RU1822972C - Method for local measuring resistivity of semiconductors and device for implementation of said method - Google Patents

Abstract

Usage: in technology, namely in the areas of technology in which materials are studied by electrical means, in particular by studying the characteristics of electric discharges. SUMMARY OF THE INVENTION: A voltage sufficient to cause a fat discharge is applied between the semiconductor under study and the probe electrode, which is separated from the surface of the investigated conductor by an air gap, the amplitude of the current in the discharge circuit is measured, and the resistivity of the semiconductor is judged from it. The device contains a flat capacitor with a through hole in the center of its plates. A probe electrode is connected to the lower plate, the tip of which is located in the hole at a distance of 0.1-1 mm from the upper plane of the upper plate, which serves as the base electrode. The studied semiconductor is placed on the base electrode. 2 s.p. f-ly, 1 z.p. f-ly, 2 ill.

Description

The invention relates to a metric of semiconductors, and in particular to its field that examines materials by electrical means, in particular by examining the characteristics of electric discharges.

The purpose of the invention is to increase the reliability of resistivity measurements of semiconductors.

The goal is achieved in that in the known method of local control of the resistivity of semiconductors, based on the application of voltage between the investigated semiconductor

and with a probe electrode pointed at the end, measuring the electric current that arises in this case and determining the resistivity of the investigated semiconductor using a calibration curve, the probe electrode is separated from the surface of the semiconductor by an air gap, the applied voltage is set sufficient to cause a spark discharge in this gap, measuring They determine the amplitude of the current in the discharge circuit and from it judge the value of the resistivity of the semiconductor. In this case, for p-type semiconductors, the voltage polarity between the sample and the probe electrode

set as follows; plus - on the probe electrode, minus - on the sample

The essence of the method is as follows: In the event of a spark discharge in the gap between the tip of the probe electrode and the surface of the semiconductor, a plasma cord forms, which can be considered as an ideal contact to the surface of any semiconductor. The ideal contact is characterized by the fact that the spark discharge plasma wets the surface of the semiconductor, regardless of the quality of its processing, and no mechanical stresses arise.

Part of the voltage U applied between the probe electrode and the test sample falls on the test sample (Uref), and part on the resistance of the plasma cord (l-Ruj)

U Wobr + 1Nsh, (1)

where I is the current in the discharge circuit; Nh - the resistance of the plasma cord.

The current flowing in the sample can be divided into two components (ohmic and injection);

Nom + 1inzh (2)

The ohmic component is determined by the equilibrium charge carriers in the semiconductor, i.e. its resistivity

Р1ом и0бр / Rp (3)

where Rp-p / (2 tag) is the resistance to spreading of a point contact of radius r (in this case, we must substitute the radius of the plasma cord as r).

The injection component of the current is associated with nonequilibrium charge carriers introduced into the semiconductor from the plasma string. This component, in contrast to the ohmic, weak dependent on, takes place even at p '.

The above ratios allow us to relate the resistivity of a semiconductor to the current in the spark circuit:

p 2 tgg Ru

(u / Rm) -i

I engineer

Thus, the possibility of constructing a calibration curve is shown, which will depend on the design of the measuring setup (it determines the values of the parameters r, B, U).

With regard to the injection current, this parameter must be determined for each semiconductor material, taking into account the type of conductivity thereof. If the polarity of the applied voltage matches the type of conductivity of the floor

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of the conductor, as indicated in the formulas for gain plus on the probe rod of a p-type semiconductor, the conditions for single-pulse injection when the plasma arrives in the semiconductor will also be discussed

ONLY UNAUSED WOULD WEAR

the injection current will be redone by the Well time Гм - fp / 4 and there will be no lifetime of nonequilibrium carriers and charges. This provides an unambiguous correlation of the injection current with the specific semiconductor (At a different voltage polarity, the injection current would depend from such a difficult to measure parameter as the time JH of equilibrium charge carriers

When controlling the resistivity of n-type semiconductors, the polarity of the voltage between the sample and the probe type is reversed minus is set on the probe electrode, and plus - on the sample. In this way, the conditions for monopolar injection will be satisfied and an unambiguous relationship between the injection current and the resistivity of the semiconductor will be ensured.

In addition, in order to provide a clear non-destructive test, the polishing resistance is varied, in the nw B-JOJ method described above, there is a game / play, ensuring: o | e. Pulse, ct low current does not lead to thermal erosion of the surface tested by .pr x vodnik

An electrospark flaw detector was chosen as a prototype of the device. This device contains a low-power source of high voltage and the bottom of the electrode, one of which is designed to scan the test insulation coating and the other to contact the metal base of the product. As follows from the sled of the flaw detector, it is not applicable for quantitative measurements, including for measuring the resistivity of semiconductors

The present invention provides a vr device using a spark to measure resistivity at various points in a semiconductor sample. At the same time, the goal of providing non-destructive testing is achieved. To this end, a flat capacitor is connected to the output of the high voltage source, with a through hole in the middle of the bpp, the lining of which serves as the base t i-1 kind, 3 LOWER

dirukchemuzl kgg / t t-

a high impedance resistor and a pulse current detection means connected in series; The tip of the probe electrode is located in the hole of the capacitor at a distance of the order of 0.1 mm from the upper plane of the base electrode.

The design of the device is shown in FIG. 1, FIG. 2 is a graph of the amplitude of current pulses.

A flat capacitor 2 is connected to the output of a high voltage source with high internal resistance 1, with a through hole in the middle, the metal plates of which 2-1 and 2-2 are separated by a layer of insulator 2-3. The top plate 2-1 of this capacitor is simultaneously the base electrode. The bottom plate 2-2 is connected to the probe electrode 5 through the pulse current recording means 3 and the high-resistance resistor 4. The probe electrode is located in the hole of the flat capacitor, while the distance from the electrode tip to the working surface of the base electrode on which the test sample 7 is placed is It is on the order of 0.1 mm. Capacitor b shown in fig. 1 by a dotted line represents the interelectrode capacitance of the resistor 4, which, as will be seen later, plays an important role in the operation of the device.

The device operates as follows.

Capacitor 2 acts as a storage capacitor; when voltage source 1 is turned on, it starts to charge; the high internal resistance of the voltage source provides a relative slowness of this process. At the same time, the potential of the probe electrode 5 with respect to sample 7 also increases, since the probe electrode is galvanically connected to the casing 2-2 of the storage capacitor, and the sample lying on its other casing (2-1) has galvanic and capacitive contact with it . When the potential at the probe electrode reaches a certain (breakdown) value, a plasma cord (spark) is formed in the air gap between the tip of the probe electrode and the surface of the sample, which closes the circuit. A current arises in the sample – storage capacitor – probe circuit. The magnitude of this current is sufficient to maintain the spark mode, since all large resistances in the discharge circuit are shunted by the corresponding capacitors (it is assumed that the resistance of the device for detecting current is negligible):

the contact resistance of the sample-base electrode is bridged by the contact capacitance, the resistor 4 is bridged by its interelectrode capacitance 6. At least 5 of these capacitances (6) completely charge and interrupt the spark discharge after a time of about 10 nsec. Further discharge of the storage capacitor 2 occurs in a non-spark way due to residual

0 ionic conductivity of air. In this case, the discharge current is negligible (less than 1 μA). T O, a current pulse is formed in the probe electrode circuit, the amplitude of which is determined by the resistance

5 of the plasma string, Jb and spreading resistance of the investigated semiconductor Pp. After the discharge is stopped, the capacitor 2 starts to charge again and the probe potential starts to rise again

0 relative to the sample potential. When the potential difference between sample 7 and probe 5 reaches the breakdown value again, a micro spark appears again, and the whole process is repeated again.

5 The invention is carried out as follows.

A device was made, the circuit of which is shown in Fig. 1.

The high voltage source with high internal resistance was made on the basis of the stabilized BC-22 rectifier; the high internal resistance was provided by two 750 MΩ resistors, which were connected in series with the output of the device.

The storage capacitor 2 was made of a sheet foil on both sides of a getinax 1 mm thick, It had the shape of a circle D 50 mm with a hole D 4 mm in

0 center.

A sewing needle was used as a probe electrode.

The resistance of resistor 4 was 150 MΩ, its interelectrode capacitance

5 (plus mounting capacitance) was 2 pF (measured using an E7-8 automatic bridge),

The amplitude of the pulsed current was measured by connecting a 51 Ohm resistor to the bit circuit and registering the voltage incident on it with a CI-65 oscilloscope (in Fig. 1, the device for detecting pulsed current has position 3).

5 On the described device, a series of n-Sl and p-Ge semiconductor wafers were tested. The plates had an area of 1 ... 2 cm and a thickness of 1 mm. The working surfaces of all plates were prepared in an identical way (chalk

grinding followed by etching in a refreshing etchant). A voltage of 2 kV was set on the BC-22 rectifier. The duration of the current pulses ranged from 7 to 20 nsec (depending on the resistivity of the samples) at a repetition rate of several tens of hertz. In FIG. Figure 2 shows the dependence of the amplitude of the current pulses in the discharge circuit on the resistivity for a series of n-Sl samples. The resistivity of each sample was previously measured by the standard 4-probe method (confidence intervals in Fig. 2). In the same figure, the solid line shows the calculation results according to formula (4) for the following values of the fitting parameters: the radius of the plasma cord is g-17 microns; resistance of a plasma cord Riu-3500 Ohm; breakdown voltage U-31 V injection current, 92 mA. As can be seen from the figure, formula (4) well describes the experimental results. This suggests that the physical model considered in which the breakdown voltage and injection current are independent of the resistivity of the semiconductor adequately describes the flow of electric current in the sample during a spark discharge. Studies have shown that this technique works more reliably than a single-probe method with a pressure probe. Good reproducibility of the results and high accuracy of the measurements of resistivity are achieved in comparison with the prototype. The radius of the plasma cord under the conditions of the described experiment was 17 μm; therefore, the inventive method provides high locality at the level of prototype capabilities.

The inventive methods and apparatus provide non-destructive testing of the resistivity of semiconductor materials. This is achieved by the fact that the energy released by the spark in the crystal is CH Ruit 2 10 10 J, which corresponds to the energy density on the surface of the semiconductor W-1500 erg / cm2. Such

lt

the impact, due to its smallness, did not cause any significant disturbances in the surface of the studied samples, which was confirmed by studying the surface of the samples with an optical microscope before and after electric spark measurements. Such a low spark energy was provided both by the size of the gap between the probe and the sample (0.2 mm), and

short duration of a spark current pulse (t 10 nsec), determined by the value of capacitance 6 (interelectrode capacitance of resistor 4). Nondestructive nature

measurement allows the use of the inventive method and device for monitoring the resistivity of thin semiconductor films (a pressure probe destroys thin films).

F o rmul and goiter n and

Claims (3)

1. A method for local monitoring of the resistivity of semiconductors, based on the application of a voltage between the studied semiconductor and the end-pointed electrode, measuring the electric current generated in this case and determining the specific resistance of the studied semiconductor from the calibration curve, characterized in that, in order to increase the reliability of measurements, the probe electrode is separated from the surface of the semiconductor by an air gap, the voltage polarity between the sample and a positive electrode is mounted on the probe electrode for p-type semiconductors, the input voltage is set sufficient to cause a spark discharge in the gap between the probe electrode and the surface of the semiconductor, the amplitude of the current pulse in the discharge circuit is measured and it is used to determine the specific resistance of the semiconductor. 2. The method according to claim 1, characterized in that for n-type semiconductors, the polarity on the probe electrode is set to minus. 3. Device for local control resistivity of semiconductors, including a high voltage source with high internal resistance, a probing electrode, a base electrode and a recording means pulse current in the probe electrode circuit, characterized in that, in order to provide non-destructive testing, a flat capacitor is connected to the output of the high voltage source a through hole in the center of its plates, the upper lining of which serves as the base electrode, and the lower is connected to the probing electrode through a series-connected high-resistance resistor and pulse current detection means and the tip of the probe electrode are located in the capacitor opening at a distance of 0.1-1.0 mm from the upper plane of the base electrode. T MA Figure 1 at Om si