Papers by Keyword: Megasonic

Abstract: The Chemical Mechanical Planarization (CMP) process (polishing and substrate cleaning) results in defects that can be classified as mechanical (i.e., scratching), chemical (i.e., corrosion), or physiochemical (i.e., adsorbed contaminants) according to the mechanism of formation. This work will focus on the rationale design of p-CMP cleaning systems for emerging materials (silicon carbide (SiC)) that activate the cleaning chemistry via external stimuli such as megasonic energy. More specifically, using megasonic energy in the presence of supramolecular assemblies such as micelles and vesicles was employed for a “soft” (low shear force) defect removal process. Results indicate a correlation between the structure of the “soft” cleaning additives and induced megasonic energy on overall simulated defect removal. It was determined that effective particle removal was a second-order kinetic process with a concentration dependency (i.e. above and below the critical micelle concentration (CMC)) emerging as a key driver for the defect removal rate. Although, one apparent drawback is the generation of post-cleaning carbon residue due to the adsorption of the supramolecular structures to the SiC substrate.

Abstract: A novel add-on hardware device is placed near the point of slurry dispense that can instantaneously activate slurry performance during polishing via megasonic irradiation. This new technology (Flucto-CMP® is able to overcome the inherent polisher-slurry weaknesses such as wafer-level defects, process vibrations, cost of ownership, slurry waste, remval rate (RR), and RR selectivity. Flucto-CMP® has been successfully applied to various types of CMP slurries resulting in significant increases in the removal rates of copper, SiC, borosilicate hard mask, ILD, TiN, and silicon carbide through chemical alteration of the passivation layer needed for material removal. Specifically, for copper CMP, using Flucto-CMP®, we see an up to 31% boost in RR which is well correlated with the amount of reactive oxidizing species generated through irradiation as well as the measured relative indentation depth of the passivation layer. In addition to boosts in RR, for copper, we see a 50X drop in the variance of shear force and a 5X drop in the variance of normal force when Flucto-CMP® is used. This dramatic reduction in process vibration for copper soft-landing processes ought to reduce wafer-level defects. Much greater rate improvements are observed when polishing SiC, and borosilicate hard masks.

Abstract: The process of quickly removing abrasive particles of silica and ceria slurries is important in the use of CMP equipment. Megasonic cleaning of nozzle injection type is one of a variety of post-CMP cleaning methods and its performance including cleaning efficiency and erosion was explored experimentally with parametric studies. In the cleaning process, it is favorable to achieve both high efficiency and low damage. The cleaning efficiency was defined by particle removal efficiency (PRE) with a glass sample spin-coated with small silica particles; the damage was detected from mass loss of aluminum foils after the cleaning. The cleaning tests show that the performance of nozzle injection megasonic cleaning depends significantly on ultrasound frequency and water temperature. Toward more efficient and less erosive cleaning, the nozzle injection angle is also expected to play a key role.

Abstract: A novel transducer for megasonic cleaning of photomasks presents an approach that differs from previous configurations, and appears to have unique features for cleaning while minimizing damage. As the cleaning and damage processes are determined by the presence of cavitation, a thorough acoustic analysis was performed on the device, by using a calibrated hydrophone scanned at the photomask location, and a quartz photomask with embedded sensors.

Abstract: Twenty years ago dissolved ozone in DIW (DiO₃) found its way into the semiconductor industry as a cleaning agent. DiO₃ provides an effective replacement for Piranha (H₂SO_4, H₂O₂) cleans. The fundamental chemistry of ozone based cleaning is due to direct and indirect reactions of ozone and oxygen radicals (the so-called radical pathway). Due to its high oxidation rate the radical pathway can accelerate the reaction. Megasonic energy can act as an initiator for the radical pathway. At the same time, due to the creation of turbulence inside the boundary layer, the available ozone close to the surface is increased. In the present study this chemical physical combination was tested for improvement of photoresist strip rate.

Abstract: Emerging ultrasonic and megasonic cleaning demands in various applications (solar cell, storage devices, wafer and mask cleaning, etc.) dictate the need to understand the acoustic cavitation under different operating conditions to optimize efficiency of cleaning and reduce damage. Major parameters that affect cavitation include frequency of the sound field, operating power of the transducer and the cleaning chemistry. Previous studies have reported the use of common techniques such as multi-bubble sonoluminescence [1] and sono-electrochemistry [2] to understand acoustic cavitation. The disadvantage with sonoluminescence technique is that it characterizes cavitation mainly in the bulk of the solution, which may not be pertinent to wafer cleaning applications where the interest is in understanding cavitation phenomena close to the wafer surface. Although, sono-electrochemical techniques employing microelectrode are capable of measuring cavitation in the vicinity of a solid surface, they are limited to measurements on an extremely small area due to the miniscule size (5-25 μm) of the electrode. In this context, hydrophone measurements offer significant benefit as they can be taken near a solid surface as well as on a relative large area (1-2 mm diameter) of the pressure sensitive tip.

Abstract: Megasonic cleaning has been one of the most successful techniques for Cu/low-k interconnects post-CMP cleaning. The structural deformation and stress of Cu and low-k materials in megasonic cleaning are examined with finite element method (FEM). The maximum stress is concentrated in the binding area between Cu and low-k. With decrease of Cu line width, the maximum stress increases and the max value exceeds the yield strength of Cu which results in the plastic deformation. The increasing frequency will change the bubble collision times. Therefore the fatigue is potential. The maximum displacement moves from center to the sides of top surface with increase of line width. When the line width is 25nm, the deformation is the largest.

Abstract: Megasonic cleaning has been one of the most successful techniques for nanoparticle cleaning in semiconductor industry. However, the megasonic energy often causes a pattern collapse and some damage to very small structure. In this study, the distribution of sonic pressure in a wet cleaning bath with different arrangement of megasonic transducers is simulated. Megasonic wave transmits directional and will be disturbed. Thus the wafer surfaces should be arranged parallel to the sound wave direction of propagation. Convergence gain in the whole cleaning space is limited but results in great variance in local areas. Thus the wafer moving, rotating and oscillating is necessary.

Abstract: A near-field megasonic system for cleaning semiconductors was designed and fabricated. For the design of the near-field megasonic system, an impedance characteristic of a quartz megasonic waveguide with the piezoelectric actuator was analyzed using a finite element method (FEM). The analysis result showed that the anti-resonance frequency of the system was 982 kHz, which agreed well with the measured value of 988 kHz. The performance of the developed system was assessed by measuring acoustic pressures and comparing the maximim values of them with a conventional megasonic system. As a result, the maximim acoustic pressure of the developed system was decreased by 46.2% compared to the commercial system. Finally, the particle removal efficiency (PRE) test was performed and the obtained PRE was 90.8%. Theses results explain that the developed megasonic has an improved uniformity of the acoustic pressures, which can raise the energy efficiency of the system and lowering the consumption of chemical and ultra pure water (UPW).

Abstract: High frequency (1 MHz, megasonic) acoustic enhanced cleaning is a well established method of removing surface particles in semiconductor manufacturing processes. There are two fundamental designs of megasonic batch cleaning systems, indirect and direct.