Formation of Copper Thin Films by a Low Kinetic Energy Particle Process

Abstract

Low kinetic energy particle bombardment of a growing film surface has been employed to grow high-quality copper thin films on silicon and SiO2 with ideal metal/substrate interface characteristics. It is shown that the energy of Ar ions concurrently bombarding a growing film surface determines the crystal structure of the film. Under relatively low-energy ion bombardment conditions, (100)-or (lll)-oriented Cu films are grown epitaxially on (100) Si or (111) Si surfaces, respectively. On the other hand, completely (lll)-oriented films are obtained either on (100) Si, (111) Si, or SiO2 surfaces when large ion bombardment energies are employed. It has been found that (111)-oriented films thus created on SiO2 are metastable and easily transform by thermal annealing into completely (100)-o~iented films with large grains of about 100 ~m. This unique transformation phenomenon has been successfully applied to the formation of almost single-crystal (100)oriented Cu islands on SIO2. In situ substrate surface cleaning by extremely low energy Ar ion bombardment has enabled the formation of ideal metal/silicon contacts without any postmetallization alloying heat cycles. Excellent adhesion of Cu thin films on SiO2 has also been demonstrated by the employment of the in situ substrate surface cleaning.

Representation surfaces of Young's modulus and Poisson's ratio for BCC transition metals

“…These films are usually fabricated by physical or chemical vapor deposition and have strong textures and thus anisotropic elasticity [1,2]. Anisotropic elasticity can result in directionally dependent stress and strain energy [3][4][5], abnormal grain growth and texture transformation [6][7][8][9][10]. In X-ray diffraction method for determining residual stresses in a polycrystalline specimen, only those grains properly oriented to diffract at each tilt contribute to the diffraction profile.…”

Dependence of stresses and strain energies on grain orientations in FCC metal films

“…The preferable growth for grains with (1 1 1) plane oriented parallel to the film surface in Au [17], Al [18,19], Si [20,21], and Ge [22] films has been explained satisfactory from surface energy minimization. However, early in 1991, Ohmi et al found that (1 0 0) and (1 1 1) preferred orientation Cu films were grown on Si substrates by a low kinetic energy particle process, and (1 1 1)-oriented Cu films thus created were metastable and easily transformed by thermal annealing into completely (1 0 0)-oriented films with large grains of about 100 mm [23]. Obviously, the formation of (1 0 0) texture and the change in the texture from (1 1 1) to (1 0 0) in FCC films on substrate after annealing are not driven by minimization of surface energy, since the (1 1 1)-oriented grains have the lowest surface energy [4].…”

Texture of Electroplated Copper Film under Biaxial Stress

“…However, Ohmi et al found that (100) and (111) preferred orientation copper films were grown on Si substrates by a low kinetic energy particle process. 9,10) A recent paper discussed the observed texture responses of copper films deposited by a variety of techniques, 11) in general, (100)-, (110)-, (111)-and (511)-oriented films dominated the response. In present paper, the electroplated copper films have strong (110) textures.…”