JPS61188072A - Polishing method of wafer - Google Patents

Abstract

PURPOSE:To eliminate any variation in a floating value of a wafer as well as to make an excellent, nondistortion mirror securable, by detecting a load current of a polisher driving motor, while adjusting a vertical position of the wafer so as to make this load current constant. CONSTITUTION:A variation in a load current of a polisher driving motor 21 is detected by a detector 23, and this signal is transmitted to a comparator 24, comparing it with the setting value. In consequence, when it is a more shifted value than the setting value, a signal is transmitted to a controller 25, and a vertical motor 26 is driven according to size of this signal whereby a vertical position of a wafer 7' on a polisher 1' is adjusted via an up-down rod 27 and a support rod 10'. With this adjustment, a gap between abrasive cloth 2' and the wafer 7' is compensated, making it a fixed value, thus mirror finishing for the wafer 7' takes place without entailing any distortion.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention aims to finish the surface of a wafer such as a compound semiconductor crystal widely used in the electronics industry into a flat surface without processing distortion (a distortion-free mirror surface), and to The present invention relates to a polishing method for processing shape accuracy such as thickness and flatness.

(Prior art and its problems) In general, distortion-free mirror polishing of a compound semiconductor crystal, such as a GaAs5 wafer, is performed by holding several wafers as workpieces simultaneously bonded with wax to a polishing holder, and polishing the wafer with a soft cloth that rotates at a constant speed. Mechanochemical polishing is carried out by applying a chemical polishing liquid to the main body of the polisher while causing them to slide.

This method involves direct contact between the wafer and the polishing cloth surface.
Processing strain remains on the surface of a soft (Mohs hardness: 3) crystal such as GaAH, and when epitaxial growth is performed, a problem arises in which a single crystal thin film without defects or defects is not formed. For the purpose of reducing distortion, attempts have been made to use a processing method, ie, a non-contact polishing method, to obtain a distortion-free mirror surface by using only the chemical polishing and ching action of a chemical polishing solution without bringing the wafer into contact with the surface of the polishing cloth.

As one of the conventional non-contact polishing methods, as shown in FIG. 2, there is a method in which a polishing machine is rotated at high speed while continuously supplying a polishing liquid to levitate the workpiece by a minute amount and polish it.

1 is a disc-shaped polishing machine that is rotated at a constant speed by a motor, etc., 2 is an abrasive cloth provided on the surface of the polishing machine, and 3 is a chemical agent that can finish the workpiece to a distortion-free mirror surface. Polishing liquid, 4 is a tank for storing polishing liquid, 5 is a cock for adjusting the flow rate of polishing liquid, 6 is #-1 polishing liquid 3 is transferred to polishing machine 1
A nozzle for feeding 7I/i wafers to the center of the workpiece, 8 can hold several wafers 7 at the same time with adhesive wax, and a spherical seat 9 at the center of the opposite side (back side).
A holder 1 (1) is a support rod with a ball 11 formed at the tip to be incorporated into a spherical seat 9, and the assembly consisting of the wafer 7 and holder 8 can freely rotate around the support rod 10, and a polishing cloth The structure is such that the surface of the wafer 7 can be set parallel to the surface of 20. 12 is a disk connected to the support rod 10, 13 is attached to one end of a roller 14 that contacts the disk 12, and the other end is a disk. The weight 15 is a horizontal rod that is screwed together, and the central part is screwed to the support 16.The weight 15Fi serves to lift up the weight of the assembly consisting of the wafer 7, holder 8, and support rod 10, and This is a method that can be adjusted by changing the position of the weight 15 so that a minute pressure is applied to the surface.

An arm 17 supports the support rod 10 so that it can move up and down, and is fixed to a substrate 18.

In the figure, when the abrasive cloth 2 on the abrasive disk is rotated in the direction of the arrow while continuously supplying abrasive liquid, the abrasive liquid layer on the surface of the abrasive cloth flows out from the center to the outer circumference due to centrifugal force and flows at high speed along with the abrasive cloth. Due to the movement, dynamic pressure is generated by the fluid between the wafer 7 and the polishing cloth 2, and a phenomenon in which the wafer floats (a microscopic amount), that is, a hydroplaning phenomenon, is achieved, and the relative relationship between the inner and outer peripheries of the polishing cloth is necessarily Wafer 7 due to speed difference
The assembly of the holder 8 and the holder 8 rotates around the support rod 10, and non-contact polishing is performed.

For example, when processing GaAs using a NaOOl-based polishing liquid and suede-type polishing cloth, the wafer flying height needs to be controlled to around 10 μm, and even if it becomes larger or smaller than this value, there will be no distortion. A mirror surface will no longer be achieved.

However, such a non-contact polishing method for sea urchins is difficult to use because of changes in conditions during processing, such as fluctuations in the flow rate of the polishing liquid, variations in the number of revolutions of the polishing machine due to voltage fluctuations, unrestrictedness and deterioration of the surface of the polishing cloth, and irregularities in the wafer surface condition. As the flow of the polishing liquid layer changes due to the change from a surface to a mirror surface, the floating height of the wafer is not always maintained constant, and the wafer may come into contact with the polishing cloth or reach a large floating height, causing damage to the processing surface. It has the disadvantage that haze and processing distortion occur.

(Object of the Invention) An object of the present invention is to provide a non-contact polishing method for a wafer that eliminates such conventional drawbacks and enables excellent distortion-free mirror polishing without defects due to variations in flying height. .

(Structure of the Invention) According to the present invention, the sliding resistance between the wafer and the polishing cloth surface is detected, and the wafer flying height is controlled by adjusting the vertical position of the wafer. A method for non-contact polishing of a wafer is obtained, which is characterized in that the change in . The vertical position of the wafer is controlled by adjusting the vertical position of the wafer according to fluctuations in the load current of the motor that drives the polishing machine, and by controlling the flying height of the wafer, that is, the gap between the wafer and the polishing cloth surface, to a constant level. Fluctuations in the flying height due to changes in the polishing liquid flow value, rotation speed of the polishing machine, polishing cloth, wafer surface, etc., which would otherwise occur when not used, are completely eliminated, resulting in a completely distortion-free mirror surface and stable polishing! This has the advantage of being achieved.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram for explaining an embodiment of the method for non-contact polishing of a wafer according to the present invention, in which 1' is a polishing machine, 2 is
' is a polishing cloth, 6' is a nozzle, 7' is a wafer, 8' is a holder, 10' is a support rod, 17' is an arm, 18' is a substrate, and 21 is a drive motor for rotating the polishing machine 1'. , are connected by a shaft 22.

23 is a detector for detecting the load current of the motor 21;
24 is a comparator for checking whether the signal from the detector 23 is different from the set value; 25 is a controller for driving the vertical motor 26 for adjusting the position of the wafer 7' based on the signal from the comparator 24; 27 The vertical rod is screwed to the rotating shaft 28 of the vertical motor 26, and the other end is connected to the support rod 10' by a pin 29. 30 is a guide stand for holding the vertical motor 26 and the vertical @27, and is the board of the device. It is fixed at 18'.

Non-contact polishing of the wafer 7' is performed by rotating the polishing cloth 2' in the direction of the arrow while continuously supplying polishing liquid from the nozzle 6', so that the aggregate of the wafer 7' and the holder 8' is aligned with the surface of the polishing cloth 2'. This is done by floating a minute amount (R) from above and rotating around the support rod 10'.

The flying height of the wafer is controlled by detecting that when the gap between the wafer and the polishing cloth changes, the sliding resistance between them changes and the load current of the drive motor 21 rotating the polishing plate 1' changes. That is, the detector 2 detects changes in the load current of the drive motor 21.
3, the signal is sent to the comparator 24, and compared with a set value. When the value deviates from the set value, a signal is sent to the controller 25, which drives the vertical motor 26 according to the magnitude of the signal, thereby moving the wafer 7' via the vertical rod 27 and support rod 10'. The vertical position of is adjusted. As a result, the gap between the polishing cloth 2' and the wafer 7' is corrected and controlled to a constant value.

In this embodiment, as a method for adjusting the gap between the wafer and the polishing cloth, a case has been described in which the wafer is moved up and down, but the same effect can be obtained by other means, such as a method in which the polishing cloth is moved up and down.

(Effects of the Invention) The wafer polishing method of the present invention uses a method of detecting the load current of the drive motor of the polishing machine and adjusting the vertical position of the wafer as a method of controlling the wafer flying height. This eliminates cloudiness and processing distortion on the machined surface due to fluctuations in flying height that occur when the wafer position is not controlled, resulting in stable polishing conditions and an excellent distortion-free mirror surface.
It is extremely effective for non-contact polishing of wafers.

[Brief explanation of the drawing]

1 is a diagram illustrating an example of the method of non-contact polishing of a wafer according to the present invention, and FIG. 2 is a diagram illustrating an example of a conventional method of polishing a wafer in a non-contact manner. and 1' are polishing machines, 2 and 2' are polishing cloths, 3
is a polishing liquid, 4 is a tank, 7 and 7' are wafers, 8 and 8' are holders, 10 and io' are support rods, 12 is a disk, 13 is a horizontal bar, 15 is a weight, 16 is a column, 17 is 17' is an arm, 21 is a drive motor, 23 is a detector, 24d is a comparator,
25 is a controller, 26 is a vertical motor, 27 is a vertical rod, 30
indicates an information desk. Agent fP Susumu Uchihara/'-”'-,'%,.,,4.-/C100V

Claims (1)

[Claims] In the method of polishing a workpiece by floating it by a minute amount by rotating the polishing machine at high speed while continuously supplying polishing liquid, the load current of the drive motor of the polishing machine is detected and the load current is kept constant. A wafer polishing method characterized by controlling the flying height of a workpiece by adjusting the vertical position of the workpiece.