Chemical dispensing system for semiconductor wafer processing

A method for dispensing a chemical, such as an edge bead removal solvent, onto a semiconductor wafer comprising the steps of dispensing the chemical selectively onto the wafer and applying a suction to the area immediately surrounding the location at which the chemical is dispensed onto the wafer. Preferably, the suction is applied substantially simultaneously with the dispensing of the chemical. One specific version of the invention provides an edge bead removal system wherein suction is applied to the area immediately surrounding the solvent dispensing nozzle to remove dissolved coating material and excess solvent from the wafer. In one aspect of this system, an apparatus for removing the edge bead includes a mechanism for dispensing a solvent selectively onto the edge of the wafer, and a mechanism surrounding the dispensing mechanism for vacuuming excess solvent and dissolved coating material from the edge of the wafer. The edge bead removal apparatus preferably also includes mechanisms for spinning the semiconductor wafer and coating material on the spinning wafer. Another aspect of the system provides a method for removing an edge bead of a coating of material that has been spun onto the surface of a semiconductor wafer. The method includes the steps of dispensing a solvent selectively onto the edge of the wafer to dissolve the coating material at the extreme edge of the wafer, and applying a suction to vacuum excess solvent and dissolved coating material from the wafer.

FIELD OF THE INVENTION

The invention relates generally to the manufacture of semiconductor devices. More particularly, the invention relates to a chemical dispensing system for semiconductor wafer processes such as removing the edge bead formed during spin coating processes.

BACKGROUND OF THE INVENTION

Coating materials such as photoresist are typically applied to a semiconductor wafer by flowing liquid coating material onto the top surface of the wafer while it is spinning. The wafer is held on a disk shaped, rotating spin chuck. The diameter of the chuck is slightly less than the diameter of the wafer. The chuck is positioned so that the wafer lies on the chuck in a level horizontal plane. In operation, the backside or inactive surface of the wafer is placed onto the chuck. The chuck applies a suction to the backside of the wafer to hold the wafer in place on the chuck. The chuck is rotated by a motor driven axle that extends down from the chuck. As the wafer is rotated on the chuck, liquid photoresist material is applied to the center of the wafer. The photoresist spreads radially outward from the center of the wafer towards the edge to coat the top of the wafer. Ideally, all excess coating material is ejected from the edge of the wafer. In practice, however, some excess photoresist tends to collect at and form a bead along the edge of the wafer.

A solvent is dispensed along the edge of the wafer to dissolve the edge bead and remove the resist from the extreme edge of the wafer. The solvent may be dispensed through a nozzle directed toward the backside edge of the wafer, in which case it curls up around to the top of the wafer to dissolve the edge bead, or the solvent may be dispensed directly onto the top edge of the wafer. In either case, the process allows solvent and dissolved photoresist to be splashed about and often leaves a jagged edge profile on the photoresist or other coating material.

SUMMARY OF THE INVENTION

Accordingly, it is one object of the invention generally to increase the effectiveness of conventional edge bead removal systems. It is another object to control solvent and particle splashing during the process of removing the edge bead from the coating material. It is a further object of the invention to improve the edge profile of the coating material. These and other objects and advantages may be achieved in general by a method for dispensing a chemical, such as an edge bead removal solvent, onto a semiconductor wafer. The method comprises the steps of dispensing the chemical selectively onto the wafer and applying a suction to the area immediately surrounding the location at which the chemical is dispensed onto the wafer. Preferably, the suction is applied substantially simultaneously with the dispensing of the chemical.

One specific version of the invention provides an edge bead removal system wherein suction is applied to the area immediately surrounding the solvent dispensing nozzle to remove dissolved coating material and excess solvent from the wafer. In one aspect of this system, an apparatus for removing the edge bead includes a mechanism for dispensing a solvent selectively onto the edge of the wafer, and a mechanism surrounding the dispensing mechanism for vacuuming excess solvent and dissolved coating material from the edge of the wafer. The edge bead removal apparatus preferably also includes mechanisms for spinning the semiconductor wafer and coating material on the spinning wafer. Another aspect of the system provides a method for removing an edge bead of a coating of material that has been spun onto the surface of a semiconductor wafer. The method includes the steps of dispensing a solvent selectively onto the edge of the wafer to dissolve the coating material at the extreme edge of the wafer, and applying a suction to vacuum excess solvent and dissolved coating material from the wafer. Preferably, the suction is applied to the area immediately surrounding the location at which the solvent is dispensed onto the wafer simultaneously with the dispensing of the solvent.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, wafer10is positioned on spin chuck12. Spin chuck12is mounted on axle14. Axle14is operatively coupled to a drive mechanism, such as an electric motor (not shown). The diameter of spin chuck12is less than the diameter of wafer10so that wafer10extends beyond the edge of spin chuck12. a first nozzle15for dispensing coating material onto wafer10is positioned above and, typically, at the center of wafer10. A second nozzle16for dispensing solvent to dissolve the edge bead is disposed above the edge of wafer10. Solvent dispensing nozzle16is surrounded by vacuum port18. Vacuum port18is operatively coupled to a source of negative pressure, such as a vacuum pump (not shown).

In operation, a suction is applied to the wafer10to hold it in place on spin chuck12. Spin chuck12is rotated to spin wafer10as a solution of coating material, such as photoresist, is applied through first nozzle15. Although photoresist is used herein as one illustrative coating, the invention is applicable to any soluble coating. The coating material is distributed across the top surface of wafer10largely due to centrifugal forces created by the spinning wafer. Excess coating material tends to collect at and form a bead along the edge22of wafer10. To remove the edge bead, a solvent is sprayed through nozzle16onto the edge22of wafer10to dissolve the coating material at the extreme edge of the wafer. At the same time, the dissolved coating material and excess solvent is suctioned away from wafer10through vacuum port18. Preferably, vacuum port18surrounds nozzle16and a suction is thereby applied to the area immediately surrounding nozzle16, as shown inFIG. 1. Also, vacuum port18preferably moves with nozzle16as it is extended and retracted into position over wafer10. This “surround vacuum” controls solvent and particle splashing during the process of removing the edge bead from the coating material. In addition, it is believed surround vacuum improves the edge profile of the coating material.

FIG. 2illustrates a second embodiment of the invention wherein the solvent is applied to both the top and bottom surfaces of wafer10. Wafer10is positioned on spin chuck12which is rotated on axle14. An edge bead removal solvent is supplied through tubes20to dispensing nozzles16. The solvent is sprayed through nozzles16onto the edge22of wafer10and, at the same time, the dissolved coating material and excess solvent is suctioned away through vacuum ports18.

Conventional spin coating machines, such as a SVG Coat Track or TEL Mark 8, can be adapted for use in accordance with the invention as described herein. With the exception of the vacuum ports, the above described components are conventional and well known to those skilled in the art. There has been shown and described an edge bead removal system wherein a suction is applied to the area surrounding the solvent dispensing nozzle to control splashing and improve the edge profile of the coating material. The particular embodiments shown and described herein are for purposes of example and should not be construed to limit the invention as set forth in the appended claims.