Etching a substrate: processes – Nongaseous phase etching of substrate – Etching inorganic substrate
Reexamination Certificate
1998-09-03
2001-10-30
Watkins, III, William P. (Department: 1772)
Etching a substrate: processes
Nongaseous phase etching of substrate
Etching inorganic substrate
C428S612000, C428S687000, C428S141000, C204S298120, C204S298130
Reexamination Certificate
active
06309556
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for manufacturing sputtering targets with an enhanced finish, and more particularly to a process for chemically etching the surface of sputter targets to achieve an enhanced finish.
BACKGROUND OF THE INVENTION
In the manufacture of sputtering targets used in the semi-conductor industry, it is desirable to produce a target with a sputter surface that will provide film uniformity and minimal particle generation during sputtering onto a semi-conductor wafer. The typical manufacturing processes for sputter targets result in targets with surface defects. Additionally, the materials comprising the sputter targets, such as titanium, aluminum, tantalum, nickel, chromium, cobalt and alloys thereof, have inherently problematic characteristics (i.e., particle size and uniformity and burn-in time requirements) that are a result of the machining process. These inherent defects and characteristics may have an adverse effect on the end user of the sputter target product.
Among the undesirable effects of sputter target manufacture is the lengthy bum-in time for a new sputter target at the customer site. Typically, sputter targets, such as titanium targets, exhibit poor film uniformity and high particle counts during the early stages of target use. As a result, a burn-in cycle, which eliminates the surface defects of the target, must be performed for as long as 30 kWh before the target surface will produce high quality thin film wafers. It is not uncommon for a standard target to go through about 50 wafers during the burn-in cycle before it produces high quality wafers, which is equivalent to about 6.7 kWh. Deposition without this burn-in cycle would result in a relatively high reject rate of poor quality wafers. Thus, the burn-in cycle is required to achieve a sputter surface that will provide the desired film uniformity and particle generation, but it requires a customer to waste valuable processing time and materials. By way of example, for titanium targets, 0.75-1.0% film uniformity is desirable, and 10 particles or less generated per 8 inch wafer is desired.
Various attempts have been made to reduce, eliminate or control the inherently undesirable characteristics resulting from the manufacturing process for sputter targets. For example, grinding, lapping, fine machining, lathes, and hand polishing have been used to remove the surface material of the target. These methods of material removal are time consuming, labor intensive, costly, dirty and provide inconsistent results. While polishing to a mirror finish may provide a good surface finish, it requires extensive preparation and time, usually 20-60 hours, which is unsuitable for a production environment, and there is no guarantee the same result may be obtained consistently for subsequent targets. Furthermore, sputter targets of marginal acceptability due to defects from unaccountable variances in manufacturing cannot be salvaged by the above techniques.
There is thus a need to provide a method for manufacturing sputter targets that provides a consistent finish with low particle counts and minimal surface defects, thereby reducing or eliminating burn-in time prior to use.
SUMMARY OF THE INVENTION
The present invention provides a method for achieving a sputter target with a surface roughness of about 10-30 &mgr;in., good film uniformity and low particle counts during initial use, thus significantly reducing burn-in time requirements. The sputter target surface is achieved by chemically etching the surface prior to use. Advantageously, the surface is etched with a first acid solution, rinsed with water, etched in a second acid solution, rinsed with water, rinsed with an alcohol solution, and dried. Although acids are the preferred etchants, other basic chemicals may be used as the etchant for the present invention. The acids or other etching chemicals used in the present invention are advantageously selected from the following: hydrofluoric acid, nitric acid, phosphoric acid, sulfuric acid, hydrochloric acid, acetic acid, lactic acid, ammonium hydroxide, chromic oxide, hydrogen peroxide, potassium ferricyanide and sodium hydroxide. The first and second etching solutions advantageously contain about 1-10% by volume and about 20-60% by volume etchant, respectively. More advantageously, the second solution contains about 1-10% by volume of a first etchant and about 20-50% by volume of a second etchant. The etching is advantageously performed for 1-15 minutes with each solution, and more advantageously, the etching is performed while the solution is agitated, either intermittently or constantly.
In one embodiment of the present invention, a method is provided for finishing the surface of a titanium sputter target. To this end, the surface is etched with a solution of hydrofluoric acid, rinsed with water, etched with a solution of hydrofluoric acid and nitric acid, rinsed with water, rinsed with an alcohol solution, and dried. In a preferred method, the titanium sputter target surface is advantageously etched first with a 1-8% by volume hydrofluoric acid solution for about 1-10 minutes, and second (after rinsing) is etched with a 1-6% by volume hydrofluoric acid/25-45% by volume nitric acid solution for about 2-10 minutes.
These and other objects and advantages of the present invention shall become more apparent from the accompanying description thereof
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Gilman Paul Sandford
Hunt Thomas John
Joyce James Elliot
Biederman Blake T.
Praxair S.T. Technology, Inc.
Watkins III William P.
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