JPS6141706B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polishing device capable of polishing a thin plate material with high precision, and in particular to a polishing device capable of polishing a thin plate material with high accuracy, and in particular, a polishing device capable of polishing a thin plate material with high accuracy, and in particular, a polishing device capable of polishing a thin plate material with high precision, and in particular, a polishing device capable of polishing a thin plate material with high accuracy, and in particular, a polishing device capable of polishing a thin plate material with high accuracy. This invention relates to precision polishing equipment.

Conventionally, precision polishing of thin plate materials has been carried out using either Figure 1 or Figure 2.
This is done using a device like the one shown in the figure.

In the apparatus shown in FIG. 1, a workpiece 3 is sandwiched between a surface plate 1 that rotates as shown by the additional arrow and a plate 2 that rotates as shown by the additional arrow, pressure is applied by an air cylinder 4, and an abrasive is Polishing is performed while pouring liquid abrasive through a supply nozzle 5. In addition, the apparatus shown in FIG. 2 applies pressure by sandwiching the workpiece 3 held by a carrier 8 between an upper surface plate 6 rotating as indicated by the additional arrow and a lower surface plate 7 rotating as indicated by the additional arrow. In addition, a carrier drive mechanism consisting of a center gear and an internal gear (both not shown) causes the carrier 8 to perform planetary motion, and the abrasive supply nozzle 5 and the abrasive pipe 5a
Polishing is performed by pouring liquid abrasive onto the surface to be polished. In the apparatus shown in FIGS. 1 and 2, the thickness of the workpiece is measured during polishing by using a dial gauge 9 or the like via the plate 2 or the upper surface plate 6. Workpiece 3
Precise measurement is difficult because there is no other suitable means other than measuring the thickness indirectly. Therefore, it has been difficult to accurately control the polished dimensions.

Further, as shown in FIG. 3, the displacement detectors 10 and 1 detect the part of the workpiece 3 held on the carrier 8 that protrudes from between the upper surface plate 6 and the lower surface plate 7 due to planetary motion.
There is also a method of measuring by method 1, but this method must be carried out after stopping the polishing work and cleaning the measurement area of the workpiece 3, which not only impairs work efficiency but also damages the surrounding area of the workpiece 3. There are drawbacks such as a high possibility of errors being introduced because only measurements can be made using this method. In order to solve the above-mentioned problems, a polishing machine equipped with a device for measuring the thickness of a workpiece during polishing operation using an ultrasonic thickness gauge as shown in FIG. 4 has been developed.

In this device, a hole 6a is formed vertically through an upper surface plate 6, which is a rotating member, and an ultrasonic transducer 14 is attached to this hole. It is electrically connected to an arithmetic processing section (not shown). In this device, while pouring liquid abrasive onto the polishing surface through an abrasive pipe 5a, a transducer 14 emits ultrasonic waves to the workpiece 3, and the reflected waves are received by the arithmetic processing section (Fig. (not shown), and the thickness of the workpiece 3 is calculated.

FIG. 5 shows the received waveform. A in the figure is the transmitted wave,
B is the first surface wave, C to F are the bottom reflected waves, and depending on the time interval T ₁ between the bottom reflected waves C and D, the thickness t of the workpiece is t = 1/2 ν ₀ T ₁ It is calculated as ν ₀ is the sound velocity within the workpiece.

The thickness of a workpiece can be measured using the ultrasonic thickness gauge described above: (a) Measurement can be performed while polishing is being continued.

(b) Measurements can be made with higher accuracy than indirect measurements using conventional dial gauges (Figures 1 and 2). Although it has the following advantages, it also has the following disadvantages.

(i) When the temperature of the workpiece changes, the sound speed inside the workpiece changes, so unless the temperature change is detected and corrected, accurate thickness calculation cannot be performed.

(ii) When a thin plate-shaped workpiece is polished, the general tendency is that the amount of polishing is small near the center, and the amount of polishing is large near the outer periphery. The non-uniformity changes depending on conditions such as the rotational speed of the surface plate during polishing, and the rotational speed and revolution speed of the carrier. An example of this state is shown in FIG. The rotational speed of Kaburu is relatively high, and the rotational speed of Kabul is relatively low. Because of this phenomenon, even if the thickness is measured without specifying the measurement point on the workpiece 3, the data is insufficient for accurate polishing.

In view of the above circumstances, the present invention provides a high-precision polishing device that has small thickness measurement errors due to temperature changes, and that can calculate the thickness distribution of a workpiece and control the deviation to be within a predetermined standard. This is what we are trying to provide.

In order to achieve the above object, the present invention provides annular upper and lower surface plates that rotate around a common axis, a carrier that holds a workpiece and moves planetarily, and a center gear and an internal gear that drive the carrier. Therefore, in a thin plate polishing machine equipped with an ultrasonic thickness gauge that non-contactly measures the thickness of the workpiece being polished, the polishing section including the upper and lower surface plates and the carrier is immersed in a liquid abrasive. The thickness of the workpiece is determined based on the measurement value of the ultrasonic thickness gauge, the gear pitch diameter of the carrier drive mechanism, and the meshing conditions. The present invention is characterized by an automatic control device that calculates the distribution and controls the drive of the surface plate and carrier based on the calculation result.

Next, one embodiment of the present invention will be described with reference to FIG.

This device works on a semiconductor wafer 3' as a workpiece.
An annular upper surface plate 6' and an annular lower surface plate 7' are rotated around a common shaft 21 to hold a workpiece 3'. The carrier 8 is caused to move planetarily by a center gear 12 and an internal gear 13. A transducer 14 of an ultrasonic thickness gauge is attached to a pedestal 19. The lower surface plate 7' has a window-shaped opening 7a, and the internal gear 13 has a window-shaped opening 1.
3a are provided respectively. 4' is an air cylinder for pressing the upper surface plate 6' toward the lower surface plate 7'.

An automatic control device (details will be described later) 23 has a function of calculating the thickness of the wafer 3' by causing the transducer 14 to receive and transmit ultrasonic waves, and a function of controlling the drive of the upper and lower surface plates and the carrier. Attach.

The motor _M1 is an electric motor that drives the upper surface plate 6' via a common shaft 25, and is controlled by the automatic control device 23 described above.

Motor M ₂ connects center gear 12, motor M ₃ connects lower surface plate 7', motor M ₄ connects internal gear 13.
are controlled by the automatic control device 23 described above.

Liquid abrasive 17 is applied to a level that almost covers the upper surface plate 6'.
A cylindrical wall 1 is installed around the pedestal 19 to collect
9a are integrally connected to each other to function as a container for the liquid abrasive 17. A constant temperature bath 22 is provided separately from the above, and the liquid abrasive 1 is stored in the wall 19a of the pedestal.
A liquid abrasive 17' in an amount several times 7 is stored, and a cooler and a heater (both not shown) are provided to maintain the temperature of the liquid abrasive in a constant temperature bath at an appropriate constant value.

The liquid abrasive in the constant temperature bath 22 is pumped up and passed through the abrasive supply nozzle 5' and the storage tank 18 to the cylindrical wall 1.
A pump P for injecting into 9a is provided. Then, the liquid abrasive 17 inside the cylindrical wall 19a is transferred to a constant temperature bath 22.
A conduit 25 for the flow to flow downward is provided, and an electromagnetically actuated throttle valve 16 is interposed within this conduit 25.

A liquid level sensor 24 is provided to detect the liquid level of the liquid abrasive 17 within the cylindrical wall 19a, and a signal representing the liquid level position is input to the automatic control device 23. The automatic control device 23 is programmed in advance to open and close the throttle valve 16 in response to the liquid level signal to maintain the liquid level at a level that almost immerses the upper surface plate 6'. put. Next, as described above, the liquid abrasive whose temperature is controlled to maintain a constant temperature is circulated in the oil reservoir formed by the cylindrical wall 19a, and the upper and lower surface plates 6', 7' and the carrier 8 are The abrasive part containing the abrasive part is immersed in a liquid abrasive.

A common shaft 2 to which an internal gear 13, a center gear 12, a lower surface plate 7', and an upper surface plate 6' are fixed.
1 is provided with a rotation sensor (not shown), respectively.
The rotational speed and angular position are input to the automatic control device 23.

Then, the automatic control device 23 calculates the thickness and measurement position of each part of the wafer 3', which is the workpiece, based on the above-mentioned signals and the received signal of the ultrasonic transducer 14, and detects the thickness distribution. urge

Since the lower surface plate 7' and the internal gear 13 rotate, the opening 7a provided in the lower surface plate 7'
and the opening 1 provided in the internal gear 13.
3a come directly above the transducer 14 for each rotation. Then, at the moment when both the opening 7a and the opening 13a come directly above the transducer 14, an ultrasonic wave is emitted from the transducer 14 toward the workpiece (wafer) 3'. It reaches the wafer 3, is reflected, is received by the transducer 14, and the thickness of the wafer 3' is calculated.

FIG. 8 shows an example of a time chart of the above operation. Curved is the workpiece 3' passing over the transducer 14, and means that the high level part is passing. The curved edge is the internal gear opening 13a that passes over the transducer 14, and means that the high level part is passing through.

Similarly, curvature means that a high level portion is passing through the opening 7a of the lower surface plate.

At the moment when the high-level parts of the three curves G, C, and I above overlap, for example, a, b, c, ~ on the time axis,
When ultrasonic waves are emitted at each point of l, the ultrasonic waves emitted from the transducer 14 reach the workpiece (wafer) 3' via the openings 13a and 7a, are reflected, and are reflected at the openings 7a and 13a. The signal is received by the transducer 14 via the . From this received waveform and the timing of the rotating member, the thickness of each part of the wafer 3, which is the workpiece, can be calculated as follows. For example, in FIG. 8, the interval M shown on the time axis is the time when the wafer is passing above the transducer 14, m ₁ is the time when it approaches the transducer, m ₂ is the point at which it has passed over the transducer. Within this time, wafer thickness measurements are performed 12 times at each time point a, b, to l on the time axis.

Therefore, the thickness measurement at time a, which is close to time _m1 , is the thickness at the wafer periphery. Then, the thickness measurement points at points b, c, and d are sequentially moved to the center of the wafer.

Then, the thickness measurement point moves drawing a cycloid curve on the surface of the wafer, and its shape is determined by the pitch diameter of the center gear 12 and internal gear 13, the rotation speed and direction, and the attachment of the wafer 3' to the carrier 8. The position is determined analytically by the geometry. By applying the above principles,
A program for calculating the thickness measurement position at each time point a, b, to l can be incorporated into the automatic control device 23.

As described above, in this embodiment, the liquid abrasive at a constant temperature in the constant temperature bath 22 is in direct sliding contact with the workpiece 3' held in the carrier 8 and the workpiece 3'. , lower surface plate) are immersed, the frictional heat generated by the workpiece 3' is absorbed by the liquid abrasive, and the temperature is always maintained at a substantially constant temperature. Therefore, the sound velocity within the workpiece 3' is kept substantially constant, and changes in the sound velocity that cause thickness measurement errors are reduced to a practically negligible extent.

In this embodiment, the automatic control device 23
is a rotation sensor (see Fig. It receives a signal (not shown), stores the pitch circle diameter of the gear of the carrier drive mechanism, performs calculations according to a pre-given program, and calculates the thickness distribution state of the workpiece. Based on this calculation result, the polishing conditions are automatically adjusted by controlling the rotation of electric motors M ₁ , M ₂ , M ₃ , and M ₄ according to a pre-installed program, and the deviation in the thickness distribution is reduced. Automatically control to keep it within the specified range. For example, when the thickness distribution shows uniformity exceeding the specified value, the polishing speed is increased to improve work efficiency within the range where the deviation of the thickness distribution does not exceed the specified value, and the polishing speed is increased to the extent that the deviation of the thickness distribution does not exceed the specified value. When the polishing speed exceeds the specified value, the polishing speed is reduced until it falls within the specified value.The drive mechanism for polishing is automatically controlled to the best condition while maintaining a balance between polishing work efficiency and polishing finish quality. .

Figure 9 shows an example of the plate thickness measurement waveform in this example, and Figure 10 shows a silicon wafer with an outer diameter of 100 mm and a plate thickness of 530 μm, which is sandwiched between a polishing cloth attached and a lower surface plate. 0.15Kg/
This is the thickness distribution as a result of polishing while pressing with cm ² .
As explained with reference to FIG. 6, there is a tendency for the area near the center to be thicker and the periphery to be thinner, but it is recognized that the variation in the finished polished thickness is within about ±/μm.

As explained above, the present invention immerses the polishing section including the upper and lower surface plates and carriers in a liquid abrasive, is equipped with a means for controlling the temperature of the liquid abrasive, and is capable of adjusting the measured value of an ultrasonic thickness gauge. , provide an automatic control device that calculates the thickness distribution of the workpiece based on the gear pitch circle diameter and meshing conditions of the carrier drive mechanism, and controls the surface plate and carrier drive mechanism according to the calculation results. This eliminates the risk of thickness measurement errors caused by temperature changes, and automatically controls deviations in the thickness distribution of the workpiece to within a predetermined standard, allowing for efficient and highly accurate thin plate measurement. Polishing of shaped objects can be performed.

[Brief explanation of the drawing]

Figures 1 and 2 are schematic vertical cross-sectional views for explaining a conventional thin plate polishing apparatus and the thickness of the workpiece, respectively, and Figure 3 is a diagram showing the thickness of the workpiece. A front view of the measuring device, FIG. 4 is a partial vertical cross-sectional view of a wafer polishing device equipped with a means for measuring the thickness of a workpiece using ultrasonic waves, and FIG. 5 illustrates a thickness measuring method using ultrasonic waves. 6 is a distribution chart of the amount of polishing of the workpiece, FIG. 7 is a vertical cross-sectional view of a high-precision polishing device for thin plate material according to an embodiment of the present invention, and FIG. 8 is a diagram showing the same time. FIG. 9 is an example of a received waveform chart for plate thickness measurement in the embodiment shown in FIG. 7, and FIG. 10 is a chart showing the thickness distribution of the workpiece in the above embodiment. 1... Surface plate, 3, 3'... Workpiece, 4, 4'...
...Air cylinder, 5,5'...Abrasive supply nozzle, 6,6'...Upper surface plate, 7,7'...Lower surface plate, 8
...Carrier, 10, 11...Displacement detector, 12
...Center gear, 13 ...Internal gear, 1
4... Transducer, 15... Coaxial cable, 16... Throttle valve, 17... Liquid abrasive, 19
... Frame, 19a... Cylindrical wall integrally connected to the frame, 20... Cover, 21... Common shaft, 22...
... Constant temperature bath, 23 ... Automatic control device, 24 ... Liquid level sensor.

Claims (1)

[Claims] 1 Consists of annular upper and lower surface plates that rotate around a common axis, a carrier that holds the workpiece and makes planetary motion, and a center gear and internal gear that drive the carrier, and the workpiece that is being polished is In a thin plate polishing apparatus equipped with an ultrasonic thickness gauge that measures thickness in a non-contact manner, the polishing section including the upper and lower surface plates and carriers is immersed in a liquid abrasive, and the temperature of the liquid abrasive is controlled. have the means, and
The thickness distribution of the workpiece is calculated based on the measurement value of the ultrasonic thickness gauge, the gear pitch circle diameter of the carrier drive gear mechanism, and the meshing conditions, and based on the calculation results, A high-precision polishing device for thin plates, characterized by being equipped with an automatic control device that controls the drive of the lower surface plate and carrier.