Papers by Author: Tom Janssens

Abstract: High velocity aerosol cleaning using ultrapure water or dilute aqueous solutions (e.g. dilute ammonia) is common in semiconductor IC fabrication [1]. This process combines droplet impact forces with continuous liquid flow for improved cleaning efficiency of sub-100nm particles. As with any physically enhanced cleaning process, improved particle removal can be accompanied by increased substrate damage, especially to smaller (<80nm) features [2]. Solvents such as N-methylpyrrolidone (NMP) and tetrahydrofurfuryl alcohol (THFA) are used for resist strip applications [3]. It is possible, and sometimes useful, to deliver these solvents through the same spray nozzle normally used for aqueous spray cleaning. In this presentation we explore the particle removal and substrate damage performance of 2-ethoxyethanol (EGEE), NMP and THFA as used in a conventional aerosol spray cleaning system

Abstract: A non uniform sound field distribution can be a problem in a megasonic cleaning system, since a higher sound intensity can cause damage, while areas exposed to a lower intensity will be insufficiently cleaned. These non uniformities can be the result of sound field reflection, leading to standing waves, and the interference related to the near field. In a single wafer tool with a transducer facing the wafer a small height difference will have a large impact on the cleaning efficiency if standing waves are present. Here we study the impact of the wafer transducer height in a cleaning system using a megasonic nozzle above a rotating wafer.

Abstract: Since the introduction of megasonic cleaning in semiconductor industry a debate has been going on about which physical mechanism is responsible for the removal of particles. Because of the high frequency range it was believed that acoustic cavitation could not occur and cleaning was attributed to phenomena like Eckart and Schlichting streaming or pressure build-up on particles [1,2]. Recently it was shown however, that the removal of nanoparticles is closely related to the presence of acoustic cavitation in megasonic cleaning systems [3]. The dependence of particle removal efficiency on the concentration of dissolved gas and the presence of sonoluminescence are clear (but indirect) indications that the underlying mechanism is related to bubble dynamics. As the requirements for cleaning in semiconductor processing are ever more stringent, it becomes necessary to obtain a thorough understanding of the physical behavior of acoustically driven microbubbles in contact with a solid wall. In particular, the forces exerted thereby which might clean or damage a substrate are of interest. Here, a step in this direction is taken by visualization of both the removal of nanoparticles and the sub-microsecond timescale dynamics of the cavitation bubbles responsible thereof.

Abstract: The local particle removal efficiency (PRE) of nano particles in megasonic cleaning experiments is studied. This approach makes it possible to quantify non uniform cleaning effects over the wafer and to look into the dynamics of particle removal at different areas on the wafer. A direct correlation between PRE and megasonic induced damage of device structures demonstrates that a considerable amount of damage is already formed at less efficiently cleaned areas of the wafer.

Abstract: The formation of shallow junctions in germanium substrates, compatible with deep submicron CMOS processing is discussed with respect to dopant diffusion and activation and damage removal. Examples will be discussed for B and Ga and for P and As, as typical p- and n-type dopants, respectively. While 1 to 60 s Rapid Thermal Annealing at temperatures in the range 400-650oC have been utilized, in most cases, no residual extended defects have been observed by RBS and TEM. It is shown that 100% activation of B can be achieved in combination with a Ge pre-amorphisation implant. Full activation of a P-implant can also be obtained for low-dose implantations, corresponding with immobile profiles. On the other hand, for a dose above the threshold for amorphisation, a concentration-enhanced diffusion of P occurs, while a lower percentage of activation is observed. At the same time, dose loss by P out-diffusion occurs, which can be limited by employing a SiO2 cap layer.