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Megasonic cleaning process as a wet cleaning process is routinely used in the
semiconductor industry for the removal of contaminant particles from wafer surfaces. The
wafer surfaces can be cleaned effectively by choosing the proper chemicals, acoustic
pressure, and the frequency of acoustic field. In the present study, we propose the design
imp...
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... schematic for acoustic pressure measurement is shown in figure 2. The acoustic pressure was measured with scanning acoustic microscope (AcouLab Inc., Korea). The hydrophone probe of the system can scan the bottom surface of the waveguide with 0.05 mm resolution. The acoustic waveguides were precisely mounted vertically dipped to about 2 mm in the water column with the aid of three axis servo motor control system. Also the distance between hydrophone probe and acoustic waveguide bottom surface is maintained to 3 mm, which is the standard condition during particle removal process. The measurements were carried out at various input power of acoustic waveguides from 1 W to 5 W, the measured data is delivered to a computer for further analysis. The pressure distribution was plotted simultaneously on a monitor, and the maximum values with the standard deviations were ...
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Citations
... Still, pressures may be of the order of 10 3 –10 4 bars. The range of driving pressures analysed here is the typical operating range of megasonic cleaning devices (Kapila et al. 2006; Holsteyns et al. 2008; Minsier & Proost 2008; Ahn et al. 2009; Keswani et al. 2009). An uncontrolled radiation by cavitation bubble fields will result in mechanical failure, when the high peak energies of the radiated sound containing highfrequency components drive unwanted mechanical oscillations. ...
Based on the theory of F. Gilmore (Gilmore 1952 The growth or collapse of a spherical bubble in a viscous compressible liquid) for radial oscillations of a bubble in a compressible medium, the sound emission of bubbles in water driven by high-amplitude ultrasound is calculated. The model is augmented to include expressions for a variable polytropic exponent, hardcore and water vapour. Radiated acoustic energies are calculated within a quasi-acoustic approximation and also a shock wave model. Isoenergy lines are shown for driving frequencies of 23.5 kHz and 1 MHz. Together with calculations of stability against surface wave oscillations leading to fragmentation, the physically relevant parameter space for the bubble radii is found. Its upper limit is around 6 μm for the lower frequency driving and 1–3 μm for the higher. The radiated acoustic energy of a single bubble driven in the kilohertz range is calculated to be of the order of 100 nJ per driving period; a bubble driven in the megahertz range reaches two orders of magnitude less. The results for the first have applications in sonoluminescence research. Megahertz frequencies are widely used in wafer cleaning, where radiated sound may be implicated as responsible for the damage of nanometre-sized structures.
In the semiconductor process, cleaning wafer surface by megasonic transducer with thin liquid film is getting more attention than conventional bath-type batch cleaner. Although its major contribution to the cleaning process, nanoparticle removal mechanism of megasonic cleaning is not fully understood yet. Thus the understanding of the cavitation bubble motion formed by megasonic wave is very important. Due to rapid motion of the bubbles experimental observation of their movement is hard to achieve. In present study, we introduce lattice Boltzmann method to simulation fluid and cavitation bubble behavior. Validation was achieved by compare the simulation result with analytical solution of fluid motion. It was shown that bubbles formed by cavitation phenomena can be expanded, shrunken, or even collapsed to emit shockwave.
Tight control of a bevel wrap of a dielectric film stack is required to prevent issues in subsequent film deposition and defectivity excursions. In this report, a structure of dielectric films consisting of a plasma SiO2 (P-SiO2: cap layer), a low dielectric constant (low-k film: middle layer), and P-SiO2 (base layer) was examined.We investigated the dependency of underlying surface wettability as well as geometric shape on dielectric film removal at the wafer edge. The hydrophobic surface on a single crystal Si (s-Si) substrate gave a smaller etching distance with a larger variation in edge etching, in contrast to that of the hydrophilic surface (silicon nitride; SiN layer), which gave a larger etching distance with smaller variation. An Si sidewall (Si step) formed on s-Si through an etching process of shallow trench isolation (STI) prevented the over-etching.
An ultrasonic dry cleaning system is a kind of air-blowing cleaning system, which clears away fine particles of dust adhering to a surface. This system does not require high cost consumables such as highly pure gases or chemical solvents. Moreover it removes micro contaminant particles without additional cooling or heating processes. In this paper, a numerical simulation of the ultrasonic dry cleaning system was carried out to propose an optimum ultrasonic generator. We evaluated the flow in the chamber according to the groove shape of ultrasonic generator, and system operating pressure using a commercial fluid dynamic simulation tool. And the trend of the sound pressure level (SPL) according to frequency was checked to determine whether or not the ultrasonic generator module could generate an ultrasonic wave. The particle trajectories were compared for several conditions and particle sizes. We confirmed that an ultrasonic wave of sufficient flow velocity can be generated through the ultrasonic generator module. And the changes of SPL according to the system operating pressure and the shape of the ultrasonic generator groove were confirmed respectively.
Megasonic irradiation of cleaning solutions removes particulate contaminants from wafer surfaces through the mechanisms of acoustic streaming and acoustic cavitation. Uncontrolled cavitation, however, also damages fragile wafer features. It has been hypothesized that damage results primarily from violent transient cavitation while cleaning results from the gentler, stable cavitation and is assisted by substrate etching at alkaline pH. A central challenge in the megasonic cleaning field is to find physical and chemical conditions that would suppress violent cavitation without adversely affecting cleaning efficiency. We have previously reported the strong ability of aqueous CO2 in suppressing sonoluminescence, a measure of transient cavitation, and wafer damage. However, dissolution of CO2 also renders solutions acidic and lowers their ability to remove particles. Here we report the development of two new systems, NH4HCO3/NH4OH and NH4OH/CO2(g) designed to suppress pattern damage and enhance cleaning efficiency. Using megasonic irradiation of bare and line-space patterned wafers in a single wafer spin cleaning tool, MegPie®, we measured the efficiencies of these systems as well as NH4OH, at pH 8.2, in removing SiO2 particles from oxide Si wafers and suppressing damage to wafer features. All systems were found to achieve high particle removal efficiencies but extent of damage was strongly reduced in the newly designed NH4HCO3/NH4OH and NH4OH/CO2(g) compared to NH4OH. This study establishes a means for well controlled generation of CO2(aq) over an extended pH range (4.0–8.5) and its application in strongly reducing wafer damage without compromising megasonic cleaning efficiency.
As devices become smaller to the extent of nano-scale, dry damage-free cleaning process has become an important area of study. Gas cluster cleaning technology has a potential to remove contaminant particles from the surface of semiconductor wafers without damage because a gas cluster is smaller than 100 nm in diameter. In this paper, a new dry cleaning process using a CO2 gas cluster beam is developed and a characterization method for gas cluster generation was studied experimentally. First, a CO2 gas cluster cleaning system was built to evaluate the feasibility of cleaning by use of a gas cluster beam, which is generated by expansion of gas through a converging–diverging nozzle and nozzle chilling. Cleaning tests were performed several times. Twenty-five to three hundred nanometers silica particles were cleaned off from the surface of a bare Si wafer and of a wafer with 60 nm poly-silicon structure by using this cleaning system. Preliminary result showed that the contaminants were successfully removed without damage to the wafer surface. To characterize the gas cluster, we used the particle beam mass spectrometer (PBMS) for the measurement of the size distribution of the gas clusters. The size distribution of clusters is measured by varying flow rate and nozzle coolant temperature. From the measurement results, the size of a gas cluster was less than 40 nm, which is expected to cause no damage on a surface based on the measurement of pattern collapse force. By using the PBMS, CO2 gas cluster cleaning system can be optimized to provide the maximum cleaning efficiency for nano-scale contaminant particles without damage to substrate surfaces.
