JP2600839B2 - Etching method of silicon nitride film - Google Patents

Description

The present invention relates to a method for etching a silicon nitride film, and more particularly to an etching method for selectively removing a silicon nitride film deposited on a thin silicon oxide film. The purpose of the present invention is to provide a method for reactive ion etching of a silicon nitride film having a large ratio of silicon nitride. When selectively etching a silicon nitride film deposited on a silicon oxide film, chlorine trifluoride is used as a main etching gas. The reactive ion etching is performed in the etching gas having a pressure of about 1.0 Torr.

[Industrial applications]

The present invention relates to a method for etching a silicon nitride film, and more particularly to an etching method for selectively removing a silicon nitride film deposited on a thin silicon oxide film.

In recent years, with higher integration and higher speed of semiconductor devices, more accurate etching is required in a dry etching process, and it is particularly important to etch a film to be etched without etching a base film. ing.

And in silicon nitride (Si ₃ N ₄ ) films,
As represented by the selective oxidation method called OS, a silicon dioxide (SiO ₂ ) underlayer is provided between the Si ₃ N ₄ film and the silicon (Si) substrate to relieve the stress. Tend to be formed thinner with Si ₃ N ₄
Etching selectivity between SiO ₂ and SiO ₂ is large, that is, Si ₃ N ₄ and SiO 2
There is a demand for an etching means having a large ratio of the etching rate to ₂ .

[Conventional technology]

When forming an oxide film for element isolation by selective oxidation in the manufacturing process of semiconductor ICs, etc., the oxidation resistance of about 1000 mm thick formed on a silicon (Si) substrate through a thin underlying SiO ₂ film after patterning with the mask shape by dry etching means an Si ₃ N ₄ film having, the Si ₃ N
_{Using the four} patterns as masks, the selective oxidation of the Si substrate surface is performed.

In the above process, the dry etching means of the Si ₃ N ₄ film has conventionally been a mixed gas of carbon tetrafluoride and oxygen [(CF ₄ / O ₂ )
Gas] or a mixed gas of sulfur hexafluoride and oxygen [(SF ₆ /
O ₂ ) gas] is often used.

[Problems to be solved by the invention]

However, in the above conventional method, the etching rate ratio of Si ₃ N ₄ and SiO ₂ is about 3 when (CF ₄ / O ₂ ) gas is used, and about 3 when (SF ₆ / O ₂ ) gas is used. In each case, which was as small as about 5, when over-etching was performed by, for example, about 50% to cover the distribution of etching in the substrate surface, the thickness of the underlying SiO ₂ film was reduced to about 100 °. When formed, the underlying SiO ₂ film is partially removed to the bottom, and the Si substrate surface is directly exposed to fluorine ions and the like, and is damaged by the impact, resulting in leakage between devices and reduction in breakdown voltage between devices. And the like, which degrades the performance of the semiconductor IC.

Therefore, an object of the present invention is to provide a reactive ion etching method for a Si ₃ N ₄ film having a large etching rate ratio with respect to an SiO ₂ film.

[Means for solving the problem]

The object is to selectively etch a silicon nitride film deposited on a silicon oxide film by using chlorine trifluoride as a main etching gas and reacting reactive ions in the etching gas having a pressure of 0.3 to 1.0 Torr. The problem is solved by a silicon nitride film and an etching method according to the present invention for performing etching.

(Operation)

FIG. 1 is an etching characteristic diagram of a Si ₃ N ₄ film and a SiO ₂ film showing the principle of the present invention. In the figure, the horizontal axis is pressure, the left vertical axis is the etching rate, the right vertical axis is the ratio of the etching rate of the Si ₃ N ₄ film to the SiO ₂ film, and A is the curve of the etching rate (ER) of the Si ₃ N ₄ film. , B shows the curve of the etching rate (ER) of the SiO ₂ film, and C shows the curve of the etching rate ratio (Si ₃ N ₄ / SiO ₂ ) between the Si ₃ N ₄ film and the SiO ₂ film.
The etching gas was chlorine trifluoride (ClF ₃ ) and the gas flow rate was 10
It is a value measured at 0 SCCM and an applied power density of 0.4 W / cm ² .

According to this figure, it can be seen that the etching rate of the Si ₃ N ₄ film is relatively high, and the etching rate gradually decreases with an increase in pressure, and decreases to about 600 ° / min near 1.0 Torr, which is a practical limit. Also, it can be seen that the etching rate of the SiO ₂ film is smaller than that of the Si ₃ N ₄ film, and the etching rate is significantly reduced near the pressure of 0.3 Torr, and is not etched at 0.7 Torr or more.

Therefore, in the present invention, RIE treatment is performed using ClF ₃ as an etching gas, and the pressure of the etching gas at this time is set to S
Practical etching rate of i ₃ N ₄ film is obtained, and SiO ₂
The ratio of the etching rate to the film is limited to a pressure of 0.3 to 1.0 Torr at which a practically sufficient 10 or more can be obtained.

〔Example〕

 Hereinafter, the present invention will be described specifically with reference to the illustrated embodiments.

2 (a) to 2 (c) are process sectional views of an embodiment of the present invention, FIG. 3 is a schematic sectional view of a reactive ion etching (RIE) apparatus, and FIGS. 4 (a) to 4 (b) are FIG. 6 is a process sectional view of another embodiment of the present invention.

 The same objects are denoted by the same reference symbols throughout the drawings.

Referring to FIG. 2 (a), when a field SiO ₂ film for element isolation in a highly integrated semiconductor IC is formed by a selective oxidation method, for example, 100 ° C. is thermally oxidized on a Si substrate 1 having a desired conductivity type. Forming a base SiO ₂ film 2 having a thickness of about
Next, a Si ₃ N ₄ film 3 having a thickness of about 1000 ° is formed on the underlying SiO ₂ film 2 by a vapor phase growth (CVD) method.

Next, as shown in FIG. 2 (b), a thickness of 1 μm having a shape corresponding to the element region is formed on the Si ₃ N ₄ film 3 by ordinary photolithography.
After forming a resist pattern 4 of about
Inserted into the apparatus, using ClF ₃ as an etching gas, for example
Power density 0.4 W / cm in the ClF ₃ gas of 0.3 Torr
^{In step 2} , using the resist pattern 4 as a mask, the Si ₃ N ₄ film 3
Is selectively etched. At this time, since the etching conditions and the distribution of the Si ₃ N ₄ film thickness exist in the substrate surface, over-etching is performed by about 50% with respect to the standard etching time in order to complete the etching of the entire substrate surface.
As shown in FIG. 1, the etching rates of the Si ₃ N ₄ film and the SiO ₂ film at the above gas pressure of ClF ₃ gas were about
Since the etching rate ratio is about 17 at 1700 ° / min and about 100 ° / min, the thickness Δt ₁ of the base SiO ₂ film 2 reduced by over-etching of about 0.3 min corresponding to the over-etching of about 50% is: At most 30Å
When the Si ₃ N ₄ film 3 is patterned, there is no region where the underlying SiO ₂ film 2 is completely removed. Therefore, at the time of the etching, the surface of the Si substrate 1 is not directly exposed to the ions and is not damaged by the impact.

FIG. 3 is a diagram schematically showing the RIE apparatus used for the above etching process. In the figure, 51 is a vacuum vessel, 52 is a vacuum exhaust port, 53 is a target electrode, 54 is an insulator, 55 is a counter electrode,
56 is a gas inlet, 57 is a gas outlet, 58 is a 13.56 MHz high frequency power supply, 59 is a ground point, and 60 is the substrate to be etched shown in FIG. 2 (b). Then, for example, from the gas inlet 56
While supplying 100 SCCM ClF ₃ gas and introducing the gas into the vacuum vessel 51 from a plurality of gas ejection holes 57 formed on the surface of the counter electrode 55, the vacuum vessel
The pressure in the inside 51 is maintained at 0.3 Torr, and in this state, high frequency power is applied from the high frequency power source 58 to the target electrode 53 to which the substrate 60 to be etched is fixed so that the power density becomes about 0.4 W / cm ^2. The Si ₃ N ₄ film is etched.

Next, after the resist pattern 4 is removed, selective oxidation is performed under normal conditions using the Si ₃ N ₄ film 3 which has been patterned into a shape corresponding to the element region in conformity with the resist pattern 4 as shown in FIG. The Si substrate 1 exposed on the side of the Si ₃ N ₄ film 3
A field SiO ₂ film 5 having a thickness of, for example, about 6000 ° for element isolation is formed on the surface.

The selective etching of the Si ₃ N ₄ film 3 on the underlying SiO ₂ film 2 may be performed by another method shown in the following embodiment.

Figure 4: (a) see i.e. resist pattern 4 as a mask, first Si ₃ N ₄
A Si ₃ N ₄ film 3 under a ClF ₃ pressure of about 0.1 Torr at which a large etching rate of about 2000 ° / min can be obtained for the film 3
Is etched until the remaining thickness Δt _{2 of the} region exposed from the resist pattern 4 becomes about 100 °.

Subsequently, the pressure of ClF ₃ is controlled to about 0.7 Torr at which the SiO ₂ film 2 is not etched at all, and the Si ₃ N ₄ film
Is completely removed by etching.

According to this method, the anisotropic shape pattern of the Si ₃ N ₄ film 3 can be formed without etching the underlying SiO ₂ film 2 at all.

〔The invention's effect〕

As described above, according to the present invention, when a silicon nitride film deposited on a silicon oxide film is selectively etched by reactive ion etching, the silicon nitride film without etching the underlying silicon oxide film is hardly etched. Can be etched into a good anisotropic shape.

Therefore, in the manufacture of semiconductor ICs and the like, even if the underlying silicon oxide film provided below the silicon nitride film is formed thinner, the substrate is not damaged by ion bombardment during the patterning of the silicon nitride film. Greatly contributes to high integration and high speed of the semiconductor IC and the like.

[Brief description of the drawings]

FIG. 1 is a view showing the principle of the present invention, FIGS. 2 (a) to 2 (c) are process sectional views of an embodiment of the present invention, and FIG. 3 is a schematic sectional view of a reactive ion etching (RIE) apparatus. 4 (a) and 4 (b) are process sectional views of another embodiment of the present invention. In the figure, 1 is a Si substrate, 2 is a base SiO ₂ film, 3 is a Si ₃ N ₄ film, 4 is a resist pattern, 5 is a field oxide film, Δt ₁ is a reduced thickness of the base SiO ₂ film, and Δt ₂ is Si shows the residual thickness of ₃ N ₄ film.

Claims (1)

(57) [Claims] When selectively etching a silicon nitride film deposited on a silicon oxide film, chlorine trifluoride is used as a main etching gas and reactive gas is used in the etching gas having a pressure of 0.3 to 1.0 Torr. A method for etching a silicon nitride film, comprising performing ion etching.