JPH10256333A - Manufacture of evaluating semiconductor wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor wafer for evaluation, which can measure cracks, processing strains and the like introduced in slicing highly accurately. SOLUTION: A rotary shaft 15 of a ring-shaped polishing tool 14 having the outer diameter smaller than the outer diameter of a wafer 11 is inclined by an inclination angle θ from a direction V intersecting the surface of the wafer at a right angle. The ring-shaped polishing tool 14 is made to face the surface of the wafer. The ring-shaped polishing tool 14 is pushed to the surface of the wafer 11. A ring-shaped polishing groove, which has the concentric pattern with the profile of the wafer 11 and has a partially cut part, is formed at the surface of the wafer. The wafer surface at both sides of the polishing groove remains as the unpolished initial surface. Since the long polishing groove is formed in this way, the distribution of the defect such as the cracks and the processing strains can be measured highly accurately. The depth of the defective part is also measured directly by the comparison with the initial surface on both sides of the polishing groove.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaluation semiconductor wafer used for detecting defects such as cracks and processing distortion introduced into the surface of a wafer cut from an ingot or a wrapped wafer. How to create.

[0002]

2. Description of the Related Art A semiconductor wafer is obtained by slicing an ingot with an internal ring, a wire saw or the like. For semiconductor wafers cut from ingots,
Cracks and distortions due to processing are introduced. For example, as shown in FIG. 1, a surface layer including a crack layer 3, a plastic flow layer 4, and the like is formed on a perfect crystal silicon 1 via an elastic deformation layer 2. In the crack layer 3, minute cracks generated by the processing are distributed and reach a depth of about 10 μm from the wafer surface. In order to set processing conditions in the subsequent lapping step according to the depth of the crack layer 3, it is necessary to measure the depth of the crack layer 3 in advance. A sample used for measuring the depth of the crack layer is usually prepared by an angle polishing method. In the angle polishing method, as shown in FIG. 2, a test piece 6 is attached to an inclined surface of an attaching block 5, attached to a guide ring 7, and the test piece 6 held in an inclined state is polished by a polishing plate 8. .

As shown in FIG. 3, the surface of the test piece 6 is polished obliquely at an inclination angle θ corresponding to the inclined surface of the sticking block 5. The crack layer 3 on the surface of the test piece 6
The crack layer cross section 9 is exposed as an inclined surface spread in the thickness direction by the angle polishing. Assuming that the thickness of the crack layer 3 is D, the length of the cross section of the crack layer generated by the angle polishing is represented by L = L / Sinθ. Usually, since the angle polishing is performed by setting the inclination angle θ to 5.7 degrees, L = D / s
in 5.7 degrees = D × 10. That is, the crack layer 3 having a thickness D is observed as a crack layer cross section 9 having a width L that is magnified ten times.

[0004]

In the conventional angle polishing method, cracks are detected by microscopic observation of the cross section 9 of the crack layer. The depth from the wafer surface at the position where the crack was detected cannot be measured by comparison with the test piece surface 10 because the entire edge portion of the test piece 6 becomes a crack layer cross section 9 inclined as shown in FIG. , Based on the angle component. However, it is not possible to know whether or not the test piece 6 is processed at the exactly set angle, and the accuracy and reliability of the measured depth are lacking. In addition, since the test piece 6 fixed to the attachment block 5 is polished, if the angle is reduced so that the length L of the crack section layer 9 increases,
The pressure distribution applied to the test piece 6 from the initial stage of processing tends to fluctuate from place to place, and the reliability in the depth direction becomes poor. As a result, the length L of the crack section layer 9 that can be formed is restricted, and a section layer in which the crack layer 3 can be observed in detail cannot be obtained. The present invention has been devised in order to solve such a problem. By forming a long ring-shaped polishing groove having a continuously changing depth, the processing strain introduced into the crack layer and the cracks are reduced. It is an object of the present invention to obtain an evaluation semiconductor wafer capable of easily and accurately detecting defects such as defects.

[0005]

In order to achieve the object, a method for preparing a semiconductor wafer for evaluation according to the present invention is arranged so that a rotation axis of a ring-shaped polishing tool having an outer diameter smaller than an outer diameter of a wafer is perpendicular to a wafer surface. The ring-shaped polishing tool is slightly inclined from the direction to be opposed to the wafer surface, the ring-shaped polishing tool is pressed against the wafer surface, and the ring-shaped polishing groove concentric with the wafer contour and partially cut off is formed on the wafer surface. It is characterized by forming.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a semiconductor wafer for evaluation is prepared as follows. The wafer 11 obtained by slicing the ingot is sampled and fixedly arranged on the polishing base 12 as shown in FIG. A predetermined tilt angle θ between a direction V perpendicular to the surface of the wafer 11 and the center of rotation C
Then, the polishing tool 14 having the polishing pad 13 attached to the lower surface is opposed to the surface of the wafer 11. Tilt angle θ
Is preferably set in the range of 0.04 to 0.1 degrees depending on the size of the polishing tool 14 and the maximum depth of the polishing groove to be formed. In this state, when the polishing tool wafer 11 is polished while being pressed against the surface of the wafer 11 along the axial direction of the rotating shaft 15, a polishing groove 15 concentric with the contour of the wafer 11 is formed as shown in FIG. . Polishing groove 1
By appropriately adjusting the distance between the wafer 11 and the polishing tool 14, a portion 5 is formed in a ring shape except for an unpolished region 17 in which a part remains the initial surface. The opposite side of the unpolished region 17 is the deepest portion 18 that has been polished deepest. As shown in FIG. 6, the polishing groove 16 is gradually deepened with a constant gradient from the unpolished region 17 to the deepest portion 18.
In addition, on both sides of the polishing groove 16, initial surfaces 19 that have not been processed by the polishing tool 14 remain.

In the polishing groove 17 thus formed, the exposed crack section layer 9 can be made sufficiently longer than in the case of the conventional angle polishing. As a result, as shown in FIG. 6, the boundary between the crack layer 3 and the healthy crystal layer 1 is exposed with a large width to the crack section layer 9, and the distribution and amount of defects such as cracks and processing strain can be accurately detected. Moreover,
Since the initial surface 19 exists on the side of the crack cross section layer 9, it is possible to directly measure the depth of the portion where the defect is detected. The obtained measurement result is fed back to the slicing step and used for adjusting the processing conditions. It is also used for setting conditions for the subsequent lapping process. Similarly, a sample for measuring a defective portion such as a crack or a processing distortion is created for a wafer subjected to processing such as lapping and grinding.

[0008]

[Example] 200m in diameter sliced from an ingot
m, a wafer having an average thickness of 1 mm was used for the test piece 6.
As the polishing tool 14, a polishing tool having an outer diameter of 150 mm and an inner diameter of 130 mm equipped with a polishing pad 13 made of nonwoven fabric was used. The inclination angle of the rotating shaft 15 with respect to a direction V orthogonal to the surface of the wafer 11 fixedly arranged on the polishing base 12 is set to 0.
The polishing tool 14 was rotated at 500 rpm, and was pressed against the wafer 11 with a pressing force of 300 N / mm ² . After polishing was continued for 30 minutes, the polishing tool 14 was retracted from the surface of the wafer 11. Polished wafer 1
Observation of the surface of No. 1 showed that a portion having a circumferential length of 380 mm and an outer diameter of 15
A ring-shaped polishing groove 16 having a diameter of 0 mm and an inner diameter of 130 mm was formed. The deepest portion 18 of the polishing groove 17 has a depth of 100 μm.
m. The unpolished area 17 has a circumferential length of 95
mm. Both sides of the polishing groove 16 were unpolished initial surfaces 19.

Observation of the cross section 9 of the crack layer exposed to the polishing groove 16 reveals that a large number of cracks are detected up to a position 30 mm from the unpolished region 17, the number of cracks gradually decreases, and that 45 mm away from the unpolished region 17. Cracks are no longer detected. The positions 30 mm and 45 mm from the unpolished area 17 were found to correspond to a depth of 20 μm and 30 μm, respectively, by comparison with the initial surfaces 18 on both sides. As described above, since the amount of crack generation and the depth of the defective portion can be measured with high accuracy, highly accurate information necessary for adjusting the slicing and polishing conditions can be obtained.

[0010]

As described above, the evaluation semiconductor wafer prepared according to the present invention has an inclined surface in which the polishing grooves formed for detecting a defective portion are continuously deepened. For this reason, a defective portion is detected with much higher accuracy than a conventional evaluation semiconductor wafer prepared by angle polishing, and the depth of the defective portion can be easily and accurately measured by comparing with the initial surface.

[Brief description of the drawings]

FIG. 1 is a cross section of a wafer having a surface layer in which cracks have been introduced by slicing.

FIG. 2 Preparation of a semiconductor wafer for evaluation by conventional angle polishing

FIG. 3 is a sectional view of a crack layer having an inclination formed by angle polishing.

FIG. 4 is a view showing the preparation of a semiconductor wafer for evaluation according to the present invention.

FIG. 5 is a semiconductor wafer for evaluation in which circumferentially extending polishing grooves are formed.

FIG. 6 is a cross section of a semiconductor wafer for evaluation in which a polishing groove is formed.

[Explanation of symbols]

1: perfect crystalline silicon 2: elastic deformation layer 3: crack layer 4: plastic fluidized bed 5: sticking block
6: Test piece (wafer) 7: Guide ring 8: Polishing board 9: Cross section of exposed crack layer 10:
Specimen surface 11: Wafer 12: Polishing base
13: Polishing pad 14: Polishing tool 15: Rotating axis 16: Polishing groove 17: Unpolished area 18: Deepest part 19: Initial surface V: Direction perpendicular to wafer surface C: Rotation center of polishing tool θ: Rotation axis Tilt angle

Claims (1)

[Claims] 1. A ring-shaped polishing tool having a ring-shaped polishing tool having an outer diameter smaller than the outer diameter of a wafer is slightly inclined from a direction perpendicular to the wafer surface so that the ring-shaped polishing tool faces the wafer surface. And forming a ring-shaped polishing groove, which is concentric with the contour of the wafer and partially cut off, on the surface of the wafer.