Michihiro Sato

Simulation of dislocation accumulation in ULSI cells with STI structure

Abstract Periodic structure of the shallow trench isolation (STI) type ULSI cells is generally used for the latest semiconductor devices. However, dislocations sometimes accumulate in the electron channel when the device size becomes small, and they have an enormous effect on the electronic state and obstruct the device from normal operation. In this paper, we numerically model the periodic structure of the STI type ULSI cells, and analyze the plastic slip that takes place during the oxidation process of oxide film area. The slip deformation is analyzed by a crystal plasticity analysis software, which has been developed on the basis of finite element technique, and we evaluate the accumulation of dislocations that accompany plastic slip. The results show stress concentrations at the shoulder part of the device area and the bottom corners of the trench for the device isolation, and the high stresses at these area cause plastic slip and dislocation accumulation. The direction of these dislocation lines are shown to be mostly parallel to the trench direction and dislocations are approximately 60° mixed type.

Crystal Plasticity Analysis of Dislocation Accumulation in ULSI Cells with Consideration of Temperature Dependence of the Lattice Friction Stress for Silicon

Representative length scale of ULSI (Ultra Large Scale Integration) cells is going to be at a nano-meter order, and the atomic level defects, such as uneven oxide films or dislocation accumulation are becoming more and more important. Among these defects, dislocation accumulation is known to be caused by thermo-plastic deformation in silicon during the processes of device fabrication. In this study, we analyse such thermal stress, plastic slip deformation and accumulation of dislocations in STI (Shallow Trench Isolation) type ULSI devices when the temperature drops from the initial at 1000 °C to room temperature. For the analysis, we use a crystal plasticity analysis code CLP, assuming that lattice friction stress for the movement of dislocations is proportional to the hardness of silicon, which is known to have strong dependency on temperature. The results show that dislocations are generated between the temperature range from 880 to 800 °C, and its maximum density is highly dependent on the lattice friction stress in the temperature range above 800 °C. For example, the difference of 16 MPa in the lattice friction stress at 1000 °C caused increase in dislocation density more than ten times. It is concluded that control of lattice friction stress at high temperatures is one of the most promising way for the suppression of dislocation accumulation.

Simulation of Dislocation Accumulation in ULSI Cells of Reduced Gate Length

We numerically evaluate the accumulation of dislocations in periodic structure of the shallow trench isolation (STI) type ULSI cells which has generally been adopted as the latest semiconductor device structure. STI type ULSI cells with gate length less than 62 nm and various trench depths are employed and subjected to a temperature drop from the initial value of 1000 °C. Dislocation accumulation is evaluated by a technique of crystal plasticity analysis. Relations between the geometry of the STI type ULSI cells and dislocation accumulation are discussed.

Evaluation of Plastic Work Density, Strain Energy and Slip Multiplication Intensity at Some Typical Grain Boundary Triple Junctions

Plastic slip deformations of tricrystals with simplified geometries are numerically analyzed by a FEA-based crystal plasticity code. Accumulation of geometrically necessary (GN) dislocations, distributions of the total slip, plastic work density and GN dislocations on slip systems, as well as some indices for the intensity of slip multiplication are evaluated. Results show that coexistence of GN dislocations on different slip systems is prominent at triple junctions of grain boundaries.

Crystal Plasticity Analysis of Thermal Deformation and Dislocation Accumulation in ULSI Cells

Thermal stress, plastic slip deformation and accumulation of dislocations in shallow trench isolation (STI) type ULSI devices when the temperature drops from 1000 し to room temperature are analyzed by a crystal plasticity analysis cord. The results show that dislocation accumulation takes place at the temperature range over 800 し, and the difference of 6 MPa in the lattice friction stress at 1000 し!causes increase of dislocation density more than 1.6 times. Dislocations generate and accumulate at the shoulder part of the device area and bottom corners of the trench. Dislocations are categorized into two groups. In one group, dislocation lines are mostly straight and parallel to the trench direction, and in the other group, dislocations make half loop type structure. Possibilities for the suppression of dislocation accumulation through control of lattice friction stress at high temperature region are discussed.