Electrical Evaluation of Wet and Dry Cleaning Procedures for Silicon Device Fabrication

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.

Section: Alternative Cleaning Techniquesmentioning

confidence: 99%

The Evolution of Silicon Wafer Cleaning Technology

Kern

1990

1,522

801

“…[1][2][3] Surface cleaning prior to epitaxy is particularly important, as improper removal of surface oxides and organic contaminants has been shown in Si homoepitaxy to result in an increase in the density of stacking faults and dislocations from <10 4 /cm 2 to >10 10 /cm 2 4-15 and a concomitant decrease in device performance and yield. [16][17][18][19][20][21][22] Studies of the heteroepitaxial growth of Si x Ge 1Ϫx alloys on Si have also shown that residual oxide and organic contaminants act as the preferred sites for nucleation of misfit dislocations. 15 The control of defects is of paramount importance in epitaxial films of SiC, as a range of structural and electrical defects are currently limiting the application of this material for several types of high power, and high temperature electronic devices and for substrates for III-N nitride heteroepitaxy.…”

mentioning

confidence: 99%

Chemical Vapor Cleaning of 6H‐SiC Surfaces

King¹,

Kern²,

Benjamin

et al. 1999

The techniques (temperature range of study) of in situ thermal desorption (500-1100ЊC) and chemical vapor cleaning (CVC) via exposure to SiH 4 and/or C 2 H 4 (750-1100ЊC) have been investigated for preparing 6H SiC [(0001) Si , (0001 ෆ) C , (112 ෆ0), and (101 ෆ0)] surfaces suitable for epitaxial growth of SiC and III-nitride films, and are compared with regard to surface purity, stoichiometry, and structural order. Oxide removal below the detection limits of Auger electron spectroscopy was achieved for all orientations via annealing in 200 L SiH 4 at 850-900ЊC or Ϸ200Њ lower than necessary by thermal desorption. No non-SiC carbon was detected on the surface by X-ray photoelectron spectroscopy. An approximately one-tenth of a monolayer of oxygen coverage and significant quantities of non-SiC carbon were detected for all 6H-SiC surfaces prepared by thermal desorption. In contrast to the predominantly non-SiC carbon-rich surfaces prepared by thermal desorption, the stoichiometry of the SiC surfaces prepared by CVC could be manipulated from Si-rich to C-rich without non-SiC carbon formation by either extending the SiH 4 exposures or by following with C 2 H 4 exposure. The latter surfaces also had lower concentrations of both oxygen and non-SiC carbon and increased surface order.

“…A UV-ozone treatment is a dry cleaning technique typically used to remove organic contamination from the Si surface. [4][5][6] This technique leaves the Si surface passivated with a "dry" oxide (ϳ1 nm thick). In both cases, the presence of the oxide may detrimentally effect next step processing.…”

mentioning

confidence: 99%

Surface Residue Island Nucleation in Anhydrous HF/Alcohol Vapor Processing of Si Surfaces

Carter

Hauser

Nemanich

2000

Anhydrous HF/methanol vapor-phase chemistries were employed to etch SiO 2 /Si surfaces at low pressure (5-50 Torr) and ambient temperature. The oxides on Si were formed from the following: (i) RCA chemical cleaning and (ii) UV-ozone treatment. Atomic force microscopy (AFM) and lateral force microscopy (LFM) were used to analyze the HF vapor-cleaned Si surfaces. AFM/LFM displayed residue islands distributed randomly upon the Si surface as a result of vapor-phase cleaning. As a result of etching RCA chemical oxides, the average lateral dimension of the residue islands is 40 nm and the average height of the islands is 6 nm. As a result of etching UV-ozone oxides, the average lateral dimension of the residue islands is 30 nm, and the average height of the islands is 3.5 nm. A decrease in residue island density is observed after the removal of a UV-ozone oxide compared to RCA chemical oxide removal. Secondary ion mass spectroscopy was used to characterize chemical impurities (O, C, F, and N) in the SiO 2 films and and the Si surface after HF vapor-phase cleaning. The constituents of the residue islands have been attributed to nitrogen impurities and silicon atoms imbedded in the passivating oxides. Results indicate that condensation of methanol vapor onto the bare Si surface, after oxide removal, is necessary for residue island formation. We suggest a model in which residue island nucleation occurs from nonvolatile N-Si complexes that form hydrogen bonds with methanol molecules and diffuse into the adsorbed alcohol layer. The molecular impurities then interact and form residue islands. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.216.129.208 Downloaded on 2015-03-22 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.216.129.208 Downloaded on 2015-03-22 to IP