Standardization etch rate

Although etch rate data for a particular polymer film yielded straight-line kinetic plots, the data from one film to another for any given polymer exhibited considerable scatter this is indicated by the large standard deviations in Tables I and II. Because of the scatter, the cause of which is under investigation, the etch rate data reported here have only semiquantitative significance. 

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. 

Figure 9. Dependence of silicon and silicon dioxide etch rates on the percentage of Hz in CF4-H2 plasmas, (seem is standard cubic centimeters per minute.) (Reproduced with permission from reference 118. Copyright 1979 The Electrochemical Society, Inc.)...

The dependence of the etching selectivity of X-8000K2 relative to PIQ (a polyimide type resin from Hitachi Chemical Co.,) on O2 RIE conditions was examined. RIE power, O2 pressure, flow rate and the distance between the electrodes were selected as the parameters to determine the RIE condition. For these parameters, values of 100 W, 10 m Torr, 10 SCCM and 6 cm were selected as a standard condition. The changes in the etching rates are shown in Figure 3a, in which one parameter is varied and the remaining three parameters are fixed. 

In alkaline solutions, silicon oxides etch at very slow rates which allows them to be used as masks during silicon etching in these solutions. For example, the etch rate of thermal oxide is about 0.2 A/s in 40% KOH at 85 and is less than 0.02 A/s in the standard SC-1 cleaning solution. Figure 4.8 shows that in KOH solutions the etch rate of thermal oxide increases with concentration reaching a peak value at about 35%. Figure 4.9 reveals that the etch rate in TMAH solution decreases with... 

FIGURE 4.37. Standardized (Fe/Vemax) etch rates versus ammonium fluoride concentration (wt %) for various silicon dioxide layers in 30 wt % NH4F and 6 wt % HF at 24 °C. After Proksehe et (Reproduced by permission of The Electrochemical Society, Inc.)... 

At certain areas of the wafer (where the thinnest film coincides with the fastest etch rate) all these effects will work together giving a total plug over etch of at least 150 nm. Since we also have to include loading effects (see back etch) we come close to what was allowed in the example above (that was 0.2 nm recess). (+/-10% thickness or etch rate spread means a standard deviation of about 3%.)... 

In this work, we provide dry-process plasma etch rate ratios versus a standard for an expanded list of novel vinyl polymeric resists and commerical photoresists. The novel vinyl resists have been synthesized as part of a larger resist development program aimed towards the development of improved x-ray and e-beam lithographic resists (6). 

Many of the above described features are quite different to published and our own data for polyimide. Polyimide (PI) has a linear absorption coefficient at 308 nm similar to the designed polymers (around 95,000 cm-1). The first pronounced differences between the ablation characteristics between PI and our polymers are the higher threshold of ablation (three times), lower etch rates, and an effective absorption coefficient which is similar to the linear absorption coefficient. A comparison of the ablation quality between a designed polymer (TP) and the standard polymer (PI) is shown in Fig. 74. 

The formation of cigar-like-shaped pores has been explained by two hypotheses (36) (a) further exposure by electrons generated in the secondary electron cascade caused by the impact of the high-energy particle and (b) an acceleration of the etching rate caused by the etching products, which are more concentrated inside the pores. It was shown that perfectly cylindrical pores could be obtained if a special PC film (PC+) is used instead of standard PC films (36). 

Figure 22. Series of mass spectra showing progression of the etching reaction of aluminum anions with oxygen. Note that magic number clusters corresponding to electron shell closings for 40 and 70 electrons (AI13 and AI23) appear as the terminal product species of reactions with oxygen at flow rates of (a) 0.0, (b) 7.5, and (c) 100.0 standard cubic centimeters per minute (seem). Taken with permission from ref. 92.

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