Erika Duda

Dielectric functions of bulk 4H and 6H SiC and spectroscopic ellipsometry studies of thin SiC films on Si

Spectroscopic rotating-analyzer ellipsometry employing a compensator and optical transmission were used to measure the dielectric functions of bulk 4H and 6H SiC from 0.72 to 6.6 eV for light propagating nearly parallel to the hexagonal axis. The measurements below the band gap show the presence of a thin surface layer, which was modeled as SiO2. The data are similar to results for cubic (3C) and 6H SiC from the literature, but differences are notable, particularly above 4 eV. At 5.56 eV, we observe a critical point in 4H SiC, which is assigned to direct interband transitions along the U=M−L axis in the hexagonal Brillouin zone after comparison with band structure calculations. No evidence for direct transitions below 6.5 eV was found in 6H SiC. We apply our results to the analysis of a 4H SiC film on insulator (SiCOI) produced by high-dose hydrogen implantation and direct wafer bonding on Si. For comparison, we also studied a 1 μm thick epitaxial layer of 3C SiC on Si, where the interference oscillations...

Two-dimensional ultrashallow junction characterization of metal-oxide-semiconductor field effect transistors with strained silicon

Strained Si has been realized as one of the most promising candidates of next generation complementary metal-oxide-semiconductor technology. Since the carrier mobility can be significantly increased with strained Si lattice, the device speed can be further increased without reducing the critical dimensions. However, ultrashallow junction engineering becomes more challenging due to much complicated dopant diffusion behavior. We have used scanning capacitance microscopy and dopant selective etching to characterize such differences by comparing the devices fabricated with strained Si channel and with conventional unstrained Si. The devices we used are p-type channel complementary metal-oxide-semiconductor field effect transistors fabricated with 130 nm technology, with strained Si channel built on SiGe pseudosubstrate. Significant differences were observed in the formation of source/drain (S/D) extensions. The junction profile shows abrupt transition from S/D extension to S/D comparing with unstrained Si. Me...

Characterization Techniques for Evaluating Strained Si CMOS Materials

The electron and hole mobility of Si complementary metal on oxide field effect transistors (CMOS) can be enhanced by introducing a biaxial tensile stress in the Si channel. This paper outlines several key analytical techniques needed to investigate such layers. Raman scattering is used to measure the strain in the Si channel as well as to map the spatial distribution of strain in Si at a lateral resolution better than 0.5 μm. Atomic force microscopy (AFM) is used to measure the surface roughness. Transmission electron microscopy (TEM) is used to reveal dislocations in the structure, the nature of the dislocations and the propagation of the dislocations. Secondary ion mass spectrometry (SIMS) is used to monitor the Ge content profile in the structure and the thickness of each layer. In the long term, inline nondestructive techniques are desired for epi‐monitoring in manufacturing. Two techniques, spectroscopic ellipsometry (SE) and x‐ray reflectivity (XRR), have shown promise at this stage.

Secondary ion mass spectrometry characterization of source/drain junctions for strained silicon channel metal–oxide–semiconductor field-effect transistors

As complementary metal–oxide–semiconductor (CMOS) devices approach the sub-100-nm dimensions in accordance with Moore’s Law, several major technical barriers exist with the formation of ultrashallow junctions. Strained silicon CMOS devices have the advantages of higher carrier mobility and high current drive. The use of silicon germanium substrates for strain in the silicon channel presents many challenges for CMOS integration including maintaining the channel strain and effect on shallow source/drain (SD) junctions. Low energy secondary ion mass spectrometry (SIMS) has been used to study boron and arsenic diffusion behavior in strained silicon and in SiGe. In addition, diffusion of germanium from the relaxed SiGe into the strained silicon layer will be discussed in relationship with SD implant and annealing. SIMS experimental results will also be compared to theoretical simulation results.

Computer aided design of sub-100 nm strained-Si/Si/sub 1-x/Ge/sub x/ NMOSFET through integrated process and device simulations

Integrated process and device simulations were performed to design sub-100 nm strained-Si/Si/sub 75/Ge/sub 25/ devices. The process and device models were carefully calibrated according to various physical and electrical device characterizations. It is observed that the dopant behavior is highly sensitive to the presence of the SSi/SiGe heterointerface, especially when the SSi thickness is reduced below 10 nm. This points to SSi thickness as a new source of process variation and careful control of the SSi layer is important to maintain consistent device performance. In addition, the Type-II energy-band alignment at the heterointerface also contributes strongly to the short-channel device behavior. This work illustrates the need for accurate heterostructure-based process and device models in order to simulate and design aggressively-scaled strained-Si devices.

High K LAON for gate dielectric application

A promising high k material, lanthanum aluminum oxynitride (LAON), with excellent material and electronic properties is reported. The LAON film has good thermal stability and CMOS process compatibility at 1000 C. The LAON material has a dielectric constant of above 20, bandgap of 6.6 eV. Well-behaved I-V and C-V were obtained for 80 A LAON on silicon.

Root‐Cause Analysis and Statistical Process Control of Epilayers for SiGe:C Hetero‐Structure Bipolar Transistors

The SiGe:C hetero‐structure bipolar transistor (HBT) has turned into a key technology for wireless communication. This paper describes various critical analytical techniques to bring up and maintain the SiGe:C epi‐process. Two types of analysis are critical, (1) routine monitoring SiGe base and Si cap thickness, doping dose, Ge composition profile, and their uniformity across the wafer; and (2) root‐cause analysis on problems due to non‐optimized process and variation in process conditions. A transmission electron microscopy (TEM) technique has been developed allowing a thickness measurement with a reproducibility better than 3 A. Charge‐compensated low‐energy secondary ion mass spectrometry (SIMS) using optical conductivity enhancement (OCE) allows a Ge composition measurement to a required precision of 0.5 at. %.

Optical Vibrational and Structural Properties of Ge1−xSn x alloys by UHV-CVD

Abstract : UHV-CVD growth based on a deuterium stabilized Sn hydride and digermane produces Ge-Sn alloys with tunable bandgaps. The Ge(1-x)Sn(x) (x=2-20 at.%) alloys are deposited on Si (100) and exhibit superior crystallinity and thermal stability compared with MBE grown films. Composition, crystal and electronic structure, and optical and vibrational properties are characterized by RBS, low energy SIMS, high resolution electron microscopy TEM, x-ray diffraction, as well as Raman and IR spectroscopies. TEM studies reveal epitaxial films with lattice constants between those of Ge and Sn. X-ray diffraction shows well-defined (004) peaks and rocking curves indicate a tightly aligned spread of the crystal mosaics. Resonance Raman indicate a E1 bandgap reduction relative to Ge, consistent with a decrease of the E2 critical point observed in spectroscopic ellipsometry. IR transmission spectra indicate an increase in absorption with increasing Sn content consistent with a decrease of the direct bandgap.