Silicon wafer and its manufacturing method

Abstract

To provide a silicon wafer in which the deformation due to slip dislocation can be suppressed while the capability of gettering metal impurities is kept after a device manufacturing process, and a manufacturing method for the same.SOLUTION: In a silicon wafer W including oxygen deposit formed by a thermal process, in each of layers sectioned from a surface of the wafer for each predetermined depth, the mean size of the oxygen deposit in a first layer from a surface including a non-defect layer to the predetermined depth is smaller than the mean size of a second layer right below the first layer. The mean size of the oxygen deposit decreases in the deeper layer than the second layer. The average density of the oxygen deposit of the respective layers is 1×109 / cm3 or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a silicon wafer and a manufacturing method thereof, and more particularly to a silicon wafer having a defect-free zone (DZ layer) in a surface layer and an intrinsic gettering layer (IG layer) formed by oxygen precipitates (BMD) in a bulk layer, and a manufacturing method thereof. [Background technology]

[0002] When strong thermal stress occurs inside the silicon wafer during heat treatment in the device manufacturing process, slips may occur starting from bone marrow deposits (BMD). When slips occur during the device manufacturing process, alignment shifts occur before and after dislocation generation, which causes the problem of so-called overlay errors in the photolithography process.

[0003] The BMD (oxygen precipitates) formed inside the silicon wafer (bulk) by heat treatment in the device manufacturing process play a role in gettering impurities. In the device manufacturing process, if the BMD size is small, the gettering effect becomes insufficient, so in order to obtain a sufficient gettering effect, it is preferable that the BMD size is larger if the BMD density is the same. However, if the BMD size becomes large, there is a risk that the BMD will become a source of slip dislocation.

[0004] Therefore, in Patent Document 1, oxygen precipitate nuclei of 20 nm or less in size are formed in a silicon wafer at a rate of 1×10 10 / cm 3 A method for forming the above-mentioned high density and suppressing slip extension has been disclosed. However, in the silicon wafer obtained by the method disclosed in Patent Document 1, the BMD size in the depth direction does not change and the amount of oxygen precipitation in the deep layer is large, which causes a problem of reduced mechanical strength.

[0005] To address this issue, Patent Document 2 (JP Patent Publication 11-135510) proposes a silicon wafer in which the BMD size decreases with increasing depth from just below the DZ layer. This reduces the amount of oxygen precipitated in the deep layers, ensuring the mechanical strength of the silicon wafer while maintaining the gettering capability against metal impurities. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2006-40980 A [Patent Document 2] Japanese Patent Application Publication No. 11-135510 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the silicon wafer disclosed in Patent Document 2, the BMD density in the deep part of the wafer is not enough to suppress the extension of slip dislocations (1×10 9 / cm 3 There was a problem that it may not be possible to maintain the above-mentioned level.

[0008] An object of the present invention is to provide a silicon wafer capable of suppressing deformation due to slip dislocations while maintaining gettering capability for metal impurities after a device manufacturing process, and a manufacturing method thereof. [Means for solving the problem]

[0009] The silicon wafer according to the present invention, which has been made to solve the above problems, is a silicon wafer in which oxygen precipitates are formed by heat treatment, and the silicon wafer is 50μm In each layer, the defect-free layer is Depth 50μmthe average size of oxygen precipitates in the first layer up to the first layer is smaller than the average size of oxygen precipitates in the second layer immediately below the first layer, and the average size of oxygen precipitates in layers deeper than the second layer becomes smaller; and The density of oxygen precipitates in all layers is 1×10 9 / cm 3 or more, the average size of oxygen precipitates in the second layer is 70 to 90 nm, and the average size of oxygen precipitates in the sixth layer having a depth of 250 to 300 μm is 60 nm or less. It is characterized by 。

[0010] In the silicon wafer thus constructed, the size of oxygen precipitates in the first layer extending from the wafer surface including the defect-free layer to a predetermined depth can be made small, thereby making it possible to prevent the oxygen precipitates from becoming the starting point of slip and spreading to the device active layer. Furthermore, by increasing the size of the oxygen precipitates in the bulk portion (second layer) below, it is possible to maintain the gettering ability so that impurities in the device active layer can be captured in a layer close to the defect-free layer. In addition, the size of oxygen precipitates in the deeper bulk portion (the third to sixth layers) is kept small, and the density of oxygen precipitates in all layers is kept below 1×10 9 / cm 3 By doing so, it is possible to suppress slip extension and prevent overlay errors due to wafer deformation.

[0011] In order to solve the above problems, the present invention provides a method for producing a silicon wafer containing oxygen precipitate nuclei, the method comprising the steps of: forming a silicon wafer having an oxygen concentration of 0.8×10 by the Czochralski method; 18 atoms / cm 3 More than 1.4×10 18 atoms / cm 3 Below, nitrogen concentration is 0.2×10 15 atoms / cm 3 Above 5.0×10 15 atoms / cm 3The method is characterized by comprising the steps of: growing a silicon single crystal as described below; and subjecting a silicon wafer obtained by slicing the silicon single crystal to a rapid temperature increase / decrease heat treatment in which the oxygen partial pressure in a furnace is set to 5% and the argon partial pressure is set to 95%, and the maximum temperature is maintained at 1350°C for 10 seconds. By this method, it is possible to manufacture silicon wafers having the above characteristics. Effect of the Invention

[0012] According to the present invention, it is possible to provide a silicon wafer capable of suppressing deformation due to slip dislocations while maintaining gettering capability for metal impurities after a device manufacturing process, and a manufacturing method thereof. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing an enlarged partial cross section of a silicon wafer according to the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of a single crystal pulling apparatus used for growing a silicon single crystal, which is applied to the silicon wafer manufacturing method of FIG. [Diagram 3] FIG. 3 is a cross-sectional view showing one embodiment of a rapid temperature increase / decrease heat treatment apparatus (RTP apparatus) to which the method for producing a silicon wafer of the present invention is applied. [Figure 4] FIG. 4 is a graph showing the results of the examples. [Diagram 5] FIG. 5 is a graph showing other results of the example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an enlarged cross section of a silicon wafer W according to an embodiment of the present invention. The silicon wafer W shown in FIG. 1 is characterized by the average size of oxygen precipitates (called BMDs) formed after heat treatment in the device process. Specifically, when the wafer is divided into sections of 50 μm in depth in the thickness direction, the average size of the surface layer (first layer) from the wafer surface including the defect-free zone (called the DZ layer) to a depth of 50 μm is smaller than the average size of the second layer immediately below it from a depth of 50 μm to 100 μm, and the average size of the bulk portion (second to sixth layers) deeper than 50 μm becomes smaller the deeper it is. The average size of the oxygen precipitates in the first layer is 67 nm, the average size of the oxygen precipitates in the second layer is 70 to 90 nm, and the average size of the oxygen precipitates in the sixth layer at a depth of 250 to 300 μm is 60 nm or less. In each layer, the BMD density is 1×10 9 / cm 3 That's all.

[0015] In this way, by reducing the BMD size in the first layer up to 50 μm from the wafer surface, including the DZ layer, it is possible to prevent BMDs from becoming slip initiating points and spreading to the device active layer. Furthermore, by increasing the BMD size in the bulk portion (second layer) below, it is possible to maintain the gettering ability so that impurities in the device active layer can be captured in a layer closer to the DZ layer.

[0016] In addition, the BMD size in the deeper bulk portion (from the third layer to the sixth layer) is kept small to suppress slip extension and prevent overlay errors due to wafer deformation. In this way, the BMD size in the bulk portion from the second layer to the sixth layer becomes smaller the deeper, and the BMD density is 1×10 9 / cm 3 The above is maintained and the extension of slip dislocations is suppressed.

[0017] The BMD density and size can be measured using IR tomography (e.g., MO-441 manufactured by System Seiko). They may also be obtained by observing real images using a TEM. The BMD size is a value calculated by creating a correlation equation between the average side length of an octahedron observed by TEM and the average infrared scattering intensity.

[0018] Next, a method for manufacturing such a silicon wafer W will be described. First, a silicon single crystal is grown and manufactured by the Czochralski method (CZ method). In growing silicon single crystals by the CZ method, a quartz crucible 51 installed in a chamber 50 as shown in FIG. 2 is filled with polysilicon as a raw material, and the polysilicon is heated and melted by a heater 52 provided around the quartz crucible 51 to obtain a silicon melt M.

[0019] At this time, the oxygen concentration of the silicon single crystal to be grown is 0.8×10 18 atoms / cm 3 More than 1.4×10 18 atoms / cm 3 Below, nitrogen concentration is 0.2×10 15 atoms / cm 3 Above 5.0×10 15 atoms / cm 3 The oxygen concentration and nitrogen concentration in the silicon melt M are adjusted to be as follows. In addition, the oxygen concentration of the silicon single crystal to be grown is 0.8 × 10 18 atoms / cm 3 If the oxygen concentration is less than 1.4×10, the strength is insufficient and the slip resistance is poor, which is undesirable. 18 atoms / cm 3 If it is more than this, excessive BMD deposition occurs, which is undesirable. In addition, the nitrogen concentration of the silicon single crystal to be grown is 0.2×10 15 atoms / cm 3 If the nitrogen concentration is less than 5.0×10, the effect of eliminating void defects by RTP treatment will be weak, and there is a risk that void defects will remain after RTP, which is not preferable. 15 atoms / cm 3If the thickness is more than this, single crystallization is hindered during crystal growth, which is undesirable. After the silicon melt M is formed, a seed crystal (seed) P attached to a seed chuck is immersed in the silicon melt M, and the seed chuck is pulled up while rotating the seed chuck and the quartz crucible 51 in the same or opposite directions.

[0020] Prior to the start of pulling, after the temperature of the silicon melt M has stabilized, a seed crystal P is brought into contact with the silicon melt M to perform necking, which melts the tip of the seed crystal P. Necking is an essential process for removing dislocations that occur in the silicon single crystal due to thermal shock caused by the contact between the seed crystal P and the silicon melt M. This necking forms a neck portion P1, which must have a diameter of 3 to 4 mm and a length of at least 30 mm.

[0021] In addition, the processes that follow the start of pulling include, after necking is completed, a shoulder portion C1 formation process that expands the crystal to the diameter of the straight body portion (e.g., a diameter of 300 mm), a straight body portion C2 formation process in which the single crystal that will become the product is grown, and a tail portion (not shown) formation process that gradually reduces the diameter of the single crystal after the straight body portion formation process.

[0022] After the silicon single crystal is grown and produced in this manner, the silicon single crystal is sliced ​​to obtain a plurality of silicon wafers each having a diameter of 300 mm. These silicon wafers are subjected to a predetermined heat treatment using, for example, a rapid temperature rise and fall heat treatment apparatus (RTP apparatus) shown in FIG. 3, the RTP apparatus 1 includes a chamber (reaction tube) 20 having an atmospheric gas inlet 20a and an atmospheric gas outlet 20b, a plurality of lamps 30 spaced apart from one another in the upper portion of the chamber 20, and a substrate support 40 that supports a silicon wafer W in a reaction space 25 in the chamber 20. In addition, although not shown, the RTP apparatus 1 includes a rotation means for rotating the silicon wafer W around its central axis at a predetermined speed.

[0023] The substrate support 40 includes a ring 10 that supports the outer periphery of the silicon wafer W, and a stage 40a that supports the ring 10. The chamber 20 is made of, for example, quartz. The lamps 30 are made of, for example, halogen lamps. The stage 40a is made of, for example, quartz. This RTP apparatus 1 can uniformly heat and process the entire silicon wafer W with a temperature rise / fall gradient of 10 to 300° C. / sec.

[0024] The temperature in the reaction space 25 in the RTP apparatus 1 is controlled by measuring the average temperature at multiple points (e.g., nine points) in the substrate surface in the radial direction of the lower part of the silicon wafer W using multiple radiation thermometers embedded in the stage 40a of the substrate support part 40, and controlling the multiple halogen lamps 30 (individual ON-OFF control of each lamp, control of the emission intensity of the emitted light, etc.) based on the measured temperatures.

[0025] In the RTP apparatus 1 configured as above, first, the silicon wafer W is placed and fixed on the ring 10. This ring 10 is then fixed to the upper part of the stage 40a installed in the reaction space 25 under an oxidizing atmosphere so that the upper surface of the silicon wafer W is approximately parallel to the upper part of the stage 40a.

[0026] Moreover, a process gas is introduced from the atmospheric gas inlet 20a, and the gas in the reaction space 25 is exhausted from the atmospheric gas outlet 20b, forming a predetermined air flow above the silicon wafer W. Here, the reaction space 25 preferably has an oxygen partial pressure of 5% and an argon gas partial pressure of 95%. Next, the halogen lamps 30 arranged in an equal arrangement are individually controlled based on feedback from the surface temperature of the silicon wafer W to rapidly heat the silicon wafer W while controlling its surface temperature, thereby carrying out a heat treatment on the silicon wafer W.

[0027] Specifically, the wafer surface temperature is heated to 1250° C. within 60 seconds after the start of heating, then the wafer surface temperature is heated to 1350° C. within 62 to 70 seconds after the start of heating, and this state is maintained for 10 seconds. Thereafter, the inside of the furnace is rapidly cooled, completing the rapid temperature increase and decrease heat treatment.

[0028] The silicon wafer W subjected to such rapid temperature increase and decrease heat treatment has the characteristics that no void defects are present in the wafer surface layer, and oxygen precipitate nuclei that are the source of BMD are present at a desired depth and density inside the wafer, and any BMD structure can be formed in the device manufacturing process.

[0029] Therefore, during the heat treatment in the device manufacturing process, for example, when heat treatment is performed at 780°C for 3 hours in an argon (Ar) atmosphere and then at 1000°C for 16 hours, a BMD structure having the size and density shown in Figure 1 is formed in the wafer. At this time, the BMD size of the first layer, which is from the wafer surface including the DZ layer to 50 μm, is made small, which prevents the BMD from becoming the starting point of slip and spreading to the device active layer. Furthermore, the BMD size of the bulk part (second layer) below is made large, so the gettering ability that can capture impurities in the device active layer in the layer close to the DZ layer is maintained. Furthermore, the BMD size in the deeper bulk portion (the third to sixth layers) is small, which suppresses slip extension and prevents overlay errors caused by wafer deformation.

[0030] As described above, according to the embodiment of the present invention, by making the BMD size of the first layer up to 50 μm from the wafer surface including the DZ layer small, it is possible to prevent the BMD from becoming the starting point of slip and spreading to the device active layer. Furthermore, by forming the BMD size of the bulk portion (second layer) below it to be large, it is possible to maintain the gettering ability so that impurities in the device active layer can be captured in a layer close to the DZ layer. In addition, the BMD size in the deeper bulk portion (layers 3 to 6) was kept small, and the BMD density in all layers was kept below 1×10 9 / cm 3By doing so, it is possible to suppress slip extension and prevent overlay errors due to wafer deformation.

[0031] In the above embodiment, the wafer is divided into sections of 50 μm in depth in the thickness direction, and the BMD sizes of the first to sixth layers are specified. However, the present invention is not limited to this configuration, and each layer may be divided at a predetermined depth. EXAMPLES

[0032] The silicon wafer and the manufacturing method thereof according to the present invention will be further described with reference to examples. In the examples, the following experiments were carried out based on the above-described embodiment.

[0033] Example 1 In Example 1, first, the oxygen concentration of the silicon single crystal to be pulled is 1.2 × 10 18 atoms / cm 3 , nitrogen concentration is 5.0×10 14 atoms / cm 3 A silicon single crystal with a diameter of 300 mm was grown by the Czochralski method so as to include the region that would become the crystal. The obtained silicon single crystal was then sliced ​​into silicon wafers, which were then heat-treated in a rapid temperature change (RTP) equipment by setting the oxygen partial pressure in the furnace to 5% and the argon partial pressure to 95%, and maintaining the maximum temperature at 1350°C for 10 seconds.

[0034] Thereafter, simulating the heat treatment in device processing, the wafer was successively heat-treated in an argon (Ar) atmosphere at 780°C for 3 hours and then at 1000°C for 16 hours, and the BMD size and BMD density of the wafer cross section were measured using IR tomography (MO441, manufactured by System Seiko Co., Ltd.). The results of the BMD size are shown in the graph of FIG. 4, and the results of the BMD density are shown in the graph of FIG. 5. The vertical axis of the graph in FIG. 4 indicates the average BMD size (nm), and the horizontal axis indicates the depth (μm) from the wafer surface. The vertical axis of the graph in FIG. 5 indicates the average BMD density (cm -3) and the horizontal axis indicates the depth (μm) from the wafer surface. The BMD size is a value calculated by converting the scattering intensity of IR tomography based on the BMD size obtained by TEM observation.

[0035] As shown in the graph in FIG. 4, the average BMD size is smaller than 70 nm up to a depth of 49 μm, and the average size is close to 80 nm from a depth of 50 to 99 μm. It can be seen that the deeper the BMD size, the smaller the BMD size becomes. In addition, as shown in the graph in Figure 5, the BMD density was 1×10 9 / cm 3 It maintains the above. In addition, the same silicon wafers were evaluated by X-ray topography (Rigaku XRT300) to confirm the presence or absence of dislocations. As a result, the total length of dislocations extending from the wafer boat position was 2 mm.

[0036] In addition, a solution containing Ni was added to the heat-treated silicon wafer at 1×10 12 atoms / cm 2 After spin-coating so that the Ni was uniform, a diffusion treatment was performed at 900°C for 0.5 hours, and the wafer was etched and visually inspected for the occurrence of shallow pits on the surface. If Ni is present on the surface when cooled, Ni silicide is formed on the surface and can be detected as shallow pits. As a result, it was determined that no shallow pits occurred in this sample, and most of the Ni that had contaminated the surface was gettered by the internal BMD.

[0037] Comparative Example 1 In Comparative Example 1, silicon wafers obtained from the same silicon single crystal as in the Example were heat-treated in a rapid temperature change heat treatment apparatus (RTP apparatus) with the oxygen partial pressure in the furnace set to 75% and the argon partial pressure set to 25%, and the maximum temperature was maintained at 1350°C for 10 seconds. Thereafter, the heat treatment in the device process was simulated by successively performing heat treatment in an argon (Ar) atmosphere at 780°C for 3 hours and then at 1000°C for 16 hours, and the BMD size and BMD density of the wafer cross section were measured by IR tomography (MO441 manufactured by System Seiko Co., Ltd.) The results of the BMD size are shown in the graph of FIG. 4, as in Example 1, and the results of the BMD density are shown in the graph of FIG. In Comparative Example 1, the total length of dislocations was 74 mm, and the effect of suppressing dislocations was small. Furthermore, when Ni contamination was performed in the same manner as in Example 1, no shallow pits were generated.

[0038] Comparative Example 2 In Comparative Example 2, the oxygen concentration of the silicon single crystal to be pulled was 1.2 × 10 18 atoms / cm 3 , nitrogen concentration is 1.0×10 14 atoms / cm 3 A silicon single crystal with a diameter of 300 mm was grown by the Czochralski method so as to include the region that would become the crystal. Next, in a rapid temperature rise and fall heat treatment device (RTP device), the oxygen partial pressure in the furnace was set to 75%, the argon partial pressure was set to 25%, and the maximum temperature was maintained at 1350° C. for 10 seconds for heat treatment.

[0039] Thereafter, the heat treatment in the device process was simulated by successively performing heat treatment in an argon (Ar) atmosphere at 780°C for 3 hours and then at 1000°C for 16 hours, and the BMD size and BMD density of the wafer cross section were measured by IR tomography (MO441 manufactured by System Seiko Co., Ltd.) The results of the BMD size are shown in the graph of FIG. 4, as in Example 1, and the results of the BMD density are shown in the graph of FIG. The total dislocation length was 5 mm in Comparative Example 2. When Ni contamination was performed using the same method as in Example 1, shallow pits were observed, and it was determined that the gettering ability was insufficient.

[0040] From the results of the above examples, it has been confirmed that the configuration of the present invention makes it possible to suppress deformation due to slip dislocations while maintaining the gettering ability for metal impurities after the device manufacturing process. [Explanation of symbols]

[0041] 1 RTP device 20 Chamber (furnace) 25 Reaction Space 30 Halogen lamp 40 Substrate support 40a Stage 50 Chamber C Silicon single crystal M Silicon melt W Silicon wafer

Claims

1. A silicon wafer in which oxygen precipitates are formed by heat treatment, In each layer divided every 50 μm from the wafer surface, the average size of oxygen precipitates in a first layer from the surface including a defect-free layer to a depth of 50 μm is smaller than the average size of a second layer immediately below the first layer, and the average size of oxygen precipitates becomes smaller in layers deeper than the second layer; and the density of oxygen precipitates is 1×10 9 / cm 3 or more in all layers; A silicon wafer, characterized in that the average size of oxygen precipitates in the second layer is 70 to 90 nm, and the average size of oxygen precipitates in a sixth layer having a depth of 250 to 300 μm is 60 nm or less.

2. A method for producing a silicon wafer containing oxygen precipitation nuclei, comprising the steps of: By the Czochralski method, the oxygen concentration is 0.8 x 10 １８ atoms / cm ３ That's 1.4 x 10 １８ atoms / cm ３ Below, the nitrogen concentration is 0.2 × 10 １５ atoms / cm ３ Above 5.0 x 10 １５ atoms / cm ３ A step of growing a silicon single crystal comprising: A step of heat-treating the silicon wafer obtained by slicing the silicon single crystal by rapid temperature increase and decrease heat treatment in a furnace with an oxygen partial pressure of 5% and an argon partial pressure of 95%, and maintaining the maximum temperature at 1350° C. for 10 seconds; A method for producing a silicon wafer, comprising:

Images