The modern systems of vision in infrared spectrum (IR) require elaboration of large-area nondefective imaging area with
small pitch (less 40 μm) IR FPA. One of the directions is fabrication hybrid FPA, consisting of several of arrays of
photodiodes based on MCT films (HgxCd1-xTe on GaAs substrates) and readout circuits on silicon. Substitution of
photodiodes array of large-area imaging area on few arrays of smaller image size, allows having the imaging area of the
required size without fault pixels. The main requirement is the permanent period of photodetectors on component imaging
areas. without loss of pixels on lines of gaps of the butting between arrays. Using concentrated laser radiation, for scribing
the surfaces MCT film on GaAs substrate, under concrete conditions, allows to realize offered above direction. The
determination of the border of zone of the influence of the laser radiation on electric characteristic of p-n junction of the
MCT films and technological ways of the reduction of area of influence of the laser radiation are presented in work.
We had studied the change of parameters of photodiodes on base MCT films depending on distances before laser dicing
grooves and condition of the laser radiation.
As source of the laser radiation we used pulsed UV laser (LGI-21) at 0,34 μm wavelength with pulse duration 7 ns,
frequency of repetition 50 - 100 Hz and power in pulse 2 KW.
We founded condition of the laser dicing on distances 18 - 20 μm from photodiodes, when initial current-voltage
characteristics of photodiodes are saved.
We designed method of the laser dicing of linear photodiodes on MCT films, and we used it to create of multichips hybrid
IR FPA. The result is non damage dicing of linear photodiodes on MCT films (λc =12 μm) on distances 18 - 20 μm from p-n
The results of laser - semiconductor interaction are presented. The characteristic zones are investigated after laser affects the semiconductor substrates by method of electro-physical (dynamic and static) performances of diagnostic structures. It has been found that: 1. Near of area of interaction of a laser radiation with a material of the target, the hot electrons generated by laser radiation, causes changes of properties of a material. It causes increase of reverse currents of the diodes. The magnification of reverse currents of the diode is observed which depends on supply voltage and distances between laser cut and diode. The distance between edge of the diode and edge of the laser cut with which begins increase of reverse currents of the diodes in Si: for supply voltage was 8,2 V - 5 micrometers , 20 V - 26 micrometers ; in HgCdTe: for working voltage (0,1 V) the distance was 18 micrometers . 2. The laser radiation causes temporary increase of reverse currents of the diodes on distances from 2 micrometers and more (measurement of a reverse currents of the diodes on distances 36 and 78 micrometers have shown reduction of a reverse currents, in time about 400 minutes). 3. Our experimental data allow us to develop criteria of definition of parameters of laser radiation for laser cutting of semiconductor materials on distances in some microns from elements of the integrated circuits. The basic criteria of a choice of laser radiation: 1. Repetition frequency of laser pulses; 2. Volume of destruction of a material for one pulse. The laser source for these experiments was an UV laser at 0,34 micrometers wavelength with 7 ns pulses, laser fluency was more than 1,1 J/cm2 that corresponding to minimum energy density required to forming pits. The diagnostic structures included p-n junctions (Si, HgCdTe) or source of MOSFETs (Si). Our experimental data showing that the powerful high- speed laser tools for cutting of materials are of limited usefulness for semiconductor materials.
We studied stages of formation of laser craters for the purpose of decreasing a defeat zone of a semiconductor material close to laser craters. The researches were carried out using SEM and optical microscopy. This paper is devoted to results of optimization of the laser radiation for applications in microelectronics. The principles of optimization of a wavelength, pulse duration and repetition frequency of laser radiation are determined. The effect of the diameter of a laser spot onto the process of formation of a laser crater is shown. It is opinion of the authors, that the main criteria that necessarily should be taken into account when doing the laser scribing of semiconductor wafers, are as follows: Selection of a laser source wavelength with maximum coefficient of absorption in a target. The energy density in a laser spot on target must be less than threshold for the material; The time gap between pulses is determined by time of the ending of processes in the material ofthe target. The decrease in diameter of a laser beam allows maximum depth to diameter relation to be achieved.
The results of laser-semiconductor material interaction are presented. The laser source for these experiments was an UV laser at 0.34 mkm wavelength with 7 ns pulses at 100 Hz repetition rate focused at the spot of 3 mkm diameter, laser fluence was more than 1.1 J/sq cm corresponding to the minimum energy density required to forming kerf. Material of target was p-Si with thermal oxide silicon. We have investigated changes of electrophysical (dynamic and static) performance of diagnostic structures vs. distance between the edge of laser kerf and the edge of diagnostic structures for definition of characteristic zones around the spot of laser - material interaction. The diagnostic structures included p-n junction or source of MOSFET. From the measurement made, back current for p-n junction and transfer characteristic for MOSFET and time carrier storage in source capacity of MOSFET were studied. We have determined the 3 zones around the spot of laser material processing: Zone 1. The electrophysical (dynamic and static) performance of diagnostic structures heavily changed at a distance as small as 4 - 5 mkm. It is bigger than length of region recrystallized material extracted from laser kerf (about 2 mkm). The leakage current increased. The length of zone depends from supply voltage to the diagnostic structures. For example, the length of zone 1 for supply voltage 8 V was 4 - 5 mkm and for supply voltage 20 V - 30 mkm. Zone 2. For distance between the edge of laser kerf and boundary of diagnostic structures larger than 5 mkm, the electrophysical (dynamic and static) performance of diagnostic structures changed, but restored in time. Time of 50 percent restore of electrophysical performance of diagnostic structure was about 408 min. Zone 3. For distance between the edge of laser kerf and boundary of diagnostic structures large than 70 mkm, the free electrons generated by laser irradiation, filled charge traps which began to release after laser material processing. Time of discharge traps was about 408 min. In our experiments we have realized a distance of 5 mkm form the laser kerf to the diagnostic structures and 28 mkm to the working multiplexer circuit.