A phenomenological model is proposed to describe sulfide passivatlon of the surfaces of III-V semiconductors as a process of charge transfer between a semiconductor and a passivating solution. The model assumes that formation of the passivating sulfide coat occurs as a result of oxidation of the semiconductor in a photoelectrochemical reaction. The growth rate of the passivating coat is determined by the rate at which electrons are transferred from the semiconductor into the solution as well as by the energy which binds atoms in the surface layer of the semiconductor and the heat evolving in the process. It is found that the growth rate of the coat is dependent upon conductivity type and doping level of the semiconductor, hydrogen ion exponent and concentration of the solution and, as well, the intensity of light incident upon the electrolyte/semiconductor interface. In terms of the model, passivation of different III-V semiconductors is considered.

Synchrotron radiation soft x-ray photoemission spectroscopy was used to characterize the surface chemistry and the electronic structure of InP(100) before and after exposure to an H2S plasma. The low power plasma was generated with an electron cyclotron resonance (ECR) plasma source, using H2S, with the plasma exposure being performed at two temperatures. In-situ photoemission measurements were acquired after each plasma exposure in order to observe changes in the valence band electronic structure and in the In4d, P2p and S2p core lines. The results revealed changes in surface chemistry and electronic properties and indicate that the H2S plasma exposure type converts the ptype InP(100) surface to an n-type surface. The magnitude of the band bending is dependent on the substrate temperature, resulting in a homojunction interface.

The effect of sulfide passivatlon on the photoluminescence properties of InAs relative to the surface orientation has been investlgated. Chemical bonds formed in the passivation process have been studied using X-ray photoelectron spectroscopy. It was found that both As-S and In-S bonds form at the (111)A face, whereas only As-S bonds form at the (111 )B face. Improvement of photoluminescence properties was found to be associated with a decrease in the surface content of the oxides and elemental arsenic. Sulfidizing results in a reduction of the surface state density by an order of magnitude.

Low temperature (50-400°C) and low pressure (10-300 mTorr) processing conditions for remote H-plasma cleaning of Si(100) substrates were investigated. After plasma exposure, ordered surfaces were obtained which displayed 2×1, 3×l and lxI LEED diffraction patterns. The surface phases following the H-plasma clean were dependent on temperature and pressure. The electronic states of the surfaces were explored with angle resolved uv-photoemission spectroscopy (ARUPS) and states due to Si-H bonding were identified. The atomic interactions at the surface were modeled in terms of several processes including Eley-Rideal abstraction, thermally activated desorption and a physisorbed weakly bound state. The kinetic model was able to describe the transitions observed in the processing results. Suitability of the cleaning process for low temperature epitaxy was demonstrated by low temperature MBE epi-growth on an H-terminated 2×1 surface. The initial oxide formation on the H-terminated surfaces were studied by ARUPS.

Three regimes of HF-H2O vapor etching of oxide can be distinguished, viz. a gas phase, an adsorption and a condensation regime with gas phase etching behaving distinctily different in terms of etch rate and surface passivation properties. Integration of a vapor etch process in a vacuum-controlled, leak-tight cluster tool equipped with vertical reactor LPCVD and oxidation modules offers important thin film interface engineering capabilities; significant process control improvement is achievable in critical device technologies, such as formation of poly-contacts, poly-emitters and NO capacitors.

Silicon etch rates and the in situ remote H plasma cleaning effectiveness in a Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) system have been measured under conditions of varying substrate temperature, exposure time, and hydrogen pressure. An incubation phenomenon is observed in the Si etch rate as a function of exposure time to the plasma species at a substrate temperature of 250°C. The etch rate is observed to increase from 20 Å/hr. for 45 min. exposure to 70 Å/hr. for a 4 hour exposure. The dependence of the etch rate on the plasma discharge pressure shows the etch rate to decrease from 72 Å/hr. at 50-55 mTorr to 4 Å/hr. for pressures greater than 125 mTorr. The substrate temperature is found to have the greatest effect on both the cleaning of the surface and the Si etch rate, with 250ÅC resulting in a surface with oxygen and carbon concentrations less than the detection limit for Auger Electron Spectroscopy. On wafers exposed to atomic H at both 150 and 400ÅC, oxygen, carbon and nitrogen were detected after 4 hr. exposures. The etch rate is inversely related to temperature, consistent with earlier results. At a substrate temperature of 150ÅC, Reflection High Energy Electron Diffraction (RHEED) shows the diffraction pattern to change from a streak pattern observed at higher temperatures to a spot pattern, indicating a roughened surface after 4 hrs. of etching. Wafers cleaned at temperatures above 150ÅC yielded streak patterns even after 4 hr. exposure. Increasing the H pressure during the clean had no effect on the final RHEED pattern.

ECR plasma etching of SiO2 films and post-etch cleaning and passivation of the Si substrate in a dual-function module are reported. The goal is development of a single-chamber etch/clean module for fabrication of FET's with a stacked gate - raised source/drain architecture. With He fed to the ECR source cavity and CF4 (5 sccm) injected downstream, an average Si0 2 etch rate of 390 A/min was measured at 1.1 mTorr under autothermal conditions. Addition of H2 inhibited etching but improved Si0 2/Si etching selectivity. Etching products (COF2 and SiF4) were monitored by quadrupole mass spectrometry, and the signals were used for real-time end-point detection. In situ, off-line AES analyses were made on wafers following interrupted-cycle processing. Over-etched wafers were coated by a fluorocarbon film. H2 -addition increased surface carbon concentrations during etching, and fluorocarbon buildup at the end point. O2 and H2 plasma cycles were investigated for post-etch surface cleaning/passivation.

The time/temperature dependencies of the surface roughness, subsurface extended defect formation, and minority-carrier lifetime are reported for n-type (100) silicon wafers exposed to a hydrogen ion beam. Surface roughness is assessed from atomic force microscopy, the distribution and nature of extended defects are determined from transmission electron microscopy, and the minority-carrier lifetime is evaluated by a non-contact laser-microwave technique. The surface roughness exhibits a weak dependence on ion-beam exposure time for the temperature range studied, whereas the distribution of extended defects may depend on exposure time at a given wafer temperature. The surface and bulk components of the minoritycarrier lifetimes are consistent with these surface and subsurface properties. Transmission electron microscopy analyses demonstrate that the associated strain field of the extended defects is compressive in nature.

The combination of ultraviolet light (UV) and ozone (O3) has been used to remove organic contamination and strip organic materials, such as, photoresist from silicon and gallium arsenide wafers during processing of electronic devices. In this work we examined the effect of key processing variables such as substrate temperature (150-300°C), O3 concentration ([03], 4-77 g m−3), O3/oxygen flow rate (0.5-3.5 L min−1), and UV (185 and 254 nm) irradiation on the etch rate of positive photoresist on silicon wafers.

The photoresist etch rate increased up to 28-fold over the substrate temperature range of 150-300°C at constant inlet [O3], flow rate and UV irradiation. At constant substrate temperature and reactant flow rate, the etch rate increased an average of 2-fold with an average 5-fold increase in the inlet [O3]. The etch rate also increased at constant substrate temperature and inlet [O3] with increased reactant flow rate.

At 150° and 200°C, UV irradiation enhanced the etch rate of photoresist 2 and 4-fold, respectively, compared to etching experiments where UV irradiation was absent. This suggested that the primary etchant species at these temperatures was atomic oxygen created by photodissociation of O3. At 250° and 300°C, UV irradiation during etching did not significantly enhance the etch rate, which suggested that at these higher temperatures, the primary etchant species was atomic oxygen generated from the thermal dissociation of O3 near the wafer surface.

The modification of silicon surface due to reactive ion etching (RIE) using a CHF3/C2F6 plasma has been characterized using X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS), and high resolution transmission electron microscopy (HRTEM). A flat and uniform residue layer of about 40 angstrom in thickness has been observed in cross-sectional HRTEM work. The interface is sharply defined and smooth. Neither point defect cluster nor distinct planar defect has been found in substrate silicon lattice image. This is also confirmed by comparison scaled and energy shifted silicon surface peak of a control sample with the reactive ion etched sample using ion channeling RBS. NF3, C12, and SF6 plasma treatments have been carried out to remove the residue layer. Among them, NF3 treatment has been revealed to be the most effective. With 10 seconds exposure to NF3 plasma, fluorocarbon residue film decomposes, and the remaining fluorine mostly binds to silicon; the fluorine completely disappears after the subsequent wet cleaning.

A new wafer cleaning technique, Aerosol Jet Cleaning (AJC), using a supersonic liquid aerosol jet was studied. AJC has been used to remove effectively both particulate and thin film contaminants from silicon wafer surfaces. Submicron polystyrene latex spheres, micron sized spherical silica particles and irregular silicon dust were successfully removed from silicon substrates using a supersonic ultrafine liquid methanol aerosol jet. The cleaning efficacy of the methanol AJC for thin film contaminants such as fingerprints has also been shown to be very effective. Surface roughness of silicon substrates before and after clean-up by AJC was measured with an atomic force microscope and virtually no change in surface roughness was observed in these studies.

Control and elimination of contamination in semiconductor manufacturing (tools and wafers) will be an enabling technology for the manufacture of devices with groundrules < 0.5 μm. The current trend in semiconductor manufacturing is towards mini-environments and cluster tools integrating several processing steps including cleaning. Relevant contaminants are now sufficiently small that wet chemical cleaning processes are unable to wet them sufficiently to effect removal by mechanical means. Wet processes are also difficult to integrate into cluster tools. In this paper, we describe a new non-reactive, “dry”, gas-phase cleaning and surface modification process. This technology utilizes photons from a high energy irradiation source in conjunction with a flowing gas to break the bonds holding contaminants to the surface and carry the freed contaminants away from the surface. Removal rates of contaminants depend on the wavelength of the irradiation source, energy flux and flow rate of the gas, not a knowledge of the chemical properties of the contaminants.

Advances in semiconductor device designs are placing demanding requirements on the semiconductor tool sets used to fabricate devices in the cleanroom. The stripping of photoresists, particularly those used as implantation masks, represents a nagging problem for which very few new tools have evolved. This is so in spite of demands for cleaner, particulate and damage free tools from the semiconductor fabrication community.

Gas-phase ozone stripping represents one of the few new, potential solutions to this semiconductor industry-wide problem. We have used a single wafer ozone ashing system, an apparatus especially developed to remove photoresist from silicon wafers, to evaluate the potential of ozone stripping technology. With a direct sampling mass spectrometer, the composition of the asher's gaseous effluent stream was monitored in real-time during operation of the ozone asher. A series of surface sensitive techniques including optical microscopy, AFM, and TXRF, were applied in order to obtain detailed information on the topography and composition of the wafer surface following ashing.

A basic understanding of the gas-phase and surface chemistry involved in ozone ashing provides a data base from which both environmentally sound disposal issues and post ashing wet cleans can be designed.

An oxygen treatment in a high density plasma system is used to effectively remove the fluorocarbon polymer that deposits on the silicon substrate surface after an oxide etch process. Schottky current-voltage analysis, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy, are used to investigate the effectiveness of the in-situ O2 clean process. Polymeric material deposited in the high density plasma system is shown to be completely removed with no polymeric residue remaining on the wafer surface after cleaning. Deep contacts, greater than 2 um, are shown to have the polymer effectively removed with the in-situ O2 clean process. Minimal oxide growth during the plasma clean is observed. Also, there is no etching of the silicon substrate with the O2 clean process. A comparison is made to an ozone clean process that is known to effectively clean organic contaminants from silicon surfaces.

An oxygen treatment in a high density plasma system is used to effectively remove the fluorocarbon polymer that deposits on the silicon substrate surface after an oxide etch process. Schottky current-voltage analysis, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy, are used to investigate the effectiveness of the in-situ O2 clean process. Polymeric material deposited in the high density plasma system is shown to be completely removed with no polymeric residue remaining on the wafer surface after cleaning. Deep contacts, greater than 2 um, are shown to have the polymer effectively removed with the in-situ O2 clean process. Minimal oxide growth during the plasma clean is observed. Also, there is no etching of the silicon substrate with the O2 clean process. A comparison is made to an ozone clean process that is known to effectively clean organic contaminants from silicon surfaces.

ECR hydrogen plasma has been studied for removal of the native oxide and for in situ surface cleaning of Si. The process induced changes on electrical properties were inspected with Schottky diode and MOS capacitor structures. Current-Voltage (I-V) measurement of the Schottky diodes showed only a moderate change (about a decade) of the reverse saturation current after the plasma exposure. The deep level majority carrier traps induced by the treatment were measured by Deep Level Transient Spectroscopy (DLTS), and were found to have activation energies of 0.40 eV in the n-type samples and 0.54 eV in the p-type samples. As the plasma exposure time increased, the defect concentration increased and a broad shoulder appeared on the low temperature side. The extent of hydrogen permeation into the silicon was inspected by Capacitance-Voltage (C-V) measurement. Bias-temperature stress measure-ments of the p-Si Schottky samples reveal redistribution of hydrogen. Polysilicon gate-oxidesilicon samples subject to the hydrogen plasma exposure exhibit negligible change of the interface state density and flatband voltage.

The removal of metals from the Si surface during aqueous cleaning is controlled by the thermodynamics of the metal ions dissolved in solution, the thermodynamics of the metal/Si surface complex, as well as the kinetics of the reactions taking place. In this paper we address one aspect of this problem: the thermodynamics of the metal/Si surface complex. We show that a number of cleaning effects can be explained by these considerations which involve the construction and application of metal/Si/oxygen ternary phase diagrams. Specifically, a class of metals with relatively unstable oxides, but stable silicides as shown by the phase diagrams are predicted to be difficult to remove from the Si surface; this prediction is born out by the available experimental data.

The effects of iron contamination on gate oxide characteristics are examined from an experimental and modeling perspective. Gate oxide integrity is measured for silicon wafers contaminated with 1010 to 1014cm−3 of iron. Thermal oxides of 8, 10,13 and 20nm are studied. Iron concentration in silicon is measured non-destructively using Surface Photovoltage (SPV) minority carrier lifetime analysis. The SPV analysis technique is described. Based on the experimental data, allowable threshold iron contamination levels for various gate oxide thicknesses are established. For 10nm oxides, iron concentration cannot exceed 8×1010cm−3 without severe degradation in oxide quality. The threshold contamination level for 20nm oxides is 200 times higher. Time dependent dielectric breakdown (TDDB) test results indicate detrimental reliability effects can occur at even lower contamination levels.

In this report we studied the single wafer spin cleaning system. We found that spin cleaning efficiency increases as the flux of chemical is increased, as the cleaning time was extended. From the metal removal test, we found that we can greatly reduce both cleaning time and chemical consumption at the same time as compare to batch process. Furthermore, we found that spin cleaning efficiency is dependant on a combination of the two parameters, chemical flux and cleaning time. We have optimized the proper nozzle position for complete coverage of the wafer surface by analyzing the fluid dynamics of the liquid on the wafer surface during spin treatment.

A wafer scrubber used in bipolar wafer front-end fabrication for particle removal showed visible evidence of deterioration. We describe the analytical work undertaken to identify the nature of the deterioration, its impact on the DI water quality exiting the nozzles and used for the high pressure scrubbing, and finally how these corrosion products manifest themselves as metal contaminants on wafer surfaces. A reasonable explanation for the long term deterioration of the tool is found in the fact that carbon dioxide has been used in the DI water at this scrub for nearly a decade. This of course acidifies the water and makes the stainless steel components more susceptible to corrosion. The scrubs are typically followed with wet chemical cleans using spray processors. The effectiveness of this clean in removing the metal contamination is incomplete. The removal of these scrubs from product log sheets has been a contributing factor in producing measurable yield improvements.