JP2902910B2 - LEP power phase fine adjustment mechanism - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching apparatus which uses a rotating electric field to convert gas into plasma.
The present invention relates to a mechanism for finely adjusting the phase of power to be applied to a P electrode.
In order to further increase the density of semiconductor integrated circuits, advances in photolithography and etching technologies are indispensable.

[0002]

2. Description of the Related Art In dry etching, a gas is converted into a plasma, which is accelerated and applied to a substrate to remove a semiconductor portion of the substrate which is not covered with a resist by a physical and chemical action. It is desirable to etch portions not covered by the resist as vertically as possible. Wet etching, which may be used in other fields, proceeds isotropically. On the other hand, etching progressing only perpendicular to the resist surface is called anisotropic etching. Dry etching is excellent in anisotropy. The above-mentioned property can be expressed by the fact that the anisotropy is high.

When the semiconductor portion is simply removed by the physical impact of ions, an inert gas may be used as the gas. It is simply called ion etching. However, this is rarely used because the etching rate is low.

At present, the most widely used etching method is reactive ion etching (RIE). The semiconductor is removed by a chemical reaction using a halogen gas as a gas. In this method, a high frequency is applied to a halogen gas or the like using a parallel plate electrode or the like to generate plasma, thereby etching a semiconductor portion. In order to cut a semiconductor vertically in a fine resist hole, the incident direction of ions must be perpendicular to the substrate surface. For this purpose, the mean free path of ions may be lengthened to reduce the scattering probability. Therefore, it is necessary to increase the degree of vacuum. However, when the degree of vacuum is increased, high-frequency discharge becomes difficult to occur. Then, the etching rate decreases.

In order to solve this problem, a magnetron reactive ion etching method and an ECR etching method have been developed. In the magnetron reactive ion etching method, for example, four electromagnets are provided around a conventional parallel plate electrode, and the phase of the exciting current of the electromagnets is changed by 2π / 4 to generate a rotating magnetic field in the chamber. It is intended to cause electron cyclotron motion to increase ionization efficiency.

In the ECR etching method, for example, a coil is provided outside a chamber to generate a DC magnetic field in a vertical direction.
A microwave of 2.45 GHz is introduced into the chamber from outside. Electrons undergo cyclotron motion due to a DC magnetic field. If the period of the electrons is made equal to the period of the microwaves, the electrons resonately absorb the microwaves. Since the electrons that have obtained the kinetic energy collide with gas atoms and molecules and turn them into ions, the ionization rate is also improved.

However, in the magnetron reactive ion etching method, the density of the rotating magnetic field is not spatially uniform. Therefore, the plasma density becomes spatially non-uniform. In the ECR etching method, since the magnetic field is still spatially non-uniform, the plasma density becomes spatially non-uniform. As described above, there is a method of maintaining a discharge even in a high vacuum and increasing an ionization rate. However, there is a disadvantage that the plasma density becomes non-uniform due to the spatial non-uniformity of the magnetic field.

Since the semiconductor portion is removed by the action of plasma or radicals, if the plasma is not spatially uniform, the etching rate will not be spatially uniform.
If a large-diameter wafer is to be etched, the etching rate in the plane of the wafer becomes non-uniform. Therefore, these methods are not suitable for etching a large-diameter wafer.

Therefore, a dry etching method using a rotating electric field has been invented by the present inventors. JP-A-4-268
727 and JP-A-4-290226. A high-frequency voltage having a phase difference of 2π / n is applied to n electrodes to generate a rotating electric field in the chamber, thereby rotating the electrons around the vertical axis, accelerating them, hitting the gas atoms into a plasma, and converting the plasma into a plasma. Is etched.

This is one in which upper and lower parallel plate electrodes and n LEP electrodes are provided in a chamber. The substrate to be etched is placed on the lower parallel plate electrode. The LEP electrodes are provided to face each other so as to be rotationally symmetric. The upper and lower parallel plate electrodes generate an alternating electric field in the vertical direction. The lateral LEP electrodes generate a rotating electric field in the horizontal direction. The high frequency applied to the upper and lower parallel plate electrodes is, for example, 50M.
Hz, the high frequency for the horizontal rotating electric field is 300 MHz.

As described above, reactive ion etching utilizes only parallel plate electrodes. Compared to this, the number of LEP electrodes provided on the intermediate side is increasing. Since the magnetron reactive ion etching method includes upper and lower parallel plate electrodes and an intermediate side electromagnet, the electromagnet is replaced by an electrode in comparison with this.

The present inventor has named such an etching method utilizing a rotating electric field as the LEP method. The entire etching apparatus is called a LEP apparatus, and the lateral rotationally symmetric electrode is LEP.
It was decided to be an EP electrode. It is not a generic name. It may be called LEP or Lissajous plasma etching apparatus. The Lissajous figure is a trajectory of a two-dimensional motion obtained by synthesizing single vibrations in directions perpendicular to each other. It has this name because it can be drawn on a machine devised by LISSAJOUS of France.

X = A cos ωt, y = B cos (Ωt + δ) (1)

Is synthesized. That is, it is the locus of the point (x, y). Various figures can be obtained depending on the difference between the angular frequencies ω and Ω, the value of δ, and the amplitudes A and B. Obtain a variety of figures in addition to circles, ellipses, straight lines, etc. Even when the angular frequencies are equal, the ellipse,
It may be a straight line or a circle.

First, the present invention provides two sets of electrodes facing each other,
In other words, the four electrodes were placed at 90 degrees shifted from each other, and high-frequency waves having different phases and voltage amplitudes equal to each other by 90 degrees were applied to generate a rotating electric field. In the above equation, ω = Ω, A = B, δ = 90 degrees. Then, the electric field starts to make circular motion with Ω.

[0016] _{E X = Acos Ωt, E Y} = Acos (Ωt + π / 4) (2)

By applying voltages having a phase difference of 90 degrees to two pairs of electrodes facing each other in the horizontal direction, a rotating electric field can be formed. The electrode arrangement is in the direction to create an orthogonal electric field,
Since the phases are different, it was named Lissajous. In practice, the electric field vector is either circular or elliptical. It is not a division of drawing a complex general Lissajous figure.

However, the present inventor goes one step further, and should be able to form a rotating electric field even when a high frequency having a phase difference of 2π / n is applied to n electrodes placed at rotationally symmetric positions. Noticed. n = 3, not limited to n = 4
However, a rotating electric field can be generated even when n = 6. The n electrodes are arranged at rotationally symmetric positions so as to form a central angle of 2π / n degrees. That is, the position of the j-th electrode (X _j , Y _j )
Is

X _j = Hcos (Ωt + 2πj / n) (3)

Y _j = H sin (Ωt + 2πj / n) (4)

Assuming that the voltage V _j of the _j -th electrode is V _j = K cos (Ωt + 2πj / n) (5)

And so on. Then, the voltage at the center surrounded by the electrodes is zero. However, away from the center, a voltage proportional to the distance is generated. As for the electric field, the electric field at an arbitrary position is almost the same, and the electric field vector rotates so as to draw a circular locus. This electric field is on the xy plane and rotates at a rotational angular velocity of Ω. This fact is most easily understood when the phase is changed by 90 ° C. by using four electrodes. However, it can be understood that the electrodes form a rotating electric field even with four or more electrodes.

That is, generally, n electrodes are provided and 2π
When a high-frequency voltage having a phase shift of / n is applied, a uniform rotating electric field can be formed. Therefore, the Lissajous plasma etching is adopted including such a case. Three or five LEP electrodes are called. The electrodes are sometimes called Lissajous electrodes to distinguish them from the device.

[0024]

The case of four electrodes will be described for simplicity. If there is a rotating electric field as in equation (2), the equation of motion of the electron is

M (dx ² / d ² t) = A cos Ωt (6)

M (dy ² / d ² t) = A sin Ωt (7)

## EQU1 ## Since it is in a vacuum and the gas density is low, the probability of ion-induced scattering of cron is low. There is no such thing as a resistance term, and nothing like a potential field. This equation has the following stationary solution:

X = − (A / mΩ ² ) cosΩt + ut + x ₀ (8)

Y = − (A / mΩ ² ) sin Ωt + vt + y ₀ (9)

U, v, x ₀ and y ₀ are integration constants and are determined by initial conditions. This indicates a motion obtained by adding a linear motion to a circular motion. Actually, they collide with gas atoms, ions, electrons, etc., so that energy is exchanged each time. A large mass such as an atom or ion has a low velocity,
In many cases, electrons lose energy and give energy to atoms and ions. This energy is the kinetic energy
In some cases, an electron in an atom may be excited, and other than the electron, it may be ionized.

At this time, the constant determined by the initial condition is ignored.
Focusing only on the expressions of sin Ωt and cos Ωt, it can be seen that the electrons make a circular motion with an amplitude of (A / mΩ ² ). The phase is 180 degrees different from the electric field. The resulting kinetic energy -W of the electron is

W = A ² / (2 m ² Ω ² ) (10)

Is as follows. Steady state electrons have this much energy. This is proportional to the square of the electric field strength A.
Of course, ions, which are charged particles, also obtain energy directly by an electric field, but the energy is very small due to the large mass. It is electrons that can obtain high energy directly from the electric field. The electrons originally obtain energy from the electric field and make a circular motion at high speed. This collides with gas atoms and gives energy. The atoms are excited to become ions or neutral radicals.

This can be said only when the electric field vector draws a clean circle. However, when a plurality of devices are manufactured, individual differences occur in the phase shifter, the RF cable, the electrode capacitance, and the like, and the phase of the power applied to each electrode is 2π.
/ N. If the phase shift of the LEP electrode is not exactly 2π / n, the electric field vector does not draw an accurate circular locus. In this case, a more complicated Lissajous figure is drawn. When a circular motion is drawn, the kinetic energy is always constant and is expressed as in equation (10). However, when the elliptical motion is performed, the kinetic energy is not constant but fluctuates. Since the value of equation (10) is obtained when the kinetic energy is the maximum, the energy of the electrons decreases when the elliptical motion occurs. In other words, electrons cannot sufficiently extract energy from the electric field.

Then, when an electron collides with an atom, the energy given to the atom also decreases. Therefore, the plasma generation efficiency also decreases. Another is the reduced probability of collision. When a circular orbit changes to an elliptical orbit, the length of the orbit also decreases, and the probability of collision with atoms or the like decreases. Therefore, the probability of exciting atoms is reduced. Also for this reason, the plasma generation efficiency is reduced.

FIG. 3 shows a configuration of a power distribution / supply unit employed in the above-mentioned prior art. The oscillator / distributor 1 oscillates a high frequency of, for example, 300 MHz or 54.24 MHz, and distributes the high frequency to n LEP electrodes. The phase shifters (phase shifters) 2a, 2b, 2c,... Give a phase difference of 2π / n thereto. For example, coaxial cables having different lengths can be used. The power amplifiers 3a, 3b, 3c,... Amplify a signal of about mW to several tens of watts or several hundred watts. The automatic matching units 4a, 4b, 4c,... Are for impedance matching.

[0037]

The present invention provides n 2π / n.
The phase of the voltage applied to the LEP electrodes provided at different positions is finely adjusted so that the phase shift is correctly set to 2π / n, and the plasma generation efficiency is increased. For this purpose, the voltage of the high-frequency oscillator is divided into voltages having different phases, and a phase fine adjuster is provided before the phase shifter (phase shifter). There is a dedicated IC as a phase fine adjuster. The phase can be finely adjusted by inserting L (coil).

[0038]

A phase fine adjuster is inserted in front of a phase shifter for applying a voltage to each LEP electrode, and the phase of the voltage applied to each LEP electrode is strictly different by 2π / n. Thus, a rotating electric field can be formed. For this reason, the electrons draw a perfect circular orbit, have high energy, and have a high probability of collision with atoms and ions. As a result, the plasma generation efficiency increases. High-performance dry etching with high anisotropy can be provided.

[0039]

FIG. 2 is a schematic diagram of the entire dry etching apparatus to which the present invention is applied. The chamber 11 is a space that can be vacuumed. It consists of a cylindrical side wall, a disk-shaped top lid, a base forming a bottom surface, and the like. An LEP electrode 12 is provided in the upper half of the chamber 11. This is 3
There are n above. In this figure, three cases are shown.
, Four, etc. A lower electrode 13 is provided below the chamber 11. The semiconductor wafer 14 is mounted thereon and etched. A resist is applied to the wafer 14, and an appropriate pattern is cut out of the resist by photolithography.

The lower electrode 13 is supplied with high frequency power from a high frequency power supply 15. A high-frequency power supply includes an oscillator and a power amplifier. This is 50M in the previous example
Hz, but for example the more general 13.56 MHz
May be applied. Since the lower electrode is heated by the impact of the ion beam, a cooling device 16 is provided to prevent the temperature of the wafer from rising. This is to keep the temperature of the wafer constant by circulating a coolant through the cooling device and the lower electrode.

In order to apply a high frequency to the LEP electrode 12,
A high-frequency oscillator 17 is provided. This is divided into n high-frequency waves having different phases by the power distribution and supply unit 18, amplified, and provided to the n LEP electrodes 12. The spatial phase difference around the central axis is matched with the high-frequency phase difference.
The present invention is an improvement on the structure of the power distribution and supply unit. The etching gas is introduced from a gas inlet 19 and discharged from a gas outlet 20. The etching gas is, for example, Cl
₂ gases, the degree of vacuum during etching is 1 Pa to 10 P
a.

FIG. 3 shows the structure of the power distribution and supply unit 18.
This is an example where n = 3, but n may be any number. Although the frequency of this high frequency is arbitrary, for example, 54.
24 MHz.

In FIG. 1, the oscillator / distributor 1 includes an oscillator for generating a desired high frequency and a distributor for dividing the oscillator into n pieces. This is divided into n phase fine adjusters 22a,
b, c, .... The addition of this is a feature of the present invention. Further, the high-frequency signal passes through phase shifters (phase shifters) 2a, 2b, 2c,.
a, 3b, 3c,..., the automatic matching devices 4a, 4b, 4
c,.. are passed to the LEP electrode 12 in the chamber. Here, the load electrode unit 5 is the LEP electrode 12
And the lower electrode 13 is included.

The oscillator generates a high frequency with a power of several mW, for example. The distributor divides this into n pieces. The phase shifter (phase shifter) 2 gives a signal a delay of 2π / n. This is, for example, a coaxial cable of different length.
This is done by passing a signal through the bull. Let α be the wavelength shortening rate of the coaxial cable. The high frequency is f.
The length per cable unit corresponds to a phase of 2πf / cα. Then, the length .DELTA.L of the cable providing the phase difference of 2.pi./n is .DELTA.L = c.alpha. / Nf.

In this case, three LEP electrodes are installed and 5
Using a high frequency of 4.24 MHz, wavelength compression ratio α = 0.7
When using the coaxial cable RG-188A / U of
ΔL = 130 cm. So, the length is 29cm,
A 159 cm, 289 cm coaxial cable gives a phase difference of 120 degrees.

The power amplifier 3 power-amplifies a high frequency. The power of mW at the input is amplified to several hundred W at the output.
In this embodiment, amplification is possible up to a maximum of 300 W. Since the frequency is fixed, a tuned amplifier can be used.
An amplifier having a flat characteristic at 0 MHz is used.

The automatic matching unit 4 is a circuit that matches the output impedance of the high-frequency power supply and the impedance of the load electrode unit 5 because these impedances are different. Although the output impedance of the oscillator is, for example, 50Ω, the impedance of the load electrode is a small impedance such as 1 to 2Ω. The automatic matching unit 4 includes, for example, an LC resonance circuit. The load electrode unit is a general term for the LEP electrode and the lower electrode provided in the chamber. The output of the automatic matching unit 4 is connected to this, and plasma is generated between the electrodes.

In this example, there are, for example, three LEP electrodes 12, which are spatially arranged so as to form a central angle of 120 degrees. The phases of the power are also shifted by 120 degrees by the phase shifters 2a, 2b, and 2c. However, in practice, there is an error in the length of the coaxial cable, and the mechanical phase difference and the electrical phase difference may be different. In this case, the phase is finely adjusted by the phase fine adjusters 22a, 22b and 22c. There is a dedicated IC as the phase fine adjuster, which can be used. For example, PSCQ2-90. As a result, the phase can be changed within a range of several tens degrees (for example, ± 20 degrees). Alternatively, the phase can be adjusted by inserting a variable L and changing the L.

The oscillation / amplifier 6 oscillates a high frequency for the lower electrode and amplifies the power. This is an automatic matching device 7
And the impedance is matched, and given to the lower electrode 13. The high frequency of the lower electrode is 13,56 MH, for example.
z.

FIG. 4 shows a case where three LEP electrodes provided at rotationally symmetric positions with a central angle of 120 ° are used.
5 is a graph showing a result of measuring an electron density in plasma at a center of a space surrounded by electrodes when a phase angle is changed. The vertical axis is an arbitrary scale, and the horizontal axis is the phase difference of the voltage applied to each LEP electrode. Since three LEP electrodes are used, the desired phase difference is 120 degrees. Since three electrodes are used, there are two independent phase differences. The two phase differences are commonly changed to 0 degree, 60 degrees, 90 degrees, 120 degrees, and the like. The conditions for plasma generation are as follows. The gas is Ar, the pressure is 1 Pa, and the power of the LEP electrode is 30 W × 3 (the number of electrodes).

On this scale, when the phase difference is 120 degrees, the electron density is about 2.05. This is the maximum value. On the other hand, when the phase difference is 90 degrees, it drops to 1.8. When the phase difference is 60 degrees, it is about 1.75. When the phase difference is 0 degree, it falls to about 1.

When the phase difference is 180 degrees, three measurement points are shown. When the phase difference exceeds 120 degrees, the phase difference between the remaining two electrodes becomes smaller. There are a number of cases where there is a difference of 180 degrees. (0,18
(0 °, 180 °) means that when there are three electrodes A, B, and C (0, 120 °, 240 °), an upper phase difference is given to an electrode that should give a phase difference. That is, with respect to the first electrode phase, a 180 ° phase difference is given to the second electrode to give a phase difference of 120 °, and a 180 ° phase difference is given to the third electrode to give a phase difference of 240 °. That is. In this case, the electron density is about 1.8.

(180 °, 180 °, 0) means
(0 °, 0 °, 180 °). This is because the phases of the first and second electrodes are equal and the phase of the third electrode is 18
It is shifted by 0 °. In this case, the electron density is about 1.5.

In the case of (0 °, 180 °, 0 °), the electron density is the lowest at about 0.8. Thus 3
In the case of a single electrode, the phase difference of the voltage applied to each electrode is 120 °
It can be seen that the electron density is highest when.
This is the case of Ar, but the same applies to a general halogen-based etching gas.

[0055]

According to the present invention, the difference between the spatial angle of the LEP electrode and the phase of the high-frequency power are finely adjusted by the phase fine adjuster. Can be matched. Therefore, the Lissajous figure of the electric field vector formed by the LEP electrode is a circle. Therefore, the electrons rotate at high speed in a circular orbit. Electrons collide with gas molecules and form radicals or ions to form plasma. The highest plasma generation efficiency occurs when the electrons follow a circular orbit.

According to the present invention, the phase difference of the electric power is adjusted so that the electrons follow a circular orbit, and the plasma generation efficiency can be increased. Since the plasma density is increased even in a high vacuum, the efficiency of dry etching can be improved while maintaining the anisotropy.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a power distribution supply unit of a dry etching apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram of a dry etching apparatus to which the present invention is applied.

FIG. 3 is a schematic configuration diagram of a power distribution and supply unit according to a conventional example.

FIG. 4 is a graph showing the result of measuring the electron density in plasma while changing the phase angle of the LEP electrode.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 oscillator / distributor 2 phase shifter 3 power amplifying unit 4 automatic matching unit 5 load electrode unit 6 oscillation / amplifying unit 7 automatic matching unit 22 phase fine adjuster

Continued on the front page (72) Inventor Norihiko Tamaki 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Mitsuhiro Okuni 1006 Odaka Kadoma Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. Person Ichiro Nakayama 1006 Kadoma Kadoma, Osaka Pref.Matsushita Electric Industrial Co., Ltd. (72) Inventor Masafumi Kubota 1006 Kadoma Kadoma, Kadoma, Osaka Pref.Matsushita Electric Industrial Co., Ltd. 1006 Kadoma Matsushita Electric Industrial Co., Ltd. (56) References JP-A-60-153129 (JP, A) JP-A-62-273731 (JP, A) JP-A-3-257823 (JP, A) 4-317324 (JP, A) JP-A-61-202438 (JP, A)

Claims (1)

(57) [Claims] 1. A chamber capable of being evacuated, and n LEP electrodes (n) provided at a rotationally symmetric position above the inside of the chamber, facing each other and forming a central angle of 2π / n.
≧ 3), a high-frequency power source for generating a high frequency to be applied to the LEP electrode, and a signal generated by the high-frequency power source for distribution.
a power distribution and supply unit for applying a phase difference of π / n to the LEP electrode, a lower electrode provided below the chamber on which a semiconductor wafer to be etched is placed, and a high frequency power supply for applying a high frequency to the lower electrode; And introducing an etching gas into the chamber and turning it into a plasma by a rotating electric field,
What is claimed is: 1. A dry etching apparatus for etching a wafer with particles contained in a plasma, wherein a power distribution supply unit provides a phase difference of 2π / n to a high frequency signal distributed for each LEP electrode. And a power amplifier that amplifies the signal given the phase difference; an automatic matching device for matching the impedance of the high-frequency oscillator and the electrode; and a front or rear portion of the phase shifter for the distributed high-frequency signal. A phase fine adjuster for finely adjusting the phase, wherein the phase fine adjuster is operated to finely adjust the phase difference of the distributed high-frequency signal to be exactly 2π / n. Fine tuning mechanism.