JP2808799B2 - Etching method of silicon nitride film - Google Patents

Description

The present invention relates to a method for etching a silicon nitride film,
More specifically, the present invention relates to a wet etching method using a phosphoric acid solution.

[Summary of the Invention] The present invention relates to a method for etching a silicon nitride film with a phosphoric acid-based solution, comprising: adding a polyoxyethylene alkyl ether-based nonionic surfactant to the phosphoric acid-based solution; 160
By performing etching at a liquid temperature of ° C., the surface tension of the surface of the silicon compound film is reduced, thereby reducing etching blur and improving the etching rate.

[Prior Art] Conventionally, when wet etching a silicon compound film such as a silicon nitride (Si ₃ N ₄ ) film, phosphoric acid (H ₃ PO ₄ ) is used as an etchant. As another etching solution, an etching method using a solution obtained by adding acetic acid, nitric acid, or the like to phosphoric acid is known. Such an etchant is usually used at a high temperature of about 150 to 160 ° C.

Although it is a cleaning agent for semiconductor surfaces,
Japanese Patent Application Laid-Open No. 274149 discloses a composition containing a quaternary ammonium hydroxide, a nonionic surfactant and hydrogen peroxide.

[Problems to be Solved by the Invention] However, in the wet etching using the etching solution as described above, since the surface tension of the phosphoric acid-based solution is high, etching of, for example, a silicon nitride film formed on the wafer surface is difficult. If performed, there is a problem that the permeability of the phosphoric acid-based solution to the surface of the silicon nitride film is low, the etch rate is reduced, and the etching becomes non-uniform.

Further, for example, in the wet etching of a wafer having a fine trench structure, a phosphoric acid-based solution having a high surface tension as described above makes it more difficult for the solution to penetrate into the inside of the trench. There are many problems that occur.

Further, a phosphoric acid-based solution as an etching solution is, for example, 2
Because it may be used for a long period of about a month,
It is required to add an activator that can withstand high temperature, high concentration and long-term use and does not change with time. However, no activator has been provided so far to withstand such severe conditions. There is a point.

The present invention has been made in view of such conventional problems, and aims to obtain a method for etching a silicon nitride film using a phosphoric acid-based solution having low surface tension and excellent permeability. Things.

Means for Solving the Problems Accordingly, the present invention provides a method for etching a silicon nitride film with a phosphoric acid solution, wherein a polyoxyethylene alkyl ether nonionic surfactant is added to the phosphoric acid solution. Then, etching at a liquid temperature of 150 ° C. to 160 ° C. is a solution.

[Action] A polyoxyethylene alkyl ether-based nonionic surfactant lowers the surface tension of a phosphoric acid-based solution. Further, the nonionic surfactant in the phosphoric acid-based solution is not degraded with time due to decomposition by an acid, and
It is stable against heat of about 160 ° C. Furthermore, since the polyoxyethylene alkyl ether-based nonionic surfactant is hydrophilic, it can be easily washed away by pure water rinsing after wet etching, for example.

EXAMPLES Hereinafter, the details of the method for etching a silicon nitride film according to the present invention will be described based on examples.

In this embodiment, wet etching of a silicon nitride film (Si ₃ N ₄ ) is performed using an etching solution obtained by adding polyoxyethylene alkyl ether to a phosphoric acid solution.
In this embodiment, the etching solution is set at 150 to 160 ° C.

Polyoxyethylene alkyl ether has the general formula _{R-OCH 2 CH 2 O n} HR: saturated and unsaturated alkyl groups of C _{12 to 18} for example, In particular, when R is And a polyoxyethylene nonylphenol ether type surfactant.

In this embodiment, the surface tension of the phosphoric acid solution is reduced by adding polyoxyethylene alkyl ether to the phosphoric acid solution.

Also, when the etchant was set at 150 to 160 ° C., the polyoxyethylene alkyl ether was stable and did not decompose due to acid.

Furthermore, since polyoxyethylene alkyl ether has hydrophilicity, it can be easily washed away by pure water rinsing after wet etching.

Although the embodiments have been described above, the present invention can be modified in various manners. For example, in the above-described embodiment, a phosphoric acid solution to which polyoxyethylene alkyl ether is added is used. A similar effect can be obtained by using a phosphoric acid solution to which acetic acid, nitric acid, or the like is added, or a solution added to another phosphoric acid-based solution.

In particular, when an etchant obtained by adding acetic acid or nitric acid to phosphoric acid is used, wet etching of an aluminum film or an aluminum-based alloy film can be performed.

Further, in the above embodiment, the silicon nitride film is applied, but an SiO ₂ film or the like can be applied.

[Effects of the Invention] As is clear from the above description, according to the method for etching a silicon compound film according to the present invention, a nonionic surfactant (polyoxyethylene alkyl ether) is added, and 150 ° C to 160 ° C. By performing etching at the liquid temperature, the surface tension of the phosphoric acid-based solution is reduced, the permeability to the silicon nitride film is increased, and the etching rate and the uniformity of etching are improved. , A stable etching can be performed on the silicon nitride film.

Even when used at a high temperature and a high concentration for a long period of time, it is not possible to cause a change over time due to the decomposition action of an acid, and there is no fear that impurities (especially metals) may be mixed. Is high, it can be easily washed away by pure water rinsing after wet etching, and the effect of improving workability and handleability of the etchant is obtained.

Claims (1)

(57) [Claims] 1. A method for etching a silicon nitride film with a phosphoric acid-based solution, comprising: adding a polyoxyethylene alkyl ether-based nonionic surfactant to said phosphoric acid-based solution;
Etching method for a silicon nitride film, characterized in that etching is performed at a liquid temperature.