Metallic Bonding

Sputtering targets can be simply clamped to the sputter source cathode inside the sputter deposition system. However, this procedure can prove costly due to cracking, warping or other damage to the target in use caused by inadequate cooling. Wherever possible, it is good practice to bond the sputter target to a strong, compatible backing plate. Target bonding is a critical process and the exact fabricating method employed can vary depending on the choice of the sputtering target material. A properly bonded sputtering target will normally give a longer working life than a non-bonded target, may enable the use of a higher power input to achieve faster sputtering rates and will enable thin film process parameters to be consistently repeated. All metallic bonded targets include a sputtered metal intermediate bonding layer on the "bonded" side of the target, which acts as a barrier layer protecting the target material integrity from diffusion of the hot primary bonding metal alloy. The metal bonding technology offers excellent thermal and electrical conductivity and is compatible with either DC or RF power supplies. A properly bonded target will stay adhered to the backing plate providing there is a continuous supply of sufficient cool water and the sputtering source cathode is not over powered. Shear stresses that develop between the target and backing plate, due to heating during sputtering, can be a cause of bonding failure when the backing plate and target materials do not have compatible coefficients of thermal expansion. Depending on the dimensional tolerances allowed, the bond thickness can be adjusted to help compensate for these stresses. Silver-Filled Epoxy The silver filled epoxy bonding cements are high quality products which have been readily accepted as having acceptably low outgassing characteristics. They contain over 90% of high purity silver for optimum thermal and electrical conductivity.

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