US3858369A

US3858369A - Machine for multiple grinding of semiconductor

Info

Publication number: US3858369A
Application number: US304834A
Authority: US
Inventors: Valentin Mikhailovich Dolgov; Vyacheslav Vasilievic Saveliev; Vladimir Konstantinovic Krylov; Valentin Mitrofano Tomashevsky; Evgeny Ivanovich Zolotarev
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-10-18
Filing date: 1972-11-08
Publication date: 1975-01-07
Anticipated expiration: 1992-01-07
Also published as: GB1377837A

Abstract

A machine for multiple grinding blanks of crystalline structure in the production of semiconductors. It accomplishes the cuttingoff, grinding and polishing operations. The machine comprises a turn table on which there are mounted carriages with blanks. Around the table there are mounted grinding heads. The process of machining blanks is carried out continuously by way of successive steps of grinding and polishing the ends of blanks and then cutting-off the latter.

Description

United States Patent [191 Dolgov et a1.

MACHINE FOR MULTIPLE GRINDING OF SEMICONDUCTOR Inventors: Valentin Mikhailovich Dolgov, ulitsa Ljublinskaya, 23, kv. 21; Vyacheslav Vasilievich Saveliev, Anadyrsky proezd, 67, kv. 48; Vladimir Konstantinovich Krylov, Yaroslavskoe shosse, 131, kv. 3; Valentin Mitrofanovich Tomashevsky, 3 Mytischinskaya ulitsa, 14a, kv. 140; Evgeny Ivanovich Zolotarev, ulitsa Kibalachicha, 15, kv. 12, all of Moscow, U.S.S.R.

Filed: Nov. 8, 1972 Appl. No.: 304,834

U.S. Cl. 51/5 B, 51/58, 5-1/215 AR,

51/215 UE Int. Cl B24b 7/04 Field of Search 51/3, 4, 5, 53, 55,133,

51/134, 215 AR, 215 UE, 216 T, 216 ND; 269/57; l25/DIG. 1

Primary Examiner-AlLawrence Smith Assistant ExaminerRobert C. Watson Attorney, Agent, or FirmWaters, Roditi, Schwartz & Nissen [57] ABSTRACT A machine for multiple grinding blanks of crystalline structure in the production of semiconductors. lt accomplishes the cutting-off, grinding and polishing operations. The machine comprises a turn table on which there are mounted I carriages with blanks. Around the table there are mounted grinding heads.

The process of machining blanks is carried out continuously by way of successive steps of grinding and polishing the ends of blanks and then cutting-off the latter.

5 Claims, 4 Drawing Figures 6 a a i o it 6'4 t 0 as 5 r Patented Jan. 7, 1975 3,858,369

4 Sheets-Sheet 2 Patented "Jan. 7, 1975 4' Sheets-Shet 4 MACHINE FOR MULTIPLE GRINDING OlF SEMICONDUCTOR The present invention relates to the production of semi-conductor devices, and more particularly, to a machine for grinding materials having, for example, crystalline structures such as silicon, germanium, gallium arsenide, sitall, quartz and ceramics suitable for the production of solar phototransducers, integrated circuits, diodes, triodes, resistors, and detectors.

The process of machining such materials is characterized in that the blanks are first cut on machines with diamond abrasive discs into plates of necessary thick ness, and the plates are then ground and polished on face grinding-polishing machines with the use of abrasive pastes or diamond lapping wheels.

Known in the art are devices for cutting and polishing materials of crystalline structure.

The known method for machining materials of crystalline structure with the use of these devices is characterized in that a blank is glued to a holder and cut into plates which are then ground and polished. This method, which is accomplished with the use of the known devices, does not provide a high productivity of labour due to the losses in time for auxiliary operations such as reloading of the devices in the process of cutting blanks into plates, when a blank cut into plates should be removed from the holder, washed and transported for a subsequent processing of grinding. Before grinding, the plates are glued to discs and ground to be flattened in the same plane, then the discs with the plates are washed to remove abrasive particles and chips; the initial thickness is measured, they are transported for a subsequent operation of polishing. The polishing is accomplished with the use of abrasives or polishing wheels in a number of steps by reducing the granularity grade of the abrasives and wheels; subse quent to each of the polishing steps, the discs with the plates are washed and the thickness of the removed layer is measured. On completion of grinding, the plates are removed from the discs and washed of the glue.

The machining of blanks with the use of the known devices inevitably results in losses of the material being treated, since the cutting of blanks into plates produces a spread in the thickness of the cut plates due to pulsations of the cutting-off head. Therefore, the plates should be ground for levelling in thickness which results in the losses of expensive materials in the form of chips.

There are known machines for cutting semiconductors with diamond abrasive discs, e.g., of the Staxs type (FRG).

The known machine comprises a bed with a body mounted thereon for a spindle assembly carrying a cutting head with a diamond abrasive disc which is able to cut blanks, for example, of silicon and germanium 60 mm in diameter. The holder with a blank is fixed on a table capable of moving longitudinally and transversely because of a pushing fork and an eccentric in the tablereturning mechanism. The cutting head with a diamond disc is rotated from a belt drive provided with a governor of rotation velocity in the range from 1,500 to 5,000 r.p.m. The cutting of blanks into measured plates is accomplished by delivering the table with the holder carrying a blank to the cutting edge of the diamond disc.

The advantage of such machines is in an improved stiffening of the diamond disc to the cutting head which provides a reduction of disc vibrations while processing, the wastes of the material being cut are considerably reduced due to a small thickness of diamond discs; the surface damage of plates is minor as compared to the other methods of cutting.

The disadvantage of this device is the necessity of frequent reloadings. Besides, there should be provided special polishing devices for subsequent processings of cut off blank plates.

There are known face grinding-polishing machines for grinding and polishing semiconductor materials provided with a spindle for fastening a polishing tool and a round table. The spindle has an electric drive with a rotation velocity control in the range from 50 to 800 r.p.m. The table for plates to be glued thereon for processing is provided with an electric drive equipped with rotation velocity control. The advantage of such devices is their high grind precision but they are disadvantageous because of a low productivity of labour.

Therefore, an increase of the productivity of labour in grinding semiconductor blanks can be provided only by a considerable increase in the number of cuttinggrinding and polishing devices now in use.

An object of this invention is to increase productivity of labour in machining materials of crystalline structure.

Another object of this invention is to reduce wastes of the material being treated.

Yet another object of the present invention is to provide reduction of floor areas occupied for accomplishing the machining processes.

Still further object of the invention is to provide a reduction of the production cost.

These and other objects are attained by providing a machine for multiple grinding of semiconductor blanks comprising a bed with a turn table mounted thereon, on which turn table there are secured rotary chucks with blanks, machining heads including grinding heads and polishing heads which are located around the periphery of the table and are made to rotate about their axes and to move along the grinding plane, in which, according to the present invention, there are provided rotary cutting-off heads, which are so positioned that they can oscillate along the grinding plane between the grinding heads and the polishing heads and the travel of which constitutes an oscillatory motion, while on the table which is mounted with a provision for a circular stepped feed, there are located carriages radially reciprocating with respect to the machining heads, each of the carriages carrying said chuck with blanks and a pusher for delivering said blanks to the cutting-off heads.

It is advisable that the cutting-off head he manufactured in the form of a hollow shaft with a transporting means mounted therein in such a way that the blank could be introduced, when it is being cut, into the cutting-off head and then the cut-off portions of the blank be fed to the transporting means.

It is advantageous that the bed he provided with a rack fixed thereon and the carriage be provided with a screw having a gear which, as the table is turned, could be engaged with the rack and, as the screw is rotated, the carriage with blanks could be moved to the cuttingoff heads for a specified distance of cutting.

The present invention in accordance with one of the variants of its embodiment may be provided with hollow shafts located in the bed, to which shafts there are fixed link gears for imparting oscillating motion to said heads the drive shaft of which is located inside of the hollow shaft.

The present invention provides simultaneous processes of polishing and cutting a large number of blanks and a reliable transportation of cut-off plates from the cutting zone. This provides a considerable increase in the productivity of labour.

Besides, the wastes of the material produced in the machining processes have been reduced.

The following example illustrates a specific embodiment of the present invention with reference to the accompanying drawings, wherein:

FIG. 1 is a plan view of the machine according to the invention;

FIG. 2 is a vertical section of the grinding head;

FIG. 3 is a vertical section of the cutting-off head;

FIG. 4 is a circuit of the control unit.

The machine includes a bed 1 and a turn table 2 (FIG. 1) carrying all the other assemblies. The guides 3 (FIG. 2) of the turn table 2 are protected with a labyrinth packing 4. On the bed 1 there are mounted grinding heads 5, polishing heads 6, cutting-off heads 7, drives thereto, a drive to the table 2 and racks 8 (FIG. 1).

The construction of the grinding heads 5, polishing heads 6 and cutting-off heads 7 is accomplished in such a way that the grinding tools (baffing wheel and diamond cutting disc) are rotated from a direct-current motor through a drive 9 (FIGS. 2 and 3) and the head is oscillated through a link gear 10 from a d.c. motor provided with a reduction gear.

Each of the grinding heads 5 and the polishing heads 6 has a body 11 (FIG. 2) which is set on the tapered end of a hollow shaft 12 and oscillated in a sliding bearing 13 mounted in the bed 1. The body 11 and the hollow shaft 12 are fixed by pins 14 and fastened between two thrust bearings 15 and 1.6 by means of a nut 17 having a stop screw.

The link gear 10 is fixed to the hollow shaft 12 with bolts 18. The hollow shaft 12 mounted in

radial bearings

19 and 20 comprises a shaft 21 rotated through a pulley 22 and the drive 9 from a d.c. motor.

The rotary motion of the shaft 21 through a pulley 23, a V-shaped belt 24, a tension roller 25 and a pulley 26 is imparted to a shaft 27 carrying a buffing wheel 28. The shaft 27 is set in a sliding bearing 29 which in turn is set in the body 11 through

radial bearings

30 and 31. The shaft 27 carrying the buffing wheel 28 has a short play along the axis of the bearing 29 due to a bayonet mechanism 32 and a friction mechanism 33.

The buffing wheel 28 with a grinding portion flexibly mounted and bearing an abrasive coating at one of its ends is covered with a casing 34. In the whole the head is covered with a casing 35.

The cutting-off head 7 has a body 36 set on the tapered end of a hollow shaft 37 which is oscillated in a sliding bearing 38 (FIG. 3) which in turn in set in the bed 1. k

The body 36 and the hollow shaft 37 are fixed by pins 39 and fastened between two thrust bearings 40 and 41 by means of a nut 42 having a stop screw 43. The link gear 10 (FIGS. 2 and 3) is fixed to the hollow shaft 37 with bolts 44. The hollow shaft 37 set in radial bearings 45 and 46 comprises a shaft 47 rotated through a pulley 48 and the drive 9 from a d.c. motor.

The rotary motion of the shaft 47 through a pulley 49, a V-shaped belt 50, a tension roller 51 is imparted to a spindle 52 which carries a diamond abrasive disc 53 having an inner cutting edge.

A sliding bearing 54 with an adjustable play and a hollow body 52 rotating therein are fastened with a nut 55 and a thrust sliding bearing 56 in the body 36. The body 52, the bearing 59 and the special nut 55 are provided with

labyrinth packings

57 and 58.

For lubricating the friction surfaces, on the body 36 there is mounted a lubricator 59, and for delivering cutoff plates from the cutting zone, inside of the body 52 there is provided a transporting means 60 firmly fastened to the bed 1 with a bracket 61 (FIG. 1). The cutting-off diamond disc 53 is covered with a casing 62 and in the whole the head is covered with a casing 63 (FIG. 3).

On the turn table 2 there are positioned a number of carriages 64 with blanks, a control unit 65 (FIGS. 1 and 4) of the turn table and lubricators 66 for lubricating the table guides.

Adjacent to the machine there is located a control desk 67 accommodating control units of the motors to the heads and an ac transformer for feeding the control unit 65.

The turn table 2 is rotated by a d.c. motor with a reduction gear through a steering knuckle.

The carriage 64 comprises the following main assemblies and parts: a base 68, a support 69, guides 70, a body 71 and a chuck 72 (FIGS. 2 and 3).

The base 68 and the support 69 are rigidly fixed to the table 2 (FIG. 1). The base 68 is provided with a threaded bush 73 in which one of the ends of a screw 74 (FIG. 3) is fastened. The other end of the screw 74 carries a bevel gear 75 fixed thereon by a key and rotated in a sliding bearing 76 which is set in the support 69. The gear 75 is covered with a casing 77. The screw 74 is hollow and internally threaded, the pitch of the internal thread being finer than that of the external. Inside of the screw 74 a screw 78 is mounted one of its ends being threaded to reciprocate the threaded bush 73. The other end of the screw 78 is smooth and positioned in a bush 79 which is fixed to the base 68.

On the smooth end of the screw 78 there is secured a key and the bush 79 is provided with a keyslot to prevent the screw 78 from turning.

On the screw 78 there is mounted a bevel bush 80 which is screwed up with a nut 81. The guides 70 are rigidly fixed on the base 68 and serve for travel of the body 71 resting on

rollers

82 and 83.

The construction of the roller 83 makes it possible to compensate the play.

The body 71 is connected with the bevel bush 80 by means of a special bevel bolt 84.

The body 71 mounts a d.c. motor with a reduction gear and an electric break for rotating the chuck 72.

The chuck 72 is rotated in radial bearings 86 and 87 mounted in the body 71. To the inner side of the chuck 72 there is fixed a sleeve 88 with holes. Inside of the sleeve 88, opposite to the holes, on the body 71 there is fixed a photoresistor 89 (FIGS. 2 and 3); on the outside of the sleeve 88 there is positioned a lamp 90. Into the chuck there are pressed a number of sliding bearings 91 which, under the action of springs 92 and a pusher 93 of an electromagnet, provide the reciprocating motion of an axle 94.

The axle 94 is provided with quick-detachable locks for mounting blanks 95 to be treated.

For lubricating the axle 94, into the chuck 72 there are pressed lubricators 96.

The electric circuit involves an input unit 97 (FIG. 4) with power transformers and a short-cricuit protection,

adjustable thyristor rectifiers

98, 99, 100, and 101, a l2-position scaling unit 102, a six-position scaling unit 103, a magnetic starter 104, a mechanism for suppying voltage to the motor of the turn table and to the control unit 65 (FIG. 3).

The control unit 65 of the turn table 2 consists of a rectifier 105, a l2-position circular counter 106, a four-position circular counter 107 and trigger

units

108, 109, 110, 111, 112, 113, 114 and 115 (FIG. 4).

The above'described machine operates as follows: the blanks 95 to be treated are put into the locks which are then fixed to the axle 94. Subsequently, a voltage is applied to the input unit 97 and the

rectifiers

98, 99, 100, and 101. From the

rectifiers

90 and 99 the voltage is applied to the motors of the cutting-off heads 7. At the same time the voltage is applied through the starter 104 (FIG. 4) to the unit 65, and from the rectifier 105 it is applied through the circular counter 107 to the

triggers

108 and 112. As the trigger operate, the electromagnet 93 compresses the spring 92 and pushes out the axle 94 with the lock which carries the blank 95 into the zone of the cutting-off head 7.

In executing an oscillating motion, the cutting-off head 7 cuts off a plate from the blank. The cut-off plate falls to the transporting means 60 (FIG. 3) and is transported thereby from the cutting zone. As the cuttingoff is over, the cutting-off head '7 is returned to its initial position and pushesthe end switch which operates the circular counter 106 to trigger the

tiggers

100 and 112, the latter, in turn, switch on the electric motors 05 positioned in the carriages 64 which are opposite to the cutting-off heads 7.

When the chuck 72 with the sleeve 88 having holes is rotated, the holes of the sleeve 08 occur to be displaced. As soon as the lamp 90 lights the photoresistor 89 through a hole, the

triggers

108 and 112 operate, the motor 05 stops and the pusher 93 of the electromagnet pushes out the subsequent blank 95 for cutting.

Following this order, the machine can cut all the blanks positioned in the chuck. Then the l2-position scaling unit 102 triggers and the signal is fed to the starter 104 to turn the table 2, and the table 2 turns by one-eighth revolution.

On completion of turning the table 2, the signal is fed to the scaling unit 103 to switch on the electric motor of the grinding heads 5. Simultaneously with the electric motors 85 the electric motors of the carriages 64 are switched on which are at this moment opposite to the grinding heads 5 rotating the chuck 72.

The buffing wheel 28 starts rotating and simultaneously advancing in the sliding bearing 29, as the friction mechanism 33 is designed for a certain force of clamping the buffing wheel to the ends of the blanks being machined.

When such a force is provided, the sliding bearing 29 starts rotating in the

radial bearings

30 and 31. The grinding process begins. At the same time the electromagnet with the pusher 93 is triggered through the

triggers

109 and 113, and the blanks on the carriage 64 (FIG. 3) facing the cutting-off heads '7 are successively pushed out into the cutting zone, where they are cut and transported as it is hereinbefore described.

Following each of the signals from the scaling unit 102 to turn the table 2, a signal through scaling unit 103 is applied to the electric motors of the

heads

5 and 6. The electric motors of these heads reverse and the buffing wheel 28 moves away from the chuck 72 by means of the bayonet mechanism 32 and the friction mechanism 33 thus turning the table 2.

When turning the table by one-eighth revolution, the bevel gear 75 engages the rack 8 which is located on the bed opposite to the cutting-off heads coincidently with the table run and is turned through a certain angle. Therewith, the gear 75 turns the screw 74 which, while being screwed into the bush 73, removes the screw 78.

In its translational motion the screw 78 advances the body 71 of the carriage 64 along the guides for a dis tance equal to the pitch difference of the

screws

74 and 78. The relationship of these values is determined by a necessary thickness of the plates to be cut and can be adjusted.

The process for the alternative switching-on of the other heads and carriages is similar to that hereinbefore described.

When there comes a point of the simultaneous operation of all the heads and carriages it means that the machine runs under automatic conditions.

When the blanks are cut to the end the carriage 64 runs over the end switch to produce a signal for switching off the machine.

The machine is switched off in the same order as it is switched on.

The body 71 of the carriage 64 is returned in its initial position by means of a detachable device.

The use of this novel machine with two cutting-off heads and six grinding-polishing heads makes it possible to increase the efficiency in grinding, for example,

silicon blanks for the production of solar phototrans ducers by about 20 times as compared to commercial machines designed for the same program, and provides considerable reduction of the floor areas necessary for the production as well as of the maintenance personnel.

Thus, for example, the productivity of labour with the use of this machine in grinding silicon blanks 45-50 mm. in diameter is about 35 sec. per plate, while with the use of the commercial devices it is about 10 min. per plate.

What is claimed is:

1. A machine for the simultaneous machining of a plurality of semiconductor blanks, comprising: a bed; a turn table mounted on said bed for moving in a circle; machining heads, including cutting-off, grinding and polishing heads, fixed about said table at identical angular spaces from one another, the operative part of each of said heads having means for oscillating about a first axis radially relative to said table and means for rotating about a second axis radially relative to said table; said means for imparting oscillating motion to each of said heads comprising link gears with a shaft secured to said bed; carriages with chucks to carry blanks, said carriages being mounted on said table at identical spaces from one another corresponding to the angular space between said heads, and means to impart reciprocating motion to said carriages toward said cuttingoff heads in a radial direction, said reciprocating means being mounted on each of said carriages; means to rotate said chucks with blanks in the course of machining; a pusher attached to each of said carriages to feed the blanks in the opertive position to said cutting-off heads; and means to convey the cut-off portions of said blanks, said conveying means being mounted in each of said cutting-off heads.

2. A machine as claimed in claim 1, including a control unit and a counter to sequentially switch the operative units of the machine.

3. A machine as claimed in claim 2, wherein each of said chucks has orificed sleeves and a photoelectric resistance for sending a signal to said counter to switch on and off the means for rotating said chucks and said said shafts for transmitting rotary motion to said heads.

Claims

1. A machine for the simultaneous machining of a plurality of semiconductor blanks, comprising: a bed; a turn table mounted on said bed for moving in a circle; machining heads, including cutting-off, grinding and polishing heads, fixed about said table at identical angular spaces from one another, the operative part of each of said heads having means for oscillating about a first axis radially relative to said table and means for rotating about a second axis radially relative to said table; said means for imparting oscillating motion to each of said heads comprising link gears with a shaft secured to said bed; carriages with chucks to carry blanks, said carriages being mounted on said table at identical spaces from one another corresponding to the angular space between said heads, and means to impart reciprocating motion to said carriages toward said cutting-off heads in a radial direction, said reciprocating means being mounted on each of said carriages; means to rotate said chucks with blanks in the course of machining; a pusher attached to each of said carriages to feed the blanks in the opertive position to said cutting-off heads; and means to convey the cut-off portions of said blanks, said conveying means being mounted in each of said cutting-off heads.

3. A machine as claimed in claim 2, wherein each of said chucks has orificed sleeves and a photoelectric resistance for sending a signal to said counter to switch on and off the means for rotating said chucks and said pusher to cut the blanks.

4. A machine as claimed in claim 1, wherein said grinding and polishing heads have a bayonet mechanism to press the grinding and polishing wheels with a given force to said blanks being machined and to withdraw said wheels at the end of the process when said table is turned.

5. A machine as claimed in claim 1, wherein said link gears of the heads are mounted on hollow shafts secured to said bed, a spindle extending through each of said shafts for transmitting rotary motion to said heads.