JPH09219295A - Liquid cooled remote plasma applicator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently cool an applicator without reducing the energy of microwaves or others by spirally providing a coolant tube at a specified position on the outer periphery of a plasma tube which passes through a guided wave passage to accept electromagnetic radiation. SOLUTION: A plasma tube 12 for a cooled plasma applicator passes through a rectangular guided wave passage 14. On all area inside the guided wave passage 14 for the plasma tube 12 around the outer periphery of the plasma tube 12, a spiral tube or a coil 16 as a coolant tube is wound. The coil is wound in a mutually separated manner to form a window through which microwaves pass into the plasma tube 12. During operation, coolant is circulated in the coil 16 and heat is deprived from the plasma tube 12. It is important that the diameter of a pipe to form the coil 16 is sufficiently small to minimize the amount of absorption.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates generally to remote plasma sources.

[0002]

BACKGROUND OF THE INVENTION Plasma-based remote excitation sources or plasma applicators must handle high input power and must withstand a combination of high temperatures and highly chemically reactive environments. For example, in a typical application of a plasma applicator, the generator will have NF ₃
Gas flows in and is decomposed by the plasma. As a result, excited species are generated which flow through the applicator and enter semiconductor processing equipment for in-situ chamber cleaning, etching, photoresist stripping and all other processes. Examples of using reactive species for in situ chamber cleaning include 1994
US patent application S. N. 08/27
No. 8605, Title A Deposition Chamber Cleaning Tec
hnique Using a Remote Excitation Source ".

The exposure of the apparatus to such a very harsh environment quickly renders the plasma applicator unusable. For example, depending on the commercial applicator,
Some use quartz tubes to accommodate such excited species. In such a system, the generated fluorine will rapidly etch the tube. Furthermore,
When the power level is high (1 to 1.5 kW or more)
Quartz is easily destroyed. Thus, after using the applicator a couple of times, or after a period of operation, the tube wall will be destroyed as soon as it is exposed to the high temperatures and vacuum prevailing in the system. It's so thin that it gets lost. Therefore, the tube must be replaced with a new tube very early in life. The inconvenience and cost of having to replace the quartz tube on a regular basis is very high.

Among the current plasma applicators are:
Some use ceramic tubes instead of quartz tubes. Ceramic tubes are more durable than quartz tubes in the often encountered chemically corrosive environments. But ceramic tubes are not a panacea. They usually have a relatively high coefficient of thermal expansion as compared to quartz and other materials. Therefore, repeated thermal cycling between room temperature and high processing temperatures, which is typically done in such systems, results in large stresses in the ceramic tube. This stress causes the tube to crack and break.

[0005]

Microwave plasma applicators have been developed which use two concentric ceramic tubes, both of which are outer and inner tubes for microwave radiation. It is made of a transparent material such as quartz or sapphire. The inner tube contains the plasma and thus
Exposed to high temperatures and highly corrosive environments. Water is flowed into the annular region between the two tubes to cool the inner tube. Such a system is available on February 1, 1995.
It is described in U.S. patent application Ser. No. 08 / 387,603, filed on the 3rd. Since water absorbs microwaves, there is a severe limit to the thickness that can form this annular region. If too thick, the microwaves are significantly reduced, making it difficult or impossible to maintain a plasma in the inner tube. On the other hand, if this region is too thin, the cooling efficiency will deteriorate significantly.

[0006]

SUMMARY OF THE INVENTION Broadly speaking, in one aspect, the invention is a liquid cooled plasma applicator for use in an output source. This applicator or generator consists of a waveguide that receives electromagnetic radiation during operation, a plasma tube that penetrates the waveguide and excites a gas that flows inside the waveguide by electromagnetic microwave radiation, and A coolant tube that is spirally wrapped around the outside and inside the waveguide of the plasma tube that is exposed to electromagnetic radiation. During use, coolant circulates in the coolant tube to cool the plasma tube.

The preferred embodiment has the following features. The applicator also has a microwave radiation source and the waveguide is a microwave waveguide. The microwave radiation source produces microwaves having a wavelength of 1 to 100 centimeters. If the wavelength of microwave radiation is λ, the outer diameter of the coolant tube is approximately λ /
Below 100, the spiral coolant tube is coiled with a winding spacing greater than about λ / 50. Alternatively, the winding interval of the spiral coolant tube may be larger than the outer diameter of the coolant tube (for example, twice or more the diameter of the coolant tube). Further, the liquid-cooled plasma applicator has an inflow connector for receiving a coolant trying to circulate in the coolant tube, and an outflow connector for outflowing the coolant after passing through the coolant tube. . Further, the coolant tube is in contact with the outer surface of the plasma tube.

In a preferred embodiment, the plasma tube is made of ceramic, such as aluminum oxide or sapphire. The coolant tube is made of a dielectric material, for example, Teflon (polytetrafluoroethylene resin). Further, the liquid-cooled plasma applicator is installed at the applicator main body in which the plasma tube is installed, the first adapter plate installed at the inflow end of the applicator main body, and the outflow end of the applicator main body. And a second adapter plate to be used. The first adapter plate has a first coupling that connects the gas line to the plasma applicator and provides a passage for the gas in the plasma tube plasma tube, and the second adapter plate is from the plasma applicator. It has an outflow passage for the outflowing excitation gas.

With the configuration of the spiral cooler, even when a coolant such as water that absorbs microwaves is used, it is possible to sufficiently cool the plasma tube without significantly reducing the microwave energy passing through the plasma tube. Becomes The liquid cooled plasma applicator of the present invention can be used with some of the most aggressive chemicals used in the semiconductor manufacturing industry, such as Cl ₂ , NF ₃ , CF. ₄ , and other fluorine compounds.

Other advantages and features of the invention will be apparent from the description of the preferred embodiment and the claims.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 1, a liquid-cooled plasma applicator 10 has a plasma tube 12. The plasma tube 12 has an inflow end 12 (a) for receiving the gas to be excited in the tube and an outflow end 12 (b) for flowing the excited gas to a remote process chamber (not shown). And have. The plasma tube 12 penetrates through the rectangular waveguide 14.
The waveguide 14 receives microwave energy from a microwave generator (not shown) connected to one end of the waveguide 14. Waveguide 1 of plasma tube 12
The portion within 4 is exposed to the microwave energy provided to the waveguide 14. Plasma tube 12
Are made of a dielectric material that is substantially transparent to the microwave radiation used, and the plasma tube 1
It is arranged in the waveguide 14 so as to optimally couple the plasma generated in 2 and the microwave field. For example, the plasma tube 12 communicates transversely to the direction of microwave radiation and is arranged such that the electric field inside the waveguide has a maximum inside the plasma tube.

In the embodiment described herein, the plasma tube 12 is made of aluminum oxide, especially single crystal sapphire. Sapphire tubes are available, for example, from Saphikon, Inc., Milford, NH, USA. However, the plasma tube 12 can be any material that can withstand the high temperature and highly corrosive environments created by the plasma-excited gas within the plasma tube. For example, it may be made of another ceramic material, or it may be made of quartz.

As mentioned above, a significant amount of heat will be generated during operation. To cool the plasma tube 12, a spiral tube or coil 16 is provided, which is spirally wound around the outside of the plasma tube and over the entire portion of the plasma tube located inside the waveguide. The turns of coil 16 are separated so that an open space is formed between the turns of coil 16. The separation of the turns of the coil 16 from each other creates a window through which the microwaves pass into the plasma tube 12, where the microwaves are not significantly absorbed by the tube itself or the coolant passing through it. Absent.

The relative size of the tubing, shown in FIG.
The number of turns and the spacing between turns are selected for ease of illustration and are not representative of actual examples. In a practical embodiment, the size of the tubing, the number of turns, and the spacing between the turns are appropriately selected according to the guidelines given below.

In the embodiment described herein, the coil 16
Is made of Teflon (polytetrafluoroethylene resin), which is resistant to the relatively high temperature generated outside the plasma tube 12. Of course, other dielectric materials that absorb microwaves, and even non-dielectric materials, can be used as long as they can withstand the conditions that would exist around the tube during operation.

An inflow connector 20 connected to a coolant supply line 22 is provided at one end of the coil 16.
An outflow connector 24 connected to an outflow line 26 is provided at the other end of the coil 16. Coil 16 during operation
The coolant circulates in the interior of the plasma tube and removes heat from the plasma tube 12. In the embodiment described herein, the coolant is filtered water. However, other coolants may be used. The advantage of using water is that it is readily available from the tap and does not need to be recirculated.
Thus, the use of tap water eliminates the need to use a heat exchanger to remove heat from the coolant for recirculation.

The applicator 12 includes an upper cylindrical hollow main body 30 attached to the upper side of the waveguide 14 and a lower cylindrical hollow main body 32 attached to the bottom of the waveguide 14. have. Both the upper body portion 30 and the lower body portion 32 are made of metal (for example, Al) and have an inner diameter slightly larger than the outer diameter of the plasma tube 12 passing through the inside of these body 30, 32. Upper body 3
0 is provided with a flange 30 (a) at the upper end thereof, which is connected to the plasma tube 12 from a remote gas source.
An adapter plate 34 for bolting gas into it is bolted.

A similar construction is located at the downstream end of the applicator 10. That is, the lower lower body 32 is provided with a flange 32 (a), which connects the plasma-excited gas from the plasma tube 12 to a line 40 connecting to a processing system (for example, a plasma processing system). Another adapter plate 38 for bolting.

Electromagnetic radiation is provided at frequencies in the microwave range (eg wavelengths 1 cm to 100 cm). In the embodiment described herein, the microwave source is about 2.
It operates at 54 GHz. Also, the output source operates at frequencies in the lower RF range. Even in this case, the method of coupling the radiation into the plasma may have to be modified from that shown and described herein.

A metal short 42 that can be moved in and out by a plunger 44 is provided at the end of the waveguide 14 opposite to the opening to which the microwave source is coupled. The metal short 42 is moved to the position suitable for igniting the plasma inside the gas flowing in the plasma tube 12, and is placed there.
This position can be easily found by trial and error. It has been found that the metal shorts 42 should be placed at or near the optimum position for the highest etch rate. Of course,
There are other design and tuning methods that are known and can be used by so-called persons of ordinary skill in the art. For example, the system described in US Pat. No. 4,851,630.
The present invention is not limited to any particular waveguide design or tuning technique.

As mentioned above, the space between the turns of the coil 16 forms a window through which microwaves pass into the plasma tube 12, without the microwaves being significantly absorbed by the cooling system. . The winding spacing or pitch should be chosen to optimize the cooling efficiency for the transmitted power. If this spacing is too small, the microwave energy transferred into the plasma tube will be significantly reduced. On the other hand, if this spacing is too large, the cooling efficiency will be unacceptable. Generally, the amount of transmission due to the distance increases with the square of the pitch or spacing of the coil windings. The allowed spacing is in the range λ / 50, where λ is the wavelength of the radiation.

Since the coolant and possibly the coil itself (depending on the choice of material used for the coil) also absorbs microwaves, it is important that the diameter of the tubing forming the coil be small enough to minimize absorption. is there. The spiral coil removes heat from the plasma tube 12 by heat conduction, and the cooling efficiency increases in proportion to the diameter of the coil pipe. On the other hand, the microwave energy absorbed by the coil increases proportionally with the diameter of the coil. Therefore, as the diameter of the coil increases, there will be points where the contribution to cooling efficiency will be greater than that offset by the reduced microwave transmission to the plasma tube. However, if the tube is too small, its ability to cool the heated plasma tube will be compromised. In general, pipe diameters on the order of λ / 100 or less are acceptable.

Although the embodiments described herein use plastic or Teflon as the material for forming the tubing, other suitable materials may be used, including non-dielectric microwave absorption such as copper. Not only materials, but also dielectric materials that do not absorb microwaves are included. Further, thermal cement may be used to further improve the heat conduction between the coolant circulating in the pipe and the outer wall of the heated plasma tube.

The wall thickness of the sapphire plasma tube is determined by the spacing between the turns of coil 16. In the embodiments described herein, the wall thickness is greater than about 0.06 inches for a coil winding spacing of 0.25 inches (1 inch = about 25.4 mm). This wall thickness ensures that the longitudinal temperature gradient of the wall matches the axial temperature gradient at the coil and minimizes thermal stress.

The thickness of the wall of the pipe forming the coil is mainly
Determined by the pressure of the liquid coolant pumped through the coil. Of course, thicker walls for higher pressures are needed to prevent the coil from breaking.

The plasma applicator can be used in a wide variety of applications. For example, as shown in FIG. 2, it can also be used as a remote source of excited gas species for plasma processing systems. In this application, a reactive gas is supplied from an external gas source 100 via conduit 102 to the gas inlet port of plasma applicator 10. Next, the excited gas species generated in the plasma applicator 10 is supplied to the plasma chamber 104 via the line 40 connected to the gas outflow port of the plasma applicator 10.
Is fed into. A pump 104 and heat exchanger 106 connected between the inlet and outlet ports of the applicator's cooling system circulate the coolant within the applicator 10 during operation. A microwave source 108 that powers the waveguide 14 causes a plasma to be generated within the plasma tube 12 of the applicator 10 to excite the gas species prior to introduction into the main plasma chamber 104.

Other components typically present in such a system include a vacuum pump for degassing the plasma chamber and an output source (eg, RF) for generating a second plasma in the plasma chamber. Power supply and DC power supply).

The excited species are transported into the processing chamber in any suitable way. Further, the applicator may be installed directly in the substrate processing chamber or may be located remotely from the substrate processing chamber, in which case an excitation gas supply line of suitable material is required. When the reactivity of the excited species is very high, as in the case of excited fluorine,
The material forming the line 40 needs to be a material that does not interact with the generated excited species, for example, stainless steel. Other suitable materials include aluminum, ceramics and some fluorine based materials and the like.

[0029]

As described in detail above, according to the present invention, there is provided a device capable of efficiently cooling an applicator or the like without significantly reducing energy such as microwaves.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a plasma applicator which is one example of the present invention.

FIG. 2 is a configuration diagram of a semiconductor processing system using the plasma applicator of FIG.

[Explanation of symbols]

10 ... Liquid cooled plasma applicator, 12 ... Plasma tube, 12 (a) ... Inflow end, 12 (b) ... Outflow end, 1
4 ... Waveguide, 16 ... Spiral tube, 20 ... Inflow connector, 22 ... Coolant supply line, 24 ... Outflow connector, 26 ... Outflow line, 30 ... Applicator upper body part, 30 (a) ... Flange, 32 ... Applicator Lower body part, 32 (a) ... Flange, 34, 38 ... Adapter plate, 40 ... Line, 42 ... Metal short, 44 ... Plunger, 102 ... Conduit, 104 ... Plasma chamber, 1
06 ... Heat exchanger, 108 ... Microwave source.

Claims (18)

[Claims] 1. A liquid-cooled plasma applicator for use in an output source, the waveguide receiving electromagnetic radiation from the output source during operation, and passing through the waveguide and in the waveguide. A plasma tube arranged to excite a gas flowing therein by the electromagnetic radiation of, and electromagnetic radiation outside the plasma tube and in a region of the plasma tube arranged in the waveguide. A spirally wound coolant tube over the area exposed to, wherein the coolant tube circulates through the coolant tube to cool the plasma tube during use. Liquid cooled plasma applicator. 2. The liquid cooled plasma applicator of claim 1, wherein the electromagnetic radiation is microwave radiation and the waveguide is a microwave waveguide. 3. The plasma applicator of claim 2, further comprising a microwave radiation source. 4. The microwave radiation source is 1-10.
The liquid cooled plasma applicator of claim 3, which produces microwaves having a wavelength in the range of 0 centimeters. 5. The microwave radiation wavelength is λ, the coolant tube outer diameter is D, and D is about λ / 1.
The liquid-cooled plasma applicator according to claim 2, which is less than 00. 6. The microwave radiation has a wavelength of λ and the spiral tube forms a coil with a spacing S between windings, where S is greater than about λ / 50. The liquid-cooled plasma applicator according to. 7. The microwave radiation has a wavelength of λ, the coolant tube has an outer diameter of D, and the spiral tube forms a coil having an interval S between turns, S Is greater than D. The liquid cooled plasma applicator of claim 2. 8. The microwave radiation has a wavelength of λ, the coolant tube has an outer diameter of D, and the spiral tube forms a coil having an interval S between turns, S Is greater than 2D (twice D). The liquid cooled plasma applicator of claim 2. 9. The liquid cooling according to claim 1, further comprising an inflow connector for receiving a coolant circulated in the coolant tube, and an outflow connector for discharging the coolant after passing through the coolant tube. Plasma applicator. 10. The liquid cooled plasma applicator of claim 9, wherein the coolant tube contacts the outer surface of the plasma tube. 11. The liquid-cooled plasma applicator according to claim 7, wherein the plasma tube is made of ceramic. 12. The liquid-cooled plasma applicator according to claim 7, wherein the plasma tube is made of aluminum oxide. 13. The liquid-cooled plasma applicator according to claim 12, wherein the plasma tube is made of sapphire. 14. The liquid cooled plasma applicator of claim 13, wherein the coolant tube is made of a dielectric material. 15. The liquid-cooled plasma applicator according to claim 14, wherein the coolant tube is made of Teflon or polytetrafluoroethylene resin. 16. The liquid-cooled plasma applicator according to claim 2, further comprising an applicator body on which the plasma tube is installed. 17. The first adapter plate according to claim 16, further comprising a first adapter plate which is installed at an inflow end of the applicator body and connects a gas line to the plasma applicator to provide a passage for flowing gas into the plasma tube. Liquid-cooled plasma applicator. 18. The liquid cooling according to claim 17, further comprising a second adapter plate installed at an outflow end of the applicator body, the second adapter plate having a passage for exhausting an exciting gas flowing out from the plasma applicator. Plasma applicator.