Selective Deposition of Thin Copper Films onto Silicon with Improved Adhesion

Magagnin, Luca; Maboudian, Roya; Carraro, Carlo

doi:10.1149/1.1344280

Cited by 70 publications

(74 citation statements)

References 12 publications

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“…The direct deposition of copper, silver or gold from aqueous fluoride-containing solutions onto silicon substrates via the galvanic displacement reaction has been described in the literature. [3][4][5][6] Reports on the deposition of copper or silver onto silicon substrates via the galvanic displacement reaction from fluoride-free aqueous solutions have not been found in the literature. The present paper describes preliminary observations on the deposition of silver onto silicon substrates via the galvanic displacement from aqueous fluoride-free solutions.…”

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confidence: 99%

Galvanic Deposition of Silver on Silicon Surfaces from Fluoride Free Aqueous Solutions

Djokić¹,

Cadien

2015

ECS Electrochemistry Letters

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Direct deposition of silver from fluoride-free alkaline solutions containing Ag(I) ions at pH higher than 12 onto silicon surfaces at room or elevated temperatures has been demonstrated. This deposition does not require a reducing agent, i.e. process proceeds via galvanic displacement reactions. This new process that is based on strong alkaline and fluoride-free solutions was experimentally illustrated through XRD and SEM analyses. Theoretically, it was confirmed that this process is thermodynamically favorable at room temperature, however for the real industrial applications elevated temperatures (up to 100 Semi-conductive silicon substrates are widely used in electronics industry for various applications. Metallization of silicon semiconductors with copper, silver and gold is very important in the production of integrated electronics devices. For this purpose, electrochemical methods e.g. electrodeposition or electroless deposition from aqueous solutions are very attractive since they are quite simple and relatively easy to scale up. Practical difficulties arise due to the fact that at the surface of silicon wafers oxide films of SiO 2 are formed. SiO 2 films are non-conductive, and consequently, they must be removed prior to direct metallization using the aqueous electrochemical processes. Although the metallization of silicon substrates can be achieved via autocatalytic deposition through the surface activation with SnCl 2 /PdCl 2 catalysts, 1 this process would not remove the SiO 2 film leading to an unacceptable electronic device performance. In order to remove the SiO 2 film and to deposit metals such as copper or silver from aqueous solutions directly onto silicon, various pretreatment steps are required during processing. These pre-treatment steps involve fluoride-containing solutions, 2 which can have deleterious effect on the environment. The direct deposition of copper, silver or gold from aqueous fluoride-containing solutions onto silicon substrates via the galvanic displacement reaction has been described in the literature.3-6 Reports on the deposition of copper or silver onto silicon substrates via the galvanic displacement reaction from fluoride-free aqueous solutions have not been found in the literature. The present paper describes preliminary observations on the deposition of silver onto silicon substrates via the galvanic displacement from aqueous fluoride-free solutions. Of course, significant detailed studies will be required before this process can be applied in the practice. If and when successful, this simple process may have a significant impact on the electronics industry.Experimental p-(boron doped) and n-(phosphorus doped) single crystal (100) silicon were used as substrates in the present work. As received, silicon substrates were very carefully washed with 3:1 (H 2 SO 4 -H 2 O 2 ) solution and then with water and ethanol. After the cleaning procedure, silicon substrates were immersed into respective proprietary fluoridefree solutions containing Ag(I) ions. For the deposition of sil...

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confidence: 99%

Galvanic Deposition of Silver on Silicon Surfaces from Fluoride Free Aqueous Solutions

Djokić¹,

Cadien

2015

ECS Electrochemistry Letters

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“…We have used this approach to deposit copper on silicon surfaces [16]. Continuous copper films are obtained galvanically on p-or n-type, single-or poly-crystalline silicon.…”

Section: Project 2: Integration Of Noble Metals As a Coating For Memsmentioning

confidence: 99%

Integrated superhard and metallic coatings for MEMS : LDRD 57300 final report.

Boer¹,

Maboudian

2004

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Two major research areas pertinent to microelectromechanical systems (MEMS) materials and material surfaces were explored and developed in this 5-year PECASE LDRD project carried out by Professor Roya Maboudian and her collaborators at the University of California at Berkeley.In the first research area, polycrystalline silicon carbide (poly-SiC) was developed as a structural material for MEMS. This material is potentially interesting for MEMS because compared to polycrystalline silicon (polysilicon), the structural material in Sandia National Laboratories' SUMMiTV TM process, it may exhibit high wear resistance, high temperature operation and a high Young's modulus to density ratio. Each of these characteristics may extend the usefulness of MEMS in Sandia National Laboratories' applications. For example, using polycrystalline silicon, wear is an important issue in microengines, temperature degradation is of concern in thermal actuators and the characteristics of resonators can be extended with the same lithography technology.Two methods of depositing poly-SiC from a 1,3-disilabutane source at 650˚C to 800˚C by lowpressure chemical vapor deposition (LPCVD) were demonstrated. These include a blanket method in which the material is made entirely out of poly-SiC and a method to coat previously released and fabricated polysilicon MEMS. This deposition method is much simpler to use than previous methods such as high temperature LPCVD and atmospheric CVD. Other major processing issues that were surmounted in this LDRD with the poly-SiC film include etching, doping, and residual strain control. SiC is inert and as such is notoriously difficult to etch. Here, an HBr-based chemistry was demonstrated for the first time to make highly selective etching of SiC at high etch rates. Nitrogen was incorporated from an NH 3 gas source, resulting in high conductivity films. Residual strain and strain gradient were shown to depend on deposition parameters, and can be made negative or positive. The tribology of poly-SiC was also 3 investigated. Much improved release stiction and in-use stiction performance relative to polysilicon MEMS was found. Furthermore, wear of poly-SiC-coated MEMS was much reduced relative to uncoated polysilicon MEMS. A prototype baseline process flow now exists to produce poly-SiC in the Berkeley Sensor and Actuator (BSAC) facility.In the second project, galvanic deposition of metals onto polysilicon surfaces has been developed. The possible applications include reflective and optical coatings for optical MEMS, microswitches and microrelays for radio frequency MEMS and catalytic surfaces for microchemical reactors. In contrast to electroless deposition, galvanic displacement deposition requires no prior activation of the surface and is truly selective to silicon surfaces. This approach was used to deposit copper, gold and rhodium onto polysilicon MEMS. A method to study the adhesion of these metals to polysilicon was developed. It was also shown that the surfaces could be rendered hydrophobic by apply...

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“…The direct deposition of copper, silver or gold from aqueous fluoride-containing solutions onto silicon substrates via the galvanic displacement reaction can be quite successful. [3][4][5][6] According to recent investigations, silver can be successfully deposited onto silicon substrates from fluoride-free aqueous solutions. 7 Reports on the deposition of copper onto silicon substrates via the galvanic displacement reaction from fluoride-free aqueous solutions have not been found in the literature.…”

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confidence: 99%

Galvanic Processes on Silicon Surfaces in Cu(II) Alkaline Fluoride-Free Solutions

Djokić

Antić

Djokic³

et al. 2016

J. Electrochem. Soc.

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Galvanic processes on silicon surfaces in alkaline fluoride-free solutions containing Cu(II) ions were investigated in this work. Deposition of copper (I) oxide (Cu 2 O) and copper metal at pH 14 onto silicon surfaces at room or elevated temperatures has been demonstrated. This deposition does not require the presence of a reducing agent in the solution. The results clearly show that Cu(II) ions can be reduced to Cu(I) or Cu (0) Metallization of silicon with copper, silver and gold can be realized using electrochemical methods such as electrodeposition or electroless deposition from aqueous solutions. These methods are very attractive since they are simple and relatively easy to scale up. Practical difficulties arise due to the fact that at the surface of silicon wafers, oxide films of SiO 2 are present. SiO 2 films are non-conductive, and consequently, they must be removed prior to direct metallization. Although the metallization of silicon substrates can be achieved via autocatalytic deposition through surface activation with SnCl 2 /PdCl 2 catalysts, 1 this process would not remove the SiO 2 film leading to unacceptable electronic device performance. In order to remove the SiO 2 film and to deposit metals such as copper or silver from aqueous solutions directly onto silicon, pre-treatment steps are required during processing. These pre-treatment steps may involve fluoride-containing solutions, 2 which have deleterious effects on the environment. The direct deposition of copper, silver or gold from aqueous fluoride-containing solutions onto silicon substrates via the galvanic displacement reaction can be quite successful.3-6 According to recent investigations, silver can be successfully deposited onto silicon substrates from fluoride-free aqueous solutions.7 Reports on the deposition of copper onto silicon substrates via the galvanic displacement reaction from fluoride-free aqueous solutions have not been found in the literature. In an attempt to further explore the behavior of silicon in fluoride free solutions without a presence of reducing agents in the aqueous phase, the present communication describes preliminary observations on galvanic reactions on silicon substrates using Cu(II) containing alkaline fluoride-free aqueous solutions.Experimental p-(B doped) and n-(P doped) single crystal (100) silicon wafers were used as substrates in the present work. As received, silicon substrates were very carefully washed with 3:1 (H 2 SO 4 -H 2 O 2 ) solution and then with water and ethanol. After the cleaning procedure, silicon substrates were immersed into respective proprietary fluoridefree solutions containing Cu(II) ions. Immersions were performed at pH 14 using a CuC 4 H 4 O 6 (copper tartrate) complexed solution. The pH of this solution was adjusted with NaOH. The concentration of Cu(II) ions in alkaline solutions was 3.54 g/L. The immersion solutions in the present work were used as prepared. Consequently it should be assumed that O 2 was present in the solutions during the immersion.The specific immersion ...

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Selective Deposition of Thin Copper Films onto Silicon with Improved Adhesion

Cited by 70 publications

References 12 publications

Galvanic Deposition of Silver on Silicon Surfaces from Fluoride Free Aqueous Solutions

Galvanic Deposition of Silver on Silicon Surfaces from Fluoride Free Aqueous Solutions

Integrated superhard and metallic coatings for MEMS : LDRD 57300 final report.

Galvanic Processes on Silicon Surfaces in Cu(II) Alkaline Fluoride-Free Solutions

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