High chemical purity is essential for achieving satisfactory device yield in submicron CMOS processing. Reprocessing of liquid chemicals to maintain high purity can drastically reduce both environmental impact and cost of ownership (CoO) of wafer cleaning operations. We propose the use of a novel membrane Filter technology for control of contamination spikes and reduction of liquid chemical usage in pre‐gate HF cleaning. To ensure filter effectiveness, we have developed an in‐process sensor that monitors solution cleanliness by measuring the deposition rate of reducible ions on silicon. Metals are detected through their effect on the surface recombination of photoexcited carriers. This detection method allows quantification of copper and noble metal ions down to 108 atoms/cm2 levels. We have investigated the effect of chemical purity during HF cleaning on the gate oxide integrity (GOI) of 70–200 Å gate oxides. A significant increase in the low‐field breakdown is observed for HF‐last cleaning using chemicals containing more than 10 ppt Cu. We present the results of Cu spiking experiments to evaluate our ability to quantify contamination down to the stringent levels required for an industrial scale wet‐bench. We observe a linear correlation between metal deposition rate and Cu concentration in the 1–5 ppb range.

The HF/water treatment of silicon surfaces is among the most frequently applied steps in surface cleaning processes. It is utilized for clearing oxides from the silicon surface. Large amounts of ultrapure water are necessary to carry out this operation, both in the HF/water solution itself and the thorough rinse which must follow HF/water processes. Therefore, a gas‐phase alternative to this process would significantly reduce deionized (DI) water consumption. The focus of this paper is the anhydrous hydrofluoric acid (AHF)/alcoholic solvent process which has shown promise as an alternative to the aqueous HF process. In particular, the AHF/methanol process has been studied extensively. This paper presents a comparison between properties of silicon surfaces prepared through the dilute HF/water (dHF) process and those of surfaces prepared through AHF/alcoholic solvent processes.

The use of resistivity‐monitored dump‐rinse tanks in semiconductor wet processing allows the rinse process to be optimized, substantially reducing DI water consumption while minimizing the deleterious effects of water on bare silicon surfaces. Optimization experiments performed on the Metals wet clean hoods at ACT yielded optimum rinse cycles consisting of two or three dump cycles plus an overflow rinse to 10ΜΩ, with a calculated savings of about 40,000 gallons of DI water (about 40%) per year compared to previously accepted standards. Experiments indicate that the time required for rinsing is a competing function of the effectiveness of each dump cycle and the time required to physically perform the chosen number of dump cycles.

Perfluorocompounds (PFCs) are critical processing gases for a number of plasma-based IC processing steps, especially dry etching and in situ CVD chamber cleaning. The long atmospheric lifetimes and large infrared absorption cross sections for such gases (which include CF4, C2F6, C3F8, NF3, SF6, and CHF3) have raised concerns about the contributions of PFC emissions to possible global warming. Global regulatory policies on greenhouse gases are expected to include the PFCs, and the specific attention given to these gases in negotiations between the U.S. government and the semiconductor industry may expand internationally as well.

Several options exist for PFC emission control, including process optimization, chemical substitution, capture/recovery/recycle, and destructive abatement (including combustion, reactive adsorption, and plasma decomposition). An assessment of each option will be made in terms of both technical effectiveness (i.e., PFC reduction achievable) as well as implementation issues (e.g., commercialization timing, cost of ownership). PFC users can expect to have several commercial options to choose from to meet future PFC emission control requirements.

Complex analytical and toxicological studies of the waste products from aluminium plasma etching were performed over a four-year period. Many different organic compounds were identified and quantified in the waste gases, vacuum pump oils, and the solid debris collected from the air pipe systems. The identified compounds were exclusively perhalogenated hydrocarbons. Toxicological investigations showed clear genotoxic, embryotoxic, and teratogenic effects resulting from the waste products.

The study left no doubt, that workers in semiconductor production processes are potentially in danger of coming in contact with small amounts of plasma by-products, either through accidents, maintenance procedures, or insufficient protection.

A critical class of semiconductor manufacturing compounds is the family of perfluorocompounds, or PFCs. Originally thought to be environmentally benign compounds, they are likely long-lived atmospheric compounds with high global warming potentials. This paper reviews the options available to industry to reduce PFC emissions. Process optimization, chemical substitution, abatement, and recovery will be discussed as they relate to specific processes. Each will be reviewed with respect to the particular gas affected and the potential impact realized. Collateral environmental impacts will also be discussed. Finally, the voluntary EPA program, the PFC Emission Reduction Partnership for the Semiconductor Industry, will be presented.

A successful method for abating PFC (perfluorinated compounds) emissions from semiconductor manufacture is presented. The method involves use of a novel thermal technique combining an inwardly fired burner with a built-in wet scrubber for removal of combustion products. The Edwards High Vacuum Thermal Processor Unit (TPU) is a Point of Use abatement device designed to destroy PFC and process gases.

The performance of pressure swing adsorption (PSA) technology was assessed for recovering PFCs from the exhaust of a semiconductor plasma process. Several PSA process conditions were run to determine an optimized system. Under well defined conditions, the PSA technique was found to be effective at separating C2F6 from nitrogen, although the balance between recovery and product purity was evident. The exhaust of a plasma chamber was analysed by mass spectrometers and plasma etching conditions were varied to determine the effects on the PSA performance. A gas reactor column (GRC) was tested as pre‐treatment of the capturing system

Many semiconductor processes, Organometallic Vapor Phase Epitaxy (OMVPE) in this case, require the use of concentrated hydride sources. The toxicity of many of these compounds (e.g. arsine, diborane) and the pyrophoric nature of others (phosphine and silane) demand that the facility provide both environmental protection and a safe work place. A facility is described which meets stringent environmental emission standards from NY State's Department of Environmental Conservation. The outlined approach also sets new standards for hydride storage and containment, laboratory alarm systems, exhaust gas treatment and dilution, and process integration into the facility. Under normal operation, we demonstrate hydride emissions of less than 10−5 ppb at the exhaust stack.

Presently, the semiconductor industry relies almost exclusively on perfluorocompounds (e.g., tetrafluoromethane, hexafluoroethane, nitrogen trifluoride. sulfur hexafluoride, and. more recently, octafluoropropane) for the etching of silicon dioxide and silicon nitride films in wafer patterning and PECVD (plasma enhanced chemical vapor deposition) chamber cleaning applications. The use of perfluorocompounds (PFCs) by the industry is considered problematic because of the high global warming potentials (GWPs) associated with these substances. Potential replacements for perfluorocompounds are presently being evaluated at MIT. In an initial stage of the study, intended to screen potential candidates on the basis of etch performance, a large number of compounds is being tested in a commercially available magnetically enhanced reactive ion etch tool. The potential alternatives discussed in this work are trifluoroacetic anhydride (TFAA) and three members of the iodofluorocarbon (IFC) family – iodotrifluoromethane, iodopentafluorocthane, and 2-iodoheptafluoropropane. This paper will present the results of etch rate comparisons between TFAA and octafluoropropane, a perfluorinated dielectric etchant. Designed experiment (DOE) methodology, combined with neural network software, was used to study a broad parameter space of reactor conditions. The effects of pressure, magnetic field, and gas flow rates were studied. Additionally, more limited tests were carried out with the three iodofluorocarbon gases. Etch rate data, as well as Auger electron spectroscopy data from substrates exposed to IFC plasmas will be presented. All gases were evaluated using both silicon dioxide as well as silicon nitride substrates. Results indicate that these compounds may be potentially viable in plasma etching applications.

The technology development needed to support the continuous improvement of Environment, Safety, and Health (ESH) characteristics of semiconductor manufacturing facilities is changing as strategies for source reduction and incident prevention and more refined schemes for assessing ESH improvement emerge. This paper summarizes the changes taking place in ESH management structure and focuses on examples of current technology development to satisfy the new model of ESH execution.

We had proposed parallel downflow rinse which was capable of draining out chemical carried over to rinsing bath together with wafer about twice as fast as overflow rinse. In an attempt to further improve rinsing efficiency of PDR, we have investigated (1) the effect of wafer carrier shape, and (2) removal of boundary layer on wafer surface. Boat‐type wafer holder is preferable to conventional cassette. Three stirring techniques adequate for PDR, namely, megasonic irradiation. N2 bubbling, liquid level shifting, are found effective to remove chemical ion remaining boundary layer in measuring conductivity and resistivity.

Chemical‐Mechanical Polishing (CMP) is one of the fastest growing market segments in the semiconductor equipment industry. One of the critical consumable in CMP is a specialized solution, or slurry, which contains both free abrasives and chemicals acting together to planarize a wafer. These chemically active slurries account for approximately one fifth of the total cost of polishing a wafer. Because of the cost and potential toxicity, there are both financial and environmental pressures to reduce the amount of slurry consumed during the CMP process. To accomplish this in a systematic manner we have developed a technique for quantifying slurry flow patterns during CMP which involves using fluorescent dyes to measure slurry mixing, temperature gradients and slurry aging during the polishing. An aqueous fluorescent solution with matching viscosity is used to model the slurry, a glass window models the wafer and a commercially available polisher provides the polishing pad/table rotating work surface. This talk will focus on the diagnostic technique used to measure the slurry behavior as well as some semi‐quantitative results on both the amount and uniformity of slurry entrained beneath the wafer as a function of pad topography, injection location and pad rotation rates.

The growth of particulates within a PECVD (Plasma Enhanced Chemical Vapor Deposition) reactor has been extensively studied in recent years. As one of the early concerns was wafer particle contamination, the attention of industry also shifted to environmental issues. In the particular case of Si3N4 film deposition, the amount of dust particles created within the plasma is great and a significant amount of dust is dragged out of the RF interelectrode region along with the exhausted process gases. On a production system, this results in solid residues accumulation in the exhaust line (or foreline), frequent maintenance and poor vacuum pump lifetime. We developed a DPA (Downstream Plasma Apparatus) placed downstream of the deposition chamber to solve the issue of solid waste treatment for thin films applications such as SiO2, Si3N4, SiC, SiOxNy,…, α‐Si,…). The DPA is designed to capture all the residue during deposition, using both a passive and an active mode. It consists of two labyrinth‐shaped electrodes that can trap particles by gravitation (passive) and electrostatically (active) by application of a DC electric field. The second function of the device is to vaporize the previously trapped residues using a periodic plasma assisted clean. The vaporization process is performed by re‐ionizing the effluent PFCs gas (PerFluoro‐Coumpounds) from the processing chamber. All byproducts of the reaction are gaseous and water soluble. This results in the elimination of solid waste as well as improving vacuum pump lifetime. There is also better clean gas utilization and the emission of PFCs in the atmosphere is reduced. In this paper, we review the particulate formation, their size and composition. We describe the DPA reactor designed to trap charged particulates with closed to 100% efficiency. We examine the plasma‐assisted cleaning process and the implications of the device in terms of solid waste treatment and environmental impact.

The level of arsenic from the effluent of a crystal grower was measured at different phases of the silicon crystal growth operation which includes arsenic doping, crystal body growth, burn‐in, and post burn‐in periods. Measurement of arsenic levels were made in the discharge water used as the sealing liquid for the liquid ring vacuum pump used for process effluent discharge. Gas phase measurements were also performed for both particulate arsenic as As2O3 as well as for compounds of arsenic in vapor phase as AsH3. Results of these analyses provided important information for developing strategy for emission treatment and control, reducing arsenic exposure to personnel and evaluating the feasibility for recycling argon used in the crystal growing process.

1,1,1‐Trichloroethane (TCA) has played a vital rôle in contemporary semiconductor fabrication as a source for chlorine during the oxidation of silicon substrates. However, TCA has been identified as an ozone depleting compound by the Montreal Protocol, and in the United States The Clean Air Act Amendments of 1990 severely restrict its use in many applications. This paper discusses oxalyl chloride (OC) and trans‐ 1,2‐dichloroethylene (DCE) as alternatives to TCA for silicon oxidation processes. Information on precursor vapor delivery, atmospheric chemistry, industrial hygiene, and combustion chemistry will be presented along with comparisons of metal decontamination efficiency and electrical properties (Qbd) for oxides grown in the presence of each precursor The suitability of OC for low temperature, ultra‐thin oxidation processes will also be addressed.

An environmental friendly, aqueous based, thin film technology is investigated that is quite versatile in forming a variety of polymer substrates. The polymer substrates are potentially capable of being utilized as high resolution resists for semiconductor chip production. This process is based on polymerization of monomers partitioned within a two dimensional surfactant template adsorbed on the surface of a silicon wafer. The surfactant template (bilayer) serves to localize the polymerization reaction at the liquid‐solid interface and thereby resulting in the coverage of the silicon wafer with a nano‐thin polymer film. On a polished silicon wafer with a 4 nm silicon oxide layer, film thickness up to 130 nm have been obtained for polystyrene and for poly(methyl methacrylate) (PMMA) which is also used as a standard photoresist mask in electron beam lithography.

The paper describes a novel chemical-microbiological method for the selective removal of cadmium, tellurium and silver from the thin film CdTe photovoltaic modules. The chemical component of the process utilizes dissolution of metals with nitric acid. The metal solution is subjected to selective biosorption of silver and cadmium by passing through biosorbent columns. The adsorbed cadmium and silver are desorbed and recovered by chemical precipitation. Tellurium in solution coming out of the biosorbent columns is converted microbiologically to its metallic form in a bioreactor. The combined chemical-microbiological treatment ensures recovery of silver, cadmium and tellurium with 86%, 80% and 99% efficiency, respectively. The treated waste can be discharged safely in the environment.

The reliance of the semiconductor industry on pyrophoric silane gas as the primary source of silicon entails high risk and attendant cost. In order to enhance safety and improve control we are engaged in a systematic study of the decomposition characteristics of alkyl silanes with a focus on chemical species and conditions that exhibit silane type behavior or that actually produce silane. We have prepared a series of air stable innocuous liquid alkyl silanes, RSiH3, that generate silane and stable organic (R-H) byproducts upon flow tube pyrolysis. T-buty1, t-hexy1, and t-decyl silane as well as the corresponding R-H products exhibit a range of physical properties : room temperature vapor pressures, for example, range from several Torr to over an atmosphere. Relevant physical properties as well as kinetics and mechanisms of the hydride transfer process will be described and correlated with structural characteristics of the RSiH3 precursors.