Wafer surface

A.irbome Basic Chemical Contamination. A critical, and at-first pu22ling problem, was encountered during early manufacturing trials of CA resists. Sporadically, severely distorted resist profiles would be formed in positive-tone CA resists, displaying what seemed to be a cap on the upper surface of the resist image (Fig. 26). In severe cases this cap or T-top would appear as a kin or cmst over the entire wafer surface that prevented development of the pattern. The magnitude of the effect varied dramatically between laboratories and appeared to grow more severe as the time interval between exposure and post-exposure bake was increased. 

Fig. 38. Diagram comparing the optical characteristics of a standard binary chrome mask with a phase-shift mask. The changes in the electric fields introduced by the phase-shift elements result in a sharper light intensity profile at the wafer surface.

Figure 4 Direct TXRF (upper spectrum, recording time 3000 s) and VPD-TXRF (lower spectrum, recording time 300 s) on a silicon wafer surface. The sensitivity enhancement for Zn and Fe is two orders of magnitude. The measurements were made with a nonmonochromatized instrument.

Figure 3.17 depicts an ultra-shallow TOF SIMS depth profile of a 100-eV B-implant in Si, capped with 17.3 nm Si. The measurement was performed with 600-eV SF5-sputtering and with 02-flooding. The original wafer surface, into which the B was implanted, is indicated by the maxima of the alkali- and C-signals. Because of these contaminants, a minimum is observed in the °Si-signal. The dynamic range of the B-profile is more than 3.5 decades and the depth resolution is <0.5 nm. 

Tab. 3.1. NR-laser-SNMS Relative sensitivity factors S (Me, ESi) and detection limits DL for metals on Si wafer surfaces.

Vapor-phase decomposition and collection (Figs 4.16 to 4.18) is a standardized method of silicon wafer surface analysis [4.11]. The native oxide on wafer surfaces readily reacts with isothermally distilled HF vapor and forms small droplets on the hydrophobic wafer surface at room temperature [4.66]. These small droplets can be collected with a scanning droplet. The scanned, accumulated droplets finally contain all dissolved contamination in the scanning droplet. It must be dried on a concentrated spot (diameter approximately 150 pm) and measured against the blank droplet residue of the scanning solution [4.67-4.69]. VPD-TXRF has been carefully evaluated against standardized surface analytical methods. The user is advised to use reliable reference materials [4.70-4.72]. 

Fig. 4.16. Wafer surface preparation system WSPS Automated VPD system for wafers of diameter from 100 to 300 mm.

Fig. 8—TEM images of wafer surfaces undergoing different colli-sional conditions, (a) without particles, (b) with particles.

Figure 18 [28] shows the variation of the particle speed and the potential energy of the silicon wafer in the collision process. The dashed line means the speed of the particle in the vertical direction and the black one indicates the variation of potential energy of the silicon disk. When the particle penetrates into the wafer surface, its vertical speed becomes lower and lower. Once the particle reaches the deepest position, the speed of the particle becomes zero and the potential energy of the silicon wafer increases to the highest one, and... 

The hrst mechanism specihcally for tungsten CMP was proposed by Kaufman et al. [67]. They thought, first, chemical action dissolves W and forms a very thin passivating him which stops growth as soon as it reaches a thickness of one or a few moleculars later. Second, the him is removed locally by the mechanical action of abrasive particles, which contact with the protrude parts of the wafer surface, and then cause material loss. In recent years, most of the analysis and models for metal CMP are built based on the Kaufman model [68,69]. However, the model is not involved in microscopic structure analysis for the polished surface, but focuses on interpreting macroscopic phenomena happening during CMP [18]. 

Zhang and Busnaina [128] proposed an equation taking into account the normal stress and shear stress acting on the contact area between abrasive particles and wafer surfaces. 

In 1996, Liu et al. [129] analyzed the wear mechanism based on the rolling kinematics of abrasive particles between the pad and wafer. They summarized that the kinetics of polishing are (1) material removal rate is dependent on the real contact area between the slurry particle and the wafer surface. The real contact area is related to the applied pressure, the curvature, and Young s modulus of the slurry... 

Sundararajan et al. [131] in 1999 calculated the slurry film thickness and hydrodynamic pressure in CMP by solving the Re5molds equation. The abrasive particles undergo rotational and linear motion in the shear flow. This motion of the abrasive particles enhances the dissolution rate of the surface by facilitating the liquid phase convective mass transfer of the dissolved copper species away from the wafer surface. It is proposed that the enhancement in the polish rate is directly proportional to the product of abrasive concentration and the shear stress on the wafer surface. Hence, the ratio of the polish rate with abrasive to the polish rate without abrasive can be written as... 

In 1999, Luo and Domfeld [110] proposed that there are two typical contact modes in the CMP process, i.e., the hydro-dynamical contact mode and the solid-solid contact mode [110]. When the down pressure applied on the wafer surface is small and the relative velocity of the wafer is large, a thin fluid film with micro-scale thickness will be formed between the wafer and pad surface. The size of the abrasive particles is much smaller than the thickness of the slurry film, and therefore a lot of abrasive particles are inactive. Almost all material removals are due to three-body abrasion. When the down pressure applied on the wafer surface is large and the relative velocity of the wafer is small, the wafer and pad asperity contact each other and both two-body and three-body abrasion occurs, as is described as solid-solid contact mode in Fig. 44 [110]. In the two-body abrasion, the abrasive particles embedded in the pad asperities move to remove materials. Almost all effective material removals happen due to these abrasions. However, the abrasives not embedded in the pad are either inactive or act in three-body abrasion. Compared with the two-body abrasion happening in the wafer-pad contact area, the material removed by three-body abrasion is negligible. 

Luo and Domfeld [110] introduced a fitting parameter H , a d5mamical" hardness value of the wafer surface to show the chemical effect and mechanical effect on the interface in their model. It reflects the influences of chemicals on the mechanical material removal. It is found that the nonlinear down pressure dependence of material removal rate is related to a probability density function of the abrasive size and the elastic deformation of the pad. 

Graf, D., Schnegg, A., Schmolke, R. et al., Morphology and Chemical Composition of Polishing Silicon Wafer Surfaces, Electrochemical Society Proceedings, Vol. 96-22,2000, pp. 186-196. 

During this process, material is selectively removed from the wafer surface as defined by the patterned photoresist in order to define the structure of the previously deposited layer. The etching process is accomplished by exposing the wafer to a plasma, which both chemically reacts with the material to be removed and ph3rslcally ablates it. At the completion of etching, the remaining photoresist is cleared from the wafer. 

The results presented in this paper focus on a systematic investigation of secondary ion formation from polymeric films prepared from TEOS on hydrophilic silicon wafer surfaces. 

Silyl radicals diffuse toward the wafer surface where recombination reactions occur ... 

All standard cleaning processes for silicon wafers are performed in water-based solutions, with the exception of acetone or (isopropyl alcohol, IPA) treatments, which are mainly used to remove resist or other organic contaminants. The most common cleaning procedure for silicon wafers in electronic device manufacturing is the deionized (DI) water rinse. This and other common cleaning solutions for silicon, such as the SCI, the SC2 [Kel], the SPM [Ko7] and the HF dip do remove silicon from the wafer surface, but at very low rates. The etch rate of a cleaning solution is usually well below 1 nm min-1. 

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