JP2006219702A - Plasma film-forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma film-forming apparatus which forms a film with uniform thickness distribution in a plane direction of a substrate by uniformizing the intensity distribution of a high-frequency power in a plane direction of an electrode. <P>SOLUTION: The apparatus is provided with a vacuum chamber 1 of which the inside can be evacuated, a first electrode 3 which is arranged in the vacuum chamber 1 and supports an article 20 to be film-formed, a gas-mixing box 8 for mixing a plurality of film-forming gases in it, a second electrode 2 which composes one part of a wall of the vacuum chamber 1, is arranged so as to face the first electrode 3, and has a gas inlet 12 for introducing the film-forming gases mixed in the gas-mixing box 8 into the vacuum chamber 1, and the high-frequency power source 18 for generating the plasma of the film-forming gas in the vacuum chamber 1 by forming a high-frequency electric field between the first and second electrodes 3 and 2, wherein the mixing box 8 is placed on the second electrode 2 through an insulating material 17, and has a gas outlet 11 of the mixed gas so as to directly connect to the gas inlet 12 of the second electrode 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a plasma film forming apparatus, and more particularly to a plasma film forming apparatus provided with a gas mixing box for mixing a plurality of types of film forming gases before introducing them into a film forming chamber.

When film deposition is performed on a substrate by plasma CVD (Chemical Vapor Deposition) method using multiple types of deposition gas, gas mixing is performed to mix these deposition gases before introducing them into the deposition chamber A plasma CVD apparatus in which a box is provided outside a film forming chamber is well known. For example, see Patent Document 1. By using such a gas mixing box, a plurality of types of film forming gases are agitated and mixed in the gas mixing box, and supplied to the film forming chamber at a uniform concentration.
JP 2001-335941 A

  In the plasma CVD apparatus equipped with the gas mixing box, if the pipe connected between the gas outlet from the gas mixing box and the gas inlet into the film forming chamber is long, the pressure in the gas mixing box is reduced. The pressure difference between the two ends of the mass flow controller that supplies the deposition gas by adjusting the flow rate from the deposition gas supply source into the gas mixing box cannot be secured sufficiently. The film forming gas cannot be supplied into the film forming chamber at the flow rate. As a result, there arise problems that the film thickness of the formed film is not uniform and the reproducibility of the film thickness deteriorates.

  In addition, if the diameter of the pipe is made large, the pressure rise in the mixing box can be suppressed, but in order to prevent the mixing effect from being lowered due to stirring of various film forming gases in the mixing box, the diameter of the pipe is not much. It cannot be made large.

  Therefore, in Patent Document 1, the mixing box is installed on the electrode, and the gas outlet of the mixing box is directly connected to the gas inlet formed through the thickness direction of the electrode, as described above. And the instability of the flow rate of the film forming gas due to the length of the pipe connecting the gas inlets.

  Note that if the gas mixing box is made of a soft material such as a fluororesin, the vacuum inside the gas mixing box cannot be maintained, and a ceramic material such as alumina is expensive, including processing costs. Generally, it is made of a metal material such as

  FIG. 2 is a side view of a conventional electrode 2 to which high-frequency power is applied and a gas mixing box 8 disposed on the electrode 2. Here, as the frequency of the high-frequency current flowing through the conductor increases, the high-frequency current supplied to the substantially central position on the upper surface of the electrode 2 is indicated by an arrow in FIG. It flows in a path and reaches the surface of the electrode 2 that faces another electrode (not shown). Here, since the gas mixing box 8 has electrical conductivity, it is in electrical contact with the electrode 2, so that high-frequency current flows on the surface of the gas mixing box 8 on the left side in the figure where the gas mixing box 8 is arranged. To the opposite side. That is, the path of the high-frequency current flowing from the approximate center of the upper surface of the electrode 2 to the opposite side through the left side of the upper surface is longer by the amount of the gas mixing box 8, and the upper surface of the electrode 2 The resistance is larger than the path of the high-frequency current flowing on the right side and flowing on the opposite side.

  As a result, the high-frequency power intensity generated between the left side in the figure where the gas mixing box 8 exists and the right side where the gas mixing box 8 does not exist and the other electrodes facing the electrode 2 are generated and generated. The plasma density is not uniform with respect to the electrode surface direction. Thereby, in the surface direction of a board | substrate, the film-forming speed | rate differs by the location where the gas mixing box 8 exists, and the location which does not exist, and film thickness distribution deteriorates. This problem appears particularly prominently in a reaction-controlled system (mainly the formation of an amorphous silicon film or a silicon nitride film) in which the film formation rate is directly proportional to the high-frequency power intensity.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to make a plasma film forming apparatus capable of making the high-frequency power intensity uniform in the electrode surface direction and uniforming the film thickness distribution in the substrate surface direction. Is to provide.

  The plasma film-forming apparatus of the present invention includes a vacuum chamber in which the inside is evacuated, a first electrode that is installed in the vacuum chamber and supports a film-forming target, and a gas that mixes a plurality of types of film-forming gases. The mixing box and a part of the wall of the vacuum chamber constitute a part of the first electrode and face the first electrode, and a gas introduction port for introducing the film forming gas mixed in the gas mixing box into the vacuum chamber is formed. The second electrode and a high-frequency power source for generating a high-frequency electric field between the first and second electrodes to generate plasma of a film forming gas in the vacuum chamber, and the mixing box has an insulator on the second electrode. The gas outlet of the mixed gas is directly connected to the gas inlet of the second electrode.

  In this invention, it was set as the structure which interposed the insulator between the gas mixing box and the 2nd electrode in which the gas inlet was formed, and avoided both electrical contact. With such a configuration, the high-frequency current supplied to the upper surface of the second electrode flows through the upper surface of the second electrode without passing through the gas mixing box, even in the portion where the gas mixing box is disposed. It flows to the lower surface facing one electrode. As a result, the high-frequency current flowing on the surface of the second electrode is not affected by the current loss caused by flowing through the gas mixing box, and the high-frequency generated between the second electrode and the first electrode provided opposite thereto. The power intensity can be made uniform in the electrode surface direction. As a result, the film thickness distribution is uniform while suppressing variations in the film formation speed in the surface direction of the film formation target.

  In particular, the present invention is such that the reaction rate-determining is directly proportional to the high-frequency power intensity, for example, the formation of a silicon nitride film using a silicon-containing gas and a nitrogen-containing gas, or a polycrystalline or This is effective for forming an amorphous silicon film.

  According to the plasma film forming apparatus of the present invention, since the insulator is interposed between the gas mixing box and the second electrode in which the gas inlet is formed, the electrical contact between them is avoided. The high-frequency power intensity generated between the first electrode and the second electrode can be made uniform in the electrode surface direction. As a result, variations in film formation speed in the surface direction of the film formation target are suppressed, the film thickness distribution becomes uniform, and film formation quality can be improved.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment, A various deformation | transformation is possible based on the technical idea of this invention.

  FIG. 1 shows a plasma film forming apparatus according to an embodiment of the present invention. This plasma film forming apparatus is a plasma CVD apparatus in which a film forming gas introduced into a vacuum chamber is exposed to a plasma discharge to cause a chemical reaction on the surface of a film forming object to be deposited.

  The vacuum chamber 1 is provided with an exhaust port 7 connected to an evacuation system (not shown) so that the inside functioning as the film forming chamber 6 can be evacuated (depressurized).

  A first electrode 3 is disposed in the vacuum chamber 1 so as to be insulated from the vacuum chamber wall. The first electrode 3 is grounded. The first electrode 3 also functions as a susceptor that supports a substrate 20 such as glass or semiconductor that is a film formation target.

  A second electrode 2 is provided on the ceiling side of the vacuum chamber 1 so as to be insulated from the vacuum chamber wall. The second electrode 2 constitutes a part of the ceiling wall of the vacuum chamber 1 and faces the first electrode 3 with the shower plate 4 interposed therebetween. The second electrode 2 is connected to a high frequency power source 18 provided outside the vacuum chamber 1 via a modulator 19.

  The second electrode 2 is formed in a container shape having an opening directed to the first electrode 3 in the vacuum chamber 1, and a shower plate 4 having a large number of small holes is attached to cover the opening. It has been. A gas storage chamber 5 is formed between the upper part of the second electrode 2 and the shower plate 4, and a gas inlet 12 leading to the gas storage chamber 5 is formed through the thickness direction of the upper part of the second electrode 2. ing. As shown in FIG. 4 when the second electrode 2 is viewed from the upper surface side, the gas inlet 12 is located at the approximate center of the upper surface of the second electrode 2.

  On the upper surface of the second electrode 2 facing the outside of the vacuum chamber 1, a gas mixing box 8 is installed via an insulator 17. The gas mixing box 8 is made of, for example, a metal material such as stainless steel, and a mixing chamber 9 and a gas flow path 10 connected to the mixing chamber 9 are formed therein.

  The insulator 17 is made of alumina or fluororesin, for example, and is interposed between the upper surface of the second electrode 2 and the lower surface of the gas mixing box 8. The insulator 17 electrically insulates the second electrode 2 and the gas mixing box 8 from each other.

  One end of the gas flow path 10 is connected to the mixing chamber 9, and the other end is connected to the gas outlet 11 of the gas mixing box 8. The gas outlet 11 is located on the gas inlet 12 formed in the second electrode 2, and the gas outlet 11 and the gas inlet 12 are directly connected. In order not to hinder the direct connection between the gas outlet 11 and the gas inlet 12, a portion of the insulator 17 located between the gas outlet 11 and the gas inlet 12 is penetrated in the thickness direction.

  From the above, the mixing chamber 9 of the gas mixing box 8 enters the film forming chamber 6 through the gas passage 10, the gas outlet 11, the gas inlet 12, the gas storage chamber 5, and the small holes of the shower plate 4. Communicates.

  A plurality of gas supply sources 13 and 16 are arranged outside the vacuum chamber 1 corresponding to a plurality of types of film forming gases, and the gas supply sources 13 and 16 are gas mixed via mass flow controllers 14 and 15, respectively. It is connected to the mixing chamber 9 of the box 8. The gas supply sources 13 and 16 are connected to the opposite side of the gas flow path 10 in the mixing chamber 9.

  At the time of film formation using the above plasma film forming apparatus, first, the inside of the vacuum chamber 1 is evacuated (depressurized) to a predetermined pressure (for example, 50 to 800 Pa) by an evacuation system, and then the film formation gas supply sources 13 and 16 The film forming gas is introduced into the mixing chamber 9 of the mixing box 8 while the flow rate is adjusted by the mass flow controllers 14 and 15. A plurality of types of film forming gases introduced into the mixing chamber 9 are mixed in the mixing chamber 9 to make the concentration of each gas component uniform, and then formed in the gas flow path 10, the gas outlet 11, and the second electrode 2. The gas is introduced into the gas storage chamber 5 through the gas inlet 12. The mixed gas introduced into the gas storage chamber 5 is sprayed from the small hole of the shower plate 4 toward the substrate 20 placed on the first electrode 3.

  At this time, since a long pipe is not interposed between the gas outlet 11 of the gas mixing box 8 and the gas inlet 12 formed in the second electrode 2, both are directly connected. There is almost no pressure loss between the mouth 12. For this reason, since the internal pressure of the mixing chamber 9 does not increase by such a pressure loss, the pressure difference between both ends of the mass flow controllers 14 and 15 for adjusting the flow rate of the film forming gas can be sufficiently increased. . As a result, the deposition gas is supplied from the mass flow controllers 14 and 15 into the deposition chamber 6 with a stable flow rate, so that the state of the mixed gas in the deposition chamber 6 is stabilized. The film thickness of the film to be formed becomes uniform. In order to obtain the above effects, the gas flow path from the mixing chamber 9 to the gas inlet 12 is preferably 300 mm or less.

  In the state described above, the substrate 20 is heated by a heater provided in the first electrode 3 to maintain a predetermined temperature (for example, 60 to 450 ° C.), and the high frequency power (for example, the oscillation frequency is supplied from the high frequency power source 18 to the second electrode 2). 10 to 100 MHz) is applied to generate a discharge between the electrodes 2 and 3 to generate plasma. The deposition gas is decomposed by the plasma, and vapor phase growth is performed on the surface of the substrate 20 to be deposited on the substrate 20.

  And in this embodiment, it was set as the structure which interposed the insulator 17 between the gas mixing box 8 which has both conductivity, and the 2nd electrode 2, and avoided both electrical contact. The gas mixing box 8 is not electrically connected anywhere and its potential is a floating potential. With such a configuration, as indicated by an arrow in FIG. 3, the high-frequency current supplied from the high-frequency power source 18 to the substantially central position on the upper surface of the second electrode 2 is on the left side in the figure in which the gas mixing box 8 is arranged. Also flows through the upper surface of the second electrode 2 without passing through the gas mixing box 8 and flows to the lower surface facing the first electrode 3. That is, a path of high-frequency current flowing from the approximate center of the upper surface of the second electrode 2 to the left side of the upper surface and flowing to the opposite surface side, and a path of high-frequency current flowing from the right side of the upper surface to the opposite surface side Have the same length and the resistance in both paths is comparable.

  As a result, in the figure where the gas mixing box 8 is present, there is no bias in the high-frequency power intensity generated between the left electrode and the right side where the gas mixing box 8 is not present, and the first electrode 3, and the high-frequency power in the electrode surface direction. The strength becomes uniform. Thereby, the film thickness distribution in the surface direction of the substrate 20 becomes uniform.

  FIG. 5 shows a simulation result of the potential distribution of the (peak to peak) potential in the surface direction of the electrode to which the high-frequency power is applied in the conventional configuration shown in FIG. 2 and the configuration of the present invention shown in FIG.

  As is apparent from the results of FIG. 5, in the conventional configuration, the magnitude of the potential at the same distance from the center of the electrode differs depending on whether the gas mixing box is present or not. On the other hand, in the configuration of the present invention, the potential at the same distance from the center of the electrode is the same at both the location where the gas mixing box is present and the location where the gas mixing box is not present. In other words, in the present invention, a symmetrical potential distribution is obtained with respect to the electrode center. This leads to a uniform film thickness distribution in the substrate surface direction.

Next, a silicon nitride film using SiH ₄ gas, NH ₃ gas, and nitrogen gas as the film forming gas, and an amorphous silicon film using SiH ₄ gas and Ar gas as the film forming gas are formed as follows. The results of film formation under film conditions and evaluation of film thickness distribution will be described. The size of the rectangular glass substrate which is the film formation target used for the evaluation is 730 mm × 920 mm, and the film thickness is measured at 25 points in the 690 mm × 880 mm region of the substrate, and σ = (maximum film thickness− The film thickness distribution defined by (minimum film thickness) / (maximum film thickness + minimum film thickness) × 100 [%] is calculated, and the value is calculated according to the conventional configuration shown in FIG. 2 and the present invention configuration shown in FIG. And compared.

The film formation conditions of the silicon nitride film are as follows: high frequency power frequency is 27.12 MHz, input power density is 0.57 W / cm ² , SiH ₄ gas flow rate is 690 sccm, NH ₃ gas flow rate is 12.5 times that of SiH ₄ gas, nitrogen The gas flow rate was 17 times that of SiH ₄ gas.

The film formation conditions for the amorphous silicon film were a high frequency power frequency of 27.12 MHz, an input power density of 0.05 W / cm ² , a SiH ₄ gas flow rate of 330 sccm, and an Ar gas flow rate of 50 times that of SiH ₄ gas.

  6 shows the thickness distribution of the silicon nitride film in the conventional configuration, FIG. 7 shows the thickness distribution of the silicon nitride film in the configuration of the present invention, and FIG. 8 shows the thickness distribution of the amorphous silicon film in the conventional configuration. FIG. 9 shows the film thickness distribution of the amorphous silicon film in the structure of the present invention. In each figure, the two horizontal axes corresponding to the longitudinal direction and the short direction of the substrate indicate the distance (mm) from the central position when the central position of the substrate is 0, and the vertical axis indicates the film thickness (Å). Indicates.

  As shown in FIG. 6, in the silicon nitride film formed by the conventional film forming apparatus, the film thickness distribution in the substrate surface direction is ± 8.9%, and the film thickness distribution is inclined. On the other hand, as shown in FIG. 7, in the silicon nitride film formed by the film forming apparatus having the configuration of the present invention, the film thickness distribution in the substrate surface direction is not inclined and is drastically as ± 3.5%. It has improved. As for the amorphous silicon film, the amorphous silicon film formed by the film forming apparatus having the structure of the present invention shown in FIG. 9 has no inclination in the film thickness distribution in the substrate surface direction, and the conventional silicon film shown in FIG. A favorable film thickness distribution of ± 2.4% is obtained with respect to the film thickness distribution of ± 5.2%.

  FIG. 10 shows the film formation speed and film thickness distribution of a silicon nitride film formed by a conventional film forming apparatus, and the film formation speed and film thickness of a silicon nitride film formed by the film forming apparatus of the present invention. FIG. 11 shows the film formation speed and film thickness distribution of the silicon nitride film formed by the film forming apparatus having the conventional structure, and the film forming speed of the silicon nitride film formed by the film forming apparatus of the present invention. The film thickness distribution is shown. In each figure, ■ indicates the deposition rate, and ◆ indicates the film thickness distribution.

  From FIGS. 10 and 11, it can be seen from the film thickness distribution of the film formed by the conventional film forming apparatus that the silicon nitride film and the amorphous silicon film are formed by the film forming apparatus of the present invention. It can be seen that the film thickness distribution of the formed film is better. In addition, the film forming speed is almost the same as the conventional one, and even if the present invention is used, the film forming speed is not lowered.

  Note that there is no difference in the effects of the present invention depending on whether the silicon nitride film or the amorphous silicon film is doped with impurities.

It is a schematic sectional drawing of the plasma film-forming apparatus which concerns on embodiment of this invention. It is a schematic diagram of the principal part of the plasma film-forming apparatus of a prior art example. It is a schematic diagram of the principal part of the plasma film-forming apparatus which concerns on embodiment of this invention. FIG. 4 is a top view of FIGS. It is the electric potential distribution map in the electrode surface in the past and this invention. It is a film thickness distribution diagram of a conventional silicon nitride film. It is a film thickness distribution map of the silicon nitride film in the present invention. It is a film thickness distribution diagram of a conventional amorphous silicon film. It is a film thickness distribution diagram of the amorphous silicon film in the present invention. It is a figure which shows the film-forming speed | rate and film thickness distribution of a silicon nitride film in the past and this invention. It is a figure which shows the film-forming speed | rate and film thickness distribution of an amorphous silicon film in the past and this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Vacuum chamber, 2 ... 2nd electrode, 3 ... 1st electrode, 4 ... Shower plate, 8 ... Gas mixing box, 9 ... Mixing chamber, 11 ... Gas outlet, 12 ... Gas inlet, 17 ... Insulator, 18 ... high frequency power supply, 20 ... film formation target.

Claims (6)

A vacuum chamber in which the inside is evacuated;
A first electrode installed in the vacuum chamber and supporting a film formation target;
A gas mixing box that mixes multiple types of deposition gases;
A part of the wall of the vacuum chamber is formed and is opposed to the first electrode, and a gas inlet for introducing the film forming gas mixed in the gas mixing box into the vacuum chamber is formed. A second electrode;
A high-frequency power source that generates a high-frequency electric field between the first and second electrodes to generate plasma of the film-forming gas in the vacuum chamber,
The gas mixing box is installed on the second electrode via an insulator, and the gas outlet of the mixed gas is directly connected to the gas inlet of the second electrode. .   The plasma deposition apparatus according to claim 1, wherein the plurality of types of deposition gases include a silicon-containing gas and a nitrogen-containing gas, and a silicon nitride film is deposited on the deposition target.   The plasma deposition apparatus according to claim 1, wherein the plurality of types of deposition gases include a silicon-containing gas and an inert gas, and a polycrystalline or amorphous silicon film is deposited on the deposition target.   The plasma film-forming apparatus according to any one of claims 1 to 3, wherein an oscillation frequency of the high-frequency power source is 10 to 100 MHz.   5. The plasma film forming apparatus according to claim 1, wherein the insulator is alumina or a fluororesin.   The gas flow path from the film-forming gas mixed in the gas mixing box to the gas introduction port of the second electrode is 300 mm or less. The plasma film-forming apparatus of description.