JPH02137228A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To enable the etching rate of silicon nitride film by phosphoric acid to be kept constant by a method wherein the specific gravity of phosphoric acid is measured to compute the evaporated water content from the displacement of the specific gravity, and automatic feeding of pure water is effected so that the concentration of phosphoric acid may be controlled. CONSTITUTION:An etching vessel 1 containing phosphoric acid etchant 9 is connected to a specific gravity measuring vessel 3 having a specific gravity meter 2 to measure the specific gravity of the phosphoric acid contained in the etchant 9 during the etching process of the semiconductor wafers 10 coated with silicon nitride films. The specific gravity is detected by a specific gravity measuring sensor 4 in the encoder system and the detected value is transferred as electric signals to a specific gravity displacement computer 5 for computing the specific gravity displacement. Furthermore, the contents evaporated from the phosphoric acid are computed from the displacement by an evaporated water content computer 8 to transmit the latest evaporated water content to a pure water feed part 7. Through these procedures, the pure water equivalent to the evaporated water content can be constantly fed from a pure water feed pipe 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for etching a silicon nitride film using phosphoric acid.

[Conventional technology]

Conventionally, etching of silicon nitride film using phosphoric acid is
As shown in FIG. 2, a semiconductor wafer 10 on which a silicon nitride film has been formed is immersed in a phosphoric acid etching solution 9 of etching 1, and the etching solution 9 is heated to a high temperature of 100° C. or higher using a heater 12.

Since the water in the phosphoric acid etching solution evaporates due to high temperature and the etching rate of the silicon nitride film decreases, an appropriate amount of pure water corresponding to the amount of evaporated water is constantly supplied from the pure water supply pipe 8.

[Problem to be solved by the invention]

In the conventional silicon nitride film etching method described above, an appropriate amount of pure water was always supplied in order to stabilize the etching rate of phosphoric acid on the silicon nitride film. Since this is not carried out, there is a drawback that the etching rate decreases over time due to fluctuations in the composition ratio of phosphoric acid or deterioration of phosphoric acid.

[Means to solve the problem]

The present invention is a method for etching a silicon nitride film on a semiconductor wafer using a phosphoric acid etching solution, in which the specific gravity of the phosphoric acid etching solution is measured with a hydrometer, the amount of water evaporated is calculated from the change in the specific gravity, and the amount of water evaporated is calculated from the change in the specific gravity. The etching rate is stabilized by automatically supplying pure water corresponding to the amount of water and keeping the concentration of phosphoric acid constant.

〔Example〕

Next, the present invention will be explained with reference to the drawings. The first section is a longitudinal cross-sectional view of one embodiment of the present invention. A specific gravity measuring tank 3 equipped with a hydrometer 2 is connected to an etching tank 1 containing a phosphoric acid etching solution 9, and the specific gravity of phosphoric acid is measured while etching a semiconductor wafer 10 with a silicon nitride film attached thereto. The specific gravity is detected by the specific gravity measurement sensor 4 using one type of encoder, and is transmitted as an electric signal to the specific gravity displacement calculating section 5, which calculates the displacement of the specific gravity. Furthermore, based on the displacement, the amount of water evaporated from the phosphoric acid is calculated by the evaporated water amount calculating section 6.
Finally, by transmitting the evaporated water amount to the pure water supply section 7, pure water corresponding to the evaporated water amount is constantly supplied from the pure water supply pipe 8.

According to this embodiment, it became possible to suppress the decrease in etching rate over time to one-third compared to the conventional method.

〔Effect of the invention〕

As explained above, the present invention measures the specific gravity of phosphoric acid with a hydrometer, calculates the amount of water evaporated from the change in the specific gravity,
By automatically supplying pure water corresponding to the water content and controlling the concentration of phosphoric acid, it is possible to stably maintain the etching rate of the phosphoric acid on the silicon nitride film.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an etching apparatus used for wet etching a silicon nitride film according to the present invention, and FIG. 2 is a longitudinal sectional view of a conventional silicon nitride film wet etching apparatus. DESCRIPTION OF SYMBOLS 1... Etching tank, 2... Hydrometer, 3... Specific gravity measurement tank, 4... Specific gravity measurement sensor, 5... Specific gravity displacement calculation part, 6... Evaporated water content calculation part, 7 ...Pure water supply section, 8...Pure water supply pipe, 9...Etching liquid, 10
...Semiconductor wafer, 11...Carrier, 12...
·heater.

Claims (1)

[Claims] In a method of etching a silicon nitride film on a semiconductor wafer using a phosphoric acid etchant, the specific gravity of the phosphoric acid etchant is measured, the amount of water evaporated is calculated from the change in the specific gravity, and the amount of pure water equivalent to the amount of water is calculated. A method for manufacturing a semiconductor device, characterized by automatically supplying water and stably maintaining the etching rate of phosphoric acid on a silicon nitride film.