Defect engineering coupled with pulsed laser annealing for p+/n junction formation and pMOSFETs device enhancement

• Main Author: Tan, Dexter Xueming.
• Other Authors: Pey Kin Leong
• Format: Theses and Dissertations
• Language: English
• Published: 2012
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Microelectronics
• Online Access: http://hdl.handle.net/10356/49978
• Institution: Nanyang Technological University

The aggressive miniaturization of the MOS technology as anticipated by the Moore’s law, demands for the constant exploration of novel methods to obtain highly activated and abrupt shallow junctions. As the devices shrink down to nanoscale dimensions, it is becoming increasingly challenging to keep up with the scaling trend. Major issues arising from defect generation during the fabrication processes resulted in anomalous phenomena such as Boron transient enhanced diffusion and dopant-defect clustering. Typically, these two effects caused adverse impact to the dopant diffusion and deactivation, hindering the formation of good semiconductor junction characteristics. Tremendous efforts have been devoted to discover new solutions for resolving these daunting problems. One of the most promising techniques proposed is the usage of the advanced defect engineering. The main objective of this research work is to leverage on the various defect engineering methodologies to improve junction characteristics and to subsequently enhance the device performance. The defect engineering approaches were studied in depth to understand fundamentally the dopant diffusion and activation phenomenon in implanted substrates. Defects that generally contribute to junction degradation are interstitial-type defects introduced by ion implantation. By monitoring the defect-dopant relationship and their associated interaction mechanisms, one can appropriately engineer and optimize the junction properties. The thesis investigates and reports on two novel defect engineering techniques. One method utilizes the melt laser pre-irradiation to reduce the detrimental end-of-range defects. The mechanism is based on facilitating the recombination of the vacancy defects generated at the maximum laser melt depth with theinterstitials from the implantation induced end-of-range band. With a significant reduction in the end-of-range defects via vacancy-interstitial annihilation, superior junction profile with low junction leakage current is realizable. Another technique involves the implementation of the high energy implantation for substrate modification. The concept is basically to create a spatial separation between the interstitial and vacancy point defects. High vacancy concentration present near the surface region promotes dopant activation. Repulsion of the interstitial defects to a relatively deep substrate depth minimizes the probability of interaction with the dopants, thereby suppressing dopant deactivation and diffusion. In addition, the creation of an intermediate amorphous layer serves as a diffusion barrier for both the downward dopant diffusion and up-migrating interstitial defects. Laser annealing has been demonstrated to be an attractive option for the formation of ultra-shallow junction due to several of its favorable features and advantages. It has a near-zero thermal budget capable of producing highly activated shallow junctions with high degree of abruptness. Integration of this advanced mode of annealing allows for a diffusionless junction with remarkable dopant activation exceeding the solid solubility limit of the substrate. The combination of both processes provide for a potentially viable option to satisfy the progressive scaling requirements in junction formation. By coupling the merits of both defect engineering and laser annealing, superior junction characteristics and significant improvement in the device electrical performance were demonstrated. Laser induced vacancies was verified to be highly effective in reducing and annihilating the implantation generated interstitial defects via the recombination mechanism of the two defect species. A 2-time enhancement in the forward current and a 50 % reduction of the reverse leakage current was reported for the laser pre-irradiated diode devices. Similar enhancement in the electrical characteristics was observed with the integration of the laser vacancy defect engineering process into transistor device. High energy defect engineering implant with a high dose implemented with low fluence laser annealing suppresses the leakage current and simultaneously achieves shallow junction formation. The key concept is to engineer the implantation induced amorphous silicon under-layer to become an insulator. Silicon germanium substrate with moderate doping of carbon was determined to attain the lowest sheet resistance. This provides for a compatible and promising technology for the advanced CMOS technology.