Low Thermal Budget Microwave Annealing for Nisige Schottky Junction Device
Authors: Li Hui-Hsuan , Tsai Yi-He , Lin Yu-Hsien , Chien Chao-Hsin 
Published: February 2020

I.           
Background/ Objectives and Goals

    As continuously scaling down the devices for logic circuit, higher mobility channel materials have been considered to boost driving current such as Ge or SiGe. However, most high mobility materials have a significantly smaller bandgap as compared to Si, which will result in higher Band-To-Band-Tunneling leakage. As a result, S/D and channel engineering must play leading role for boosting the device performance. We, therefore, propose a NiSiGe/n-Si Schottky Junction formed microwave-annealing for the Si capped SiGe quantum well devices (Si/SixGe1-x/Si,x=0~1).

II.         
Methods

    Fig. 1 shows Process flow of fabricating NiSiGe/n-Si Schottky diodes. The multi-layer structure of Si/Si0.57Ge0.43/Si was grown by ultra-high vacuum chemical vapor deposition system. The channel composed of a 5nm-thick SiGe with biaxial compressive strain and Si cap was grown at 420~500 and 550 °C, respectively. Isolation film SiO2 was deposited on multi-layer architecture after series surface cleaning. Then, the definition of junction active area was accomplished with lithography and wet-etching. Because of bulk annealing characteristic of microwave, the technique was utilized to form NiSiGe as low leakage Schottky junction ranging from 370 to 470 °C for 150 s in N2 ambient. The un-reacted Ni film was removed, followed by Al deposition as the back contact. The characteristics of microwave-annealed-NiSiGe Schottky junction was investigated with AFM, SEM, TEM, XRD, and electrical analyzer.

III.      
Expected Results

    The SEM images demonstrated the surface morphologies of NiSiGe layer with various annealing temperatures in Fig.2   NiSiGe agglomeration emerged as forming temperature up to 600 °C by rapid thermal annealing (RTA) which will lead to unstable junction current. Relatively, microwave annealing can suppress the formation of junction defects and prevent the agglomeration due to lower forming temperature. For the purpose of distinguishing the pros and cons between the rapid thermal annealing (RTA) in Fig.3(a) and microwave annealing in Fig.3 (b), I-V characteristics were evaluated to check the electrical performance of Schottky junction. Microwave-annealed Schottky junction exhibited better ION/IOFF ratio about 3×105 formed at 390 °C and more stable off-current characteristic as compared to the one with rapid thermal annealing (RTA). In addition, barrier height and ideality factor of the microwave-annealed Schottky was 0.62 eV and 1.07, respectively. High resolution TEM images showed the polycrystalline structure, good uniformity of the NiSiGe and a distinct interface between NiSiGe and Si in Fig.4.

IV.         Conclusion

    Microwave annealing is beneficial in integrating quantum well p-channel MOSFETs with Schottky S/D because of its low temperature feature. We believe our microwave-cooperated quantum well architecture is promising for the high performance logic circuits and enable SiGe or Ge channel devices to be integrated on the Si substrate for the future applications.

V.         
R
eferences

[1]       M. S. Datta, G. Dewey, M. Doczy, B. Doyle, B. Jin, J. Kavalieros, R. Kotlyar, M. Metz, N. Zelick, and R. Chau, “High Mobility Si/SiGe Strained Channel MOS Transistors with HfO2/TiN Gate Stack,” IEEE International Electron Devices Meeting, p.28, Dec. 2003.

Figure 1