DE19705884A1 - Plasma ignition system - Google Patents

Abstract

The system for ignition of a plasma for cathode sputtering is characterised by means (4) serving for generation of charge carriers (15). With use of an electric potential applied between the gas to be ignited as a plasma and the means (4), these charge carriers are accelerated in the direction of the plasma space (2). As a result, the gas introduced into the plasma space is impact-ionised and ignited as a plasma discharge by the charge carriers. Preferably the means (4) for generation of charge carriers (15) include at least one electrical conductor (6) heatable by current to a glow temperature, so that electrons from the conductor surface are thermally emitted in the direction of the plasma space (2). The conductor (6) preferably takes the form of a tungsten wire. Before ignition of a plasma discharge the wire (6) heated to its glow temperature has a potential within a range from -15 V to -25 V, with the corresponding emission current lying within a range of 1.0-1.8 mA. In the presence of a plasma the potential of the wire is within a range from +15 V to +25 V, with the corresponding emission current lying within a range of 1.4-2.2 mA. The potential and/or the emission current are measurable during burning of the plasma, and are foreseen for control the latter.

Description

The invention relates to a generic type Direction to ignite a plasma for the Katho atomization according to the preamble of the patent saying 1.

The treatment of workpiece surfaces by means of plasma-assisted processes is known. Such methods are e.g. B. known as plasma diffusion, plasma chemical vapor deposition, physical vapor deposition (PVD), plasma etching, plasma polymerization or ion implantation. In such processes, the workpieces to be treated are first introduced into a closed treatment chamber, which is then evacuated to negative pressure, and then with a gas or gas mixture up to a pressure p between 1 × 10 ^-2 mbar and 1 × 10 ^-4 mbar to be filled.

To be suitable for the above-mentioned processes Producing plasma is in the treatment a cathode and an anode, between which set an electric field like this is that after ignition of the plasma the latter between maintain the cathode and anode becomes. For applying thin layers on substrate te, the cathode itself consists of the atomized end, e.g. B. to be applied to the workpieces Layer material. The ions generated in the plasma are accelerated to the cathode and zer Dust this, leaving the sputtered cathode material in layers on the workpiece surface forming a homogeneous single layer or an alternating layer sequence to one Total layer precipitates. With all of the above called plasma treatment process is desired that the plasma without delay and without training formation of plasma instabilities during plasma ignition phase on the workpieces to be treated can work. In the conventional devices such could be used to generate a plasma temporal fluctuations in the plasma parameters both in plasma ignition as well as during plasma operation cannot be prevented sufficiently, which e.g. B. disadvantageous in sputtering sputtered inhomogeneous layer thickness Layer sequences leads.

The invention has for its object to to provide reliable plasma ignition devices, by means of which both the plasma ignition process repro is adjustable, but also with that  Plasma with defined reproducible plasma parameters can be operated.

This object is accomplished according to the features of the patent claims 1 solved in that in the plasma enclosing treatment chamber means hen are used to generate free charge carriers are bar, which with the one to be ignited, not yet ionized gas and / or the ignited plasma interact. Due to their thermi kinetic energy encounter this free La Manure carriers with individually in the treatment chamber existing gas atoms together, this gas particles are ionized. This ionized gas particles are then in the between the Sputter cathode and the associated anode accelerated such electric field that further load avalanches arise, which across the entire discharge zone of the plas extend so that the plasma becomes a self-igniting discharge is ignited.

The advantage achieved with the invention is especially in that the plasma because of the defi nated regulation of the amount of freely generated Load carriers with no temporal instabilities both but also during the actual ignition timing generated during the subsequent plasma discharge can be. By the shock ionization of the freige placed load carrier is especially at the beginning the plasma ignition, the plasma gas is particularly effective and with a much higher degree of ionization and efficiency than with conventional devices  gen ionized. Through the invention Influence of plasma on the machined, esp to be coated in particular by means of cathode sputtering material surfaces stable over time, where through the applied layers homogeneous and free of released by plasma instabilities Particles grow up.

As suggested in claims 2 and 3, exist the means generating the charge carriers from one wire that can be heated above its annealing temperature element or filament. To heat this heater thread is this with an electrical supply connected. It has been particularly advantageous proved to be the glow wire before and for ignition of the plasma to an electrical potential in the loading range from - 15 V to - 25 V, preferably up - 20 V to lay. The heating current is between 1.0 mA and 1.8 mA, preferably 1.4 mA.

After ignition of the plasma, the emission current of the filament is set to a value between 1.4 mA and 2.2 mA, preferably 1.8 mA and the bias voltage U _P to a value between + 15 V and + 25 V, preferably + 20 V set.

Due to the above potential conditions, the filament is advantageously ge particularly protects against the action of the burning plasma itself, since the positive charge carriers generated in the plasma z. B. ions are repelled at the bias potential of the heating wire. It is also proposed that by measuring the bias voltage U _P and the emission current I _E, the plasma discharge can be detected during the burning phase of the plasma.

Further advantageous features of the invention are specified in the subclaims.

An embodiment of the invention is in the single figure and is shown below described in more detail.

In a plasma treatment chamber 1 are arranged essentially opposite one another, at least one electrode connected as a cathode 9 and as an electrode 11 , which are connected to the current or voltage supply 14 , 16 by conductor leads 5 electrically insulated from the chamber wall 3 are. For coating or for etching material surfaces are the workpieces not shown in the drawing z. B. between the anode 11 and the Ka method 12 or the workpieces to be coated are part of the anode 11 itself and the material to be sprayed, part of the cathode 9th To ignite a plasma between the cathode 9 and the anode 11 , the plasma treatment chamber 1 is first evacuated to a negative pressure of approx. 10 ^-4 mbar by means of the vacuum pumping devices (not shown in the drawing) through the pumping nozzle 17 . Through a gas inlet 7 is subsequently to be used, the plasma gas, eg. B. a noble gas or N ₂ , O ₂ , let into the treatment chamber 1 , a chamber pressure p being set in the range from 5 × 10 ^-4 mbar to 5 × 10 ^-2 mbar. To ignite the plasma, an ignition voltage is first applied between the cathode 9 and the anode 11 . In order to cause the plasma ignition, the glow wire 6 protruding into the chamber wall 3 with a vacuum-tight conductor bushing 5 is then heated up by means of a current passage above its glow temperature. The electrons emitted from the glow wire 6 trigger ionization processes in the plasma gas located between the cathode 9 and the anode 11 , by means of which the subsequent discharge of the plasma gas is initiated. For the ignition of the plasma 2 , the glow wire 6 is electrically biased to a negative potential U _P of −20 V relative to the chamber wall. The emission current I _E is 1.4 mA. After igniting the plasma, the emission current I _{E increases} to a value of 1.8 mA, the bias voltage U _{P of} the filament 6 changing to + 20 V.

The bias voltage U _P is supplied via a resistor 10 connected between the filament 6 and an additional bias voltage supply 12 . To control the plasma 2 both the falling across the resistor 10 bias voltage U _P with the voltage measuring device 13 and the emission current I _E , z. B. in the emission current supply 12 , measured electrically. Since temporal instabilities in the burning behavior of the plasma influence both the value U _P and I _E , a comparison of these current and voltage values enables a plasma control under control of the cathode or anode current or voltage, by means of which time Fluctuations in the characteristic plasma parameters can be suppressed.

Reference list

1

Plasma treatment chamber

2nd

Plasma room

3rd

Chamber wall

4th

Plasma igniter

5

Conductor bushing

6

filament

7

Gas inlet device

8th

Heating power supply

9

cathode

10th

Resistance element

11

anode

12th

Emission power supply

13

Tension meter

14

Cathode supply

15

charge carrier

16

Anode supply

17th

Pump outlet

Claims (6)

1. A device for igniting a plasma for sputtering, characterized by charge carriers ( 15 ) generating means ( 4 ), the charge carriers ( 15 ) in a between the gas to be ignited as plasma ( 2 ) and the charge carriers ( 15 ) generating Means ( 4 ) applied electrical potential U _P in Rich direction on the plasma space ( 2 ) can be accelerated, whereby the gas left in the plasma space ( 2 ) is ionized by shock ionization of the charge carrier ( 15 ) and ignites as a plasma discharge. 2. Apparatus according to claim 1, characterized in that the charge carrier ( 15 ) it generating means ( 4 ) has at least one heatable by current flow electrical Lei ter ( 6 ), the electrical Lei ter ( 6 ) heatable to at least one annealing temperature is, whereby electrons ( 6 ) are thermally emitted from the surface of the conductor, preferably in the direction of the plasma space ( 2 ). 3. Apparatus according to claim 1 and / or 2, characterized in that the electrical conductor made of tungsten, preferably in the form of egg nes wire ( 6 ). 4. The device according to at least one of Ansprü che 1 to 3, characterized in that before ignition of a plasma discharge on the wire heated to its ne annealing temperature ( 6 ), a voltage U _{P is present} in the range of - 15 V to - 25 V, and wherein the emission current I _P emitted from the wire ( 6 ) is in the range from 1.0 mA to 1.8 mA. 5. The device according to at least one of Ansprü che 1 to 4, characterized in that in the presence of a plasma on the heated to its annealing temperature wire ( 6 ) a voltage U _P in the range of + 15 V to + 25 V, and the emission current I _P in the range from 1.4 mA to 2.2 mA. 6. The device according to at least one of claims 1 to 5, characterized in that the voltage variable U _P and / or the current variable I _{P can be} measured during the burning period of the plasma and these as electrical parameters of the ignited plasma for its control, which che preferably carried out by means of electronic means are provided.