SU1068554A1 - Method and apparatus for heat treatment of semiconductors - Google Patents

Abstract

1. A method of heat treating semiconductors that includes a heating sample and an electric field applied to it, characterized in that, in order to increase the carrier mobility, the treatment is carried out in an ionized medium by passing a current through the sample with a voltage of no more than 300 volts. 2. A device for heat treatment of semiconductors, including a container for placing a sample, g equipped with means for supplying electric current, and a heater, which is designed so that, in order to increase the mobility of current carriers, the device is equipped with a cylinder for ionized environment, which is installed under the container, inside the axis of the cylinder is placed electrically insulated electrons (O kind, and in the upper part the cylinder has the shape of a truncated cone for feeding the ionized medium along the periphery of the sample. About a CP cd 4 ;;

Description

The invention relates to the field of electronics related to the manufacture of semiconductor devices and integrated circuits, and can be used to improve their quality. Currently used semiconductor materials have uncontrolled impurities and defects that limit the mobility of the main current carriers and lead to a decrease in the cut-off frequency of transistors and a decrease in the gain of transistors to a decrease in the speed of integrated circuits, etc. There is a known method of removing defects of a crystal structure in semiconductor wafers, including their preliminary polishing with an abrasive followed by their thermal treatment in an atmosphere containing oxygen Cll. However, this method can contaminate the surface layer of the plates. Closest to the invention is a method of heat treatment of semiconductors, including heating the sample and exposing it to an electric field. The method is carried out in an apparatus comprising a container for placing a sample, equipped with means for supplying an electric field, and a heater L21. A disadvantage of the known method and device is the long duration of the process at high temperatures, which leads to structural disturbances in the crystals and does not provide good electrical properties, in particular, sufficiently high carrier mobility. The aim of the invention is to increase the carrier mobility that, according to the method of heat treatment of semiconductors, which includes heating the sample and exposing it to an electric field, the treatment is carried out in an ionized medium with prop accelerating a current through a sample with a voltage of no more than 300 V. For this purpose, a device for heat treatment of semiconductors, including a container for placing a sample, equipped with means for supplying electric current, and a heater, is equipped with a cylinder for ionized medium, which is packed under the container, inside the axis The cylinder is placed electrically isolated electrode, and in the upper part of the cylinder has the shape of a truncated cone for supplying ionized medium around the periphery of the sample. Figure 1 shows the processing scheme of the sample in the form of a plate; on . figure 2 - processing circuit of the sample in the form of a rod; on fig.Z - the device, a longitudinal section; 4 shows a mobility measurement circuit by the van der Pauw method. Sample 1 in the form of a plate or rod is connected to the negative pole of the DC generator and placed in the electrolyte 2, and the anode 3 is connected to the positive pole. The plates 4 are made of metal, which conducts electrical current rapidly. The device (Lig.C) contains a mechanism for crimping semiconductor samples 5 and a container 6 for their placement. Using the crimping mechanism, the semiconductor sample 1 is pressed against the support washer 7 with a certain force, which prevents its destruction. To accomplish this task, the mechanism provides for an elastic washer 8, a hydraulic cylinder 9 with a smooth stroke, elastic elements and limit stops. G using the units and aggregates located in the container, the ionized medium flows to the outer surface of sample 1. The cylinder 10 serves as a source of ionized medium, in which the ionized medium is placed coming from the unit 11. The cylinder 10 also circulates the ionized medium. In the tank 12 and again supplied by the unit 11. In the cylinder 10. In the cavity of the cylinder there is a rod 13 made of electrically insulating material. It is provided in the central part with an electrode 14, by means of which sample 1 is connected to the negative pole of a dc generator. The cylinder 10 itself is connected to the positive pole of the generator. The rod 13 covers a large part of the surface of the sample 1, preventing contact with the ionized medium. A narrow slit is formed between the rod 13 and the cylinder 10 in the upper part, through which the ionized medium flows, which washes the sample's annular area - 1 small width, due to the fact that in the upper part, the cylinder 10 has the shape of a truncated cone. Example. The device works as follows. An aqueous solution of potash (KgCOg) at a concentration of 250 g per 1 l is used as the ionized medium, which is loaded into the cylinder 10. The sample in the form of a plate of silicon EEF 0.3 / 0.1 1.25 mm thick and 40 mm in diameter has The resistance is 0.2 Ohm-cm and the electron mobility is 1340 s. The sample is fixed with the help of washers 7 and 8. The immersion depth of the sample into the electrolyte at the periphery is 3 mm, the temperature on the heated surface at the end of heating, the heating time is 5 s, with a voltage across the electrodes of 150 V and surface, 4 A / cm . After heating, the semiconductor wafer, when hot, is removed from the electrolyte and cooled in air. The mobility after treatment was 1800 cm2 / v, which is 34% higher than the original. In the element from the same plate at a distance of 15 mm from the heated surface, the mobility was 1432, which exceeded the initial one by 6.7%. As an ionized medium, a concentrated aqueous solution, NaC2, etc., can be used. their melts or ionized gas at voltages of no more than 300 volts. To reduce the voltage on the electrodes, the single crystal is preheated to a temperature of at least 400 ° C. When semiconductors are heated in a plasma of an ionized medium, the latter are exposed to special, extreme conditions. The heated surface of the sample forms an electrical double layer composed of potassium or sodium ions, which are metals with the properties of highly active surfactants that can significantly reduce the free surface energy. The effect of lower surface energy leads to a change in the physical properties in the entire volume of the sample being processed. I. 1 In addition, the entire electric field of the sample being heated in a plasma-ionized medium is high. If the electric field near the metal surface during the electrolysis process has a voltage of V / cm, then when heated in an electrolyte, the field strength of the cathode is even more significant. The intensity, equal to V / cm, is a consequence of a drop in the voltage of the current at the cathode (UK) of a few volts (usually up to 10-15 V). While with electrolytic heating at the surface of the test, the voltage drop reaches 100-110 V. Thus, short-term treatment of the semiconductor in the plasma of the ionized medium is accompanied by sharply non-uniform and non-standard temperature and electromagnetic fields, which play a decisive role in the processes leading to an accelerated change in the electrophysical properties of alloys and semiconductors. In the considered form of heating, electrical energy is converted at the cathode surface into heat, which enters the sample. The amount of energy entering the sample depends on the voltage drop at the cathode. The temperature on the surface of the sample, the depth of temperature penetration depend on the magnitude of the same energy. a metal in a semiconductor and the rate of increase in temperature at points in the body. Therefore, the temperature on the surface of a semiconductor can vary widely from (B) to the melting point of semiconductors of 936 ° C (germanium) and 1417 ° C (silicon) (IR, 120 V). In the specified temperature range, a state of thermal equilibrium may occur. Thus, for steel 40, the thermal equilibrium temperature of 900 ° C is set at 125 V. The temperature is at 150 V. The field strength and its depth distribution into the sample material also depend on the voltage drop at the surface of the semiconductor. Experimental data show that the mechanical and electrophysical properties of materials depend on the magnitude of the voltage and the duration of the electric field. It is highly inhomogeneous and non-stationary, since the field is concentrated mainly at the surface of the semiconductors and is formed over a certain period of time. For semiconductors, these positions are confirmed by a number of experimental data. For example, the type of conductivity of silicon was determined by means of heating in an electrolyte using the thermo-emf method. At the same time, it turned out that the type of conductivity, measured after local short-term heating (2-3 s) in the electrolyte, is directly opposite in comparison with heating by the conventional method (thermal probe). Thus, a p-type silicon wafer when heated in an electrolyte was defined as n-type and vice versa. After cooling the plate, the reversible conductivity effect disappears. In germanium, after heating in an electrolyte, the type of conductivity also varies, but with its own characteristics. If, after local heating in a p-type electrolyte in silicon, it becomes p-type semiconductor, and p-type becomes p-type, then n-type germanium, after local heating, does not change the type of conductivity in the electrolyte,

p-type germanium after the same heats the type of conduction to the opposite, i.e. on p-type. As a result of the conventional heat treatment of germanium, the transformation of an n-type semiconductor into a p-type is observed. This is a long process at high temperature in an atmosphere of gels. But the possibility of transforming a p-type semiconductor into a p-type semiconductor by thermal processing is unknown. . ;

Thus, the obtained data on the conversion of silicon i-germanium after local heating of fl electrolyte ea 2-3 s up to temperature ZOO-BOO C is a direct evidence of the influence of the electromagnetic field on significant changes in the structure of semiconductors.

The reversible transformations of semiconductors according to the type of conductivity result in irreversible changes in their electrophysical properties, for example, r to a change in charge carrier mobility. Therefore, a comparative method for measuring the mobility of charge carriers was used to evaluate the results of thermal processing of silicon semiconductors of pi p-types.

Measurement of mobility and resistivity in the elements was carried out on semiconductor ones. silicon wafers G using the Hall effect of the modernized method Va.n-der-11au (figure 4).

On the surfaces of the samples, 4 a were deposited by vacuum deposition; luminescent contacts along the vertices of the square. In this slone, the individual semiconductor resistance

| , RA "b | Rftcj A; d „..

semiconductor wafer thickness; p U "gt uba

 KASS carrier mobility; charge

.j., d ugbifto

. hr t p,

where B is magnetic field induction; the change in resistance due to the magnetic field B,

When measuring the sample before heat treatment

Ab Zva Zyo Oma-, Lmtl, UAc 6M &

UA.O change under the action of the magnetic field AAD 2.15 mV;

2.15

0.215 ohm; Ueu, iSk bliAo - 1Q

 350 mV; d 1.25 mm; R

VSVA Om.

Resistivity

1 pz (35 + 35.

3.a4

1.25 1U (2

0.694

 2-10 ohm-m 0.2 ohm-cm. Carrier mobility

Of215 U-MI 2.10-3 U / J.J4

The sample after heat treatment was measured in the same modes. In this case, only d Pdo / which was 2.2 mV changed. The same calculations performed determined the carrier mobility, which turned out to be equal to 1800 CMVB-c, i.e. increased by 34%

Depending on the technological modes of heat treatment, various samples showed an increase in mobility of 6.74%; 2.75% and 18.7%.

Thus, from the given data it follows that the proposed

The processing method is significantly different from the known methods for heat treatment of semiconductors. By known methods, crystals are completely heated to 900 ° C and higher temperatures, diffusion processes occurring at high temperatures in semiconductors play a major role, and the electric field applied in individual cases is a secondary role

for the directional movement of elementary particles. These. types of heat treatment for ten hours. According to the proposed method, the main role in the structural changes is played by the electromagnetic field, which accompanies the local heating of semiconductors to 300–500 ° C in an ionized medium. The duration is only 3-7 seconds.

.

The proposed method of heat treatment of semiconductors allows one to control the change in the mobility of charge carriers within certain limits by varying the voltage on the electrodes, the concentration of the ionized medium of the contact surface of the semiconductor with the ionized medium, and the distance between the electrodes.

Claims (2)

. 1. The method of heat treatment of semiconductors, including heating the sample and the influence of an electric field on it, characterized in that, in order to increase the mobility of current carriers, the treatment is carried out in an ionized medium when a voltage of not more than 300 V is passed through the sample. 2. A device for heat treatment of semiconductors, including a container for placing a sample ^ equipped with means for supplying electric current, and a heater, which includes the fact that, in order to increase the mobility of current carriers, the device is equipped with a cylinder for of the ionized medium, which is installed under the container, an electrically isolated electrode is placed inside the cylinder axis, and in the upper part the cylinder has the shape of a truncated cone for supplying the ionized medium around the periphery of the sample.