Thermal Stability of Sputtered Tungsten Carbide as Diffusion Barrier for Copper Metallization

Abstract

This work investigated the thermal stability of tungsten carbide (WC x) films deposited by a sputtering process with a WC target as diffusion barrier layer between Cu and Si. The as-deposited WC x film has a nanocrystalline structure and a low electrical resistivity of around 227 ⍀ cm. Film characterization reveals that the WC x film was able to preserve the integrity of the Cu (2000 Å)/WC x ͑500 Å͒/n-Si structure without formation of Cu 3 Si, up to a 600°C annealing for 30 min. In addition, diode leakage current measurements on the same contact structure, but with a p ϩ n-Si substrate did not show deterioration of electrical characteristics up to a 550°C annealing. As the thickness of the WC x barrier was reduced to 150 Å, the WC x film retained the integrity of diodes up to 500°C without increasing the diode leakage current. The failure of WC x film after high temperature annealing is attributed to the Cu diffusion into the Si substrate through grain boundaries or local defects of the WC x barrier layer, in which some local defects may arise from the formation of W 5 Si 3 .

Nano-Scale Surface Morphology Evolution of Cu/Ti Thin Films

“…[8][9][10][11][12][13][14][15] Film thickness significantly influences the progress of agglomeration. 16 20 After the same heat-treatment, the film thickness is thinner, the agglomeration occurs easier.…”

“…1 2 In order to overcome the disadvantages of Cu such as fast diffusion into Si 3 and SiO 2 , 4 and poor adhesion to most dielectric materials, a suitable diffusion barrier/adhesion promoter is necessary. [5][6][7][8][9][10][11][12][13][14][15] However, it is observed that after high temperature annealing, copper films on some barriers may exhibit agglomeration, such as MoN, 8 TiN, 9 Ti-Si-N, 10 TiB 2 , 11 12 WC, 13 Ta, 14 ITO. 15 With the annealing temperature increasing, Cu films systems exhibit grain growth, void formation, agglomeration and chemical reaction with the Si substrate (formation of Cu 3 Si).…”

“…15 With the annealing temperature increasing, Cu films systems exhibit grain growth, void formation, agglomeration and chemical reaction with the Si substrate (formation of Cu 3 Si). [8][9][10][11][12][13][14][15] Ti can also be employed as the barrier material. However, there are lacks of investigations on agglomeration of Cu in Cu/Ti systems.…”

Tungsten nitride thin films deposited by MOCVD: sources of carbon and effects on film structure and stoichiometry

“…2b shows that grain size generally increases with temperature for films grown from both PhCN and 1,2-DCB solutions, with films from PhCN solutions having larger grain size relative to those grown from 1,2-DCB across the entire temperature range. This effect is due to enhanced carbon deposition in the films from 1,2-DCB solutions, as carbon is reported to decrease grain size when added to polycrystalline tungsten films [26]. The drop in grain size at 615 C indicates increased disorder in the film, which again is likely caused by a transition between carbon deposition processes.…”

Diffusion Barriers

“…(1) polycrystalline and amorphous Me-N, Me-C, Me-O and Me-B compounds, such as TiN x [25], VN x [26], ZrN x [27], NbN x [28], MoN x [21], HfN x [29], WN x [30], TaN x [31], WC x [32], TaC x [33], MoO x [34], TaO x [35] and TiB 2 [36], (2) polycrystalline and amorphous Me-Si compounds, such as MoSi x [37], WSi x [38] and TaSi x [39], (3) polycrystalline and amorphous Me alloys, such as TiW x [40], TaCo x and TaFe x [41], TaW x [42], NiNb x [43] and CuZr x [44].…”