the reason for this correlation as follows. As described above, while the oxide film is formed on the wafer W in one of the film-forming shells 2, film-forming shells are present on both sides in the conveying direction of this film-forming shell 2, but no film-forming shells 2 are present on both sides in the conveying width direction. Thus, the temperature on both sides in the conveying direction of the shell body 22 is higher than the temperature on both sides in the conveying width direction. Therefore, heat on both sides in the conveying direction of the shell body 22 is transferred through the leg 212 and the contact sections 223 on both sides in the conveying direction to the placement section 211 of the support element 21.Furthermore, the amount of heat transferred to the placement section 211 of the support element 21 in the manner described above increases as the contact area between the contact sections 223 and the leg 212 increases. Accordingly, as the contact area between the contact sections 223 and the leg 212 increases, the temperature on both sides in the transport direction of the wafer W rises, and the oxide film on both sides in the transport direction becomes thicker. From the conclusion described above, it is also assumed that if the contact area between the leg 212 and the contact sections 223 decreases at points in the transport direction of the shell body 22, the temperature near these points in the outer circumference of the wafer W will be lower, and the oxide film near these points in the transport direction will be thinner than in the central section. It is also assumed that if no contact sections 223 are provided at locations in the conveying direction of the shell body 22, heat is less likely to be transferred on both sides in the conveying direction of the shell body 22 to the placement section 211 of the support element 21, compared to a case where the contact sections 223 are provided. This suggests that if no contact sections 223 are provided at locations in the conveying direction of the shell body 22, the oxide film in areas adjacent to these locations on the outer circumference of the wafer W will be thinner than in the central section, compared to a case where the contact sections 223 are provided. This means that it was confirmed that the contact area between the leg 212 and the contact sections 223 at locations in the conveying direction of the wafer body 22 and the ratio of the oxide film thickness in areas adjacent to these locations on the outer circumference of the wafer W to the oxide film thickness in the central section of the wafer W exhibit a correlation (which can be referred to below as the "third correlation"). The third correlation can also be described as the correlation between the contact area between the leg 212 and the contact sections 223 at locations in the conveying direction of the wafer body 22 and the oxide film thickness in areas adjacent to these locations on the outer circumference of the wafer W. Concluding remarks The inventors have determined that the configuration requirements of the grooves 222 and the contact sections 223 of the shell body 22, which are provided for the film formation shell 2, and the film thickness distribution of the oxide film on the wafer W exhibit the first to third correlation, as described above. The inventors then obtained the following knowledge: that an oxide film with a desired film thickness distribution can be formed on the wafer W by: forming a first oxide film on a first wafer W using a first shell body 22 in a predetermined film-forming device 1; determining a correlation between at least one configuration requirement of the grooves 222 and the contact sections 223 and the film thickness distribution of the oxide film; determining a target film thickness distribution of the oxide film; and determining, as an application requirement, the at least one configuration requirement that enables the formation of the oxide film with the target film thickness distribution, based on the film thickness distribution of the first oxide film and the correlation.and forming a second oxide film on a second wafer W using a second tray body 22 that meets the application requirement in the predetermined film-forming device 1, which leads to the invention. Exemplary embodiment Method for forming an oxide film Next, a method for forming an oxide film according to an exemplary embodiment of the invention is described. Fig. 5 is a flowchart illustrating a method for producing a wafer. Fig. 6 is a flowchart illustrating an oxide film formation process. In the exemplary embodiment, a wafer manufacturing process is described as a method for producing an epitaxial wafer, which includes: a product wafer W as the second wafer formed from silicon; an epitaxial layer provided on a surface of the product wafer W; and a backside oxide film (LTO film) as the second oxide film provided on a surface of the product wafer W. As illustrated in Fig. 5, the process for producing a wafer includes: a drawing step S1, a block processing step S2, a cutting step S3, a pretreatment step S4, a double-sided polishing step S5, an oxide film formation step S6, a single-sided finishing step S7, a first cleaning step S8, a step to form an epitaxial layer S9 and a second cleaning step S10. In the drawing step S1, a cylindrical silicon single crystal is drawn from a silicon melt using the Czochralski method. In block processing step S2, the outer circumference of the single-crystal block is ground and notched according to the crystal orientation. The single-crystal block is then cut into a multitude of blocks, for example, by a band saw. In the cutting step S3, the blocks are cut into a variety of product wafers W, which have a thickness of approximately 1 mm, for example, by an inside diameter blade saw or a wire saw. In pretreatment step S4, chamfering is performed and coarse polishing (lapping) is carried out, for example with an aluminum oxide abrasive, so that both surfaces of the product wafer W become parallel. Then, after etching or other processing as required, a planarization process is carried out to remove surface irregularities of the product wafer W. In the double-sided polishing step S5, a mirror finish is performed to increase the flatness of the product wafer W, which has undergone pretreatment, using a double-sided polishing device. The oxide film formation step S6 corresponds to a method for forming an oxide film of the invention and includes a method for determining an oxide film formation condition of the invention. In the oxide film formation step S6, a backside oxide film is formed on a backside surface of the product wafer W. In the one-sided finishing step S7, a front surface of the product wafer W obtained in the oxide film formation step S6 (a surface on which no back oxide film is formed) is polished. By performing the polishing in the one-sided finishing step S7, scratches and damage on the front surface of the product wafer W can be removed, and the surface roughness of the front surface can be adjusted. In the first cleaning step S8, the product wafer W obtained in the one-sided finishing step S7 is cleaned, for example, with an alkaline solution. In the step to form an epitaxial layer S9, an epitaxial layer is formed on the front surface of the product wafer W. In the second cleaning step S10, the epitaxial wafer obtained in step S9 for the formation of an epitaxial layer is cleaned, for example, with an alkaline solution. Next, details of the oxide film formation step S6 will be described. As illustrated in Fig. 6, the oxide film formation step S6 comprises: a shell preparation step S61, a preliminary oxide film formation step S62, a correlation acquisition step S63, a target film thickness distribution acquisition step S64, a shell configuration determination step S65, and a film formation step S66. The preliminary oxide film formation step S62, the correlation acquisition step S63, the target film thickness distribution acquisition step S64, and the shell configuration determination step S65 constitute the procedure for determining the oxide film formation condition. Each of the steps S61 to S66 is described below. In the shell body preparation step S61, an operator prepares a variety of shell body types 22 that differ from each other in at least one configuration requirement of the grooves 222 and the contact sections 223 (for example, a combination of number, shape, and position), as in the shell bodies 23 to 26 of the experimental examples 1 to 4 described above. In the preliminary oxide film formation step S62, the predetermined film formation device 1 forms a test oxide film as the first oxide film on a test wafer W as the first wafer using a first film formation tray 2, which includes the first tray body 22 and the support element 21. A measuring device (not shown) measures the film thickness distribution of the test oxide film. A computer (not shown) acquires the film thickness distribution of the test oxide film, for example, from the measuring device or based on the operation of an input unit (not shown) by the operator. The configuration requirements of the grooves 222 and the contact sections 223 in the first shell body 22 are not particularly restricted and can, for example, be the configuration requirements of the shell body 22 of experimental example 1 described above. The first shell body 22 can be selected from the multitude of shell body types 22 prepared in shell body preparation step S61, or it can be a shell body type 22 that differs from the shell bodies 22 prepared in shell body preparation step S61. In the correlation acquisition step S63, the computer, for example, from a bearing (not shown), acquires a correlation between at least one configuration requirement of the grooves 222 and the contact sections 223 and the film thickness distribution of the oxide film. The correlation includes at least one of the first to third correlations described above. The correlation can be obtained through experimentation or simulation. In the target film thickness distribution acquisition step S64, the computer acquires a target film thickness distribution of the oxide film, for example based on the operation of an input unit by the operator. In the shell body configuration determination step S65, the computer determines as an application requirement at least one configuration requirement of the grooves 222 and the contact sections 223 that enables the formation of the oxide film with the target film thickness distribution, based on the film thickness distribution of the test oxide film and the correlation. For example, if the target film thickness distribution is a film thickness distribution where the first film thickness ratio becomes a predetermined value based on the above equation (1), and if the first film thickness ratio in the test oxide film is larger than the predetermined value, it is determined based on the first correlation that the width of the grooves 222 is made larger than that of the grooves 222 of the first shell body 22 than the application requirement of the grooves 222, which enables the formation of the oxide film with the target film thickness distribution. If the target film thickness distribution on the outer circumference is a uniform film thickness distribution and if the thickness in areas on both sides in the conveying width direction on the outer circumference of the test oxide film is greater than in other areas on the outer circumference, it is determined, based on the second correlation, that the contact sections 223 provided at locations in the conveying width direction are made longer than the contact sections 223 of the first shell body 22 in order to increase the contact area with the leg 212, as required by the application requirement of the contact sections 223, which enables the formation of the oxide film with the target film thickness distribution. If the target film thickness distribution on the outer circumference is uniform, and if the thickness in areas on both sides in the conveying direction on the outer circumference of the test oxide film is smaller than in other areas of the outer circumference, it is determined, based on the third correlation, that the contact area between the leg 212 and the contact sections 223, which are provided at locations in the conveying direction, is made larger than the contact area in the first shell body 22, as required by the application requirement of the contact sections 223, which enables the formation of the oxide film with the target film thickness distribution. At least one of the following methods can be used to increase the contact area: increasing the length of the contact sections 223 or increasing the number of contact sections 223. In film formation step S66, the operator selects the second shell body 22 that meets the application requirement from the plurality of shell body types 22 prepared in shell body preparation step S61. If the plurality of shell body types 22 does not include a shell body 22 that meets the application requirement, the operator selects as the second shell body 22 the shell body 22 with a configuration requirement that most closely matches the application requirement. It should be noted that selecting the shell body 22 with a configuration requirement that most closely matches the application requirement is equivalent to selecting the second shell body 22 that meets the application requirement in the invention. The predetermined film forming device 1 forms a backside oxide film on the backside surface of the product wafer W using the second tray body 22, which was selected by the operator. Effects of the exemplary embodiment The procedure for forming an oxide film includes the preliminary oxide film formation step S62 described above, correlation acquisition step S63, target film thickness distribution acquisition step S64, shell body configuration determination step S65 and film formation step S66. As described above, based on the correlation between at least one configuration requirement of the grooves 222 and the contact sections 223 and the film thickness distribution of the oxide film and the film thickness distribution of the test oxide film, the at least one configuration requirement that enables the formation of the oxide film with the target film thickness distribution is determined as the application requirement, and the backside oxide film is formed on the product wafer using the second shell body 22 that fulfills the application requirement, thereby enabling the formation of the oxide film with a desired film thickness distribution on the wafer W. Additionally, the method for forming an oxide film, in which the second shell body 22 is used, which corresponds to the device properties of each of the film-forming devices 1, can reduce variations in the film thickness distribution of the oxide film among these film-forming devices 1. Since the oxide film can be formed with a desired film thickness distribution, it is also possible to improve the yield of the wafer W and to achieve an improvement in energy efficiency, an improvement in production efficiency and a reduction in rejects. The correlation recorded in correlation acquisition step S63 includes the first correlation between at least a part of the width in the circumferential direction of the groove 222 and the thickness of the oxide film in an area adjacent to the at least a part in the outer circumference of the wafer W. It is therefore possible to form the oxide film with a desired film thickness distribution using the second shell body 22, in which at least a part of the width in the circumferential direction of the groove 222 is suitably adjusted. The correlation recorded in correlation acquisition step S63 includes the second correlation between the contact area between the leg 212 and the contact sections 223 at locations in the conveying width direction of the shell body 22 and the thickness of the oxide film in areas next to these locations in the outer circumference of the wafer W. It is therefore possible to form the oxide film with a desired film thickness distribution using the second shell body 22, in which the contact area between the leg 212 and the contact sections 223 is appropriately set at points in the conveying width direction of the shell body 22. The correlation recorded in correlation acquisition step S63 includes the third correlation between the contact area between the leg 212 and the contact sections 223 at locations in the conveying direction of the shell body 22 and the thickness of the oxide film in areas next to these locations in the outer circumference of the wafer W. It is therefore possible to form the oxide film with a desired film thickness distribution on the wafer W using the second shell body 22, in which the contact area between the leg 212 and the contact sections 223 is appropriately set at points in the conveying direction of the shell body 22. In particular, if the correlation captured in correlation capture step S63 includes all of the first to third correlations, the film thickness distribution can be controlled in a more detailed way using the shell body 22 obtained based on the first to third correlations. The process for forming an oxide film includes the shell preparation step S61. It is therefore possible to form the oxide film with a desired film thickness distribution by a simple process in which an operator in film formation step S66 selects the second shell body 22 that meets the application requirement from the multitude of types of shell bodies 22 that were prepared in shell body preparation step S61. Modifications As described above, the exemplary embodiment of the invention has been described in detail with reference to the drawings. However, the specific configurations are not limited to the exemplary embodiment described above, and various modifications and design changes within a scope that does not deviate from the core of the invention are included in the invention. For example, a portion of the preliminary oxide film formation step S62, the correlation acquisition step S63, the target film thickness distribution acquisition step S64, and the shell body configuration determination step S65 can be performed by an operator. Specifically, the operator can verify the film thickness distribution of the test oxide film as measured by a measuring device (preliminary oxide film formation step S62), verify the correlation as displayed on a computer display unit or on a sheet-like medium such as paper (correlation acquisition step S63), verify the target film thickness distribution of the oxide film based on product specifications or the like (target film thickness distribution acquisition step S64), and perform the shell body configuration determination step S65. The grooves 222 and contact sections 223 with predetermined configuration requirements can be provided by attaching a fastener to the recess 221, and the second shell body 22, which meets the application requirement, can be manufactured by selecting a fastener from a variety of fastener types. In a top view, the shell body 22 can be a rectangle with long sides parallel to the conveying direction, a square, a polygon other than a quadrilateral, a circle or an ellipse. Commercial applicability According to the method for determining an oxide film formation condition, the method for forming an oxide film, and the method for producing a wafer of the invention, it is possible to form the oxide film with the desired film thickness distribution, thereby improving the wafer yield and achieving improved energy efficiency, increased production efficiency, and a reduction in rejects. The product relating to the invention (an epitaxial silicon wafer with an LTO film serving as a back-side oxide film) is mainly used for logic devices. The invention contributes to higher precision in semiconductor devices and thus plays an important role in industrialization as a fundamental technology necessary for the development and improvement of advanced industrial products.The product relating to the invention can be used, for example, in control systems for automobiles, household appliances and medical devices, thereby achieving high-quality and highly reliable products. EXPLANATION OF THE CODES 1...Film forming device, 2...Film forming tray, 21...Support element, 211...Placement section, 212...Leg, 22, 23, 24, 25, 26...Tray body, 221...Recess, 222, 232, 242, 252, 262...Groove, 223...Contact section, 233, 243...First contact section, 254...Second contact section, G1...Output gas, W...Wafer

Claims

Method for determining an oxide film formation condition for forming an oxide film on a wafer using a film-forming device, wherein the film-forming device is configured to form the oxide film on the wafer using a film-forming shell comprising: a support element supporting an outer circumference of the wafer, and a shell body supporting the support element by heating the film-forming shell and supplying an initial gas to the wafer, wherein the support element comprises an annular placement section on which the wafer is placed and a leg extending downward from the placement section, wherein the shell body comprises: a cylindrical recess in which the support element is housed; a plurality of grooves along an outer edge of a bottom surface of the recess;and a contact section provided between a pair of adjacent slots and supporting the leg of the support element, wherein the wafer comprises a first wafer, wherein the shell body comprises a first shell body, wherein the oxide film comprises a first oxide film, wherein the method comprises: forming the first oxide film on the first wafer using the first shell body; determining a correlation between at least one configuration requirement of the slots and the contact section and a film thickness distribution of the oxide film; determining a target film thickness distribution of the oxide film; and determining, based on the film thickness distribution of the first oxide film and the correlation of the at least one configuration requirement, that enables the formation of the oxide film with the target film thickness distribution as an application requirement. Method for determining the oxide film formation condition according to claim 1, wherein the correlation includes a first correlation between at least a part of a width in a circumferential direction of each of the grooves and a thickness of the oxide film in a region adjacent to the at least a part in the outer circumference of the wafer. Method for determining the oxide film formation condition according to claim 1, wherein the film formation tray comprises a plurality of film formation trays, the tray body comprises a plurality of tray bodies, the film formation device is configured to form the oxide film on the wafer, which is supported by each of the film formation trays, while the plurality of film formation trays, which are provided with the tray bodies and arranged in the feed direction, are conveyed in a feed direction, and the correlation comprises a second correlation between a contact area between the leg and the contact section at a location in a conveying width direction orthogonal to the feed direction of the tray body and a thickness of the oxide film in a region adjacent to the location in the outer circumference of the wafer. Method for determining the oxide film formation condition according to claim 3, wherein the second correlation is a correlation in which, if the contact area at the point in the conveying width direction is larger, the oxide film in the area next to the point is thinner. Method for determining the oxide film formation condition according to claim 1, wherein the film formation shell comprises a plurality of film formation shells, the shell body comprises a plurality of shell bodies, the film formation device is configured to form the oxide film on the wafer, supported by each of the film formation shells, while the plurality of film formation shells, which are provided with the shell bodies and arranged in the feed direction, are conveyed in a feed direction, the contact section comprises a plurality of contact sections, and the correlation comprises a third correlation between a contact area between the leg and the contact sections at locations in the feed direction of the shell body and in a direction opposite to the feed direction and a thickness of the oxide film in areas adjacent to the locations in the outer circumference of the wafer. Method for determining the oxide film formation condition according to claim 5, wherein the third correlation is a correlation in which, if the contact area is larger at the locations in the feed direction and in the opposite direction to the feed direction, the oxide film is thicker in the areas next to the locations. Method for forming an oxide film, wherein the method comprises: performing the method for determining the oxide film formation condition according to any one of claims 1 to 6; and forming a second oxide film on a second wafer using a second tray body that meets the application requirement, wherein the oxide film includes the second oxide film, the wafer includes the second wafer, and the tray body includes the second tray body. Method for forming the oxide film according to claim 7, wherein the shell body comprises a plurality of shell body types that differ from one another in at least one configuration requirement, wherein the method further comprises preparing the plurality of shell body types that differ from one another in at least one configuration requirement, wherein in the formation of the second oxide film the second oxide film is formed using the second shell body by selecting the second shell body that satisfies the at least one configuration requirement for any one of the plurality of shell body types. Method for producing a wafer, comprising forming the oxide film on the second wafer by the oxide film forming method according to claim 7.

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