Stress development and relaxation during reactive film formation of Ni₂Si

Abstract

Using continuous wafer-curvature measurements, stress generation was monitored as nickel thin films reacted with silicon substrates to form Ni 2 Si during isothermal anneals. A large compressive force developed during the reaction, but gradually relaxed after the reaction was complete. From a model for reactive film formation, a lower limit for the instantaneous stress associated with compound formation was found to be −2.00 ± 0.75 GPa. This instantaneous stress can be explained by a volumetric strain of 1.65 ± 0.62%, which is much smaller than the theoretical volume expansion of 62% in this system. These results suggest that significant inelastic deformation occurs during silicide formation. It was also found that diffusive creep relaxes the growth stress after the reaction. The observed instantaneous stress indicates that the energy of deformation associated with the reaction is of the same order as the energy that drives it, suggesting that stress generation and stress relaxation can play a significant role in the kinetics of reactive film formation.

Structural changes during the reaction of Ni thin films with (100) silicon substrates

“…Another aspect that should be considered is that Ni films deposited on SiO 2 carry an intrinsic stress, which scales with film thickness [18][19][20]. Thin films of Ni on SiO 2 are kinetically constrained after low-temperature growth and agglomerate when annealed at or above 200°C [13,17,[21][22][23].…”

“…Interfacial stresses have so far only been considered for silicidation processes in the absence of any diffusion barriers [19]. The literature overview provided above indicates that ultrathin stoichiometric SiO 2 films act as excellent diffusion barriers below about 800°C [13][14][15][16]23].…”

Medição de tensões residuais em filmes finos durante o processo de deposição.

“…Alguns deles se baseiam em métodos ópticos [1][2][3][4], outros em métodos capacitivos [5][6][7][8] e alguns fazem a medição por difração de raios-x [9][10][11].…”

“…O raio é refletido pela extremidade do substrato e, medindo-se o deslocamento do raio, pode-se chegar ao deslocamento do substrato [6]. Gill [1,2] propôs utilizar uma câmera de vídeo para gravar e medir o deslocamento do substrato por processamento de imagens.…”

“…Já no método capacitivo, o deslocamento da extremidade do substrato é medido por um sensor capacitivo e, a partir dessa informação, é calculada sua curvatura [5][6][7][8]. Na grande maioria dos casos, o capacitor é formado por uma placa fixa e uma placa móvel, presa à extremidade livre do substrato.…”