We have already proposed chemical vapor free and room temperature wet cleaning (UCT cleaning) for Si substrate surface, instead of conventional RCA cleaning, which consumes very little amount of chemicals and ultrapure water compared to that of RCA cleaning. This new wet cleaning has been developed by scientifically understanding contaminants removal mechanism as follows;

(1) Particles can be removed by simultaneously satisfying following two conditions,

(a) particles and substructure surface must have same polarity of zeta potential in the cleaning solution to exhibit repulsive electric coulomb force with each other.

(b) adhered particles must be lifted off from substrate surface by slight etching to make electric repulsive force greater than van der Waals force,

(2) Redox potential of the cleaning solution must be larger than a critical value to enable removal of electrons from adhered metals in order to dissolve them into the cleaning solution as positive ions and to decompose adhered organic molecules to CO2, H2O etc.

Megasonic irradiation is very essential in UCT cleaning, particularly to remove particles by lifting them off from substrate surface. In this study, chemical reaction in the cleaning solution induced by megasonic irradiation is mainly discussed. Irradiation of ultrasonic having frequencies higher than a few hundred KHz (Megasonic) to ultrapure water has been confirmed to be able to decompose H2O molecules to H radicals and OH radicals. Decomposition efficiency of H20 molecules is strongly dependent on remaining gas components and their volume in the ultrapure water. When the remaining gas volume is decreased to less than 0.2 ∼0.3ppm, H2O molecules decomposition to H radicals and OH radicals has not been observed. Generated OH radicals have been confirmed to produce H2O2, and NH4+, NO2−, NO3− ions by reacting. with remaining N2 gas. Thus the cleaning capability of the cleaning solutions can be controlled by irradiating megasonic.

In this study, critical hardware and process parameters are evaluated for their effect on performance in megasonic cleaning applications. Experimental data is presented which shows the impact of transducer design, bath temperature, process time, SC1 chemistry, and wafer gap spacing on particle removal and surface roughness. The ability to remove particles smaller than 0.1 um in size is also demonstrated.

This paper demonstrates the use of megasonic energy to enhance particulate removal in dilute SC1 solutions. Ideal, as well as “real world”, particles were deposited on silicon wafers to challenge the SCl/megasonic particle removal system. Different dilute SCI concentrations were used, e.g., 1:4:20, 1:10:120, and 1:1:100. Bath temperature was varied between 50 and 70°C with megasonic energy kept constant at 800 W. Results showed that the megasonic energy enhanced the particle removal even in dilute solutions. The chemical concentrations were shown to be a significant factor and must be monitored or controlled in dilute SC1 solutions for particle removal to take place. A lower cost of ownership can be obtained from these techniques as a result of using dilute chemicals and extending current bath lives.

Controlling particle contamination in wafer cleaning is important to reduce defect density and improve device performance and yield. In this study, a screening experiment was employed to evaluate particle removal efficiency among different cleanings, including FSI BCLN, bench rinse and dry only, bench SC1/megasonic only, bench RCA cleaning, and bench RCA-based cleaning. To optimize particle removal efficiency in RCA-based cleaning, a design of experiment (DOE) has been done to investigate the impact of SC1/megasonic cleaning on Si3N4 particle removal efficiency. Bath temperature, megasonic power, and solution chemistry of SCI bath were evaluated. The removal efficiency in relations to particle sizes was also investigated

NH4OH/H2O2/H2O (called APM or SC–1) cleaning combined with megasonic irradiation is found to feature outstanding removal efficiency for various types of particulate contaminant. The conventional APM cleaning, however, allows metallic impurity in solution to adhere onto substrate surface, and it must be followed by acid cleaning such as HCI/IH2O2/H2O (called HPM or SC–2) cleaning to remove metallic impurity from substrate. The advanced APM cleaning using MC–1 which is alkali cleaning agent containing chelating agent has been developed, and this new cleaning is found capable for preventing various metallic impurities including Al in solution from contaminating substrate surface. Besides, with cleaning conditions optimized, the advanced APM cleaning using MC–1 can also remove metallic impurity from substrate surface. In short, this modified APM cleaning is capable for removing particle and metallic impurity at the same time, which is not possible with the conventional cleaning technology. The cleaning process of semiconductor manufacturing process can be simplified if HPM cleaning is eliminated by introducing the advanced APM cleaning using MC–1. This leads to drastic reduction of cleaning cost and improvement of throughput of the cleaning process.

The RCA Standard Clean, developed by W. Kern and D. Puotinen in 1965 and disclosed in 1970 [1] is extremely effective at removing contamination from silicon surfaces and is the defacto industry standard.[2]. The RCA clean consists of two sequential steps: the Standard Clean 1 (SC-1) followed by the Standard Clean 2 (SC-2). The SC-1 solution, consisting of a mixture of ammonium-hydroxide, hydrogen-peroxide, and water, is the most efficient particle removing agent found to date. This mixture is also referred to as the Ammonium- Hydroxide/Hydrogen-Peroxide Mixture (APM). In the past, SC-1 solutions had the tendency to deposit metals on the surface of the wafers, and consequently treatment with the SC-2 mixture was necessary to remove metals. Ultra-clean chemicals minimize the need for SC-2 processing. SC-I solutions facilitate particle removal by etching the wafer underneath the particles; thereby loosening the particles, so that mechanical forces can readily remove the particles from the wafer surface. The ammonium hydroxide in the solution steadily etches silicon dioxide at the boundary between the oxide and the aqueous solution (i.e., the wafer surface). The hydrogen peroxide in SC-I serves to protect the surface from attack by OH" by re-growing a protective oxide directly on the silicon surface (i.e., at the silicon/oxide interface). If sufficient hydrogen peroxide is not present in the solution, the silicon will be aniostropically etched and surface roughening will quickly occur. On the other hand, hydrogen peroxide readily dissociates and forms water and oxygen. If the concentration of the resulting oxygen is too high, bubbles will appear in the solution. The gas liquid interfaces that result from the bubble formation act as a “getter” for particles that can re-deposit on the wafer surface if a bubble comes in contact with the wafer.

The adsorption-desorption of various cations at the silica-water interface is discussed in terms of electrical double layer and surface complexation models. Some experimentally determined surface equilibria constants from the literature are tabulated for Fe, Cu, and Mg. The adsorption phenomena of those cations onto silica gel is described using the stability calculation (STABCAL) computer program based on the suggested models.

A chemical oxide (silica) is grown on the silicon surface during the SC1 and/or SC2 processes. Adsorption of Fe, Cu, and Mg onto this chemical oxide is studied as a function of pH and compared to the modeling results. In general, there is a qualitative correlation between the experimental and modeling data, which can be used as a basis to develop a quantitative model for cation adsorption-desorption on the wafer surface.

It is found that Fe in a ppb level Fe-spiked SC1 solution precipitates in-homogenous. The local high iron concentrations are difficult to rinse, create micro-roughness, and induce weak spots in capacitors. With AFM it has been shown that rings of 3–8 μm are etched in the silicon and that the etch products (silicates) are deposited on one side just outside the ring. The capacitor yield loss induced by this SC1 treatment can not be recovered fully by a subsequent SC2 or dHCL step, while a dHF/dHCl does fully recover the yield and removes the iron and silicate rim.

The UV-excited chlorine radical treatment effectively removed trace metal contaminants from Si ans SiO2 surfaces. We have found that this is predomonantly attributed to reactions between metal and chlorine, and metal oxides and silicon chloride, respectively. The former process was subjected to identify a breakdown spot on a thin gate dielectric film. After dielectric breakdown, a silicon crystallized filament as small as a few nanometers in diameter was formed and was selectively etched with chlorine radicals revealing a successively-etched region of the Si substrate. Nonuniformities of native exides on silicon were also detected using the same method. Gettering and etching wi:h a poly Si layer showed a possibility to make a gate dielectric film damage free and contamination free. Densification of native oxides formed after conventional wet cleaning of silicon was made with UV-excited oxygen radicals. Electrical characteristics of gate dielectrics treated with UV-excited chlorine and oxygen radicals showed high reliability.

Metal contamination level will be decreased in order to maintain a device reliability according to device size reduction. Metal contamination from various processes are surveyed. The influence of metal contamination for 7–15nm thick gate oxides is discussed in order to clarify the critical concentration to gate oxides. NIG(Non Intrinsic Gettering) substrates are used in a worst case for gettering. Fe contamination with 4×1010 cm−2 strongly affects the TDDM characteristics, although there is no serious influence in the breakdown voltage even at the concentration of 5×1011 cm−2. The same tendency is observed for Cu contaminant and the critical concentration for TDDB characteristics is around 3×1011 cm−2. High energy B implantation is carried out to form gettering sites near device region. Breakdown voltage and TDDB characteristics are almost the same as epitaxial substrates at Fe concentration up to l×1012 Cm−2. Detailed examination such as SIMS, C-t and DLTS measurements is also supported the effectiveness in high energy gettering.

The present study reviews the use of Cl in gate oxidation furnaces for growth of high quality gate oxides with a thickness in the range of 2 to 15 1nm. The following, commercially available, “state of the art” Cl-precursors have been tested: 1,1,1- trichloroethane (TCA), trans-1,2-dichloroethylene (DCE) and oxalyl chloride (OC). Different parameters were evaluated including: metal removal efficiency, poly-silicon haze, Fe bulk incorporation, carrier lifetime and Cl-incorporation in the oxide. Cl2 was identified as the active component in Cl-oxidation. As a consequence, OC was identified as being the most efficient Cl-source. In particular, OC is the most suited Cl-source for applications requiring reduced oxygen concentration, such as the manufacturing of ultra thin gate oxides.

Organic adsorbates on silicon wafer surfaces exposed to superclean room air were measured to evaluate organic contamination level of silicon wafers stored in a clean bench up to 180min. Such Si wafers were thermally oxidized and the dielectric degradation behavior were systematically investigated. It is found that a carbon contamination level of half a monolayer influences the charge to quasi-breakdown although the degradation mechanism itself remains unchanged.

This paper addresses an important process issue in tie integration of chemical mechanical polishing (CMP) with interlayer dielectric (ILD) deposition for advanced back end processing. Gap fill between metal lines is achieved by using a dep-etch-dep technique for the tetraethylorthosilicate (TEOS) ILD deposition. The ILD layer is then planarized by CMP. Vias are etched through the ILD and filled with tungsten plugs in a blanket tungsten deposition and tungsten CMP sequence. Delamination has been observed at the interface between the TEOS layers following the blanket tungsten deposition and before or during tungsten CMP. The weak interface between the TEOS layers was found to be the result of residual carbon and fluorine from the tetraflouromethane (CF4) doped etch process. The interface between the TEOS layers was examined using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Experiments were carried out to determine if the residue and subsequent delamination could be eliminated by modifying the dep-etch-dep process. An improved process was identified and has been implemented on a 0.5μm CMOS and mixed-mode BiCMOS production line with no subsequent occurrence of interfacial delamination.

The use of malonic acid as an additive in alumina slurries used for the chemical mechanical polishing ( CMP ) of tungsten has been explored for the reduction of particulate contamination. The principal objective of this work was to delineate conditions under which alumina contamination on polished surfaces could be reduced.

The interaction between malonic acid and alumina particles has been investigated through electrokinetic and adsorption measurements. At suitable malonic acid concentrations and pH values, tungsten and alumina surfaces develop a negative zeta potential resulting in conditions conducive to reduced particulate contamination. Small scale polishing experiments have been carried out to relate electrokinetic results to the level of particulate contamination after polishing.

Etching behaviors of various Al alloy thin films in H2O2-based acidic etchants are investigated in this study. The pH and H2O2 content in the etchant are varied in order to simulate the case where Al thin films are subject to chemical-mechanical polishing (CMP) using slurries of different compositions. Corrosion current and thickness of the native oxide on pure-Al, AI-1%Si, Al-0.5%Cu, AI-1%Si-0.5%Cu, and AI-1%Cu thin films are determined from Tafel and ESCA analyses respectively. Comparisons between etch rate and CMP polish rate data suggest that Al-CMP removal process depends strongly on the chemical reactions by the oxidizer (slurry). Mechanical abrasion by the abrasive particles plays only an auxiliary role during Al CMP. In addition, alloy composition (% Si and % Cu) influence both etching and polishing behaviors to a great extent. The underlying mechanisms for etching and polishing are discussed.

Surface planarization of BK7 glass gratings with periods of 130, 30, 16, 8 and 5 gm was performed with the magnetorheological finishing (MRF) process at the Center for Optics Manufacturing (COM). Approximately 0.5 μm of material was removed in the experiments. Grating height decreased as a function of grating period, going from ∼0.44 μm to ∼0.044 μm for a 130 μm period, and ∼0.44 μm to ∼30 Å for grating periods of 30, 16, 8 and 5 gm. The microroughness on ridges and in valleys of the grating structures also decreased with material removal from ∼100 Å to ∼10 Å for gratings with 30 and 16 μm periods.

Double-sided brush scrubbing has become a dominant method for post-CMP cleaning applications. Chemicals delivered in-situ with brush scrubbing greatly enhance the cleaning capabilities. In this paper, the effect of dilute HF on reducing particulate defects and trace metal contamination on polished oxide surface is studied using a HF-compatible double-sided scrubber. AFM data on the interaction of dilute HF with oxide / tungsten plug array after tungsten CMP is also presented. Scrubbing with dilute HF is shown to be highly effective is removing slurry agglomerates that strongly adhere to the post-CMP oxide film.

The applications of wet chemical cleaning at the ‘back-end’ of Integrated Circuit (IC) or Metal-Oxide Semiconductor (MOS) fabrication are reviewed from chemical, environmental and cost perspectives. The various classes of commercially available “solvents” and “cryogenic” cleans are reviewed from the perspective of process suitability, impact on device yield and waste management. Strategies for minimizing processing concerns, as well as alternatives to organic solvent based wet chemical processing will also be discussed. Bulk photoresist (PR) stripping, post metal definition-, and post window etch cleaning are used to illustrate the discussion.

The use of radiotracing as a diagnostic tool in understanding the mechanism for metallic contamination during solvent cleans is also discussed. Data suggesting how the chemistry and solvent composition affects alkali metal (for example, sodium) contamination of dielectric- and barrier films during IC processing will also be presented.

Corrosion control and passivation of post metal etch structures are critical for submicron applications and overall yield performance. This study focused on 0.6 micron metal line spaces and the development of a process utilizing an integrated metal etch, photoresist strip and passivation tool. Data collected to characterize the corrosion/passivation mechanism included: veil and photoresist strip chemistries, passivation steps, time delays, subsurface material versus veil formation and electrical and defectivity yield. A post metal etch process was tested and integrated into a manufacturing environment that has provided minimal line loss, complete removal of etch veils, robust corrosion control and substantial reduction of intermetal shorts.

Hydrogen and water vapor plasma downstream treatment with the downstream injection of NF3 removes native oxide from silicon surfaces. In contact hole cleaning, this dry processing is a promising alternative to HF wet treatment, which has a problem of expansion of hole diameter. We examined the etching characteristics of boron-phosphosilicate glass (B-PSG) films, as a typical oxide material for the side-walls of the contact holes and compared the etching depths of B-PSG and thermal oxide films. We found that the etching depths of B-PSG films fell to one third of those of thermal oxide films at lower treatment temperature. This result indicates that the expansion of contact hole diameters can be minimized.