Effects of Various Chemistries on Silicon-Wafer Cleaning

The influence of aqueous chemical cleaning on the dry oxidation of Si (100) was studied for ten different preoxidation treatments at thicknesses ranging between 800 and 1200~ The surface treatments included mixtures of acids or bases with hydrogen peroxide as well as HF:H20. Below 1200~ only the treatment with NH4OH:H202:H20 as a final step showed a deviation in oxidation kinetics compared to the other cleans. At 1200~ variations in surface cleans had no affect on oxidation. A series of two-step oxidations with an intermediate treatment were performed to determine if the cleaning effect occurs at the Si/SiO2 interface, in the bulk of the oxide, or at the free surface of the oxide. The results indicate that the physical mechanisms associated with the surface cleans affected the outer surface of the thermal oxide. These experiments, and SIMS analysis of the surfaces, show that A1 on the surface of the wafer is responsible for the retardation in kinetics. A mechanism is proposed where the surface A1, which causes the retardation, reduces the density of sites on the surface of the thermal oxide where the oxidant is incorporated into the bulk of the oxide.

supporting

confidence: 81%

“…Thermal Oxide Surface It is well known that A1 is present on the surface of Si wafers after treatment with NH4OH:H202 (15,(17)(18)(19). However, to establish any connection between this A1 and the retardation in NH4OH:H202 kinetics, it is important to determine the effects of subsequent processing on the surface A1.…”

Section: Ai Surface Contamination and Thementioning

confidence: 99%

The Effect of Aqueous Chemical Cleaning on Si (100) Dry Oxidation Kinetics

deLarios

Kao

Deal

et al. 1991

“…A great deal of research activity is taking place in this important area of technology, as evidenced by the scheduled presentation of over 40 with titanium tetrachloride and ammonia as reactants. Both hydrogen and nitrogen are evaluated as diluents.…”

Section: Resultsmentioning

confidence: 99%

The Evolution of Silicon Wafer Cleaning Technology

Kern

1990

1,522

801

The purity of wafer surfaces is an essential requisite for the successful fabrication of VLSI and ULSI silicon circuits. Wafer cleaning chemistry has remained essentially unchanged in the past 25 years and is based on hot alkaline and acidic hydrogen peroxide solutions, a process known as "RCA Standard Clean." This is still the primary method used in the industry. What has changed is its implementation with optimized equipment: from simple immersion to centrifugal spraying, megasonic techniques, and enclosed system processing that allow simultaneous removal of both contaminant films and particles. Improvements in wafer drying by use of isopropanol vapor or by "slow-pull" out of hot deionized water are being investigated. Several alternative cleaning methods are also being tested, including choline solutions, chemical vapor etching, and UV/ozone treatments. The evolution of silicon wafer cleaning processes and technology is traced and reviewed from the 1950s to August 1989.

“…SIMS studies showed that modified RCA processes of intentionally contaminated wafers significantly reduced the REAs of many elements (46,47). The aqueous RCA process results in Mg and Ca REAs which are significantly lower than the initial unprocessed wafers.…”

Section: Discussionmentioning

confidence: 99%

“…SIMS studies showed that modified RCA processes of intentionally contaminated wafers significantly reduced the REAs of many elements (46,47). Hydrogen peroxide (H~O2) is a potential source of A1; elevated A1 contamination following basic H202 solutions are frequently reported (47,50,51). Significant REA reductions resulted when the unprocessed wafer was exposed to a HF gas-rinse process or a HF(aq)-rinse process.…”

Section: Discussionmentioning

confidence: 99%

XPS and SIMS Study of Anhydrous HF and UV/Ozone‐Modified Silicon (100) Surfaces

Zazzera

Moulder

1989

X-ray photoelectron spectroscopy and secondary ion mass spectrometry are used to study the surface chemistry of silicon single-crystal wafers. Anhydrous HF and UV/ozone processes modify the surface chemistry by altering the concentration and bonding environments of the most abundant surface atoms: Si, O, C, H, and F. Anhydrous HF in conjunction with water vapor [HF(g)] removes the silicon native oxide. Native oxides with initial thicknesses of 1 lfi~, four monolayers, are exposed to a HF(g)-H~O rinse, HF~g), and an aqueous HF-H20 rinse and are reduced to 0.4, 0.2, and 0.1 monolayers, respectively. The carbon concentration exhibits an inverse relationship with the submonolayer oxide coverage. The HF(g) process results in less than a monolayer of silicon fluorides. The silicon fluoride species decrease with air exposure resulting in mostly oxyfluorides after lh. Rinsing the fluorinated surface with H20 reduces the fluorine concentration, removes trace metal impurities initially bonded to the native oxide, and promotes initial S iO2 formation. UV/ozone exposure reduces the hydrocarbon concentration on the HF-etched surface while producing 8A, three monolayers, of SiO2. Exposing the HF(g)-treated surface to UV/ozone removes the silicon fluoride species; only oxyfluorides are observed with the ozoneinduced SiO2. The cleanest silicon surface with respect to metallic and hydrocarbon impurities was achieved with a HF etch-H20 rinse-UV/ozone oxidation process.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.230.243.252 ABSTRACT Crystallographic faceting of unmasked monocrystalline SiC (100) thin film surfaces during plasma etching in SF6 has been observed using scanning electron microscopy. Although the faceting produced a rough surface, Auger electron spectroscopy showed it to be very chemically clean, having less native oxide than unetched SiC. The facets were determined to be {210} planes using a combination of selected area channeling and small angle tilt measurements. The facet nucleation appears to be surface sensitive and is caused by either crystal defects or compounds formed by reaction of SF6 with adsorbed gases on the sample and chamber wall. It is proposed that the subsequent facet growth is due to a surface reconstruction that causes the {210} planes to etch slower.