A.G. Spencer

Pressure stability in reactive magnetron sputtering

Abstract In high rate reactive magnetron sputtering the film deposition results in a substantial pumping rate of the reactive gas. When the depositing film is substoichiometric, the films consumption of the reactive gas is limited by the arrival rate of that gas and so consumption increases with reactive gas partial pressure. When the film is saturated with gas, the reactive gas consumption is limited by the metal arrival rate. As the reactive gas pressure is increased reaction products form on the target (it is “poisoned”) and the metal flux falls, leading to a decreasing consumption of the reactive gas. At pressures where a stoichiometric film is formed the consumption of the reactive gas by the film will be falling. This can lead to an uncontrollable transition between a metallic and a poisoned target that makes the control of optimum deposition conditions difficult. We have investigated this instability and its causes and our results indicate various means of getting a stable deposition system.

Substrate effects from an unbalanced magnetron

Abstract The manipulation of the plasma of a d.c. planar magnetron may be achieved easily by adjusting the magnetic field of the magnetron, in conjunction, with the placing of the anode. Such an arrangement of an “unbalanced” magnetron has been studied with regard to the bias voltage that appears on the substrate and the resultant ion and electron currents that flow to it. These are compared with the heat load experienced by it, which is related to the energy dissipation of the magnetron system. The magnetron source is considered from the point of view of providing energy bombardment of the substrate, and the growing film, and the efficacy of this bombardment in initiating structural and chemical reactions of the surface, as well as giving a heat load. A typical unbalanced magnetron, made by us, gave an insulated substrate a bias voltage of 25–30 V with an ion current of 3.4 mA cm−2. The heat load was 100 mW cm−2. Of the energy supplied to the magnetron 82% went into the cooling water and 3% into the substrate; the rest was dissipated by the plasma.

Activation of reactive sputtering by a plasma beam from an unbalanced magnetron

Abstract A magnetron with its magnets on the outer edge and little or no magnetic material in the centre has poor plasma confinement and gives plasma bombardment of the growing film. We have used such ‘unbalanced’ magnetrons for reactive sputtering and present results for indium oxide and titanium dioxide which show that this plasma bombardment activates the reaction at the substrate. This is seen as a lower reactive gas pressure required to produce a stoichiometric film. The predicted result of this is that less reaction products should form on the target and the deposition rate should consequently be higher than with no plasma bombardment. Effects on film properties are also investigated.

Reactive sputtering of electrically conducting tin oxide

Abstract Tin was sputtered from a d.c. planar magnetron target in a confined volume. Stability was maintained in the reactive sputtering by controlling the oxygen partial pressure through observation of the light emitted by the oxygen in the plasma of the magnetron. The material deposited on the walls of the chamber was used to getter the system of impurities. The oxygen consumption at the set point was a good indication of the approach to stoichiometry of the film. It was observed that transparent conducting films were prepared at the point where the oxygen consumption indicated a break from full incorporation into the growing film. Films there had a resistivity of 100 micro ohm m for a 600 ohm/▭ sheet resistance, a thickness of about 150 nm.

Dynamic control of reactive magnetron sputtering: A theoretical analysis

The deposition of compound films by reactive magnetron sputtering can exhibit an unstable transition from a metallic target surface to one covered in reactino products. One solution to this is simply to “overpump” the deposition chamber so that the consumption of reactive gas by the pumps dominates the reactive gas consumption by the growing film. This involves additional expense at the construction stage and can be impractical in existing machines. Dynamic control of the reactive gas pressure can remove the instability and allow higher deposition rates and new film compositions to be achieved. Such dynamic control can exhibit oscillations about the control point. A theoretical analysis is presented here that gives a guide to system design and setting up. Practical results are given to show that with such a guide stable control can be achieved.

Reactive ion-plating at low ion energies with an unbalanced magnetron

Abstract An unbalanced magnetron uses changes in the configuration of the magnetic field, which confines the plasma close to the sputtering cathode, to allow some of it to ‘leak’ out to impinge on the substrate. A device which can produce ion bombardment of an isolated surface at a bias ofover 100 V with a current density of 100 mA cm−2 is described. The dependence of the surface bombardment on process parameters such as magnetron power and gas pressure is reported; a general diminution of the bombardment occurs as the pressure is increased beyond 0.2 Pa, but the effect becomes greater when oxygen replaces argon as the sputtering gas. The operation of the magnetron under conditions using extra electron injection is shown to result in additional ion current, whilst the bias potential is maintained. Reactive sputtering with such a source allows the growing film to be improved in structure whilst the reactive gas is made more reactive which allows a lower partial pressure to be used for the creation of stoichiometric films. Electron injection allows the pressure of the inert sputtering gas to be low, so that operation is possible at pressures giving mean-free paths greater than the source to substrate distance. Line of sight transfer of material having energies appropriate to sputtered material is then possible. The application of such a device to the preparation of thin films of indium-tin oxide and diamond-like carbon and the etching of a polymer surface is described.

Reactive sputtering of hard optical films of tin oxide

Tin was sputtered from a DC planar magiistrcn target in a confined volume , stabilitywas maintained in the reactive sputtering by controlling the oxygen partial prire throogh observation of this liajit emitted by the oxygen in the -ofthe magnetron. The material deposited on this walls of the chamber was designed to getter this system of imt, The oxygen coisumption at the set point was a good indication oftlis approach to stoichiometiy of tbo film. It was observed that trazspazent oonckxting filnis were prepared at the point where this oxygen comaimption indicated a break from fill izxorporalion into the growing film. Films there had a resistivity of 100 micro ohm-meters for a 600 ohms per sqisze sheet restance, a thickne ofabont 150 naix>.meters. Tlisse filnis showed some o1 absorption in the bhis regkm oftho spectziim. Optically clear filnis required preparation in a greater oxygen rteeane which reckd the rate ofdeposition by a factor c(two. The refractive index was measuied as2.Oat633nm.

System Design For High Rate Deposition Of Indium Oxide Solar Coatings

Indium oxide solar coatings have been extensively investigated and the conditions for their small scale production well characterized. For widespread use of these solar coatings they must be produced at high rate over large areas. Reactive magnetron sputtering is a suitable process and problems in extending this process to larger areas and higher rates are discussed. This is illustrated by results from a 0.5m wide coater. In a typical commercial coater the process is unstable and so process control by plasma emission monitoring (PEM) is required to give a stable deposition process. To get good film uniformity the gas must be distributed by a gas manifold and there is some interplay between the gas manifold and the PEM control. Experimental results are given to adjust the manifold design for optimum control. On a small scale coater with inherent stability we have achieved a deposition rate of 8 nm/s for indium oxide (with a resistivity of 4 x 10-6ohm.m). In a larger unstable coater with PEM control we have produced deposition rates of 6 nm/s with a slightly degraded resistivity of 6 x 10-6 ohm.m.