JP3076843B1 - Plasma beam generator - Google Patents

Abstract

Abstract: [PROBLEMS] In the field of semiconductor processing,
Controllable low energy (100 eV) required for plasma etching and plasma doping of insulators and metal materials
(Below) Generate a focused ion beam with large current, large diameter, and low cost. SOLUTION: A high-density plasma is generated by a plasma source, a distance between an extraction electrode 1 and an acceleration electrode 2 is set to 1.0 mm or less, and a thickness of the extraction electrode 1 is set to 1.0 mm or less. Extraction is performed using three porous electrodes 1, 2, and 3 that perform extraction, acceleration, and deceleration, which are composed of a melting point and a high thermal conductive material. Beam energy 100e
Plasma beam composed of a high-current ion beam with an energy spread of 2.5% or less, a space divergence of 5 degrees or less, and an electron whose temperature can be controlled at an electron temperature of 0.5 eV or less and a space potential of 0 to 50V. Get. Thereby, charge-up of the insulator is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of semiconductor processing, which comprises a converged low-energy ion beam and low-temperature electrons that can be controlled in plasma etching and plasma doping of insulators and metal materials. The present invention relates to a generator for generating a plasma beam with a large current.

[0002]

2. Description of the Related Art Conventionally, as ion sources for plasma etching, mainly, Hiroharu Fujita; Nuclear Fusion Research Vol. 68,
No. 6 (1992) 556 (hereinafter referred to as known document A), O. Tsukakoshi, S. Shimizu, S. Ogata, N. Sasak
i & H. Yamakawa; Nuclear Instruments and Methods in
Physics Research B55 (1991) 355-358, or "Evaluation Report on Research and Development of Super Advanced Machining System"; Industrial Technology Council, Industrial Science and Technology Development Subcommittee, Super Advanced Machining System Evaluation Committee, August 1994, pp200-210 (Publication B
That. 2) There are two methods.

As shown in the left figure of FIG. 1, the system described in the known document A shows a system using a sheath formed at the boundary of the plasma. When rf discharge is performed between the anode and the cathode, the anode and the plasma, and the plasma and the cathode are separated. A sheath forms between them. The appearance of the sheath at that time is shown in the right diagram of FIG. The ions are accelerated by the negative potential to etch or dope an object (wafer). It is the simplest, high yield, large diameter, and low cost ion source.

[0004] The system described in the known document B is a normal ion source as shown in FIG. A plasma is generated by the ion power source on the left, and about three electrodes are used to extract the ion current.
Accelerate to 0kV and run a long distance. Then, just before the object (wafer), the deceleration is reduced by 29.9 kV to obtain a low energy ion beam of 100 eV. Compared to the method described in known document A,
Since the convergence of the ion beam is good and the energy and the energy distribution can be controlled, improvement in etching or doping performance can be expected.

[0005]

However, since the method described in the known document A utilizes ion acceleration in a plasma sheath, there are the following problems. (1) The sheath voltage is determined by the plasma density, temperature, neutral gas pressure, and the like, and is difficult to control. (2) The electron temperature of the plasma is generally several eV, and the dissociated molecules are reionized and cause impurities. (3) When the object is a metal, the sheath voltage may be controlled by applying a voltage to the object. However, when the object is an insulator, the voltage cannot be applied, and the sheath voltage is controlled. And damage to the object due to ionic charge accumulation. (4) Since the sheath shape is determined by the properties of the plasma,
Since ions have a range of energy and are obliquely incident on the space, it is difficult to perform rectangular vertical etching.

[0006] The method disclosed in the known document B is a low energy ion beam which compensates for the disadvantages other than the above (3). However, in order to obtain a beam current, first, ions in the plasma are accelerated at a high voltage over a long distance, so that the size and cost are increased. Nevertheless, the current is small, the aperture cannot be increased, and the beam expands during deceleration, resulting in poor convergence. Hajime, Akira Ohara; Electronic Technology Research Institute, Vol. 58 (1994) 73).

[0007] In order to be used in the industrial world, a controllable converged large current plasma beam must be stably generated for a long time. However, the problem to be solved by the present invention is this point.

[0008]

According to the present invention, there is provided a plasma beam generating apparatus having an ion energy of 100 eV or less, comprising: a plasma source for generating a high density; 1.0 mm or less, the thickness of the extraction electrode is set to 1.0 mm or less, only the ions in the plasma, high melting point, extraction using high heat conductive material, acceleration, using three porous electrodes to decelerate By extracting and neutralizing the space charge of the ions using a neutralizing electron source, the space potential comprised of a converged high-current ion beam and electrons whose electron temperature can be controlled at 0.5 eV or less. Provided is a plasma beam generation apparatus characterized in that a plasma beam controllable to 50 V is generated stably for a long time.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an ion beam generating apparatus according to the present invention will be described based on embodiments with reference to the drawings. FIG. 3 is an apparatus showing an embodiment of the present invention.
In FIG. 3, a high-density plasma is generated by a plasma source, and only ions in the plasma are accelerated by three porous electrodes arranged close to the plasma source, namely, an extraction electrode, an acceleration electrode 2, and a deceleration electrode 3. I do.

Since the ion current drawn from the extraction electrode is proportional to the plasma density of the plasma source, a plasma source capable of generating a high density is used. In this example, it is of a bucket type, and tungsten heaters are provided in the discharge square container 4 at two places in the upper, lower, left and right, or both four places to serve as the cathode 5, and the discharge is performed using the surrounding discharge vessel 4 as the anode.

The discharge rectangular container is made of a copper block in which a cooling pipe is embedded so as to withstand a heat load, and is water-cooled. Further, the inner surface is lined with molybdenum so as to withstand the heat load, and the plasma heat is transferred to the copper block for cooling. Square vessel for discharge to reduce plasma particle loss
A permanent magnet 6 is embedded around the outside of 4. permanent magnet
6 is also water cooled.

The discharge voltage of the plasma source is 80 to 150 V, the discharge current is 2 to 20 A, the gas pressure is 2 to 10 mTorr, and the type of plasma is argon plasma.
Plasmas such as helium, krypton, xenon, and nitrogen, as well as fluorocarbon-based gas, fluorine-based gas, and chlorine-based gas plasma diluted with argon, hydrogen, and the like can be used. This plasma source can extract ions of about 1 A at an ion transmittance of 50% when the discharge power is 2 kW as an ion source.

[0013] Even if the plasma density of the plasma source is sufficiently high, ions extracted from the extraction electrode are limited by their own space charges, and their space charge limited current density j
Is represented by the following equation (1).

[0014]

(Equation 1)

[0015] Here, epsilon ₀ is the dielectric constant in vacuum, e is elementary charge, M is the mass of the ion, V _E is the beam energy (accelerating voltage), d is the distance the accelerating electric field extends over approximately the extraction electrode This is the distance between 1 and the acceleration electrode 2 (see FIG. 4). Therefore, in order to obtain a large current with a beam energy of 100 V or less, it is necessary to make d as short as possible.

Accordingly, the thickness w1 of the extraction electrode 1 also needs to be reduced. Actually, j is increased by setting the distance d to 1 mm or less and the thickness w1 to 1 mm or less. At this time, extraction electrode 1 and acceleration electrode 2
Since it is necessary to create a lens action of the electric field between the two, the aperture diameter a and the shape of the extraction electrode 1 are determined with respect to d so as to be a convergent beam. The value of a / (d + (w1-w11)) is 0.5 to 1.5. To improve the convergence of the beam, the value of a / d is reduced, and if a current is desired, the value of a / d is increased.

As shown in FIG. 4, the hole shape of the extraction electrode 1 is processed so as to form a concave lens in the direction of the acceleration electrode 2. Acceleration electrode hole diameter a2, deceleration electrode hole diameter a3 and their spacing
d2 is determined with respect to d so as to be a convergent beam. These ratios are kept constant, and d is set to 1.0 mm or less. Incidentally, in the present embodiment, the hole diameters of the extraction electrode 1, the acceleration electrode 2, and the deceleration electrode 3 are a = 1.2 mm, a1 = 1.5 mm, a2 = 1.0 mm, a3 = 1.0 mm. Distance d = 1.0-1.5 m
m, the distance d2 between the acceleration electrode 2 and the deceleration electrode 3 is 1.0 mm.

Electrode thickness w1 = 1.0 mm, w11 = 0.3 mm, w2 =
1.0 mm, w3 = 1.0 mm. So far w1 is 0.5
The maximum current is obtained when mm and d are 0.5 mm. Number of holes 1
000 pieces or more, transmittance 50% or more.

The extraction electrode 1, the acceleration electrode 2, and the deceleration electrode 3
When the thickness of the extraction electrode 1 is reduced, the extraction electrode 1, acceleration electrode 2, deceleration electrode 3
However, those having a large diameter may be deformed due to thermal distortion or the like due to the thermal load of the DC discharge plasma, and the lens function may not work. Therefore, extraction electrode 1, acceleration electrode 2, deceleration electrode
3 is made of a material having a high melting point and high thermal conductivity such as tungsten, molybdenum, and graphite.

When the thickness of each electrode is 0.5 mm or less, tungsten is used, and the hole is formed by photoetching. In the case of drilling a hole with a thickness larger than that, it shall be machined. The draw-out, acceleration, and deceleration electrode flanges 7, 8, 9 are assembled and assembled via an insulating flange 11, and cooling pipes are embedded in these flanges 7, 8, 9 to connect cooling water in series. The temperature of the porous three electrodes is made the same. As a result, a large-diameter, large-current beam can be stably generated for a long time by DC discharge.

[0021] Since the beam energy V _E is not current can be obtained in the following 100V, once raising the V _g2 to about 2 kV, V
_E + V Accelerates to _g2 , draws out ion current, and immediately after V
and _g2 reduction, produces the following beam V _{E =} 100 eV. However, this V _g2 is adjusted so as to obtain an optimum convergent beam. Usually, it is 2 kV ± 1 kV. The potential of the deceleration electrode 3 is 0V. Voltage difference between extraction electrode 1 and deceleration electrode 3 (100
V or less) is the ion energy. The energy of ions can be controlled by changing the difference voltage.

When the beam decelerates to 100 eV or less, the beam has an energy width due to its own space charge and diverges spatially.
Space potential rises. When the wafer is made of an insulating material, as in the method of the related art (B), the wafer is charged up. In view of this, an electron source 10 made of a tungsten heater is provided behind the three-electrode porous electrode to eliminate the space charge of ions and produce a plasma beam. By adjusting the number of electrons, an electron temperature (about 0.3 eV) whose minimum electron temperature is determined near the heater temperature can be obtained.

Further, a plasma beam or a collector (not shown in the figure, but usually having a potential of 0 V
By applying a suitable voltage V _n with respect to), can to be substantially 0 V completely neutralized plasma space potential space charge of the ion. Wafer charge-up is avoided.

By changing the potential of the electron source from the plasma potential, the electron temperature of the plasma beam can be controlled. Further, the plasma space potential can be controlled.

According to this method, the energy is 50 to 100 eV
A current of 50 to 70 mA has been obtained with these ions.

FIG. 5A shows the result when the porous three electrodes are made of copper and the effective drawing area is 10 cm ² . Density of ion beam (100 eV) against current of neutralizing electron source
_{(I ion),} the electron density _{(n e),} shows an electron temperature _{(T e).} With the optimum neutralizing electron source current, the ion beam density is increased about three times, the electron density is increased by about one digit, and the electron temperature is 0.35 eV. FIG.
(B) shows the electron temperature (T _e ), the electron density ( _ne ), and the plasma space potential when the potential from the collector potential of the electron source is changed.
(V _s ).

The electron temperature and the plasma space potential can be controlled. At this time, the plasma potential was 1 V or less, the energy width of the ions was 2.5% of the energy, and a converged plasma beam with a space spread of 5 degrees or less was obtained.

Although this copper material is a high heat conductive material, the beam current tends to decrease and the beam tends to expand with the passage of time, and it has been difficult to further increase the aperture and reduce the electrode plate thickness. Since thermal distortion is suppressed when the effective area of a refractory material of the present invention shown in FIG. 3 is 60 cm ^2, about 6
Double ion current should be obtained stably for a long time.

Therefore, according to the present invention, the ion energy is 10
A plasma beam generating apparatus of 0 eV or less, wherein a plasma source for generating high density and an extraction electrode-acceleration electrode distance
1.0 mm or less, the thickness of the extraction electrode is set to 1.0 mm or less, and only the ions in the plasma are extracted using three porous electrodes that are made of a high melting point and high heat conductive material and accelerate and decelerate. By neutralizing the space charge of the ions using a neutralizing electron source, the space potential is composed of a converged high-current ion beam and electrons whose electron temperature can be controlled at 0.5 eV or less. A plasma beam generation apparatus characterized in that a plasma beam that can be controlled in a stable manner is generated with a direct current for a long time.

[0030]

According to the present invention, it is possible to generate a low-energy, focused ion beam with a large current, which has been conventionally difficult. Therefore, rectangular vertical etching can be realized. Plasma etching is possible even with an insulator. It is possible to form a film with high precision in the thickness direction of the film, to produce a film having a larger diameter than a conventional ion beam, and to produce a small-sized apparatus at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a conventional technique.

FIG. 2 is a diagram illustrating another conventional technique.

FIG. 3 is a diagram showing an embodiment of the present invention.

FIG. 4 is a diagram illustrating electrode thickness, hole diameter, and interval between electrodes according to an example of the present invention.

FIG. 5 is a graph illustrating the role of an electron source for ion space charge neutralization in the present invention. FIG. 5B shows the electron temperature when the potential from the collector potential of the electron source is changed.
(T _e ), electron density ( _ne ), and plasma space potential (V _s ).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Extraction electrode 2 Acceleration electrode 3 Deceleration electrode 4 Square vessel for discharge 5 Cathode 6 Permanent magnet 10 Electron source

Claims (1)

(57) [Claims] An ion is extracted from a plasma source that generates high-density plasma by using three porous electrodes of an extraction electrode, an acceleration electrode, and a deceleration electrode, and the space charge of the ions is neutralized by using a neutralizing electron source. A plasma beam generating apparatus having an ion energy of 100 eV or less for semiconductor processing, wherein a distance between the extraction electrode and the acceleration electrode is 1.0 mm or less, and a thickness of the extraction electrode is 1.0 mm or less . ,drawer
The electrode is processed like a concave lens in the direction of the accelerating electrode,
The three porous electrodes are made of a material having a high melting point and a high thermal conductivity, and are composed of a high-current ion beam converged by controlling the neutralizing electron source and electrons that can be controlled at an electron temperature of 0.5 eV or less. Space potential of the plasma beam is 0-5
A plasma beam generation apparatus for stably generating a plasma beam that can be controlled to 0 V for a long time.