Cleaning of silicon wafer

V.B. Menon and R.P. Donovan, Review of Particle Control Methods During Wet Chemical Cleaning of Silicon Wafers, in Semiconductor Qeaning Technology/1989, PV90-9, eds. J. Ruzyllo and R.E. Novak, The Electrochemical Society, Inc., 10 S. Main St., Pennington, NJ 08534-2896 (1990), p. 167. 

J. A. Amick, Cleanliness and the cleaning of silicon wafers. Solid State Technol. 33, November 1976. D. Tolliver, LSI wafer cleaning techniques, Solid State Technol. 33, November 1975. 

Thin films of PEO can be prepared by spin coating filtered (mesh size ca. 0.2 pm) solutions of PEO in chloroform onto precleaned silicon wafers or glass cover slips using a conventional spin-coater (typical concentrations of 1.0-20.0 mg/ml and typical spinning speeds of 2,000-3,000 rpm for 1 min are recommended for film thicknesses between ca. 15 and 300 nm). The cleaning of silicon wafers can be carried out in a plasma cleaner or using oxidizing solutions [59]. The films should be dried for at least 24 h in vacuum to remove residual solvent. 

Typically, the vapor phase of hydrofluoric acid is used instead of HF liquid. HF vapor is known to strip native oxides during cleaning of silicon wafers [21] and was suggested for sacrificial oxide etching [22]. However, even using the vapor phase can be critical in terms of stiction, because a byproduct of the chemical reaction is water ... 

Figure 5 Effect of cleaning on the surface purity of silicon wafers, as measured by VPD-...

More recently, Gould and Irene (96) studied surface-cleaning effects on the oxidation of silicon wafers for oxide thicknesses up to 4300 A. They found... 

Busnaina A, Park J, Bakhtari K. Particle deposition and adhesion. In Reinhardt K, Kem W, editors. Handbook of Silicon Wafer Cleaning Technology. 2nd ed. Norwich, NY William Andrew Publishing 2006. 

Spin-coated PS/PMMA films were used as samples to study silica-polymer interactions. For this purpose, solutions of 10 mg polymer in 1 mL toluene were prepared flom each polymer. The PMMA and PS solutions were mixed in a ratio of 2 1. When the mixed solution was spin-coated on a fleshly cleaned silicon surface a phase-separated film of 100 nm thickness was obtained. Cantilevers were modified either by deposition in the saturated atmosphere of hexamethyldisilizane or immersion in a 2% solution of dimethyldichlorosilane in toluene. Typically, measuring the contact angle of the sample after modification gives proof of hydrophobization. However, because of the small size of the tips the contact angle cannot be estimated. Thus, at the same time as the cantilever modification, small pieces of silicon wafers were modified to enable contact angle measurements to be made. 

W. Kern, The evolution of silicon wafer cleaning technology, J. Electrochem. Soc. 137, 1887, 1990. 

The mechanisms of particle removal have been studied in detail in the case of silicon wafers [3, 44]. At present, particle removal from polymers has been analyzed along similar lines. The different cleaning mechanisms that seem to be relevant include ... 

Carefully clean the silicon wafer with canned air. Then add about 4 mL of the bubble-free silicone elastomer/curing reagent mixture on the wafer. Plasma clean round cover glasses at high intensity for 2 min. Then place them with the plasma-cleaned surface facing the silicone elastomer/ curing reagent mixture on the wafer. Press them down to the silicon wafer and make sure to get rid of aU the bubbles. 

Ultra-small concentrations in sub-parts-per-billion levels of plasticizers in ultrapure water can seriously undermine cleaning efficiency of silicon wafers. Thermal desorption-gas chromatography-mass spectrometry was successfully used to determine these very small quantities of plasticizers. " Many plasticizers such as texanol, trichloroethyl phosphate, diethyl phthalate, dibutyl phthalate, benzyl butyl phthalate, dioctyl phthalate and dioctyl adipate were identified in water at lower than 0.2 ppb levels. " ... 

Samples were prepared from dilute toluene solutions by spincoating thin films onto the wafers. The polymer adsorbed onto the oxide surface of silicon wafers which were cleaned in a water-saturated UV-ozone atmosphere. By this cleaning procedure, we created a surface with a high density of hydroxyl groups. The initial film thickness has been determined by eUipsometry. Crystallization and subsequent thermal treatment (annealing) were performed directly under an optical microscope in an inert atmosphere (nitrogen flow). 

Wafers. From this cylinder, thin wafers or slices are cut using a continuous wire saw that produces several uniform slices at the same time. The slices are subjected to numerous stages of polishing, cleaning, and quality checking, the end result of which is a consistent set of silicon wafers suitable for use as substrates for integrated circuits. 

LB films were also formed on the silicon plate after the asperity array was processed by FIB. Before depositing the LB film, we cleaned the silicon wafers in a mixture of benzene and ethanol, rinsed them in pure water, and then exposed them to a UV-ozone atmosphere. Then the plate was immersed in ultrapure water where a monolayer of stearic acid (Ci7H35COOH CH) or fluorocarboxylic acid (QFi3CiiH22COOH CFCH) was confined at a pressure of 30 mN/m. The monolayer on the water migrated onto the silicon surface and formed the LB film (CH-/CFCH-LB film) when the plate was removed from the ultrapure water. The temperature of the ultrapure water was 20°C. Table 2.3 shows the chemical modifications and the geometries of the asperity. 

The SC-1 cleaning solution is used as part of the RCA cleaning process for silicon wafers and is a mixture of ammonium hydroxide, hydrogen peroxide, and water. This process is used to remove undesired particles and contaminants from silicon wafers. It is important to maintain the composition of the solution because an improper ratio of ammonium hydroxide to hydrogen peroxide can lead to etching of the silicon surface, ineffective cleaning of the wafer, or damage to both the thermal oxide or doped silicon dioxide layers. 

These kinds of environmental contamination problems are everyday occurrences in the semiconductor industry because of the strict cleanliness demands required for the fabrication of silicon wafers and production of semiconductor devices. The purity of silicon wafers has a direct effect on the yield of devices, so it is crucial that trace element contamination levels are kept to a minimum in order to reduce defects. This means that any analytical methodology used to determine purity levels on the surface of silicon wafers, or in the high-purity chemicals used to mauufacture the devices, must use spotlessly clean instruments. These unique demauds of the semiconductor industry have led to the development of special air filtration systems that continually pump air through ultraclean high-efficiency particulate air (HEPA) filters to remove the majority of airborne particulates. 

For some materials, the most notable being silicon, heating alone sufiBces to clean the surface. Commercial Si wafers are produced with a thin layer of silicon dioxide covering the surface. This native oxide is inert to reaction with the atmosphere, and therefore keeps the underlying Si material clean. The native oxide layer is desorbed, i.e. removed into the gas phase, by heating the wafer in UHV to a temperature above approximately 1100 °C. This procedure directly fonus a clean, well ordered Si surface. 

Undeniably, one of the most important teclmological achievements in the last half of this century is the microelectronics industry, the computer being one of its outstanding products. Essential to current and fiiture advances is the quality of the semiconductor materials used to construct vital electronic components. For example, ultra-clean silicon wafers are needed. Raman spectroscopy contributes to this task as a monitor, in real time, of the composition of the standard SC-1 cleaning solution (a mixture of water, H2O2 and NH OH) [175] that is essential to preparing the ultra-clean wafers. 

A (100) oriented p-silicon wafer (Wacker Chemitronic) was cut into 5x5 mm pieces. These were cleaned in a UV/ozone dry stripper (Samco) for 15 min followed by a two minute rinse in doubly deionized water. The samples were dried in clean air for several minutes. A 10 pi amount of TEOS (purchased by Aldrich, electronic grade, as received) was dropped onto the dried surfaces. The film was allowed to dry in ambient air for 10 minutes and then immediately transferred into the vaccum-chamber of the TOF-SIMS spectrometer. 

RCA [Radio Corporation of America] Also called RCA-2 and HPM. A process for cleaning silicon wafers used in electronics. They are washed successively by three solutions. 

Apart from new low-dielectric materials, a clean method to deposit the dielectric as a uniform film is also required. Owing to the way fabrication technology in the microelectronics industry has developed and because larger silicon wafers (> 8 in.) are being used (currently, the technical difficulty of... 

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