Semiconductor device manufacturing: process – Including control responsive to sensed condition – Optical characteristic sensed
Reexamination Certificate
1998-11-17
2001-07-03
Fourson, George (Department: 2823)
Semiconductor device manufacturing: process
Including control responsive to sensed condition
Optical characteristic sensed
C438S757000, C216S085000
Reexamination Certificate
active
06255123
ABSTRACT:
TECHNICAL FIELD
The invention pertains to methods of monitoring and maintaining concentrations of selected species in solutions during semiconductor processing, with the term “solution” referring to any fluid, including, for example, a liquid or a gas. In a particular aspect, the invention pertains to methods of monitoring and maintaining a predetermined water concentration in phosphoric acid solutions during etching of silicon nitride.
BACKGROUND OF THE INVENTION
Modern semiconductor processing frequently utilizes etchant removal of selected materials. For instance, a common insulative material in semiconductor circuitry is silicon nitride (Si
3
N
4
), which is typically patterned into desired configurations by etching processes. A typical etching process for removing silicon nitride comprises exposing the silicon nitride to a liquid phosphoric acid solution. A phosphoric acid solution etch of silicon nitride has a particular advantage in that it is generally selective for silicon nitride relative to silicon dioxide. Accordingly, if both silicon nitride and silicon dioxide are exposed to the conditions of a phosphoric acid solution etch, the silicon nitride will be removed at a faster rate than will the silicon dioxide.
The reaction chemistry of a phosphoric acid solution etch of silicon nitride is as follows:
Si
3
N
4
+4H
3
PO
4
+10H
2
O→Si
3
O
2
(OH)
8
+4NH
4
H
2
PO
4
As can be seen from the above equation, water is a reactant that is consumed during etching of the silicon nitride with the phosphoric acid solution. The reaction conditions of the etch typically comprise a temperature of from about 150° C. to about 170° C., and typically comprise a pressure of about atmospheric pressure.
Under the typical etching conditions, a water concentration within the phosphoric acid solution can be reduced by water evaporation, as well as by water being consumed in the reaction process. Problems occur as a water concentration within the phosphoric acid solution decreases. For instance, a reaction rate can slow (or even stop) if water is not replenished. In an effort to overcome this problem, water (typically in the form of deionized water) is generally replaced at selected times, or selected temperature drifts, during a reaction process. Present methods for replacing deionized water have several associated problems, including: 1) it is difficult to accurately control etch rates; 2) the deionized water concentration in a reaction solution is not known, and accordingly a reaction rate can vary significantly from a beginning of a reaction to an end of the reaction; and 3) if an error occurs in a water replenishment mechanism and water is inadvertently not replenished at various points in a reaction process, the problem will not be detected until product wafers are removed and found to have an incomplete nitride strip.
For the above-discussed reasons, it would be desirable to develop alternative methods for maintaining a water concentration in a phosphoric acid solution during a nitride etch. More generally, it would be desirable to develop alternative methods for maintaining concentrations of selected species in solutions during semiconductor fabrication processes.
SUMMARY OF THE INVENTION
In one aspect, the invention encompasses a semiconductor processing method. A layer of material is provided over a substrate and reacted in a solution to remove at least some of the material. The reacting comprises a reaction chemistry that alters a concentration of a species in the solution. An absorbance of the solution is monitored for at least one wavelength of light that the species absorbs, and a concentration of the species in the solution is monitored by the monitoring of the absorbance. The concentration of the species in the solution is adjusted utilizing information obtained from the absorbance monitoring.
In another aspect, the invention encompasses a semiconductor processing method wherein a layer of material is provided over a substrate and reacted with a solution to remove at least some of the material. The reaction consumes a component of the solution, and an absorbance of the solution is monitored for at least one wavelength of light that the consumed component absorbs. The concentration of the consumed component in the solution is monitored during the reaction by monitoring the absorbance. The consumed component is added to the solution to maintain a substantially constant rate of reaction during the removal of the first material.
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patent: 5437761 (1995-08-01), Koide
patent: 5595916 (1997-01-01), Fujimura et al.
patent: 5674410 (1997-10-01), Nakajima et al.
patent: 5922606 (1999-07-01), Jenkins et al.
patent: 5963336 (1999-10-01), McAndrew et al.
patent: 6077452 (2000-06-01), Litvak
Fourson George
Garcia Joannie Adelle
Wells St. John Roberts Gregory & Matkin
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