Workpiece centering apparatus and method of centering workpiece

The workpiece centering apparatus is capable of highly reducing damage of a workpiece. The workpiece centering apparatus comprises: a guide plate being provided in a tray and covering a water inlet so as to horizontally introduce water into the tray; and at least three overflow outlets for overflowing the water from the tray, the overflow outlets being formed in a peripheral wall of the tray and arranged in the circumferential direction at regular intervals. The workpiece, which is horizontally fed on a surface of the water stored in the tray, is received and floated by surface tension of the water. Then, the workpiece is centered in the tray by water flows radially overflowing from the tray via the overflow outlets.

BACKGROUND OF THE INVENTION

The present invention relates to a workpiece centering apparatus and a method of centering a workpiece.

Various types of polishing apparatuses for polishing workpieces have been known.

Each of the polishing apparatuses has a polishing plate, in which polishing cloth is adhered on an upper face, and a top ring pressing a workpiece, which is held on the lower side, onto the polishing cloth. The polishing plate is relatively moved with respect to the top ring so as to polish a lower face of the workpiece.

The workpiece, which has been polished by the polishing apparatus, is put into a tray storing water and washed therein, and then the workpiece is transferred to a next stage, e.g., accommodating cassette, by a holding unit, e.g., robot hand. To hold the workpiece by the holding unit, the workpiece must be centered.

A conventional workpiece centering apparatus is disclosed in Japanese Patent Gazette No. 2003-62750. In the workpiece centering apparatus, water is jetted toward an upper face of a tray so as to form water film, a polished workpiece, which is held on a lower face of a chucking mechanism, is dropped into the tray with jetting water, the polished surface of the workpiece is cleaned by the jetted water, a cylinder rod of an elevating unit is extended upward so as to center the workpiece by picots of a positioning mechanism, the workpiece, whose outer edge has been fixed by the picots, is moved upward until reaching a position above a fringe section of the tray, which is upwardly extended from an outer edge of the tray, and an end part is clamped by a robot arm and transferred to an accommodating cassette.

However, in the conventional workpiece centering apparatus, the workpiece is dropped into the tray and washed, and then the tray is moved upward by the picots, whose upper end parts are formed into tapered shapes, and compulsorily positioned by the tapered parts. Therefore, the picots moving upward apply shocks to the workpiece, so that the workpiece will be damaged. Namely, when the picots are moved upward, a shifted end part of the workpiece, which is not centered, strongly collides with the tapered part of the picot and moved downward along the tapered part, and the other end part of the workpiece collides with the picot, so that the workpiece is centered. With this action, the strong shock is applied to the workpiece by the picots.

SUMMARY OF THE INVENTION

The present invention was conceived to solve the above described problems.

An object of the present invention is to provide a workpiece centering apparatus and a method of centering a workpiece, which are capable of highly reducing damage of the workpiece.

To achieve the object, the present invention has following structures.

Namely, the workpiece centering apparatus of the present invention comprises:

a tray having a peripheral wall;

a water supply section supplying water into the tray via a water inlet provided at a center of a bottom face of the tray;

a guide plate being provided in the tray and separated a prescribed distance away from an inner bottom face of the tray, the guide plate covering the water inlet so as to horizontally introduce the water, which is supplied via the water inlet, into the tray; and

at least three overflow outlets for overflowing the water from the tray, the overflow outlets being formed in the peripheral wall and arranged in the circumferential direction at regular intervals,

a workpiece, which is horizontally fed on a surface of the water stored in the tray, is received and floated by surface tension of the water, and

the workpiece is centered in the tray by water flows radially overflowing from the tray via the overflow outlets.

In the apparatus, drawing forces applied to the workpiece, each of which is caused by viscosity of each of the water flows overflowing via each of the overflow outlets, may be equal.

In the apparatus, the overflow outlets may have the same length and the same height.

In the apparatus, an inner face of the peripheral wall may be a female tapered face, whose diameter is gradually reduced toward the inner bottom face of the tray, and

the overflow outlets may be designed to make a diameter of the surface of the water overflowing via the overflow outlets slightly larger than that of the workpiece.

The workpiece centering apparatus may further comprise: a transferring section including; and at least three positioning pins, each of which has an upper end part, a lower end part whose diameter is larger than that of the upper end part, and a tapered part which connects the upper end part and the lower end part; and a driving section for vertically moving the positioning pins, and

the workpiece may be received by the positioning pins when the positioning pins are moved upward by the driving section, and then the workpiece is centered.

In the apparatus, the workpiece may be centered and further upwardly moved above the peripheral wall, by moving the positioning pins upward, so as to transfer the workpiece to an external apparatus.

In the apparatus, the workpiece, whose lower face has been polished, may be fed on the surface of the water stored in the tray, and

the polished workpiece may be correctly positioned so as to convey the polished workpiece for the next process.

On the other hand, the method of centering a workpiece in a workpiece centering apparatus comprising: a tray having a peripheral wall; a water supply section supplying water into the tray via a water inlet provided at a center of a bottom face of the tray; a guide plate being provided in the tray and separated a prescribed distance away from an inner bottom face of the tray, the guide plate covering the water inlet so as to horizontally introduce the water, which is supplied via the water inlet, into the tray; and at least three overflow outlets for overflowing the water from the tray, the overflow outlets being formed in the peripheral wall and arranged in the circumferential direction at regular intervals, comprises the steps of:

supplying water into the tray by the water supply section;

horizontally feeding the workpiece onto the surface of the water in the tray with overflowing the water via the overflow outlets;

receiving the workpiece floated by surface tension of the water; and

centering the workpiece in the tray by water flows radially overflowing from the tray via the overflow outlets.

In the present invention, the workpiece can be centered in the tray without colliding with the tray, so that damaging the workpiece can be highly prevented.

Especially, by employing the positioning pins, the workpiece is tentatively centered in the tray by the water flows radially overflowing from the tray via the overflow outlets. Therefore, the work piece is not compulsorily positioned by the positioning pins moved upward, so that damaging the workpiece can be avoided.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1is an explanation view of a polishing apparatus10.

InFIG. 1, polishing cloth13made of, for example, polyurethane, is adhered on an upper face of a polishing plate12by, for example, an adhesive. The polishing plate12is rotated in a horizontal plane with a spindle14. The spindle14is rotated by a known driving unit (not shown).

A top ring16is fixed to a lower end of a shaft17. The shaft17is rotated about an axial line and moved upward and downward by a known mechanism. The top ring16is moved between a first position, at which the top ring16is located above the polishing plate12, and a second position, at which the top ring16is located outside of the polishing plate12.

A workpiece transferring unit18is located at a workpiece transferring position X. A workpiece conveying unit19has a robot hand (not shown) for conveying a workpiece to be polished to the transferring unit18or taking out a polished workpiece from the transferring unit18.

The workpiece is transferred from the transferring unit18to a lower face of the top ring16, and the top ring16presses the workpiece onto the polishing cloth13of the polishing plate12. At that time, the polishing plate12and the top ring16are rotated, so that the workpiece can be polished. Upon completing the polish, the workpiece is transferred from the top ring16to the transferring unit18, and then the workpiece is taken out from the transferring unit18by the robot hand.

FIG. 2is a sectional view of the top ring16. The top ring16is a known top ring, so its structure will be briefly explained.

A main body section20has a ceiling plate21fixed to the shaft17and a cylindrical part22fixed to a lower face of an outer edge part of the ceiling plate21.

A holding plate24is provided in a lower part of the main body section20, The holding plate24is connected to the main body section20by a ring-shaped diaphragm, so that the holding plate24can be moved upward and downward. Namely, an outer edge of the diaphragm25is fixed to a lower face of the cylindrical part by a fixing member26; an inner edge of the diaphragm25is fixed to an outer edge part of the holding plate24by a fixing member27.

A first chamber29is formed between the main body section20and the holding plate24and tightly closed by the diaphragm25. A pressurized fluid is introduced into the first chamber29from a pressure source (not shown) via a joint30. With this structure, the workpiece can be pressed onto the polishing cloth13.

Second chambers31are coaxially formed in the holding plate24. The second chambers31are mutually communicated by radially-extended grooves (not shown). Many small holes32, which are communicated to the second chambers31, are uniformly formed in a lower face of the holding plate24.

The pressurized fluid is introduced into the second chambers31from the pressure source (not shown) via a joint34and a pipe35, and the fluid is jetted out from the lower face of the holding plate24via the fine holes32. As shown inFIG. 3, a bucking pad36having fine holes is provided to the lower face of the holding plate24, an a ring-shaped template37is provided on a lower face of an outer edge part of the bucking pad36. The fluid jetted out from the lower face of the holding plate24is further jetted out from the lower face of the bucking pad36via the fine holes. With this structure, the workpiece W is pressed onto the polishing cloth13by the jetted fluid.

To hold the workpiece W, the fluid in the second chambers31is sucked, so that the workpiece W is sucked and held on the lower face of the bucking pad36.

Note that, an inner face of the cylindrical part22is a female tapered face, and an outer face of the fixing member27is a male tapered face, so that the both faces mutually engage and form an engaged part38. By the engaged part38, the holding plate24can be centered and stayed in the main body section20.

The present invention is characterized by the workpiece transferring unit18, which acts as the workpiece centering apparatus.

The workpiece centering apparatus and the method of centering the workpiece will be explained with reference toFIGS. 4 and 5.

A first embodiment of the workpiece transferring unit18is shown inFIGS. 4 and 5.

A tray40has a peripheral wall41and is horizontally supported on a base42by a plurality of supporting rods43. Preferably, an inner face41aof the peripheral wall41is a female tapered face, whose diameter is gradually reduced toward an inner bottom face of the tray40.

The center of the inner bottom face of the tray40is located in a lower part40a, whose level is lower than other parts thereof. A water inlet45is provided at the center in the lower part40a, and a water supply pipe46is connected to the water inlet45. A joint47is provided to one end of the water supply pipe46, and a water supply hose (not shown) can be detachably attached to the water supply hose46by the joint47. The water supply hose is connected to a water source (not shown). A water supply section is constituted by the water supply pipe46, the joint47, etc.

A guide plate50is provided in the inner bottom face of the tray40and covers the water inlet45. The guide plate50is separated a prescribed distance away from the inner bottom face (the lower part40a) of the tray40by a plurality of pillars51and fixed by screws52. The water supplied from the water inlet45collides with a lower face of the guide plate50, and then the water is horizontally introduced outward and introduced into the tray40via spaces formed between the pillars51. Since the water once collides with the guide plate50and is introduced into the tray40, the water can spread in the tray40without waving its surface.

Overflow outlets54for overflowing the water are formed in the peripheral wall41of the tray40by notching the peripheral wall41and arranged in the circumferential direction at regular intervals. The notched overflow outlets54have the same length and the same height. By forming the overflow outlets54, a fixed amount of the water can overflow from each of the overflow outlets54of the tray40at the same speed. In the present embodiment, the heights, etc. of the overflow outlets54are designed to make a diameter of the surface of the water overflowing via the overflow outlets54slightly larger than that of the workpiece W.

At least three overflow outlets54must be formed. Note that, the concept of the overflow outlets54includes through-holes having the same size and the same height.

The structure of the workpiece centering apparatus18will be explained.

When the top ring16is moved to a position above the centering apparatus18and the second chambers31are pressurized, the workpiece W, e.g., wafer, whose lower face has been polished by the polishing apparatus10, is released from the lower face of the top ring16to horizontally fall into the center part of the tray40.

At that time, the water is supplied into the tray40via the water inlet45, the supplied water collides with the guide plate50and horizontally spreads in the tray40without waving its surface, and the water is introduced outside of the tray40via the overflow outlets54, from each of which the fixed amount of water overflows at the same speed.

The workpiece W, which has been fed onto the surface of the water stored in the tray40from the top ring16, received and supported by surface tension of the water. Since the water in the tray40is radially overflowing from the overflow outlets54at the same flow speed as described above, the workpiece W is centered in the tray40by the water flows. The workpiece W is centered and cleaned. Note that, the water overflowed from the tray40is discharged by a gutter56.

In the present embodiment, the overflow outlets54have the same length and the same height so as to overflowing the water therefrom at the same flow speed and center the workpiece W in the tray40, but the present invention is not limited to this manner. Namely, the size and the height of the overflow outlets54is designed so as to make drawing forces applied to the workpiece W, each of which is caused by viscosity of each of the water flows overflowing via each of the overflow outlets54, equal, so that the workpiece W can be centered in the tray40.

As described above, the overflow outlets54are designed to make the diameter of the surface of the water overflowing via the overflow outlets54slightly larger than that of the workpiece W. Therefore, the workpiece W is initially fallen into the center part of the tray40, and then the workpiece W is centered and kept at the center by the radial water flows, which have the same flow speed. Note that, even if the workpiece W is eccentrically fallen into the tray40and one outer part of the workpiece W collides with the female tapered face41a, the workpiece W is immediately floated on the surface of the water by buffer action of the water. Therefore, the workpiece W is not so damaged.

The workpiece W, which has been centered in the tray40, is held by a proper holding unit having a chucking mechanism (not shown) and conveyed to the next stage, e.g., accommodating cassette. Note that, in case of chucking three points of the outer edge of the workpiece W, extended parts, in which chucking members of the chucking mechanism can respectively enter, may be formed in the tray40so as to hold the workpiece W in the tray40. Further, the workpiece W may be held by sucking the center part of the upper face of the workpiece W by a sucking mechanism of the holding unit.

As described above, the workpiece W is centered in the tray40without contact the tray40, so that damaging the workpiece W can be highly prevented.

Successively, a second embodiment of the workpiece centering apparatus18will be explained with reference toFIGS. 6 and 7. Note that, the structural elements explained in the first embodiment are assigned the same symbols and explanation will be omitted.

In the second embodiment too, the tray40has the peripheral wall41including the overflow outlets54.

Each of positioning pins58has: an upper end part59having a tapered end; a lower end part60whose diameter is larger than that of the upper end part59; and a tapered part61which connects the upper end part59and the lower end part60. At least three positioning pins58must be provided. In the present embodiment, five positioning pins58are provided (seeFIG. 7). The positioning pins58correspond to the outer edge part of the tray40, and their upper ends enter the tray40. Further, the positioning pins58can be moved upward and downward.

Lower ends of the positioning pins58are respectively supported by arms63, which are radially arranged under the tray40, and the arms63are vertically moved by a driving section65, e.g., cylinder unit, so that the positioning pins58can be moved upward and downward. Note that, a guide cylinder66of the arm63is guided by the supporting rod43, so that the up-down motion of the arm63is guided.

In the second embodiment, the positioning pins58are respectively moved in half cylinder grooves, which are formed in the peripheral wall41and extended in the vertical direction. The half cylinder grooves longitudinally intersect the mid part of the female tapered face41aso as to form the overflow outlets54. Therefore, edges of the half cylinder grooves in the female tapered face41aact as the overflow outlets54.

Four stoppers67are provided to the outer edge of the tray40. Inner side faces of the stoppers67are slope faces. With this structure, even if the workpiece W is greatly shifted outward in the tray40, the stoppers67prevent the workpiece W from falling outside of the tray40.

Optical sensors70are provided on a bottom face of the outer edge part of the tray40. The optical sensors70emit light toward the workpiece W and receive the reflected light reflected from the workpiece W. Therefore, the optical sensors70can detect if the workpiece W is fed into the tray40or not. Transmission sensors68detect an abnormal state of the workpiece W so as to stop further actions. For example, if the transmission sensors68detect the work piece W being greatly shifted with respect to the tray40and engaged with the stoppers67, the next action, e.g., conveying the workpiece W is stopped.

In the centering apparatus18of the second embodiment, the water is supplied into the tray40via the water inlet45, the supplied water collides with the guide plate50and horizontally spreads in the tray40without waving its surface, and the water is introduced outside of the tray40via the overflow outlets54, from each of which the fixed amount of water overflows at the same speed.

The positioning pins58are initially located at the lowermost positions under the surface of the water.

When the top ring16is moved to the position above the centering apparatus18and the second chambers31are pressurized, the workpiece W, e.g., wafer, whose lower face has been polished by the polishing apparatus10, is released from the lower face of the top ring16to horizontally fall into the center part of the tray40, as well as the first embodiment.

The workpiece W, which has been fed onto the surface of the water stored in the tray40from the top ring16, received and supported by surface tension of the water. Since the water in the tray40is radially overflowing from the overflow outlets54at the same flow speed as described above, the workpiece W is centered in the tray40by the water flows. The workpiece W is centered and cleaned.

Next, the cylinder unit65is driven so as to softly move the arms63and the positioning pins58upward, so that the workpiece W, which has been tentatively centered, is received by the tapered parts61of the positioning pins58and correctly centered.

The positioning pins58are further moved upward until the workpiece W reaches a position above the upper end of the peripheral wall41of the tray40. By lifting the workpiece W to the position above the upper end of the peripheral wall41, the workpiece W can be easily held by the holding unit having the chucking mechanism or the sucking mechanism and conveyed to the next stage, e.g., accommodating cassette.

In the second embodiment, the workpiece W is tentatively centered in the tray40by the water flows overflowing from the overflow outlets54. In the conventional apparatus, shocks are applied to the workpiece when the workpiece is compulsorily positioned. On the other hand, even if the positioning pins58are moved upward, no such shocks are applied to the workpiece W so that damaging the workpiece W can be prevented.

The workpiece centering apparatus of the second embodiment can be used for not only the above described unloading process to transfer the polished workpiece W but also a loading process, in which a workpiece W to be polished is taken out from a cassette by a sucking unit, the workpiece W is fallen into the tray40and centered, and then moved upward to transfer the top ring16.