Shigeki Hirasawa

Analysis of drying shrinkage and flow due to surface tension of spin-coated films on topographic substrates

In semiconductor manufacturing processes, it is important that the SiO/sub 2/ isolation films around aluminum connection lines have flat surfaces in order to produce the multilayered connection lines used in high-density devices. In this paper, we analyzed transient changes, in the thickness distributions of a liquid-SOG (Spin-on-Glass) film on a two-dimensionally (2-D) grooved substrate during the evaporative shrinking process. The flow due to surface tension of the shrinking liquid film was calculated. Since the film is thin, a boundary layer approximation could be applied, and fourth-order differential equations of film thickness were solved using an iteration method. The viscosity and the shrinkage rate were assumed to be functions of the concentration of the solvent in the film. When the parameter of ratio [(surface tension)/{(viscosity)/spl times/(shrinking speed)}] is large and the width of the grooves is small, final surface undulations of the film are shallow. The effect of the centrifugal force was also analyzed.

Direct measurement of localized joule heating in silicon devices by means of newly developed high resolution IR microscopy

A high resolution IR microscope, especially designed for measuring localized joule heating effect in silicon devices, has been developed by combining a ZnS objective lens and a HgCdTe infrared detector. This microscope has achieved the practical spatial resolution of 10 mu m and practical temperature resolution of 0.24 K. With this IR microscope, the joule heating effect in poly-Si (polycrystalline silicon) thin film resistors formed on SiO/sub 2/ thin layer has been measured, simulating SOI (silicon on insulator) structures. A significant temperature rise was observed in this device structure, because of the low thermal conductivity of the SiO/sub 2/ layer, suggesting the possibility of new reliability problems caused by the joule heating effect in SOI structures.<<ETX>>

Radiation thermometry of silicon wafers in a diffusion furnace for fabrication of LSI

A radiation thermometry technique suitable for measuring the temperature of silicon wafers in a diffusion furnace has been developed. A principal feature of this technique is that it measures the temperature of wafers that are not in the line of sight of a conventional pyrometer. An optical guide, consisting of two quartz prisms, gives optical access to interior wafers in the load. A measuring wavelength of 0.9 mu m is selected since a silicon wafer is opaque and its emissivity does not depend on temperature at this wavelength. The accuracy of the thermometry is examined by comparing the measured value of the pyrometer with that of a thermocouple. The two measured values agree within +or-2 degrees C in a steady state. When wafers are being inserted into or drawn out from the furnace, however, an error is caused by the veiling glare at the optical guide and the wafer. >

A FAST METHOD OF RADIATIVE HEAT TRANSFER ANALYSIS BETWEEN ARBITRARY THREE-DIMENSIONAL BODIES COMPOSED OF SPECULAR AND DIFFUSE SURFACES

The radiation element method by ray emission model (REM2) has been improved by using the law of reciprocity for the specular view factor and the incomplete Cholesky conjugate gradient (ICCG) method to reduce computational time. This improved method was applied to analyze the radiative heat transfer between arbitrary three-dimensional bodies composed of specular and diffuse surfaces. The accuracy of the improved method was evaluated by comparing analytical solutions. And the method was used to calculate radiative heat transfer between machine elements and heater panels. CPU time to calculate the radiative exchange for a model composed of 3193 elements was reduced to 1/430 of that by the previous numerical method using a decomposition method.The radiation element method by ray emission model (REM2) has been improved by using the law of reciprocity for the specular view factor and the incomplete Cholesky conjugate gradient (ICCG) method to reduce computational time. This improved method was applied to analyze the radiative heat transfer between arbitrary three-dimensional bodies composed of specular and diffuse surfaces. The accuracy of the improved method was evaluated by comparing analytical solutions. And the method was used to calculate radiative heat transfer between machine elements and heater panels. CPU time to calculate the radiative exchange for a model composed of 3193 elements was reduced to 1/430 of that by the previous numerical method using a decomposition method.

Thermal Characteristics of Si Mask for EB Cell Projection Lithography

We evaluated the thermal characteristics of a single crystal Si mask for electron beam (EB) cell projection lithography by computer simulation. Due to the low thermal conductivity, the thermal characteristics of the Si mask are more critical than that of a conventional heavy metal mask. If the Si mask is assembled by the conventional method which thermal dispersion is due to only radiation, the temperature at the beam position rises drastically with the irradiation power of the EB. Moreover, the displacement caused by thermal expansion can not be ignored for a quarter-micron lithography. The Si mask assembly using thermally conductive adhesion and a new Si mask structure with ribs gives good thermal characteristics satisfying the necessary conditions for a high-throughput and highly accurate EB lithography.

Autonomous decentralized file system and its application

From the standpoint of system construction/expansion, it is required that a computer system is flexible and tolerant for change of the system structure and has software productivity. A computer system is also required to be easily operated by users regardless of its structure and status. In order to achieve these requirements, the EVERUN (EVEr RUNning) computer system has been developed based on the autonomous decentralized system concept. The distributed file system for this EVERUN computer system is proposed. This file system realizes flexible fault-tolerance, and easy expansion, operation and maintenance. The EVERUN computer system including this file system has been applied to production management systems and so on. The effectiveness of this computer system has been verified.<<ETX>>

Temperature distribution in semiconductor wafers heated in a vertical diffusion furnace

The transient temperature distribution in a row of wafers heating in a vertical diffusion furnace was calculated as the heating power of the furnace was PID (proportional plus integral plus derivative) controlled. Radiative heat transfer was combined with axisymmetric unsteady conduction in wafers and the furnace. With feedforward control of the heating power (which means that when wafers are inserted into the furnace, the heater temperature is set higher than the desired heating temperature), the temperature of the wafers reached the heating temperature rapidly. The radiative properties of silicon wafers changed from semitransparent to opaque at 500 degrees C, and the effect of this change on the temperature distribution in the wafers was calculated. Thermoplastic deformation of the wafers is more likely to occur during withdrawal than during insertion.<<ETX>>

Analysis to Reduce Thermal Stress in Oxide Single Crystal During Czochralski Growth

Temperature distributions and thermal stress distributions in a semi-transparent GSO crystal during Czochralski (CZ) single crystal growth were numerically investigated by thermal radiation heat transfer analysis and anisotropy stress analysis. As GSO has special optical properties, such as semi-transparency at a wavelength shorter than 4.5 μm, thermal radiation heat transfer was calculated by the Monte Carlo method. These calculations showed that thermal stress is caused by the radial temperature distribution on the outside of the upper part of the crystal. To reduce this temperature distribution, the following three manufacturing conditions were found to be effective: use a sharp taper angle of the crystal, install a lid to the top of the insulator, and install a ring around the tapered part of the crystal.Copyright

Analysis of Gas Convection and Temperature Distribution in a Rotating Wafer in a Cylindrical Lamp Heating Apparatus

A three-dimensional radiation-heat-transfer analysis and a convection-heat-transfer analysis are combined in order to determine the temperature distribution in a rotating wafer in a cylindrical lamp heating apparatus for rapid thermal processing. The calculated results show that the temperature variation in the wafer increases 1.4 K by the effect of natural convection, when inlet gas velocity is 0.1 m/s during 1273 K steady-state heating of the non-rotating wafer. The effect of gas convection on the temperature variations in the wafer can be minimized when the wafer is rotating in an axisymmetric apparatus and the heating rates of the lamps are optimally controlled.Copyright

Optimal heating control conditions to unify temperature distribution in a wafer during rapid thermal processing with lamp heaters

To unify temperature distribution in a wafer during rapid thermal processing, we calculated the effect of the heating control conditions on the temperature distributions during heat-up and at steady state by using a program for analyzing three-dimensional radiative heat transfer. We calculated optimum monitoring positions on the wafer in order to minimize the temperature distribution in the wafer. The effect of the number of heating zones in an axisymmetric heating apparatus was also calculated. The minimum steady-state temperature distribution in the wafer at the optimum condition was calculated as /spl plusmn/0.1 K during 100 K/s heat-up and /spl plusmn/0.02 K at 1273 K steady state. We also developed two rapid computation techniques to find the optimum heating conditions: a parallel-computation technique to find the optimum conditions for the whole heating process; and a technique that uses a reduced number of calculation elements under the assumption of almost uniform temperature in the wafer. Computation time using the latter technique is reduced to 1/250 compared to that using conventional method.