Mechanistic Studies of CVD Metallization Processes: Reactions of Rhodium and Platinum -Diketonate Complexes on
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- 作者：Elizabeth L. Crane ; Yujian You ; Ralph G. Nuzzo ; and Gregory S. Girolami
- 刊名：Journal of the American Chemical Society
- 出版年：2000
- 出版时间：April 12, 2000
- 年：2000
- 卷：122
- 期：14
- 页码：3422 - 3435
- 全文大小：514K
- 年卷期：v.122,no.14(April 12, 2000)
- ISSN：1520-5126
文摘
The hexafluoroacetylacetonate complexes Rh(hfac)(C2H4)2 and Pt(hfac)2 are known to serve aschemical vapor deposition precursors to Rh and Pt thin films. In the absence of a reducing carrier gas, thedepositions are surface-selective and occur preferentially on copper, but under these conditions, the metallizationprocesses are unexpectedly inefficient relative to the rapid deposition of Pd on Cu seen for the palladiumanalogue Pd(hfac)2. Mechanistic studies of the reactions of Rh(hfac)(C2H4)2 and Pt(hfac)2 on copper surfacesunder ultrahigh vacuum conditions have now been performed in order to elucidate the factors responsible forthe differences among these surface-selective metallization processes. The studies demonstrate that adsorptionof the rhodium complex Rh(hfac)(C2H4)2 on copper surfaces is accompanied by the loss of the coordinatedethylene groups, even at 100 K. At these low temperatures, the adsorbed Rh(hfac) fragments are oriented inseveral ways with respect to the surface. Heating the substrate above ~150 K causes the hfac ligands torealign to a perpendicular orientation relative to the surface. The platinum precursor Pt(hfac)2 adsorbs molecularlyat 100 K with the molecular planes of the hfac ligands oriented parallel to the copper surface. Heating thesubstrate to temperatures above 150 K again results in a realignment of the hfac ligands to a perpendicularorientation. This reorientation is accompanied by a partial reduction of the Pt centers (as judged from shiftsseen in X-ray photoelectron spectroscopy core level data), a result suggesting that the hfac ligands begin todissociate from the platinum centers near 150 K. At temperatures above 220 K, the transfer of the hfac ligandsfrom both complexes to the copper surface is complete, as signaled by the reduction of the metal centers tothe zero-valent state. The copper-bound hfac ligands are further transformed upon heating, either reactingwith copper surface atoms to yield Cu(hfac)2 (which desorbs at temperatures above 250 K) or decomposing(with fragments desorbing above 350 K). The presence of platinum on the copper surface promotes the formerreaction as judged by the appearance of a new reaction-limited desorption process for Cu(hfac)2. The presenceof rhodium on the copper surface does not promote the formation of Cu(hfac)2, although autocatalysis is notedin the steady-state reactive scattering data. The inability of the Rh and Pt precursors to engage in a sustainedtransmetalation reaction with the copper surface is attributed to the slow interdiffusion of copper through theRh/Cu and Pt/Cu alloys that are produced in the near-surface region.