The Standard Clean 1 (SC-1), developed by W. Kern and D. Puotinen in 1965 and disclosed in 1970 [1], consists of a mixture of ammonium-hydroxide, hydrogen-peroxide, and water. (SC-1 is also called the Airfmonium-Hydroxide Peroxide Mixture or APM). Originally, this chemical mixture was developed for cleaning silicon wafers and it has proven to be the most efficient particle removing agent found to date. SC-1 can, however, also be used for etching. SC-1 will etch the following materials: SiO2, Si3N4, Si, Ti and TiN. On top of this, SC-1 will grow an oxide on several materials (i.e., bare silicon).

In this paper, a quantitative model for the SC-1 solution is presented. The etching of Ti and TiN is shown to be fundamentally different from the etching of SiO2. The mixture of Ammonium-hydroxide and Hydrogen Peroxide must be optimized differently for Ti and TiN etching than for the particle removal from Silicon wafers.

The use of poly-buffered LOCOS processing is a common feature of many sub-micron integrated circuit fabrication processes. However, the silicon layer interposed between the nitride oxidation mask and the pad oxide is often difficult to remove. Different strategies involve dry and/or wet etching of the film. We have demonstrated the utility of adding metals such as Fe or Cu to a conventional phosphoric bath used to etch silicon nitride. Briefly, the presence of the metals is thought to result in a classic oxidation-reduction reaction between the metal and the silicon. Additions of 60ppm of Cu+2 resulted in etch rates of 20Å /min. on undoped polysilicon at a process temperature of 165°C, whereas, the etch rate of SiO2 was less than 1Å/min. Similar results were obtained for additions of Fe+3 and other metals.

An improved method for quenching a Buffered Oxide Etch (BOE) process in a DI water overflow rinse tank is shown. Many different factors were investigated in several preliminary experiments. Most of these factors were thought to influence etch uniformity yet proved not to be significant. The transfer process from chemical to rinse was identified as contributing negatively to etch uniformity. A chemical carryover layer formed during the transfer process was identified as the most significant factor. The hydrodynamics of liquids are outlined to help explain how the carryover layer is formed and shaped. Several sensitivity analysis experiments show transfer speeds to significantly affect carryover layer thickness and uniformity. Slow transfer speeds are determined to produce consistent and improved uniformity. Results of a follow up experiment quantify the uniformity improvement.

In the this paper, we have examined the particulate removal efficiency of laser from solid surfaces. The silicon wafers were contaminated with alumina particles with sizes ranging from 0.05 μm to 0.5 μm. The silicon wafers with uniform surface-distribution of alumina particles were subjected to pulsed laser beams at varying conditions. The results obtained have shown that line beam lasers can remove submicron particles more efficiently from solid surfaces. The mechanism responsible for higher particulate removal-efficiency of line beam laser has also been discussed.

Si(100) surfaces were cleaned using HF/IPA vapor chemistries at ambient pressure and temperature with nitrogen as the carrier gas. Three distinct cases for oxide removal were studied: vapor etching of native oxides, RCA chemical oxides, and thermal oxides. Atomic Force Microscopy (AFM) was used to characterize the surface morphology after the HF vapor etching process. The AFM indicated exaggerated peaks in random places on the surface, These peaks were identified as residue remaining after the vapor etching process. The average lateral width of the peaks were ∼ 50 nm. The average height of the peaks for native and chemical oxide etched surfaces was relatively the same, approximately 8 nm. The average height of the peaks after thermal oxide removal was significantly smaller, approximately 1–2 nm. Peak density for native oxide etched surfaces was significantly greater than chemical or thermal oxide etched surfaces. We suggest that impurities in the oxide contribute to residue formation on the surface.

Ni removal from Si wafers by low-pressure UV/Cl2 chemical vapor cleaning (CVC) was investigated at substrate temperatures of 150–200°C. Sub-monolayer Ni coverages were applied to Si(100) by ultrahigh-vacuum physical vapor deposition (UHV-PVD). The Ni surface concentration was reduced to the Auger electron spectroscopy (AES) detection limit by a 2-min UV/Cl2 exposure at 300 mTorr and 200°C. AES depth profiling revealed that Ni was not contained within nor buried beneath the chlorosilyl layer formed by UV/Cl2 CVC. In contrast, Ni was not removed under similar conditions from Si surfaces covered by a thin UV/air oxide layer. These results indicate that Ni removal from Si occurs by a photochemical etching mechanism and not by direct volatilization of NiCl2. Atomic force microscopy (AFM) of Si surfaces after UV/Cl2 CVC indicated that Si etching was limited ˜20 å and that the surface was smooth (RMS roughness = 1.6 å).

We have investigated a novel surface cleaning technique of native oxide on Si wafer, in which carbon-related contaminants are removed effectively at room temperature with a pure ozone beam from an ozone jet generator that we developed. Although ozone alone was likely to be little reactive to saturated carbons and byproducts in the reaction of ozone with unsaturated carbons which could be assigned to either carbonyl- or carboxyl-related compounds, a high-dose pure ozone under ultraviolet light irradiation to generate atomic oxygen by the photo-dissociation of ozone removed most of them at room temperature. The effectiveness of the ozone cleaning was also demonstrated for selected oxide surfaces.

To reduce the consumption of chemicals and ultra pure water (UPW) in cleaning processes used in device manufacturing, we have developed wet processes that use electrolytic ionized water (EIW), which is generated by the electrolysis of a diluted electrolyte solution or UPW. EIW can be controlled for wide ranges of pH and oxidation-reduction potential. Anode EIW with diluted electrolyte, which has high oxidation potential, can remove metallic contamination such as Cu and Fe on Si surfaces. EIW contains less than 1/100 of the amount of chemicals contained in conventional cleaning solutions, thus drastically reduces chemical consumption in wet processes. Moreover, electrolyzed UPW can be used as a substitute for conventional UPW to achieve better rinsing characteristics. Electrolyzed UPW reduces the level of residual SO42− ions after SPM cleaning more efficiently than conventional UPW. Thus the amount of rinse water needed is reduce to 1/6 that of the conventional UPW rinse.

We also developed a method for analyzing remaining metallic contamination and residual ions in deep-submicron-diameter holes with high aspect ratios. The method is based on conventional atomic absorption spectrometry (AAS), and uses device patterns with high density contact holes. With this method, metallic (Fe) contamination on the order of 1010 atoms/cm2 can be easily analyzed inside 0.1 μm-diameter holes with an aspect ratio of 10. The residual ions in the fine holes can also be detected by thermal desorption spectroscopy (TDS).

The purpose of this paper is to explore the formation of water residues on wafers during drying. To investigate this DI water droplets were intentionally placed on the surface of substrates with various wettabilities and then left to dry in both N2 and O2 atmospheres. It was found that both hydrophobic and hydrophilic surfaces created the water mark in N2 and O2. The size and dry time of residues were dependent on the wettability of surfaces. Auger analysis of residues showed that the oxidation of surface in water might be one of causes of water mark formation. Considering the pore size of final filters in DI water generation is 0.05 μn, a large number of particles less than 0.05 μm ay be in DI water. In order to investigate the effect of small particles less than 0.05 μm on water mark formation, PSL particles less than 0.05 μm were added to DI water. DI water containing particles was left to dry as a function of particle concentrations. The size of water marks was dependent on the concentration of particles in DI water after they reached a critical concentration.

Recent studies have shown that extremely dilute HCl mixtures can offer considerable cost savings and improved particle performance relative to traditional SC2 formulations. This work indicates, however, that extreme levels of dilution are not necessary to secure many of the benefits suggested for dilute HCI. Significant benefit can be attained by pursuing moderate concentration and temperature alterations. In this study, an intermediate dilution and temperature reduction are evaluated to assess potential production advantage. Comparison of a 1:1:20 formulation at 60 C is made to a more traditional 1:1:6 mixture at 85 C. The impact of the chemistry and temperature alteration on peroxide decomposition rate is shown to be dramatic. While initial pour-up ratios suggest that the dilute recipe could require 1/3 as much peroxide as the traditional chemistry, chemical savings are significantly more dramatic due to the ability of the solution to maintain concentration over time. An additional benefit associated with the alternative pour-up is a marked reduction in particle levels on silicon surfaces; particle levels on thermal oxide wafers have not shown the same trend. VPD-ICPMS measurements are used in this study to illustrate that the recipe change results in comparable metallic removal efficiency.

This work is an effort to determine if we can use less water effectively in rinse processes. We have run experiments to examine our current usage and to determine if we can use water more effectively.

This work will describe the experiments which have been done relating the amount of chemical remaining on the wafers to variables of the: rinse such as flow rate, wafer spacing and the cycling of the rinse valves. We will discuss the conclusions we have reached based on those experiments and the directions we will be taking to improve rinsing efficiency.

We evaluated the rate limiting steps in a post sulfuric acid/hydrogen peroxide mix dump rinsing process. The parameters we examined include, the pull-out velocity from the chemical bath, the draining during transport into the rinse tank, immersion into the rinse tank, dumping, draining after a dump cycle and flow rate during fills between dumps. Based on our investigations an optimized dump rinsing process was developed using programmed flow rates and dumping cycles. The quality of the optimized rinsing process was determined by measuring sulfur residue and light point defects on wafer surfaces that had undergone the optimized rinsing process. This optimized process requires 5 minutes and 75 liters of water, replacing a process that initially ran for up to 16 minutes and consumed 600 liters of water. Our optimized rinsing process, resulted in a factor of five saving in water consumption and two in cycle lifetime with no statistical degradation in surface quality.