JP2005327798A - Silicon support for heat treatment and its production process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon support for heat treatment in which outward diffusion of metallic impurities and adhesion during heat treatment can be prevented. <P>SOLUTION: A silicon block is cut into a supporting plate and then the supporting plate is flattened by lapping (#1200). It is then immersed into NaOH solution of 48% concentration at 80°C for 1 min and subjected to alkali etching. Subsequently, it is cleaned with pure water and immersed into mixture liquid of hydrofluoric acid and nitric acid (hydrofluoric acid: nitric acid: pure ware=1:6:9) for 1 min and subjected to acid etching. Thereafter, it is cleaned with pure water and subjected to SC-1 cleaning. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a support member used at the time of heat treatment of a silicon wafer and a method for manufacturing the same, and more particularly to a support member for silicon heat treatment that supports a silicon wafer with a single wafer and a method for manufacturing the same.

  A silicon wafer (hereinafter referred to as a wafer) is subjected to heat treatment such as diffusion, oxidation, and donor killer according to various uses in forming a semiconductor element.

  As a support member used when heat-treating a wafer, a vertical boat is used in which a groove for supporting a wafer is formed on a support column arranged in parallel. In recent years, as the diameter of a wafer increases, a plate-shaped support member that supports the wafer over the entire surface or a ring-shaped support member that supports the entire outer periphery is also used. Silicon carbide, quartz, silicon, or the like is used as the material for these support members. Of these materials, silicon carbide is a material having good heat resistance, but it is difficult to process the support member, resulting in high costs. In addition, the quartz member is not very good in heat resistance and is easily deformed at about 1100 ° C. or higher, so that it is not suitable for heat treatment at a high temperature.

  Therefore, recently, a silicon support member that is relatively high in heat resistance and easy to process is preferably used.

  However, the support member made of silicon has a property of conversely diffusing impurities in the silicon outward during heat treatment. Moreover, since the material is the same as that of the wafer to be heat-treated, the wafer and the support member are bonded to each other, and slip is likely to occur. Further, the support member is thermally deformed, and the wafer's own weight stress is concentrated on the deformed portion. As a result, there is a problem in that slip occurs at that portion.

  Thus, for example, it has been proposed that the surface roughness of the wafer support be 0.05 μm or more in Ra and 50 μm or less in Rmax (see, for example, Patent Document 1). When the surface of such a support plate is evaluated by a surface shape measuring instrument, it is as shown in FIG. That is, the surface shape of the support plate shown in FIG. 4 (a) is formed with gentle undulations as shown in the schematic explanatory view of FIG. 4 (b).

In addition, after performing a predetermined amount of acidic etching to remove contamination due to machining, the surface roughness of 0.3 μm to 100 μm (RMS) is obtained by alkaline etching, so that the surface that has become too smooth during acidic etching can be obtained. It has also been proposed that the adhesion to the wafer can be prevented by roughening (for example, see Patent Document 2). Furthermore, a support member made of a silicon single crystal grown by the Czochralski method at a predetermined nitrogen concentration and oxygen concentration is heat-treated at, for example, 600 to 1000 ° C. for 10 minutes to 24 hours, thereby causing impurities to the wafer. It has been proposed to suppress the transfer of metal contamination (see, for example, Patent Document 3).
Japanese Patent Laid-Open No. 10-321543 JP 2004-63617 A JP 2003-86525 A

  However, although the invention described in Patent Document 1 is effective in reducing slip, there is no description or suggestion regarding prevention of reduction of contamination from the support. In addition, the invention described in Patent Document 2 cannot completely suppress the occurrence of slip because the surface of the portion in contact with the wafer is a processed surface after alkaline etching, and it can be machined by acid etching. Since the crushed layer generated in this way is also removed, the impurity gettering effect is small, and the outward diffusion from the heat treatment jig to the wafer cannot be suppressed. Further, the heat treatment jig described in Patent Document 3 can provide a heat treatment jig in which an internal defect (Bulk Micro-Defect, hereinafter referred to as BMD) having a gettering effect is formed. BMD only has an IG (Intrinsic Gettering) effect at a very micro level, and does not reach the gettering force of the fractured layer. Further, there is no description or suggestion regarding the bonding surface between the heat treatment jig surface and the wafer during heat treatment.

  Accordingly, an object of the present invention is to provide a silicon heat-treating support member and a method for producing the same that can reduce metal contamination of the wafer during heat treatment and can suppress slippage. .

  According to one aspect of the present invention, there is provided a support member for heat treatment made of silicon for placing a silicon wafer and performing a heat treatment, wherein the convex portion having a substantially spherical top portion on the surface on which the silicon wafer is placed. A support member for heat treatment made of silicon is provided in which a plurality of layers are formed and a crushed layer is formed on the surface layer portion thereof.

  According to another aspect of the present invention, a step of processing a silicon block having a desired size into a shape of a desired support member for mounting a silicon wafer, and a step of alkali etching the support member And a step of acid etching the alkali-etched support member. A method for producing a silicon heat-treating support member is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the support member for silicon heat processing which can prevent the outward diffusion of the metal impurity from a support member, and can prevent the adhesion | attachment at the time of heat processing, and its manufacturing method are provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same portions are denoted by the same reference numerals, and redundant description is omitted.

  (First Embodiment) First, the first embodiment of the present invention will be described. This embodiment is a heat treatment support member to which the present invention is applied.

  What is shown in FIG. 1A is a plate-like support plate 1 that supports a wafer in a single wafer among the heat treatment support members. FIG. 1B is an explanatory diagram schematically showing the surface shape of the support 1. The surface of the support plate 1 can be measured with a known surface shape measuring instrument.

  As shown in FIG. 1 (b), a plurality of convex portions 2 whose top portions are substantially spherical are formed on the surface of the support plate 1. A concave portion 3 is formed between the convex portion 2 and the convex portion 2. For example, the surface roughness of the support plate 1 is preferably 0.25 μm to 0.45 μm in Rms when evaluated by a surface shape measuring instrument (measurement range: 5 mm, measurement speed 0.1 mm / sec).

  Furthermore, a crushing layer 4 is formed on the surface layer portion of the surface of the support plate 1. The crushing layer 4 suppresses outward diffusion of metal impurities from the support plate 1 itself, and also has an effect of gettering metal impurities floating in the heat treatment furnace. Further, since the crushing layer 4 can also suppress deformation due to thermal stress generated in the support plate 1 during heat treatment, it is possible to prevent concentration of the wafer's own weight stress due to deformation of the support plate 1.

  The depth of the crushed layer 4 is preferably in the range of 0.2 to 2.0 μm, for example. When the depth of the crushed layer 4 is less than 0.2 μm, it is difficult to obtain sufficient metal impurity gettering ability. Moreover, when the depth of the crushing layer 4 exceeds 2.0 micrometers, while the durability of the support plate 1 falls, the crushing layer 4 becomes a dust generation source, such as a particle, and is not preferable.

  When the wafer is placed on the support plate 1 having such a structure and heat treatment is performed, the wafer comes into contact with the support plate 1 at a plurality of convex portions 2 having a substantially spherical top portion. Therefore, since the contact area is small, diffusion of metal impurities from the surface of the support plate 1 to the wafer can be suppressed.

  Furthermore, since the wafer self-weight stress can be relaxed when supporting the wafer, slip during heat treatment can be suppressed.

  In addition, it is preferable that the recessed part 3 of the uneven | corrugated | grooved part of a surface is also a corner | angular shape. By curving not only the convex portion 2 but also the concave portion 3, it is possible to increase the strength of the protruding portion of the convex portion 2 and prevent the convex portion 2 from peeling off due to adhesion during heat treatment.

  The heat treatment support member according to the embodiment of the present invention is not limited to the support plate shown in FIG. For example, the present invention can also be applied to a heat treatment support member such as a ring-shaped support plate, various heat treatment components of a wafer boat, a susceptor for film formation, a chuck, and a holder.

  (Second Embodiment) Next, as a second embodiment of the present invention, an embodiment of a method for manufacturing a heat treatment support member will be described with reference to the drawings. FIG. 2 is an explanatory view showing a method of manufacturing the support plate 1 shown in FIG.

  As shown in FIG. 2A, for example, a silicon block 5 grown by the Czochralski method or the like is prepared, and is processed into a support plate shape by machining as shown in FIG. In processing the support plate 1, the silicon block 5 is cut into a thin plate shape and both surfaces are lapped. By this lapping process, a crushed layer is generated on the surface.

  Next, the support plate 1 processed into a thin plate shape is subjected to alkali etching with a sodium hydroxide or potassium hydroxide solution (see FIG. 2C). The concentration of these alkaline solutions is preferably 5% or more. When the concentration of the alkaline solution is less than 5%, square edge pits due to anisotropic etching peculiar to alkaline etching are formed wide and large. Therefore, the contact area with the wafer cannot be reduced, and metal contamination from the support plate 1 is likely to occur.

  In addition, since the maximum density | concentration of the alkali marketed now is 48%, the density | concentration of the alkali which can be utilized is 5%-48%.

  Alkali etching selectively etches the crushed layer that occurs during lapping, so to remove the crushed layer during lapping by alkali etching, an etching allowance that exceeds the crush layer depth is required. And By utilizing the above properties, the crushed layer 4 can be left on the surface layer of the support plate by alkali etching, and a support plate having high gettering ability can be manufactured.

  As shown in FIG. 2D, the surface subjected to high concentration alkali etching of 5% or more has a shape in which the tip of the convex portion is pointed.

  Therefore, if the wafer is supported in this state, the wafer's own weight stress concentrates on the tip of the sharp convex part and slip occurs. Therefore, it is difficult to use it as a support plate on the surface as it is. The process requires acid etching.

  Next, as shown in FIG. 2E, acid etching is performed with a mixed solution of hydrofluoric acid and nitric acid on the alkali-etched support plate. This acid etching is for making a portion formed by alkali etching into a spherical surface (see FIG. 2F).

  The acid etching amount is preferably about 0.5 to 2 μm. If the thickness is less than 0.5 μm, it is difficult to sufficiently spheroidize the surface formed by alkali etching, and it is difficult to control acid etching allowance. On the other hand, when the thickness exceeds 2 μm, the concavo-convex portion formed by alkali etching is corrected and approaches the surface shape of the conventional support plate as shown in FIG. 4, so that the contact area with the wafer increases. In addition, unlike the alkali etching, the acid etching etches the surface without deepening the crushed layer. Therefore, if the thickness exceeds 2.0 μm, the crushed layer is completely removed, which is not preferable.

  Acid etching has the property of forming spherical pits on the silicon surface. That is, the pointed part by the alkali etching can be smoothly made spherical. By utilizing this property, the convex part sharpened by alkali etching can be made spherical, and the concave part can also be curved.

  EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limited by the following Example.

(Example)
A silicon block grown by the Czochralski method was cut into a support plate, and the cut support plate was lapped (# 1200) to flatten the support plate. Next, the substrate is immersed in a NaOH solution at a temperature of 80 ° C. and a concentration of 48% for 10 minutes to perform alkali etching, washed with pure water, and then mixed with hydrofluoric acid and nitric acid (hydrofluoric acid: nitric acid: pure water = 1: 6: 9). Acid etching was performed by immersion for 1 minute. After pure water cleaning, SC-1 cleaning was performed to prepare a support plate.

  The evaluation wafer was mounted on the obtained support plate, and heat treatment was performed at 1200 ° C. for 1 hour in an argon atmosphere. The bulk Fe concentration of the obtained evaluation wafer was evaluated by the SPV (Surface Photovoltaic) method, and the presence or absence of slip was evaluated by the X-ray transmission method (N number: 6 sheets). The depth of the crushed layer of the support plate was evaluated by breaking the support plate into a strip shape, obliquely polishing (angle 5 ° 44 ″) to expose the cross section, and acid etching (nitric acid: hydrofluoric acid: acetic acid = 1: 3: This is the value obtained by observing the distance from the wafer surface with an optical microscope and measuring the depth of the crushed layer of 6 samples on average at 0.5 μm. .

(Comparative Example 1)
A silicon block grown by the Czochralski method was cut into a support plate, and the cut support plate was lapped (# 1200) to flatten the support plate. Next, without performing alkali etching, acid etching is performed with a mixed solution of hydrofluoric acid and nitric acid (hydrofluoric acid: nitric acid: pure water = 1: 6: 9), and the crushed layer generated by the lapping process is completely removed. After pure water cleaning, SC-1 cleaning was performed to prepare a support plate. After the heat treatment was carried out by the same method as in the example using the obtained support plate, the evaluation of the bulk Fe concentration of the evaluation wafer, the presence or absence of slip, and the crushing layer depth of the support plate were the same as in the example. Evaluation was made by the method (N number: 6 sheets). The crushed layer of the support plate was not confirmed for all six samples.

(Comparative Example 2)
A silicon block grown by the Czochralski method was cut into a support plate, and the cut support plate was lapped (# 1200) to flatten the support plate. Next, acid etching was performed with a mixed solution of hydrofluoric acid and nitric acid (hydrofluoric acid: nitric acid: pure water = 1: 6: 9), and the crushed layer generated by the lapping treatment was completely removed. Next, the substrate was immersed in a NaOH solution having a temperature of 80 ° C. and a concentration of 48% for 10 minutes to perform alkali etching. After cleaning with pure water, cleaning with SC-1 was performed to prepare a support plate. After the heat treatment was performed by the same method as in the example using the obtained wafer support plate, the evaluation of the bulk Fe concentration of the evaluation wafer, the occurrence of slip, and the crushing layer depth of the support plate were performed in the example. Evaluation was performed in the same manner (N number: 6 sheets). The crushed layer of the support plate was not confirmed for all six samples.

The presence or absence of occurrence of slip was observed for each of the above 6 samples of Examples and Comparative Examples 1 and 2. The results are shown in Table 1. Bulk Fe concentration was also measured. The result is shown in FIG.

  As shown in Table 1, slip occurs in Comparative Example 1 as compared to the Example. This is presumably because the used support plate is deformed during the heat treatment, and the self-weight stress of the wafer concentrates on the support plate deformation convex portion, and as a result, slip occurs in that portion. Further, in Comparative Example 2, since the support plate surface has a surface shape after alkali etching, the evaluation wafer was placed in a state where a sharp convex tip portion after alkali etching was formed. It is considered that slip occurred in

  Next, it considers from a viewpoint of Fe contamination. As shown in FIG. 3, in Comparative Example 1, the crushed layer is completely removed by acid etching, and the contact area with the wafer is large, so that impurity contamination due to outward diffusion from the support plate is suppressed. It is thought that was not possible. In Comparative Example 2, the bulk Fe concentration is improved slightly compared to Comparative Example 1. This is because the roughness of the surface in contact with the wafer was increased by alkali etching, resulting in a reduction in contamination from the jig surface because the contact area was reduced, and the acid etching was performed after the acid etching. It is considered that the bulk Fe concentration was slightly lower than that of Comparative Example 1 due to the fact that a small crushed layer that could not be evaluated due to the etching remained slightly after selective etching by alkali etching. However, the bulk Fe concentration is clearly higher than in the examples.

  The present invention is suitable for, for example, a support plate for mounting a wafer on a support member for heat treatment, but is not limited thereto, and various changes can be made without departing from the scope of the invention. .

Explanatory drawing which showed the supporting member for heat processing which concerns on the 1st Embodiment of this invention, and its surface shape. Explanatory drawing which shows the process of the manufacturing method of the supporting member for heat processing which concerns on the 2nd Embodiment of this invention. The figure which shows the measurement result of the bulk Fe density | concentration in the Example and comparative example of this invention. Explanatory drawing which showed the supporting member for heat processing by the prior art, and its surface shape.

Explanation of symbols

1: Support plate 2: Convex part 3: Concave part 4: Shatter layer 5: Silicon block

Claims (4)

  A support member for heat treatment made of silicon for placing a silicon wafer to perform heat treatment, wherein a plurality of convex portions having a substantially spherical shape at the top are formed on the surface on which the silicon wafer is placed, and A support member for heat treatment made of silicon, wherein a crush layer is formed on a surface layer portion.   The silicon heat treatment support member according to claim 1, wherein a depth of the crush layer formed in the surface layer portion is 0.2 μm to 2 μm.   A step of processing a silicon block of a desired size into a shape of a desired support member for mounting a silicon wafer, a step of alkali-etching the support member, and an acid-etching of the alkali-etched support member A process for producing a silicon heat-treating support member.   The alkali etching step is performed with a sodium hydroxide or potassium hydroxide solution having a concentration of 5% or more, and the acid etching step is performed with a mixed solution containing hydrofluoric acid and nitric acid. 3. A method for producing a silicon heat-treating support member according to 3.

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