Am Barklund

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 ...

Influence of different etching mechanisms on the angular dependence of silicon nitride etching

Results from etching experiments where Si3N4 films have been bombarded by argon ions at different angles of incidence, with or without a simultaneous exposure to XeF2 molecules, are presented. The experiments have been performed using a Kaufman‐type ion beam source. With these experiments, one obtains the angular dependence of physical sputtering and ion enhanced chemical etching by fluorine. The results are compared with reactive ion beam etching (RIBE) of silicon nitride, silicon dioxide, and polysilicon using CHF3+O2 in order to find the influence of a polymer layer that may be formed on the surface of silicon nitride during etching. Such a polymer layer will strongly affect the angular dependence of the etching process. The formation of the polymer layer, responsible for the variations in the angular dependence, is a result of the flux of polymer precursors, atomic fluorine, and energetic particles to the etched surface. This means that the angular dependence of the RIBE process can be changed by vary...

Numerical and experimental studies of the sputter yield amplification effect

Abstract Recently we have demonstrated the existence of the so-called sputter yield amplification (SYA) effect, based on the preferential sputtering of the lighter species during ion bombardment of composite solids and resulting in enhanced partial sputtering yield of the lighter species as compared to the elemental sputtering yield. In specific cases the enhancement of the sputtering yield could reach one order of magnitude or more. This effect has been both numerically studied and experimentally observed during low energy ion bombardment of i) thin films of low mass on heavy substrates; ii) thin films of high mass on light substrates; iii) simultaneous high mass atom deposition on light substrates; iv) simultaneous low mass atom deposition on heavy substrates. In all cases sputter yield enhancement of the low mass species is observed but in each individual case different specific goals are achieved. For example, in case i) much faster etch rate of the thin film is achieved than what is expected from the...

Ion-assisted selective deposition of aluminium for via-hole interconnections

Abstract Recently we have demonstrated the existence of the so-called sputter yield amplification effect, based on the preferential sputtering of a particular species during the ion bombardment of composite solids. This work presents a more elaborate study of the sputter yield amplification effect using the dynamic Trim version T-DYN. General rules are given as to when the amplification effect is most pronounced and when it is suppressed, as well as its dependence on various parameters. The potential applications of the amplification effect are also discussed. In particular, the use of the effect as a planarization technique during ion-assisted deposition of Al is studied both theoretically and experimentally. It is shown that under low-energy argon ion bombardment Al can be selectively deposited onto Al surfaces while at the same time its growth on W covered SiO2 surfaces is totally prohibited.

Sputter erosion amplification

Abstract A novel method for enhancing the sputtering yield during ion bombardment of a target is presented. It is based on the introduction of a third species (impurity) in the surface layer which increases the nuclear stopping power of the surface layer and hence results in an increased sputtering yield which in some cases could be of an order of magnitude higher. A further extension T-DYN of the dynamic version TRIDYN was specifically written for the study of this effect. Extensive calculations revealed the physical mechanisms, leading to increased sputtering as well as the conditions under which it is achieved. Experimental studies unequivocally confirmed the existence of this effect for a number of impurity/target combinations and show excellent agreement with numerical simulations. On the other hand, experimental investigation of using heavy inert gas atoms as impurity species in a number of different targets in both magnetron and r.f. diode systems did not show noticeable increase in the sputtering yield. The possible reasons for these results are presented.

High bias sputtering for large-area selective deposition

Abstract Bias sputtering is a widely used technique for improving the quality of sputter-deposited thin films. Normally a 50–100 V negative bias voltage is used. Higher bias voltages have been used to produce planarization of patterned substrates during sputter metallization. At even higher substrate bias values the resputtering rate becomes comparable with the deposition rate. In this mode of operation all deposited material may be resputtered. At steady state, however, a certain concentration of the deposited film material will be built up at the substrate surface. A film-bulk concentration depth profile will thus be established which enables the resputtering rate to balance the deposition rate exactly. This will define a partial sputtering yield value of the resputtered film material which is found both theoretically and experimentally to depend strongly on the substrate material. Because of this substrate dependence it is possible to bias sputter deposit thin films selectively onto patterned substrates. By this simple and inert technique we have selectively deposited aluminum onto silicon oxide windows interconnecting two metal layers on an integrated circuit.

Patterning with the use of ion-assisted selective deposition

Abstract High bias sputtering in inert argon may be used to selectively deposit thin films on patterned substrates. Simultaneous sputter etching and film deposition will, at the initial stage of film formation, cause a newly discovered interface phenomena. The sputtering yield of a monoatomic thin film will strongly depend on the underlying bulk substrate. During ion bombardment of a growing ultra-thin film on top of a patterned substrate the film may be preferentially sputter eroded on areas where the sputtering yield of the thin film has the largest value. If a critical balance between deposition rate and sputter erosion rate is selected, actual selective large area deposition may be obtained. No degradation of the pattern was observed after selective deposition. This rules out the possibility of any contribution from local variations in the glow discharge to this selective deposition effect. We will also show that it is possible to predict the selectivity between different substrate materials by simulation of the sputtering yield values of the thin film by Monte Carlo calculations of the collision cascade process.

Patterning of silicon wafers using the plasma jet dry etching technique

Abstract A very high rate dry etching system based on the plasma jet principle has recently been presented. With this device it is possible to create high concentrations of reactive species. This is done by passing the active gases through a hollow cathode discharge inside a nozzle. A jet stream of radicals will be formed. Silicon substrates can be etched by placing them in the jet stream. With this new technique it is possible to obtain etch rates in silicon which are two orders of magnitude larger than obtained by standard dry etching techniques. Aluminum and SiO 2 have been investigated as mask materials in order to study the possibility of using the plasma jet for micro-patterning. The influence of different processing parameters on the etched structures has been studied.