JPH02159027A - Plasma treatment device - Google Patents

Abstract

PURPOSE:To allow produced plasma to arise almost uniformly in the inside of a reaction tube and improve the uniformity of plasma treatment in the face of a semiconductor wafer by making the rise direction in plasma move with the elapse of treatment in a device to perform treatment by causing plasma to arise in a reaction vessel. CONSTITUTION:When a switch 31 is connected to a terminal (a) and high frequency signals RF are impressed to electrodes 21A and 21B, an electric field E in the reaction tube 10 takes place in a vertical direction. When the switch 31 is connected to a terminal (b) and the high frequency signals RF are impressed to electrodes 22A and 22B, the electric field E takes place in a state that it rotates 60 deg. to the vertical direction. When the switch 31 is connected to a terminal (c) and the high frequency signals RF are impressed to the electrodes 23A and 23B, the electric field E takes place in a state that it rotates 120 deg. to the vertical direction. Consequently, a rotating electric field takes place in a reaction tube 10 and it not only overcomes the ununiformity of electric field distribution in the peripheral direction of the reaction tube but also makes the radial electric field distribution in the reaction tube almost uniform.

Description

[Detailed description of the invention] [Industrial application field]

This invention is a plasma processing device that performs plasma etching, plasma CVD, etc.! Regarding.

[Conventional technology]

Reaction products such as polycrystalline silicon and 3102 gradually adhere to the inner wall of a reaction tube, which is a reaction container of a semiconductor manufacturing apparatus that performs CVD processing, due to a chemical reaction between the heated reaction tube and a reaction gas. If this is left unattended, the deposits will peel off and adhere to the surface of the semiconductor wafer being processed, contaminating it, so it is necessary to periodically remove the deposits from the inner wall of the reaction tube. As a method for removing this deposit on the inner wall of the reaction tube, a method using plasma etching has been proposed, which does not require the removal of the reaction tube and can be carried out with a simple operation (see Japanese Patent Laid-Open No. 196820/1982). . Fig. 8 shows an example of a processing apparatus used in this method, and Fig. 9 is a view of this apparatus from above. A gas supply port 3 is a gas exhaust port from the reaction tube 1. A heater 4, which has a hollow cylindrical coil wound around the outer periphery of the reaction tube 1, is placed at a predetermined distance from the reaction tube 1.The reaction tube 1 is heated by the heat of the heater 4. It is heated to a predetermined temperature. A pair of t-poles 5A are provided in the space between the heater 4 and the reaction tube 1.
, 5B are provided. As shown in FIG. 9, the counter electrode 5
A and 5B each have a curved surface adapted to the external shape of the reaction tube 1, and are made of conductors having a width spanning a predetermined angular interval on the outer circumference of the reaction tube 1, and are opposed to each other with the reaction tube 1 interposed therebetween. It is arranged like this. For example, 13.
A high frequency signal of 75HH2 is supplied, which generates an electric field between the picture electrodes 5A and 5B, and the reaction gas in the reaction tube 1 is turned into plasma.1 When removing deposits from the inner wall of the reaction tube 1, This reaction gas is, for example, HF3 or CF4+0.
It is said to be an etching gas such as 2. The deposits on the inner wall of the reaction tube 1 are etched and removed by this etching gas.

[Problem to be solved by the invention]

By the way, since the conventional processing device shown in FIGS. 8 and 9 has one pair of electrodes, the electric field E (see FIG. 9) generated when a high frequency signal is supplied to the poles is When viewed in terms of direction, there are strong and weak areas. Therefore, in order to improve the non-uniformity of the electric field in the circumferential direction, there was a risk that etching would not be done uniformly when cleaning the inner wall of the reaction tube.
As shown in Figure 0, eight poles 7 are provided on the outer periphery of the reaction tube.
Next to each other! It is conceivable to use the poles as a pair of electrodes and to supply a high frequency signal from the high frequency signal generation source 8 between these pairs of electrodes. In this way, as shown in FIG. 10, the electric field E is generated uniformly in the circumferential direction, and the inner wall of the reaction tube can be cleaned well. However, in this method, the electric field becomes non-uniform in the radial direction of the reaction tube. Therefore, when performing plasma processing on a semiconductor wafer etc. placed in the reaction tube, There is a drawback that the uniformity of etching and film formation deteriorates. The present invention takes advantage of the above points and aims to provide a plasma processing apparatus that can uniformly generate an electric field in the circumferential direction and radial direction of a reaction tube.

[Means to solve the problem]

This invention is an apparatus for processing by generating plasma in a reaction vessel, in which the direction in which the plasma is generated is moved over time. Multiple pairs inside the reaction vessel! By providing poles and supplying high-frequency signals with mutually different phases or frequencies to the multiple pairs of electrodes, an electric field whose direction changes over time is generated, and the direction of plasma generation can be moved over time. .

[Effect]

Since the direction in which plasma is generated inside the reaction vessel is moved chronologically, plasma can be generated uniformly within the reaction vessel.

【Example】

FIG. 1 shows an example in which the present invention is applied to a vertical reactor. In this example, the reaction vessel is composed of a cylindrical reaction tube 10 made of quartz, and has a double tube structure including an outer quartz tube 11 and an inner quartz tube 12. However, the reaction tube 10 does not have to have such a double tube structure. In the quartz inner tube 12 of the reaction tube 10, for example, 100
A boat 13 is provided that can horizontally place up to 150 sheets, one sheet at a time. A heat insulating cylinder 14 is provided below the boat 13. The boat 13 and the warming chamber 14 are rotatable by a rotating shaft 15 provided at their central positions. That is, the rotating shaft 15 is rotated by a motor (not shown) in the direction shown by the arrow in the figure, thereby rotating the entire boat 13 and rotating each semiconductor tool 9 in a horizontal plane. As a result of this rotation of boat 13,
Processing, cutting, and film formation on the surface of the semiconductor wafer 9 are performed uniformly. 16 is a reactant gas supply port. The reactant gas supplied from this supply 016 is guided to a multi-hole injector 17 made of a quartz tube in this example, and has holes in this inlet tube 17, as shown by arrows in the figure. Therefore, the gas is injected toward the semiconductor wafers 9 stacked in large numbers in the knitting direction, and the gas can be uniformly introduced into the reaction tube 10. The introduced gas flows through the quartz inner tube 12 and the quartz outer tube 1.
1 and is exhausted to the outside from the exhaust port 18. A filter 19 having a hollow cylindrical coil wound around the outer periphery of the reaction tube 10 is arranged at a predetermined distance from the outer tube 11. In the space between the heater 19 and the outer tube 11 of the reaction tube 10,
Multiple pairs of electrodes 20 are provided. In this example, the electrode 20
are provided in three pairs. FIG. 2 is a view of the apparatus shown in FIG. 1 viewed from the top of the reaction tube 10, and as shown in FIG.
electrodes 21A, 22^, 23A, 218, 228, 2
3B are provided, and those with the same number are used as paired electrodes. Each electrode has a curved surface adapted to the external shape of the reaction tube 10, and is made of a conductor having a width spanning a predetermined angular interval on the outer circumference of the reaction tube 10. facing the direction. Then, the pair of electrodes 21A, 21
B, 22^, 22B, 23A, and 23B are arranged to face each other via the reaction tube 10, respectively. This electrode 20 has a uniform heating effect inside the reaction tube 10, and is made of heavy metals such as Inconel, Na, K, H (J, Fe, C).
It is made of a material that does not transmit U, Ni, etc., such as silicon carbide, conductive ceramic, graphite, etc. And these three pairs of t-poles 21^, 21B, 22A,
A high frequency signal RF from a high frequency power supply 30 is sequentially switched and supplied to 22B, 23A, and 23B by a switch circuit 31. That is, as shown in FIG. 3A,
A high frequency signal RF from a high frequency power source 30 is sequentially supplied to each pair of opposing electrodes for a predetermined time by switching the switch circuit 31 to terminals a, b, and c sequentially for a predetermined time. In this case, when the switch 31 is connected to the terminal a and the high frequency signal RF is applied to the electrodes 21A and 21B, the electric field E in the reaction tube 10 as shown in FIG.
occurs vertically. A switch 31 is connected to the terminals 22A and 22B.
When a high frequency signal RF is applied to , an electric field E is generated rotated by 60 degrees with respect to the vertical direction, as shown in FIG. 3C. Switch 31 is connected to terminal C and the current is 123A.
, 23B, the electric field E is generated in a state rotated by 120 degrees with respect to the vertical direction, as shown in the third diagram. Therefore, a rotating electric field is generated within the reaction tube 10, and it is possible to eliminate non-uniform electric field distribution in the circumferential direction of the reaction tube, and also to make the electric field distribution in the radial direction of the reaction tube substantially uniform. This rotating electric field generates a discharge in the reaction tube 10, converting the reaction gas supplied into the reaction tube 10 into plasma, and this plasma cleans the inner wall of the reaction tube, plasma etches semiconductor wafers, etc. placed in the reaction tube, and performs plasma etching. Plasma processing such as CVD can be performed. The following configuration can also be used to generate a rotating electric field. That is, as shown in FIG. 4, two pairs of electrodes 41A, 41B each made of a conductor have an angular width of about 90 degrees.
42^ and 42B are arranged so as to be perpendicular to each other. Also,
High frequency power supplies 43 and 44 that respectively generate high frequency signals RF1 and R[2 having phases different from each other by 90 degrees are provided, and the high frequency signal RF1 from the high frequency power supply 43 is transmitted to the pair of electrodes 41^,
41B, a high frequency signal RF2 from a high frequency power source 44 is supplied to the pair of electrodes 42A and 42B, respectively. In this way, electric fields E1 and E2 that are orthogonal to each other are generated in the reaction tube 10, so that a rotating electric field can be generated. Alternatively, a uniform electric field may be generated within the reaction tube by changing the frequencies of the high-frequency signals RFI and RF2. Some examples of plasma treatment processes using the above apparatus will be described below. (1) Cleaning the inner wall of the reaction tube 10 The boat 13 inside the reaction tube 10 is taken out, and the lower end of the reaction tube 10 is covered to make it airtight. Then, the inside of the reaction tube 10 is controlled to be evacuated using a vacuum pump so as to maintain, for example, IXI' Torr. In this state, for example, increase the flow rate to 10
An etching gas such as NF3 is supplied into the reaction tube 10 from the gas supply port 16 for a predetermined period of time while adjusting the etching gas to approximately 0.003 CCH. At this time, the inside of the reaction tube 10 is 0.2 to I Torr.
Then, as described above, the frequency is set to 400 kHz to the plurality of pairs of electrodes 20
, high frequency signals of output IKW are supplied, and the etching gas in the reaction tube 10 is turned into plasma. Then, deposits on the inner wall of the reaction tube 10 are removed by plasma etching. In this case, plasma is generated uniformly in the circumferential direction of the reaction tube 10 due to the rotating electric field.
Cleaning inside 0 is done well. (11) Removal of the native oxide film on the surface of the semiconductor wafer 8 and subsequent film formation by thermal CVD.For example, as shown in FIG. 5, 5102 insulation Jl! 52 is deposited, and this 5IO2
Consider a case where a predetermined position of the insulating film 52 is removed by etching, and a wiring film 54 of, for example, polysilicon is produced by thermal CVD on the surface of a semiconductor wafer in which an open area 53 is formed in the etched away portion. At this time, if the wafer is exposed to the atmosphere before forming the polysilicon film 54, an S i 02 natural oxide film 55 will be formed on the surface of the region 53, as shown with diagonal lines in the figure. Since this 5i02 natural oxide film 55 is an insulating film, if the polysilicon wiring WA 54 is produced as it is, the conductivity of the contact portion between the wiring film 4 and the M region portion 53 of the base film will deteriorate. Therefore, when inserting a semiconductor wafer into a reaction tube of a thermal CVD apparatus, after carefully removing the natural oxide film 5102 generated on the polysilicon film on the surface of the wafer before film formation, A process for forming a wiring film such as the following will be explained. 100 to 150 semiconductor wafers before forming a wiring film are placed on the boat 13. At this time, the temperature of the furnace is set to 700° C. by the heater 19. The temperature of this furnace is maintained at 700° C. during all the following steps. In this state, after evacuating the inside of the reaction tube 10 with the vacuum bomb 1,
NF3 is supplied as an etching gas into the reaction tube 10 from the gas supply port 16 at a flow rate of 10O3CCH. In addition to etching gas NF3, hydrogen H2
is supplied into the reaction tube 1° at a flow rate of 100 SCCH. At this time, the gas can be almost uniformly supplied to a large number of wafers using the injector 17. Note that at this time, the pressure inside the reaction tube 10 is controlled to be 0.5 TOrr. Hydrogen H2 was added when the thickness of the natural oxide film SiO2 was 2
Since it is thin, the etching speed is 10 to 30 people/
It's there to slow it down to nin. The radical of NF3 is H
It reacts with 2 and is consumed as HF, reducing F radicals and slowing down the etching rate. The slower etching rate makes it easier to control the control time and improves the uniformity of etching both within and across the wafer. In this state, a high frequency signal with a frequency of 500 kHz and an output of 200 - is supplied to the plurality of pairs of electrodes 20 for a predetermined period of time in the same manner as described above. Then, a rotating electric field is generated within the reaction tube 10 and discharge occurs, thereby turning the etching gas NF3 into plasma. Here, the temperature dependence of the plasma etching rate of silicon and 5102 film is as shown in FIG. The etching rate of the 5102 film is approximately 20 times faster than that of the 5102 film, but at the high temperature of 700°C used in thermal CVD equipment, the etching rate is 1. As is clear from FIG. 6, the etching speeds of both are approximately the same. Therefore, for example, if a semiconductor wafer with a natural oxide film formed on the polysilicon film on the surface is heated to 700°C,
When 5 plasma etching is performed at a high temperature, the thick 5L021112 film is hardly etched compared to its thickness, but the thin S10□ native oxide film is etched and removed by 10 to 20 people. . After the natural oxide film is removed, the N area is over-etched.
Since the etching speeds of the regions 102 and 81 are almost the same, the region (2) is not etched too much. At a high temperature of 700° C., thermal CVD treatment can be continued. Therefore, in a subsequent second step, after the etching gas is exhausted, a film forming gas is supplied to the reaction vessel, thereby making it possible to produce, for example, a polysilicon wiring film by thermal CVD processing. After the natural oxide film is removed from the semiconductor wafer obtained as a result of the above process, a wiring film such as polysilicon is continuously formed in a vacuum without being exposed to the atmosphere. Since there is no natural oxide film in the contact area between the wiring film and the underlying film, the resistance value of this contact area can be made smaller than in the conventional case, and the adhesion between the wiring film and the underlying film is improved. The above description has been made by taking as an example the case where the present invention is applied to the process of forming a polysilicon film, but the present invention is also effective in the process of forming a silicon nitride film S i H4, a tungsten W film, and a 5102 film. This is because the natural oxide film has many pinholes, its thickness is not constant, and its properties as an insulating film are significantly inferior to that of a 5IO2 film formed by CVD. For example, in the capacitor formation process. By removing the native oxide film on polysilicon before forming a SiH4 film on polysilicon, a high-quality capacitor can be formed. Note that under the above conditions, the etching rate is approximately 10
The etching rate was uniform within ±10% within the wafer surface and between wafer surfaces. Naturally oxidized 1111SiOz can be removed using only the etching gas NF3 without adding any other gas. However, in this case, the etching speed is 100 people/
lin or more, and the uniformity of etching is worse than the above example. The injector 17 is used to supply gas, and the rotating shaft 1
If the boat is rotated around 5 and the wafer is rotated, the uniformity of etching will be further improved both within and between the wafer surfaces. That is, since the injector 17 injects gas almost uniformly between a large number of wafers arranged in the vertical direction, unevenness in gas concentration due to differences in the vertical position of the wafers is eliminated, and etching is uniform between the wafer surfaces. Sexuality improves. In addition, when the wafer is rotated, the points on the wafer surface are not fixed at a fixed position in the reaction tube, but are exposed to the atmosphere at various positions, so etching within the wafer surface is affected. Improved uniformity. Since the discharge electric field near the electrode is strong, plasma generation is thought to occur near the electrode. Therefore,
The boat 13 is positioned in the reaction tube 10 at a position offset from the center of the inner tube 12 of the reaction tube 10, as shown in FIG. Make the boat rotate around the center. In this way, the wafer is rotated near a location where plasma generation is strong, so that uniformity within the wafer surface is further improved. Further, by devising the method of supplying the high frequency signal to the T4 pole as described below, it is possible to achieve more uniform generation of plasma within the reaction tube. That is, this method is a method in which a high frequency signal is applied in a burst manner to a plurality of pairs of electric currents 20 at a period of, for example, 0.1 to 0.5 seconds. That is, after etching gas flows between the wafers, a high frequency signal is applied to the electrode 20 for, for example, 0.1 seconds to remove the native oxide film, and after 0.1 seconds, the high frequency signal is supplied to the electrode. After the etching has stopped and the etching gas has sufficiently flowed, for example 0.1 seconds, a high frequency signal is again applied to the electrode 20 for 0.1 seconds. During the period when no voltage is applied, there is no non-uniformity in the electric field within the reaction tube, so the plasma is uniformly distributed within the reaction tube, and the process progresses.
Etching within the surface is made uniform. Note that the etching gas is not limited to NF3, for example, CF,
It is also possible to use etching gas such as +02 or the like. (iii) The interior of the reaction tube 10 for 7 plasma CVD is controlled to be evacuated to a predetermined low pressure state, for example, 0.1 to 3 orr, and the heater 19 is used to control the interior of the reaction tube 10 at, for example, 300 degrees. Set to C. Thereafter, the film forming gas is supplied into the reaction tube 10 for a predetermined time while controlling the flow rate from the gas supply port 16 while controlling the exhaust. For the 5102 film, the film forming gas is, for example, N 20 +S i
Ha, T E OS + 02.5i3NaJIl
For example, NH3+S i H4 is used. In this state, in the same manner as described above, a high frequency signal is supplied to the plurality of t-poles 20 to generate a rotating electric field in the reaction tube 1G,
A discharge is generated to turn the film-forming gas into plasma. As a result, a 5102 film and a 513N4 film are formed on the wafer surface. In this film-forming process, as in the process of removing the natural oxide film on the wafer surface, an injector is used to introduce gas into the reaction tube 10, and the boat is rotated to send a high-frequency signal to the electrodes. By applying in bursts at a predetermined period, the uniformity of film formation can be further improved. In the above example, by applying a high frequency signal with the electrode in close contact with the outer periphery of the reaction tube, a reaction tube made of quartz with a high dielectric constant exists between each pair of Ti, and the electrostatic Since the capacity is increased, plasma can be easily generated and the plasma intensity is increased. Therefore, the frequency of the high-frequency signal supplied to the electrodes is not as high as 13.75 MHz, which has been commonly used in the past, but is now as low as 10 MHz or less as described above, making it easier to shield surrounding equipment. becomes easier.

【Effect of the invention】

According to this invention, an electric field whose direction changes over time is generated inside a reaction tube by sequentially switching a plurality of pairs of electrodes or by supplying high-frequency signals having mutually different phases and frequencies to two pairs of electrodes. Therefore, the electric field inside the reaction tube becomes uniform in the circumferential direction and radial direction. Therefore, since the plasma generated based on this electric field is generated almost uniformly inside the reaction tube, the uniformity of plasma processing such as plasma etching and film formation within the semiconductor wafer surface is improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a plasma processing apparatus according to the present invention, FIG. 2 is a diagram of the apparatus shown in FIG. 1 viewed from above, and FIG. 3 is a diagram for explaining an example of the configuration of multiple pairs of electrodes. , FIG. 4 is a diagram showing another example of the configuration of multiple pairs of electrodes, FIGS. 5 and 6 are diagrams for explaining an example of a process using the plasma apparatus according to the present invention, and FIG. Fig. 8 is a diagram showing an example of a conventional plasma processing apparatus, Fig. 9 is a view of the apparatus of Fig. 8 viewed from above, and Fig. 10 is a diagram showing an example of the apparatus according to the invention. It is a figure which shows the structural example of multiple pairs of 1 poles. 10; Reaction tube 16: Gas supply port 18: Gas exhaust port 19: Heater 21A, 21B, 22^, 22B, 23A, 23
B, 41A, 41B, 42^, 42B, counter electrodes 30, 43, 44, high frequency power supply 31; Switch circuit agent Patent attorney Masami Sato'fI! 11 Figure 2 Figure 2 Data processing *Lise deposit Figure 1 Text letter ≦ n column Figure 10

Claims (2)

[Claims] (1) A plasma processing apparatus that performs processing by generating plasma in a reaction vessel, in which the direction in which the plasma is generated is moved over time. (2) In the plasma processing apparatus according to claim (1),
A plasma processing apparatus that generates an electric field whose direction changes over time inside the reaction vessel by supplying high-frequency signals having mutually different phases or frequencies to a plurality of pairs of electrodes.