Planarized metallization process

A variation of the selective Cu deposition process, limited to electroless Cu deposition, is the lift-ojfprocess, a planarized metallization process (16). Figure 19.5 shows a stepwise process sequence for this technology. 

Fig. 39 The process sequence for the lift-off process (the planarized metallization process) (a) a resist film is patterned on a dielectric film, (b) dielectric patterning, (c) thin catalytic film layer (PVD or CVD Ti, Al) is deposited, (d) a lift-off technique removes the excess material, leaving the catalytic layer in the trench only,...

A p-type HgCdTe layer 13 is formed on a CdTe insulating substrate 11. Trenches 15 are formed by an anisotropic planar etching process or by an ion-etch. P-type ions are implanted in the bottom of the trenches to form a p-type layer and n-type ions are implanted to form n-type regions 37. Metal is deposited to form a contact 47, which connects to the p-type layer, and electrical contacts 45. Contacts 45 and 47 are separated by an insulating layer 21. 

If local equilibrium is assumed, then the reaction kinetics can be calculated from the flux equation for A ions in the product layer and from the solution of Pick s second law in the alloy. The continuity condition at the phase boundary must also be observed. The calculations are analogous to those in sections 7.2.1 and 8.1.4. However, one additional important point must be considered. If diffusion in the alloy is the rate-controlling step in the overall process, then a slight disturbance in the planar metal/oxide phase boundary will be unstable. That is, if the phase boundary bows into the metal phase at some spot, then the growth rate of AO is increased at this point, and the disturbance increases in magnitude. The result is a fissured phase boundary. The morphology of this phase boundary depends upon a variety of factors such as the ratio of molar volumes pAo/ aiioy plastic behaviour of the oxide and the metal, and the adherency between oxide and alloy. Examples of reactions in which strongly fissured phase boundaries form are the reactions of Ag-Au and Cu-Au alloys with sulphur at 400 °C [31 ]. 

Here, we focus on slurry reduction for certain silica slurries used for dielectric and metal planarization in processes that use pads with an underlying foam stracture. The reasons for these qualifications will be explained below. We note first that there is a simple way to reduce slurry use simply turn down the flow rate. For some processes, this works. However, in most processes there are undesirable side effects, as will be seen later, such as a decrease in removal rate that affects throughput or an increase in defects. Our goals are more ambitious and are as follows ... 

Planarization (semiconductor processing) The smoothing of a surface, generally by polishing, after filling a via with metallization. 

INORGANIC COMPLEXES. The cis-trans isomerization of a planar square form of a rt transition metal complex (e.g., of Pt " ) is known to be photochemically allowed and themrally forbidden [94]. It was found experimentally [95] to be an inhamolecular process, namely, to proceed without any bond-breaking step. Calculations show that the ground and the excited state touch along the reaction coordinate (see Fig. 12 in [96]). Although conical intersections were not mentioned in these papers, the present model appears to apply to these systems. 

Other metals can also be used as a catalytic species. For example, Feringa and coworkers <96TET3521> have reported on the epoxidation of unfunctionalized alkenes using dinuclear nickel(II) catalysts (i.e., 16). These slightly distorted square planar complexes show activity in biphasic systems with either sodium hypochlorite or t-butyl hydroperoxide as a terminal oxidant. No enantioselectivity is observed under these conditions, supporting the idea that radical processes are operative. In the case of hypochlorite, Feringa proposed the intermediacy of hypochlorite radical as the active species, which is generated in a catalytic cycle (Scheme 1). 

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