DD237331A1 - HOLLOW CYCLE REACTOR FOR PLASMACHEMICAL APPLICATION - Google Patents

Abstract

The invention relates to a hollow cathode reactor for plasmachemisches etching of metal, insulator or semiconductor substrates. The invention can be used during dry-setting during the structuring of microelectronic components. The object of the invention is to exploit the advantages of DC glow discharge versus RF discharge in conjunction with the effective fragmentation and activation of an etching medium under discharge conditions having the hollow or double cathode effect.

Description

For this 3 pages drawings

Field of application of the invention

The invention relates to the use of DC low pressure glow discharge in the hollow cathode regime in the plasma chemical etching of solid surfaces.

The invention can be used for the etching of metal, insulator or semiconductor layers in the structuring of microelectronic components.

Characteristic of the known technical solutions

The plasma-chemical dry etching of solid surfaces currently takes place predominantly by means of high-frequency gas discharges in planar reactors.

The use of high frequency (usually 13.6 or 27.3 MHz) creates a significant disadvantage of the risk of radiation of electromagnetic energy, which is a serious disturbance in the vicinity of electrical and electronic measuring instruments is connected. As a remedy special shielding and Abblockmaßnahmen are required. Another shortcoming is the considerable effort required to determine the RF reactor data (eg, injected RF power) as well as the RF plasma data (eg, using probe-measured electron concentrations). In addition, due to the absence of high energy electrons, RF discharge is due to relatively low fragmentation of the etching gases used, i. relatively low production rates of active etching species.

The use of DC glow discharges is only set out in a few invention descriptions. For use of a hollow cathode, only a patent (DD WP 155181) could be identified, the hollow cathode being mentioned only as one among various arrangements for producing a localized and inhomogeneous plasma without specification as a glow or arc discharge and without reference to the high-mode effect. The essence of the invention DD WP 155181 is the use of a periodic plasma etching operation.

Object of the invention

The aim of the invention is to avoid the use of a direct current discharge, the RF interference of the environment as well as the various problems and difficulties of the RF measuring technique hitherto conventional etching reactors. By exploiting the so-called hollow cathode effect, a high degree of effectiveness is achieved in the fragmentation and activation of the etching medium, as shown by studies in various material systems (see, for example, BJF BEHNKE, H. LANGE, HEWAGNER, Polish J. of Chemistry 56 [1982 ] 1175).

Explanation of the essence of the invention

In certain areas of the gas pressure and the current strength forms in concave or z. T. closed cathode arrangements of a DC low-pressure glow discharge of Hohikatodeneffekt whose electrical characteristic compared to ordinary (eg flat) cathodes is characterized by significantly lower burning voltages at the same current. In the negative glow of the hollow cathode are relatively high concentrations of high-energy electrons, which were accelerated in the cathode trap space (under normal conditions to about 200 ... 80OeV).

The invention exploits the high efficiency of the hollow cathode glow light plasma in the dissociation of molecular gases and the generation of plasma-chemically active radicals. Already at low powers P <100 W, conversion rates close to 100% (eg in fragmentation of CCU) can be achieved.

An analogous behavior as hollow cathodes show Doppelkatoden, consisting of two flat, parallel cathodes arranged when the glow of the opposing cathodes merge (Doppelkatodeneffekt).

The operation of the hollow or double-cathode discharge takes place with DC voltage, so that the difficulties occurring in RF discharges omitted.

The substrates to be etched can be introduced into the interior of the hollow or double cathodes or arranged outside on a special substrate holder in the vicinity of the glowing light. By applying an appropriate bias voltage, ions from the glowing light plasma can be accelerated onto the substrate holder, which increases the etching rate and improves the anisotropy of the etching process (induced etching).

Suitable etching media are the known halogen compounds such as CF ₄ , CCl ₄ , CCl ₂ F _2, etc., possibly in admixture with noble gases (Ar) and simple molecular gases (O ₂ , H ₂ ).

Through the use of DC glow discharges in conjunction with the utilization of the hollow or double cathode effect, an easily manageable and effective plasma-chemical etching reactor could be developed, which is characterized by a high etching rate

embodiment

The invention will be explained with reference to the following embodiments

 Flg. 1 shows a convenient arrangement in a cylindrical design.

The hollow cathode consists of a stainless steel cylinder (1) of 16mm diameter and 30mm length, the anode (2) of a nickel cylinder of 10 mm diameter and 40 mm in length. To achieve high discharge rates, both the cathode and the anode are water cooled. The anode cylinder is electrically isolated from the coolant by an umavit insulating body (4). Flanges (fl) connect the discharge arrangement to the gas inlet system and the pumping system. The toxic and corrosive discharge products are frozen in a cold trap charged with liquid nitrogen.

The substrate holder (3) consists of a stainless steel cylinder (diameter: 8 mm). It is flown by the activated reactant / carrier gas mixture and can receive a selectable bias voltage with respect to the cathode. Maximum substrate area 28mm ² . Larger substrates require an enlargement of the cathode diameter. While maintaining the hollow cathode effect, values of up to about 4 cm (or about 10 cm ^{2 of} substrate area) can be achieved here. For etching of substrates with a high surface area, a parallel arrangement with a plurality of hollow cathodes can be used (packet cathode).

Fig. 2 shows as an example the dependence of the etch rate of Al and GaAs measured with an arrangement according to Fig. 1 as a function of the hollow cathode power (etching gas mixture: CCl ₄ / Ar in the ratio '/ 32 (Al) and V 24 (GaAs); p _Ar = 53 Pa;

Flow rate Q = 12.5 Pal / s). ,

A convenient Doppelgitterkatoden arrangement is shown in Fig. 3. The cathode (K) consists of two stainless steel grids arranged at a distance of 10 mm (wire diameter 0.55 mm, wire spacing 2.5 mm). Between them is an anode ring isolated

(A) fastened from Ni-8lech. Electrical insulation and the setting of defined flow conditions are provided by mica disks (G).

The sample holder (C) for receiving the substrates (S) is located in the flow direction behind the double cathodes. It is made of stainless steel (0 = 10 mm) and can optionally be compared to the Doppekatode an electrical bias voltage V _c .

As the experiment showed, a pronounced double cathode effect in the pressure range 10 ... 300Pa could be achieved with the reticulated double cathode (etching medium CCI ₄ / Ar = ¹ ZS).

The measured etching rates are comparable to those of the cylindrical arrangement. A considerable increase in the etching rate can be achieved by admixing oxygen (for example, an admixture of 20% O ₂ resulted in an increase in the etching rate by a factor of 3).

One advantage of the double-cathode arrangement is the simple possibility of developing large-area etching reactors (etching of large-surface substrates).

In addition, the lattice double cathode has the advantage that the substrate surface adjacent to the cathode is hit even in the absence of additional biases by a directed ion current that misses the cathode through the grid gaps (channel beams). This ion current improves the parameters of the etching process (etching rate, anisotropy).

Claims (5)

-1- Z3 / 33 Invention claim: 1. Hohlkatoden reactor for plasma chemical etching, characterized in that a DC low-pressure glow discharge with hollow or double cathodes is used for fragmentation and activation of the etching gas mixture. 2. Arrangement according to item 1, characterized in that by selecting the operating conditions (gas pressure, current, cathode dimensions) a discharge state with pronounced hollow or double cathode effect is present. 3. Arrangement according to item 1 and item 2, characterized in that can be etched by the bundling of a plurality of cylindrical hollow cathodes or by execution of the double cathodes in a wire mesh form in the flow direction behind the cathode arranged large-area substrate. 4. Arrangement according to item 1 ... 3, characterized in that the occurring behind a lattice-shaped double cathode directed ion current (channel beams) is used for the etching. 5. Arrangement according to item 1,2 and 3, characterized in that the substrate relative to the cathode, a bias voltage can be impressed.