Barrier Capabilities of Selective Chemical Vapor Deposited W Films and WSiN / WSi x  /  W  Stacked Layers Against Cu Diffusion

Wang, M. T.; Chen, L. J.; Chen, M. C.

doi:10.1149/1.1391671

Cited by 11 publications

(2 citation statements)

References 26 publications

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“…Due to the difference in density among W 5 Si 3 (14.53 g/cm 3 ͒, WC x (15.63 g/cm 3 ͒, and Si ͑2.33 g/cm 3 ͒, the formation of WSi x inevitably induces structural defects such as voids or microcracks inside the barrier layer and/or at the WC x /Si interface. 12,17,18 The same phenomenon was reported by Wang et al 19 In their study, a pure metallic W layer was used as the diffusion barrier between Cu and Si. Such defects then serve as diffusion paths for Cu diffusion.…”

Section: Resultssupporting

confidence: 53%

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

Wang

Tsai

Sun³

et al. 2001

J. Electrochem. Soc.

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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 .

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Section: Resultssupporting

confidence: 53%

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

Wang

Tsai

Sun³

et al. 2001

J. Electrochem. Soc.

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“…Many studies used p-n diodes with Cu layers to evaluate different materials for their diffusion barrier properties. [33][34][35][36][37][38][39][40][41][42][43][44][45][46] Among them, Baumann et al 46 studied the impact of Cu on the leakage current of p + -n diode with and without barrier layers. For the case where Cu was in direct contact with the Si diode, Cu 3 Si silicide spikes were clearly observed by TEM-EDS after annealing the device at 120 • C for 30 min.…”

Section: Effect Of the Thickness And Plating Chemistry Of Ni Layer On...mentioning

confidence: 99%

A Study on the Long-Term Degradation of Crystalline Silicon Solar Cells Metallized with Cu Electroplating

Huang¹,

Reuter²,

Zhu³

et al. 2015

ECS J. Solid State Sci. Technol.

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While using Cu electroplating to metallize silicon cells is of great interest, the long term reliability of such cells have not been well understood. In this paper silicon solar cells metallized with electroplated Cu were thermally stressed. The cell performance was characterized in conjunction with microscopic structure analysis to understand the long-term degradation mechanism and the effect of each different metal layer. The Ni silicide layer had little impact on the performance degradation at 200 • C. Increasing the thickness of a second Ni layer between the silicide and Cu significantly delayed this degradation, acting as a diffusion barrier. A series of cells annealed at different temperatures were used to extrapolate the degradation kinetics. Two different mechanisms were observed. Further silicidation of the second Ni layer was observed and was believed to cause the degradation at a higher temperature of 250 • C. However, this silicidation reaction rate dropped quickly as the temperature decreased and Cu diffusion became the dominant mechanism for cell degradation at temperatures below 200 • C. These two different mechanisms cross over at about 200 • C in this study, where both silicidation and Cu diffusion were observed. An improvement in the cell lifetime by replacing pure Ni with NiCo alloy was studied. In the standard manufacturing process flow of silicon solar cells, the front grids are formed with Ag screen printing. Replacing the screen-printed Ag with electroplated high aspect ratio Cu line has been proposed decades ago.1,2 This method has been of great interest primarily because of the lower conductivity and higher cost of Ag paste. In addition, the plated Cu potentially allows a higher aspect ratio or a smaller shadowing of the front grid and thus enables higher cell efficiencies. More importantly, the most recent development in laser patterning of the front grid allows an easy integration of the electroplating on the selective emitter formed by laser doping. [3][4][5] Different Cu metallization schemes have been reported before. 6,7 The schemes included electroless deposition of Ni and silicidation, [8][9][10] Cu electrodeposition on printed thin seed layer, 11 and electrodeposition of Ni and Cu.12-14 Among them, most of the schemes involve the formation of Ni silicide by annealing either electroless or electrolytic deposited Ni. The main purpose of the silicide is to lower the contact resistance between the metal and emitter and thus to improve the cell performance.Ni silicidation has been extensively studied for the application in complementary metal oxide semiconductor (CMOS) contacts. [15][16][17] Ni 2 Si silicide formation starts at as low as about 300• C, followed by monosilicide phases at around 400• C and silicon rich phases at above 800• C. However, small amount of Ni-richer phases such as Ni 3 Si and Ni 5 Si 2 could be observed at as low as 200• C. 15 All the studies for CMOS applications were performed on extremely thin Ni films fabricated using vacuum deposition. The silicide forme...

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Impact of the Unique Physical Properties of Copper in Silicon on Characterization of Copper Diffusion Barriers

Istratov

Flink

Weber

2000

phys. stat. sol. (b)

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Barrier Capabilities of Selective Chemical Vapor Deposited W Films and WSiN / WSi x / W Stacked Layers Against Cu Diffusion

Cited by 11 publications

References 26 publications

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

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

A Study on the Long-Term Degradation of Crystalline Silicon Solar Cells Metallized with Cu Electroplating

Impact of the Unique Physical Properties of Copper in Silicon on Characterization of Copper Diffusion Barriers

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