RU2324255C2 - Flexible arc source of vuv photons and reactive particles - Google Patents

Abstract

FIELD: sources of VUV photons and reactive particles.

SUBSTANCE: flexible arc source of VUV comprises discharge tube made of cooled metal sections with protective coating, field arc cathode with containment of arc cathode spots in working space, anode, and system for working gas export or puffing. In tube sections, perpendicular to discharge axis, side holes are made, their size comparable to section length. These holes are used for tight securing of supports being treated, either with masks or without them.

EFFECT: possibility for irradiation, etching and buildup of materials on supports of large total area of treatment, using reactive particles and VUV photons emitted by nearly entire discharge side surface.

2 cl, 1 dwg

Description

The invention relates to the field of producing low-temperature plasma, and more particularly to gas-discharge sources (generators) of VUV photons and chemically active particles (atoms, molecules, ions, radicals) for surface treatment and plasma-chemical etching or buildup of materials on substrates (samples).

Known sources of continuous vacuum ultraviolet (VUV) radiation — synchrotron radiation and gas-discharge sources with differential pumping chambers for outputting radiation [1,2] —are not widely used due to their bulkiness, high cost, and small area of the output radiation beams. To increase the area of a single processed substrate (with a diameter of up to 100 mm) during arc plasma-chemical build-up of materials, a system of several arc sources (ie, a system with several cathodes) is usually used [2], which complicates the design, worsens the uniformity of the build-up layer, and reduces the efficiency process (due to significant losses of electricity in the electrode areas).

The prototype of the claimed device is a high-current discharge tube developed by the author [3] with end windows (openings) for radiation output, consisting of separate aluminum sections cooled with water [2] with a protective Al ₂ O ₃ coating and developed by the author [5] cold arc cathode with retention of the cathode spots of the arc inside the working cavity. Gas is pumped out from one end of the tube, and gas (gases) is admitted from the other end.

When such a tube is filled with inert gas and an arc discharge is ignited, the population of excited levels of ion lines reaches ~ 10 ¹⁰ cm ^-3 , which provides powerful continuous spontaneous emission from these levels. However, the most powerful and shortest wavelength radiation of resonant ion lines with wavelengths in the range of ≈230 ÷ 304 Å, 330 ÷ 460 Å and 550-750 Å for He ⁺ Ne ⁺ Ar ⁺ ions, respectively, experiences strong resonance absorption, since the concentration of ions in the ground state high ~ 10 ¹⁴ cm ^-3 . Due to resonance absorption, the most intense VUVs - photons entering the end windows are emitted only from the end sections of the discharge of a small length (~ 1-2 cm), while VUV - radiation from the entire discharge column (length (~ 1-2 m) heats the side walls of the tube aimlessly.

This main disadvantage is eliminated in the present invention, where the increase in the total area of the irradiated (processed) surface of the substrates is achieved through the use of VUV photons emitted from almost the entire side surface of the discharge.

To do this, in the tube sections perpendicular to the discharge axis, side holes are made, comparable in size to the section length, in which the processed substrates with masks (or without masks) are hermetically fixed using holders. As a result, it becomes possible to use radiation from the entire discharge column.

When applying voltage to the electrodes (cathode, anode) and forming an arc discharge with a cold cathode and holding cathode spots inside the cathode cavity [5], a high-current discharge is established with a “positive” column passing through the central openings of the sectioned tube and radiating from its entire side surface spontaneous emission from excited levels.

As an example, we consider the case of a high-current (hundreds of amperes) discharge in helium at a filling pressure of ~ 1 Top. Then, high-power VUV radiation will be focused on resonant ion transitions in the range 230–304 Å. It is significant that the resonance radiation of atomic lines (≈505-590 Å) will be absorbed by a gas located between the side surface of the discharge column and the irradiated substrate.

Chemically active particles can form in the positive column of the arc discharge [2]. In particular, when filling the proposed source with halogen-containing gases, it can be used for chemical etching of semiconductor substrates. In this case, to optimize the process, it is necessary to fix the substrate with the possibility of changing its distance from the discharge axis. The latter is achieved using the proposed design, in which the substrate holder is made of two parts: fixed and inserted into it movable with a fixed substrate.

The fixed part seals the side openings, and the movable part (with a fixed substrate) is inserted into the first and fixed in position with the help of a sealing ring connection.

The proposed source can also be used for plasma-chemical build-up of materials, for example, diamond on substrates. In this case, a frequently used mixture of gases with a high hydrogen content and a small admixture of carbon-containing gas can be used at a total pressure of ~ 50-100 Top. To heat the substrate and control the temperature when building the material, it is proposed to place a heater and a temperature sensor, for example thermocouple, in the substrate holder (near the surface in contact with the substrate).

The novelty of the proposed arc source is:

- in the design of the discharge tube, in which holders with substrates are located laterally in the holes of the sections of the discharge tube along the entire length of the discharge column without any additional sealing window (which is available in known sources) for outputting radiation;

- in the proposed design of the holder, in which the movable part is mounted coaxially inside the stationary part sealing the hole in the tube section with the substrate, heater and temperature sensor fixed.

The universality of the proposed source lies in the fact that with its help it is possible to perform both surface treatment and plasma-chemical etching of substrates, and the buildup of materials on substrates (samples). Known sources of radiation can perform only any one of the above operations for processing substrates.

The drawing (FIG. 1) illustrates a general view of the proposed universal arc source (FIG. 1 a), a separate section (FIG. 1 b) of a discharge tube with holes for round-shaped substrate holders, and a section view to the right (FIG. 1 c) using the symbols:

K is the cathode with retention of the cathode spots of the arc inside its cavity,

A is the anode

C - water-cooled aluminum section of the tube with Al ₂ About ₃ - coating (section length L),

P is the positive column of the discharge of length i (in Fig.1A is highlighted by a dotted line),

O - end window

1 - hole for the discharge (diameter D),

2-6 holes for water cooling,

3-6 holes for tightening bolts (the centers of holes 2 and 3 are located on circles crossing the boundaries of 60 degree sectors),

4 - groove under the vacuum seal,

5 - groove under the seal for water,

6 - side hole (diameter d),

7 - substrate holder,

8 - processed substrate,

9 - mask

10 - holes for bolts of vacuum tight fastening of the substrate holder.

). В случае квадратной формы боковых отверстий (со стороной квадрата равной d ) суммарная площадь обрабатываемых подложек увеличивается, примерно, до 64% от боковой поверхности разряда. (Ранее, в прототипе, для обработки подложек использовалось излучение лишь с площади, определяемой размерами двух выходных торцевых окон).The vacuum-tight assembly of all sections of the universal arc source, as in [4], is carried out through O-rings (located in the grooves 4) when the structure is pulled together with insulation bolts (passing in the holes 3). At the same time, through the ring seals (located in the grooves 5), the sections are water-cooled. Bolt fasteners of the electrodes, the window O and the substrate holders 7 are also carried out through ring vacuum seals (Fig. 1c schematically shows the substrate holder 7, consisting only of a fixed part). Gas is usually pumped from the discharge tube from the anode end of the device, and gas is supplied from the cathode. With a discharge diameter D = 40 mm and a section length L = 30 mm, side openings with a diameter of d = 20 mm (i.e., the size of the irradiated substrates 20 mm) can be made, therefore, the total area of the irradiated (processed) substrates can be at least 50% from the lateral surface of the entire discharge column (area S = πD

) In the case of the square shape of the side holes (with the side of the square equal to d), the total area of the processed substrates increases to about 64% of the side surface of the discharge. (Previously, in the prototype, for processing the substrates, radiation was used only from the area determined by the size of the two output end windows).

High-current discharge tubes of cooled metal sections with a protective coating and cathode [5] have been used for more than thirty years to produce high-power (hundreds of watts) short-wave laser radiation on argon ions both at the institutes of the SB RAS and at other domestic and foreign enterprises.

The presence of VUV radiation in high-current discharge tubes was evidenced by a color change occurring under the influence of such radiation and subsequent destruction of the laser mirrors (located at position O of FIG. 1a). To prevent the destruction of mirrors, it was necessary to take special measures, for example, to spray an additional protective Al ₂ O ₃ coating.

The possibility of obtaining chemically active particles in the proposed device is confirmed by direct experiments with a mixture of gases with a high hydrogen content, and with a halogen-containing gas. In particular, the laser for the first time that was launched [6] in the cw regime of UV transitions of the Cl ⁺⁺ ion had an output power and I – V characteristic comparable to that of an Ar ⁺⁺ laser, which showed that in the high-current discharges used, chlorine was in the atomic state (i.e. in chemically active).

Information sources

1. Seidel A.N., Schreider E.Ya. Vacuum ultraviolet spectroscopy. - M .: "Science", 1967.

2. Encyclopedia of low-temperature plasma / Ed. Fortova V.E., vol. 4. - M.: “Science” - 2000.

3. Donin V.I. ZHETF, 1972, v. 62, v.5, p. 1648.

4. Donin V.I., Klementyev V.M., Chebotaev V.P. Zhurn. adj. spectrum., 1966, v. 5, No. 3, p. 388.

5. Donin V.I. Auth. testimonial. USSR No. 289458, cl. H01j 17/06, publ. 1970.

6. Donin V.I., Timofeev T.T., Yatsenko A.S. Letters to the ZhTF, 1983, vol. 9, v.6, p. 373.

Claims (3)

1. A universal arc source of VUV photons and chemically active particles, comprising a discharge tube of cooled metal sections with a protective coating, a cold arc cathode with the cathode spots of the arc inside the working cavity, an anode, a pumping system and a working gas inlet, characterized in that sections of the tube perpendicular to the discharge axis carry out side openings of a size comparable to the length of the section, in which the processed substrates with masks (or without masks) are hermetically fixed using holders. 2. The universal arc source according to claim 1, characterized in that the substrate holder is made of two parts: fixed and inserted into it - movable with a fixed substrate. 3. The universal arc source according to claim 1 or 2, characterized in that the substrate holder comprises a heater and a temperature sensor, for example thermocouple.