C Nender

Modeling of reactive sputtering of compound materials

An experimentally verified useful new model for reactive sputtering is presented. By considering the total system (target erosion, gas injection, chamber wall deposition, reactive gas gettering at all surfaces, etc.) during deposition it is possible to evaluate quite simple relationships between processing parameters. We have expanded earlier treatments to include these phenomena. The model involves that gettering of the reactive gas takes place at the target and at the walls opposite to the target. Arguments are also presented for how the sputtered materials (elemental target atoms and the formed compound) contribute to the formation of the surface composition of the walls opposite to the sputtering electrode. The mass flow of the reactive gas has been chosen as the independent parameter in this presentation. Results for partial pressure and sputter rate are presented. The theoretical values are compared with experimental results from reactive sputtering of TiN. It is also pointed out that the calculated...

Predicting thin‐film stoichiometry in reactive sputtering

The electrical, optical, and mechanical properties of a compound film depend strongly on the composition of the film. Therefore, it is interesting to study a wide variety of compositions of many new compound materials. Reactive sputtering is a widely used technique to produce compound thin films. With this technique it is possible to fabricate thin films with different compositions. However, it has not yet, to any great extent, been possible to predict the composition of the sputtered film. In this article we will present a model that enables us to predict both sputtering rate and film composition during reactive sputtering. The results point out that there exists a very simple linear relationship between processing parameters for maintaining constant thin‐film composition in the reactive sputtering process. Based on these results, it is possible for the first time to combine information of both sputtering rate and film composition into the same graphical representation. Access to this new and simple grap...

T-DYN Monte Carlo simulations applied to ion assisted thin film processes

Abstract The need for computer aided fabrication of modern semiconductor devices calls for reliable algorithms describing complex processes. A number of programs exist for predicting the outcome of several processing steps. In this article we present a new Monte Carlo program, T-DYN, version 2 (1990), which is an extension of the TRIM-CASCADE code. The standard TRIM codes give information about all collisional effects caused by single ions impinging on a virgin target. It does not take into account the target alterations which occur at high dose exposures. A previous TRIM version, TRIM-DYN, takes these alterations into consideration but has the drawback of requiring “super computers” with high operating speed. Process modeling, however, has to be performed in an environment where super computers are normally not available. The new version T-DYN uses different concepts which are more suitable for computer realizations and hence may be operated on advanced personal computers. This makes the program more attractive for applications also by processing engineers. Thin film processing normally involves atom deposition or atom sputter ejection from a surface exposed to some particle fluxes. Thin films are therefore built up or removed. Simulation of thin film processes calls for a code which takes into consideration gradual alterations in the thin film/bulk structure during exposure to the incoming flux. The new T-DYN program can handle energetic ion bombardment and simultaneous deposition of neutral atoms at the surface of the structure. The changes due to previous events are stored and subsequent events will then take into account such updated information. The present paper describes some computational details of the T-DYN program and also presents results obtained.

Process modeling of reactive sputtering

Reactive sputtering is a very complex and nonlinear process. There are many parameters involved. Normally it is not possible to vary a single parameter independently of the others. It is therefore very difficult to characterize the process based on experimental observations. A better understanding of the reactive sputtering mechanism is needed. We have suggested a simple model for the reactive sputtering process. This model is primarily based on well‐known gas kinetics, transferred to this application. With this model it is possible to theoretically predict different processing conditions and actually study the influence of a change in an individual parameter value. The results may then be used to predict optimal experimental conditions. With this technique it is also possible to study means of affecting the well‐known hysteresis effect. This article is specially devoted to explain the width of the hysteresis region and how it is affected by the sputtering intensity. Experimental results are presented tha...

Reactive sputtering using two reactive gases, experiments and computer modeling

The reactive sputtering process is very simple to use as long as one wants to deposit fully formed compounds. If, however, an intermediate composition is required it is necessary to use quite advanced process control. Reactive sputtering from an elemental target in argon with the addition of one reactive gas have been extensively studied. Also studies of reactive cosputtering have been reported. The interest for such studies increased dramatically when the high‐temperature superconductive thin films were introduced. In this article we will treat the process of reactive sputtering from an elemental target in argon with the addition of two reactive gases. In such a process, e.g., oxy‐nitride films can be formed. The fundamental reactive sputtering model has been modified to handle two reactive gases. By this new model it is possible to simulate two gases having different reactivity and sticking coefficients to the elemental metal involved. It is possible to predict complex effects in the processing region w...

Hysteresis effects in the sputtering process using two reactive gases

The reactive sputtering process involving two reactive gases has been investigated. Sputtering titanium in the presence of oxygen and nitrogen in argon was studied by means of optical emission and mass spectrometries. The experiments reveal the mechanism

Atom assisted sputtering yield amplification

At first sight one might assume that it is unlikely to influence the sputtering yield of a specific ion/substrate combination by any external means. However, we have found that such an influence may well be introduced. The sputtering yield is predominantly determined by the ion/substrate momentum transfer efficiency and the energy of the incoming ion. Sputter erosion of, e.g., carbon atoms by argon ions from a carbon substrate exhibits a very low sputtering yield. Due to the difference in masses between carbon and argon much of the momentum is transferred into the bulk of the carbon substrate. This situation could be changed by simultaneous codeposition of Pt atoms onto the carbon substrate surface during the argon sputtering. Keeping the argon flux at a level well above what is needed to sputter remove all the deposited Pt atoms the following effect occurs. Some of the deposited Pt atoms will be forward implanted by the energetic argon ions into the near surface region of the carbon substrate. Collision ...

Modeling of multicomponent reactive sputtering

Computer process modeling has become an important tool in the development of new thin‐film processes. Previously, we presented a model that successfully describes the complex behavior of the reactive sputtering of a single‐element target. The model enables one to predict, e.g., the hysteresis effect and the composition of the deposited film. There exists, however, a demand for developing reliable reactive‐sputtering processes for more complicated materials. This calls for an extended reactive‐sputtering model including more than one target element. In this article, we will for the first time present an extension of our previous model now taking the effect of multicomponent targets into consideration. The transition from metallic‐ to compound‐sputtering mode normally occurs at different levels for different single‐element targets. The new extended reactive‐sputtering model predicts the transition from metallic to compound mode during multicomponent reactive sputtering of thin films. The results indicate th...

Studies of reactive sputtering of multi-phase chromium nitride

We have presented a model for reactive sputter deposition of two-phase materials. This model has been applied to reactive sputtering of chromium nitride where it is assumed that either Cr2N or CrN is formed. In order to test the validity of the model, a number of deposition experiments has been performed where the film composition for different reactive gas supplies has been estimated by means of in situ soft x-ray emission spectroscopy. The results have been compared with predicted film compositions according to the model and the experimental findings agree qualitatively with the simulations.

Enhanced sputtering of one species in the processing of multielement thin films

We discuss two mechanisms for enhanced selective sputtering which may strongly influence the composition of thin films deposited under energetic particle bombardment. The first mechanism occurs on sloping substrate surfaces which experience a higher fraction of material resputtered than flat surfaces. 500 eV Ar+ ion bombardment during deposition of Al–5 at. % Cu causes an increase in Cu concentration by up to a factor of 2 on sloping surfaces. This effect is modeled with the dynamic Monte Carlo code T‐DYN, which simulates film growth under ion bombardment and confirms the selective sputtering of Al. The second mechanism occurs if diffusion of the film constituents is significant, and the film is situated on top of an underlying material containing one of the film components. Enhanced sputtering of one component occurs if that component maintains a high surface concentration by diffusion or segregation. Raising the temperature of TiSi2 on (100) Si to the range in which Si atoms are mobile (500–700 °C) incr...