Photoresist coater

Details Photoresist coater Photoresist coater

1998-11-23

2001-10-16

Crispino, Richard (Department: 1734)

Coating apparatus

With means to centrifuge work

C118S320000, C118S321000, C118S663000, C118S681000, C134S153000, C134S067000, C239S596000, C239SDIG001

Reexamination Certificate

active

06302960

ABSTRACT:

BACKGROUND
The present invention relates generally to integrated circuit fabrication, and more particularly to a coater for dispensing photoresist onto a substrate.
An initial step in the photolithographic fabrication of an integrated circuit is to coat a substrate, such as a silicon wafer, with a layer of photoresist. In one process, generally known as “spin-on” coating, the substrate is positioned on a rotating chuck and photoresist is dispensed onto the center of the substrate as it rotates. The centrifugal force generated by the rotation of the substrate urges the photoresist radially outward, in the process covering the substrate surface. Once the substrate has been coated, it may be removed from the coater and baked to cure the photoresist. Finally, the cured photoresist is exposed and chemically developed, and the substrate is etched to define circuitry features.
One problem encountered in photoresist coating is non-uniformity of the photoresist layer thickness. For example, during etching, the thicker portions of the photoresist layer may be underexposed whereas the thinner portions may be overexposed, resulting in defects and, thus, a decrease in process yield. One source of this non-uniformity is fluctuation in the droplet size and flow rate from the photoresist dispenser. Premature curing, in which the photoresist cures before it reaches the substrate edge, also produces a non-uniform surface.
Another problem is that some conventional photoresist coaters are inefficient and waste significant amounts of photoresist. As much as ninety-seven percent of the photoresist may be spun off the substrate surface during the coating process. There may also be additional costs in properly disposing of the photoresist if it is considered a hazardous waste.
SUMMARY
In general, in one aspect, the invention is directed to a photoresist coater. The photoresist coater has a rotatable chuck to support a substrate, a source of photoresist, a pivotable dispensing arm extendable over the chuck, and a nozzle at the end of the dispensing arm. The arm is movable between a first position in which an end of the arm is located substantially adjacent to a center portion of the substrate and a second position in which it is located substantially adjacent to an edge portion of the substrate. The nozzle is coupled to the photoresist source and has an aperture with a dimension sufficiently small that photoresist directed therethrough forms an aerosol which is directed onto the substrate.
Implementations of the invention may include one or more of the following. The aperture may be substantially circular and the dimension may be a diameter. The diameter of the aperture may be between about 100 and 300 microns. The nozzle may be part of a dispensing head located at the end of the dispensing arm. A flexible tube may extend between the photoresist source and the dispensing head to direct photoresist through the nozzle. The dispensing head may include a funnel-shaped section to direct photoresist from an end of the tube to the nozzle. The nozzle may include a generally cylindrically-shaped body with a passage therethrough and a nozzle head at an end of the passage. The aperture may extend through the nozzle head and may be in fluid communication with the passage through the generally cylindrically-shaped body. The generally cylindrically-shaped body may be made of metal and the nozzle head may be made of a crystalline material, such as ruby or sapphire. A motor may be coupled to the dispensing arm to cause it to pivot, and a motor may rotate the chuck. The photoresist source may provide photoresist at a controllable flow rate and or a controllable pressure.
In another aspect the invention is directed to a nozzle for a photoresist coater. The nozzle has a nozzle body and a nozzle head. The nozzle body has a first fluid passage with a first cross-sectional dimension and an inlet side to receive photoresist. The nozzle head has a second fluid passage with a second cross-sectional dimension less than the first cross-sectional dimension, the second fluid passage coupled to an outlet of the first fluid passage. The second cross-sectional dimension is between about 100 and 300 microns.
In another aspect, the invention is directed to a dispensing head for dispensing photoresist onto a substrate. The head has a housing with a frustroconical-shaped first passage with an inlet side and an outlet side. The outlet side of the first passage has a first cross-sectional dimension. A nozzle is disposed downstream of the outlet side of the first passage. The nozzle includes a second passage which has a second cross-sectional dimension less than the first cross-sectional dimension, and a third passage having a third cross-sectional dimension less than the second cross-sectional dimension. The photoresist can be directed from the inlet side to the outlet side of the first passage, and through the second and third passages onto a substrate.
In another aspect, the invention is directed to a method of dispensing photoresist onto a substrate. The substrate is supported on a chuck. A dispensing arm is moved between a first position in which an end of the dispensing arm is located substantially adjacent a central portion of the substrate and a second position in which the end of the dispensing arm is located substantially adjacent an edge portion of the substrate. A photoresist fluid is directed through an aperture in a nozzle at the end of the dispensing arm. The aperture has a dimension sufficiently small that the photoresist forms an aerosol which is directed onto the substrate.
Advantages of the invention may include the following. The coater of the present invention dispenses a photoresist layer having a substantially uniform thickness, thereby decreasing fabrication defects and increasing process yield. The coater also uses less photoresist.
Other features and advantages of the invention will become apparent upon reading the following description, including the claims and drawings.


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Bureau et al., “Photoresist Deposition with Nitrogen to Supress the Dewetting Problem,” IBM Technical disclosure bulletin, vol. 22, No. 5, Oct. 5, 1979, pg. 1884.

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