Initial resist thickness

Figure 3. Typical lithographic response or contrast plots for (a) positive resists and (b) negative resists in terms of the developed thickness normalized to initial resist thickness (p) as a function of log (dose).

As an example, with a lOOOmPa.s viscosity resist, a 13 bar pressure and an optimized initial resist thickness (final residual layer <20 nm), the mean free path (or fiowing distance) of a resist molecule was experimentally estimated to be about 1 mm [28]. This value is important for design of the mold, which has to exhibit homogeneous protrusion density (protrusion to cavity area ratio) on any 1 mm areas on its surface in order to favor a uniform residual layer. In this example, the resist redistribution area was quite small but, when using lower viscosity resists (qo < 50 mPa.s), this area should reach almost the stamp size in the case of small stamps. 

In Figure 1.4, some examples of imprinted resist layers, made by our group on an EVG 770 step-and-repeat system, are illustrated. With an optimized initial resist thickness and a known mold design, an excellent contrast between the feature height and the residual layer thickness can be obtained this is a very important point in the case of additional process steps. 

For Ca < 0.1 in Figure 7 the critical capillary pressure is also independent of the initial film thickness. In this case, the hydrodynamic resistance to fluid filling or draining is small enough that the film reaches the periodic steady state in less than half a pore length. Figure 7 confirms the trend observed by Khatib, Hirasaki and Falls that P falls with increasing flow rate (5). c... 

The value in units of incident dose per unit area for either a positive or negative resist system is of little value unless accompanied by a detailed description of the conditions under which it was measured. This description should include, at the minimum, the initial film thickness, the characteristics of the substrate, the temperature and time of the post- and pre-bake, the characteristics of the exposing radiation, and the developer composition, time and temperature. The structure, copolymer ratio, sequence distribution, molecular weight, and dispersity of polymers included in the formulation should also be provided. 

A variety of techniques have been used in the present work to establish the relative sensitivity of positive electron-beam resists made from copolymers of maleic anhydride (Table I). The term sensitivity is used rather loosely at times. In the most practical sense, sensitivity is a comparative measure of the speed with which an exposure can be made. Thus, the exposure conditions, film thickness, developing solvent and temperature may be involved. Most often, the contrast curve is invoked as a more-or-less objective measure of sensitivity. The dose needed to allow removal of exposed film without removing more than about 70% of the unexposed film can be a measure of sensitivity. The initial film thickness and the developing conditions still must be specified so that this measure is not, strictly speaking, an intrinsic property of the polymeric material. 

To determine the lithographic properties 2 copolymers of different composition (Table II) were prepared. The parameter Dg0> is defined as a dose to give a resist thickness after development,corresponding to a thickness 0.7 times the initial resist... 

Fig. 4 Computer simulation (Cell-Design ) of copper deposition on a resistive wafer. An axi-symetric cross-section through a 200 mm wafer is shown, with the wafer center on the left and the electrical contact on the right. Current density 35 mA/cm2. Five growth steps, 20 sec. each, are simulated. The darker region is proportional to the deposit thickness (for clarity, the vertical axis has been magnified). Copper kinetics (no additives) are assumed io = 1 mA/cm2 ac = 0.5 aA = 1.5 T = 25°C. Initial seed thickness is 1000A. Substrate resistivity is updated with deposit build-up. (Left) 0.24 M CuSC>4 + 1.8 M H2SO4. Deposit thickness range 1.08 - 1.52 p. (34% variation). (Right) 0.85 M CuSC>4. Deposit thickness range 1.28 - 1.41 p. (9.6% variation).

All of these factors are easily controlled in the design of such apparatus. Initial film thickness is controlled by hydrodynamic action of the blade, defined as that resulting from the balance of centrifugal force, water resistance, and a journal bearing type of lift. Rate of evaporation is controlled by the selection of the operating temperature difference across the heat transfer tube and the rate of film renewal is controlled by choice of output speed of the gear motor which drives the blade. 

However, numerical calculation shows that the solution approaches very rapidly to a solution with uniform film thickness. Thus, it can he concluded that a spin-coating process using a Newtonian resist solution produces a uniform film thickness regardless of the initial film thickness profile. ... 

The significance of the non-Newtonian characteristics of the resist solution is illustrated in Figure 3. It is apparent that the assumption of Newtonian behavior leads to a weaker dependence of film thickness on spin speed than is observed experimentally, and one which is independent of polymer concentration in the initial resist. The non-Newtonian model not only gives quantitative predictions of the film thickness, but also generates the correct dependence on spinner speed. The dependence on spinner speed is stronger for the higher concentration solutions. This is attributable to the more prominant non-Newtonian behavior of the resist at higher concentrations. 

In order to achieve satisfactory planar surfaces over wide trenches (>10 pm) on a wafer, a double resist coating method was employed. (Refer to Figure 3). The initial resist layer, after application, is exposed with an undersized block-off mask, and, with appropriate processing, will leave the resist only in the depressions of the wide area trenches. The resist thickness of this layer should be about equivalent to, or slightly more than, the depth of the depression - in the present case about 4-5 pm. The resist thickness is also dictated in part by the dimensional difference between the block-off mask size and the trench depression area. 

The thickness of the encapsulating layer has been taken from Tannenberger to be 0.2 fj,m. The resistance of the insulating layers were calculated from the recorded voltammograms obtained between 1.0 V and —1.0 V in the solution immediately after the thermal curing step and then at various intervals during continuous immersion in 0.1 M NaCl. The resistivity was calculated using the determined value of the insulator thickness. The initial resistivity was 1.2 X 10 ft cm and after the period of 10 days was decayed to 0.3 X 10 ft cm. 

The thickness of poly(oxyphenylene) layer on carbon fiber was estimated from the deposition curve of poly(oxyphenylene) on Pt-glass substrate shown in Fig.3 and from the SEM-photograph of the encapsulated carbon fiber shown in Fig.4. The initial resistivity for the poly(oxyphenylene) encapsulation was 4.5 X 10 ft cm and after the period of 9 days was decayed to 7.3 X 10 ft cm. 

As the resist film thickness shrinks, the interactions of photoresist polymers and substrates become increasingly important. Dissolution rates of photoresist polymers were found to change as the film thickness decreases. Figure 57.8 shows variation of the dissolution rates of poly(4-hydroxystyrene) and polyfnorbomene-methylene-hexafluoroisopropanol) as a functimi film thickness. The dissolution rates of both polymers increase with decreasing initial film thickness [41]. 

Gauge type Alloy composition, (%) Thickness and size of active element Insulation Insulation thickness Initial resistance, n... 

The initial resistivity value in the as-deformed state is about 5% higher than that of the recrystallized sample. This difference in initial resistivity is mainly due to dislocations produced by the cold rolling deformation of about 60% reduction in thickness. 

Pickling (acidic or alkaline) often weakens the resistance to pitting corrosion of aluminium. The dissolution of the initial, rather thick oxide layer that covers cathodic intermetallics of the AlgFe type favours the development of pitting corrosion [6]. 

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