JPH0752149A - Wafer manufacturing method - Google Patents

Abstract

(57) [Summary] (Modified) [Objective] The present invention provides a wafer having a highly accurate thickness obtained by cutting an ingot such as a semiconductor ingot or a synthetic quartz ingot mechanically fed to a wire with a wire saw. A method of manufacturing is provided. [Composition] In a method for manufacturing a wafer by cutting a round ingot along its diameter direction with a wire saw,
The feed speed of the ingot at a position 55 to 70% in diameter from the cutting start portion of the round ingot is set as the minimum feeding speed, and the feeding speed of the ingot at the cutting start portion and the cutting end portion is 2 to the minimum feeding speed, respectively. Four
Double and 1.2 to 2 times, and during the cutting, the method for manufacturing a wafer is characterized in that the feeding speed of the ingot is continuously changed at each speed change point, and a round ingot is cut by a wire saw. In the method for producing a wafer, the amount of wire wear is controlled so that the wire diameter is 10 μm or less in the case of reciprocating traveling, and 5 μm or less in the case of traveling in one direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a wafer having a highly accurate thickness by cutting an ingot such as a semiconductor ingot or a synthetic quartz ingot mechanically fed to a wire with a wire saw. is there.

[0002]

2. Description of the Related Art When cutting a wafer from an ingot with a wire saw, generally, a method of mechanically raising or lowering the ingot while applying a slurry of abrasive grains suspended in oil or water to the wire and pressing it against the wire is used. It is being appreciated. There are two methods of feeding this ingot, one is mechanically feeding and the other is hydraulic actuator.However, in the latter case, there is a problem that the hydraulic pressure changes subtly with the oil temperature change and the cutting speed changes.
The former mechanical feeding method, which is not easily affected by temperature, is adopted. At this time, if the thickness accuracy of the wafer obtained after cutting is poor, various problems occur in the polishing process by the lapping machine in the next step. One is that if there is a large variation in the thickness between the wafers just after cutting or if there is a large variation in the thickness within one wafer, it becomes difficult to obtain the thickness accuracy of the wafer in the lapping process, and the finishing accuracy is poor. Is a problem. In the cutting of an ingot with a wire saw, several hundred wafers are continuously manufactured by one cutting. Therefore, if there is a large difference in the thickness between the cut wafers, the lap polishing is performed batchwise by grouping several wafers of similar thickness to improve the finishing accuracy after lapping. However, there is a drawback in that a considerable amount of labor is required for the work of measuring the thickness and making the batch so that the thickness falls within a certain range in advance. Another problem is that if a wafer with poor thickness accuracy is lap-polished, the thick part of the wafer will be in contact with the lapping plate for a long time, resulting in uneven wear of the plate and deterioration of the finishing accuracy with the number of processing batches. Occurs significantly faster than a wafer with high accuracy, and there is a drawback that the shape of the lapping plate must be frequently modified to maintain the accuracy of lapping.
Therefore, it is necessary to set the accuracy of variation in the thickness of the wafer immediately after cutting with a wire saw to 5 μm or less.

In the case of cutting a square ingot, as in Japanese Patent Application No. 4-337965 proposed by the same applicant, the feed speed of the square ingot at the beginning of cutting is increased and thereafter the cut is made at a constant feed speed. By setting such conditions, it is possible to accurately cut the thickness of the wafer, but in the case of a round ingot, even if the method was used, sufficient accuracy could not be obtained.

[0004]

SUMMARY OF THE INVENTION The present invention is intended to solve the above problems and to provide a method of manufacturing a wafer having a high thickness accuracy from a round ingot by a cutting method using a wire saw.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have studied the conditions for cutting a round ingot with a wire saw in detail, and have conducted repeated experiments to complete the present invention. The first invention is a method for manufacturing a wafer by cutting a round ingot along a diametrical direction thereof with a wire saw, wherein the ingot at a position 55 to 70% in diameter from the cutting start portion of the round ingot is The feeding speed is set to the minimum feeding speed, the feeding speed of the ingot at the cutting start portion and the cutting end portion is set to 2 to 4 times and 1.2 to 2 times the minimum feeding speed, respectively, and each cutting speed of the ingot feeding speed is changed during cutting. A method for manufacturing a wafer, which is characterized in that the feeding speed at a point is continuously changed, and the second invention is a round ingot using a wire saw. A method of manufacturing a wafer by cutting the door, in the case of 10μm or less in the wire diameter in the case of round trip wire wear amount, and the one-way travel 5μ
A method for manufacturing a wafer is characterized in that the wafer is controlled so as to be not more than m.

The present invention will be described in detail below. First, with respect to the second invention, a study was conducted to suppress the difference in thickness between wafers obtained by cutting a round ingot with a wire saw to 5 μm or less. In the case of a wire saw, we first analyzed the cause by focusing on the difference in the thickness of the wafer between the wire supply side and the outlet side, and as a result, the wire was worn during cutting of the ingot and became thin on the outlet side. Then, it was found that the thickness was finished thick at the end of cutting of the wafer. For this reason, the present invention has been completed by examining the amount of wire wear at a level that does not affect the lapping process.

Regarding the first invention, as a result of manufacturing the wafer under the wire wear amount condition, the accuracy is improved to a level where the variation in the thickness between the wafers does not affect the lapping process, but it is still 1 Since there was a large variation in the thickness of each wafer, further studies were conducted. As a result, we have found a regularity in which the thickness gradually becomes thinner at the beginning of cutting, becomes thickest at the part corresponding to the center of the wafer, and becomes thinner at the end of cutting. As a result of investigating the cause, as shown in FIG. 1 (a), the wire stretched straight before the start of cutting gradually bends due to an increase in cutting resistance at the same time as the start of cutting, ), The portion corresponding to the vicinity of the center of the wafer is most bent, and
As shown in (c), it was found that the bending decreased toward the end of cutting. Therefore, the substantial cutting speed changes in each part of the wafer, which means that the substantial cutting speed decreases from the start of cutting to the central part of the wafer and increases from the center to the end of cutting. It was found that when the substantial cutting speed is high, the wafer becomes thick, and when the cutting speed is slow, the wafer becomes thin, so that the thickness in the wafer varies.
Therefore, it was found that if the feeding speed of the ingot is controlled so that the substantial cutting speed becomes constant, the variation in the thickness within the wafer can be solved, and the present invention has been completed.

The present invention will be described in more detail below. In the second aspect of the invention, since the wire saw involved in cutting wears in proportion to the operating time, the wire diameter becomes thin, and the cutting thickness accordingly increases. Since the thickness tends to become thicker, the usable limit of the wire is reciprocated with a diameter that is a constant value that the wire wear amount is determined in advance from the relationship with the material hardness of the material to be cut, ingot feed speed, wire saw feed speed, wire saw hardness, etc. In case of 10μm or less, in case of traveling 5μm
Below, this is 10 μm (round trip) or 5 μm (one side)
If it exceeds, the wire becomes too thin and the wafer thickness accuracy exceeds the set value. By controlling the wear amount of the wire to a certain level or less in this manner, the thickness accuracy of the wafer is improved, and the difference in thickness between the wafers can be reduced to 5 μm or less.

The wire wear amount is calculated by the following equation: wire wear amount (μm) = [(diameter of supply wire) −
(Diameter of used wire)]. When a round ingot is cut by reciprocating the wire, the amount of wire abrasion is preferably 10 μm or less for reciprocation and 5 μm or less for one side. 10 μm
(Reciprocation) If the wear exceeds 5 μm (one side), there will be a considerable difference in the thickness of the wafer between the wire supply side and the exit side. Therefore, when performing lap polishing, the batch configuration (those with almost the same thickness difference) It becomes necessary to collect several pieces and put them on a lap machine. Here, the reciprocal movement of the wire means a method in which a new wire is fed while being fed for 500 m in one direction, and then is cut backwards while being rewound for 400 m, which is repeated. When the wire is fed and cut in only one direction, the wire wear amount is preferably 5 μm or less. If it exceeds 5 μm, it becomes necessary to form a batch when lapping is performed.

In the first aspect of the invention, the relationship between the cutting position of the round ingot and the feeding speed is shown in FIGS. 1 (a), 1 (b),
A description will be given based on (c). Starting off from the lower end 3 of the section of the round ingot feeding speed of the ingot in (5-6 of FIG. 1 (b)) (FIG. 1 (a)) cutting diameter on 55 to 70% position from the point of beginning top
Set to low (hereinafter called minimum feed rate). This is an item that must be considered because the actual wire does not reach the radial depth of the ingot due to the bending of the wire itself even when the ingot feed amount reaches the ingot radius value (center). . Since the deflection of the wire increases until the contact length between the wire and the ingot becomes maximum (until the portion corresponding to the diameter of the ingot (the center) is cut), the substantial cutting speed must be minimized at this portion. If the feed amount of the ingot at this position is not set to the minimum, the accuracy of the wafer thickness will deteriorate. The range that does not affect the thickness accuracy corresponds to a position 55 to 70% in diameter from the starting point of cutting. The feeding speed of the round ingot at the beginning of cutting is set to 2 to 4 times the minimum feeding speed (Fig. 1 (a)). If this is less than double, the starting portion of cutting becomes thin and the effect of improving the thickness is small. If it exceeds 4 times, the thickness at the beginning of cutting becomes unstable. It is speculated that this is because the feeding speed is too fast at the start of cutting, and the wire slips before cutting into the round ingot, causing a slight deviation from the original cutting position.

At the end of cutting, the minimum feeding speed
The feed rate is 1.2 to 2 times higher (Fig. 1 (c)). Outside this range, the thickness accuracy becomes thicker or thinner, which adversely affects the wafer accuracy after lapping. The above points are connected so that the ingot is fed at a smooth speed. Further, more preferably, at a depth corresponding to 1/6 (17%) of the diameter from the start of cutting, the feed speed of the ingot is 1.5 to 2 times the minimum feed speed. If it is less than 1.5 times, it will be thin, and if it exceeds 2 times, it will be thick, which is not preferable in consideration of the accuracy of the wafer after polishing.

In order to continuously change the feeding speed, it is preferable that the feeding speed at the diametrical position of the ingot be stored in a computer in advance and controlled. FIG. 2 shows an example of the relationship between the cutting position and the ingot feeding speed of the round ingot of the present invention. As described above, by controlling the feeding speed of the ingot so that the substantial cutting speed of the round ingot becomes substantially constant, it becomes possible to manufacture a wafer with high thickness accuracy.

[0013]

The thickness accuracy of the wafer obtained by cutting the round ingot with the wire saw is determined by setting the wire wear amount of the present invention and changing the feeding speed of the round ingot at a specific cutting position. The thickness accuracy could be 5 μm or less.

[0014]

EXAMPLES The embodiments of the present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. (Examples 1 and 2 and Comparative Examples 1 and 2) A multi-wire saw manufactured by Hihei Toyama Co., Ltd. is used. As the round ingot, a synthetic quartz round ingot with a diameter of 150 mmφ and a length of 250 mmL was used. The target wafer thickness after cutting was 1,000 μm. A wire with a diameter of 200 μm was used, the wire speed was 700 m / min at the maximum, and one-way and reciprocating running was performed. The new wire was fed 500 m and reciprocating 400 m in the case of reciprocating cutting was repeated. At this time, the maximum wear of the wire is 5 μm or 8 μm on one side and 10 μm or 15 μm on the back and forth.
The wire supply amount was set to be m. The slurry for cutting is oil of GP # 600 (trade name of Shinano Denki Smelting Co., Ltd.)
The SiC abrasive grains were suspended and used.

The feed rate of the synthetic quartz round ingot starts to be cut from the lower end of the ingot, and the cutting depth from the lower end of the ingot is 105 mm (70% of diameter 150 mm).
It was set to 20 mm / Hr and this was the minimum feed speed. The feed speed of the ingot at the start of cutting was set to 60 mm / Hr, which is 3 times the minimum feed speed, and the feed speed of the ingot at the end of cutting was set to 1.5 times, and the feed speed was determined so that the speed changed smoothly at each shift point. Table 1 shows the variation in thickness of the synthetic quartz wafer obtained by cutting.

[0016]

[Table 1]

(Examples 3 and 4, Comparative Examples 3 to 8) Example 1
The cutting was performed under the same conditions as in Example 1 except that the setting position of the minimum feeding speed of the ingot and the feeding speed of the ingot at the cutting start portion and the cutting end portion were changed. The results are shown in Table 2.

[0018]

[Table 2]

(Comparative Example 9) As a result of cutting under the same conditions as in Example 1 except that the feeding speed of the synthetic quartz round ingot was made constant at all positions of the ingot cross section, the variation in the thickness in the wafer was 14.5. was μm.

(Measurement method of thickness accuracy) (1) Variation in thickness between wafers is 15 points at an interval of 10 mm on the diameter line of the wafer with respect to the total number of cut wafers at an interval of 10 mm (both ends are 1 mm from the circumference). The position near the center) was measured, and the average value of the maximum values and the average value of the minimum values were obtained and the difference was shown. (2) For the variation in the thickness within one wafer, the thickness was measured in the same manner as described above, and the difference between the maximum value and the minimum value was calculated to obtain the average value.

[0021]

EFFECTS OF THE INVENTION By improving the cutting conditions of a round ingot with a wire saw, the thickness accuracy (variation between wafers, variation within a wafer) of a manufactured wafer can be significantly improved, and post processing The accuracy of the wafer after lapping and polishing in the process is improved, and at the same time, the number of surface plate modifications for maintaining the accuracy of the lapping surface plate is reduced, and the productivity of high-precision wafers can be improved. Further, the labor required to measure the wafer thickness one by one due to the batch configuration at the time of lapping can be reduced, and its industrial utility value is extremely high.

[Brief description of drawings]

FIG. 1 (a) Cutting start portion, (b) 55-70% diameter cut position, (c) Cutting end portion: each drawing illustrates the cutting position of the round ingot of the present invention and the state of the wire saw. FIG.

FIG. 2 is an explanatory diagram showing a feeding speed of an ingot at a cross-sectional position of the round ingot of the present invention.

[Explanation of symbols]

1 round ingot 2 wire, 3 starting point of cutting 4 center (radius depth) 5 55% on diameter line 6 70% on diameter
Line 7 Cutting end part 1

Claims (2)

[Claims] 1. A method for manufacturing a wafer by cutting a round ingot along a diametrical direction thereof with a wire saw, the diameter of which is 55 to 70 from a cutting start portion of the round ingot.
The minimum feeding speed is the feeding speed of the ingot at the position of%, and the feeding speed of the ingot at the cutting start portion and the cutting end portion is 2 times the minimum feeding speed.
.About.4 times and 1.2 to 2 times, and during the cutting, the feed speed of the ingot at each shift point is continuously changed, and the wafer manufacturing method is characterized. 2. A method for manufacturing a wafer by cutting a round ingot with a wire saw so that the amount of wire wear is 10 μm or less in the case of reciprocating traveling, and 5 μm or less in the case of traveling in one direction. A method for manufacturing a wafer, which is characterized by controlling.