JPS6139730B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plasma processing apparatus using a plasma transport method, and is mainly directed to a processing apparatus for performing deposition or etching processing on a semiconductor substrate using a plasma flow.

The basic principle of this invention is a technology for transporting and depositing a desired substance onto a desired substrate using a plasma flow, which was filed and patented by the applicant (Patent No.
No. 611184) is publicly known. The outline of this technology will be explained below. FIG. 1 is a diagram explaining the principle of this plasma transport method, in which 1 is a plasma generation chamber in which gas or vapor of a desired substance is turned into plasma by electric discharge, 2 is a plasma outlet provided in the plasma generation chamber 1,
Reference numeral 4 represents a power source for applying an appropriate potential to the plasma generation chamber 1, and 5 represents a plasma gain body serving as the end point of the plasma flow, which corresponds to a desired substrate to be processed in the present invention. 6 is an ammeter for measuring the plasma current that has reached the profit unit 5; 7 is an airtight wall for keeping the plasma generation chamber 1 and the plasma flow path in a vacuum;
The inside of this surrounding wall is evacuated by a vacuum exhaust system (not shown). Reference numeral 8 denotes an electromagnetic coil that generates a coaxial magnetic field centered on the plasma flow path connecting the plasma outlet and the receptor 4.

In the above configuration, when plasma 3 is generated in the plasma generation chamber 1 by electric discharge, this plasma flows out from the plasma outlet 2 due to the diffusion effect due to the density difference inside and outside the generation chamber 1, and this plasma flows as a plasma flow 9. The coaxial magnetic field generated by the electromagnetic coil 8 condenses the beam into a beam and guides it to the plasma collector 5, so that ionic substances in the plasma are deposited on the plasma collector 5. That is, by transporting the desired material that has been turned into plasma from the plasma generation chamber 1 to the profit generating unit 5, a unique material transport method is achieved.

The degree of convergence and plasma density of the plasma flow, which is this means of transportation, change depending on the plasma density in the plasma generation chamber and the strength of the coaxial magnetic field. Therefore, when the magnetic field is weak, the plasma flow spreads greatly, and the fixed area of the receptor 5 However, if the magnetic field strength is increased to a certain level (e.g., 200 Gauss or more), the plasma density can be reduced from the plasma outlet 2, which is the starting point of the plasma flow 9, to the receiver at the terminal point 5. It can be kept constant without weakening. In other words, the coaxial magnetic field can be regarded as forming a magnetic pipe for the plasma flow 9.

FIG. 2 shows a sectional view of a specific configuration for carrying out this plasma transport method. In order to generate plasma, this device uses a method in which high-frequency oscillation power is generated by a magnetron, and this oscillation power is applied to a quartz discharge tube to cause discharge and generate plasma. In the figure, a magnetron 10 injects microwave power of about several GHz generated by the magnetron into a quartz discharge tube 13, which is a plasma generation chamber in a plasma generation section, by an outer wall 11 of the coaxial tube and a central antenna 12 of the coaxial tube. do. Microwave transmission through this coaxial tube can be achieved by setting an appropriate ratio of the diameter of the outer wall to the diameter of the central antenna.
Microwaves in TEM mode can be efficiently injected into discharge tubes, allowing relatively small discharge tubes to be made. Since the internal pressure of this discharge tube is maintained at a pressure suitable for discharge, that is, a pressure of 10 ^-2 to ^{10 -3} Torr, discharge is caused by injection of microwave power, and plasma 14 is generated. This quartz discharge tube has the role of keeping the discharge part for plasma generation and the vacuum chamber connected to it airtight above atmospheric pressure, and keeping the introduced target gas at a pressure suitable for discharge. This prevents plasma contamination from the outer wall, and is particularly effective when used for the purpose of semiconductor processing in this method.

Since the temperature of this discharge tube rises significantly due to the discharge inside the tube, a pressurized cooling air inlet 15 is provided in a part of the coaxial tube, from which cooling air is introduced, and through the gap between the discharge tube and the coaxial tube, an exhaust port is provided. 16, the air that has cooled the outside of the discharge tube is discharged. The center antenna 12 is connected to the magnetron antenna at the left end, but there is a hollow part 1 in a part of it.
Cooling air is introduced into this hollow portion through a pressurized air inlet 17 having a diameter of 8, and the air is jetted out from the tip of the antenna 12, thereby cooling the inner recess of the discharge tube 13 and discharging it through the discharge port 16.

Coaxial electromagnets 20 and 22 are located on the outer periphery of the plasma generation section via support stands 19 and 21, and the magnetic fields created by these electromagnets lengthen the orbit length of the electrons in the discharge generated by the injection of microwave power and generate the plasma 14. In addition to increasing the degree of ionization, the following coaxial electromagnet for transportation 2
Together with the coaxial magnetic field created by 4 and 25, a magnetic pipe for plasma transport is formed. Reference numeral 27 denotes a magnetic shielding plate for the magnetron 10, which is attached so that the oscillation characteristics of the magnetron are not affected by the magnetic field generated by the coaxial electromagnet.

The plasma processing chamber 32 is made of non-magnetic stainless steel, etc., and its internal pressure is 10 ^-5 to ^{10 -7} Torr.
It is maintained at a certain level. Plasma 14 generated in a quartz discharge tube 13 serving as a plasma generation chamber is introduced as a plasma stream 30 into this processing chamber through a plasma outflow tube 29 made of quartz. In addition, 28a, 2
Reference numeral 8b indicates an introduction part for introducing the target raw material gas into the discharge tube. This plasma processing chamber 32 is exhausted by an exhaust system 33 through an exhaust port 34 .
There are coaxial electromagnets 24 and 25 supported by support stands 23 and 25 around the plasma processing chamber, and a plasma flow is transported onto a target semiconductor substrate 35 by a magnetic pipe formed by these electromagnets. At this time, the magnetic field strength of the electromagnet is adjusted so that the plasma flow 30 spreads uniformly over the entire surface of the substrate 35. Although the electromagnets 24 and 26 are shown spaced apart from each other in the figure, in general, a spacing between the electromagnets of this order (40 cm) will not cause the plasma to diverge significantly in practice, and will not interfere with the intended plasma transport.

The semiconductor substrate 35 is held on a support stand 36 made of stainless steel or the like, which is heated by a heating mechanism (not shown) as necessary, and a plasma current is measured through this support stand, but a support stand 36 is installed before that. Plasma is sent onto the substrate for a desired time by opening and closing the shutter 37. Further, in this figure, by introducing a probe 31, an arbitrary potential can be applied to the transport plasma.

As described in detail in Japanese Patent Application No. 11976/1983 filed by the present applicant, the plasma processing apparatus constructed in this manner has extremely excellent processing effects in deposition etching on semiconductor substrates. However, when this configuration was operated for a long time, it was found that it had the following drawbacks and could not fully demonstrate its function as it was.
These drawbacks are the following three points.

Referring to FIG. 2, coupling occurs between the tip of the central antenna 18 of the coaxial tube and the semiconductor substrate 35, and the surface of the semiconductor substrate is heated in a spot-like manner, increasing the temperature. This is a particularly strong phenomenon because the antenna and the board are connected in a straight line by a magnetic pipe. In general, there is a possibility of coupling with other ground parts as well.

Inside the discharge tube, a cylindrical plasma is first generated because it is a coaxial tube, but this is not sufficiently diffused and becomes a plasma flow, so the cylindrical plasma flow with low density in the center becomes Occur. In addition, coaxial plasma with high density is generated in the center and is transported as a plasma flow.

When power is concentrated at the center antenna of a coaxial tube in connection with the above, the concave part of the discharge tube is structurally complex and fragile, so the bottom of the concave part breaks during operation, causing an accident where atmospheric pressure enters the discharge tube. occurs often.

These phenomena depend on the strength of the magnetic field in the discharge area, the degree of vacuum,
It appears and disappears depending on the application state of the microwave output, but is extremely unstable, and is a major hindrance to the application of this device to the production process of deposition and etching, which is the purpose of this device.

The present invention will be described in detail below with reference to Examples.

FIG. 3 shows the plasma generation section of the plasma transport device according to the present invention. In FIG. 2, this corresponds to the coaxial tube 11, the discharge tube 13, and the portion to the left of the mounting flange. What characterizes the new configuration shown in FIG. 3 is that the coaxial output of the magnetron 38 is coupled at right angles to the rectangular waveguide 39, thereby performing so-called coaxial line to rectangular waveguide conversion.
This is to generate microwaves in the TE ₁₀ mode, which is the main mode, in the rectangular waveguide 39 from the microwaves in the TEM mode. As shown in the figure, this rectangular waveguide 39 is connected to a circular waveguide 41 via a tapered matching section 40. In this case, microwaves in the TE ₁₁ mode, which is the main mode, are excited in the circular waveguide, and microwave power is injected into the quartz discharge tube 42 to cause discharge and generate the desired plasma. Since power can be injected into the cylindrical waveguide in this way, the quartz discharge tube 42 has a very simple shape as shown in FIG. have In addition, a compressed air introduction hole 44 and an exhaust port 45 are provided to cool the quartz discharge tube. The plasma generated in the discharge tube has the effect of increasing the trajectory length of the electrons generated by the discharge by the coaxial electromagnet on the outside, increasing the degree of ionization of the plasma.At the same time, the plasma generated in the discharge tube is connected to the next coaxial electromagnet along with a magnetic pipe for plasma transport. form.

By using the above structure, the above-mentioned drawbacks can be solved as follows.

By employing a circular waveguide, it is possible to eliminate the cause of coupling with the semiconductor substrate and other grounded parts.

Since the TE ₁₁ mode, which is the main mode, is used, electric lines of force are generated in the diametrical direction perpendicular to the waveguide, so a uniform plasma is generated on the cross section of the cylinder, and a plasma flow with a uniform density distribution can be obtained. Further, since the electrons in the plasma are accelerated perpendicularly to the direction of the magnetic field, the horizontal component of the electrons in the plasma flow can be reduced.

The structure of the discharge tube is simplified, making it possible to make a durable one, and since there is no damage due to electric field concentration, it has a long life.

For example, if we choose the oscillation frequency of the magnetron to be 5.45 GHz, which is easily available commercially, the wavelength will be 12.245 cm as a constant related to a circular waveguide, and if the waveguide diameter is 10 cm, the cutoff wavelength will be 17.06 cm. ,
Since the oscillation wavelength is shorter than the cutoff wavelength, microwave power can be introduced using a circular waveguide with a diameter of 10 cm. Note that the tube wavelength in this case is 17.586 cm. Figure 3 shows an example of using a tapered matching section to generate a TE ₁₁ mode wave in a circular waveguide, but the same purpose can also be achieved using a step converter or orthogonal converter. can.

The microwave power injected into this circular waveguide is consumed as microwave discharge in the discharge tube, but the microwaves not consumed in discharge pass through the discharge tube, and some are connected to the waveguide. It is reflected at the connection point with the vacuum chamber, but most of it enters the vacuum chamber as it is and is diffused. This becomes the inactive part of the injected microwave power. Therefore, as shown in Fig. 4, a disk 46 or cylinder 47 with an aperture diameter smaller than the cutoff wavelength is attached next to the waveguide to reflect the microwaves that have proceeded without being absorbed within the discharge tube and discharge them again. It can be re-passed through the plasma in the tube to improve absorption efficiency.

In general, this plasma transport device can generate plasma for deposition or plasma for etching in a plasma generating section, and have the function of a deposition or etching process. In the case of this etching, microwave discharge of a fluorinated ethylene gas such as Freon (CF ₄ ) is mainly performed. The fluorine ions generated at this time are transported as a plasma stream and etch the semiconductor substrate, but at the same time, they may also etch the tube wall of the quartz discharge tube, resulting in holes in the discharge tube due to long-term use.

In particular, a coaxial tube-connected discharge tube as shown in FIG. 2 has a complicated structure with a recessed portion, so the tube wall becomes thinner in the recessed portion and tends to be prone to holes.

In the present invention, by introducing a circular waveguide, the structure of the discharge tube is simplified as shown in Fig. 3, and it is now possible to form a discharge tube with a uniform wall thickness. A lining 48 can be inserted into the discharge tube as shown. If this lining is made of boron nitride (BN), which is resistant to attack by fluorine ions, the life of the discharge tube can be significantly extended. In addition, even in the case of deposition, since the deposition substance adheres to the lining, when cleaning the discharge tube, simply replacing the lining allows the user to immediately move on to the next task, resulting in the effect of shortening the time required for cleaning the device.

As described in the above embodiments, for example, by using a plasma generation section using a circular waveguide in the plasma transport device, the configuration can be simplified, and the various drawbacks of using a conventional coaxial tube can be eliminated. The above objective was achieved.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the general principle of transporting materials using plasma flow using the plasma transport method, and Figure 2 is an example of a plasma transport apparatus for performing deposition and etching using the principle shown in Figure 1. The cross-sectional views shown in FIGS. 3 to 5 are cross-sectional views showing essential parts of the plasma transport device in each embodiment according to the present invention. DESCRIPTION OF SYMBOLS 1... Plasma generation chamber, 2... Plasma outlet, 3... Generated plasma, 4... Power source, 5... Receiver, 6... Ammeter, 7... Vacuum chamber, 8... Coaxial electromagnet, 9 ...Plasma flow, 10 ... Magnetron, 11 ... Coaxial tube outside, 12 ... Coaxial tube antenna, 13 ... Discharge tube, 14 ... Generated plasma, 1
5... Cooling air inlet, 16... Cooling air outlet, 1
7...Cooling air inlet, 18...Hollow part, 19...
Electromagnet support stand, 20... Coaxial electromagnet, 21... Electromagnet support stand, 22... Coaxial electromagnet, 23... Electromagnet support stand, 24... Coaxial electromagnet, 25... Electromagnet support stand, 26... Coaxial electromagnet, 27 ... Magnetic shielding plate, 28 ... Gas inlet, 29 ... Plasma outflow tube, 30 ... Plasma flow, 31 ... Probe, 3
2... Vacuum chamber, 33... Exhaust system, 34... Exhaust port, 35... Receiver, 36... Receiver support stand, 3
7...Shatsuta, 38...Magnetron, 39...
...Rectangular waveguide, 40...Taper matching part, 41...
Circular waveguide, 42...Discharge tube, 43...Support flange, 44...Cooling air inlet, 45...Cooling air outlet, 46...Microwave reflecting disk, 47...Microwave reflecting cylinder, 48... …lining.

Claims (1)

[Claims] 1 a plasma generation chamber having a plasma outlet;
a plasma processing chamber that performs a deposition or etching process on a semiconductor substrate installed therein;
In a plasma processing apparatus equipped with a magnetic field that transports plasma generated in a plasma generation chamber from a plasma outlet to a semiconductor substrate, microwaves injected into a circular waveguide are used to generate plasma in the plasma generation chamber. A plasma processing device characterized by: