Michael Zeuner

Sputter process diagnostics by negative ions

We measured the energy distributions of negative ions during reactive sputtering of silicon in oxygen. Various oxygen containing negative ions are formed in the cathode sheath or directly at the sputter target, respectively. These negative ions are accelerated away from the cathode by the electrical field, and can be detected using a mass spectrometer facing the sputter magnetron. The origin of each ion can be determined from peak structures in the energy distribution. Additionally the flux of different negative ions provides information on poisoning of the target by oxide films.

DESIGN OF ION ENERGY DISTRIBUTIONS BY A BROAD BEAM ION SOURCE

We characterize the performance of a built‐in hot filament broad beam ion source by mass spectrometry, energy analysis, and beam profile measurements. In the ion energy distribution we detect various peak structures which can be explained by the potential across the ion source and different charge transfer processes. Depending on the typical cross sections for these processes, differences between the energy distributions of the ion species are observed. The total ion current obtained with the source is determined by the ionization rate in the discharge and the current share directed toward the extraction grid system. The performance of the source is strongly dependent on the process gas used. We observe much broader energy distributions in oxygen and nitrogen than in argon. This broadening is explained by spatial inhomogeneities in the discharge region and can be reduced by a suitable setting of the source parameters. The main contribution to the ion flux is caused by species generated directly from the p...

Ion energy distributions in a dc biased rf discharge

We measured quasisimultaneously the energy distributions of positive ions at the powered rf and grounded electrode of a parallel plate 13.56 MHz discharge using an energy selective mass spectrometer. The resulting ion energy distributions reflect the discharge potential conditions expected from a capacitive plasma sheath model. By means of an externally supplied dc bias of the powered electrode we are able to influence the potential structure and to control ion energy and ion flux independently. The ratio between mean ion energy and mean sheath thickness reflects the effect of collisions on the ion energy distributions and enables estimates of sheath thickness and bulk plasma parameters to be made which are compared with values obtained by Langmuir probe measurements. We are able to demonstrate that changes in sheath potential also affect, via secondary electrons, the ionization regime in the discharge and this can be utilized to control the species composition in the discharge.

Optimisation and characterisation of a TCP type RF broad beam ion source

A very compact type of broad beam ion source based on transformer coupled plasma excitation (TCP) is described. Our ion source consists of a cylindrical RF coil surrounding the discharge vessel and a very compact, patented matching unit from special ceramics capacitors attached directly to the discharge arrangement. However, the TCP excitation as well as the sophisticated layout of the matching unit require an optimum source arrangement due to the beam parameters, the source lifetime and the performance of the RF elements. For that reason, a global discharge model was applied together with an RF replacement circuit diagram to calculate for the optimum source layout. An advanced plasma and beam diagnostics is used for controlling the source performance due to beam composition, beam profile and ion energy distribution. In this way, our RF source is adapted to different beam requirements in inert and reactive beam processes for etching, modification and sputter deposition.

Plasma diagnostics for surface modification of polymers

Capacitively coupled RF discharge in oxygen is investigated for polymer surface modification. The discharge is studied by means of ion analysis at the powered and grounded discharge electrode, optical emission spectroscopy and Langmuir probe measurements. Correlations are shown between discharge properties, internal plasma parameters and the surface modification of polyethylene (PE) and polystyrene (PS) characterized by FTIR (ATR) spectroscopy and ellipsometry.

Fundamental investigations in plasma modification of polymers

Polyethylene and polystyrene as model polymers are treated in a low temperature plasma of oxygen, nitrogen, tetrafluoromethane, and argon. The modification, incorporation of plasma particles and plasma etching are studied by means of in situ Fourier transform IR spectroscopy, spectroscopic ellipsometry and in situ microgravimetry. Major changes in the surface region are observed after a few seconds of treatment time in the plasma.

A unique ECR broad beam source for thin film processing

We present the special microwave excited ECR (electron cyclotron resonance) type broad beam ion source EC/A 125 together with first results in ion beam deposition. Our source concept overcomes different disadvantages of common broad beam ion sources. By means of a modular source design and an autotuning microwave power supply, an adaptation at different process requirements is possible. The efficiency of the source is demonstrated analysing the performance in inert and reactive environment. We analyse and discuss the resulting beam composition and draw important conclusions on the plasma-chemical processes occurring in the source from the measurement of the ion energy distributions. The source is operated at the CYBERITE ion beam equipment and results in deposition of magneto-resistive films and multilayer films are illustrated.

HIGH ENERGY NEGATIVE IONS IN A RADIO-FREQUENCY DISCHARGE

We measured energy distributions of negative ions at the grounded electrode of an oxygen parallel‐plate rf discharge. Negative ions are generated in the plasma sheath in front of the rf electrode, are accelerated away from the driven electrode, and can be detected at the grounded electrode. The maximum energy of the negative ions corresponds to the negative self‐bias voltage of the rf electrode. Structures in the energy distribution reflect sheath properties and characteristics of the ion generation processes.

Ion kinetics in collisional rf-glow discharge sheaths

Abstract Ion kinetic investigations are performed on a 27.12 MHz capacitively coupled parallel plate discharge configuration using argon and oxygen as the process gases. The incident ions on the grounded electrode are separated, according to their mass and energy, and the influence of rf-power density and total pressure on the ion mass spectra and, especially, on the ion energy distribution are discussed. In the observed parameter range, a transition from space charge-limited to mobility limited ion transport in the plasma sheath occurs. The ion sheath thickness can be calculated from the change of the shape of the energy distribution with pressure.

Characterization of a modular broad beam ion source

We characterize the performance of a modular broad beam ion source by energy resolved mass spectrometry and beam profile measurements. Using the same source housing and grid system, we performed our experiments powering the source with a hot filament or an ECR excitation, respectively. In the ion energy distribution we detect various peak structures reflecting the potential profile across the ion source as well as different charge exchange and dissociation processes occurring in the beam. The position of these peaks on the energy scale allows conclusions to be formed about the original charge state of the ion, when produced by charge exchange, or on the original molecule, when produced by dissociation. The most important contribution to the ion beam is caused by process gas ions with important impurities from source materials appearing with reactive process gases. Using electronegative gases, a large amount of negative ions generated in the beam is observed. The performance of both excitation types due to the beam parameters is very similar. A comparable power supplied to the source plasma delivers similar beam currents and profiles. The resulting beam current is determined by the density and the potential structure in the source plasma. The axial potential gradient in the plasma, and with it the resulting beam current, is strongly affected by the total voltage applied between the grids and can be derived from the shape of the main peak in the ion energy distribution. The detected radial beam profile is determined simultaneously by the ion optical parameters of the grid system and the space charge potential in the beam. For a fixed grid geometry the shape of the plasma sheath at the screen grid is an important factor controlling the source performance. The shape of the plasma sheath is simultaneously controlled by the voltage difference between the grids and the Debye length. Changes in the shape can be derived from the ion energy distribution with the experimental results being in good agreement with numerical beam simulations. The only important difference between both excitation types is that using the Kaufman type excitation the potential of the source plasma is exactly fixed by the beam potential, whereas with the ECR source it deviates by several tens of volts depending on microwave power and process gas.