JPH0494121A - Dry etching method - Google Patents

Abstract

PURPOSE:To improve etching velocity of a copper or copper alloy thin film and to enable directional etching by using mixture gas containing at least silicon compound gas and nitrogen hydrite gas for etching gas. CONSTITUTION:Etching gas whose flow rate is controlled by a gas introduction system 8 such a gas containing silicon tetrachloride as silicon compound gas and ammonia as nitrogen hydrite gas is introduced, an inside of an etching chamber 7 is held at a specified gas pressure by evacuation through a evacuation port 11 and a high frequency power is applied to an etching electrode 1 by a high frequency power supply 10. Then, glow discharge is produced between the etching electrode and a couter electrode 3, and gas is formed into a plasma and activated, chroline radical is produced, accelerated ions are vertically applied to the side of the etching electrode 1 and a titanium nitride film 14, a copper thin film 15 and a titanium nitride film 16 are etched by synergetic effect of ion collision and chroline radical.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for etching copper or a copper alloy thin film. The present invention relates to a method for processing and etching copper alloy thin films at high speed while giving them directionality.

[Conventional technology]

Conventionally, when forming electrode wiring using a W4 thin film on a substrate, the W4 thin film processing method is a wet etching method in which the tRF1i film is partially covered with a mask material, immersed in an acidic or alkaline solution, and etched by a chemical reaction. Alternatively, a dry etching method using a reactive gas is used. In the wet etching method, fine etching is difficult because the etching has no directionality and etches uniformly.

On the other hand, the dry etching method is known as a directional etching method, for example, G, C, Schimart etching.
Paper by Z and P. M. 5chable ("Reactive Ion Etching of Copper Films", Journal of the Electrochemical Society, Vol. 130, p. 1777, 1983. ("Reac
tive Ion Etching of Coppe
r Fi1ms', Journal of Eiectr
chemical 5ociety, 130.177
7 (1983)) and a paper by the applicant (``Reactive Ion Etching of Copper Films in 5iC1a and N2 Mixtures''
”, Japanese Journal of Applied Physics, Volume 7, Volume 28, Page 1070, 1989. (”
Reactive Ion Etching of C
opper Films in 5iC1aandN
z Mixture, Jpn-J, Appl,
Phys, Lett, 28, 1070 (1989)
).

In the mixed gas system of carbon tetrachloride and argon shown in the paper by G. C. Schwartz et al., the copper film between the fine lines is etched at a high power density, resulting in poor contact with the underlying layer. There were problems such as a low selectivity and the inability to use an organic resist as a mask material.

On the other hand, the method using a mixed gas system of silicon tetrachloride and nitrogen proposed by the applicant solves these problems, basically enables microfabrication, allows the use of an organic resist as a mask, and allows selection of the mask. It was a method of etching copper thin films that also provided high properties.

[The invention aims to solve a! However, in the mixed gas system of silicon tetrachloride and nitrogen previously proposed by the applicant, the etching rate is slow at about 200 angstroms per minute, and high throughput cannot be expected in the manufacturing process of semiconductor devices. There was a problem.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for etching a copper or copper alloy thin film, which improves the etching rate and also enables directional etching.

[Means to solve the problem]

To achieve this objective, the present invention uses a chlorine-based mixed gas containing a silicon compound gas and a nitrogen hydride gas to increase the etching rate and maintain directional etching.

In addition, by heating the electrode on which the substrate to be etched is placed, the substrate is heated to a temperature at which the reaction products can volatilize.
Typically heated to 280°C.

[Effect]

In the etching method of the present invention, copper reacts with chlorine radicals generated by decomposition of a chlorine gas, which is an etching gas, by electric discharge to form copper chloride, but the substrate is heated to a temperature at which the copper chloride can volatilize. As a result, copper chloride volatilizes and etching progresses. In addition, a silicon nitride film is formed on the substrate surface by the reaction between silicon radicals produced by the decomposition of silicon compound gas and nitrogen radicals produced by the decomposition of nitrogen hydride gas. Etching progresses as the silicon nitride film on the surface is removed. However, since ions do not hit the sidewalls of the pattern covered with the mask material, directional etching of the copper or copper alloy thin film becomes possible because it is covered with the silicon nitride film.

It is clear from the following experiment conducted by the inventor of the present invention that the etching rate is improved by increasing the number of chlorine radicals that react with copper.

The experiment was carried out by etching a copper thin film formed on a thermally oxidized silicon film using a reactive ion etching device with a substrate heating mechanism. Using a mixed gas of chlorine, silicon tetrachloride, and nitrogen as the etching gas, silicon tetrachloride,
The nitrogen flow rate was set to 20. 80SCCM, pressure 2P
a. While setting the RF power to 100 W, the amount of chlorine added was varied to examine the relationship between the etching rate and the amount added. As shown in FIG. 1, the experimental results show that as the amount of chlorine added increases, the etching rate increases dramatically. However, in this chlorine-added gas system, when pattern sidewalls of a copper thin film are etched using an organic resist/titanium nitride film as a mask, directional etching becomes difficult because chlorination and etching of the copper thin film progresses to the inside of the pattern.

Therefore, to protect the pattern sidewalls from chlorine radicals,
For stronger coverage, it is necessary to cover with a silicon nitride film. A silicon nitride film formed by decomposing silicon tetrachloride and nitrogen does not have a sufficient sidewall protection effect, so nitrogen hydride gas is added to promote the formation of the silicon nitride film.

FIG. 2 shows the relationship between the etching rate and the amount added when ammonia, which is one of the nitrogen hydride gases, is added to the above-mentioned mixed gas consisting of silicon tetrachloride, nitrogen and chlorine. It can be seen that as the amount of ammonia added increases, the etching rate decreases, and the formation of a silicon nitride film is promoted. By promoting the formation of the silicon nitride film, the processed sidewalls are sufficiently protected from chlorine radicals and directional etching of the copper thin film is promoted.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 3 is a schematic diagram of an example of an etching apparatus according to the present invention. In the figure, l is the etching electrode, 2 is the substrate to be etched, and 3 is the opposite! 4 is an electrostatic charger/substrate stand for fixing the substrate 2 to be etched, 5 is a heater for heating the etching electrode, 6 is a heater for heating the counter electrode, 7 is an etching chamber, 8 is a gas introduction system, 9 is a matching box, 10 is a high frequency power source, and 11 is a vacuum exhaust port for reducing the pressure inside the etching chamber 7 to a predetermined etching gas pressure.

FIG. 4 is a sectional view of the substrate to be etched used for etching. In the figure, 12 is a silicon wafer;
Semiconductor elements are normally formed on this silicon wafer 12, but are omitted in the figure. Reference numeral 13 denotes a silicon dioxide film for insulating the electrode from the silicon substrate, and here it was formed by the CVD method. 14 and 16 are titanium nitride films, which were formed here by reactive sputtering. 1
5 is a copper thin film made by sputtering. It was formed to a thickness of m. No. 17 is an organic resist, which was subjected to a curing treatment using deep ultraviolet light and a high-temperature hake to improve its heat resistance.

Next, a method for etching the thin copper film shown in FIG. 4 using the apparatus shown in FIG. 3 will be described.

A substrate 2 to be etched is fixed onto an etching electrode 1 via an electrostatic chuck substrate stand 4. The etching electrode 1 and the counter electrode 3 are heated in advance by heaters 5 and 6, respectively, and the substrate 2 to be etched is heated to a predetermined temperature, typically 280° C., by heat conduction from the electrodes. Thereafter, an etching gas whose flow rate is controlled from the gas introduction system 8, for example, a gas containing silicon tetrachloride as a silicon compound gas and ammonia as a nitrogen hydride gas, that is, silicon tetrachloride: 2 Q 5 CC11, ammonia: 1105
A mixed gas of CC nitrogen: 80 SCCM and chlorine: 20 SCCH is introduced, and the inside of the etching chamber 7 is brought to a predetermined gas pressure, for example, 2 Pa, by exhausting through the vacuum exhaust port 11.
and the etching electrode 1 is heated by a high frequency power source 10.
For example, a high frequency power of 200W is applied.

Then, a glow discharge is generated between the etching electrode 1 and the counter electrode i3, the gas is turned into plasma and activated, chlorine radicals are generated, and the etching electrode 1 side is vertically irradiated with accelerated ions. With this, the board 2
The upper titanium nitride film 14.degree. copper thin film 15 and titanium nitride film I6 are etched and notched by the synergistic effect of ion bombardment and chlorine radicals.

FIG. 5 shows the cross-sectional shape of the substrate to be etched after etching. Figure 5 (al) A mixed gas of silicon tetrachloride, nitrogen, and chlorine without the addition of ammonia caused undercuts, making microfabrication difficult;
As shown in Figure 3, the addition of ammonia promoted the formation of a sidewall protective film, thereby preventing undercuts and resulting in a pattern with a nearly vertical cross-sectional shape. At this time, the etching rate of the copper thin film was about 1000 etchings per 5 h, making it possible to form a pattern at a rate 4 to 5 times faster than in the case of a conventional mixed gas of silicon tetrachloride and nitrogen.

As described above, the etching method of this embodiment enables sufficiently high-speed etching compared to the conventional etching method using a mixed gas of silicon tetrachloride and nitrogen, and achieves directional etching without undercuts.

Although this example shows only the etching of a thin copper film, the present invention is not limited to the etching of only a thin copper film, but can also be applied to the etching of a copper alloy film containing copper as a constituent, such as an Al-Cu film. Applicable.

In addition to silicon tetrachloride shown in the examples, the silicon compound gas includes, for example, monosilane and disilane.

Gases such as dichlorosilane and trichlorosilane are also used, and as the nitrogen hydride gas, in addition to ammonia shown in the examples, gases such as hydrazine are also applicable.

〔Effect of the invention〕

As explained above, according to the present invention, when etching a copper or copper alloy thin film, by using a mixed gas containing at least a silicon compound gas and a nitrogen hydride gas as an etching gas, etching can be performed at high speed and in a direction without undercuts. This method has the effect that a copper or copper alloy wiring pattern with high properties can be easily obtained and high throughput etching can be achieved.

[Brief explanation of drawings]

Figures 1 and 2 show the results of experiments based on the dry etching method of the present invention. A characteristic diagram showing the relationship between the etching rate and the amount of chlorine added. Figure 2 is a characteristic diagram showing the relationship between the etching rate of a copper thin film and the amount of ammonia added when ammonia is added to a mixed gas of silicon tetrachloride, nitrogen and chlorine. Fig. 3 is a schematic diagram of an apparatus for carrying out an embodiment of the present invention, and Fig. 4 shows the workpiece and
FIG. 5 is a diagram showing a cross section of a processed substrate according to the present invention. l... Ethochink 7J, pole, 2... Substrate to be etched, 3... Counter electrode, 4... Substrate stand for electrostatic chuck, 5... Heater for heating the etching electrode, 6... Opposing Electrode heating heater, 7... Etching chamber, 8.
...Gas introduction system, 9. .・Matching box, 10...High frequency power supply, 11・
...Vacuum exhaust port, 12...Silicon wafer, 13...
・Silicon dioxide film, 14...Titanium nitride film, 15.
... Copper thin film, 16 ... Titanium nitride film, 17 ... Organic resist film. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] The copper or copper alloy thin film coated on the substrate is partially covered with a mask material, the substrate is placed on one electrode of a counter electrode type reactive ion etching apparatus, and the substrate placed on the electrode is heated. , a method of etching the copper or copper alloy thin film by introducing an etching gas into the etching apparatus and applying high frequency power between opposing electrodes to generate glow discharge, the etching gas containing at least a silicon compound gas and nitrogen; A dry etching method characterized by using a mixed gas containing hydride gas.