JPH02274464A - Polishing device and method for semiconductor wafer - Google Patents

Abstract

PURPOSE:To manufacture a semiconductor wafer having a very good flatness with deformation of the surface plate of a polishing device due to polishing heat extremely reduced by providing plural cooling water paths on the surface plate to measure the temperatures at plural points and controlling the temperature distribution on the surface plate to be uniform. CONSTITUTION:According to the measurement values of thermometers 3 provided on two or more places of a surface plate 1, the quantity and temperature of water flowing through two or more concentric circlelike cooling water paths 5 of the surface plate 1 is adjusted for each cooling water path 5. Thus, the temperature distribution on the surface plate 1 is kept constant to polish a semiconductor wafer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a technique for polishing a semiconductor wafer, which requires a high degree of flatness, using a surface plate.

[Prior Art] As the degree of integration of semiconductor devices increases, the flatness of wafers is increasingly required. In particular, with the shift in wafer exposure from a batch transfer method to a reduction projection exposure method, this demand has become even stronger.

Final polishing of wafers is performed using a surface plate, and there are two methods: one for each side and one for both sides at the same time. Figure 4 shows an example of a conventional double-sided polishing apparatus that rotates and rotates the wafer while applying a constant polishing pressure, in which 1 is an upper surface plate, 2 is a lower surface plate, 3 is a thermometer, 4 is a temperature controller, 5 is a water channel, 9 is a sun gear, 1° is an internal gear, 11 is a planetary carrier, 12 is a wafer, 1
3 is a polishing cloth. Polishing cloth 1 is placed on the upper surface plate 1 and lower surface plate 2.
3 are attached and facing each other. A wafer 12 is inserted between the upper surface plate 1 and the lower surface plate 2 for polishing, and the wafer 12 is loosely inserted into a holding hole formed in the planetary carrier 11. The planetary carrier 11 rotates on its own axis due to the rotation of the sun gear 9, and as it rolls on the internal gear due to this rotation, it simultaneously performs a revolution. The surface plate is used to flatten the wafer, but the temperature of the surface plate changes due to the heat generated during polishing. Temperature changes in the surface plate change the shape of the surface plate and greatly affect the variation in thickness within the wafer, so the temperature is adjusted by cooling the surface plate with water (for example,
"Mirror Finishing Technology", Osamu Imanaka et al., October 31, 1982, p.
375-383), for this reason, the upper surface plate 1 and the lower surface plate 2 are provided with water channels 5 inside them to cool the surface plates, and at the same time,
The surface plate temperature is adjusted by changing the amount of water. The water channel 5 is constructed so that water enters from the center of the surface plate, flows to the circumference, returns to the center, and flows out.
The temperature of the upper surface plate 1 is constantly measured by a thermocouple 3 at a fixed point on the lower surface of the upper surface plate 1. Regarding the cooling effect of such a device, it has been reported that by keeping the cooling water temperature constant and adjusting the flow rate with the temperature controller 4, temperature fluctuations at fixed points can be kept within ±0.4°C. .

[Problems to be Solved by the Invention] However, in conventional polishing machines, each surface plate has one system of cooling water channels, and the contact area between the surface plate and the cooling water in one water channel is large, and the amount of water is small. Moreover, since the structure is such that the cooling water reciprocates from the center of the surface plate to the circumference through the water channel, stagnation of cooling water tends to occur. In other words, although there is a tendency for temperature distribution to occur in the radial direction of the surface plate, since temperature measurement is performed at a fixed point, it is impossible to detect even if a temperature distribution occurs on the surface plate. Furthermore, due to the structure of the water channel, it is not possible to adjust this temperature distribution, and therefore, there is a problem in that the change in shape of the surface plate during polishing cannot be adjusted.

In other words, the surface plate used for polishing is generally a circular surface plate because the object to be polished rotates and revolves around its axis. However, when examining the relationship between the deformation of the surface plate during polishing and the flatness of the semiconductor wafer, it was found that the surface plate The radial deformation of the semiconductor wafer reduces the flatness of the semiconductor wafer. This deformation of the surface plate in the radial direction during polishing is caused by fluctuations in the temperature distribution of the surface plate in the radial direction based on heat generated by polishing.

This invention was made to solve such problems, and it detects the temperature distribution of the surface plate caused by heat generation during polishing, and adjusts this to keep the shape of the surface plate constant.
The purpose of this invention is to provide a technology for manufacturing semiconductor wafers with excellent flatness.

[Means and effects for solving the problem] The means for achieving this objective is a surface plate having two or more concentric cooling channels, and two or more points at different distances from the center of the concentric circles. A surface plate provided with a thermometer for measuring the temperature distribution of the surface plate is used as a polishing surface plate, and this surface plate and each of the cooling water channels are provided with a flow rate control device for controlling the amount of water flowing through each of the cooling water channels. The polishing apparatus is a semiconductor wafer polishing apparatus, and the polishing apparatus is used to adjust the amount and temperature of water flowing into the cooling waterways to 1lliL for each cooling waterway based on the measured value of the thermometer, and to maintain a constant temperature distribution on the surface plate. This is a method of polishing semiconductor wafers in which the shape of the surface plate is maintained constant by polishing.

If there are two or more cooling channels on the surface plate, the amount of water flowing into each cooling channel can be changed independently. If this cooling water channel is concentric, the water flow will be in one direction in the circumferential direction, eliminating stagnation. This, combined with sharing the contact area between the surface plate and the water by dividing, will result in constant cooling. Effects can be obtained. At the same time, since each water channel shares the cooling of a zone according to its radius, the cooling effect in the radial direction of the surface plate can be reliably and easily adjusted. The amount of water is controlled by a flow control device, and the controlled amount is based on a measurement value taken by a thermometer. Therefore, in a polishing device for double-sided polishing, it is preferable that both of the two surface plates are the same as described above, and the thermometers are provided at two or more points at different distances from the center of each surface plate.
By comparing each measurement value, the temperature distribution in the radial direction of the surface plate can be grasped. If this temperature distribution is fixed during polishing, deformation of the surface plate during polishing can be prevented, but to fix it, the amount and temperature of water flowing into each concentric cooling channel can be adjusted. In 17, etc., flow low-temperature water or increase the amount of water in the waterway closest to the part, and for an immediate effect, flow or increase the amount of high-temperature water in the waterway closest to the low-temperature part. be.

[Example] (Example 1) A circular surface plate with a diameter of 1,400 mm was provided with six concentric water channels, a surface plate with thermometers attached at six locations was created, and a polishing device was manufactured by combining it with a flow rate regulator. The created surface plate is shown in Figure 1. (a) is a partial cross-sectional view of the surface plate, (b)
) The figure is a sectional view taken along the line A-A in figure (a), and 6 is a flow rate controller.

There are two water channels 5 near the top surface of the surface plate 1 and four channels near the bottom surface, and they are all concentric circles so that the cooling water that flows in flows out after making almost a full circle. A thermometer 3 was attached to each water channel 5, and each measured value was sent to a temperature controller 4, from which a control signal was sent to a flow rate controller 6 so that the flow rate to each water channel could be controlled.

In this example, a thermocouple is used as the thermometer, but other thermometers such as a thermistor may also be used.

(Example 2) A silicon semiconductor wafer having a diameter of 150 m was polished using the upper and lower surface plates of Example 1 to control the temperature distribution of the surface plate. Cooling water at two levels of temperature, hot and cold, was used for control.

This control system is shown in Figure 2 in Figure 2, where 7 is a water cooler and 8 is a water heater. Thermometers at six locations on upper surface plate 1 and lower surface plate 2
The measured values from the same six thermometers are sent to temperature controller 4.
Based on this input, a control command is output from the temperature controller 4 to the water flow controller 6. The water flow controller 6 is configured to be supplied with 15°C cold water and 35°C hot water from a water cooler 7 and a water heater 8. The water amount controller 6 selects cold water or hot water in response to a command from the temperature controller, and controls the amount of water supplied. This control is performed on each waterway side of the upper surface plate 1 and lower surface plate 2.
In other words, by predetermining the reference temperature at each point on the surface plate during polishing and the minimum flow rate of the water channel, and by controlling only the amount of cold water at all times, the difference between the actual temperature at the control point and the reference temperature is determined in advance. Although the temperature is within 0.3 degrees Celsius, there are sometimes spots where the temperature is 0.3 degrees Celsius or more lower than the standard temperature, and the amount of water in the waterway reaches the minimum standard. In such a case, warm water will be mixed with the waterway and cooling water at a slightly higher temperature will be sent. Polishing was performed while controlling the temperature distribution of the surface plate in this way, but the difference between the temperature at each point and the reference temperature was smaller than 0.5°C. Moreover, the flatness of the wafer after polishing did not exceed 1.0 μm/150×. This proves that a remarkable effect has been obtained compared to the fact that conventionally it has been difficult to obtain a flatness of 2 μm/150 mm.

(Example 3) The upper surface plate of Example 1 and the conventionally used upper surface plate shown in FIG. 4 with a diameter of 1400 m + g were polished while controlling the temperature distribution using a method suitable for each. The deformation was investigated and compared. The state of deformation is shown in Figure 3. Figure 0 is a cross-sectional view of the radius of the surface plate, and 1-0
is the center of the concentric circle, 1-E is the outer periphery, and ΔD is the amount of deformation. When the temperature distribution of the surface plate becomes non-uniform, the amount of deformation ΔD increases as it approaches the outer peripheral portion 1-H. The maximum value of the deformation amount ΔD measured while polishing for one hour was 2 for the conventional surface plate.
The surface plate of Example 1 had a very small diameter of 20 μm.

[Effects of the Invention] As described above, according to the present invention, a plurality of cooling channels are provided on the surface plate, the temperature is measured at multiple points, and the temperature distribution on the surface plate is controlled to be constant. Deformation of the surface plate due to polishing heat is extremely small, and therefore semiconductor wafers with extremely good flatness can be manufactured. Wafer flatness is an indispensable condition for high integration of semiconductors, and the effect of this invention, which achieves revolutionary high flatness, is truly significant.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a surface plate for explaining one embodiment of the present invention, Fig. 2 is a temperature control system diagram of the surface plate for explaining another embodiment, and Fig. 3 is a deformation state of the surface plate. FIG. 4 is a partial sectional view of a conventional polishing device. 1... Upper surface plate, 3... Thermometer, 4... Temperature controller, 5
...Cooling water channel, 6...Water flow controller.

Claims (2)

[Claims] (1) It has two or more concentric cooling water channels, and
A semiconductor wafer polishing apparatus comprising: a surface plate having thermometers installed at two or more points at different distances from the center; and a control device for controlling the flow rate of water flowing into the cooling water channel. (2) By adjusting the amount and temperature of water flowing into two or more concentric cooling channels of the surface plate for each cooling channel based on the measured values of thermometers installed at two or more locations on the surface plate. A semiconductor wafer polishing method characterized by polishing while maintaining a constant platen temperature distribution.