JPH04285174A - Ecr plasma treating device - Google Patents

Abstract

PURPOSE:To form a diffused magnetic field capable of uniformizing the infrasurface distribution of the speed to treat the surface of a substrate in the ECR plasma treating device in which ECR plasma is produced by the interaction between the magnetic field and microwave in the cylindrical microwave resonator, and the plasma is introduced into the adjacent reaction chamber from the plasma drawing port in the end face of the resonator by the diffused magnetic field to apply CVD, etc., to the surface of the substrate in the reaction chamber. CONSTITUTION:A diffused magnetic field is formed by the cylindrical solenoid 6 arranged coaxially with a cylindrical microwave resonator 5, the length of the solenoid 6 is controlled to 0.8 times its inner diameter to reduce the axial thickness of the ECR resonance magnetic flux density region, hence the effect of the radial thickness distribution of the region on the radial distribution of the plasma density is reduced at the substrate position, and the end of the solenoid where the radial distribution of the magnetic flux density is uniformized or an external magnetic field is utilized for the treatment.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is an apparatus used in the manufacture of semiconductors, etc., which converts plasma generated by electron cyclotron resonance (hereinafter abbreviated as ECR) between microwaves and a magnetic field into CVD (Chemical Vapor Deposition).
The present invention relates to an ECR plasma processing apparatus used for processing substrate surfaces, such as thin film formation and etching by por deposition.

0002

[Prior Art] As this type of microwave plasma processing apparatus, an ECR (Electron Cyclotron) is used.
(Resonance) Process technology using plasma is attracting attention. ECR plasma is based on the principle of accelerating electrons using the resonance effect of a magnetic field and microwaves, and using the kinetic energy of the electrons to ionize gas to generate plasma. Electrons excited by microwaves move circularly around magnetic lines of force, and the condition in which centrifugal force and Lorentz force are balanced is called the ECR condition. When the centrifugal force is represented by mrω2 and the Lorentz force is represented by -qrωB, the condition for these to be balanced is ω/B=q/m. Here, ω is the angular frequency of the microwave, B is the magnetic flux density, and q/m is the specific charge of the electron. Microwave frequencies are industrially recognized2
．． 45 GHz is commonly used, with a resonant magnetic flux density of 875 Gauss.

As an example of the ECR plasma CVD and etching apparatus described above, the one shown in FIG. 5 is known. The configuration and operation of this device will be outlined below. First, the plasma generation chamber 3 and the reaction chamber 9 are evacuated by an evacuation means (not shown), and the microwave generated by the microwave generator 17 is supplied to the plasma generation chamber 3 by flowing O2 gas from the gas supply means 4 into the plasma generation chamber 3. Waves are introduced into the plasma generation chamber 3 via a waveguide 1 which is a means of transmitting the waves. A vacuum window 2 is provided between the waveguide 1 and the plasma generation chamber 3 to airtightly isolate the waveguide 1 side under atmospheric pressure from the evacuated plasma generation chamber 3. A metal plate aperture 7 having a large-diameter opening 7a in the center is attached to the upper part of the plasma generation chamber 3, and this aperture 7 and the plasma generation chamber 3 constitute a semi-open microwave resonator. . An excitation solenoid 6 is arranged outside this resonator, and a resonant magnetic flux density region is formed within the resonator 5 to efficiently generate plasma. This plasma is pushed out into the reaction chamber 9 along the magnetic field lines formed by the solenoid 6, and is supplied from the reaction gas supply shower 20 into the space facing the substrate table 10 using, for example, monosilane gas (SiH).
4) is supplied and this gas is activated by the plasma, the activated species react with the substrate 11, which is the sample to be processed, and a silicon oxide film is formed on the surface of the substrate.

0004

[Problem to be solved by the invention] Conventional ECR of this type
In addition to Japanese Patent Publication No. Sho 62-43335, various technical contents have been disclosed as a plasma processing apparatus.

Generally speaking, one of the most important characteristics of a semiconductor processing process is the uniformity of the in-plane distribution of processing speed. For example, in the 6-inch wafer processing equipment most commonly used today, the in-plane distribution of processing speed normally required is ±5% or less. However, in ECR plasma, the technology for reaction control to make the in-plane distribution uniform is still immature, so for a 6-inch wafer, at best the in-plane distribution is ±15%. That was the limit.

An object of the present invention is to provide an ECR processing apparatus that can significantly improve the in-plane distribution of processing speed.

[0007]

[Means for Solving the Problems] In order to solve the above problems, the present invention has an opening formed in a cylindrical shape and hermetically closed by microwave transmission windows on both end faces, and a plasma drawer formed by an aperture. ECR plasma is generated in a microwave resonator equipped with an opening by the interaction of a magnetic field and microwaves, and this plasma is guided to an adjacent reaction chamber from a plasma extraction port on the end face of the resonator by the magnetic field diffusion effect, and a reaction occurs. ECR uses the action of active species and ions generated by plasma to perform processing reactions such as CVD and etching on a semiconductor substrate mounted on a substrate stand in the room.
In the plasma processing apparatus, a cylindrical solenoid disposed coaxially with the microwave resonator is used as a means for generating the magnetic field, and its axial length is 0.8 times or less the inner diameter.

The cylindrical solenoid thus formed has a geometric center located inside the microwave resonator of the microwave transmission window that hermetically closes the opening on one end face of the microwave resonator. It is preferable to arrange it so that it is located on the side opposite to the internal space on the surface on the space side.

[0009] Furthermore, the resonant magnetic flux density region formed by a cylindrical solenoid whose axial length is 0.8 times or less the inner diameter is spaced axially from the geometric center of the solenoid by at least 1/4 of the solenoid length. It is preferable to use a device in which the solenoid current is adjusted so that the solenoid is located at the same position.

[0010] Furthermore, it is even more preferable that the device is provided with means for driving and positioning the cylindrical solenoid in order to vary the relative position in the axial direction between the cylindrical solenoid as the means for generating a magnetic field and the microwave resonator. It is.

[0011] The cylindrical solenoid is also preferably constructed using an internally water-cooled copper tube for the winding.

0012

[Operation] In an ECR plasma processing apparatus, in order to make the in-plane distribution of processing speed uniform, it is important to ensure uniformity of plasma density in the plasma generation region. EC
R plasma is generated by the interaction between the electric field generated by microwaves and the magnetic field generated by the solenoid.
The effect of the electric field is that the electron energy that contributes to ionization is proportional to the electric field strength, so in the same magnetic field, increasing the electric field strength can improve the uniformity of the radial distribution of plasma density. However, the degree of ionization when a magnetic field and a microwave electric field are combined suddenly decreases when the magnetic flux density deviates from the resonant magnetic flux density, and the radial distribution of the resonant magnetic flux density region becomes critical to the radial distribution of the plasma density. Affect. It is now difficult to compensate for the non-uniformity of plasma density due to the radial distribution of the resonant magnetic flux density region by the strength of the electric field. Mechanics (described in detail in Corona Publishing). Therefore, the uniformity of the resonant magnetic flux density region in the radial direction within the resonator is decisively more important than the uniformity of the microwave intensity.

The present invention provides a uniform distribution in the radial direction of the ECR resonance magnetic flux density region by devising the shape of the solenoid using a method different from the conventional method, thereby improving the in-plane distribution of wafer processing that could not be obtained with the conventional method. The aim is to improve the

[0014] In order to equalize the radial distribution of magnetic flux density, the usual idea is to use an ideal solenoid. An ideal solenoid is a solenoid with infinite length, and in order to approximate this in concrete design, it is common to create a solenoid with a longer length than its diameter and use a magnetic field near its geometric center. Met. In fact, when viewed from the geometric center of the solenoid, the distribution of magnetic flux density in the radial direction is more uniform the longer the solenoid is.

FIG. 2 shows a diagram regarding the shape of the solenoid and the uniformity of the radial magnetic flux density. The magnetic flux density at the geometric center of the cylindrical solenoid is Bo, the magnetic flux density at the axial center of the inner peripheral surface of the solenoid is Bm, and κ=Bm/Bo
Therefore, it is considered that the closer the solenoid is to κ = 1, the better the solenoid is, and for this purpose, the ratio of the solenoid's length to inner diameter, that is, β = b / a1, should be increased, and in fact, such a design is not practical. has been adopted by However, experiments have revealed that there are major disadvantages to the method of using such a long and thin cylindrical solenoid with a large β near its center. If we consider this theoretically, we can see that the ``elongated'' solenoid has a highly uniform magnetic flux density distribution in the axial direction, and this constitutes the cause of the disadvantage. What are its disadvantages?
The ECR resonance magnetic flux density region (hereinafter also referred to as the ECR zone) created using a "slender" solenoid has a deep depth in the axial direction, so when electrons move downstream along the magnetic field lines, the acceleration of the electrons around the magnetic field lines is extremely strong. It will be done. On the other hand, even a slight non-uniformity in the radial depth distribution of the ECR zone results in an extreme difference in the reaction rate. Taking CVD as an example, there are areas where the film quality is extremely good and the film thickness is large, and where the film quality is very thick. The problem is that areas with poor quality and small film thickness coexist on the wafer, leading to the result that the in-plane distribution of plasma processing ability is too poor to be practical.

The present invention is a method for overcoming such drawbacks of the "long and thin" coil, and its features can be simply described as a device using a "thick and short" solenoid. The advantages are described below.

One of the methods for calculating the magnetic flux density produced by a cylindrical solenoid with a finite length is to subtract the magnetic flux density produced by four semi-infinite length cylindrical coils, as shown in FIG. It is being This method is shown at the bottom of the figure, with a length of z1 - z2, an inner diameter of 2a1,
To find the magnetic field at position P on the axis z1 and radial direction ρ of a cylindrical coil with an outer diameter of 2a2, apply an axial current to the first cylindrical coil with a radius a2 and an infinite length from the end face to the left. The magnetic field h1 generated at position P when an excitation current is passed so that the density is 1 over the entire longitudinal section of the coil, and the magnetic field h1 which is generated at position P and whose radius is a2 and whose end face is z1 − from the first cylindrical coil.
When an excitation current is passed at the same current density in the opposite direction to the first cylindrical coil through a second cylindrical coil which is located at a position shifted to the left by z2 and has an infinite length to the left, it reaches position P. Using the generated magnetic field h2, an excitation current is applied in the opposite direction to the second cylindrical coil to a third cylindrical coil with a radius a1 and an end face located at the same position as the second cylindrical coil and having an infinite length to the left. Magnetic field h3 generated at position P when flowing with the same current density
Then, an excitation current is applied to a fourth cylindrical coil whose radius is a1, whose end face is located at the same position as the first cylindrical coil, and which has an infinite length to the left with the same current density in the opposite direction to that of the third cylindrical coil. It is calculated by vectorially adding the magnetic field h4 generated at position P when flowing at If we know how the axial component of the magnetic field generated by the finite length cylindrical coil changes in the radial direction, we can know the axial change in the radial distribution.

The magnetic flux density vector B (ρ, z) at the point P (ρ, z) due to the cylindrical coil is:

[0019]

[Math 1]

It is expressed by the function: Here, μ is the vacuum permeability, i is the current density of the current around the axis of the cylindrical coil,
a is the radius of the cylinder, and the origin of z is chosen at the end face of the cylinder.
The function h represents the magnetic field strength vector and is given in the form of a diagram in publicly known materials (for example, the Superconductivity Handbook published by the Institute of Electrical Engineers of Japan), and the axial component hz of the magnetic field strength is ρ,
When z is normalized by a, the graph shown in FIG. 4 is obtained.

In this graph, for example, ρ=0 and ρ=0.1
When comparing the curves, it can be seen that hz has a ratio of about 10:9 at z=-2, but as z approaches 0, the ratio approaches 1, and when z≧0, the ratio becomes 1. This means that as the magnetic flux diverges as it travels axially from the geometric center of the solenoid, the way the magnetic flux diverges on the axis is greater than the way the magnetic flux diverges off-axis, and the magnetic flux This shows that the density becomes uniform in the radial direction as the distance in the axial direction increases, and even with a "thick and short" solenoid, the uniformity of the magnetic flux density in the radial direction can be maintained by using it near the end of the solenoid or outside. It means that. Since the ECR plasma processing process uses the magnetic field divergence effect, the lateral dimension required of the ECR plasma that is the source of processing is not so large, even for wafers of about 6 inches or more. A thick and short solenoid provides a practically sufficient radial magnetic flux density distribution. Moreover, since the ECR resonance magnetic flux density region obtained in this way has a shallow depth in the axial direction, there is still room to compensate for the depth distribution of the resonance region by electron acceleration in the non-resonance region, and from a comprehensive perspective. ECR with excellent uniformity
It has been found that plasma processing equipment is provided.

Furthermore, if the geometric center of the cylindrical solenoid is located outside the surface of the microwave transmission window facing the microwave resonator internal space, the plasma will move in the direction of low magnetic flux density of the divergent magnetic field. As a result, there is no plasma moving toward the microwave transmission window, and thermal damage to the microwave transmission window can be prevented. (formation position, microwave power, etc.) can be changed significantly.

[0023] Furthermore, an EC is installed at a position axially away from the geometrical center of a short solenoid whose axial length is 0.8 times or less than the inner diameter.
When the R resonance magnetic flux density region is formed, the depth of the ECR resonance magnetic flux density region that contributes to electron acceleration becomes sufficiently short,
Experiments have shown that the influence of the radial depth distribution on the radial distribution of plasma density virtually disappears at the wafer position, and that the plasma density at the wafer position changes in the radial direction according to the uniform magnetic flux density. It was confirmed that the distribution was uniform.

[0024] The ECR plasma apparatus is an apparatus provided with means for driving and positioning the cylindrical solenoid in order to vary the relative axial position of the cylindrical solenoid as a means for generating a magnetic field and the microwave resonator. given that,
When the formation position of the ECR resonance magnetic flux density region is changed by changing the solenoid current, the optimum relative position of the solenoid with respect to the wafer can be easily determined.

Furthermore, if a cylindrical solenoid is formed using an internal water-cooled copper tube for the winding, a large current can be passed through the winding, so the formation position of the ECR resonance magnetic flux density region can be varied widely. , the optimal processing conditions can be determined more completely.

[0026]

Embodiment FIG. 1 shows an embodiment of the present invention. In the figure, the same members as in FIG. 5 are given the same reference numerals. In this embodiment, the microwave resonator 5 is formed in the TE113 mode, and the excitation solenoid 6 has an inner diameter D of 350 mm, a length L of 250 mm, and a thickness of 40 mm. arranged coaxially. The solenoid 6 is a drive/positioning device that drives the solenoid 6 in the axial direction and fixes it at a desired position.Although the detailed structure is not shown here, there is a screw that drives the table on which the solenoid 6 is placed up and down. Rotating rod and threaded rod,
From the relationship between the drive mechanism consisting of a motor equipped with a deceleration means, the rotation speed of the motor, and the amount of vertical movement of the solenoid,
The motor is equipped with a drive/positioning mechanism comprising a positioning device comprising a control means for setting a required number of revolutions in advance and stopping the rotation of the motor when the motor has rotated at the set number of revolutions. By increasing the current in the solenoid 6, the region where the ECR resonance magnetic flux density occurs can be located farther from the geometric center 21 of the solenoid 6 than 1/4 of the solenoid length. At this time, an internal water-cooled copper tube is used for the winding of the solenoid 6 to prevent the coil from becoming overheated due to the increase in current density in the coil.

In the apparatus of this embodiment, when the ECR resonance magnetic flux density region is formed at a distance of more than 1/4 of the solenoid length from the geometric center 21 of the solenoid 6 and the plasma density is measured using a probe, it is found that the plasma density in the reaction chamber is It showed a uniform distribution in the radial direction at the substrate position. In forming the silicon oxide film, a film thickness distribution of ±4% was obtained on a 6-inch substrate.

[0028]

[Effects of the Invention] According to the present invention, the following effects can be obtained.

In the device of the first aspect, since the ECR resonance magnetic flux density region is formed using a thick and short solenoid whose axial length is 0.8 times or less the inner diameter, the ECR resonance magnetic flux is The axial depth of the density region becomes shallower, and the influence of the radial distribution of the depth of the ECR resonance magnetic flux density region on the radial distribution of plasma density at the substrate position becomes smaller as the depth of this region becomes deeper. , it is smaller than the conventional thin and long solenoid, and the way the magnetic flux on the axis diverges as the magnetic flux formed by the cylindrical solenoid diverges as it advances in the axial direction is different from that of the magnetic flux at a position off the axis. The magnetic flux near the end of the solenoid or outside the solenoid can be used to form a plasma by utilizing the property of the divergent magnetic field, which is larger than the way it diverges, and as a result, the radial distribution of magnetic flux density becomes uniform with the axial distance. As a result, a sufficiently uniform in-plane distribution of plasma density can be obtained at the substrate position.

In the apparatus of the second aspect, due to the property that the plasma moves in the direction of low magnetic flux density of the divergent magnetic field, there is no plasma moving in the direction of the microwave transmission window, and thermal damage to the microwave transmission window can be prevented. It has become possible to significantly change the processing conditions (for example, the formation position of the ECR resonance magnetic flux density region, microwave power, etc.) in order to uniformize the in-plane distribution of the processing speed of the semiconductor substrate.

In the apparatus of the third aspect, the depth of the ECR resonance magnetic flux density region that contributes to the acceleration of electrons is sufficiently short;
The influence of the radial distribution of depth on the radial distribution of plasma density virtually disappears at the wafer location. According to experiments, it has been confirmed that the plasma density at the wafer position exhibits a uniform distribution in the radial direction in accordance with the uniform magnetic flux density. Thickness distribution was obtained.

In the device of the fourth aspect, when the formation position of the ECR magnetic flux density region is changed by changing the solenoid current,
The optimal relative position of the solenoid with respect to the wafer can be easily determined, and the optimal processing conditions can be set in a short time.

In the apparatus of the fifth aspect, since a large current can be passed through the winding, the formation position of the ECR resonance magnetic flux density region can be varied widely, and the optimum processing conditions can be determined more completely.

[Brief explanation of the drawing]

FIG. 1: E using a solenoid according to an embodiment of the present invention.
Vertical cross-sectional view showing an example of the overall configuration of a CR plasma processing apparatus

[Figure 2] Diagram showing how the ratio of magnetic flux density between the geometric center of the solenoid and the axial center of the inner peripheral surface changes depending on the axial cross-sectional shape of the solenoid.

[Figure 3] An explanatory diagram showing a method for determining the strength of the magnetic field outside the vicinity of the end face of a cylindrical solenoid using a semi-infinitely long cylindrical solenoid.

[Figure 4] Diagram showing changes in magnetic field strength near the solenoid end face depending on position in the magnetic field created by a semi-infinitely long cylindrical solenoid

[Figure 5
] A vertical sectional view of the entire device showing an example of the axial cross-sectional shape and arrangement position of a solenoid used in a conventional ECR plasma processing device.

[Explanation of symbols]

2 Vacuum window (microwave transmission window) 3 Plasma generation chamber 5 Microwave resonator 7 Aperture 9 Reaction chamber 10 Substrate stand 11 Substrate 17 Microwave generator

Claims (5)

[Claims] Claim 1: A magnetic field and a microwave are transmitted in a microwave resonator formed in a cylindrical shape and equipped with an opening hermetically closed by a microwave transmission window on each end face, and a plasma extraction port formed by an aperture. ECR plasma is generated by the interaction, and this plasma is guided from the plasma extraction port on the end face of the resonator to the adjacent reaction chamber by the magnetic field diffusion effect, and CVD,
In an ECR plasma processing apparatus in which processing reactions such as etching are performed by the action of active species and ions generated by plasma, a cylindrical solenoid arranged coaxially with a microwave resonator is used as a means for generating the magnetic field. An ECR plasma processing apparatus characterized in that its axial length is 0.8 times or less the inner diameter. 2. The ECR plasma processing apparatus according to claim 1, wherein the cylindrical solenoid as a means for generating a magnetic field is arranged such that the geometric center of the solenoid is located at an opening in one end face of the microwave resonator. An ECR plasma processing apparatus characterized in that a microwave transmission window that airtightly closes the microwave resonator is located on the opposite side of the inner space side of the microwave resonator. Claim 3: ECR according to claim 1 or 2.
In the plasma processing apparatus, the solenoid current is adjusted so that the region where the magnetic flux density that satisfies the ECR condition exists is located at least 1/4 of the solenoid length in the axial direction from the geometric center of the solenoid. E to be
CR plasma processing equipment. Claim 4: ECR according to claim 1 or 2.
An ECR in a plasma processing apparatus, characterized in that it is provided with means for driving and positioning a cylindrical solenoid for varying the relative axial position of a cylindrical solenoid serving as a means for generating a magnetic field and a microwave resonator. Plasma processing equipment. Claim 5: ECR according to claim 1 or 2.
An ECR plasma processing apparatus characterized in that a cylindrical solenoid serving as a means for generating a magnetic field is made using an internal water-cooled copper tube as a winding.