Electrochemical Deposition of Metals on Semiconductors

Abstract

The general concepts governing the electrochemical deposition of metal films on semiconductors are discussed, and recent results on the fabrication of Schottky junctions consisting of silicon electrodeposited with platinum, copper and gold are presented. In order to obtain good adherent metal films, the density of nuclei should be high and the films should be grown at low current densities where the charge transfer process is rate limiting. This situation can be realized using potential controlled electrochemical deposition. For metal deposition on silicon, the surface should be pretreated in HF to dissolve the oxide layer. Furthermore, the surface should be stable during deposition which can be achieved by tailoring the deposition solutions and by using electrochemical deposition at negative potentials. It is shown that by using this approach, n-type silicon / Pt, Au, and Cu Schottky junctions can be fabricated of a quality comparable to that of junctions prepared by sputter and vapor deposition techniques.

Investigations of Electrochemical Silver Nanocrystal Growth on Hydrogen-Terminated Silicon(100)

“…It is the etching of the Si(100) surface, we believe, which varies slightly from day to day and which yields subtle differences in the surface chemistry which are not detectable in NC-AFM images of these surfaces. The nucleation rates obtained from this analysis vary from a high of 2.2 × 10 9 cm -2 ms -1 to 7.6 × 10 7 cm -2 ms -1 , and nucleation became independent of time after ≈15−25 ms, leading to a “saturation” nucleation density of between 1.3 × 10 9 and 2.3 × 10 9 cm -2 approximately an order of magnitude lower than that seen for silver and platinum nanocrystals at graphite surfaces. , We should note here that the nucleation density was not measured for pulse durations greater than 30 ms in this study, and it is likely that progressive nucleation continues at a much lower nucleation rate (which is undetectable here) and on a time scale of seconds, as previously reported. ,,,,,,, A final point is that an induction time of 2−3 msbefore which no silver is seen on the surfaceexists for all three series of measurements. We do not yet understand the origin of this delay in the onset of nucleation.…”

“…25,26 We should note here that the nucleation density was not measured for pulse durations greater than 30 ms in this study, and it is likely that progressive nucleation continues at a much lower nucleation rate (which is undetectable here) and on a time scale of seconds, as previously reported. 7,8,10,11,13,18,20,38 A final point is that an induction time of 2-3 mssbefore which no silver is seen on the surfacesexists for all three series of measurements. We do not yet understand the origin of this delay in the onset of nucleation.…”

“…prompt three-dimensional growth of metal nuclei). [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] The generality of this observation for different metals and semiconductor surfaces is not surprising, since all semiconductor surfaces must be coordinatively saturated in order to possess stability in liquids, and such surfaces tend to have a low surface energy which favors the V-W growth mode. 24 In this work, the deposition of silver on hydrogen-terminated Si(100) is followed as a function of the deposition time using noncontact atomic force microscopy (NC-AFM).…”

“…Studies of electrodeposition of other metals (Pt, Cu, and Au) on Si(100) and n-GaAs(100) at higher metal coverages (above 10 monolayers) have shown that the nucleation and growth of metals (e.g., Pb, Cu, Ag, and Ni) occurs via a Volmer−Weber (V−W) mechanism (i.e. prompt three-dimensional growth of metal nuclei). − The generality of this observation for different metals and semiconductor surfaces is not surprising, since all semiconductor surfaces must be coordinatively saturated in order to possess stability in liquids, and such surfaces tend to have a low surface energy which favors the V−W growth mode . In this work, the deposition of silver on hydrogen-terminated Si(100) is followed as a function of the deposition time using noncontact atomic force microscopy (NC-AFM).…”

Electron-Beam Induced Nanomasking for Metal Electrodeposition on Semiconductor Surfaces

“…Electrochemical deposition of metals on semiconductors has recently found renewed interest. [18][19][20][21][22][23][24] Due to its advantages and performance, electrodeposition has been adopted by the semiconductor industry, e.g., to deposit copper for on-chip interconnections leading to a decreasing resistance and reducing process complexity. [25][26][27] In order to achieve selective electrodeposition, masking approaches based on conventional lithography or new developments such as the LIGA technique have been applied.…”