JPH02128422A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To specify the etching ratio of Si3N4 at around 10 for selectively etch away Si3N4 by a method wherein the flow rate of HBr is selected not to exceed the flow rate of SF6 and then RIE process is performed using the mixed gas of SF6 and HBr. CONSTITUTION:The flow rate of HBr is selected not to exceed 50% pf the flow rate of SF6 and then the mixed gas of SF6 and HBr is led into a reaction chamber to perform RIE process at specified vacuum degree and voltage density. In such a constitution, the selection ratio (b) of Si3N4/SiO2 can be specified at 10. Consequently, when the film thickness of SiO2 is around 80Angstrom in LOCOS process, even slightly over-etching process shall not damage an Si substrate thereby improving the etching precision and etching efficiency.

Description

[Detailed Description of the Invention] [Summary] Among dry etching methods, this method is suitable for etching a silicon nitride film on a silicon oxide film, and has a high etching selectivity of Sl 3N a /Si O 2 and is suitable for etching a silicon nitride film on a silicon oxide film. With the aim of increasing the etching rate, reactive ion etching was performed using a mixed gas of sulfur hexafluoride and hydrogen bromide, with the flow rate of hydrogen bromide being 50% or less of the flow rate of sulfur hexafluoride. , which is characterized by etching a silicon nitride film.

[Industrial application field]

The present invention relates to a dry etching method among semiconductor device manufacturing methods, and particularly to an etching method that involves etching a silicon nitride film on a silicon oxide film.

In semiconductor device manufacturing methods, dry etching methods, which can form patterns with high precision, have been widely used in place of conventional wet etching methods. However, in dry etching, it is important to have a high etching selectivity, and the present invention relates to a dry etching method that has a high etching selectivity of silicon nitride (Si3Na) to silicon oxide (SiOz).

[Conventional technology]

For example, in the process of forming a field insulating film using the LOCO3 method, a Si3N4 film is used as an oxidation prevention film. To explain the outline of the process, as shown in FIG.
, a film 3 is deposited, and the Si3N4 film 3 is patterned to remove the 5iaN4 film on the field insulation film forming region. Note that the SiO□ film 2 interposed here is 5i3
The Na film serves as a buffer film to prevent stress from being applied to the silicon substrate 1. Next, as shown in FIG. 3 (bl), a field insulating film 4 made of a Si film is formed by oxidation treatment at a high temperature of 1000° C. or higher.Then, the 543N film 3 is etched and removed. A semiconductor element is formed in the portion.

However, in this method of forming a field insulating film using the LOCO3 method, patterning of the Si3N4 film was conventionally performed by wet etching using hot phosphoric acid, but with wet etching, side etching progresses and it is not possible to form the Si3N4 film accurately. Since it is difficult to do this, recently a dry etching method has been used which allows for even higher precision patterning, and this is because the semiconductor element formation region can be formed finely and accurately. In addition, for the formation of the field insulating film, a bird's beak (see Fig. 3
The problem is that the bird's beak (indicated by the arrow in b)) is important for miniaturization and high precision to make the bird's beak part as small as possible.
(For example, 200 Å or less) is also a necessary condition.

However, if the SiO□ film 2 is formed thinly, as shown in Fig. 3(a).
When patterning the 5i3Na film 3 explained in
If the etching selection ratio of the Si3N4 film 3 to the i02 film 2 is not made sufficiently large, the 5iOz film 2 will be etched, and there is a fear that further etching damage will be caused to the underlying silicon substrate 1.

[Problem to be solved by the invention]

By the way, reactive ion etching (RIE) with directional etching is used for dry etching of such Si3N4 films.
Conventionally, carbon tetrafluoride (CF4), carbon trifluoride (NF3), or a mixed gas containing oxygen (0□) is used as the reaction gas. ing. However, these gases are 5iO
5i3Na (Si: + N4/5fOz
) has an etching selectivity of about 3, and there is a risk that a thin SiO□ film with a thickness of 200 Å or less will be etched away.

Also, methane fluoride (CH.F) or methane difluoride (C.
There are reports that etching with a high selectivity can be obtained when H2F2) is used as the reaction gas, but since it contains carbon (C), there is a problem that carbon tends to remain on the etched surface, and the desired The disadvantage is that the gas pressure tolerance range is narrow and stability is poor.

The present invention solves these problems and makes Si3N a
/ SiO□ has a large etching selectivity ratio, and
Si3N. This invention provides a dry etching method aimed at increasing the etching rate of a film.

[Means to solve the problem]

The challenge is to reduce the flow rate of hydrogen bromide (HBr) to sulfur hexafluoride (
The flow rate of sulfur hexafluoride (SF6) was reduced to 50% or less of the flow rate of sulfur hexafluoride (SF6).
) and hydrogen bromide (Illr) to perform reactive ion etching to etch the silicon nitride film.

[For production]

Flow rate H Br/ S F b + H Br < 50
When reactive ion etching is performed using a reactive gas of
Problems such as those in the OCO3 method can be solved.

〔Example〕 Hereinafter, embodiments will be described in detail with reference to the drawings.

FIG. 1 shows a schematic diagram of the main parts of a dry etching apparatus to which the present invention is applied, in which 11 is a reaction chamber made of quartz;
2 is a wafer of material to be etched, 13 is a frequency 13.
56MH2 high frequency power supply, 14 is stage.

15 is a gas injection nozzle, 16 is a gas inlet, and 17 is an exhaust port.

Next, Fig. 2 shows an etching characteristic diagram, where the horizontal axis is HBr/S F b + HBr flow rate ratio (%), the left vertical axis is the etching gray (nm/min), and the right vertical axis is 5i3
Etching selectivity ratio of N-/5i()z, - in the figure is Si, N4 film etching rate curve, -0- is Si
Etching rate curve of O□ film, -△- is Si3N4
This is a curve of etching selectivity of /Si○2.

This characteristic diagram is S F b 1 HBr flow rate 25 SCCM
, Pressure 0゜2Toor, Power density 0.4W/c
d, but from this diagram, HBr
/ SFb flow rate 20 SCCM, HBr flow rate 5 SCC so that the SF b + HBr flow rate ratio is 20%
If the pressure and power density are set to the above conditions, Si
The etching selectivity ratio of 3N a/SiO2 is 10, and the etching rate of the 5isN4 film is 1100n/
minutes, and from the same figure, the flow rate HBr/SF6 +HB
It is clear that if r<50%, both the etching selectivity of Si3N4/5iOz and the etching rate of the S+3Na film can be increased.

In this way, HBr alone does not etch, but S
By adding HBr to F6, it is possible to perform reactive ion etching of a Si3N4 film with a high selectivity to 5i02 and a high etching rate.If this etching method is applied, the etching rate can be 1000 people/min. , the etching selection ratio of Sia Na /5in2 is 8
Considering the above, in the above-mentioned LOCO3 method, if the thickness of the Sin film is about 80 mm, even if some overetching is performed, the problem of damaging the silicon substrate will not occur.

Thus, if this reactive ion etching method is used, the etching efficiency can be improved and the etching accuracy can also be improved.

Although the above example has been explained using the LOCO3 method, it goes without saying that the present invention can be applied to other forming steps using 5i3Nn films in semiconductor device manufacturing methods.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, etching accuracy and etching efficiency in a semiconductor device manufacturing method can be improved, which is useful for improving the performance and quality of semiconductor devices such as ICs, and also contributing to improved throughput. It is something to do.

[Brief Description of the Drawings] Figure 1 is a cross-sectional view of the main part of a dry etching apparatus to which the present invention is applied, Figure 2 is an etching characteristic diagram, and Figures 3 (a) and (b) explain the problems of the conventional method. This is a diagram. In the figure, 1 is a silicon substrate, 2 is a 5iOz film, and 3 is a Si3
11 is a reaction chamber, 13 is a high frequency power source, 15 is a gas injection nozzle, and 17 is an exhaust port. 4 is a field insulating film, 12 is a wafer 14 is a stage, 16 is a gas inlet,

Claims (1)

[Claims] Etching the silicon nitride film by performing reactive ion etching with a mixed gas of sulfur hexafluoride and hydrogen bromide in which the flow rate of hydrogen bromide is 50% or less of the flow rate of sulfur hexafluoride. A method for manufacturing a semiconductor device, characterized by: