THE METHODS BY CONTROL OF THICKNESS TAPES IN CdSe/ZnTe GOT BY METHOD OF QCV

Considered various methods of measuring lines of semiconductor tapes and comparison with experimental data got the method of receipt in the quasi-closed volume.

In this research a device was used for the all-epitaxial increase of tapes of VCC-5М, which shows by itself QCV ( fig. 1). At thermal evaporation distance of L between a vaporizer and lining folded from a 100 mm a to 500 mm. Radius of ring of vaporizer -r = 5 mm. Vaporizer was cuttingin in tungsten thin (¤ to the wire a 0,8 mm) with quartz crucible, where halhogenide was loaded. Mass of evaporant folded from 50 mg to 200 mg. A lining area is covered by the layer of tape of F = 3·10 -4 m 2 . Pressure of remaining gas of Р = 10 -1 S te p . A c l o se n e s s o f m a t te r o f t a p e i s ρ (CdSe) = 5,81·10 3 kg/m3, a closeness of matter of tape is ρ (ZnTe) = 6,34·10 3 kg/m 3 . Fig. 1. Chart of device for the synthesis of tapes of CdSe and ZnTe in QCV: 1, 2 are the evaporated compartments; 3,4 are heaters of walls; 5-7 are afterheaters; 8-10 are thermocouples; 11 is lining; 12 is a lining heater; 13 are stands; 14 are heater elements of vaporizer [12] During research were is got semiconductor tapes in the wide range of thin. A necessary condition for the receipt of devices on the basis of semiconductor tapes of group AIIBVI is control of thickness of used standards. Measuring of thickness of tapes possibly both after and in the process of (in situ) their vaporise.
Will consider at first "in situ" methods. These methods are widely enough widespread, and most modern vacuum options of vaporise are equipped by the corresponding supervisory systems. A photometric method and method of quartz resonator behave to them.
The photometric method of control of thickness is used both for opaque and for transparent in the visible range of light of tapes.
Essence of him is taken to measuring of transmissivity (whether reflection) of vaporised tape on the special control standard (witness, companion). For transparent tapes this method is very effective, but requires the use of monochromatic light, as the phenomenon of interference is here used. In this work a device was used for the all-epitaxial increase of tapes of VCC-5М in which control of thickness of tapes was carried out by means of sensors which work exactly on the photometric method of control.
Will consider the method of quartz resonator more more detailed. Frequency of vibrations of quartz crystal of f with mass of M arcwise changes with the change of mass of material of m, that is besieged.
(1) Knowing a closeness ρ and area of S of tape, it is possible to get expression for determination of her thickness: (2) The choice of frequency depends on the range of measureable thickness of tapes. For thinfilms and large sensitiveness use high-frequencies. The sensitiveness of quartz resonator is estimated as m/Δf = 10 -10 g/Hertzs. Application of radiotechnical apparatus at f = 20 Mhz allows to define the change Δ of f = 20 Hertzs, that enables to measure the increase of mass an about 10 -9 g/sm 2 or 0,01-0,1 nm thickness. Practically exactness folds 2-20 nm. Will mark, that with high enough exactness it is possible this method to control speed of height of tape.
Farther of will consider a few most widespread methods of verification of thickness of standards after their receipt.
1. Experimental method -if to examine a vaporizer as ring of certain radius which is in QCV, then it is possible on the basis of initial data of receipt of standards to expect the value of thickness of semiconductor tape. Speed of evaporation в inid est the amount of matter which evaporating for one second from unit of area of surface of vaporizer calculates in obedience to the formula of Hertz-Knudsen [13] but looks like: where Р s is pressure of pair of matter. In times of t evaporation an amount of the evaporated matter is from the vaporizer of radius of r: σ = в ·π·r 2· t.
(4) On condition that all atoms of evaporant condense on lining, it is possible to consider that σ = m, where m is mass of the got tape.
The thickness of tape can be certain from correlation: where m is mass of evaporant, t is time of evaporation.

2.
Theoretical method -if to examine a vaporizer as ring of certain radius which is athwart to the normal to the surface of lining.
The thickness of tape on a flat subspoon which is athwart to the normal to the surface of vaporizer is determined by expression [14]: where an is distance from a vaporizer to the viewing point, L is distance from a vaporizer to the center of lining. For determination of thickness of d it is necessary to examine evaporation from all elements of ring [14]. The angular co-ordinates of element of vaporizer are determined by a corner ά, and for the stowage of holding from every element it is necessary to integrate for ά from 0 to 2π.
where h is distance from the center of lining to the viewing point, r is a radius of ring of vaporizer.
At calculations for a "constant ring which consists of point or superficial vaporizers". Integration for ά equalization (6) taking into account equality (7) gives for a size d expression:

3.
A spectral method is determination of thickness of tapes by means of spectrums of key-in.
Research of spectral dependence of optical key-in in a visible and near infra-red area is conducted with the use of spectrophotometer of Shimadzu UV-3600. All optical researches were conducted at a room temperature.
For determination of thickness of the investigated tapes it is possible to use equalization: where λ 1 and λ 2 are lengths of waves, corresponding to the nearby extreme points on the spectrum of key-in, M = 1 for two nearby extremums one to the type (max -max, min -min) and M = 1/2 for two nearby extremums of opposite type (max -min, min -max). The value of index of refraction is taken from his spectral dependence, resulted in [15]. Farther expect on equalization (9) the mean value of thickness for all combinations of extreme points.

4.
A gravimetrical (gravimetric) method is determination of thickness by means of weighing. A gravimetrical method (whether method of mikro weighing) is based on the exact weighing of lining to and after besieging of tape. Thickness of tape: , where m 1 , m 2 is lining mass without tape and with her, accordingly; ρ it is a closeness of tape; S is her area. This method is simple, but requires, that a lining form was to the outage, and her surfaceviewly. In addition, the closeness of the inflicted material which can change depending on the terms of the technological modes (remaining pressure, contaminations by the molecules of gas and other) influences on exactness of measuring. Exactness of determination of thickness of tape depends this method, first of all, from the sensitiveness of scales and weighing exactness, and also from exactness of determination of area of tape and her closeness. Test-sensitivity of weighing folds 1-10 mkm/m 2 .

5.
Method of multibeam interferometry -consists in a supervision in the microscope of interference stripes, which arise up at consideration in the monochromatic light of two surfaces, located under a corner to each other.
For that, not to damage the got standards of measuring of thickness conducted on the so-called "alarm" standard which turned out at the same terms and has sizes. Before measuring get on a standard a "step" -sharp lateral limit of tape on lining. For this purpose part of lining at vaporize of tape is chemically deleted. In a microscope look after the change of interference stripes ( fig. 2).
Light and dark interference stripes alternate with the step of L on the surface of both tape and lining and moved in relation to each other on a limit tape is lining on the value of l. Measuring the change of some certain stripe by means of mikro interference microscope, expect the thickness of tape after a formula: , (11) where λ c is a wave-length of monochromatic light; L is a step between nearby interference stripes; l is a change of interference stripe. Exactness of this method of measuring of thickness of tape folds 15-30 nm. If tape is transparent, in the place of "step" on her and on lining besiege opaque metallic tape which well beats back light additionally, a thickness of which, to decrease the brought in error, must be far less thickness of measureable tape.

6.
A method of capacitance-resistance sensor is measuring of thickness of tape on the basis of data of resistance of tape.
At measuring preliminary make the special control lining "witness" from an insulant, on which inflict flat blivets from material of high conductivity. Then this lining is a "witness" set in a working chamber the nearest to the working lining. It is necessary in order that both linings at causing of tape were in identical terms. Tape is inflicted on the control and working linings simultaneously.
The thickness of tape in this case can be defined after a formula: , where ρ is specific resistance of tape; R is resistance of tape on a "witness" between contacts; L and h is length and width of tape on a "witness". Test-sensitivity folds 1-5 nm, and maximum thickness of measureable tapes -about 1 mkm.

Fig. 2. Changes of interference stripes
In future will compare data of thickness tapes got photometric sensors with the calculations of thin, expected by different methods. As evidently from a tabl. 1 most near are calculations conducted by the methods of quartz resonator, gravimetrical and method of capacitance-resistance sensor. A method of quartz resonator is "in situ" by a method, while gravimetrical and a method of capacitance-resistance sensor is measuring methods on receipt. Each of them has as the advantages so defects. Advantages of gravimetrical and capacitance-resistance methods is relative simplicity of their implementation, while their defects are rigorisms enough to the cleanness and quality of used tapes. A method of quartz resonator in turn is let in on the ground also and defects. His advantages are high enough exactness of measuring and possibility in the process of receipt operatively to react on speed of besieging of tapes. Defects is complication of establishment of quartz sensors, if they construction are not planned and necessity enough frequent replacement of quartz resonators, as a result of their contamination by materials of tapes.
Summarizing the above-mentioned it is possible to draw conclusion, that for every case the method of measuring of thickness of the got tapes is accepted. For thin-films the most exact measuring will be for method of quartz resonator, while for more thick thin acceptable results will be and for the methods of capacitance-resistance sensor and gravimetrical method.
Conclusions Considered different methods of control of thickness of semiconductor tapes. Within the framework of the considered methods the chosen methods which most acceptable in certain terms.
By means of the brought methods over the measured thickness of semiconductor tapes. Comparison of results of thin of different tapes is conducted, at it data of experiment with high exactness of equal with data by the expected different methods. The most optimal methods of control of thin are chosen.