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 between both argon (M=40) and carbon (M=12) atoms with the implanted Pt atom (M=195) can result in reflection of some of the light atoms. Therefore implanted Pt atoms will act as effective reflection centers pushing the collision cascade to take place closer to the surface region, thereby contributing to an effective increase of the number of collision cascades in this region. This reflection effect will result in a substantial increase of the sputtering yield of carbon atoms. Experimental verification of this effect for the (Ar+C+Pt) and the (Ar+Si+Pt) systems will be presented. It will be also shown that this sputter amplification process can be predicted from computer simulations using the t-dyn version of the Monte Carlo trim code.

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Ion bombardment of a growing film is one known way of changing film properties. Also in reactive etching, ions may assist surface reactions. We will present a study where different substrates are bombarded by energetic argon ions during deposition of titanium. If titanium is deposited onto three different substrates without influencing the substrate by any ion irradiation, a thin titanium film, equally thick, will be formed on all three substrates. If, however, the substrates are bombarded by energetic argon ions (500–800 eV) during deposition of titanium, we have found that quite different film thicknesses may be obtained on different substrates. In fact, a balance may be found where actually one substrate is sputter etched while another substrate under identical deposition conditions (same run) is deposited by titanium. Results from rf-bias sputtering in argon shows selectivity, e.g., between Si and Pt at 10 mTorr pressure, 1600 V target voltage and 800 V substrate bais. Ti is deposited onto silicon but the net surface effect on Pt is substrate etching. This demonstrates that selective deposition is possible to achieve by ion assisted thin film growth.

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