Enhancement of the Stability of Ti and Ni Ohmic Contacts to 4H-SiC with a Stable Protective Coating for Harsh Environment Applications

Abstract

We report on wafer-level measurements of the long-term stability of Ti and Ni ohmic contacts to n-4H-SiC during thermal treatments in air or air/moisture environments up to 500°C. Contact metallizations with and without a sputtered Ti (20 nm)/TaSi x (200 nm)/Pt (150 nm) diffusion barrier stack and Ti (20 nm)/TiN (10 nm)/Pt (150 nm)/Ti (20 nm) interconnects were compared. A protective coating consisting of a SiO x (250 nm)/SiN y (250 nm) stack deposited by plasma-enhanced chemical vapor deposition (PECVD) was used. The stability of the contact metallizations during long-term thermal treatments in air and air/moisture was studied. The best performance was achieved with Ti ohmic contacts without the Ti/TaSi x /Pt stack. This system successfully withstood 1000 h thermal treatment at 500°C in air followed by 1000 h at 500°C in air/10% moisture. After the aging, the contact failure ratio was below 1% and the specific contact resistivity amounted to (2.5 ± 1.1) 9 10 À4 X cm 2 . Scanning electron microscopy (SEM) cross-sectional analysis indicated no degradation in the contact metallization, demonstrating the effectiveness of the SiO x /SiN y protective coating in preventing oxidation of the contacts. These results are very promising for applications in harsh environments, where the stability of ohmic contacts is crucial.

Structural and Reliability Analysis of Ohmic Contacts to SiC with a Stable Protective Coating for Harsh Environment Applications

“…The contacts were considered as ohmic if the condition R 2 > 0.999 was satisfied, whereas R 2 is the reduced chi-square associated to the fitting. 13 The specific contact resistivity ρ c was measured at room temperature after each aging step by means of TLM and modified cTLM test structures. For each experiment, a set of 5 TLM and 5 cTLM structures per sample type was used for the ρ c extraction.…”

“…The layout of the cTLM structures and the method employed for the ρ c extraction are described more in detail in Ref. 13. The TLM model after Reeves requires an additional measurement of the 'end resistance' but is more precise than the other models, since it eliminates the assumption that the semiconductor sheet resistance under the contacts R sk is equal to the sheet resistance between the contacts R sh .…”

Temperature and Stress Simulation of 4H-SiC during Laser-Induced Silicidation for Ohmic Contact Generation

“…The thermal conduction inside the material and the charging of thermal capacities were calculated with Equation (3).…”

“…These advantages, compared to those of electronics based on silicon substrates, result from the higher band gap, higher thermal conductivity, higher dielectric disruptive strength, and higher saturation electron drift velocity of SiC [1,2]. Unfortunately, however, some important process steps for silicon carbide-based devices are not yet well established, e.g., the deposition of ohmic contacts, which has continuously been a topic of current research [3][4][5][6]. To generate ohmic contacts on SiC, metals such as nickel, tungsten, or titanium are deposited on the wafer using physical vapor deposition (PVD) [3] followed by a so-called rapid thermal process (RTP) to transform the contact's Schottky behavior into an ohmic one.…”

“…Unfortunately, however, some important process steps for silicon carbide-based devices are not yet well established, e.g., the deposition of ohmic contacts, which has continuously been a topic of current research [3][4][5][6]. To generate ohmic contacts on SiC, metals such as nickel, tungsten, or titanium are deposited on the wafer using physical vapor deposition (PVD) [3] followed by a so-called rapid thermal process (RTP) to transform the contact's Schottky behavior into an ohmic one. This RTP process is usually performed for several minutes at temperatures between 900 and 1000 • C to generate silicides at the metal to semiconductor boundary such as Ni 2 Si or TiSi 2 [7,8].…”