Apparatus for grinding semiconductor wafer

Abstract: This invention relates to an apparatus for grinding a semiconductor wafer (W) which includes a table (2) having a work stage (10) on which a semiconductor wafer to be ground is placed, at least the work stage being rotated, and a grinding wheel (3) which is moved in a direction perpendicular to or parallel to the work stage while being rotated about an axis parallel to a rotational axis of the work stage (10). In this apparatus, a semiconductor wafer (W) is cooled during grinding. In order to perform cooling, the apparatus has an inlet flow path (21, 22) for guiding cooling liquid to a grinding surface (S) of the semiconductor wafer (W), and an outlet flow path (13, 23, 24) for collecting the cooling liquid flowed onto the work stage. The apparatus also includes temperature detector (32), arranged in the outlet flow path (13, 23, 24), for detecting a temperature of the recovered cooling liquid. The rotational speed of the grinding wheel (3) or the rotary table (2) is controlled based on the temperature of the cooling liquid detected by the temperature detector (32).

Description: (Field of the Invention) The present invention relates to an apparatus for grinding a semiconductor wafer and, more particularly, to an apparatus which cools a semiconductor wafer using cooling water during grinding. (Related Background Art) In a conventional grinding apparatus, a semiconductor wafer is cooled by cooling water which is kept flowing. In this case, the cooling wafer absorbs heat generated by grinding, and is then discharged (see, for example PATENT ABSTRACTS OF JAPAN vol.10, no.51 (M-457) (2108)). In particular, in a so-called back-grinding process before dicing of a GaAs semiconductor wafer, if this wafer is damaged, the yield of semiconductor device chip is decreased because circuit patterns on them are already completed. Excessive grinding heat generated during grinding of a semiconductor wafer causes compositional deformation, grinding burning, grinding cracks, or a residual stress. This drawback is conventionally well known. It is also experienced that grinding heat is abruptly increased by abnormal grinding. Therefore, in order to find an abnormally grinding state, a temperature of a wafer which is ground should be measured. In this case, a thermocouple is brought into contact with a semiconductor wafer or is embedded in a grinding wheel to measure a temperature of the semiconductor wafer. However, it is very difficult to bring the thermocouple into contact with a semiconductor wafer. This is because a semiconductor wafer is formed of a very thin, fragile material, and ground while being rotated. Even if a thermocouple is embedded in a grinding wheel, as known from JP-A-60-201868, a grinding temperature of a semiconductor wafer is indirectly measured. Therefore, a grinding temperature of the semiconductor wafer cannot be accurately measured. Summary of the invention It is a first object of the present invention to provide a grinding apparatus which can accurately measure a grinding temperature. It is a second object of the present invention to provide a grinding apparatus which can control the grinding condition to prevent a semiconductor wafer from suffering from compositional deformation, grinding burning, grinding cracks, or a residual stress. In order to solve the above objects, according to the present invention, there is provided an apparatus for grinding a semiconductor wafer, comprising a table having a workstage on which a semiconductor wafer to be ground is placed, at least said workstage being rotatable, a grinding wheel which is movable in a predetermined direction to said workstage while being rotatable about an axis parallel to a rotational axis of the workstage, an inlet flow path for guiding cooling liquid to a grinding surface of the semiconductor wafer, an outlet flow path for collecting the cooling liquid flowed onto the workstage, temperature detecting means arranged in said inlet and outlet flow paths, for detecting a temperature of the cooling liquid, and control means which determine and control of the flow rate of the cooling liquid. Preferrably, a circulating flow path for causing an up-stream side portion of the inlet flow path to communicate with a downstream portion Of said outlet flow path is provided. A livid pump, a filter, and/or a heat exchanger or radiator may be arranged in the circulating flow path. The apparatus solving the above second object preferrably comprises a flow control valve arranged in the inlet flow path, wherein the control means comprises a microcomputer for controlling the flow rate of the cooling liquid using the flow control valve. In a preferred embodiment of the apparatus solving the above second object the control means comprises a microcomputer for controlling the rotational speed or the moving speed of the grinding wheel. In a further preferred embodiment the control means comprises a microcomputer for controlling the rotational speed of the workstage. Preferrably, cooling liquid collecting means are arranged around the workstage. The cooling liquid collecting means may comprise a peripheral wall formed by projecting peripheral edge portion of the workstage upward, a communication flow path for causing an inner stage of the peripheral wall to communicate with the discharge formed in a side surface of the table, and a liquid gatter arranged along a rotational pipe of the discharge port. The cooling liquid collecting means may alternatively comprise a collar-like-cover surrounding the table, and a liquid gutter for collecting the cooling liquid guided outside the table by said drip-proof cover. The liquid gutter may be mounted on a side table arranged to surround the table. The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only and thus are not to be considered as limiting the present invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side sectional view of a grinding apparatus for a semiconductor wafer according to the first embodiment of the present invention; Fig. 2 is a side sectional view of a grinding apparatus for a semiconductor wafer according to the second embodiment of the present invention; Fig. 3 is a partial side view showing a modification of the second embodiment; Fig. 4 is a side view of a grinding apparatus for a Semiconductor wafer according to the third embodiment of the present invention; and Fig. 5 is a partial side view showing a modification of the third embodiment. DESCRIPTION OF THE PREFERRED EMBODIMENTS A grinding apparatus for grinding a semiconductor wafer to a desired thickness before a dicing process according to an embodiment of the present invention will be described below with reference to the accompanying drawings. As shown in Fig. 1, a grinding apparatus 1 for a semiconductor wafer W comprises a rotary table 2 for chucking and carrying the semiconductor wafer W, and a grinding wheel 3 arranged above the table 2 for grinding the semiconductor wafer W. The rotary table 2 is rotated by a drive motor 4 while carrying the semiconductor wafer W. On the other hand, the grinding wheel 3 is rotated by a drive motor 5, and is vertically moved by an actuator 6. Therefore, the surface (for example (100) surface) of the semiconductor wafer W which is rotated slowly is evenly ground to a desired thickness by the rotating grinding wheel 3 which is gradually moved downward during grinding. During grinding, the outer peripheral edge of the grinding wheel 3 is located at the center of the semiconductor wafer W. Thus, the grinding wheel 3 always grinds a half portion of the semiconductor wafer W. A mounting unit 7 for mounting the semiconductor wafer W is arranged at the center of the rotary table 2. The mounting unit 7 is formed of a porous ceramic. Vacuum pipes 8 are connected to the lower surface of the mounting unit 7. The semiconductor wafer W is chucked at the center of the rotary table 2 by the mounting unit 7. Each vacuum pipe 8 has a valve 9 for evenly chucking the semiconductor wafer W. Frictional heat generated by grinding is cooled by cooling liquid (e.g., deionized water) supplied to a grinding surface S of the semiconductor wafer W which contacts with the grinding wheel 3. Thus, a thermal influence on the semiconductor wafer W can be eliminated. The cooling liquid is supplied from an inlet port 22 communicating with an inlet pipe 21 to the grinding surface S and absorbs grinding heat on the grinding surface S. Thereafter, the cooling liquid is flowed from a stage 10 of the rotary table 2 via communication flow paths 11, and is recovered into a liquid gutter 13 mounted inside a side table 12. The cooling liquid is then drained outside the apparatus via an outlet port 24 communicating with an outlet pipe 23. More specifically, a peripheral wall 10a whose peripheral edge portion projects upward, an annular groove 10b formed inside the peripheral wall 10a along it, and a plurality of drain ports 10c formed in the annular groove 10b and communicating with the liquid gutter 13 are formed in the stage 10 of the rotary table 2. The cooling liquid flowing outwardly from the center by the centrifugal force of the rotary table 2 is blocked by the peripheral wall 10a, is collected in the annular groove 10b, and is then guided from the drain ports 10c to the liquid gutter 13. The communication flow paths 11 for causing the drain ports 10c to communicate with discharge pipes 14 formed in the side surface of the rotary table 2 are formed in the rotary table 2. Note that a heat insulating layer 15 is formed on the surface of the stage 10 by coating vinyl chloride or the like. The liquid gutter 13 is mounted on the side table 12 to be located between the rotary table 2 and the side table 12 which surrounds the table 2. Note that the liquid gutter 13 is formed into an annular shape, so that the shape of the liquid gutter 13 matches with a rotating pipe of the discharge pipes 14. The liquid gutter 13 is inclined so that cooling liquid is guided toward the outlet port 24. An inlet thermometer 31 is arranged in the inlet pipe 21 communicating with the inlet port 22, and an outlet thermometer 32 is arranged in the outlet pipe 23 communicating with the outlet port 24. These inlet and outlet thermometers 31 and 32 measure entrance and exit temperatures of cooling liquid. If the inlet cooling liquid temperature is constant, only the outlet thermometer 32 can be arranged. With this arrangement, a heat quantity produced during grinding can be obtained based on a temperature difference between the entrance and exit temperatures measured by the thermometers 31 and 32, and a flow rate of cooling liquid. The relationship between a change in heat quantity and a frequency of manufacturing defective products caused by cracks during grinding of the semiconductor wafer or warp caused by a residual stress can be numerically obtained by the monitoring of the heat quantity. The thermometers 31 and 32 are connected to a microcomputer 33. The microcomputer 33 is connected to a cooling liquid flow control valve 34 provided to the inlet pipe 21, the drive motor 4 for rotating the grinding wheel 3, and actuator 6 for feeding the grinding wheel 3, and the drive motor 5 for rotating the rotary table 2. The drive units of these devices are individually or systematically controlled by the microcomputer 33. When the flow control valve 34 is controlled by the microcomputer 33, the quantity of cooling liquid corresponding to a target heat quantity is calculated from the temperature difference of the two thermometers 31 and 32 supplied to the microcomputer 33. Thereafter, a degree of valve opening of the flow control valve 34 is adjusted by a control signal based on the calculation result, i.e., a flow rate of cooling liquid is adjusted. Similarly, in an apparatus using only the outlet thermometer 32, the quantity of cooling liquid corresponding to a target heat quantity is calculated from the gradient of an ascending curve of the heat quantity, and a flow rate of cooling liquid is adjusted by a control signal based on the calculation result. When the drive motor 4 of the grinding wheel 3 is to be controlled by the microcomputer 33, a rotational speed of the grinding wheel 3 corresponding to the target heat quantity is calculated from the temperature difference of the two thermometers 31 and 32. The rotational speed of the drive motor 4 is controlled by a control signal based on the calculation result. Similarly, when the actuator 6 of the grinding wheel 3 is to be controlled, a feed speed of the grinding wheel 3 corresponding the target heat quantity is calculated, and is controlled by a control signal based on the calculation result. When the drive motor 5 of the rotary table 2 is to be controlled, a rotational speed of the rotary table 2 corresponding to the target heat quantity is calculated, and is controlled by a control signal based on the calculation result. In this manner, since the respective devices are feedback-controlled by the microcomputer 33, grinding can be performed at a constant temperature. When the outlet thermometer 32 detects an abrupt increase in temperature, an alarm may be generated regardless of the above-mentioned control. In this case, it can be considered that some abnormal grinding has occurred, and an operator must quickly take a countermeasure against it. In this embodiment, a system for vertically feeding the grinding wheel 3 has been described. In a system for horizontally feeding the wheel 3, a horizontal feed speed of the actuator 6 is controlled. The second embodiment of the present invention will be described below with reference to Fig. 2. The characteristic feature of this embodiment is that an upstream side portion of an inlet pipe 21 communicating with an inlet port 22 communicates with a downstream side portion of an outlet pipe 23 communicating with an outlet port 24 through a circulating flow path 25, and that an outlet thermometer 32, a liquid pump 26, a filter 27, and a radiator (hear exchanger) 28 are arranged midway along the circulating flow path 25. Cooling liquid is supplied along the circulating flow path 25 under pressure by the liquid pump 26. In this case, ground chips in cooling liquid are removed by the filter 27, and cooling liquid is then cooled by the radiator 28. Thereafter, the cooled liquid is supplied from the inlet port 22 to a grinding surface S. The cooling liquid which absorbs grinding heat on the grinding surface S is collected to the circulating flow path 25 via a liquid gutter 13. After the temperature of cooling liquid is measured by the outlet thermometer 31, the cooling liquid is returned to the liquid pump 26. A liquid replenishing pipe 29 is connected in a portion of the circulating flow path 25 between the filter 27 and the liquid pump 26, so that cooling liquid is replenished from the replenishing pipe 29 to the circulating flow pipe 25. The temperature of cooling liquid measured by the outlet thermometer 32 is gradually increased from the beginning of grinding, and reaches a steady temperature after the lapse of a predetermined period of time. Therefore, the relationship between an increase or the gradient of an ascending curve of a temperature of cooling liquid and a frequency of manufacturing defective semiconductor wafers W can be numerically obtained with reference to a temperature indicated by the outlet thermometer 32 in the steady state. In the steady state, the following relationship can be basically established. Grinding Heat = Heat Quantity Discharged Outside System More specifically, when a temperature of cooling liquid is kept constant, this means that absorbed heat is balanced with discharged heat. In this case, a heat absorption factor is grinding heat, and a heat discharging factor is mainly heat discharged from the circulating flow path 25 into air. Therefore, if a heat quantity discharged from the circulating flow path 25 into air can be calculated, grinding heat in the steady state can be obtained. The heat quantity discharged from the circulating flow path 25 into air can be estimated from a capacity of the radiator 28. Therefore, according to this embodiment, the above-mentioned devices are controlled by a microcomputer 33. Fig. 3 shows a modification of the second embodiment. In this modification, a cooling liquid tank 30 is arranged at the downstream side of the liquid pump 26. With this arrangement, recovered cooling liquid is stored in the cooling liquid tank 30, so that temperature measurement by the outlet thermometer 32 and supply of cooling liquid under pressure by the liquid pump 26 can be very smoothly performed. The third embodiment of the present invention will be described below with reference to Fig. 4. In this embodiment, cooling liquid supplied from an inlet port 22 to a grinding surface S absorbs grinding heat on the grinding surface S, and is then flowed from a rotary table 2 to a side table 16 surrounding the rotary table 2. The cooling liquid flowed into the side table 16 is drained outside an apparatus from a liquid gutter 13 mounted on an outer wall 16a of the side table 16. More specifically, a collar-like drip-proof cover 17 formed of rubber extends between the rotary table 2 and the side table 16. The drip-proof cover 17 is brought into tight contact with and fixed to the rotary table 2. Therefore, cooling liquid discharged onto the rotary table 2 is smoothly flowed toward the side table 16 by the centrifugal force of the rotary table 2 without being dripped into a gap between the two tables 2 and 16. An inclined surface 16b is formed on the upper surface of the side table 16, so that cooling liquid flowed from the rotary table 2 is guided outwardly. Furthermore, the liquid gutter 13 is mounted on the outer wall 16a of the side table 16 so as to surround the side table 16. The liquid gutter 13 is obliquely mounted so that cooling liquid is guided toward an outlet port 24. An inlet thermometer 31 is provided to a portion of an inlet pipe 21 on the upstream side of the inlet port 22, and an outlet thermometer 32 is provided to a portion of an outlet pipe 23 on the downstream side of the outlet port 24. Entrance and exit temperatures are measured by the two thermometers 31 and 32. With the above arrangement, grinding heat can be measured from a temperature difference between entrance and exit temperatures of cooling liquid and a flow rate of cooling liquid. Control operations of the microcomputer 33 of the first embodiment can be performed based on the grinding heat. Fig. 5 shows a modification of Fig. 4. In this modification, the liquid gutter 13 is provided on the upper surface of the side table 16 at a position adjacent to the drip-proof cover 17. In this manner, natural heat radiation of cooling liquid after heat absorption can be eliminated, and the temperature of cooling liquid can be more precisely measured.

Claims: An apparatus for grinding a semiconductor wafer, comprising: a table (2) having a work stage on which a semiconductor wafer (W) to be ground is placed, at least said work stage (7) being rotatable; a grinding wheel (3) which is movable in a predetermined direction to said work stage while being rotatable about an axis parallel to a rotational axis of said work stage; an inlet flow path (21, 22) for guiding cooling liquid to a grinding surface (S) of said semiconductor wafer; an outlet flow path (11, 13, 23) for collecting the cooling liquid flowed onto said work stage; first and second temperatur detection means (31, 32), arranged in said inlet and outlet flow paths, respectively, for detecting a temperatur of the cooling liquid; and control means (33, 34, 5, 6, 4) which determine and control the flow rate of the cooling liquid. An apparatus according to claim 1, further comprising a circulating flow path (25) for causing an upstream side portion of said inlet flow path to communicate with a downstream portion of said outlet flow path. An apparatus according to claim 2, wherein a liquid pump (26) is arranged in said circulating flow path. An apparatus according to claims 2 or 3, wherein a filter (27) is arranged in said circulating flow path. An apparatus according to claims 2, 3 or 4, wherein a heat exchanger or a radiator (28) is arranged in said circulating flow path. An apparatus according to any one of claims 2 to 5, wherein a cooling liquid tank (30) is provided to said circulating flow path. An apparatus according to any one of claims 1 to 6, wherein a flow control valve (34) is arranged in said inlet flow path, and said control means comprises a microcomputer (33) for controlling the flow rate of the cooling liquid using said flow control valve. An apparatus according to any one of claims 1 to 7, wherein said control means comprises a microcomputer (33) for controlling the rotational speed of said grinding wheel. An apparatus according to any one of claims 1 to 8, wherein said control means comprises a microcomputer (33) for controlling the moving speed of said grinding wheel. An apparatus according to any one of claims 1 to 9, wherein said control means comprises a microcomputer (33) for controlling the rotational speed of said work stage. An apparatus according to claims 1 to 10, further comprising cooling liquid collecting means (13) arranged around said work stage. An apparatus according to claim 11, wherein said cooling liquid collecting means comprises: a peripheral wall (10a) formed by projecting a peripheral edge portion of said work stage upward; a communication flow path (10b) for causing an inner stage of said peripheral wall to communicate with a discharge port formed in a side surface of said table; and a liquid gutter (13) arranged along a rotational pipe of said discharge port. An apparatus according to claim 11, wherein said cooling liquid collecting means comprises: a collar-like drip-proof cover (17) surrounding said table; and a liquid gutter (13) for collecting the cooling liquid guided outside said table by said drip-proof cover. An apparatus according to claims 12 or 13, wherein said liquid gutter (13) is mounted on a side table arranged to surround said table.

Inventors: GOTOH NOBORU C O YOKOHAMA WORK, NISHIGUCHI MASANORI C O YOKOHA, GOTOH, NOBORU, C/O YOKOHAMA WORKS OF, NISHIGUCHI, MASANORI, C/O YOKOHAMA WORKS OF
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1990
Main classification: B24B37
IPC codes: B24B7, B24B55, B24B37