Film dissolution

Fig. rV-26. Steady-state diffusion model for film dissolution. (From Ref. 293.)... 

C2.8.6(c). This increase occurs far below eitlier transpassive dissolution (oxide film dissolution due to tire fonnation of soluble higher oxidation states (e.g. Cr,0., ... 

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cycHzed mbber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenoHc stmcture renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxyHc acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubiHty is controUed by chemical and polarity differences rather than molecular size. 

Some metals and alloys have low rates of film dissolution (low /p) even in solutions of very low pH, e.g. chromium and its alloys, and titanium. In these cases the value of /p is quite low, and although it increases as the temperature increases, a maximum is reached when the solution boils. The maximum current is below and breakdown does not occur. However, in certain alloys, e.g. Cr-Fe alloys, the protective film may change in composition on increasing the anode potential to give oxides that are more soluble at low pH and are therefore more susceptible to temperature increases. This occurs in the presence of cathode reactants such as chromic acid which allow polarisation of the anode. 

For many metals and alloys the determination of /p is complex, and its magnitude is governed by many factors such as surface finish, rate of formation, alloying constituents, and the presence of those anions, such as halides, that promote localised breakdown. In many instances the attack on passive films by halide ions shows a temperature and concentration dependence similar to the effect of hydrogen ions, i.e. the rate of film dissolution increases with concentration in accordance with a Freundlich adsorption relationship... 

Tin anodes dissolve by etching corrosion in acid baths based on stannous salts, but in the alkaline stannate bath they undergo transpassive dissolution via an oxide film. In the latter the OH" ion is responsible for both film dissolution and for complexing the tin. Anodes must not be left idle because the film dissolves and thereafter corrosion produces the detrimental divalent stannite oxyanion. Anodes are introduced live at the start of deposition, and transpassive corrosion is established by observing the colour of the film... 

The breakdown and repair of a passive film prior to pitting dissolution creates a kind of nonequilibrium fluctuation all over the electrode surface, which results from the localized inequality of film dissolution and formation. Since this type of film is too thin for direct observation of the... 

Local breakdown of passive film results from a localized increase in the film dissolution rate at the anion adsorption sites that are attacked by chloride ions, as will be discussed later, in the same manner as substrate metal dissolution. Such acceleration of the dissolution rate was ascribed to the formation of metal chlorides24 or the local degeneration of film surface by the formation of surface electron levels.7... 

Film dissolution behavior Cross-link density gel nature chemical vs. physical. 

Despite the small amount of acid generated in these experiments, the film dissolution behavior following postbake is dramatically affected. Acid content exceeding 5 x 10 6 mmol per 2 inch wafer is sufficient to change the solubility characteristics of the resist such that exposed resist film is no longer soluble in nonpolar developer solvent. 

Acid diffusion. Acid catalyzed resist systems are particarly noteworthy for their high sensitivity toward radiation. However it has been suggested that the amplification effect observed with catalytic resist systems is achieved only at the expense of lost resolution. Some diffusion of catalyst is necessary to achieve sufficient loss of BOC groups in order to impart sufficient difference in polarity for discriminatory film dissolution. Yet unlimited acid diffusion would result in loss of resolution. 

The SPR s are much greater for systems where solvent permeation is accompanied by polymer film dissolution. Therefore, the determination of SCP in such systems would require a technique that is quicker and less cumbersome for repeated measurements. 

The interferometry trace shows the change in the optical thickness of the polymer film with respect to time. Both the completion of the polymer film dissolution and the DR can be determined. 

Figure 1. Flow Cell for Monitoring solvent Permeation and PMMA Film Dissolution Simultaneously. The cell is placed in the sample chamber of a fluorescence spectrometer. (Reproduced with permission from Ref. ll. Copyright 1988 Wiley Sons.)...

When the surface is completely covered by an oxide film, dissolution becomes independent of the geometric factors such as surface curvature and orientation, which are responsible for the formation and directional growth of pores. Fundamentally, unlike silicon, which does not have an atomic structure identical in different directions, anodic silicon oxides are amorphous in nature and thus have intrinsically identical structure in all orientations. Also, on the oxide covered surface the rate determining step is no longer electrochemical but the chemical dissolution of the oxide.1... 

In the active state, the dissolution of metals proceeds through the anodic transfer of metal ions across the compact electric double layer at the interface between the bare metal and the aqueous solution. In the passive state, the formation of a thin passive oxide film causes the interfadal structure to change from a simple metal/solution interface to a three-phase structure composed of the metal/fUm interface, a thin film layer, and the film/solution interface [Sato, 1976, 1990]. The rate of metal dissolution in the passive state, then, is controlled by the transfer rate of metal ions across the film/solution interface (the dissolution rate of a passive semiconductor oxide film) this rate is a function of the potential across the film/solution interface. Since the potential across the film/solution interface is constant in the stationary state of the passive oxide film (in the state of band edge level pinning), the rate of the film dissolution is independent of the electrode potential in the range of potential of the passive state. In the transpassive state, however, the potential across the film/solution interface becomes dependent on the electrode potential (in the state of Fermi level pinning), and the dissolution of the thin transpassive film depends on the electrode potential as described in Sec. 11.4.2. 

In the stationary state of anodic dissolution of metals in the passive and transpassive states, the anodic transfer of metallic ions metal ion dissolution) takes place across the film/solution interface, but the anodic transfer of o Q en ions across the Qm/solution interface is in the equilibrium state. In other words, the rate of film formation (the anodic transfer oS metal ions across the metal lm interface combined with anodic transfer of osygen ions across the film/solution interface) equals the rate of film dissolution (the anodic transfer of metal ions across the film/solution interface combined with cathodic transfer of oitygen ions across the film/solution interface). 

For metallic iron and nickel electrodes, the transpassive dissolution causes no change in the valence of metal ions during anodic transfer of metal ions across the film/solution interface (non-oxidative dissolution). However, there are some metals in which transpassive dissolution proceeds by an oxidative mode of film dissolution (Sefer to Sec. 9.2.). For example, in the case of chromium electrodes, on whidi the passive film is trivalent chromium oxide (CrgOj), the transpassive dissolution proceeds via soluble hexavalent chromate ions. This process can be... 

Figure 7.14 illustrates that in the initial stage of polarization of the pyrite electrode in xanthate solution at about 120 mV, the radius of high value capacitive reactance loop increases with the increase of the polarization potential and reaches the maximum at 320 mV, indicating that the oxidation of xanthate increases gradually and collector film on pyrite surface becomes thicker. It increases the conduction resistance and the growth of collector film is the controlled step resulting in pyrite surface hydrophobic. When the polarization potential increases from 320 mV to 400 mV, the capacitive reactance loop radius decreases, indicating the decrease of transferring conduction resistance as can be seen in Fig. 7.15. It belongs to the step of film dissolution. Capacitive reactance loop radius decreases obviously when the potential is larger than 400 mV, at where the collector film falls off and the anodic dissolution of pyrite occurs. The controlled step is the anodic dissolution of pyrite and the surface becomes...

UV-visible studies were done that showed that the switching times and stability toward multiple cycling was excellent for this material. In the context of the reports by Hammond discussed above, it is interesting that the oxidation process described in Equation 4.3 did not lead to film dissolution, since the net charge of the formula unit for CuPB in its oxidized form should (at least formally) be zero. This suggests that the... 

Analysis by Dissolution Curves. Most performance indicators require only an operational definition these concepts are explained by a film dissolution curve. Figure 2 shows a family of such curves, in which the individual curves correspond to resist behavior in developer solution after exposure to the indicated radiation dose level. Figure 2 is constructed for... 

Oxidations for varying times showed systematic variations in the U +/U + ratios that fell into three values stable for significant periods of time (Fig. 5). These ratios of U +/U + = 0.5, 1.0 and 2.0 are believed to correspond to the presence of U3O7 (U02 U02 U03), U205 (U02 U03), and U30g (U02-U03-U03), respectively. The surface film composition is controlled by various rates of surface dissolution, oxygen diffusion into the UO2 and precipitation. Film dissolution is believed to occur upon oxidation to UO3. Because no appreciable layer of UO3 was found on the surface, it is concluded that dissolution of UO3 occurs at a rate faster than solid-state oxidation. 

Fig. 4 shows a simple phase diagram for a metal (1) covered with a passivating oxide layer (2) contacting the electrolyte (3) with the reactions at the interfaces and the transfer processes across the film. This model is oversimplified. Most passive layers have a multilayer structure, but usually at least one of these partial layers has barrier character for the transfer of cations and anions. Three main reactions have to be distinguished. The corrosion in the passive state involves the transfer of cations from the metal to the oxide, across the oxide and to the electrolyte (reaction 1). It is a matter of a detailed kinetic investigation as to which part of this sequence of reactions is the rate-determining step. The transfer of O2 or OH- from the electrolyte to the film corresponds to film growth or film dissolution if it occurs in the opposite direction (reaction 2). These anions will combine with cations to new oxide at the metal/oxide and the oxide/electrolyte interface. Finally, one has to discuss electron transfer across the layer which is involved especially when cathodic redox processes have to occur to compensate the anodic metal dissolution and film formation (reaction 3). In addition, one has to discuss the formation of complexes of cations at the surface of the passive layer, which may increase their transfer into the electrolyte and thus the corrosion current density (reaction 4). The scheme of Fig. 4 explains the interaction of the partial electrode processes that are linked to each other by the elec-... 

A second possibility is that a linear corrosion rate could also be maintained by the finite dissolution rate of the film in the environment. For this situation, the rate of film thickening would eventually be counterbalanced by the rate of film dissolution, leading to both a constant film thickness and a constant corrosion... 

Figure 23 Various reaction scenarios for the passive corrosion of titanium alloys (A) linear oxide film growth due to film recrystallization (B) linear Him growth kinetics maintained by film dissolution.

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