JP2009277805A - Product semiconductor wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a product semiconductor wafer that secures high pattern precision, by preventing a pattern from decreasing in resolution and depth of focus owing to gravitational flexure. <P>SOLUTION: A surface of the product semiconductor wafer is gently curved in a convex shape such that a center portion projects from an outer peripheral portion, and the maximum thickness of the wafer center portion equals the sum of the thickness of the wafer outer peripheral portion and the maximum flexure amount of the wafer center portion, when the wafer outer peripheral portion is supported at a point. Consequently, the wafer surface is substantially planar, when the wafer outer peripheral portion is supported at the point. High pattern precision is therefore secured, by suppressing the decreases in resolution and depth of focus of the pattern due to flexure of the wafer center portion due to the weight of the product semiconductor wafer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a product semiconductor wafer, for example, a product semiconductor wafer capable of preventing exposure failure due to the flatness of the wafer surface during exposure in a device process.

In the device process, during exposure, for example, a stepper (reduction projection type exposure apparatus) irradiates light emitted from an exposure light source onto a pattern formed on a mask (reticle), and the light passing through the pattern is reduced by a reduction projection lens. After the reduction, the product silicon wafer (product semiconductor wafer) is transferred to the surface coated with the photoresist.
As shown in FIG. 4a, the product silicon wafer 100 shipped from the wafer manufacturing factory increases the parallelism of the front and back surfaces of the wafer (thickness distribution within the wafer surface) and the flatness of the wafer surface, so that the outer periphery of the wafer is reduced. The thickness within the wafer surface was uniform.
Usually, the product silicon wafer 100 is placed on a wafer stage disposed under a stepper or the like while holding the outer periphery. For example, the outer peripheral portion was supported at six points from below by six support pins 101 arranged every 60 ° in the stage circumferential direction (wafer circumferential direction) (FIG. 4b).

JP 2005-228978 A

As described above, the conventional product silicon wafer 100 has a uniform thickness in the wafer surface excluding the outer peripheral portion of the wafer. Therefore, when the outer peripheral portion of the wafer is point-supported during exposure, a deflection (a deflection amount c) due to its own weight occurs in the central portion of the silicon wafer 100, and the surface of the wafer is gently concave with the central portion depressed from the outer peripheral portion. It was curved (Fig. 4b). Thereby, at the time of exposure, the flatness of the surface of the product silicon wafer 100 was lowered, and the pattern transferred to the surface of the wafer was distorted. In addition, due to this deflection, the focal position shifts between the central part and the outer peripheral part of the exposure area on the surface of the wafer, causing defocusing, reducing the resolution and depth of pattern, and ensuring high pattern accuracy. could not.
Moreover, such a phenomenon tended to become prominent in a large-diameter wafer having a diameter of 450 mm, which has been developed recently. This is because the diameter of the product silicon wafer 100 increases due to the increase in the diameter, and the deflection of the central portion of the wafer when the outer periphery of the product silicon wafer 100 is point-supported increases.

  Therefore, as a result of diligent research, the inventor, as a product silicon wafer, placed the wafer surface on the horizontal flat plate without applying external force in an environment of room temperature and atmospheric pressure, so that the center portion of the wafer surface is more than the outer peripheral portion. While curving gently into a protruding convex shape, the maximum thickness at the center of the wafer is set to the thickness of the outer periphery of the wafer without applying an external force in an environment of room temperature and atmospheric pressure. It has been found that the above-mentioned problem can be solved if the thickness is increased by adding the maximum deflection amount at the center of the wafer when supported. That is, since the thickness of the center portion of the product silicon wafer is set in consideration of the deflection amount due to the weight of the wafer, the surface of the wafer is substantially flat when the outer peripheral portion of the wafer is point-supported before exposure ( The present invention was completed by discovering that a reduction in the resolution and depth of focus of the pattern caused by deflection due to the weight of the wafer can be suppressed, and a high pattern accuracy can be secured.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a product semiconductor wafer that can suppress a decrease in pattern resolution and depth of focus caused by deflection due to the weight of the wafer and ensure high pattern accuracy.

  According to the first aspect of the present invention, a surface that is gently curved into a convex shape whose central portion protrudes from the outer peripheral portion in a state where it is placed on a horizontal flat plate without applying external force in an environment of room temperature and atmospheric pressure. A product semiconductor wafer having a maximum thickness of a central portion of the product semiconductor wafer, wherein an external force is not applied to an outer peripheral portion of the product semiconductor wafer in an environment of room temperature and atmospheric pressure. This is a product semiconductor wafer having a thickness added with the maximum deflection amount at the center of the product semiconductor wafer when the outer periphery of the wafer is supported from below at a plurality of positions in the circumferential direction of the product semiconductor wafer.

According to the first aspect of the present invention, the center portion of the product semiconductor wafer protrudes from the outer peripheral portion in a state where the surface of the product semiconductor wafer is placed on a horizontal flat plate without applying an external force in an environment of room temperature and atmospheric pressure. It has a gentle convex shape, and the maximum thickness at the center of the wafer is not applied to the outer peripheral thickness of the wafer at room temperature and atmospheric pressure. A thickness obtained by adding the maximum deflection amount of the central portion of the wafer when supported from below (point support) at a plurality of positions in the circumferential direction.
Thereby, when the outer peripheral part of the wafer is supported from below, the surface of the wafer becomes substantially flat (planar). As a result, it is possible to suppress a decrease in pattern resolution and depth of focus due to deflection of the central portion of the wafer due to the weight of the product semiconductor wafer, and high pattern accuracy can be ensured.

A product semiconductor wafer refers to a semiconductor wafer shipped from a wafer manufacturing factory after the wafer manufacturing process is completed.
The diameter of the product semiconductor wafer is, for example, 200 mm, 300 mm, 450 mm, or the like.
Examples of the process for supporting the outer periphery of the product semiconductor wafer include particle measurement on the wafer surface, various heat treatment processes, and the like during exposure in the device formation process.
As the product semiconductor wafer, a single crystal silicon wafer, a polycrystalline silicon wafer, or the like can be adopted. The surface of the product semiconductor wafer is mirror-finished to form a device formation surface. Further, it may be a wafer having added value such as a bonded wafer, an epitaxial wafer, a diffusion wafer, or the like.

“The surface of the wafer is gently curved into a convex shape with the center protruding from the outer periphery” means that the surface of the product semiconductor wafer is not exposed to external force under the environment of room temperature and atmospheric pressure. The center is the highest with no steps, and the top is a gentle mountain shape (copper bowl shape).
As a product semiconductor wafer having such a shape, (1) only the front surface of the wafer is a copper cage shape and the back surface of the wafer is flat, and (2) the wafer surface is a copper cage shape, and the back surface of the wafer is centered from the outer periphery. A wafer that is gently curved into a concave shape with a recessed part (however, the curvature of the wafer surface is smaller than the curvature of the back surface of the wafer), But you can.
“Wafer surface is substantially flat” means that at least the device formation area of the wafer surface is flat (flat surface, horizontal surface) in an environment of room temperature and atmospheric pressure and no external force is applied. Say. Specifically, the state in which the warpage of the wafer surface is 0 to 10 μm in terms of the surface reference measurement value.

The “outer peripheral part of the product semiconductor wafer” means a wafer chamfered part (in the case of a 300 mm wafer, for example, an area from the outermost peripheral edge of the wafer to the center side in the radial direction up to 3 mm, in the case of a 450 mm wafer, The area up to 2 mm toward the center in the radial direction).
The “center portion of the product semiconductor wafer” refers to the remaining portion excluding the wafer chamfered portion (the portion inside the wafer from the wafer chamfered portion).
The “thickness of the outer periphery of the product semiconductor wafer” is the thickness at the support position of the product semiconductor wafer. In the case of a 300 mm wafer, for example, the thickness is 3 mm from the outermost peripheral edge of the wafer to the center in the radial direction, and in the case of a 450 mm wafer, the thickness is, for example, 2 mm from the outermost peripheral edge of the wafer to the center in the radial direction. is there.

“Supporting the outer periphery of the product semiconductor wafer from below at a plurality of positions in the circumferential direction of the product semiconductor wafer” means that the back surface of the outer periphery of the product semiconductor wafer is partially supported at two or more positions by a support member. Support from below.
As a support member for supporting the outer periphery of the product semiconductor wafer from below, for example, a pin member can be employed.
The support position in the wafer circumferential direction of the outer periphery of the product semiconductor wafer is arbitrary. For example, it may be supported in the circumferential direction every 120 °, every 90 °, or every 60 °.
The “maximum deflection amount at the center of the product semiconductor wafer” refers to the maximum height difference between before and after the wafer center that has been bent by its own weight when the both ends of the product semiconductor wafer are supported.
The relationship (ratio) between the thickness of the outer periphery of the product semiconductor wafer and the maximum thickness of the center of the product semiconductor wafer is, for example, that the maximum thickness of the center of the product semiconductor wafer is 100.3% of the thickness of the outer periphery. -102.5%.

  In the lapping process using a lapping machine with an upper surface plate and a lower surface plate, the manufacturing method of the product semiconductor wafer is forced on the outer periphery of the wafer by increasing the rotation speed of the upper and lower surface plates from the conventional rotation speed. It can be produced by generating sagging. In addition, in the double-side polishing process, it is manufactured by forcibly generating sagging at the outer periphery of the wafer by increasing the rotation speed of the upper and lower surface plates of the double-side polishing apparatus and the wafer rotation speed from the conventional rotation speed. be able to.

  The invention according to claim 2 has a surface that is gently curved into a convex shape in which the central portion protrudes from the outer peripheral portion in a state where it is placed on a horizontal flat plate without applying external force in an environment of room temperature and atmospheric pressure. A product semiconductor wafer having a maximum height of a central portion of the product semiconductor wafer of 100.3% to 102.5% of a thickness of an outer peripheral portion of the product semiconductor wafer.

  According to the second aspect of the present invention, in a state of being placed on a horizontal flat plate without applying an external force in an environment of room temperature and atmospheric pressure, it is gently curved into a convex shape in which the central portion protrudes from the outer peripheral portion. In the product semiconductor wafer having a surface, the maximum height of the central portion of the product semiconductor wafer is set to 100.3% to 102.5% of the thickness of the outer periphery of the product semiconductor wafer. When supported, the surface of the wafer becomes substantially flat. As a result, it is possible to suppress a decrease in pattern resolution and depth of focus due to deflection of the central portion of the wafer due to the weight of the product semiconductor wafer, and high pattern accuracy can be ensured.

  If the maximum height of the center portion of the product semiconductor wafer is less than 100.3% of the thickness of the outer periphery of the product semiconductor wafer, it becomes difficult to maintain a desired warp shape in the outer periphery holding type. Further, producing a wafer exceeding 102.5% causes a problem in stability in terms of the manufacturing method. Specifically, it becomes difficult to maintain the wafer surface cleanliness (particle quality) uniformly over the entire wafer surface. The preferable maximum height of the center part of the product semiconductor wafer is 100.7% to 101.5% of the thickness of the outer peripheral part of the product semiconductor wafer. Within this range, the surface warp shape can be flattened as desired in the outer peripheral holding state without causing any particular problems in wafer processing.

  According to the first aspect of the present invention, the surface of the product semiconductor wafer protrudes from the outer peripheral portion of the surface of the product semiconductor wafer in a state where it is placed on a horizontal flat plate without applying an external force in an environment of room temperature and atmospheric pressure. While curving into a gentle convex shape, the maximum thickness at the center of the wafer was supported from below on the outer periphery of the wafer without applying external force to the outer periphery of the wafer at room temperature and atmospheric pressure. Since the thickness is obtained by adding the maximum amount of deflection at the center of the wafer, the surface of the wafer becomes substantially flat when the wafer is supported. As a result, it is possible to suppress a decrease in pattern resolution and depth of focus due to deflection of the central portion of the wafer due to the weight of the wafer, and high pattern accuracy can be ensured.

  According to the invention described in claim 2, since the maximum height of the central portion of the product semiconductor wafer is set to 100.3% to 102.5% of the thickness of the outer periphery of the product semiconductor wafer, the outer periphery of the wafer Is supported from below, the surface of the wafer becomes substantially flat. As a result, it is possible to suppress a decrease in pattern resolution and depth of focus due to deflection of the central portion of the wafer due to the weight of the product semiconductor wafer, and high pattern accuracy can be ensured.

  Examples of the present invention will be specifically described below.

  In FIG. 1, reference numeral 10 denotes a product silicon wafer (product semiconductor wafer) according to Embodiment 1 of the present invention. The surface (device formation surface) is mirror-finished, cleaned, and subjected to product inspection from a wafer manufacturing factory. It is a 450 mm, specific resistance 10-11 Ω · cm, P-type silicon single crystal wafer. Here, the product silicon wafer 10 is point-supported on a wafer stage 15 of a stepper (reduction projection type exposure apparatus) 11 of a device process.

First, the stepper 11 will be described with reference to FIGS. 1 and 2.
The stepper 11 includes an exposure light source 12, a mask stage 13 that is sequentially spaced immediately below the exposure light source 12, a reduction projection lens 14, and a wafer stage 15.
The mask stage 13 clamps the mask 16 that is the original of the exposure pattern, and scans the mask 16 with respect to the light from the exposure light source 12. The reduction projection lens 14 reduces and projects the pattern on the mask 16 onto the surface 10 a of the product silicon wafer 10. The wafer stage 15 scans light (exposure light) from the exposure light source 12 while supporting the outer peripheral portion b of the product silicon wafer 10 coated with the photoresist on the surface 10 a from below and synchronizing with the mask stage 13. To expose.

  At the time of exposure, a position 3 mm from the outermost peripheral edge of the product silicon wafer 10 to the center in the radial direction of the outer peripheral portion b of the product silicon wafer 10 is placed on the wafer stage 15 via the six support pins 20 at room temperature and atmospheric pressure. In the state where no external force is applied, the wafer is point-supported every 60 ° in the circumferential direction of the wafer and with the front and back surfaces 10a and 10b of the wafer being horizontal. In this state, light is irradiated from the exposure light source 12. The irradiated light passes through the pattern formed on the mask 16, and the passing light is reduced by the reduction projection lens 14 and transferred to the photoresist on the surface 10 a of the product silicon wafer 10.

Next, the product silicon wafer 10 will be described with reference to FIGS.
The product silicon wafer 10 has a front surface 10a and a back surface 10b that protrude from the outer peripheral portion b with a central portion a protruding in a state where the product silicon wafer 10 is placed on a horizontal flat plate without applying external force in an environment of room temperature and atmospheric pressure. It is a double-sided copper bowl shape that is gently curved in shape (FIG. 2a). In addition, the maximum thickness t of the center portion a of the product silicon wafer 10 is a supporting position of the outer peripheral portion of the product silicon wafer 10 (in the radial direction from the outermost peripheral edge of the wafer) in a state where no external force is applied in an environment of room temperature and atmospheric pressure. The thickness is obtained by adding the maximum deflection amount c of the center of the wafer when the outer periphery of the product silicon wafer 10 is point-supported to the thickness t1 (position 3 mm toward the center) (FIG. 2b). Specifically, the thickness t1 of the outer peripheral portion and the deflection amount c are 2 μm. The relationship between the thickness t1 of the outer peripheral portion of the product silicon wafer 10 and the thickness of the central portion a of the product silicon wafer 10 is 101.0% of the thickness t1 of the outer peripheral portion, which is the maximum thickness of the central portion a. t. Thereby, the flatness of the wafer surface can be ensured.

This product silicon wafer 10 is manufactured by the following manufacturing method. That is, the silicon single crystal pulled by the Czochralski method is subjected to peripheral grinding, block cutting, and slicing sequentially to obtain a silicon wafer. Thereafter, each process of chamfering, lapping, etching, and polishing (including simultaneous polishing of the front and back surfaces of the wafer) is performed on the silicon wafer, and only the wafer that is evaluated as a non-defective product by the product inspection becomes the product silicon wafer 10.
As a method of making the front and back surfaces of the product silicon wafer 10 into a copper bowl shape, in the lapping process using the lapping apparatus having the upper surface plate and the lower surface plate, the rotational speed of the upper and lower surface plates is increased from the conventional 15 rpm to 45 rpm, A method of forcibly generating peripheral sag on the front and back surfaces 10a and 10b of the wafer is employed. Or, in double-sided simultaneous polishing using a double-side polishing machine having an upper surface plate with a polishing cloth and a lower surface plate with another polishing cloth, the rotational speed of the upper and lower surface plates is increased from 30 rpm to 50 rpm. Alternatively, a method of forcibly generating a peripheral sag on the front and back surfaces 10a and 10b of the wafer may be used.

  Further, as another product silicon wafer 10, a wafer surface 10a having a copper bowl shape and a flat wafer back surface 10b may be employed (FIGS. 3a and 3b). In this case, if the wafer outer peripheral portion is supported by the six support pins 20, the wafer surface 10a becomes a product silicon wafer 10 in which the wafer front surface 10a is flat and the wafer back surface 10b is copper cup-shaped.

  Thus, in Example 1, the surface 10a of the product silicon wafer 10 was placed on the outer peripheral portion b in a state where the product silicon wafer 10 was placed on a horizontal flat plate without applying an external force in an environment of room temperature and atmospheric pressure. Further, the wafer is bent into a gentle convex shape with a protruding central portion a, and the maximum thickness t of the central portion a of the wafer is applied to the thickness t1 of the outer peripheral portion of the wafer by applying an external force in an environment of room temperature and atmospheric pressure. The thickness obtained by adding the maximum deflection amount c of the central portion a of the wafer when the outer peripheral portion b of the wafer was point-supported. Thereby, the surface a of the wafer is substantially flat (planar) when the point is supported on the outer peripheral portion b of the wafer. As a result, it is possible to suppress a decrease in pattern resolution and depth of focus due to deflection of the central portion b of the wafer due to the weight of the product silicon wafer 10, and high pattern accuracy can be ensured.

Here, the result of the experiment of suppressing the amount of deflection at the center of the wafer at the time of exposure of the product silicon wafer performed using the stepper of Example 1 while manipulating the shape of the product silicon wafer will be reported. As the product silicon wafer, a P-type silicon single crystal wafer having a diameter of 450 mm, a specific resistance of 10 to 11 Ω · cm, and the same as in Example 1 was employed.
A laser displacement meter fixed to a separate jig was used as the deflection measuring device. The results are shown in Table 1. In Table 1, t1 is the thickness of the outer peripheral portion (support position) of the product silicon wafer, t is the maximum thickness of this central portion, and c is the maximum deflection amount of the central portion of the wafer.

  As is clear from Table 1, in Test Examples 1 to 3, the maximum deflection c of the product silicon wafer was about 10 to 500 μm, whereas in Comparative Example 1, the deflection was 1000 μm and the deflection was significantly large. As a result, the surface of the product silicon wafer is curved into a gentle convex shape with the center protruding from the outer periphery, and the maximum thickness of the center of the wafer is changed to the thickness of the outer periphery of the wafer. It was found that the surface of the product silicon wafer becomes substantially flat when this point is supported, if the thickness is obtained by adding the maximum deflection amount of the center of the wafer when the point is supported. As a result, it was possible to suppress a decrease in the resolution of the pattern and the depth of focus due to the deflection of the center of the wafer caused by the weight of the product silicon wafer, and a high pattern accuracy could be ensured.

It is a front view during the exposure operation | work of the product semiconductor wafer which concerns on Example 1 of this invention. It is a front view before the outer periphery support of the product semiconductor wafer which concerns on Example 1 of this invention. It is a front view of the outer periphery support state of the product semiconductor wafer which concerns on Example 1 of this invention. It is a front view before the outer periphery support of the product semiconductor wafer which concerns on Example 1 of this invention. It is a front view of the outer periphery support state of the product semiconductor wafer which concerns on Example 1 of this invention. It is a front view before the outer periphery support of the product semiconductor wafer which concerns on the conventional means. It is a front view of the outer periphery support state of the product semiconductor wafer which concerns on the conventional means.

Explanation of symbols

10 Product silicon wafer (Product semiconductor wafer),
10a center,
10b outer periphery,
c Maximum deflection,
t Maximum thickness at the center,
t1 Maximum thickness of the outer periphery.

Claims (2)

A product semiconductor wafer having a gently curved surface in a convex shape with the center portion protruding from the outer peripheral portion in a state of being placed on a horizontal flat plate without applying external force in an environment of room temperature and atmospheric pressure,
The maximum thickness of the center of the product semiconductor wafer,
When the outer periphery of the product semiconductor wafer is supported from below at a plurality of positions in the circumferential direction of the product semiconductor wafer without applying an external force to the thickness of the outer periphery of the product semiconductor wafer at room temperature and atmospheric pressure. A product semiconductor wafer having a thickness obtained by adding the maximum amount of deflection at the center of the product semiconductor wafer. A product semiconductor wafer having a gently curved surface in a convex shape with the center portion protruding from the outer peripheral portion in a state of being placed on a horizontal flat plate without applying external force in an environment of room temperature and atmospheric pressure,
A product semiconductor wafer in which a maximum height of a central portion of the product semiconductor wafer is set to 100.3% to 102.5% of a thickness of an outer peripheral portion of the product semiconductor wafer.

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