Ultra Clean Processing of Semiconductor Surfaces IX

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Authors: Hiroshi Tomita, Minako Inukai, Kaori Umezawa, Li Nan Ji
Abstract: It is well known that the physical force cleaning such as megasonic (MS) and ultrasonic (US) cleaning are used in FEOL (front-end-of-line) and BEOL (back-end-of-line). Recently, with scaling down below 43 nm, the influence of pattern damage by physical force methods such as MS and US irradiation has been reported. Hence, for the 2x and 3x nm node devices, it will be very difficult to apply MS cleaning for particle removal process without understanding the cavitation force. Cavitation is a complex phenomena based on bubble formation and explosion in the liquid. To control “MS cleaning” and “cavitation” induced pattern damage, many studies using “Sonoluminescence” have been reported. This method is able to demonstrate the existence of high energy fields such as cavitation throughout the megasonic field. The damage clustering distribution was investigated for the damage size and damage length in batch MS conditions using gate structure patterned [1]. In this method, it is difficult to discuss the cavitation force, quantitatively. And this method can not obtain the quantitative physical force on the wafer surface, directly. To understand “cavitation force” induced pattern damage, the observation of “cavitation force” is highlighted with “imaging films” such as blanket aluminum film and resist film, directly.
Authors: Aaldert Zijlstra, Tom Janssens, Kurt Wostyn, Michel Versluis, Paul W. Mertens, Detlef Lohse
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.
Authors: Andrea Otto, Till Nowak, Robert Mettin, Frank Holsteyns, Alexander Lippert
Authors: Guillaume Briend, Pascal Besson, Thierry Salvetat, Sébastien Petitdidier
Abstract: More and more, 300mm manufacturing promotes a single wafer tool approach in FEOL cleaning. Previously, we reported an advanced surface preparation process based on dilute HF/HCl/DIW and O3/HCl/DIW chemistries coupled with megasonic activation during the ozone step only, on a 300mm single-wafer platform [1]. As throughput consideration implies shorter process time, the activation of megasons during the whole cleaning step could be of interest for very small particle removal efficiency. Nevertheless, extending megasonic activation to the entire process sequence leads to degraded results on silicon surface. Indeed, damages are created at 90 and 65nm defect inspection levels when megasonic activation is used in the presence of both HF species and on hydrophobic silicon surface. In this paper, we demonstrate that the megasonic activation (Megs) generates randomly and locally oxidized species which may be the main cause of damages in the presence of HF chemistry. Additional characterizations are performed to understand this problem (haze inspections, ATR analysis and contact angle measurements).
Authors: Cole Franklin
Abstract: It has been shown that megasonics can accelerate strip processes such as doped and plasma treated photoresist [1]. However, applied megasonic energy can also damage sensitive semiconductor devices. It was shown that adding a solvent such as IPA or lowering the temperature helps to control cavitation in semi-aqueous fluids [2]. Sonochemical reactions have been observed in various industries, however, there are no published observations in semiconductor cleaning. Ions may form in megasonic driven bubble collapse impacted by the characteristics of a gas or liquid that enters the bubble from the bulk liquid. Lower ionization potential gases or liquids may form ions earlier in the bubble collapse, so as to use up some of the total available energy through sonochemical reactions and possibly reducing the cavitations implosive energy. Here, tests are conducted to vary the liquid and gas type based on ionization potential to look into the impact this would have on cleaning and damage. It is shown that lower ionization or liquid additives lower the device damage.
Authors: Tom Janssens, G. Doumen, S. Halder, Kurt Wostyn, Paul W. Mertens, Joachim Straka
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.

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