Silicon wafers and methods for their production

Abstract

A method for producing a silicon wafer, characterized in that it comprises: a step to cut a silicon single crystal containing boron as an acceptor to obtain a non-heat-treated silicon wafer, which is a wafer that has not been subjected to heat treatment at a temperature of 300°C or more; a step towards determining a boron concentration with respect to the unheat-treated silicon wafer; and a step towards determining an oxygen donor concentration with respect to the non-heat-treated silicon wafer; wherein a determination of whether a heat treatment at a temperature of 300°C or more and 800°C or less should be carried out on the non-heat-treated silicon wafer is made on the basis of a boron concentration, determined in the step to determine a boron concentration, and an oxygen donor concentration, determined in the step to determine an oxygen donor concentration, where in one case, if a condition exists that the boron concentration is 5x10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and the oxygen donor concentration is 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3or less, is not fulfilled with regard to the non-heat-treated silicon wafer, the provision is a provision to carry out polishing with regard to the non-heat-treated silicon wafer without carrying out heat treatment with it at a temperature of 300°C or more.

Description

TECHNICAL AREA

[0001] This invention relates to a silicon wafer in which LPDs are reduced and which can be advantageously used as a substrate for a semiconductor device or the like, and to a method for producing the silicon wafer. BACKGROUND OF THE INVENTION

[0002] A semiconductor substrate used in a semiconductor device is fabricated from a silicon wafer cut from a silicon single-crystal ingot. A silicon single crystal for this purpose is typically produced by the Czochralski method (hereinafter referred to as the "CZ method"). In the CZ method, a starting crystal material is melted inside a crucible located at the bottom of a chamber. A seed crystal is brought into contact with the surface of the resulting melt and pulled upwards while the seed crystal (and the crucible) rotates around its own axis, growing a single crystal beneath it.

[0003] A single crystal obtained by the CZ process contains a conical shoulder region, which is a region whose diameter gradually increases from the diameter of the seed crystal; a cylindrical body region located at the bottom of the shoulder region; and an inverted conical tail region located below the body region. The body region is machined to a specific diameter by cylindrical milling using a cylindrical milling machine, and then the shoulder and tail regions are removed from the single crystal. The body region is then cut to obtain silicon wafers, and processes such as lapping, chamfering, etching, and grinding are performed on the silicon wafers to obtain silicon wafers used for semiconductor substrates.

[0004] Various inspections are performed on such silicon wafers. For example, a method that uses the reflection of a laser beam from a wafer surface is employed to check for defects that appear as concavities and convexities on the surface of a silicon wafer. When a laser beam with a wavelength in the visible to ultraviolet range is emitted, these defects (LPDs: light spot defects) are observed as points of light. That is, a defect detectable as an LPD is a defect that is present on the surface of a wafer.

[0005] Fig. Figure 1 illustrates an example of the distribution of laser photons (LPDs) observed as points of light on a silicon wafer. This type of LPD distribution can be obtained by measuring the reflected light (including scattered light) of a laser beam at any part of the wafer along its entire surface. For example, reflected light from a laser beam across the entire surface of a wafer can be determined by shining a point laser beam onto the surface of the wafer while the wafer rotates in the plane around its center and by moving a beam array radially around the wafer. The presence or absence, as well as the size, of LPDs can be determined based on the intensity distribution of the reflected light. Using this method, LPDs down to a minimum size of approximately 26 nm can be determined.Because it is not necessary to perform a specific treatment on the wafer before observing LPDs, defects that appear as convexities and concavities on the surface of a wafer can be easily observed according to this method.

[0006] When LPDs are observed using a scanning electron microscope (SEM), it is found that some LPDs are protrusions from the wafer surface and some LPDs are concavities formed in the wafer surface. Fig. 2 is a SEM image of an LPD in the form of a protruding part, and Fig. Figure 3 is a SEM image of an LPD in the shape of a concavity.

[0007] Various factors cause the formation of LPDs. For example, some LPDs are caused by machining (see patent literature 1) and some LPDs are associated with defects introduced during crystal growth (growth defects) (see patent literature 2).

[0008] Patent reference 3 discloses a method for producing a silicon wafer, comprising a heat treatment process in which a silicon wafer, cut from a defect-free silicon single crystal and subjected to mirror polishing, is heat treated for a period of 4 hours or more and 6 hours or less at a temperature of 500°C or more and 600°C or less, and a repolishing process in which the silicon wafer undergoing the heat treatment process is repolished to achieve a polishing amount of 1.5 µm or more. According to patent reference 3, this process reduces low defect rates (LPDs) to an absolute minimum, and silicon wafers exhibiting low rejection rates in inspection and shipping can be produced with advantageous yield. LITTE OF PRINT PATENT LITERATURE Patent Literature 1: JP 2011-42536 A Patent Literature 2: JP 2001-261493 A Patent Literature 3: JP 2013-4825 A Patent Literature 4: JP 2010-267846 A SUMMARY OF THE INVENTIONAL PROBLEM

[0009] These inventors discovered a new type of LPD that has never been reported before. Specifically, the LPDs they discovered are closely related to boron and oxygen donor concentrations on a silicon wafer and are unevenly distributed across the wafer. These LPDs are referred to as "unevenly distributed LPDs." Because the density of the unevenly distributed LPDs is extremely low compared to the density of previously reported LPDs, it is currently believed that they do not affect the properties of devices fabricated using the silicon wafers. However, there is a possibility that in the future, the unevenly distributed LPDs could cause problems, such as in the advancement of microfabrication of conduction patterns for semiconductor devices.

[0010] Therefore, an objective of this invention is to provide a method for producing a silicon wafer that can eliminate or reduce the unevenly distributed LPDs, and a silicon wafer wherein the unevenly distributed LPDs are eliminated or reduced.

[0011] Another objective of this invention is to provide a method for producing a silicon wafer that can modify or suppress the occurrence of unevenly distributed LPDs, and a silicon wafer in which the occurrence of unevenly distributed LPDs is prevented or suppressed. SOLUTION TO THE PROBLEM

[0012] The inventors observed LPDs on the surface of wafers undergoing processing steps equivalent to those of a processed product and obtained data on the distribution of the LPDs. When the observational data for at least 25 wafers were compiled, it was found that unique LPDs (non-uniformly distributed LPDs) were present on the wafers, distributed unevenly in a circular or ring shape (the area between two concentric circles). Therefore, the inventors investigated the conditions under which such non-uniformly distributed LPDs occur.

[0013] As a result, the inventors found that a large number of unevenly distributed LPDs occur on a wafer in which the boron (B) concentration and the oxygen (O) donor concentration are approximately equal and in which these concentrations lie within a specific range. In other words, the unevenly distributed LPDs are a unique phenomenon that occurs only when the boron and oxygen donor concentrations are approximately equal, and does not occur when there is a concentration difference of a certain magnitude between the boron and oxygen donor concentrations.

[0014] These inventors further discovered that a large number of unevenly distributed LPDs appear on wafers cut from a silicon single-crystal ingot 50 days after ingot growth is complete. In other words, the unevenly distributed LPDs do not appear when the time period from completion of the silicon single-crystal ingot growth until the wafer is cut from the ingot is short to a certain extent.

[0015] When areas where unevenly distributed LPDs were observed on wafers were subjected to elemental analysis, nickel (Ni) was found in the unevenly distributed LPDs that form protruding parts of the wafer surface (see Fig. 2), and copper (Cu) in the unevenly distributed LPDs that form concavities in the wafer surface (see Fig. 3). The analysis of nickel and copper was carried out using Auger electron spectroscopy.

[0016] Based on the above results, it is considered that the unevenly distributed LPDs are formed with a contribution factor that nickel or copper are trapped in p / n-type inversion (mixing) regions, wherein a boron concentration and an oxygen donor concentration lie within specific ranges, over time after completion of crystal growth, where the p / n-type inversion region is a region in which a boron concentration and an oxygen donor concentration are approximately equal.

[0017] As a result of intensive studies, the inventors have found that the unevenly distributed LPDs disappear or decrease when heat treatment is performed. Although the detailed mechanism by which the unevenly distributed LPDs, which appear as concavities and convexities on the surface, disappear or decrease as a result of the heat treatment is not well understood, it is thought that the release of trapped nickel or copper upon application of heat is involved in the mechanism.

[0018] The inventors also found that when a wafer is cut from a silicon single-crystal ingot within 50 days of ingot crystal growth being complete, even if the boron and oxygen donor concentrations of the ingot are within the specific ranges described above, virtually no (or absolutely no) unevenly distributed LPDs appear in the cut wafer, and virtually no unevenly distributed LPDs appear thereafter. That is, the occurrence of unevenly distributed LPDs is prevented or suppressed by cutting a wafer from the ingot within a specific period.Although the detailed mechanism of this phenomenon is not well understood, it is thought that once a wafer is cut from an ingot, Ni or copper is more likely to be concentrated on the surface of the wafer than to be trapped in p / n-type inversion regions, and this fact is involved in the mechanism mentioned above.

[0019] Patent literature 3 describes how LPDs are determined on wafers where the surface Cu concentration is 1.19 × 10 9 cm -2 (Atoms / cm² 2 ) is, and in wafers where the surface Ni concentration is 2.6 × 10 8 cm -2 In contrast, when the inventors measured using the wafer surface analysis (WSA) method, the surface copper concentration and the surface nickel concentration of wafers on which the unevenly distributed LPDs were determined were 1 × 10 7 cm -2or less for both the surface copper concentration and the surface nickel concentration. Specifically, the WSA procedure involved the analysis of a recovered liquid containing impurities using the inductively coupled plasma mass spectrometry (ICP-MS) method.

[0020] It is difficult to identify the route by which nickel and copper are introduced into the wafers. Sources of such nickel and copper could include, for example, the starting material and quartz crucibles used to produce the silicon single crystal, as well as components used during the processes from an initial step to the final wafer fabrication process, such as consumables like slurries used in the respective processes.

[0021] The density of LPDs in wafers, as observed by the inventors, was low (e.g., 5 to 30 LPDs per wafer with a diameter of approximately 300 mm (approximately 12 inches)), and thus, when observing a single wafer, it is difficult to determine that a property exists in the distribution of the LPDs. However, when data from a large number of wafers are aggregated, the inventors found that a property exists regarding the distribution of the LPDs among the wafers. For wafers with a diameter of, for example, approximately 300 mm, in which the observed LPDs are distributed in the form of concentric circles around the center of the wafer, there are cases where the LPD density is relatively high in a circular area with a radius of 100 mm from the center, and there are cases where the LPD density is relatively high in an annular area with a radius of 50 to 100 mm from the wafer center.

[0022] When semiconductor devices are fabricated using silicon wafers in which the LPDs (non-uniformly distributed LPDs) are formed, as observed by the inventors, although a problem would not currently arise, there is a possibility that a problem may arise in the future as the microfabrication of conduction patterns of semiconductor devices progresses or the like.

[0023] This invention has been completed in view of the findings described above, and the object of this invention is a method for producing a silicon wafer, described in the following points (A) to (F), and silicon wafers, described in the following points (G) and (H).

[0024] (A) Method for producing a silicon wafer, comprising, when in relation to a non-heat-treated silicon wafer, a boron concentration of 5 × 10 14 atoms / cm² 3 or more and 7 × 10 14 atoms / cm²3 or less and an oxygen donor concentration of 4 × 10 14 Donors / cm 3 or more and 8 × 10 14 Donors / cm 3 or less, is the performance of a heat treatment at a temperature of 300°C or more with the unheat-treated silicon wafer.

[0025] (B) Method for producing a silicon wafer, containing, when in relation to a silicon single-crystal ingot or a block cut from the ingot, a boron concentration of 5 × 10 14 atoms / cm² 3 or more and 7 × 10 14 atoms / cm² 3 or less and an oxygen donor concentration of 4 × 10 14 Donors / cm 3 or more and 8 × 10 14 Donors / cm 3 or less, cutting a wafer from the ingot or block within 50 days of completion of crystal growth of the ingot.

[0026] (C) Method for producing a silicon wafer comprising: a step to cut a silicon single crystal containing boron as an acceptor and obtain a non-heat-treated silicon wafer; a step towards determining a boron concentration with respect to the unheat-treated silicon wafer; and a step towards determining an oxygen donor concentration with respect to the non-heat-treated silicon wafer; wherein a determination of whether a heat treatment at a temperature of 300°C or more should be carried out on the non-heat-treated silicon wafer is made on the basis of a boron concentration, determined in the step to determine a boron concentration, and an oxygen donor concentration, determined in the step to determine an oxygen donor concentration.

[0027] (D) Method for producing a silicon wafer, comprising: a step to determine a boron concentration with respect to a silicon single-crystal ingot containing boron as an acceptor, or a block cut from the ingot; and a step towards determining an oxygen donor concentration in relation to the bar or block; wherein a determination of whether a wafer is cut from the ingot or block is made within 50 days after completion of the crystal growth of the ingot, based on a boron concentration determined in the step to determine a boron concentration, and an oxygen donor concentration determined in the step to determine an oxygen donor concentration.

[0028] (E) A method for producing a silicon wafer, wherein, with respect to a silicon single-crystal ingot containing boron as an acceptor, or with respect to a block cut from the ingot, when the wafer is cut from the ingot or block at a time more than 50 days after completion of the crystal growth of the ingot, which is a case that satisfies a condition that the boron concentration is 5 × 10 14 atoms / cm² 3 or more 7 × 10 14 atoms / cm² 3 or less, and the oxygen donor concentration is 4 × 10 14 Donors / cm 3 or more and 8 × 10 14 Donors / cm 3 or less, a heat treatment is carried out at a temperature of 300°C or more with the wafer that has been cut.

[0029] (F) A method for producing a silicon wafer, wherein, with respect to a silicon single-crystal ingot containing boron as an acceptor, or a block cut from the ingot, then, if a wafer is cut from the ingot or block within 50 days after completion of the crystal growth of the ingot, which is a case that satisfies a condition that the boron concentration is 5 × 10 14 atoms / cm² 3 or more and 7 × 10 14 atoms / cm² 3 or less and the oxygen donor concentration 4 × 10 14 Donors / cm 3 or more and 8 × 10 14 Donors / cm 3 or less, a heat treatment at a temperature of 300°C or more is not carried out on the cut wafer.

[0030] (G) Silicon wafer, which is a particle monitor wafer for recording particles on a semiconductor device manufacturing line, wherein the silicon wafer is produced by one of the manufacturing processes according to (A) to (F) as described above.

[0031] (H) Silicon wafer that does not contain COPs and dislocation clusters, wherein the silicon wafer is produced by one of the manufacturing processes according to (A) to (F) as described above.

[0032] The term "non-heat-treated silicon wafer" refers to a wafer that has not undergone heat treatment at a temperature of 300°C or higher.

[0033] In this case, the point in time of “completion of crystal growth” with respect to an ingot refers to a point in time at which, after separation of a single crystal from a melt used for single crystal growth, the surface temperature of the single crystal becomes room temperature (30°C) or less. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0034] According to a method for producing a silicon wafer of this invention, by appropriately determining the necessity of carrying out a heat treatment at a temperature of 300°C or more, based on a boron concentration and an oxygen donor concentration of a non-heat-treated silicon wafer, a silicon wafer in which unevenly distributed LPDs are absent or reduced can be obtained.

[0035] According to another method for producing a silicon wafer of this invention, by appropriately determining the need to cut a wafer from a silicon single-crystal ingot or block cut from the ingot, a silicon wafer can be obtained within 50 days after completion of the crystal growth of the ingot, based on a boron concentration and an oxygen donor concentration of the ingot or block, wherein the occurrence of unevenly distributed LPDs is prevented or suppressed.

[0036] In a silicon wafer of this invention, unevenly distributed LPDs are either absent or reduced. BRIEF DESCRIPTION OF DRAWINGS [ Fig. 1] Fig. Figure 1 is a view that illustrates an example of a distribution of LPDs on a silicon wafer. [ Fig. 2] Fig. 2 is a SEM image of an LPD that has the shape of a bulge. [ Fig. 3] Fig. 3 is a SEM image of an LPD that has the shape of a concavity. [ Fig. 4] Fig. Figure 4 is a diagram that illustrates a relationship between boron concentration, oxygen donor concentration, and whether or not LPDs occur. [ Fig. 5] Fig. Figure 5 is a diagram showing a relationship between types of ingots and the number of days until wafers are cut after crystal growth is complete. DESCRIPTION OF EXAMPLES OF EXECUTION

[0037] A characteristic feature of a first manufacturing process of this invention is "that in a case where, with respect to a non-heat-treated silicon wafer, a boron concentration of 5 × 10 14 atoms / cm² 3 or more and 7 × 10 14 atoms / cm² 3 or less and an oxygen donor concentration of 4 × 10 14 Donors / cm 3 or more and 8 × 10 14Donors / cm 3 or less, a heat treatment is carried out at a temperature of 300°C or more with the unheat-treated silicon wafer.”

[0038] The resistance (resistance measured after performing a donor removal heat treatment) of the silicon wafer with a boron concentration of 5 × 10 14 up to 7 × 10 14 atoms / cm² 3 The resistance is 19 to 26 Ω·cm, which corresponds to normal resistance. The term "donor removal heat treatment" refers to a heat treatment to eliminate oxygen donors (dioxygen complexes acting as n-type dopants), and, for example, a heat treatment at 650 to 700°C for 10 to 60 minutes can be used as a donor removal heat treatment.

[0039] In an area where the boron concentration is 5 × 10 14 up to 7 × 10 14 atoms / cm² 3 and the oxygen donor concentration 4 × 10 14 up to 8 × 1014 Donors / cm 3 It can be said that the boron (acceptor) concentration and the donor concentration are approximately equal. In this range, unevenly distributed LPDs can occur, contributing to p / n-type inversions, where nickel or copper may be trapped. These unevenly distributed LPDs can be eliminated or reduced by heat treatment at a temperature of 300°C or higher.

[0040] LPDs include LPDs that exhibit a non-uniform distribution (non-uniformly distributed LPDs) on a wafer and LPDs that do not exhibit a non-uniform distribution on a wafer. It is assumed that the causes of these types of LPDs are different. LPDs for which the presence / absence of the LPDs (whether the density is high or low) can be estimated based on the boron concentration and oxygen donor concentration according to this invention are LPDs that exhibit a non-uniform distribution on a non-heat-treated silicon wafer.

[0041] Whether LPDs are "unevenly distributed LPDs" or not is determined as described later. Using a Surfscan SP2, manufactured by KLA-Tencor Corporation, as an LPD evaluation system, LPDs on the surface of a wafer are analyzed in high-sensitivity mode using "dark field," "composite," "tilted," and "37 nm" (minimum grain size) as settings for measuring ch / size, obtaining data regarding the distribution of the LPDs. When observational data for at least 25 wafers are combined, LPDs distributed in a circular or ring shape (area between two concentric circles) on the wafers are considered unevenly distributed LPDs.

[0042] The area of ​​a region in which the LPDs are distributed in a circular or ring shape is within a range of 10 to 70% of the total surface area of ​​the wafer. In this case, the expression "LPDs are distributed in a circular or ring shape" means that the LPD density in the relevant circular or ring shape is five times or more greater than the LPD density in any region other than the circular or ring shape on the wafer. In other words, if a suitable circle or ring, concentric with the wafer, is drawn on the wafer (the area of ​​the circle or ring being within a range of 10 to 70% of the total surface area of ​​the wafer), and the LPD density within the circle or ring is five times or more greater than the LPD density in any region other than the circle or ring, then the LPDs are determined to be unevenly distributed on the wafer.

[0043] A boron concentration N can be determined by converting (conversion according to ASTM-F723) a resistance ρ (Ω·cm) of a silicon wafer, measured by the four-point sampling method after donor removal treatment according to the following formula (1). N(atom / cm3)=(1.330×1016) / ρ+(1.082×1017) / (ρ×[1+(54.56×ρ)1.105])

[0044] An oxygen donor concentration TD can be determined with respect to a silicon wafer using the relationship between the resistance of the silicon single crystal and the carrier concentration using the following formula (2) or (3) based on a resistance ρ BEF (Ω·cm) before performing donor removal heat treatment and resistance ρ Aft(Ω·cm) after performing donor removal heat treatment. The following formula (3) can be used for a p / n inversion region, and the following formula (2) can be used for a region other than a p / n inversion region. TD(donors / cm3)=1.39×1016×(1 / ρAft−1 / ρBef) TD(donors / cm3)=1.39×1016 / ρAft+0.5×1015 / ρBef

[0045] A feature of a second manufacturing process of this invention is that “in a case where, with respect to a silicon single-crystal ingot or block cut from the ingot, a boron concentration of 5×10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and an oxygen donor concentration of 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3or less, a wafer is cut from the ingot or block within 50 days of completion of the ingot's crystal growth."

[0046] The measurement of boron concentration and oxygen donor concentration can be carried out in a similar manner to the measurement in the first manufacturing process of this invention. For example, the measurement can be performed on a wafer selected for measurement from the ingot or block, and it is not necessary to slice all production wafers en bloc together with the slice of a wafer selected for measurement. To perform the slicing of production wafers within 50 days after completion of the ingot's crystal growth, it is necessary, depending on the measurement results for the boron and oxygen donor concentrations of the ingot or block, to carry out the measurement within 50 days of completion of the ingot's crystal growth.

[0047] A characteristic feature of a third manufacturing process of this invention is that the process includes: "a step for cutting a silicon single crystal containing boron as an acceptor, obtaining an unheated silicon wafer; a step for determining a boron concentration with respect to the unheated silicon wafer; and a step for determining an oxygen donor concentration with respect to the unheated silicon wafer; wherein a determination of whether or not heat treatment is carried out on the unheated silicon wafer at a temperature of 300°C or more is based on a boron concentration determined in the step for determining a boron concentration, and an oxygen donor concentration determined in the step for determining an oxygen donor concentration."

[0048] Regarding the determination, if a condition exists that the boron concentration is 5x1014 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and the oxygen donor concentration is 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3 or less, is not fulfilled with respect to the non-heat-treated silicon wafer, the provision shall be a provision for carrying out polishing with respect to the non-heat-treated silicon wafer without carrying out heat treatment at a temperature of 300°C or more.

[0049] Regarding the determination, if a condition is met that the boron concentration is 5x10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and the oxygen donor concentration is 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3or less, in relation to the non-heat-treated silicon wafer, the provision shall be a provision for carrying out polishing after carrying out heat treatment at a temperature of 300°C or more in relation to the non-heat-treated silicon wafer.

[0050] A feature of a fourth manufacturing process of this invention is that the process includes: "a step for determining a boron concentration with respect to a silicon single-crystal ingot containing boron as an acceptor, or a block cut from the ingot; and a step for determining an oxygen donor concentration with respect to the ingot or block; wherein a determination of whether a wafer is cut from the ingot or block within 50 days of completion of the crystal growth of the ingot or not is based on a boron concentration determined in the step for determining a boron concentration, and an oxygen donor concentration determined in the step for determining an oxygen donor concentration."

[0051] Regarding the determination, if a condition exists that the boron concentration is 5x10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3or less and the oxygen donor concentration is 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3 or less, in relation to the ingot or block, the provision shall be a provision to cut a wafer from the ingot or block within 50 days after completion of the crystal growth of the ingot.

[0052] In the first and third manufacturing processes of this invention, it is not necessary to perform the measurement of the boron concentration and the oxygen donor concentration with respect to the unheated silicon wafer within 50 days after completion of the ingot's crystal growth. If the measurement is performed within 50 days after completion of the ingot's crystal growth, unevenly distributed LPDs are not expected to be formed in the unheated silicon wafer at that time. In such an unheated silicon wafer, wherein the boron concentration is 5 × 10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and the oxygen donor concentration 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3If the wafer is less than or equal to the surface area, there is a possibility that unevenly distributed LPDs will appear over time. The occurrence of unevenly distributed LPDs on such a wafer can be prevented or suppressed by heat-treating it at a temperature of 300°C or higher.

[0053] In the fifth and sixth manufacturing processes of this invention, heat treatment is carried out at a temperature of 300°C or more, or not, depending on the boron concentration and the oxygen donor concentration of the ingot or block, as well as the time at which a wafer is cut from the ingot or block.

[0054] A feature of the fifth manufacturing process of this invention is that "with respect to a silicon single-crystal ingot which receives boron as an acceptor, or with respect to a block which is cut from the ingot, in a case where a wafer is cut from the ingot or block at a time period of 50 days after completion of crystal growth of the ingot, i.e., in a case which satisfies the condition that the boron concentration is 5x10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and the oxygen donor concentration 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3 or less, a heat treatment is carried out on the cut wafer at a temperature of 300°C or more.

[0055] Regarding a bar or block that meets a condition that the boron concentration of it is 5x10 14 atoms / cm² 3or more and 7×10 14 atoms / cm² 3 or less and the oxygen donor concentration is 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3 If the LPD is less than 50 days old, there is a possibility that unevenly distributed LPDs have formed in a wafer cut from the ingot or block more than 50 days after the ingot's crystal growth was complete. Performing heat treatment at 300°C or higher on such a wafer can eliminate or reduce any unevenly distributed LPDs that have already formed.

[0056] A characteristic of the sixth manufacturing process of this invention is that "with respect to a silicon single-crystal ingot containing boron as an acceptor, or a block cut from the ingot, then, if a wafer is cut from the ingot or block within 50 days after completion of the crystal growth of the ingot, which is a case where a condition is met that the boron concentration is 5×10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and the oxygen donor concentration is 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3 or less, heat treatment at a temperature of 300°C or more is not carried out on the cut wafer.

[0057] Regarding a bar or block that meets a condition that the boron concentration of it is 5x10 14 atoms / cm² 3 or more and 7×1014 atoms / cm² 3 or less and the oxygen donor concentration is 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3 If the ingot or block is less than 50 days old, the probability that unevenly distributed LPDs will not form in a wafer cut from the ingot or block within 50 days of ingot crystal growth is complete is extremely high, and the probability of unevenly distributed LPDs forming thereafter is also low. In this case, even if heat treatment at 300°C or higher is not performed on the cut wafer, a silicon wafer with essentially no unevenly distributed LPDs can be obtained in most cases. By omitting heat treatment, the time and cost required to produce the silicon wafer can be further reduced.

[0058] A feature of a silicon wafer of this invention is that a silicon wafer is “a particle monitor wafer for recording particles on a semiconductor device manufacturing system, wherein the silicon wafer is produced by one of the manufacturing processes described above”.

[0059] A particle monitor wafer is a so-called "dummy wafer" and is fed into a semiconductor device production line separately from the wafer fabrication process. Particles are detected by a surface inspection system that inspects the surface of a wafer. A surface inspection system also detects crystal defects on the wafer surface. The detected crystal defects cannot necessarily be distinguished from particles. In the silicon wafer of this invention, because the number of LPDs (Limited Photon Defects) is significantly reduced, using the silicon wafer as a particle monitor wafer makes it possible to precisely evaluate the number (density) of particles present on the wafer surface when an inspection is performed by a surface inspection system.

[0060] A characteristic of another silicon wafer of this invention is that "the silicon wafer contains no COPs and dislocation clusters, wherein the silicon wafer is produced by one of the manufacturing processes described above".

[0061] Crystal-derived particles (COPs) are aggregates of vacancies (microholes) that lack atoms and form a crystal lattice during single-crystal growth, while dislocation clusters are aggregates of interstitial silicon excessively inserted between lattices. During semiconductor device fabrication, when COPs present near the wafer surface are introduced into an oxide film during thermal oxidation of the wafer surface, the gate-oxide integrity (GOI) properties of the semiconductor device are degraded, and the dislocation clusters also become a source of defects in device properties. Thus, COPs and dislocation clusters adversely affect device properties.

[0062] By fabricating a semiconductor device from a silicon wafer formed from a defect-free region containing no COPs or dislocation clusters, the degradation of properties or defects described above can be avoided. A silicon wafer free of COPs and dislocation clusters can be obtained by slicing the wafer from a silicon single-crystal ingot free of COPs and dislocation clusters. When fabricating a silicon single crystal using the Czochralski method, a silicon single crystal free of COPs and dislocation clusters can be produced by appropriately controlling the ratio V / G of a silicon single-crystal pull rate V to a temperature gradient G in a growth direction within the interior of the single crystal immediately after pull (see, for example, the patent literature cited above 4).

[0063] A process for producing a silicon wafer according to a first embodiment of this invention is described below. First, a silicon single crystal is grown using the CZ process. At this stage, the silicon single crystal is doped with boron as an acceptor. Then, a silicon single-crystal ingot obtained is cut, yielding an unheat-treated silicon wafer. Subsequently, lapping, circumferencing, milling, and etching are performed successively on the unheat-treated silicon wafer.

[0064] The boron and oxygen donor concentrations of the resulting unheated silicon wafer are then determined. When cutting the wafer from the silicon single-crystal ingot, the silicon single crystal can first be cut, subdivided into several blocks in the axial direction, and a wafer can be cut from the respective blocks. Unheated silicon production wafers can be cut separately from the unheated silicon single-crystal ingot (sample for evaluation) for measuring the boron and oxygen donor concentrations, e.g., after determining the boron and oxygen donor concentrations. The boron and oxygen donor concentrations of the respective wafers (unheated silicon wafers) can be determined based on the formulas (1) to (3) described above.

[0065] Using the determined boron concentration and oxygen donor concentration, a determination is made, depending on whether heat treatment is carried out on the unheat-treated silicon wafer or not, based on whether the boron concentration of the silicon wafer is 5×10 14 up to 7×10 14 atoms / cm² 3 and the oxygen donor concentration 4×10 14 up to 8×10 14 Donors / cm 3 Regarding a portion (area) where the boron and oxygen donor concentrations of the unheat-treated silicon wafer are measured, the measurement can be performed at multiple points on the wafer's surface or at a single center point. In either case, it is possible to determine whether or not heat treatment has been carried out.

[0066] Determining whether or not heat treatment should be performed can also be carried out in multiple batches. Silicon wafers cut from the same block are used to ensure they belong to the same batch. If a block is long, silicon wafers obtained after subdividing the block can be defined as a batch. When performing a determination in batch units, the boron and oxygen donor concentrations can be determined from a portion of the batch or from a sample extracted from a portion of the block that is the source of that batch, based on formulas (1) to (3) described above, and the boron and oxygen donor concentrations determined can be used as the boron and oxygen donor concentrations for the entire batch.

[0067] The heat treatment can be performed for 1 to 3,600 seconds at a temperature of 300°C or more and 800°C or less. The time period for this heat treatment is extremely short compared to the time period required for the heat treatment according to the method described in patent literature 3. The heat treatment of this invention can be carried out, for example, by performing a lamp coating suitable for short-term heat treatment. A heat treatment performed, for example, at a temperature of 650 to 800°C for one second or more can also be used as a heat treatment. It is also possible to perform a heat treatment for a different purpose, such as donor removal (heat treatment to eliminate or reduce unevenly distributed LPDs), as a heat treatment of this invention.

[0068] Therefore, there is a high probability that unevenly distributed LPDs are present in a wafer whose boron concentration is 5x10 14 up to 7×10 14 atoms / cm² 3 and its oxygen donor concentration of 4×10 14 up to 8×10 14 Donors / cm 3 If unevenly distributed LPDs are present, they are eliminated or reduced by heat treatment. After heat treatment, the silicon wafer is polished. Polishing is performed regardless of whether the unheated silicon wafer contains unevenly distributed LPDs (polishing is not a special process based on the presence of unevenly distributed LPDs) and is a standard polishing process in the fabrication of silicon wafers for semiconductors.

[0069] It is desirable that the heat treatment of this invention be carried out before the polishing process, and even in the event that the polishing is carried out again for some reason after the polishing process has been carried out once, it is desirable to carry out the heat treatment before the (initial) polishing process.

[0070] If there is one or a large number of the non-heat-treated silicon wafers or samples for evaluation that meet the condition that the boron concentration is 5x10 14 up to and 7×10 14 atoms / cm² 3 is and the oxygen donor concentration is 4×10 14 up to 8×10 14 Donors / cm 3 If the heat treatment can be carried out in a batch unit with respect to the batch containing the unheat-treated silicon wafers or samples.

[0071] On the other hand, in a case where it is not determined with respect to a silicon wafer that the boron concentration is 5x10 14 up to 7×10 14 atoms / cm² 3 is and the oxygen donor concentration is 4×10 14 up to 8×10 14 Donors / cm 3 Based on the determined boron and oxygen donor concentrations, the probability that the unevenly distributed LPDs are not formed in the silicon wafer is high. In this case, polishing is performed on the silicon wafer without heat treatment. A case where polishing is performed without heat treatment can also be one that simultaneously fulfills conditions A and B, for example. A: It is determined that the boron concentration is 5x10 14 up to 10×10 14 atoms / cm² 3 and the oxygen donor concentration 1×10 14 up to 11×10 14 Donors / cm3 is. B: It is not determined that the boron concentration is 5x10 14 up to 7×10 14 atoms / cm² 3 and the oxygen donor concentration 4×10 14 up to 8×10 14 Donors / cm 3 is.

[0072] In a case of applying the boron concentration and the oxygen donor concentration of a non-heat-treated silicon wafer or sample for evaluation as the boron concentration and oxygen donor concentration of a batch, in which the non-heat-treated silicon wafer or sample for evaluation is contained, if a condition is met that the boron concentration is 5x10 14 up to 7×10 14 atoms / cm² 3 and the oxygen donor concentration of 4×10 14 up to 8×10 14 Donors / cm 3If the requirements are not met, polishing of all silicon wafers in the relevant batch can be carried out without heat treatment. In any case, after polishing, the silicon wafer is washed, and a polished wafer is obtained.

[0073] A method for producing a silicon wafer according to a second embodiment of this invention is described below. First, a silicon single-crystal ingot is grown in the same manner as in the production method of the first embodiment. At least one wafer for measuring a boron concentration and an oxygen donor concentration is cut from the ingot. The ingot can also be cut into a block, and a measurement wafer and a production wafer can be cut from the block.

[0074] The boron concentration and the oxygen donor concentration of the wafer are then measured within 50 days after completion of crystal growth. If the result shows that the boron concentration is 5 x 10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and the oxygen donor concentration 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3 If the ingot's crystal growth rate is less than 50 days, the production wafers are cut from the ingot within that time. This prevents or suppresses the occurrence of unevenly distributed LPDs after wafer cutting. The thickness of the cut wafers can be, for example, 0.8 to 1.5 mm, with a diameter of approximately 300 mm.

[0075] If it is not determined that the boron concentration is 5x10 14 atoms / cm² 3or more and 7×10 14 atoms / cm² 3 or less and the oxygen donor concentration 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3 If the ingot is less than 50 days old, the time period for cutting the wafers from the ingot is not particularly limited. That is, in this case, even if the ingot is stored as is, because the probability of unevenly distributed LPDs occurring over time is extremely low, the production wafer can be cut from the ingot within 50 days of the ingot's crystal growth being complete, or it can be cut from the ingot after 50 days or more have passed since the ingot's crystal growth was complete.

[0076] After cutting the wafers, the processes beginning with polishing are carried out in the same way as in the first embodiment of this invention. EXAMPLES<Beispiel 1>

[0077] Boron concentration and oxygen donor concentration at a single center point of the wafers were determined with respect to the unheated silicon wafers in which unevenly distributed LPDs were observed and with respect to the unheated silicon wafers in which unevenly distributed LPDs were not observed. None of these unheated silicon wafers contained COPs or dislocation clusters. The boron concentration was determined by the procedure described above using formula (1). The oxygen donor concentration was determined by the procedure described above using formulas (2) or (3). Whether unevenly distributed LPDs were present on the respective wafers was determined by the procedure described above with respect to the distribution of LPDs by combining the data for 25 wafers.In areas of the aforementioned non-heat-treated silicon wafers where the unevenly distributed LPDs were observed, the LPD density was high, equivalent to 5 to 14 times the LPD density in other areas.

[0078] Fig. Figure 4 is a diagram summarizing the above results and showing the relationship between boron concentration, oxygen donor concentration, and whether or not unevenly distributed LPDs occur. (Related to...) Fig. 4. It is noted that in most of the non-heat-treated silicon wafers where unevenly distributed LPDs were observed, the boron concentration was within a range of 5x10 14 up to 7×10 14 atoms / cm² 3 and the oxygen donor concentration within a range of 4×10 14 up to 8×10 14 Donors / cm 3 was.

[0079] By subjecting the untreated silicon wafers to heat treatment at 650°C for 3 seconds to 30 minutes, the density of the unevenly distributed LPDs observed at the wafer surface could be significantly reduced. As a result of the heat treatment, although the density of the LPDs located within the unevenly distributed LPD region became a fraction of its original density, the LPD density outside the unevenly distributed LPD region remained almost unchanged. Consequently, the large difference between the region of unevenly distributed LPDs and the region outside the unevenly distributed LPD region disappeared, and the ratio of the LPD density within the unevenly distributed LPD region to the LPD density outside the unevenly distributed LPD region was less than 5 after the heat treatment.

[0080] Thus, it was confirmed that unevenly distributed LPDs can be eliminated or reduced by this invention. Unheat-treated silicon wafers, in which unevenly distributed LPDs were not observed, are also present within the aforementioned range of boron and oxygen donor concentrations. However, time and effort are required to check for the presence of unevenly distributed LPDs in each individual wafer, and this can be eliminated by uniformly performing the heat treatment on the unheat-treated silicon wafers within this range.

[0081] In this test, unevenly distributed LPDs were not observed in the unheat-treated silicon wafers where the boron concentration was less than 5×10 14 atoms / cm² 3 or more than 7×10 14 atoms / cm² 3 was and in which the oxygen donor concentration was less than 4×10 14 Donors / cm3 or more than 8×10 14 Donors / cm 3 was. <Beispiel 2>

[0082] The Czochralski method was used to grow 420 silicon single-crystal ingots, the number of days (hereinafter referred to as "turnover time") until cutting the wafers from the ingots after completion of crystal growth was varied, and the boron concentration and oxygen donor concentration of the cut wafers were measured, and the presence / absence of unevenly distributed LPDs on the cut wafers was also investigated.

[0083] Fig. Figure 5 is a diagram that explains the throughput time for each type of wafer. An area on the right side of Fig. Figure 5 shows histograms of the throughput times.

[0084] Regarding the types of wafers, the wafers described as “(a) wafers without the occurrence of unevenly distributed LPDs” (hereinafter referred to as “Type(a)”) are wafers in which the unevenly distributed LPDs do not occur. The Type(a) wafers include wafers that meet the condition that the boron concentration is 5 × 10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and the oxygen donor concentration is 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3 or less, and also include wafers that do not meet the above condition. Among the type(a) wafers, wafers for which the lead time was more than 50 days were all wafers that did not meet the condition that the boron concentration was 5×10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and the oxygen donor concentration is 4×10 14 Donors / cm3 or more and 8×10 14 Donors / cm 3 or less.

[0085] The wafers described as “(b) wafers with occurrence of unevenly distributed LPDs” (hereinafter referred to as “Type(b)”) are wafers in which the unevenly distributed LPDs occur, and all of these wafers met the condition that the boron concentration was 5×10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and the oxygen donor concentration is 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3 or less.

[0086] The average throughput time for the type(a) wafers was 39.8074 days, while the average throughput time for the type(b) wafers was 60.2720 days. A t-test was performed and the difference between the average throughput time of the type(a) wafers and the average throughput time of the type(b) wafers was found to be significant, with a significance level of 5%. (Related to...) Fig. In 5, it was found that all wafers exhibiting unevenly distributed LPDs were wafers cut from the ingot after 50 days or more had elapsed since completion of crystal growth. Based on this result, it was concluded that the occurrence of unevenly distributed LPDs can be prevented by cutting wafers from an ingot within 50 days of completion of crystal growth.

Claims

[1] Method for producing a silicon wafer, characterized by , that it includes: a step to cut a silicon single crystal containing boron as an acceptor to obtain a non-heat-treated silicon wafer, which is a wafer that has not been subjected to heat treatment at a temperature of 300°C or more; a step towards determining a boron concentration with respect to the unheat-treated silicon wafer; and a step towards determining an oxygen donor concentration with respect to the non-heat-treated silicon wafer; wherein a determination of whether a heat treatment at a temperature of 300°C or more and 800°C or less should be carried out on the non-heat-treated silicon wafer is made on the basis of a boron concentration, determined in the step to determine a boron concentration, and an oxygen donor concentration, determined in the step to determine an oxygen donor concentration, where in one case, if a condition exists that the boron concentration is 5x10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and the oxygen donor concentration is 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3or less, is not fulfilled with regard to the non-heat-treated silicon wafer, the provision is a provision to carry out polishing with regard to the non-heat-treated silicon wafer without carrying out heat treatment with it at a temperature of 300°C or more. [2] Method for producing a silicon wafer characterized by , that it includes: a step to cut a silicon single crystal containing boron as an acceptor to obtain a non-heat-treated silicon wafer, which is a wafer that has not been subjected to heat treatment at a temperature of 300°C or more; a step towards determining a boron concentration with respect to the unheat-treated silicon wafer; and a step towards determining an oxygen donor concentration with respect to the non-heat-treated silicon wafer; wherein a determination of whether a heat treatment at a temperature of 300°C or more and 800°C or less should be carried out on the non-heat-treated silicon wafer is made on the basis of a boron concentration, determined in the step to determine a boron concentration, and an oxygen donor concentration, determined in the step to determine an oxygen donor concentration, where in one case, if a condition exists that the boron concentration is 5x10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and the oxygen donor concentration is 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3or less, in relation to the non-heat-treated silicon wafer, the provision is a provision to carry out polishing after performing heat treatment at a temperature of 300°C or more and 800°C or less in relation to the non-heat-treated silicon wafer. [3] Method for producing a silicon wafer according to claim 1 or 2, characterized by , that the determination of whether the heat treatment is carried out on the non-heat-treated silicon wafer at a temperature of 300°C or more and 800°C or less is made in batch units. [4] Method for producing a silicon wafer, characterized by , that it includes: a step to determine a boron concentration with respect to a silicon single-crystal ingot containing boron as an acceptor, or a block cut from the ingot; and a step towards determining an oxygen donor concentration in relation to the bar or block; wherein a determination of whether a wafer is cut from the ingot or block is made within 50 days after completion of the crystal growth of the ingot, based on a boron concentration determined in the step to determine a boron concentration, and an oxygen donor concentration determined in the step to determine an oxygen donor concentration, where in one case, if a condition exists that the boron concentration is 5x10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and the oxygen donor concentration is 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3or less, with respect to the ingot or block, the requirement is to cut a wafer from the ingot or block within 50 days of completion of the crystal growth of the ingot. [5] Method for producing a silicon wafer according to claim 4, characterized by , that the determination of whether a wafer is cut from the ingot or block within 50 days of completion of the ingot's crystal growth is carried out in batch units. [6] Method for producing a silicon wafer, characterized by, that with regard to a silicon single-crystal ingot containing boron as an acceptor, or a block cut from the ingot, heat treatment is carried out on the cut wafer at a temperature of 300°C or more and 800°C or less, in a case where a wafer is cut from the ingot or block at a time over a period of 50 days after completion of the crystal growth of the ingot, which is a case that satisfies a condition that a boron concentration of 5x10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and an oxygen donor concentration of 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3 or less. [7] Method for producing a silicon wafer, characterized by, that with respect to a silicon single-crystal ingot containing boron as an acceptor, or with respect to a block cut from the ingot, in a case where a wafer is cut from the ingot or block within 50 days of completion of the crystal growth of the ingot, which is a case that satisfies a condition that as a result of the determination of the boron concentration and the oxygen donor concentration a boron concentration of 5x10 14 atoms / cm² 3 or more and 7×10 14 atoms / cm² 3 or less and an oxygen donor concentration of 4×10 14 Donors / cm 3 or more and 8×10 14 Donors / cm 3 or less, heat treatment at a temperature of 300°C or more is not performed on the cut wafer. [8] Silicon wafer, which is a particle monitor wafer for recording particles in a semiconductor device manufacturing plant, characterized bythat the silicon wafer is produced by a manufacturing process according to at least one of claims 1 to 7. [9] Silicon wafer that does not contain COPs and dislocation clusters, characterized by that the silicon wafer is produced by a manufacturing process according to at least one of claims 1 to 7.

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