JPH04211115A - Rf plasma cvd apparatus and thin film forming method - Google Patents

Abstract

PURPOSE:To increase filming rate and to make uniform the thickness and the quality of film by forming a uniform and stabilized plasma with high density in a space between a substrate constituting a ground electrode and a shower supply face of an RF electrode being fed with high frequency power from the RF electrode. CONSTITUTION:Diameter of many holes 52, made through a shower supply face 51, is set 0.4 times or less of the interval between a substrate and the shower supply face 51 and 0.75 times or less than the interval between the centers of the holes thus constituting an electrode for forming an uniform and stabilized glow discharge. Gas pressure is increased by decreasing the opposing interval of electrode thus increasing the density of plasma for same RF power supply while furthermore active species, including neutral active species, are distributed uniformly thus obtaining an RF plasma CVD apparatus for increasing the filming rate with improved uniformity in film thickness and film quality. When a film is formed on the substrate, electrode interval is set such that the density of plasma is increased and all active species are distributed uniformly and the pressure of filming gas is set at a level for causing inter-electrode discharge thus increasing the density of plasma.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is an RF plasma CVD apparatus used in a process of forming a thin film on a substrate surface during a series of steps in a semiconductor manufacturing process. A substrate stand on which a substrate to be film-formed is placed, and an opposing surface facing the substrate stand formed as a shower supply surface having a large number of holes for supplying film-forming gas to the opposing space as a shower. A device configuration of an RF plasma CVD device equipped with an RF end electrode aimed at improving the film formation rate and uniformity of film thickness and film quality, and a method for forming a thin film on a substrate surface using this device. The present invention relates to a thin film forming method. [0002]

[Prior Art] Conventionally, in this type of RF plasma CVD apparatus, a substrate to be deposited is placed on a substrate stand with a built-in heater and constitutes a ground electrode, and an RF
The facing distance between the end electrode and the shower supply surface is 20 to 40 mm.
The gas pressure in the vacuum container housing these electrodes is reduced to several tons.
An RF voltage is applied to the RF end electrode as orr to generate a uniform and stable glow discharge between both electrodes, and a film forming gas is uniformly supplied to the entire surface of the substrate to be filmed from the shower supply surface of the RF end electrode. At the same time, a thin film with uniform thickness and quality is formed by evacuating the gas inside the vacuum container using a vacuum evacuation system and keeping the gas pressure inside the vacuum container constant. An example of the arrangement of holes to provide a uniform gas flow to the substrate surface in order to obtain a uniform film thickness is disclosed in Japanese Patent Application Laid-Open No. 1-149964. [0003]

[Problem to be solved by the invention] Conventional RF plasma C
In a VD device, in order to generate a uniform and stable glow discharge between the electrodes, the facing distance between the heated substrate serving as the ground electrode and the shower supply surface of the RF end electrode (hereinafter also referred to as electrode distance) is set to 20 to 40 mm. and increase the gas pressure to several tons.
I'm keeping it as low as orr. Therefore, the density of plasma obtained by glow discharge is low, and the density of active species contributing to film formation is low. For this reason, the deposition rate is low,
There was a problem that the productivity of the device was low. In addition, because the electrode spacing is large, it is easy to form a distribution of neutral active species that are not constrained by the electric field in the gas flow from the shower supply surface to the substrate, resulting in uniform film thickness and film quality when the substrate area becomes large. There was a problem with low sex. [0004] An object of the present invention is to create an RF plasma that can stably obtain a high-density, uniform plasma in a space facing an RF end electrode and a grounded electrode using the same RF power source, and in which active species are uniformly distributed. The electrode configuration of the CVD device and the thin film that can increase the deposition rate when forming a thin film on a substrate to be deposited using this device, and that can provide uniformity in film thickness and film quality even when depositing on a large area substrate. Another object of the present invention is to provide a forming method. [0005]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a substrate stand which has a built-in heater in a vacuum container and on which a substrate to be film-formed is placed on its flat upper surface;
The RF plasma CVD apparatus includes an RF end electrode whose opposing surface facing the substrate table is formed as a shower supply surface having a large number of holes for supplying film-forming gas to the opposing space as a shower. The diameter of the hole in the shower supply surface is set to be 0.4 times or less of the facing distance between the deposition target substrate placed on the substrate stand and the shower supply surface, and 0.75 times or less of the center distance between the holes. The device shall be formed in the following manner. [0006] In the RF plasma CVD apparatus in which the diameter of the hole in the shower supply surface is formed as described above, the distance between the film-forming substrate and the RF end electrode shower supply surface is set to 20 m.
It is more preferable to set it to less than m. [0007] Additionally, the hole formed in the shower supply surface is
A common point is passed on the shower supply surface. It is preferable to form them at the respective vertices of a large number of minimum equilateral triangles formed by three groups of equally spaced parallel lines each including three straight lines whose directions are shifted by 60°. [0008] Then, when forming a thin film on a substrate to be film-formed,
In an apparatus in which the relationship between the diameter of the hole in the shower supply surface of the RF end electrode, the facing distance between the shower supply surface and the substrate to be film-formed, and the center distance between the holes is set as described above, the pressure of the film-forming gas is Assume that a thin film forming method is used in which a thin film is formed on a substrate at a pressure that can be discharged under the RF voltage supplied to the RF electrode. [0009]

[Operation] In order to obtain high-density plasma using the same RF power source, it is necessary to increase the pressure of the film-forming gas and reduce the electrode spacing to generate a uniform and stable glow discharge. According to the inventor's experiments, in order to generate a uniform and stable glow discharge at high gas pressure, low vacuum, and a similar gap, it is necessary to eliminate unevenness on the electrode, especially the cathode surface, to make it flat, and to induce discharge concentration. I found it very important to avoid. That is, since the holes on the shower supply surface correspond to the irregularities on the electrode surface, a stable glow discharge can be obtained only when a certain relationship is established between the size, the electrode spacing, and the center spacing between the holes. In other words, when the hole size (diameter) becomes larger compared to the electrode spacing,
The electric field strength E at the periphery of the hole is the average electric field strength &E = V/D
(V: the voltage applied between the film-forming substrate and the RF electrode) becomes abnormally large, making it impossible to obtain a uniform glow discharge. Furthermore, when the distance between the centers of the holes, that is, the pitch p, approaches the diameter d of the holes, the part between the holes acts as a protruding electrode, and the electric field is concentrated in this part, causing a filamentary arc. As a result, a uniform glow discharge cannot be obtained. A uniform glow discharge can be obtained if the relationship d(0,4XD d<0.75Xp) is established between the hole diameter d, the distance between the deposition substrate and the shower supply surface, and the hole pitch p It has been confirmed through experiments that the relationship is true only when High-density, uniform plasma can be stably obtained by increasing the gas pressure using the power supply and reducing the electrode spacing. [00101 In this case, as detailed in the Examples section, the electrode spacing can be reduced , 20m from the conventional 20-40mm
By making it less than m, the plasma density becomes significantly higher even at the same gas pressure. The neutral active species in the high-density plasma obtained in this way are not given the opportunity to form a distribution due to the small electrode spacing, and all active species are uniformly distributed and It is also possible to form a thin film with uniform thickness and quality. [0011] Also, the hole formed in the shower supply surface,
passing through a common point on the shower supply surface. If holes are formed at the vertices of a large number of minimum equilateral triangles formed by three groups of equally spaced parallel lines each including three straight lines whose directions are shifted by 60 degrees, holes can be formed on a shower supply surface with a constant area. If the minimum pitch of the holes is constant, the largest number of holes can be formed and the gas flow will be uniform. Furthermore, since the pore diameter can be made smaller to obtain a predetermined gas flow, the electrode spacing for obtaining a uniform glow discharge can be made smaller, thereby further increasing the plasma density. [0012] From the above, when forming a film on a film-forming substrate, the electrode spacing is kept as small as possible within the range that maintains the above-mentioned pore diameter conditions, and the pressure of the film-forming gas is By adopting a thin film formation method that forms a thin film on a substrate as a pressure that can be discharged under the RF voltage supplied to the RF electrode,
The plasma density in the plasma formation space (the space facing the electrodes) can be increased, and the film formation rate can be increased. Moreover, the neutral active species in the high-density plasma obtained in this way are not given an opportunity to form a distribution due to the small electrode spacing, and all active species are uniformly distributed and Uniformity in film thickness and film quality can also be obtained during film formation. [0013]

[Example] Fig. 1 shows an example of the structure of an RF electrode shower supply surface according to the present invention, and Fig. 2 shows an example of the configuration of an RF plasma CVD apparatus using an RF electrode having a shower supply surface according to this embodiment. show. [0014] Gate valves 3a and 3b for loading and unloading the substrate 2 to be film-formed are provided on both walls of the vacuum chamber 1.
Vacuum sealable. Film-forming substrate 2
was installed in the vacuum container 1 so as to be movable up and down from the outside of the vacuum container by a drive device (not shown). It is installed in contact with the upper surface of the substrate stand 4 that has a built-in heater. An RF electrode 5 whose shower supply surface is a facing surface 51 facing the substrate table 4 is attached to the vacuum container 1 via an insulating bushing 9 and connected to an RF power source 6 . A gas supply pipe 8 made of an insulating material is further connected to the RF electrode 5 for supplying film-forming gas to the back side of the shower supply surface 51. Note that the reference numeral 7 in the figure indicates that the inside of the vacuum vessel 1 is heated at 0°5 while the film-forming gas is continuously supplied to the space facing the shower supply surface 51 and the substrate 2 via the gas supply pipe 8. To maintain a constant gas pressure within the range of ~10 torr,
This is a vacuum exhaust system that exhausts the gas inside the vacuum container at a predetermined flow rate. [00151 When forming a film on the substrate 2, the substrate 2 is placed on the substrate stand 4.
After reaching a certain temperature by heating from Film formation is performed by supplying high frequency power to the RF electrode 5 from the RF power supply 6. [0016] By the way, the shower supply surface 5 of the RF electrode 5
The number of holes No. 1 is formed as many as possible within a limited area, so that the diameter of the hole when supplying a predetermined amount of gas to the discharge formation space (the space facing the shower supply surface 51 and the substrate 2) can be adjusted. In order to make it smaller and more easily satisfy the relationships given in the section ``Means for Solving the Problems'': d<0.4D, d<0.75p, the hole is made smaller as shown in Figure 1. It is placed at the apex of an equilateral triangle. Here, d is the diameter of the hole, D is the facing distance between the shower supply surface and the substrate, and p is the center distance between the holes. [0017] Experimental results of investigating how the discharge state in the space where the shower supply surface faces the substrate changes depending on the combination of the hole diameter d and the spacing between the shower supply surface and the substrate. is shown in Figure 3. The ◯ marks in the figure indicate that a uniform glow discharge was formed, and the X marks indicate that a filamentary arc was formed and a uniform glow discharge was not obtained. From this experimental result, it can be seen that a uniform glow discharge is obtained in the region to the right of the straight line d=o, 4D, that is, when d<0.4D. [0018] Further, FIG. 4 shows the results of an experiment in which it was investigated how the discharge state changes depending on the combination of the diameter d of the holes and the center distance p between the holes. From this experimental result, it can be seen that a uniform glow discharge is obtained in the region to the right of d=0.75p, that is, when d(0.75p). Condition: d〈0
．． 4D, in a state where d<0.75p is satisfied, how does the density ne of the plasma formed between the shower supply surface and the deposition target substrate change with the facing distance between the shower supply surface and the deposition target substrate? The results of an experiment using gas pressure as a parameter are shown to determine whether the This experimental result shows that the plasma density changes approximately in proportion to the gas pressure when the opposing spacing is equal. It can also be seen that as the spacing becomes smaller, the plasma density increases in approximately inverse proportion to the opposing spacing when the gas pressure is constant. Therefore, by changing the facing distance from the conventional range of 20 to 40 mm to, for example, a range of 20 mm or less, forming holes to obtain a uniform glow discharge, and increasing the gas pressure,
Compared to the conventional method, it is possible to obtain plasma with a significantly higher density, and to make the distribution of active species including neutral active species uniform. By setting the gas pressure to the maximum pressure that can be discharged under the RF voltage supplied to the RF electrode, the plasma density reaches the maximum possible value and the deposition rate is increased to the maximum. [0020]

[Effect of the invention] In the present invention, RF plasma CVD
Since the apparatus is configured as described above, the following effects can be obtained. [00211 In the device of claim 1, a uniform and stable glow discharge can always be formed between both electrodes. For this reason, the pressure of the film-forming gas is increased under the same RF power source.
By reducing the electrode spacing and generating a uniform and stable glow discharge, it is possible to obtain a high-density plasma and therefore a high-density active species, increasing the deposition rate of the device, and using small electrodes. Due to the spacing, all the active species are uniformly distributed on the front surface of the substrate without forming a distribution of neutral active species, making it possible to form a film with uniform thickness and quality even on a large-area substrate. Furthermore, since stable film formation is possible by reducing the electrode spacing, reactions in the gas phase are reduced, and particles generated by this reaction ride on the substrate surface in the form of grains. A secondary effect of reducing so-called particle contamination can also be obtained. [0022] In the apparatus of claim 2, as shown in the embodiment of FIG. 5, when the gas pressure is the same, the plasma density is inversely proportional to the electrode spacing under the same RF power source, and the electrode spacing is equal. In this case, it is almost proportional to the gas pressure, so the electrode spacing is set to be as small as possible, for example, within the range of 5 to 15 mm, taking into account the hole diameter that can maintain the required accuracy, from the conventional 20 to 40 mm range to 20 mm or less. By increasing the gas pressure, it is possible to obtain a plasma with a significantly higher density compared to conventional methods, and the active species are evenly distributed.
The film formation speed is improved and the film thickness and quality are made uniform. [0023] In the apparatus of claim 3, when the minimum pitch of the holes is constant, the maximum number of holes can be formed on the shower supply surface, and the gas flow can be made uniform. Moreover, this allows the hole diameter to be made smaller to obtain a predetermined gas flow rate, and the electrode spacing for obtaining a uniform glow discharge can be made smaller, so that the density of uniform plasma can be further increased. [0024] In the apparatus of the present invention, the electrode system is configured so that a uniform and stable glow discharge is always formed. 4, the electrode spacing is kept as small as possible, and the pressure of the film-forming gas is adjusted to RF
By using a thin film formation method in which a thin film is formed on a substrate under pressure that allows discharge under the RF voltage supplied to the electrodes, it is possible to increase the plasma density in the plasma formation space (the space facing the electrodes) and increase the plasma density in the plasma formation space (space facing the electrodes). Membrane speed is increased. Moreover, the neutral active species in the high-density plasma obtained in this way are not given an opportunity to form a distribution due to the small electrode spacing, and all active species are uniformly distributed and Uniformity in film thickness and film quality can also be obtained during film formation.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the structure of a shower supply surface of an RF electrode according to an embodiment of the present invention, in which FIG. 1(a) is a plan view and FIG. 1(b) is a line AA in FIG. Cross-sectional view along

FIG. 2 is a vertical cross-sectional view showing an example of the configuration of an RF plasma CVD apparatus equipped with an RF electrode having a shower supply surface having the structure shown in FIG.

[Figure 3] A diagram showing changes in the discharge state depending on the combination of the diameter of the hole in the shower supply surface of the RF electrode and the distance between the shower supply surface and the substrate to be film-formed. [Figure 4] Shower supply of the RF electrode A diagram showing the change in the discharge state depending on the combination of the diameter of the holes on the surface and the distance between the centers of the holes Diagram showing parameters as parameters [Explanation of symbols] 1 Vacuum vessel 2 Substrate (substrate to be film-formed) 4 Substrate stand 5 RF electrode 6 RF power source 51 Shower supply surface 52 holes

[Figure 1]

[Figure 2]

[Figure 3]

[Figure 4]

[Figure 5]

Claims (4)

[Claims] 1. A substrate table having a built-in heater and on which a substrate to be film-formed is placed on the flat upper surface of the substrate table in a vacuum container, and an opposing surface facing the substrate table showering a film-forming gas into an opposing space. RF plasma CVD comprising an RF end electrode formed as a shower supply surface with a number of holes for supplying
In the apparatus, the diameter of the hole in the shower supply surface is 0.4 times or less the facing distance between the deposition target substrate placed on the substrate stand and the shower supply surface, and 0.75 times the center distance between the holes. RF characterized by being formed as follows:
Plasma CVD equipment. Claim 2: RF plasma CVD according to claim 1.
In the apparatus, the opposing distance between the substrate to be film-formed and the RF end electrode shower supply surface is set to 20 mm or less.
F plasma CVD equipment. Claim 3: RF plasma CVD according to claim 1.
In the apparatus, holes formed in the RF end electrode shower supply surface pass through a common point on the shower supply surface. direction is 6
RF plasma CVD characterized by being formed at each vertex position of a large number of minimum equilateral triangles formed by three groups of equally spaced parallel lines each including three straight lines shifted by 0°
Device. 4. Using the apparatus according to any one of claims 1 to 3, the pressure of the film-forming gas is set to a pressure that can be discharged under the RF voltage supplied to the RF end electrode on the substrate. A thin film forming method characterized by forming a thin film on.