JPH0260467B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a wrapping operation method for surface polishing a semiconductor silicon wafer or the like.

Conventionally, as a wrapping operation method for performing surface polishing processing on semiconductor silicon wafers, etc., the following methods are used:
The lower surface plates rotate in opposite directions, and the carrier sandwiched between both surface plates rotates on its own axis and revolves in the rotational direction of the lower surface plate, thereby causing the workpiece (wafer) placed in the carrier to be exposed in four directions. A wrapping operation method is applied that applies motion and simultaneously polishes both sides of the workpiece.

The above-mentioned wrapping operation method is considered to be the optimal wrapping operation method in that it can obtain a high degree of processing accuracy for items that require precision on the micron order, such as wafers that are the basis of integrated circuits. To date, there has been no satisfactory measurement method for adjusting the finished thickness of a wafer, which requires the same precision as the surface smoothness, and the development of one is strongly desired.

Conventionally, the method of measuring the finished thickness of a wafer is to empirically determine the polishing time depending on the material of the wafer, the physical properties of the abrasive, and other conditions, and then measure the thickness between the upper and lower surface plates after polishing. The method used is to remove the wafer and measure it with a thickness gauge, but with this method, if the wafer is not polished to the desired thickness, the wafer is returned between the upper and lower surface plates and polished again. As a result, the work efficiency is very low, and the polishing process requires experienced skill.

As a method for measuring the finished thickness of a wafer without removing the wafer from between the upper and lower surface plates, there is an indirect measurement method that detects the distance between the upper and lower surface plates as the wafer thickness, which changes depending on the wafer polishing process. is possible.

However, this indirect measurement method has the disadvantage that measurement errors occur due to the presence of abrasives supplied between the upper and lower surface plates during polishing. If this problem can be solved, the indirect measurement method can be said to be the simplest and most practical method.

This invention eliminates measurement errors caused by abrasives in the above-mentioned wrapping operation in which a workpiece is sandwiched between the upper and lower surface plates for polishing. The object of the present invention is to provide a wrapping operation method that can accurately detect the thickness of the workpiece.

Another object of the present invention is to provide a wrapping operation method in which the polishing process is automatically stopped when the thickness of the workpiece reaches a predetermined finishing dimension in the polishing process using the above-mentioned upper and lower surface plates. That's what you're trying to get.

The wrapping operation method according to the present invention first supplies only abrasive between the upper and lower surface plates, rotates them for a certain period of time, detects the minimum value of the surface plate interval at the center of the surface plates, and stores it in the counting controller. The difference between the surface plate interval detected while performing polishing with a workpiece placed between the surface plates and the minimum value is compared with a predetermined finished dimension stored in advance in the counting controller,
The gist of this is to stop the wrapping operation when the two become equal.

The present invention will be explained in detail below based on the drawings showing an example of its implementation.

In Figures 1 and 2, 1 is the upper surface plate of the wrapping device, 2 is the lower surface plate, 3 is the sun gear, and 4 is the upper surface plate of the wrapping device.
is an internal gear, 5 is an upper surface plate lifting shaft, 6 is an upper surface plate lifting tool, and the upper surface plate 1 is rotated via the center rotating shaft 7, the cap body 8, and the rotary ring 6',
The lower surface plate 2 is rotated via the rotating tube shaft 9 and the seat 10, the sun gear 3 is rotated via the rotating tube shaft 11 and the seat 12, and the internal gear 4 is rotated via the rotating tube shaft 13 and the seat 12. 14.

15 is a carrier, 16 is a workpiece (wafer), an annular abrasive receiving gutter 17 is installed on the upper surface of the upper surface plate 1, and a hose 18 is installed in this receiving gutter 17.
The slurry-like abrasive supplied from the upper surface plate 1 is guided between the upper and lower surface plates through a through hole 19 formed in the upper surface plate 1.

A sensor 20 for detecting the downward displacement of the upper surface plate 1 is mounted on the upper surface plate hanger 6 directly above the central rotating shaft 7 via a housing 21 .

The sensor 20 has a well-known structure generally called a linear scale, and has a sleeve 20a.
and a rod 20b, a magnetized linear scale (not shown) is incorporated in the rod 20b, and a magnetic head (not shown) is incorporated in the sleeve 20a. The tip of the rod 20b is brought into contact with the upper end surface of the rotating shaft 7, and
When the upper surface plate 1 descends during the polishing process using the lower surface plate,
The downward displacement is transmitted to the sleeve 20a,
The induced voltage generated by the relative displacement between the magnetic head and the linear scale is extracted as a detection output signal of the sensor, which is sent to the counting controller 22.
It is digitally displayed on its internal storage display section, and each time it receives a stop signal, it stores the detection output signal at that time. The counting controller 22 also includes comparators A ₁ and A ₂ .

Next, a method of polishing a wafer using the wrapping apparatus constructed as described above will be explained with reference to the flow sheet shown in FIG.

In FIG. 3, G is a gate circuit and T is a timer. First, the rubbing rotation is performed while supplying only the slurry abrasive between the upper and lower surface plates 1 and ₂ .
Put S ₂ into terminal R and switch S ₃ into terminal O, and set the digital display on the memory display section to zero. When the start/stop controller 23 is set to start, the power supply voltage is supplied to the wrapping motor (not shown) and the sun gear 3 and internal gear 4 are driven, and the upper and lower surface plates begin to rub together and rotate. , At the same time, a start signal is sent to the timer T via the gate circuit G. If you set the timer T to a set time (the time required for the slurry to be evenly distributed between the upper and lower surface plates and for the upper surface plate to descend the most and settle down, which is determined in advance by experiment), this set time can be set. When this period has elapsed, a stop signal is automatically sent from the timer T to the start/stop controller 23, the supply of power supply voltage to the wrapping motor is cut off, and the polishing process is stopped (at this time, the upper and lower plates are lowered to the lowest position). ) At the same time, the stop signal is also sent to the storage display unit, and the above-mentioned lowest value of the upper surface plate lowered by the sensor is stored here.

Next, insert the wafer between the upper and lower surface plates via the carrier, set the upper setting value to the specified finishing thickness of the wafer, set switch S ₁ to terminal P, and switch S ₃ to terminal P.
is connected to terminal LA and the start/stop controller 23 is set to start, power supply voltage is supplied to the wrapping motor and polishing begins. As the polishing process progresses, the downward displacement value of the upper surface plate at each moment detected by the sensor 20 is sent to the comparator A ₁ via the memory display section.
When the value matches the upper setting value set for the finished thickness of the wafer, a stop signal is output from the comparator _A1 , and the signal is sent to the start/stop controller 23 via the gate circuit, and the power supply voltage to the wrapping motor is supply is cut off, the motor automatically stops. At the same time, in response to the stop signal, the current lowering value of the upper surface plate detected by the sensor 20 is stored in the storage display section. At this time, the wafer 16 is not affected by the slurry and is accurately polished to a predetermined finished thickness.

When polishing a wafer next time, if you set switch _S1 to terminal L and set the lower setting value to a value smaller than the wafer's previous finished thickness, the polishing process will automatically start when the wafer reaches the smaller thickness. stop and finish the wafer to a thinner thickness than the previous one. Conversely, if you set switch _S1 to the terminal P side and set the upper setting value to a value greater than the finished thickness of the previous wafer, the polishing process will automatically stop when the finished thickness of the previous wafer is reached, and the wafer will be Finish to a thicker thickness.

The mounting position of the sensor 20 for detecting the downward displacement of the upper surface plate 1 is not limited to the illustrated position, but may be changed to another position as long as it is not subject to mechanical fluctuations. Also sensor 20
Optionally, other measuring instruments may be used.

As described above, this invention is the simplest measuring method for detecting the distance between the lower surface plates as the thickness of the wafer, which changes depending on the polishing process of the wafer. Even if the particle size of the grain changes, the difference between the predetermined finished thickness of the wafer and the actual finished thickness can be adjusted as a correction value in the next polishing process, allowing for high-quality processing with a stable finished wafer thickness. Accuracy (±2 microns)
is obtained.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of one embodiment of a wrapping apparatus for implementing the method of the present invention, FIG. 2 is a perspective view of a sensor and a counting controller, and FIG. 3 is a block diagram of a wrapping operation circuit. 1...Upper surface plate, 2...Lower surface plate, 3...Sun gear, 4
...Internal gear, 5...Upper surface plate lifting shaft,
6...Upper surface plate hanging tool, 7...Center rotating shaft, 8...Cap body,
9, 11, 13... tube shaft, 10, 12, 14... seat, 15... carrier, 16... workpiece (wafer),
17...Gutter, 18...Hose, 19...Through hole, 20...
Sensor, 21...Housing, 20a...Sleeve, 20b...Rod, 22...Counter controller, 23...
Start/stop controller, _S1 , _S2 , _S3 ...switch, T...timer, _A1 , _A2 ...comparator, G...gate.

Claims (1)

[Claims] 1 First, only the abrasive is supplied between the upper and lower surface plates and the machine is rotated for a certain period of time, the minimum value of the surface plate interval at the center of the surface plate is detected and stored in the counting controller, and then the workpiece is placed between the surface plates. The difference between the surface plate interval and the minimum value detected while performing the polishing process is compared with a predetermined finishing dimension stored in advance in the counting controller, and when the two become equal, the wrapping operation is stopped. A wrapping operation method characterized by: