JP3013576B2 - Dry cleaning method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for forming a thin film using plasma CVD in a semiconductor manufacturing process or the like so that a reproducible film can be formed while maintaining a clean state inside the apparatus. For this purpose, the present invention relates to a cleaning method for dry cleaning, in which an NF ₃ gas is introduced as a cleaning gas into a plasma space of the apparatus to generate plasma and clean the inside of the apparatus.

[0002]

2. Description of the Related Art In a plasma CVD apparatus, there is a problem that the number of particles increases due to the deposition of a film on the inner wall of the apparatus as the film forming process is repeated and the film forming characteristics fluctuate. As one method for solving this, a cleaning method called so-called dry cleaning or plasma cleaning is known, in which a cleaning gas is introduced into a plasma space to convert the inside of the apparatus into plasma after a predetermined number of film formations, thereby purifying the inside. A general operation method of the apparatus is to operate the apparatus while maintaining the characteristics of the apparatus by alternately performing the film forming process and the cleaning.

Conventionally, as a dry cleaning method,
In order to increase the cleaning speed, a magnetic field is used to control the plasma flow to guide the plasma to a desired site, and when using a magnetic field, cleaning is performed while changing the gas pressure, paying attention to the difference in the gas pressure effect. Method was taken.

[0004]

However, in the conventional cleaning method, the cleaning time is very long because the absolute value of the cleaning rate is low, which lowers the operating efficiency of the apparatus for film formation and lowers the throughput. Was invited. An object of the present invention is to provide a dry cleaning method that can significantly increase the absolute value of a cleaning rate.

[0005]

According to the present invention, there is provided, in accordance with the present invention, a plasma space for converting an introduced gas into a plasma, and a constituent element of a thin film to be formed on a substrate is provided. In a dry cleaning method in which an NF ₃ gas is introduced into the plasma space to convert the gas into a plasma, the inside of the plasma CVD apparatus for forming a thin film on a substrate by introducing a gas having the gas into the plasma space is formed. _{In this} dry cleaning method, cleaning is performed by introducing _two gases simultaneously with the NF ₃ gas, and the amount of the N ₂ gas introduced into the plasma space is set to be 40 to 65% of the NF ₃ gas in a flow ratio.

In this case, the gas pressure in the plasma space at the time of cleaning is preferably maintained at a high pressure of 0.5 to several Torr.

[0007]

[Function] As is well known, a plasma CVD apparatus uses a high-frequency (normally 13.56 MHz) power as a plasma generation energy for converting a gas introduced into a plasma space into a plasma, and a microwave (normally 2.45 GHz). Some use electricity. High frequency plasma C using high frequency power
In a VD apparatus, a plasma space is formed between two opposing electrodes to which a high-frequency voltage is applied, and at the time of film formation, a gas containing a component element of a thin film to be formed on a substrate placed in the plasma space. Is supplied to the plasma space in the form of a shower from a large number of pores formed in the counter electrode, for example. Further, in the microwave plasma CVD apparatus, the plasma space is formed in a cylindrical container having a microwave window provided on one end face and inside the cavity of the microwave, and the other end face of the cavity resonator. And a reaction chamber into which a CVD gas is introduced at the time of film formation and a cleaning gas is introduced at the time of cleaning. In a microwave plasma CVD apparatus, a coil is usually arranged coaxially with a cavity resonator, and this coil forms an electron cyclotron resonance magnetic field region with a microwave in the cavity resonator. The gas having one of the introduced thin film component elements is efficiently turned into plasma in this region, travels to the substrate in the reaction chamber along the magnetic field formed by the coil, and activates the CVD gas on the way.

Introduced into the plasma space of the plasma CVD device
Cleaning gas NF _ThreeGas becomes plasma
When receiving energy, NF_Three→ NF_Two+ F^*(* Means radical) NF_Two→ NF + F^* The reaction of Si + F^*→ SiF_FourCleaning is performed using 基本 (↑ means gas) as a basic reaction.

By the way, when supplying a plasma energy to a mixed gas of NF ₃ and N _2, low ionization potential N ₂
Is selectively ionized and more vibrationally excited, and the resulting nitrogen ions or excited molecules excite NF ₃ to promote the dissociation of F ^* , thereby improving the dry cleaning efficiency. In the cleaning equipment, recontamination with intermediate substances such as re-dissociation (→ SF ₃ etc.) of volatile substances (SiF ₄ etc.) followed by re-reaction (SiF ₃ + O ₂ → SiO ₂ + 3F ^* etc.) Phenomena also occur at the same time, and the actual phenomenon is that these substances are cleaned simultaneously with the substances to be cleaned from the beginning. By adding a small N ₂ reactive binding activity at this time, the cleaning material to reduce the probability of being regenerated, also be regenerated material resulting bound to N ₂ of these substances are relatively etch rate Since the material is fast, the cleaning speed can be improved.

Further, the gas pressure at the time of cleaning is set to 0.5
If the pressure is as high as several Torr, the dissociation effect of the NF ₃ gas by vibrational excitation does not decrease even if the ionization degree of the N ₂ gas is reduced due to the small mean free path of the gas molecules. Cleaning is carried out at high speed in the presence of. There is an appropriate range of the mixing ratio of NF ₃ gas and N ₂ gas for increasing the cleaning speed under a constant gas pressure, and if the amount of N ₂ gas is too small, the NF ₃ gas is reduced by N ₂ gas. If the amount of dissociation is small and the amount of N ₂ gas is too large, the amount of NF ₃ gas will be small, so that the amount of fluorine radicals generated by dissociation will be small. According to the experiment (details will be described in the examples section), the amount of N ₂ gas was changed to NF ₃ by the flow ratio.
When the gas content is 5 to 80%, particularly 40 to 65%, the cleaning rate can be effectively increased.

[0011]

FIG. 1 shows an example of a configuration of a microwave plasma CVD apparatus which uses microwave power to convert a gas introduced into a plasma space into plasma, as a plasma CVD apparatus according to the present invention. Reference numeral 1 denotes a reaction chamber, which contains a wafer stage 3 on which a wafer 31 is set. The wafer 31 is taken in and out of a wafer transfer port 32 that can be opened and closed by a gate valve (not shown) by a transfer mechanism (not shown). The gas supply ports 41 and 42 are connected to a gas supply system (not shown). The gas supply port 41 includes a CVD gas at the time of film formation, an NF ₃ gas as an etching gas at the time of cleaning, and a gas supply port 42. O ₂ gas for film formation and N ₂ gas for cleaning are supplied. The exhaust port 16 is connected to an exhaust system (not shown) so that the pressure in the reaction chamber 1 can be kept constant. A magnetic field control coil 6 is provided on the outer periphery of the reaction chamber 1.
At a position facing the wafer stage 3 in the reaction chamber 1, a plasma generation chamber 2 constituting a microwave cavity resonator is airtightly connected. A waveguide 7 for supplying microwave power is connected to the plasma generation chamber 2 through a microwave window 21. The main coil 8 has its geometric center
The microwave window is disposed so as to be closer to the atmosphere than the vacuum-side end face.

FIG. 2 shows the NF according to the present invention._Three= 200sc
cm / 1 Torr level N_TwoRate when adding
6 is a graph showing the transition of the graph. As is clear from FIG.
And N _Two/ NF_ThreeAt a rate of 5 to 80%,
As a result, a value of 800 ° / min or more was obtained.
Especially in the range of 40 to 65%, the etching rate is 15
It is about 00Å / min.

In the above embodiment, the etching rate in the plasma CVD apparatus using microwave power for gasification of gas is shown. However, from the operation of the invention, the same effect can be obtained in the plasma CVD apparatus using high frequency power. It is clear that can be expected.

[0014]

As described above, according to the present invention, a low N ₂ of ionization potential by performing dry cleaning with the addition of N ₂ at the same time NF ₃ is selectively ionized and are more vibrationally excited nitrogen ions generated by this Alternatively, since NF ₃ is excited by the excited molecules to promote the dissociation of fluorine radicals, the cleaning rate can be greatly improved, thereby shortening the time spent for cleaning and improving the operation rate of the apparatus. , Can improve throughput.

[Brief description of the drawings]

FIG. 1 is a diagram showing one configuration of an apparatus embodying the present invention.

FIG. 2 shows an etching rate of NF ₃ gas according to the present invention,
Diagram showing change due to N ₂ gas flow ratio

[Explanation of symbols]

 Reference Signs List 1 reaction chamber 2 plasma generation chamber 3 wafer stage 8 main coil 31 wafer (substrate) 41 gas supply port 42 gas supply port

Claims (2)

(57) [Claims] 1. A plasma CVD method comprising the steps of: forming a thin film on a substrate by introducing a gas having a constituent element of a thin film to be formed on the substrate into the plasma space; In the dry cleaning method of cleaning the inside of the apparatus by introducing NF ₃ gas into the plasma space and converting it into plasma, the dry cleaning method of introducing N ₂ gas into the plasma space simultaneously with the NF ₃ gas to perform cleaning. A dry cleaning method characterized in that the amount of N ₂ gas introduced into the plasma space is 40 to 65% of the NF ₃ gas in flow rate ratio. 2. The dry cleaning method according to claim 1, wherein the gas pressure in the plasma space at the time of cleaning is 0.5 to several Torr.