Apparatus For Handling Workpieces To Be Polished

Abstract

Disclosed is an apparatus for handling workpieces to be polished on a rotatable disc type of polishing machine and comprising a workholder mounted on an arm oscillatable in a vertical plane through substantially 180.degree. so that in one position the workholder is inverted to facilitate loading and unloading thereof, and in another position the workholder supports the workpieces by differential pressure thereon over the polishing disc. The movement of the arm may be arrested as the workpieces touch the polishing disc, and an air cylinder on the arm moves the workholder against the disc and presses the workholder against the disc with a higher pressure than is permissible with wax-adhered workpieces. At the termination of the polishing operation the workholder is raised from the polishing disc and the arm is rotated to invert the workholder, after which a cleaning spray is automatically applied to the workpieces.

Description

This invention relates to abrading machines such as lapping and polishing machines and particularly to a means for handling workpieces of a thin disc-like shape to be abraded by said machine.

An important component used in the electronic art is the silicon wafer. This wafer varies from 0.005 inch to 0.015 inch thick and is disc-shaped in outline. It is important for its electrical characteristics that such wafer is made with parallel, highly polished surfaces, and that for uniformity the polishing be done automatically and under controlled conditions.

Rotating disc-shaped polishing tools have been used for polishing wafers, the latter being adhered by wax to a flat platen which is pressed against the rotating tool and held there for a predetermined time. For maximum production per hour, it is desirable that the time required to polish a wafer, or a batch of wafers, be kept to a minimum, which means that the pressure on the wafer during polishing should be as high as surface finish will permit. The higher pressures, however, increase the friction between the wafer and polishing disc which then heats up the wafer and melts the wax holding the wafer to the holder. The wafers thus loosened are destroyed, as are those at other stations on the polishing machine contacted by the loose wafers, resulting in an appreciable monetary loss to the polisher.

In my co-pending application, Ser. No. 202,965 filed Nov. 29, 1971 for APPARATUS FOR POLISHING WAFERS, there is disclosed and claimed a differential pressure-operated workpiece holder which eliminates the use of wax as an adherent for the wafers and which permits higher pressure to be used on the wafers to speed up the polishing operation. Although the wafers are heated by the polishing tool, it has been found that the higher temperature assists in breaking down the surface of the wafer and hence speeds the polishing operation. It is necessary, however, to go through several steps each time a polishing cycle is effected, the steps being to load, invert, press upon the polishing tool, return, wash the wafers while on the holder, and unload; and it is accordingly an object of this invention to provide means for automatically providing each of these operations for a wafer polishing machine except the load and unload operations.

More specifically, it is an object of this invention to provide a pressure-differential operated means for oscillating a workholder from a load position to a work position and, back again, the work position being held under a predetermined pressure.

For another object, this invention seeks to provide a pressure-differential operated arm on which is mounted a workholder, the arm being oscillated about a horizontal axis, wherein the mounting for the workholder on the arm includes a pressure-differential operated motor for providing operating pressure to the workholder, with control means automatically operated by the position of the arm for applying and releasing the pressure, and with timer means for moving the arm to invert the workholder and to apply a cleansing spray to the workpieces.

These and other objects of this invention will become apparent from the following detailed description of a preferred embodiment of the invention when taken together with the accompanying drawings in which

FIG. 1 is a plan view of a polishing machine incorporating this invention;

FIG. 2 is a side elevational view, partly in section of the machine of FIG. 1;

FIG. 3 is a side elevational view, partly in section and on an enlarged scale of the workholder of this invention; and

FIG. 4 is a schematic diagram of the controls for the workholder of FIG. 3.

The form of polishing machine selected to illustrate this invention is shown in plan view in FIG. 1. The workpieces are thin wafers of silicon or the like used as electronic components and are of disc form. The flat surfaces of the wafers are required to be polished to a predetermined standard, and with the polishing cycle calculated to produce such standard polish upon the wafers and the time required to load and unload a workholder it has been determined in the illustrative machine that a single polishing disc with four work stations could be readily tended by one operator.

Thus, the machine shown in FIG. 1 is comprised of a frame 10 on which is mounted a polishing disc 11 rotatable about a vertical axis and driven by an appropriate motor shown at 12 in FIG. 2. A control panel 13 extends over disc 11 in proximity to four work stations 14, 15, 16 and 17 and contains four sets of manually-operated switches only one of which sets is shown in outline at 18. One set of switches is supplied for each station. A separate master control panel 19 is located on a post 20 supporting the sets 18 of station switches. Said master control panel contains switches (not shown) for controlling (1) motor 12 for driving disc 11, (2) a vacuum pump for generating the vacuum used to hold the wafers on the workholder, (3) a polishing compound pump for supplying the disc with abrasive for the polishing operation and (4) a master switch which controls the electrical energy to the entire machine. These controls, though necessary for the successful operation of the machine as a whole, form no part of this invention and hence will not be described in detail.

The four work stations 14, 15, 16 and 17 and their controls are identical and hence for brevity only one station 17 will be described. Said station is shown in elevation in FIG. 2 and in enlarged elevation in section in FIG. 3. As shown in FIG. 2, it is comprised of a vertically disposed pneumatic rotary actuator 21 which is essentially a pneumatic cylinder 22 (FIG. 3) the rod 23 of which carries a gear rack 24 meshing with a pinion 25 the shaft of which is connected to an arm 26. A workholder, shown generally at 27 in FIG. 2, is mounted on the end of arm 26 through a pressure-differential operated motor 28, said arm in one position overlying polishing disc 11 and pressing the workpieces upon the surface of said disc and in another position, shown dotted in FIG. 2, substantially 180.degree. away from the said one position, supporting the workholder 27 in an inverted position so that the workpieces rest on top of the holder and can readily be placed upon and removed from the workholder.

Referring now specifically to FIG. 3, the cylinder 22 of pneumatic rotary actuator 21 is double acting and has ports 29 and 30 leading to opposite sides of a piston 31 therein. Extending below cylinder 22 is a rod 32 on which is an abutment 33 the function of which is to operate limit switches 34 and 35 at the ends of the reciprocating movements of rod 32. Said switches control certain operations of the station as will be described in detail hereinafter.

The workholder 27, as shown more clearly in FIG. 3, comprises a plate 36 preferably circular in outline and having a flat surface 37 upon which the workpieces 38 are held by differential pressure. To this effect surface 37 is provided with relieved areas under the workpieces 38 connected by passages 39 to a source of sub-atmospheric pressure. The details of construction of the relieved areas are disclosed in my co-pending application for APPARATUS FOR POLISHING WAFERS filed Nov. 29, 1971 Ser. No. 202,965.

Plate 36 is secured to a piston rod 40 of a double acting pressure-differential operated motor 41 having ports 42, 43 for conducting fluid under pressure to one side or the other of the piston 44 of motor 41. Motor 41 is secured to the end of arm 26 and hence is movable therewith. It is contemplated that arm 26 will be rotated through 180.degree. to invert workholder 36 so that the workpieces can be readily loaded upon and unloaded from said workholder. It is also contemplated that workholder 36 will be moved and held against the polishing disc 11 to press the workpieces thereagainst and thus accelerate the polishing process. Finally, it is desirable that the polished workpieces, while still on the workholder, be sprayed with water to wash off any polishing compound that may adhere to them. The means by which the movements of cylinder 22 and motor 41, and the application of water spray are controlled will be described with reference to the diagram of FIG. 4 to which attention is now directed.

Inasmuch as air under pressure is generally available in shops and factories where polishing is done, the motive fluid for cylinder 29 and motor 41 is air under pressure. Although hydraulic power can also be used, it involves the use of a separate pump, a reservoir and filters, all of which add to the cost of the machine. Furthermore, to avoid the use of a large solenoid-operated valve to control the water for the spray, the motive power for the water spray valve is also air under pressure controlled by a solenoid-operated valve. For brevity the components of the machine and its controls are shown schematically in FIG. 4.

The sequence of operations for a full cycle at one station is as follows, assuming that the disc has been set in rotation and the polishing compound is flowing upon the rotating disc: (1) the workholder is loaded with workpieces (manual); (2) the vacuum is turned on to establish the differential pressure by which the workpieces are held on the workholder (manual); (3) a switch is turned on to start the timer for the polishing cycle (manual); (4) arm 26 is rotated to a positive stop where the workholder holds the workpieces just above the disc. The weight of the workholder, and absence of any air under pressure in the motor 41, allows the workholder to descend slowly to the polishing disc; (5) motor 41 is operated to press the workpieces against the disc which had previously been set in rotation, and to hold the workpieces against the disc for the entire polishing operation (automatic); (6) a second timer (to be hereinafter described) operates the motor 41 to raise the workpieces off the disc 11 (automatic); (7) arm 26 returns to its starting position (automatic); (8) a water spray is automatically turned on to wash the workpieces (automatic); (9) vacuum is turned off (manual); (10) workpieces are removed from workholder 36 (manual).

In the control diagram shown in FIG. 4, air under pressure is connected to a station supply pipe 45 from which it is conducted through a pipe 46 to a solenoid-operated valve 47 and thence as dictated by valve 47 to ports 42 and 43 on motor 41 the function of which is to move workholder 36 against polishing disc 11. A second branch pipe 47 conducts air under pressure to an air valve 48 which controls a small pressure differential motor on a water valve 49 controlling in turn the spray water from a water line 50.

Pipe 45 is connected to a valve 51 which controls the admission of air under pressure to cylinder 22 of the fluid actuator 21 (FIG. 2) for arm 26. Valves 47, 48 and 51 are solenoid operated to open and spring-returned to closed position. The solenoids in turn are controlled by timers 52, 53 and 54, timer 52 controlling the polishing cycle and being manually adjustable to the length of time required to polish a workpiece, and timers 53 and 54 being fixed as to duration and designed to produce a short delay in the application of electric current to the solenoid valves operated thereby. Each station has a manually-operated "start" switch 55 which controls all electrical equipment for that station and a manually-operated "cycle" switch 56 which energizes timer 52 to start the polishing cycle.

The operation of the machine is as follows:

Initially, cylinder 22 is in the position wherein its piston and attached gear rack 23 are in their lowermost position. Workholder plate 36 is therefore in its inverted position radially removed from polishing disc 11 and ready to be loaded. The vacuum has been turned off by manually-operated switch 57 which controls the solenoid-operated valve 58 for the vacuum to plate 36. Workpieces are placed upon plate 36 over the areas influenced by vacuum as described in detail in my aforesaid co-pending application Ser. No. 202,965; and when the plate is filled, the station switch 55 is turned on to activate the electrical components of the station following which the vacuum switch 57 is turned on to cause the workpieces to be held by differential pressure on plate 36. Next, cycle switch 57 is turned on to energize timer 52 and start the automatic sequence of operations.

The energization of timer 52 actuates a series of switches 58, 59, 60 and 61 which are reversed when the timer times out. Switch 58 is a holding switch for timer 52 so that manual switch 56 need not be held down during the polishing cycle. Switch 59 energizes a solenoid 62 on air valve 51 to cause said valve to admit air under pressure to the bottom of actuator 22 and thus raise rack 23 to rotate pinion 25 and arm 26 toward polishing disc 11. When rack 23 reaches the end of its stroke, limit switch 34 is actuated to activate timer 53 which when it times out energizes a solenoid 63 on valve 47 to admit air under pressure to port 42 of pressure cylinder 41 and thus move workholder plate 36 toward polishing disc 11 and hold it against the disc with a predetermined pressure. Since the polishing disc had been set in motion previously and remains in motion until the machine is to be shut down, the polishing operation commences and continues until timer 52 times out.

With timer 52 timed out, switches 58 and 59 are opened and switch 60 is closed to energize a solenoid 68 on valve 51 to condition said valve to admit air under pressure to the top of cylinder 22 which lowers rack 23 and raises workholder plate 36 off the polishing disc 11. Simultaneously, with the energization of switch 60 a switch 61 is closed by timer 52 which energizes a solenoid 65 on valve 47 to remove air pressure from plate 36 and to raise said plate with respect to cylinder 41.

Upon completion of the reverse rotation of arm 26, limit switch 35 is activated by abutment 33 to energize a solenoid 66 on air valve 48 the air from which then operates water valve 49 to spray water upon the polished workpieces. A timer 54 is activated simultaneously with solenoid 66 and when it times out, a switch 67 is opened to de-energize solenoid 66 and thus, through the spring-returned valves 48 and 49 shut off the water to the spray. Vacuum switch 57 is then opened to remove differential pressure from the workpieces and the polished workpieces are subsequently removed and replaced with workpieces to be polished. The operator moves to the next station that has timed out and that is ready for removal of polished workpieces and loading of workpieces to be polished.

The machine herein described thus automatically brings the workpieces to the polishing disc, brings pressure to bear upon the workpieces while they are being polished, to speed up the polishing operation both from the standpoint of increased abrading action as well as of disintegration through chemical action which is accelerated by the increased temperature of the workpiece surface, removes the pressure and brings the workpieces back to the loading position.

It is understood that although the invention has been described with reference to its application to a machine for polishing wafers, it can be used with machines for lapping or grinding other workpieces, and the scope of this invention therefore is not to be limited to the wafers and polishing machine herein disclosed but is to be determined by the appended claims.

Claims

I claim:

1. Apparatus for applying workpieces to and removing them from a substantially horizontally operating abrading tool, said apparatus comprising a platen, means for mounting the workpieces on said platen for a movement therewith, an arm having a horizontally disposed pivot located to one side of the tool, means for oscillating said arm about its pivot through substantially 180.degree., means for mounting the platen on the arm to cause said platen at one extreme position of the arm to assume an inverted position to permit loading of the workpieces thereon and at the other extreme position to be located over said abrading tool with the workpieces adjacent said tool, said platen mounting means comprising means for advancing said platen toward said tool independently of said arm oscillating means and independently of said workpiece mounting means, and fluid pressure means for holding said workpieces against said tool with a predetermined pressure while said tool is abrading said workpieces.

2. Apparatus as defined in claim 1, and means, automatically operable upon said arm reaching its extreme position opposite said first-mentioned extreme position, for spraying said articles with a cleaning fluid.

3. Apparatus as defined in claim 2, said means for supporting said workpieces comprising a platen having a plurality of stations thereon one for each workpiece, means at each station for applying sub-atmospheric pressure to the workpiece to hold said workpiece on the platen, manually operable means for controlling the application of subatmospheric pressure and means controlled by movement of the platen for controlling the application of the cleaning liquid.

4. Apparatus as defined in claim 1, and comprising further means operated in timed relation to the position of the portion of said arm over the tool for initiating the operation of the means for advancing said workpiece-supporting means toward said tool.

5. Apparatus as defined in claim 2, said means automatically operable upon said arm reaching its extreme position opposite said first-mentioned extreme position for spraying said articles with a cleaning fluid comprising an air-operated valve, a source of air under pressure, a solenoid-operated valve for controlling application of air under pressure from said source to said air-operated valve, and a switch operated by said platen for energizing said solenoid-operated valve.

6. Apparatus as described in claim 1, said tool comprising a polishing disc, and means for driving said disc about a vertical axis, said workpieces comprising discs of a thickness varying from 0.005 inch to 0.015 inch, and pressure-differential operated means on said workpiece supporting means and comprising the sole means for holding said workpieces on the workpiece supporting means, said workpieces being of a material characterized by increased abrading action by the tool as the temperature of the material increases, and said predetermined pressure increasing the friction between the workpiece and tool thereby increasing the temperature of the workpieces above the melting point of wax to increase the abrading action of the tool thereon.