Selective Cu deposition

The selective Cu deposition process was suggested by Ting and Paunovic (13) as an alternative means of fabricating multilevel Cu interconnections (Fig. 19.4). The first step in this through-mask deposition process (14) is the deposition of a Cu seed layer on a Si wafer, and then a resist mask is deposited and patterned to expose the underlying seed layers in vias and trenches. In the next step, Cu is deposited to fill the pattern. After the Cu deposition mask is removed, the surrounding seed layer is etched and dielectric is deposited. Electroless Cu deposition has been suggested for the blanket and selective deposition processes (15). 

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. 

The selective Cu deposition process was suggested, among others, by Ting and Paunovic. This is an alternative process to... 

When an n-type semiconductor which is in contact with a metal ion containing electrolyte is illuminated, then two equal partial currents occur under open-circuit conditions (Figure 11.33a). The anodic current is due to O2 formation whereas the cathodic partial current corresponds to the reduction of the metal ions such as Cu ". Since the holes cannot diffuse very far, most of them are collected by a hole scavenger or by HjO at the illuminated interface. Concerning the electrons, they are everywhere in an n-type semiconductor, in the dark and illuminated sites (Figure 11.33b). Accordingly, a selective Cu deposition should not be possible. 

Eqn. 3.106 must be considered as an approximate relationship for at least two reasons first, the assumption of a rapid complete coverage of the Pt electrode surface by Ag right from the start of the electrolysis is certainly incorrect (cf., Bard and Faulkner150) second, at the end of the electrolysis the remaining Cu2+ solution is virtually in contact with a silver electrode instead of a copper electrode, for which E u2+, Cu = 0.340 V is valid. Practice has shown that by means of CPE, selective electro-deposition and thus electrogravimetry of silver in addition to copper is possible down to 10 8MAg+, as the above calculation indicates. 

The maximal Y value for Cu-PPX catalyst is 1150 [116], It is much more than the activity of all known catalysts of this reaction. For comparison, the same reaction of C-Cl bond metathesis was investigated on the special prepared catalyst containing 1 mass% of high-dispersed metallic Cu deposited on silica. In conditions analogous to those of the reaction with the nanocomposite Cu-PPX film, Y for this catalyst was 4. Moreover, it has low selectivity in this case the formation of by-products from condensation processes takes place along with the main reaction, whereas Cu-PPX catalyst gives monochlorosubstituted decanes only [116]. 

Fig. 24. Plane-oriented ZSM-5 crystals, embedded into a copper matrix (Cu deposition by sputtering). The [100] and [010] faces were selectively opened for adsorption by abrasion. Because of the random orientation of the crystals in the plane, the mean (D + Dyy)/1 is determined in sorption kinetics (7/3).

This laser approach three-step approach to patterned Cu deposition on PTFE. Step one is chemical etching of the entire sample with- sodium naphthalenide, a solution step which can be carried out in a fume hood. Step two consists of laser patterning of portions of the etched layer. This step is self reguiatlng and can be carried out in air. Finally, step three can be either Cu CVD or electroless Cu deposition. The Cu CVD reaction giving selective-area nucleation and growth of Cu is carried out in a simple reactor with minimal vacuum requirements. The electroless Cu variation is a solution process extensively used in the electronics industry which can be carried out in an efficient fume hood... 

The-preparatlon of Pd+Cu catalysts has been studied by consecutive reduction of Cu onto Pd or Pd/C. In general, bulk Cu deposition is kinetically more favourable, although adsorbed Cu (submonolayer) is more stable. Various methods for the elimination of bulk metal deposition, are discussed. Hydrogenation in formic acid or ionadsorption followed by hydrogenation are found to be suitable methods for practical application. Pd/C catalysts modified by bulk or adsorbed Cu, have different selectivities in the partial reduction of 4-... 

Modification of the surface by bulk Cu deposition caused practically no change in the selectivity. This is due to the fact that even at a ratio of 60 at% Cu/Pdg, a small proportion of surface Pd atoms are covered by inactive Cu... 

Only about 10 elements, ie, Cr, Ni, Zn, Sn, In, Ag, Cd, Au, Pb, and Rh, are commercially deposited from aqueous solutions, though alloy deposition such as Cu—Zn (brass), Cu—Sn (bronze), Pb—Sn (solder), Au—Co, Sn—Ni, and Ni—Fe (permalloy) raise this number somewhat. In addition, 10—15 other elements are electrodeposited ia small-scale specialty appHcations. Typically, electrodeposited materials are crystalline, but amorphous metal alloys may also be deposited. One such amorphous alloy is Ni—Cr—P. In some cases, chemical compounds can be electrodeposited at the cathode. For example, black chrome and black molybdenum electrodeposits, both metal oxide particles ia a metallic matrix, are used for decorative purposes and as selective solar thermal absorbers (19). 

Thus excess of Mn(IV) hydroxide represents itself as a collector of thallium which practically completely passes into a deposit, and interfering metal ions (Cu, Cd, Pb, Ni, etc.) remain in a solution and are separated providing high selectivity of thallium determination. Effect of some factors on the value of analytical signal of thallium has been investigated at the stages of water pretreatment. Based on of these data the unified technique for thallium determination has been developed and tested on natural waters. The method proposed allows to determine content of thallium in waters which is 10 times lower than it is required by maximum allowable concentration limits. 

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