JP3646901B2 - Plasma excitation antenna, plasma processing equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for generating plasma, and more particularly, to a plasma excitation antenna that radiates electromagnetic waves to a gas introduced into a plasma generation tank to form plasma.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an apparatus for processing an object to be processed using plasma of a desired gas has been widely used in an etching process or a thin film forming process. For example, the etching apparatus 100 in FIG. 3A is an apparatus that etches a thin film on the surface of a substrate using plasma, and includes a reaction tank 105 made of metal, a plasma generation tank 106 made of a dielectric, And a loop antenna 102.
[0003]
The plasma generation tank 106 is attached to the upper part of the reaction tank 105, and the loop antenna 102 is provided on the outer periphery of the plasma generation tank 106, as shown in FIG. The other end is connected to the ground potential.
[0004]
A substrate 108 is placed in advance in the etching apparatus 100, a vacuum pump (not shown) is started, the inside of the reaction tank 105 and the plasma generation tank 106 is brought into a high vacuum state, an etching gas is introduced, and the high frequency power supply 110 is supplied. When a high frequency voltage is applied to the loop antenna 102, the etching gas is excited by the electromagnetic wave radiated from the loop antenna 102, and an etching gas plasma 107 is generated.
[0005]
Electromagnets 114 ₁ and 114 ₂ are provided outside the reaction tank 105 and the plasma generation tank 106, and a magnetic field is formed so that the generated etching gas plasma 107 is transported to the surface of the wafer 108. When contacted with the etching gas plasma 107, the thin film is etched.
[0006]
In such an etching apparatus 100, it is necessary to make the etching gas plasma 107 uniform in order to reduce the etching variation on the wafer 108 surface. For this purpose, it is desirable that the electromagnetic wave is uniformly radiated from the entire loop antenna 102. Therefore, both ends of the loop antenna 102 need to be close to each other, as indicated by reference numeral 115, in a loop shape.
[0007]
On the other hand, the substrate to be etched has been gradually increased in size in recent years, and in order to cope with this, the loop antenna 102 described above is also increased in size and the power to be input is increased.
[0008]
The loop antenna 102, the high-frequency power supply 110, and the matching box 111 form an equivalent circuit as shown in FIG. 5C. However, in order to pass a large current through the enlarged loop antenna 102, the matching box When the high-frequency voltage V applied via 111 is increased, a discharge occurs between the terminals in the portion 115 where the power supply side terminal and the ground side terminal are close to each other, and the plasma becomes unstable. there were.
[0009]
In addition, when the high-frequency voltage applied to the loop antenna is increased, the inner wall of the plasma generation tank 106 near the power supply side terminal of the loop antenna 102 may be sputtered, resulting in a problem of being mixed as impurities into the etching gas plasma. It was.
[0010]
[Problems to be solved by the invention]
The present invention was created to solve the above-described disadvantages of the prior art, and an object of the present invention is to provide a plasma excitation antenna capable of flowing a large current with a small applied voltage.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention described in claim 1 is a plasma excitation antenna to which a high-frequency voltage is applied , and includes a plurality of partial antennas configured to radiate electromagnetic waves, and a plurality of capacitors. The partial antenna and the capacitor are electrically connected alternately, and a partial LC series circuit composed of one capacitor and one partial antenna connected to each other is applied. It is configured to be placed in a resonance state with respect to the frequency of the high frequency voltage .
[0012]
In this case, the plasma excitation antenna according to claim 1, wherein one end of the plasma excitation antenna is connected to a power source via a matching box having a capacitor , as in the invention according to claim 2. The capacitor in the box is included .
[0013]
On the other hand, the invention according to claim 3 is a plasma processing apparatus, comprising the antenna for plasma excitation according to any one of claim 1 or claim 2, and a plasma generation tank for introducing a gas to be converted into plasma. It is characterized by that.
[0014]
As for the invention according to claim 3, as in the invention according to claim 4, a plurality of the plasma excitation antennas are provided, and the gas in the same plasma generation tank is converted into plasma by each of the plasma excitation antennas. It is preferable that the natural resonance frequencies of the plasma excitation antennas are different from each other by 1 kHz or more.
[0015]
Conventionally, in a loop antenna such as that used for plasma excitation, when it is desired to flow a current I at a frequency ω, if the inductance value of the loop antenna is L ′,
V = ω ・ L '・ I
It was necessary to apply a high-frequency voltage V having a magnitude of.
[0016]
When a large-diameter loop antenna is used to generate a high-density plasma, the value of the frequency ω increases and the value of the current I also increases, so that the value of the applied high-frequency voltage V also increases. End up.
[0017]
However, since the loop antenna is generally close to the terminals to which the high frequency voltage is applied, when a large high frequency voltage V is applied, a discharge occurs between the power supply side terminal and the ground side terminal.
[0018]
According to the configuration of the present invention described above, the loop antenna is divided into a plurality of partial antennas, and each partial antenna is electrically connected by the capacitor. In this case, when a plasma excitation antenna is configured by n partial antennas having a total inductance value of L ₀ and n−1 capacitors, each of the partial antenna and the capacitor including the capacitors in the matching box is included. N partial LC series circuits are formed. Therefore, the voltage generated across the partial LC series circuit is 1 / n of the voltage applied to the whole.
[0019]
Assuming that the inductance per such partial antenna is L _n and the capacitance per capacitor is C _n , the value of ω ² · L · C is possible for the frequency ω of the applied high-frequency voltage as much as possible. When it is close to 1, a partial LC series circuit composed of one partial antenna and one capacitor can be placed in a resonance state.
[0020]
When a partial LC series circuit is in a resonance state, the impedance of that part is the smallest. Therefore, if the inductance value of the partial antenna and the capacitance value of the capacitor are selected so that the n partial LC series circuits including the capacitor in the matching box are as close to the resonance state as possible, the entire plasma excitation antenna can be obtained. The impedance of becomes smaller. Therefore, since a large current can flow with a small high frequency voltage, even when large power is applied, the voltage difference between the power supply side terminal and the ground side terminal of the plasma excitation antenna becomes small, Discharge does not occur.
[0021]
By the way, when the plasma excitation antenna is attached to the plasma generation tank, conventionally, the distance between the plasma generation tank and the plasma excitation antenna is such that the one connected to the power supply is far away and the one connected to the ground potential is closer. Some have been arranged so that the electric field in the plasma generation tank is uniform, and impurities are not mixed into the plasma. In the plasma excitation antenna according to the present invention, the applied high-frequency voltage may be low, so that the gas in the plasma generation tank can be uniformly converted to plasma even when the distance from the plasma generation tank is constant.
[0022]
In the plasma generation tank provided with a plurality of plasma excitation antennas of the present invention, when the plasma introduced into one plasma generation tank by applying a voltage from a high frequency power source independent to each plasma excitation antenna, The values of the natural resonance frequencies of the plasma excitation antennas are different from each other by 1 kHz or more. In that case, when causing resonance in the partial LC series circuit of each plasma excitation antenna, the frequency of each high frequency power supply can be made different, so that mutual interference between the plasma excitation antennas can be prevented. .
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1, reference numeral 2 denotes a loop antenna that is an example of a plasma excitation antenna according to the present invention, and includes five partial antennas 21 to 25 and four capacitors 71 to 74.
[0024]
Each of the partial antennas 21 to 25 has inductance portions 31 to 35 that emit electromagnetic waves, and terminals 41a to 45a and terminals 41b to 45b are provided at both ends of the inductance portions 31 to 35, respectively. Yes.
[0025]
The inductance portions 31 to 35 and the terminals 41a to 45a and 41b to 45b are formed of a thin metal plate, and each of the inductance portions 31 to 35 is bent into an arc shape and has a single loop shape (in this example, (300 mmφ). The terminals 42a to 45a, 41b to 44b and the inductance portions 31 to 35 are provided in the same direction so as to be perpendicular to the surface on which the terminals are located.
[0026]
Between the terminal 41b and the terminal 42a, between the terminal 42b and the terminal 43a, between the terminal 43b and the terminal 44a, and between the terminal 44b and the terminal 45a, high-voltage capacitors 71 to 74 are arranged, respectively, as shown in FIG. Thus, one electrode 70a of each capacitor 71 to 74 is fixed to the terminals 42a to 45a, and the other electrode 70b is fixed to the terminals 41b to 44b.
[0027]
The loop antenna 2 is used in a plasma processing apparatus 3 having a plasma generation tank 6 as shown in FIG. 2A, and spacers 91 to 91 are provided on a glass window 8 provided on the ceiling of the plasma generation tank 6. 93.
[0028]
A terminal 41a at one end of the loop antenna 2 is connected to a high frequency power source via a matching box 11 whose equivalent circuit is shown in FIG. 2B (the matching box and the high frequency power source are omitted in FIG. 2A). )), The other terminal 45b is connected to the ground potential, and when the high frequency power source 10 is activated and a high frequency voltage is applied between the terminals 41a and 45b, the gas introduced into the plasma generating tank 6 is turned into plasma.
[0029]
In this loop antenna 2, as shown in the equivalent circuit shown in FIG. 4B, the inductance components of the inductance portions 21 to 25 are L _{1 to} L ₅ , the capacitance components of the capacitors 71 to 74 are C _{2 to} C ₅ , matching. When the capacitance component of the capacitor 12 connected between the loop antenna 2 and the high-frequency power source 10 in the box 11 is represented by C ₁ , the inductance components L _{1 to} L ₅ and the capacitance components C ₁ to ₅ are alternated. Therefore, five partial LC series circuits of C ₁ L ₁ , C ₂ L ₂ , C ₃ L ₃ , C ₄ L ₄ , and C ₅ L ₅ are formed.
[0030]
The capacitors 12 and 71 to 74 having capacitance components C _{1 to} C ₅ of 1000 pF are used, the high frequency power supply 10 is activated, and a high frequency voltage with a frequency of 13.56 MHz is applied via the matching box 11, and the loop antenna 2 The voltage inside was measured. The voltages _{obtained at} the respective measurement points from V _{0pp to} V _6pp shown in FIG.
[0031]
V _0pp = 2.3 kV
V _1pp = 4.3 kV
V _2pp = _4.5kV
V _3pp = 4.4 kV
V _5pp = 4.5kV
V _6pp = 4.3 kV
The voltage value between the terminals 41a and 45b at the closest ends was as low as 2.3 kV (V 0 _pp ), and no discharge occurred between the terminals 41a and 45b.
[0032]
On the other hand, in the loop antenna 102 of FIG. 3, when a high frequency voltage is applied so that the same current flows at the same frequency as in the above case, the voltage V across the loop antenna 102 is 13.8 kV. In some cases, discharge occurred between the terminals at both ends. The loop antenna 102 having a diameter of 350φ was used, and the stray capacitance was 20 to 30 pF. A capacitor having a capacitance value of 500 pF was used as the capacitor in the matching box 111.
[0033]
In the plasma processing apparatus 3 described above, the plasma excitation antenna is disposed on the ceiling. However, as shown in FIG. 3B, it may be disposed on the outer periphery of the plasma generation tank. As long as it is generated stably, the attachment location is not limited.
[0034]
<Etching device>
The loop antenna 2 described above has a diameter of 300φ and uses four capacitors. However, as another embodiment, three capacitors each having 500 pF are used and four partial inductances (about 1 μH each) are alternately arranged. Was connected in series to form one loop antenna. In addition, a matching box is configured using a capacitor having a capacitance value of 500 pF, a high frequency voltage of 13.56 MHz is applied through the matching box, and etching of a silicon wafer (8 inches) having a silicon oxide film formed on the surface is performed. Went.
CHF ₃ was used as an etching gas. The flow rate was 50 SCCM, the pressure was 0.1 Pa, and the input power to the loop antenna was 1 kW. 200 W of power was supplied to the substrate at a frequency of 13.56 MHz.
[0035]
When a total of 100 wafers were processed for each 25 cassettes, the etching variation of the silicon oxide film within the wafer surface was within ± 3%.
[0036]
When etching was performed using the conventional loop antenna 102 under the same conditions, 6 wafers out of 25 cassettes were insufficiently etched.
[0037]
In the above-described plasma excitation loop antenna of the present invention, each partial antenna is arranged in a circular loop shape. However, in the plasma excitation antenna of the present invention, each partial inductance is arranged in a square loop shape. Includes antenna.
[0038]
As an example of a plasma excitation antenna arranged in a square loop shape, 10 capacitors of 500 pF and 11 partial inductances were used, and the capacitors and partial inductances were alternately arranged in a rectangular shape of 400 mm × 500 mm. I prepared something.
[0039]
The capacitor connected in series with the loop antenna in the matching box was 500 pF, and the ITO film formed on the surface of the rectangular substrate was etched. The inductance value of each partial antenna was about 0.15 μH.
[0040]
The etching gas was a mixed gas of SiCl ₄ gas and Cl ₂ gas, and the flow rate was 100 SCM and the pressure was 1.0 Pa. A high frequency voltage with a frequency of 13.56 MHz was applied to the plasma excitation antenna, and 5 kW of power was applied. A high frequency voltage with a frequency of 13.56 MHz was applied to the substrate, and 200 W of power was applied.
[0041]
As a result, a high etching rate of 1500 Å / min was obtained. The etching variation in the substrate surface at this time was ± 8% or less, and the etching uniformity was good.
Using a conventional loop antenna, the same power was applied to perform etching, but discharge occurred between the end on the power supply voltage side and the end on the ground potential side, and stable etching could not be performed. .
[0042]
<Plasma CVD>
Next, a loop antenna was formed using five capacitors of 500 pF and six partial antennas, and applied to a plasma CVD apparatus to form a silicon oxide film on the substrate surface. A mixed gas of TEOS gas with a flow rate of 100 SCCM and O ₂ gas with a flow rate of 600 SCCM was used as a raw material gas, a pressure of 5 Pa, a 500 pF capacitor connected in series with a loop antenna in a matching box, and an input power of 500 W were used.
[0043]
Two frequencies of 13.56 MHz and 40.1 MHz were applied as the frequency of the high-frequency voltage, and the film formation rates were compared. In either case, plasma of the source gas was stably generated, and high film formation speeds of 180 mm / min and 560 mm / min were obtained, respectively.
In the conventional loop antenna, the plasma is not stable at 40.1 MHz, and a silicon oxide film cannot be formed.
[0044]
【The invention's effect】
Even when a large high-frequency current flows, the value of the applied high-frequency voltage is small, so that no discharge occurs between the terminals. In addition, since the value of the high frequency voltage to be applied is small, the material constituting the plasma generation tank is not sputtered, and impurities are not mixed into the plasma.
[0045]
Since a high-frequency voltage can be applied, high-density plasma can be generated efficiently.
[Brief description of the drawings]
FIG. 1A is a perspective view showing an example of a plasma excitation antenna according to the present invention.
(b): A diagram for explaining the connection between the partial antenna and the capacitor. [FIG. 2] (a): A diagram for explaining a state in which the plasma excitation antenna of the present invention is arranged on the plasma generation tank.
(b): Diagram for explaining an equivalent circuit of the plasma excitation antenna of the present invention. FIG. 3 (a): An example of an etching apparatus using a loop antenna of the prior art.
(b): Perspective view of the loop antenna
(c): Diagram for explaining the equivalent circuit of the loop antenna [Explanation of symbols]
2 …… Plasma excitation antenna 3 …… Plasma processing devices 21 to 25 …… Partial antennas 31 to 35 …… Inductance portions 12, 71 to 74 …… Condensers

Claims (4)

A plasma excitation antenna to which a high frequency voltage is applied,
Having a plurality of partial antennas configured to radiate electromagnetic waves and a plurality of capacitors;
The partial antenna and the capacitor are electrically connected alternately to each other, and a partial LC series circuit composed of one capacitor and one partial antenna connected to each other includes the applied high-frequency voltage. A plasma excitation antenna characterized by being placed in a resonance state with respect to a frequency of . The plasma excitation antenna according to claim 1, wherein one end is connected to a power source via a matching box having a capacitor.
The antenna for plasma excitation, wherein the plurality of capacitors includes a capacitor in the matching box .   3. A plasma processing apparatus comprising: the plasma excitation antenna according to claim 1; and a plasma generation tank for introducing a gas to be converted into plasma. The plasma processing apparatus according to claim 3, wherein the plasma processing apparatus has a plurality of the plasma excitation antennas and is configured to convert the gas in the same plasma generation tank into plasma with each plasma excitation antenna.
A plasma processing apparatus, wherein each plasma excitation antenna has a characteristic resonance frequency different from each other by 1 kHz or more.

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