JPH0724239B2 - Method and apparatus for generating a large volume of magnetic plasma - Google Patents

Description

TECHNICAL FIELD The present invention relates to plasma generation. Specifically, it relates to generating high density plasma at low pressure. The present invention is
Especially effective for dry etching and for generating large volume plasma in insulating cavities used to modify the surface properties of materials,
It is not limited to these uses.

BACKGROUND ART The use of plasma for purposes such as etching is well known. Good work on plasma etching, Hewlett
There is "Jet Dry Etching: A Perspective" by Paul J Marcoux in the Packard Journal (August 1982, p. 19-23).

The equipment used for plasma generation consists of:

a) Electrically insulating chamber (commonly called a discharge tube in which plasma is generated).

b) Vacuum pump (holding the inside of the discharge tube at a low pressure).

c) A gas supply source (which drives air out of the discharge tube and becomes a source of ions and electrons that form an ion plasma).

d) Radio frequency oscillator, amplifier and coupling network (as a power source to establish the plasma).

e) An antenna that couples the rf power from the output of the coupling network to the plasma.

Usually, the plasma tube is made of a metal cylindrical tube having a circular cross section. However, we have used cylindrical tubes of pyrex or quartz glass (see the following publications in this section). Among the antennas used to couple rf power into the plasma, the most effective is the dual loop antenna, which fits snugly on the sides of the discharge vessel (eg (a) R.
W. Boswel's Physics Letters, Volume 33A, December 1970,
Pages 457-458, (b) RW Boswell et al., "Physics Letter"
s ", Volume 91A, September 1982, pp. 163-166, and (c) R.
W. Boswell's "Plasma Physics and Controlled Fusio
n, Vol. 26, pp. 1147-1162, 1984).

DISCLOSURE OF THE INVENTION The productivity of silicon chips (and other semiconductor devices) for computers depends on the silicon wafer (or wafer of other semiconductor material) that is etched to form the chip.
It has been accepted so far that the higher the area of the, the higher. Efficient production of high-density plasmas in large volumes (ie, in discharge tubes with a large inner diameter), while theoretically possible, has never been done before the present invention. In addition, a large volume of plasma is beneficial unless the plasma is substantially homogeneous and the density of uncharged atomic species (usually fluorine) used to perform etching is reasonably high. Is small.

It is an object of the present invention to provide a means of producing a plasma having a substantially larger volume than previously produced and having a substantially uniform volume of uncharged atomic species.

This object is achieved by generating a plasma in a cavity that persists in the auxiliary zone, making the internal pressures of the cavity and the auxiliary zone the same and allowing the plasma to extend into the auxiliary zone.

In the preferred embodiment of the present invention, the plasma is generated at a much lower pressure than before and is subjected to resonant conditions (discovered by the inventor), creating a large volume of atomic gas species.

With respect to the basic form of the invention, the inventor has discovered that when a plasma is generated in a plasma tube that is coupled to the same auxiliary pressure zone as the plasma tube, the plasma extends into the auxiliary zone. The auxiliary area can be a volume that is significantly larger than the volume of the plasma. The sample to be etched is supported in a plasma tube, or (preferably) an auxiliary area, in which it contacts the plasma.

Regarding low-pressure operation of plasmas, the inventors have found that in applying their scientific work (see above) to the field of dry etching of semiconductor materials, a gas containing a reactive species (eg, six foot) is used. It has been found that the use of (sulfurized) for the dry etching of silicon substantially increases the etching rate of silicon under certain conditions with a given discharge tube shape and for a given rf power. As a result of continued research by the present inventor, the conditions under which this unexpected resonance effect occurs can be experimentally determined. These conditions apply an input rf power frequency of 7.5M
Hz, antenna length 20 cm, magnetic field 100 Gauss,
It is expressed by the following formula.

DWp15,000 (I) where D is the inner diameter (cm) of the tube where plasma is generated,
W is the rf power (watt) and p is the operating pressure (millitor) of the plasma tube.

In order to create this resonance condition, the present inventor further depends on the antenna length (L), the magnetic field in the plasma tube (B), and the frequency (f) of the rf power, which is expressed by the following equation. Found out.

Where f is MHz, L is cm, and B is Gauss.

It is considered that when the resonance condition in the plasma tube is established, the interaction between the ions and electrons in the plasma and the uncharged gas molecules is increased. That is, the dissociation of the gas that produces the atomic species is significantly increased, and the density of atomic species in the plasma tube is increased. When the plasma gas is sulfur hexafluoride SF ₆ (which is commonly used for plasma etching of silicon wafers), it is believed to dissociate into atomic sulfur and atomic fluorine. Atomic fluorine reacts with and etches exposed silicon in the plasma tube or in the auxiliary area.

According to the present invention, there is provided a plasma production apparatus including the following elements.

a) An electrically insulated, elongated, uniform circular cross-section (diameter D) tubular cavity. In this, a source of ions and electrons is contained in a gaseous state at a pressure p.

b) A first magnetic field forming means provided outside the cavity in order to create a magnetic field B in the cavity.

c) A radio frequency antenna of length L adapted to couple rf power to the gas in the cavity.

d) Frequency f connected to the antenna outside the cavity
Rf power source.

This device is characterized by:

e) An electrically insulating auxiliary zone of the same internal pressure as the cavity is connected to the cavity.

f) Second magnetic field forming means for forming the required magnetic field in the auxiliary area are provided. Also, g) the parameters for operating the device are defined by the following equations.

And [Where W is the power (watts) applied to the radio frequency antenna, and D, p, f, L, and B are expressed in cm, millitor, MHz, cm, and Gauss, respectively. According to the present invention, there is provided a method for forming a large magnetic plasma including the following steps.

a) A plasma is created in a tubular cavity of electrically insulated, elongated, uniform circular cross section (diameter D), in which there is a gaseous source of ions and electrons at pressure p, the plasma being in the cavity Is created by coupling a rf power of frequency f to a gaseous source using a radio frequency antenna of length L outside the cavity, b) connecting to the cavity and having the same internal pressure p as the cavity The plasma is allowed to extend into the auxiliary zone, and c) the operating conditions of the plasma are adjusted so that the following two equations hold.

[Where W is the power (watts) applied to the radio frequency antenna, and D, p, f, L, and B are expressed in cm, millitor, MHz, cm, and Gauss, respectively. Using the apparatus and method of the present invention, the density of atomic species obtained from the gas in the cavity is significantly increased by the generation of plasma.

Under typical operating conditions, the value of f · L ² / B should be about 50.

In a normal environment, the pressure p in the cavities and the auxiliary zone is maintained at an approximately constant value by balancing the pump speed of the vacuum pump and the gas feed rate.

An embodiment of the present invention will be described below with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial cross-sectional explanatory view seen from one side of a plasma etching apparatus configured to include the present invention.

FIG. 2 is a diagram showing a preferred antenna shape for coupling rf power to plasma.

FIG. 3 is a typical explanatory view showing a combination of a plasma cavity and an auxiliary area.

FIG. 4 is a graph showing the relationship between the rf power supplied to the antenna of the apparatus of FIG. 1 and the density of atomic fluorine in the plasma tube of FIG. 1. Sulfur hexafluoride was used as the plasma gas. This is the case when using.

Detailed Description of the Illustrated Embodiment In FIG. 1, the apparatus of the present invention comprises a cylindrical member 10 of ceramic or glass, the cylindrical cross-section of which has an inner diameter D and the shape of the second cylindrical member 20. Circular member with auxiliary area
Connected to 10. Cylindrical member 10 and second cylindrical member 20
Can be integrally formed. The cylindrical member 10 is closed at its end remote from the second cylindrical member 20 by a flange 11, to which one or more observation windows 11A are hermetically fitted. The source of gas 14 is provided by pipe 19 through valve 15 and flange.
It is maintained inside the cylindrical member 10 via 11. Tube 21
Is the flange 12 (the cylindrical member farther from the cylindrical member 10).
From the inside of the cylindrical member 20 to a vacuum pump 22 via (sealing the ends of 20).

A coil 13 surrounds the cylindrical member 10. The coil 13 is connected to a DC power supply 25 and forms a magnetic field B in the cylindrical member 10. The uniformity of the plasma formed in the cavity formed by the cylindrical member 10 can be controlled by varying the diameter of the coil 13 along its length, if desired.

The output of the radio frequency power generator 30 and matching network is coupled to an antenna 32, which is a cylindrical member 10
Resonantly couple rf power into the gas medium within. Generator 30
It produces power in the range of about 1 MHz to about 30 MHz. Antenna 32 is r
It can take any suitable form of an f-antenna, but the resonance equations (I) and (I
It must have a length L that satisfies I). The inventor has tested antennas of various lengths and diameters with complete success. The preferred shape of the antenna (used in our previous published work) is shown in FIG. As shown in FIG. 1, the antenna 32 is placed under the coil 13 near the wall of the cylindrical member 10.

The auxiliary area formed by the cylindrical member 20 does not have to be cylindrical and can take any shape as required. Since the plasma created in the cavity formed by the cylindrical member 10 extends into the auxiliary zone, the auxiliary zone is provided with a means for limiting the extended area of the plasma, i.e. forming a suitable magnetic field in the auxiliary zone. Means are provided. If the auxiliary section is a cylindrical member, a magnetic field can be created by the coil 16 connected to the second DC source 24, as shown in FIG. If the auxiliary area has a complicated shape as shown in FIG. 3, a permanent magnet 33 is arranged near the wall 34 defining the auxiliary area to contain the plasma in the auxiliary area, as is known. Can form a magnetic "fence".

When plasma is used for etching purposes, the material to be etched 17 (for example, a silicon wafer covered with a mask so that a matrix of many silicon chips can be etched at the same time) is a plasma cavity (cylindrical member 10).
It is supported by a support 18 in, or preferably in an auxiliary area as shown in FIG. Support 18 is a second rf source
It can be connected to 31 and applies a bias potential to the support 18.

In order to use this device, the cylindrical member 10 and the cylindrical member
Jet gas from source 14 into 20. Vacuum pump 22
Evacuate so that the pressure in the cavities and auxiliary areas is below 0.01 mTorr. The high pressure determined by the resonance relationship of equation (I) is then maintained in the cavity by the equilibrium between the gas flow from source 14 and the pump speed of pump 22.

The required pressure and magnetic field are created in the cylindrical member 10,
As the power level from the generator 21 rises from zero to zero, a plasma is generated, the atomic species density increases with increasing power, reaching the maximums achieved with conventional plasma devices.
This maximum value is indicated by A in the graph of FIG. Conventional plasma scientists would expect that as the power from the generator 21 continues to increase, the maximum A will be maintained or will increase slightly, as shown by the dotted line B in FIG. However, when the inventor operates at the low pressure required by the present invention,
It was discovered that a resonance phenomenon occurred and the density of atomic species created in the cavity rapidly increased to the second maximum value shown by C in FIG.

Since the atomic species generated in the plasma are neutral,
It is not affected by the magnetic field formed by the coil 13 or the magnetic field formed in the auxiliary area. These species have a long life of approximately 0.1 seconds or more. Thus, the seeds are evenly distributed within the cylindrical member 10,20 and the material etching is highly homogeneous. Another advantage of the uniform distribution of atomic species is that the location of the material to be plasma etched or surface treated is not critical. Thus, the material can be placed almost anywhere in the auxiliary zone (cylindrical member 10 if desired).

The etching angle of material 17 can be modified by the appropriate application of rf voltage and frequency to press the substrate of material 17. If the RMS amplification of this bias voltage is 2-3 volts, the material is isotropically etched. 2 RMS amplification of bias voltage
From 0 to 30 volts to 200 to 300 volts, the etching of material 17 is anisotropic. In the intermediate bias voltage amplification, the etching anisotropy changes variously in proportion to the amplification of the bias rf voltage.

The gas from source 14 may be a single component gas or a mixture of gases. This is selected according to the type of material 17 required for etching and surface treatment.

When the apparatus of the present invention is utilized in etching applications such as manufacturing computer chips from silicon wafers, the
The gas from 14 is a gas that dissociates to form reactive atomic species (eg, sulfur hexafluoride (SF ₆ ), carbon tetrafluoride (CF ₄ ), carbon tetrachloride (CCl ₄ )), or etching. Is a mixture of gases containing one or more gases that are solved to create a reactive atomic species that is particularly useful in.

However, as mentioned above, the device of the present invention is not limited to semiconductor material etching applications. By replacing oxygen as the working gas, very high etching rates of polymers such as photoresists are obtained. If the plasma gas is nitrogen, neutral nitrogen atoms are generated, which can be used to form nitrides on the surface of the steel and harden the steel. Using experimental equipment, extremely hard surface coatings could be formed on steel samples up to several meters in length.

In the study of the present invention, the present inventor utilized a double cylindrical member as shown in FIG. 1, and the inner diameter of the cylindrical member 10 was 2 cm to 20 cm.
Then, the inner diameter of the second cylindrical member 20 was 2 cm to 80 cm.
The resonance maximum value C shown in FIG. 4 appears for each cylindrical member used. The larger the diameter of the cylindrical member, the more
Operating at pressures in the range of 0.1 millitorr to about 1.0 millitorr provided a large volume of plasma suitable for use in etching large diameter silicon wafers.

Although specific embodiments of the present invention have been described, the present invention is not limited to these embodiments and many modifications can be made without departing from the scope of the present invention.

Claims (16)

[Claims] 1. A method for forming a large magnetic plasma comprising the following steps. a) An electrically insulated, elongated, uniform circular cross section (diameter D) tubular cavity is filled with a gaseous source of ions and electrons at a pressure p to form a magnetic field B and is located outside the cavity. A radio frequency antenna of length L is used to couple the rf power of frequency f into the gaseous source to create a plasma. b) connecting to said cavity so that the plasma extends into an auxiliary zone with the same internal pressure p as the cavity. c) The operating conditions of plasma are adjusted so that the following two expressions are established. DWp15,000 (I) [Where W is the power (watts) applied to the radio frequency antenna, and D, p, f, L, and B are expressed in cm, millitor, MHz, cm, and Gauss, respectively. ] 2. The method according to claim 1, wherein the following formula is satisfied. 3. The pressure p in the cavity is maintained by balancing the pump speed of a vacuum pump connected to the cavity with the supply speed of the ion and electron gas sources.
The method according to any one of item 2. 4. The gas source of ions is a gas that produces dissociated reactive atomic species, or a gas mixture containing one or more gases that dissociate to produce reactive atomic species. The method according to any one of items 1 to 3. 5. The ion or electron source is selected from the group consisting of sulfur hexafluoride, carbon tetrafluoride, carbon tetrachloride, oxygen and nitrogen, and any one of claims 1 to 3 is claimed. The method described in. 6. A gas in which an ion or electron gas source is dissociated to generate reactive halogen atoms in the cavity, a wafer of semiconductor material is included in the auxiliary zone, and the wafer is etched by the halogen atoms. The method according to any one of claims 1 to 3. 7. An ion and electron gas source is oxygen, which dissociates to give oxygen atoms, the polymer is contained in the auxiliary zone and is etched by oxygen gas. The method described in any one of. 8. The gas source of ions and electrons is nitrogen,
The dissociation in a cavity produces | generates a nitrogen atom, a steel product is contained in an auxiliary area | region, and a nitride is formed in the surface of a steel product, The claim in any one of Claims 1-3. the method of. 9. The method comprises the following elements a) to d) and e) to
A plasma generator characterized by f). a) A tubular cavity with an electrically insulated, elongated, uniform circular cross section (diameter D) and containing a gas source of ions and electrons with a pressure p. b) first magnetic field forming means arranged outside the cavity so as to establish a magnetic field B in said cavity. c) A radio frequency antenna of length L for coupling rf power into the gas in the cavity. d) A source of rf power at frequency f located outside the cavity connected to the antenna. e) An electrically insulating auxiliary zone kept at the same internal pressure p as the cavity is connected to the cavity. f) A second magnetic field forming means for forming a necessary magnetic field in the auxiliary area is additionally provided in the auxiliary area. Also, g) the parameters for operating the device are defined by the following equations. DWp = 15,000 (I) and [Where W is the power (watts) applied to the radio frequency antenna, and D, p, f, L, and B are expressed in cm, millitor, MHz, cm, and Gauss, respectively. ] 10. The apparatus according to claim 9, wherein the following formula is satisfied. 11. A vacuum pump is connected to the auxiliary area, a gas supply means is connected to the cavity, the gas supply means serves as a gas source of ions, and the operation of the vacuum pump and the gas supply means substantially controls the pressure p in the cavity. A device according to claim 9 or 10 adjusted to hold it substantially constant. 12. The gas source of ions and electrons is a gas that dissociates to produce reactive atomic species, or a gas mixture containing one or more gases that dissociate to produce reactive atomic species. The apparatus according to claims 9 to 11 in the range. 13. The ion and electron source is selected from the group consisting of sulfur hexafluoride, carbon tetrafluoride, carbon tetrachloride, oxygen and nitrogen, and any one of claims 9 to 11 is claimed. The device according to. 14. A masked wafer of semiconductor material is mounted in the auxiliary area, and the exposed area of the wafer is etched with a gas that dissociates the ion and electron gas sources in the cavity to produce halogen atoms. The apparatus according to claims 9 to 11 in the range. 15. A polymeric material is mounted in the auxiliary area, the gas source of ions and electrons is oxygen, which dissociates in the cavity,
An apparatus according to claims 9 to 11 which produces oxygen atoms which etch the polymeric material. 16. A steel product is disposed in the auxiliary area, and a gas source of ions and electrons is nitrogen, and dissociates in the cavity to generate nitrogen atoms, which reacts with the surface of the steel product to the surface. A device for forming a nitride according to claims 9-11.