Review and analysis of laser annealing

The new microelectronic processing technology: a review of the state-ofthe-art R. L. M A D D O X Microelectron. J. 11, (1)4 (1980). This paper discusses advances in the lithographic process. Emphasis will be on resist modelling, developing, and removal methods. Next, the various dey etching techniques are presented. The rest of the paper discusses processing advances outside the category of dry processing. This includes lift-off patterning, ion implantation techniques, laser annealing, R F annealing, and plasma deposition. X-ray lithography unit gains speed by printing six wafers at a time CHARLES COHEN Electronics p. 73 (28 February 1980). Japan's VLSI Cooperative Laboratories has taken an entirely new step to boost the throughput of an experimental X-ray lithography system. It has devised a machine that exposes six wafers simultaneously. As a result, it is comparable in speed to step-and-repeat optical units. Furthermore, as 1-micrometer line widths, it prints finer patterns than those units. Design for the upcoming generation of very large-scale integrated circuits, it processes 50 4-in. wafers an hour when a negative resist (polyglycidyl methacrylate) is used and about 12 such wafers an hour when the resist is positive. Its alignment is accurate to +-0.25 ram. Pinhole elimination in hard masks M. P A U E R and R. C. AUBUSSON Proc. lnternepcon. UK '79 p. 286, Brighton (16-18 October 1979). Faults in the metal layer of hard masks restrict the workable complexity of VLSI circuits. The problem is particularly acute with positive acting photoresists; these generally require large areas of the slice to be unexposed and hence use dark-field or "negative" masks for oxide photolithography. This paper describes a technique whereby small holes in the metal layer can be eliminated. The work was undertaken at Middlesex Polytechnic by Magdolna Pauer, a visiting Research Fellow from Tungsram, Budapest. Review and analysis of laser annealing A. E. BELL RCA Rev. 40, p. 295 (September 1979). A review of the recently published literature indicates that laser annealing is a technique that is widely applicable to the thermal processes commonly required during semiconductor device fabrication. The experimental results for annealing with Q-switched ruby (k= 0.69 p.m) and Nd: YAG (k= 1.06 p.m) lasers as well as cw lasers are reviewed. Applications discussed include the annealing of implantation damage, annealing of electrically active defects in the surface regions of pure semiconductors, and laser-induced surface reactions leading to the formation of metal-silicide compositions at the surface of the silicon. A one-dimensional thermal model for laser annealing is developed and used to model the thermal evolution of the silicon wafer over a very wide range of pulse durations and absorption coefficients, the latter being determined by the choice of laser wavelength. The model calculations are specifically used to predict threshold pulse energies, recrystallisation velocities, melt depths, and the onset of surface boiling. The model is compared with experimental data and good agreement is found for a wide range of pulse times (2x 1 0 - 8 - 2 x 10 -4 sec) and absorption coefficients (102-106 cm-I). In particular the effect of the increased optical coupling to an amorphous surface layer on a single-crystal wafer was computed and found to be in good aggreement with experiments on the laser annealing of ion implantation damage.

8. Testing Description and use of electron beam accessed memory systems D O N A L D O. SMITH Microelectron. J. 10 (4) 5 (1979). EBAM systems having capacities in the range of 256 Mbytes, access time of less than 100 p-see, and 2 Kbyte read transfer times of 424 p-see, are currently under development. The unique technical features of these systems are described and a brief discussion of potential applications in computer systems is given. Future EBAM systems of much greater capacity are predicted.

Potential distribution and multi-terminal DC resistance computations for LSI technology C. M. SAKKAS IBMJ. Res. Develop. 23, (6) 640 (November 1979). Computer time and storage requirements are the two main considerations in the design of a packaging analysis software tool for the problem of calculating the electric potential distribution in arbitrary geometrical shapes. The FEM (Finite Element Method) is the accepted approach for solving such problems. A new formulation for the linear triangular element is presented which is used to derive a very simple and computationally inexpensive linear rectangluar element equation interrelating only the geometrical centres of the elements. The result is a much sparser assembly matrix with a maximum of five non-zero entries per equation compared with the usual nine of the FEM formulation. In addition, a method to obtain the minimum bandwidth of the matrix is given for the efficient and static use of external storage, permitting the solution of any size problem. The methods are applicable to multi-plane, multi-terminal configurations for the production of equivalent-resistance networks and for the calculation of the potential distribution throughout the configurations. VLSI tester rushes along at 100 MHz C. COHEN Electronics p. 7E (20 December 1979). System features up to 384 separate input and output channels to speed testing of ECL, MOS, and 12L devices.

X-ray lithography R. K. WATTS SolidSt. Technol. p. 68 (May 1979). X-ray lithography has for a number of years been under development in many laboratories. This article reviews the status of development in the areas of exposure systems, masks, and mask-wafer registration and attempts to predict the direction of future progress.

9. Applications Microprocessor implementation of the Kalman filter M. PAGE Microelectron. J., I0, (3) 16 (1969). The Kalman filter has proved an enormous asset in the processing of noisy measurement signals, but its use for the control of processes has, in the past, been limited to projects where the large cost of a suitably powerful computer system could be justified. Undoubtedly, there exist many problems in process control where a Kalman filter could be used to good effect, but where the cost of great computing power is prohibitive. With the recent drop in price of microprocessors, a microcomputer system can often be sufficiently cheap for such applications. However, certain modifications must be made to the Kalman filter algorithm to enable it to run sufficiently fast and efficiently on such a small and often slow system. Various modifications to the Kalman filter algorithms have been investigated and it has been shown that, with no severe limitations, Kalmar filters can be implemented on microprocessors. The sampling rate limitation for a Texas Instruments TMS 9900 microprocessor has been determined and the memory storage requirement estimated. The implementation is at present undergoing research. Microprogrammable digital filter implementation using bipolar microprocessors. M. E. W O O D W A R D Microelectron. J., 10, (3)23 (1979). The paper describes an implementation technique for digital filters based on the use of micro-programmable bipolar bit-slice microprocessors. The filter characteristics are determined by a set of microprograms stored in a programmable read-only memory, a particular filter response being selected by calling up an appropriate microprogram. Fast operation can be achieved by a ternary coding of the filter coefficients plus the use of the bipolar technology, whilst the use of microprogrammable bit-slice computing elements gives a high degree of flexibility. By making use of the redundancies introduced due to the restricted microinstruction set required to compute the filter algorithm, and the simple sequencing requirments of the microprograms, system complexity can be considerably reduced. 41