JP2920999B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] A dry etching method for a silicon nitride film has a high etching selectivity to a SiO ₂ film, and
Nitrogen trifluoride (NF ₃ ) gas to which _{20 to 5} % by volume of hydrogen sulfide (H ₂ S) gas is added as a reaction gas for the purpose of etching a Si ₃ N ₄ film at a high etching rate, 0.15 ~ 0.3
The method is characterized by including a dry etching step in which the silicon nitride film is plasma-etched at Torr.

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for dry-etching a silicon nitride film.

When a semiconductor device such as an IC is manufactured, various types of insulating films are used. For example, a silicon oxide film, a phosphor silicate glass film, and a silicon nitride film are typical insulating films. Among them, the silicon nitride film is used not only as an insulating film but also as a shielding mask, and is an essential material for semiconductor devices. The present invention relates to such a dry etching method for a silicon nitride film.

[Prior Art] Conventionally, a prominent method using a silicon nitride film (Si ₃ N ₄ ) film as a shielding mask is the LOCOS method, and FIG.
FIG. 4 is a cross-sectional view in the order of steps of the OS method. First, FIG. 3 (a)
As shown in the figure, silicon oxide (Si)
O ₂ ) silicon nitride (Si ₃
N ₄ ) A film 3 (with a thickness of about 2000 °) is deposited, and the Si ₃ N ₄ film / SiO ₂ film is selectively etched using the resist film 4 as a mask. This Si ₃ N ₄ film / SiO ₂ film serves as a shielding mask covering the element formation region. Next, after removing the resist film 4 mask, as shown in FIG. 3B, the silicon substrate surface excluding the shielding mask is thermally oxidized in a high-temperature, high-humidity oxidizing atmosphere to form an insulating film made of a thick SiO ₂ film. A film 5 (thickness of about 6000Å; element isolation region) is formed. Here, the reason why the SiO ₂ film 2 is interposed is that when the hard Si ₃ N ₄ film 3 comes into direct contact with the silicon substrate, a stress is applied to the silicon substrate (part of the element formation region). This is to make it work.

Next, FIG. 4 shows a main part diagram of the dry etching apparatus, in which symbol 11 is a vacuum chamber, 12 is an upper electrode, 13
Is a lower electrode, 14 is a silicon substrate, 15 is a gas introduction port, 16 is an exhaust port, and 17 is a high frequency power supply (frequency 5 KHZ to 13.56 MHZ). As shown in the drawing, a parallel plate type in which a lower electrode 13 to which a high frequency is applied and an upper electrode 12 are arranged to face each other, and an etching gas is vertically applied from a lower surface of the upper electrode 12 to a silicon substrate 14 mounted on the lower electrode 13. The etching is performed by injecting the gas into a plasma and colliding the plasma gas with the silicon substrate for etching. When a gas accompanied by a chemical reaction is used as the etching gas, it is called reactive ion etching.

For example, when etching a Si ₃ N ₄ film on a silicon substrate surface, a reactive gas such as carbon tetrafluoride (CF ₄ ; trade name of Freon) + oxygen (O ₂ ) is used to perform reactive ion etching (Re).
active Ion Etching). Note that there are two types of such dry etching apparatuses: an anode-coupled type in which a wafer is mounted on the ground electrode side and a cathode-coupled type in which a wafer is mounted on the high-frequency power supply side as shown in FIG. There is no difference in its performance.

In recent years, semiconductor devices have been highly integrated and miniaturized. For example, the shielding mask of the Si ₃ N ₄ film / SiO ₂ film in the LOCOS method described above has a SiO ₂ film thickness of 200 Å in order to reduce bird's beak. It is important to form fine dimensions with high precision, and there is a demand for an etching method with a high etching rate and a high etching selectivity with respect to other material films. Especially Si ₃ N
_{The four} films are required to have a high etching selectivity with respect to the closely related SiO ₂ film.

[Problems to be Solved by the Invention] When reactive ion etching is performed on a Si ₃ N ₄ film using a dry etching apparatus as described above, usually, reactive ions using CF ₄ + O ₂ as a reactive gas are used. Although etching is performed, a problem is that the etching selectivity to the SiO ₂ film is as low as 3 or less. Further, when sulfur hexafluoride (SF ₆ ) is used as the reaction gas or when SF ₆ + O ₂ is used, the etching selectivity to the SiO ₂ film is increased to about 6, but the etching rate is 500
The disadvantage is that it is as low as Å / min.

In addition, when CH ₃ F (fluoromethane; trade name: Freon 32) or CH ₂ F ₂ (difluoromethane; trade name: Freon 41) is used as the reaction gas, the etching selectivity to the SiO ₂ film is reduced.
Although there is a report that the value is 15 or more, the other setting conditions are narrow, and the reaction gas is easily precipitated, so that the inside of the vacuum chamber is contaminated, and there is a problem that it is difficult to apply to the manufacturing process. Furthermore, it has been known that the use of microwave plasma etching can provide a high etching selectivity to the SiO ₂ film. However, since it is a downflow type etching apparatus (an apparatus in which a plasma generation chamber and an etching chamber are separated), Vertical anisotropic etching becomes impossible, resulting in isotropic etching, and controllability of fine dimensions is reduced.

Therefore, the present invention reduces such problems,
High etching selectivity to O ₂ film and Si ₃ N
_{The present} invention proposes a dry etching method for etching _four films at a high etching rate.

[Means for Solving the Problems] The problem is that nitrogen trifluoride (NF ₃ ) gas to which hydrogen sulfide (H ₂ S) gas of 20 to 5% by volume is added is used as a reaction gas, and the degree of pressure reduction is 0.15 to 0.3. This is achieved by a dry etching method in which the silicon nitride film is plasma-etched at Torr.

[Operation] That is, in the present invention, plasma etching is performed by using NF ₃ + H ₂ S ( _{20 to 5} % by volume) as a reaction gas and reducing the pressure to 0.15 to 0.3 Torr.

Then, the etching rate of the Si ₃ N ₄ film is 1000-1500〜
By setting the etching selectivity to the SiO ₂ film to about 8 to 15 per minute, etching suitable for miniaturization of semiconductor devices can be performed.

[Example] Hereinafter, an example will be described in detail with reference to the drawings. As the dry etching apparatus, a parallel plate type dry etching apparatus similar to that described with reference to FIG. 4 is used. FIGS. 1 and 2 show data diagrams created by changing the H ₂ S flow rate and changing the degree of pressure reduction.

FIG. 1 is a data diagram of an etching rate and a selectivity with respect to a change in H ₂ S flow rate. NF ₃ flow rate is 100 sccm, pressure is 0.2 Torr, high frequency output is 100 W, and H ₂ S flow rate is changed from 0 to 30 sccm. The horizontal axis is H ₂ S flow rate (scc
m), left vertical axis is etching rate (nm / min), right vertical axis is SiO ₂
It is the selectivity of the Si ₃ N ₄ film to the film. And curve I is Si ₃
The etching rate of the N ₄ film, curve II is the etching rate of the SiO ₂ film, and curve III is the selectivity of the Si ₃ N ₄ film to the SiO ₂ film.

From this, it can be seen that when the H ₂ S flow rate is 5 to 20 sccm, the etching rate of the Si ₃ N ₄ film is 1000 to 1700 ° / min, and the etching selectivity of the Si ₃ N ₄ film to the SiO ₂ film is 8 to 17.

FIG. 2 is a data diagram of the etching rate and the selectivity with respect to the change in the degree of reduced pressure. NF ₃ flow rate 100sccm, H ₂ S flow rate 15scc
m, high frequency output 100W constant, pressure from 0.1 Torr to 0.3
In the data diagram changed to Torr, the horizontal axis is pressure (Torr),
The left vertical axis shows the etching rate (nm / min), and the right vertical axis shows the selectivity of the Si ₃ N ₄ film to the SiO ₂ film. Curve I is the etching rate of the Si ₃ N ₄ film, curve II is the etching rate of the SiO ₂ film,
Curve III shows the selectivity of the Si ₃ N ₄ film to the SiO ₂ film.

Than this, the etching rate of the Si ₃ N ₄ film when the degree of vacuum in 0.15~0.3Torr is 1000～1700A / min, Si ₃ for SiO ₂ film
It can be seen that the etching selectivity of the N ₄ film is 6 to 17.

Therefore, in the dry etching method according to the present invention,
The Si ₃ N ₄ film can be etched at an etching rate of 1000 ° / min or more, and the high etching selectivity with respect to the SiO ₂ film can be set to about 10.

[Effects of the Invention] As is clear from the above description, when the method for etching a silicon nitride film according to the present invention is used, the etching rate is increased, and the silicon nitride film is most easily related to the SiO ₂ film.
The etching selectivity of the Si ₃ N ₄ film can be increased,
This significantly contributes to higher integration and higher performance of semiconductor devices.

[Brief description of the drawings]

FIG. 1 is a data diagram of an etching rate and a selection ratio with respect to a change in H ₂ S flow rate, FIG. 2 is a data diagram of an etching rate and a selection ratio with respect to a change in a degree of reduced pressure, and FIGS. FIG. 4 is a main part view of the dry etching apparatus. In the figure, 1 is a silicon substrate, 2 is a SiO ₂ film, 3 is a Si ₃ N ₄ film, 4 is a resist film, 5 is an insulating film (element isolation region), 11 is a vacuum chamber, 12 is an upper electrode, 13 is The lower electrode, 14 is a silicon substrate, 15 is a gas inlet, 16 is an exhaust port, and 17 is a high frequency power supply.

Claims (1)

(57) [Claims] A silicon nitride film is plasma-treated at a reduced pressure of 0.15 to 0.3 Torr using nitrogen trifluoride (NF ₃ ) gas to which hydrogen sulfide (H ₂ S) gas of 20 to 5% by volume is added as a reaction gas. A method for manufacturing a semiconductor device, comprising a dry etching step for etching.