JPH071442A - Manufacture of wafer - Google Patents

Abstract

PURPOSE:To obtain a highly accurate wafer of little surface undulation and thickness irregularity by suppressing the temp. rise of an abrasive grain slurry by controlling the temp. in the close vicinity of the surface of the roller of a wire saw for cutting an ingot. CONSTITUTION:An abrasive grain slurry 12 controlled in its temp. is allowed to directly flow to a roller 2 and the temp. control of the slurry 12 is performed directly under the roller 2 by a temp. sensor 5. When the temp. rise of the abrasive grain slurry 12 caused by the generation of heat in an ingot 3 and a wire saw 1 is detected by the sensor 5, the abrasive grain slurry 12 cooled by a heat exchanger 10 is immediately supplied from a slurry tank 6 by a slurry supply pump 8 and rapid temp. control can be performed without generating a time lag. In the case of ON/OFF control, when a cooled slurry supply valve 15 is turned ON/OFF little by little, the temp. control directly under the roller 2 is extremely reduced in temp. change rate as compared with the temp. control in the slurry tank 6 and the deflection of the roller is stabilized and cutting accuracy is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a wafer for suppressing the surface waviness of the wafer generated when an ingot is cut by a wire saw and improving the accuracy of thickness variation.

[0002]

2. Description of the Related Art The shape of a wafer obtained by cutting a semiconductor ingot (round shape), a quartz ingot (round shape, a square shape), etc. with a wire saw has a difference in thickness at the start and end of cutting. As shown in 4-a), it tends to be wedge-shaped,
It is thin at the beginning of cutting and thick at the end. Further, the waviness of the surface also tends to be arcuate or corrugated as shown in FIG. This phenomenon has been analyzed from various directions such as deterioration of abrasive grains in the abrasive grain slurry, cutting speed, roller displacement, etc., but no definitive analysis results have been obtained yet. However, paying attention to the waviness shape in FIG. 4-a), there is a characteristic that all the cut wafers are warped in the same direction, and it can be inferred that this is caused by the displacement (or expansion / contraction) of the rollers. In other words, the amount of displacement of the roller (based on the length of the roller at the start of cutting, referred to as the amount of expansion and contraction of the length during cutting) at the start of cutting and during cutting is different for some reason, resulting in a wavy state. It is speculated that

[0003]

While investigating the cause of this roller displacement, it became clear that the temperature of the abrasive grain slurry rose sharply during cutting. This was generated by frictional heat between the wire and the ingot. For example, the abrasive grain slurry temperature before the start of cutting was 26 ° C, but it increased to 27 ° C at the same time as the start of cutting. As a result of the reproduction experiment so far, it is 17 μm / ° C with a polyethylene roller.
Since the elongation of / 26-27 ℃ is confirmed, the roller expands and contracts even with a slight temperature change. It is considered that the waviness is determined by the expansion and contraction (displacement) of the roller.

Further, since the cutting diameter of a round ingot changes as the cutting progresses, the heat generation amount also changes with time. When the roller displacement at this time is observed with time, FIG.
It can be seen that it corresponds to the waviness shape of the wafer. In a normal wire saw, the slurry is circulated between the slurry tank 6 and the cooling heat exchanger 10 in order to keep the temperature of the abrasive grain slurry 12 constant as shown in FIG. However, it has not been able to cope with this sudden change in the calorific value. Therefore, an object of the present invention is to immediately detect this rapid temperature change to suppress the temperature rise of the abrasive grain slurry, and to provide a method for producing a highly accurate wafer with less surface waviness and thickness variation.

[0005]

Means for Solving the Problems The inventors of the present invention have studied the temperature control method of the roller of the wire saw in order to solve the above-mentioned problems, and conducted many tests to scrutinize the conditions to arrive at the present invention. So, the gist is in the method of manufacturing the wafer by cutting the ingot with a wire saw,
A method for manufacturing a wafer, characterized in that the temperature of the roller surface of the wire saw is controlled, and particularly, the temperature control of the roller surface of the wire saw is controlled, and a temperature-controlled abrasive slurry is flowed over the roller surface. And a temperature sensor for controlling the temperature of the abrasive grain slurry is installed at a position near the surface of the roller.

The present invention will be described below in detail with reference to the drawings. In the conventional wire saw, as shown in FIG. 2, the bath temperature sensor 9 in the slurry tank 6 is used for the abrasive grain slurry 1
2 is controlled, and since the position of the nozzle 4 for the abrasive grain slurry is between the roller 2 and the ingot 3, the temperature of the abrasive grain slurry near the roller 2 increased by the frictional heat between the wire 1 and the ingot 3 is measured. Was not done. Since the heat is absorbed by the slurry receiving tank 11 and the return pipe, the temperature is lower than the actual value when returning to the inside of the slurry tank. For this reason, a temperature difference occurs between the supply temperature (non-measurement) of the abrasive grain slurry and the return temperature, and it is not possible to follow the actual change in the heat generation amount. In particular, in a round ingot, the cutting diameter changes depending on the position of the wire saw (moves up and down), and in fact, the temperature of the abrasive slurry near the roller changes in proportion to it, which in turn causes the roller to expand and contract, Since the temperature of the latest abrasive slurry has not been measured, the temperature control cannot follow this temperature change, and therefore the cutting accuracy deteriorates in proportion to the expansion and contraction of the roller.

The greatest feature of the present invention is that, as shown in FIG. 1, the abrasive grain slurry 12 whose temperature is controlled to a certain set temperature is directly applied to the roller 2, and the temperature is controlled by the temperature sensor 5 directly below the roller. In the method, as soon as it is detected that the temperature of the abrasive grain slurry has risen due to the heat generated by the ingot 3 and the wire 1, the abrasive grain slurry cooled by the heat exchanger 10 is supplied from the slurry tank 6 by the slurry supply pump 8. Therefore, quick temperature control can be performed without time lag. In this case, since it is not possible to measure the heat generated by the roller rotating at high speed by directly contacting the sensor with the roller, as shown in Fig. 3, install a temperature sensor in the immediate vicinity avoiding the wire within 5 cm from the lower end of the roller. We decided to measure indirectly. As a result, heat absorption by the slurry receiver 11 and the return pipe does not occur, and the measured value is closer to the actual value. Therefore, in the case of on-off control, if the cooling slurry supply valve 15 is turned on and off in small increments, the cooling slurry supply valve 15 shown in FIG.
The temperature control curve is as shown in Fig. 2, and the temperature control just below the roller has a much smaller temperature change rate than the temperature control inside the slurry tank, stabilizing the roller displacement and improving cutting accuracy. become.

Further, in order to improve the temperature control accuracy, the temperature of the slurry supplied can be set to a set temperature ± 0.5 to 1.0 ° C. to easily detect the temperature rise value just below the roller. Further, a proportional control method or a cascade method may be adopted for temperature control, and a high precision temperature control method according to the accuracy required for the wafer may be adopted. The number and arrangement of the abrasive grain slurry nozzles should also be taken into consideration. As shown in FIG. 3, the absolute number is increased (from 2 to 4), and 2 is placed between the roller and the ingot.
The cooling efficiency has been improved by adding two locations directly above the rollers and two locations between the rollers and the ingot.

[0009]

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 to 3, Comparative Example) A multi-wire saw manufactured by Nippira Toyama Co., Ltd. was used. The material to be cut is a round synthetic quartz ingot, and the abrasive grain slurry is SiC abrasive grains (GP # 600: Shinano Electric Refining Co., Ltd.) and oil (PS-LW-1: Palace Chemical Co., Ltd.)
(Manufactured) was used with a mixing ratio of 1.4: 1, and a 200 μmφ piano wire was used. The operating condition is a cutting speed of 20 mm / Hr.
And the wire speed was also constant at 500 m / min.
Regarding the new wire supply amount, the values shown in Table 1 were operated so that the wire friction amount was 10 μm or less. Slurry supply pump 8
Discharge rate of 200 liters / min., Heat exchange pump discharge rate of 130
Liter / min., And pure water at 12 ℃ is used as a refrigerant in the heat exchanger.
Supplied at 70 l / min. As shown in FIG. 3, the number of abrasive grain slurry nozzles is four, two for wire 1 and two for roller 2.
It was made into two, and it flowed over both. The position of the temperature sensor was 3, 4, 5 cm just below the roller in the examples, and the positions were set as the examples 1, 2, and 3, respectively. Further, in the comparative example, cutting was performed under the same conditions as in the example except that the position of the temperature sensor was in the slurry tank. A platinum resistance thermometer was used as the temperature sensor. Table 1 shows the cutting conditions for round ingots and the results. Both waviness and thickness variation are improved.

[0010]

[Table 1]

[0011]

According to the present invention, by suppressing the roller displacement of the wire saw and stabilizing it, the surface waviness and the thickness variation of the wafer obtained by cutting the ingot to be cut are suppressed, and a high precision wafer is obtained. Can be manufactured, and its utility value is extremely high in industry.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a wire saw temperature control method according to the present invention.

FIG. 2 is an explanatory diagram showing a conventional wire saw temperature control method.

FIG. 3 is a detailed explanatory view showing positions of an abrasive grain slurry nozzle and a temperature sensor according to an embodiment of the present invention.

FIG. 4 a) of a wafer cut by a wire saw
Sectional drawing, b) It is explanatory drawing which shows the surface waviness shape in each position of a diameter direction, a bow shape, and a waveform.

FIG. 5 is an explanatory diagram showing changes over time in roller displacement when a round ingot and a square ingot are cut.

FIG. 6 is an explanatory diagram showing a temperature control state of an abrasive grain slurry of Examples and Comparative Examples when a round ingot is cut.

[Explanation of symbols]

1 Wire 2 Roller 3 Cut Ingot 4 Abrasive Grain Slurry Nozzle 5 Temperature Sensor 6 Slurry Tank 7 Stirrer 8 Slurry Supply Pump 9 Tank Temperature Sensor 10 Heat Exchanger 11 Slurry Receiving Tank 12 Abrasive Grain Slurry 13 Heat Exchange Pump 14 Slurry Return Pump 15 Cooling slurry supply valve

Claims (3)

[Claims] 1. A method for manufacturing a wafer by cutting an ingot with a wire saw, wherein the temperature of the wire saw in the vicinity of the roller surface is controlled. 2. The method for producing a wafer according to claim 1, wherein the temperature control of the wire saw in the vicinity of the roller surface comprises flowing the temperature-controlled abrasive grain slurry over the roller surface. 3. The method for producing a wafer according to claim 1, wherein a temperature sensor for controlling the temperature of the abrasive grain slurry is provided at a position near the surface of the roller.