Holding table

A holding table for holding a platelike workpiece which includes a base and an annular holding member attached to the base. The annular holding member has an annular holding surface for holding the outer circumferential portion of the platelike workpiece thereon. Accordingly, a central recess is defined by the base and the annular holding member so as to be surrounded by the annular holding member. The annular holding member is formed with a suction opening exposed to the annular holding surface, a vacuum line having one end communicating with the suction opening and the other end connected to a vacuum source, a discharge opening exposed to the annular holding surface at a position radially outside of the suction opening, and a fluid line having one end communicating with the discharge opening and the other end connected to a fluid source.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a holding table for holding a platelike workpiece such as a wafer.

2. Description of the Related Art

A processing apparatus such as a grinding apparatus, cutting apparatus, and laser processing apparatus for processing a platelike workpiece such as a wafer includes a holding table (chuck table) having a holding surface for holding the platelike workpiece under suction as disclosed in Japanese Patent Laid-open No. Hei 5-23941 and Japanese Patent Laid-open No. 2008-140832, for example. In processing the workpiece held on the holding table under suction, there is a possibility that contaminants may adhere to the contact surface of the workpiece which comes into contact with the holding surface of the holding table.

As a result, there is a possibility that the contaminants adhering to the workpiece may contaminate a transporting unit for transporting the workpiece or contaminate the inside of a cassette for storing the workpiece after processing. When a clean workpiece is transported by the transporting unit once contaminated or stored into the cassette once contaminated, there is a possibility that the clean workpiece may also be contaminated. As disclosed in Japanese Patent Laid-open No. 2004-107606, there is a case that a platelike workpiece is attached through an adhesive or wax to a support plate in order to facilitate the handling of the workpiece. Further, as disclosed in Japanese Patent Laid-open No. 5-21763, there is widely used a technique of directly bonding a workpiece to a support plate.

SUMMARY OF THE INVENTION

In the case that a stacked workpiece formed by attaching a workpiece to a support plate is held on the holding table under suction in the condition where the support plate comes into contact with the holding surface, the support plate may be flawed. Even when the support plate thus flawed is reused, there is a possibility that the support plate cannot be held under suction on the holding table, depending on the size of flaws. Further, when the workpiece attached to the support plate having flaws is subjected to processing with heat, there is a possibility that the support plate may be broken from the flaws and the workpiece may also be broken. Accordingly, the support plate once used is conventionally discarded. This is very uneconomical and the reuse of the support plate has been desired.

It is therefore an object of the present invention to provide a holding table which can reduce the possibility of adhesion of contaminants to a platelike workpiece held under suction or flawing of the workpiece.

In accordance with an aspect of the present invention, there is provided a holding table for holding a platelike workpiece, including a base; and an annular holding member attached to the base, the annular holding member having an annular holding surface for holding the outer circumferential portion of the platelike workpiece thereon, whereby a central recess is defined by the base and the annular holding member so as to be surrounded by the annular holding member; the annular holding member being formed with a suction opening exposed to the annular holding surface, a vacuum line having one end communicating with the suction opening and the other end connected to a vacuum source, a discharge opening exposed to the annular holding surface at a position radially outside of the suction opening, and a fluid line having one end communicating with the discharge opening and the other end connected to a fluid source. Preferably, the annular holding member is formed of resin.

In the case that the platelike workpiece is a stacked workpiece formed by attaching a platelike workpiece to a support plate, only the outer circumferential portion of the support plate is held under suction on the annular holding member. Accordingly, it is possible to reduce the possibility of flawing of the support plate or adhesion of contaminants to the support plate, so that contamination of the transporting unit or the cassette can be prevented and the support plate can be reused.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will now be described in detail with reference to the drawings. Referring toFIG. 1, there is shown a perspective view of a cutting apparatus2including a holding table (chuck table)18according to a preferred embodiment of the present invention. The cutting apparatus2includes an operation panel4for allowing an operator to input instructions such as processing conditions to the apparatus2. The operation panel4is provided at the front portion of the cutting apparatus2. The cutting apparatus2further includes a display unit6such as a CRT for displaying a guide view to the operator or an image obtained by an imaging unit to be hereinafter described. The display unit6is provided at the upper portion of the cutting apparatus2.

A plurality of (e.g., 25) platelike workpieces such as wafers are stored in a cassette8. The cassette8is placed on a vertically movable cassette elevator9. A handling unit10is provided on the rear side of the cassette8to take any one of the workpieces out of the cassette8before processing and also bring back the workpiece into the cassette8after processing. The handling unit10has a clamp11for gripping the workpiece in handling the workpiece with respect to the cassette8. The handling unit10is linearly movable in the Y direction.

A temporary setting area12for temporarily setting the workpiece before cutting or after cutting is formed between the cassette8and the handling unit10. A pair of positioning members14for centering the workpiece is provided in the temporary setting area12. A first transporting unit16having a swivel arm is provided in the vicinity of the temporary setting area12to transport the workpiece by holding it under suction. The workpiece to be processed is transported from the temporary setting area12to the holding table (chuck table)18by the first transporting unit16under suction. The workpiece thus transported to the holding table18is held on the holding table18under suction.

The holding table18is rotatable and reciprocatable in the X direction. An alignment unit30for detecting a subject area of the workpiece to be cut is provided above a path of movement of the holding table18along the X direction. The alignment unit30includes an imaging unit32for imaging the front side of the workpiece. The imaging unit32has an imaging device and a microscope. The alignment unit30can detect the subject area to be cut by imaging processing such as pattern matching according to an image obtained by the imaging unit32. The image obtained by the imaging unit32is displayed by the display unit6.

A cutting unit34for cutting the workpiece held on the holding table18is provided on the left side of the alignment unit30as viewed inFIG. 1. The cutting unit34is integral with the alignment unit30, and they are movable together in the Y direction and the Z direction. The cutting unit34includes a spindle36adapted to be rotationally driven and a cutting blade38mounted to the front end of the spindle36. The cutting unit34is movable in the Y direction and the Z direction. The cutting blade38is located on an extension line extending from the imaging unit32in the X direction. Reference numeral40denotes a second transporting unit for transporting the workpiece from the holding table18to a spinner cleaning unit42after performing a cutting operation by the cutting unit34. The spinner cleaning unit42functions to perform spin cleaning and spin drying to the workpiece.

Referring toFIG. 2, there is shown a vertical sectional view of the holding table18according to this preferred embodiment. The holding table18includes a base (frame)20formed of metal such as stainless steel and an annular holding member22attached to the base20. The annular holding member22has an annular holding surface22afor holding the outer circumferential portion of the workpiece thereon. Accordingly, the holding table18has a central recess24defined by the base20and the annular holding member22so as to be surrounded by the annular holding member22. Preferably, the annular holding member22is formed of a conductive resin, so that it is possible to prevent the adhesion of contaminants to the annular holding member22due to static electricity.

The whole of the holding table18is not formed of resin, but the base20is formed of metal such as SUS and only the annular holding member22is formed of resin. Accordingly, the rigidity of the holding table18can be maintained. The base20is formed with a vacuum line21selectively connected through an electromagnetic on-off valve (not shown) to a vacuum source26. The base20is further formed with a fluid line23selectively connected through an electromagnetic on-off valve (not shown) to a fluid source28.

The annular holding member22is formed with an annular vacuum line25connected to the vacuum line21of the base20and an annular fluid line27connected to the fluid line23of the base20. The annular holding surface22aof the annular holding member22is formed with an annular suction opening25acommunicating with the annular vacuum line25and an annular discharge opening27acommunicating with the annular fluid line27. The annular discharge opening27ais located radially outside of the annular suction opening25a. The annular suction opening25amay be replaced by a plurality of suction openings spaced from each other in the circumferential direction of the annular holding member22. Further, the annular discharge opening27amay be replaced by a plurality of discharge openings spaced from each other in the circumferential direction of the annular holding member22.

Referring toFIG. 3, there is shown a vertical sectional view of the holding table18in the condition where a stacked workpiece15is held on the holding table18under suction. The stacked workpiece15is formed by bonding a platelike workpiece11on a support plate13through an adhesive. For example, the support plate13is formed from a silicon wafer having no pattern, and the platelike workpiece11is formed from a silicon wafer having semiconductor devices on the front side11a. An arcuate chamfered portion11cis formed on the entire circumference of the platelike workpiece11, and an arcuate chamfered portion13cis also formed on the entire circumference of the support plate13. The support plate13may be formed of glass.

Referring toFIG. 4, there is shown a partially sectional side view in the condition where trimming is being performed on the chamfered portion11cof the platelike workpiece11held under suction on the holding table18through the support plate13. Trimming of the chamfered portion11cis performed by feeding the cutting blade38being rotated at a high speed in the direction shown by an arrow A so as to cut the outer circumferential portion of the platelike workpiece11having the chamfered portion11cat a predetermined depth and then rotating the holding table18at a low speed in the direction shown by an arrow B, thereby removing the chamfered portion11cformed on the entire circumference of the platelike workpiece11. Preferably, a fluid29such as pure water is discharged from the discharge opening27aof the annular holding member22of the holding table18in performing this trimming. Although a cutting waste is generated during this trimming, this cutting waste is washed away by the fluid29discharged from the discharge opening27a, thereby suppressing the adhesion of the cutting waste to the stacked workpiece15and the holding table18.

WhileFIG. 4shows the condition where the outer circumferential portion of the platelike workpiece11constituting the stacked workpiece15is being trimmed, the cutting operation for the platelike workpiece11held on the holding table18is not limited to trimming, but the holding table18is also applicable to cutting of the platelike workpiece11along division lines. Further, the holding table18may be used as a holding table in a laser processing apparatus in performing laser processing of the platelike workpiece11.

In the holding table18according to this preferred embodiment, only the outer circumferential portion of the support plate13is held under suction on the annular holding member22. Accordingly, it is possible to reduce the possibility of flawing of the support plate13or adhesion of contaminants to the support plate13, so that contamination of the transporting unit or the cassette can be prevented and the support plate13can be reused. Further, the holding table18according to this preferred embodiment is applicable not only to the case of holding the support plate13under suction, but also to the case of directly holding the platelike workpiece11.