Acoustic Wave Enhanced Spin Coater

1. Field of the Invention

This invention relates to a process for reducing surface irregularities of a coating upon a substrate in general and more particularly to a process for reducing surface irregularities of a photoresist or spin-on-glass coating upon a semiconductor wafer.

2. Description of the Prior Art

When a photoresist or spin-on-glass coating is deposited on a substrate pattern the coating is not totally planar because the coating somewhat follows the underlying contours of the pattern.

Prior art regarding reduction of surface irregularities on photoresist are disclosed in U.S. Pat. No. 5,395,803 (Adams). In this patent, coverings such as resist-type materials are dispersed onto a substrate in a spiral pattern to produce a more uniform coating than possible up to now. A method of planarizing spin-on-glass is disclosed in U.S. Pat. No. 5,454,871 (Liaw et al.). Here, a first coating of a silicate spin-on-glass is applied, filling the valleys of the irregular structure of the conductor layer. A second coating is then applied and both layers are cured. A uniform spin-on-glass dielectric layer is claimed.

It is an object of the present invention to provide a method and an apparatus to improve the planarization of a coating upon a substrate, in particular to improve the planarization of photoresist or spin-on-glass coatings upon a semiconductor wafer.

These objects have been achieved by providing an ultrasonic generator and coupling its ultrasonic wave in-to the semiconductor wafer by way of the chuck upon which the semiconductor wafer rests. This ultrasonic wave creates vibrations in the photoresist or spin-on-glass coating, causing material to flow from the peaks to the valleys of the coating. A much more planar surface is thus produced.

FIG. 1 is a block diagram illustrating the method of the present invention.

FIG. 2 is a side view of the ultrasonic generator, wafer, and chuck assembly, depicting one embodiment of the present invention.

FIG. 3A is a detail of FIG. 2, showing a view of the photoresist or spin-or-glass coating and the pattern underneath, without the application of an ultrasonic wave.

FIG. 3B is a detail of FIG. 2, showing a view of the photoresist or spin-on-glass coating and the pattern underneath, illustrating the effects of applying an ultrasonic wave as embodied in the present invention.

This invention improves the flatness of a coating, especially those photoresist or spin-on-glass coatings with a high topography, by causing an ultrasonic wave to vibrate this coating and have the coating flow from the peaks to the valleys.

Referring now to FIG. 1, we show a block diagram of the method of the present invention. Block 101 shows the dispersing of a coating upon a substrate. This is done in a spin coater. The coating could be a photoresist coating or a spin-on-glass coating. In Block 102 an ultrasonic wave generator provides an ultrasonic wave, which couples, in Block 103, into the substrate and causes the substrate to vibrate. This vibration, in turn, agitates the coating, Block 104, increasing its mobility and causes the coating to flow better and become more planar, Block 105. Because of the agitation of the molecules in the coating, material flows from the higher sections of the coating to the lower sections, thereby making the surface smoother.

Referring now to FIG. 2, an apparatus is disclosed which provides acoustic power to a spin coater 200 which will flatten the surface of a coating 203 on a substrate 204 through ultrasonic means. Chuck 205 supports substrate 204. Attached to chuck 205 is spindle 206. Spin motor 207 turns spindle 206, thereby rotating spin coater 200. In one embodiment of this invention an ultrasonic wave generator 208 couples to chuck 205 through appropriate means (not shown). In another embodiment of this invention the ultrasonic wave generator 208 attaches to ball bearing assembly 209. An ultrasonic wave emanating from the ultrasonic wave generator couples from the ball bearing assembly 209 into spindle 206. Ball bearing assembly 209, in turn, is supported by resilient means 210.

FIG. 3A is an enlargement of coating 203 and substrate 204 of FIG. 2, showing in detail how the surface 301 of the coating follows the pattern 302 of substrate 204 when the coating is not agitated. FIG. 3B is the same view, but now the coating is agitated, the valleys have been filled in, and the surface 301 is quite smooth.

Benefits of the ultrasonic method and apparatus are improved surface flatness at a modest cost in extra equipment.

While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.