RU2309417C2 - Method for detecting potentially unreliable bipolar transistors - Google Patents

Abstract

FIELD: micro-electronics, namely, ensuring of reliability of a batch of bipolar transistors due to detection of potentially unreliable devices, possible use during production and during usage.

SUBSTANCE: method for detecting potentially unreliable bipolar transistors includes measuring low frequency noise of transistor, which is performed at two transitions emitter-base, collector-base at two current values, and decision of reliability of devices is made on basis of quality control criterion B, determined as

, where I₁, I₂ - current power values, U² _ne1, U² _ne2 - square voltage of emitter-base transition noise with current power respectively for first and second values; U² _nc2 - square voltage of collector-base transition noise with current power for second value.

EFFECT: increased trustworthiness of method, simplification of method due to measurement of different transitions of one and the same transistor.

Description

The invention relates to microelectronics, and in particular to ensuring the reliability of batches of bipolar transistors by identifying potentially unreliable devices, and can be used both at the production stage and in application.

There is a known method [1], by which, finding the criterion of the noise parameter and rejecting transistors with high noise values, it is possible to filter out all potentially unreliable devices, but including up to 15% reliable ones.

A method for rejecting transistors by noise is based on the fact that the low-frequency noise generated in a transistor with a direct current is used to diagnose potentially defective devices. The transistor under study is compared in terms of noise level with a control "defect-free" transistor and in terms of a significant difference in noise values, the transistor is rejected as potentially unreliable.

The disadvantage of this method is its low reliability due to a comparison of the noise of different transistors.

A known method for detecting latent defects in linear integrated circuits, based on the measurement of impulse noise [2], the disadvantage of which is that impulse noise is observed only in linear integrated circuits, but not in transistors [3].

Closest to the proposed is a method of rejecting potentially unstable semiconductor devices [4], adopted as a prototype.

The prototype method consists in the fact that after measuring the intensity of the noise in the operating mode, a current pulse is passed through the device, 1.5-5 times higher in amplitude than the maximum permissible value of the current pulse in the steady state, and then the noise intensity is measured again. The relative magnitude of the change in noise intensity determines the potential instability of semiconductor devices.

The disadvantage of this method is the need for a current pulse exceeding the value acceptable by the technical conditions, which can cause irreversible changes in the structure of the device.

The invention is aimed at increasing the reliability of the method and its simplification due to the fact that different transitions of one transistor are measured.

This is achieved by the fact that in the method for determining potentially unreliable bipolar transistors, which consists in measuring the low-frequency noise of the emitter-base (E-B) and collector-base (K-B) transitions at bipolar transistors at two operating current values, according to the invention the potential reliability of the device is judged by the value of the rejection criterion B, which is defined as

where I ₁ , I ₂ are the values of current,

U ² _ШЭ1 , U ² _ШЭ2 - squared voltage of the noise of the transition E-B with current strength, respectively, for the first and second values;

U ² _ШК2 is the square of the noise voltage of the K-B transition for the second value of the current strength, while the critical value In _{cr is} set experimentally for each type of device.

The physical meaning of the rejection criterion B is the current strength at which the relative magnitude of the difference in the low-frequency noise of the transitions is maximum.

The potential reliability of the device is judged by the value In _cr determined experimentally for each type of device.

The noise was measured in the diode mode for the E-B and K-B junctions, at a direct current of 5 and 10 mA using a direct measurement setup, at a frequency of 1 kHz, after which the signal was detected by a quadratic detector and measured with a digital voltmeter. These current values were chosen because the dependences of the ampere-noise characteristics, determined at currents of 5, 10, 20, 30, 50, showed that the largest spread in low-frequency (LF) noise occurs at currents of 5 and 10 mA.

An example implementation of the method.

At 15 transistors KT3107A, the noise intensity at the transitions E-B and K-B was measured by random sampling and found the value of the rejection criterion B. The data are shown in the table.

Table
Noise intensity of various transitions N p / p Noise intensity U ² _Ш , mV ² , transitions The value of the rejection criterion, mA Eb KB at 10 mA 5 mA 10 mA one 47 67 62 1.25 2 49 69 63 1.5 3 51 73 64 2.05 four fifty 65 63 0.66 5 57 68 65 1.36 6 51 69 66 0.83 7 49 72 66 1.3 8 53 70 67 0.88 9 48 64 60 1.25 10 51 66 61 1.66 eleven fifty 67 64 0.88 12 46 71 68 0.6 13 52 73 69 0.99 fourteen 49 70 66 0.95 fifteen 51 68 67 0.29

Accepting, for example, In _cr ≥2, we obtain that the transistor N3 is potentially unreliable, and having adopted B≤0.5, we select a transistor of increased reliability - N15.

This is due to the fact that in a single technological cycle for a manufactured batch of transistors, the noise parameters determined by surface and volume defects differ significantly between different transistors, which indicates the presence of large violations in the structure of transistors that reduce their reliability.

Information sources

1. Gorlov M.I., Anufriev L.P., Bordyuzha O.L. "Ensuring and improving the reliability of semiconductor devices and integrated circuits in the process of mass production." Minsk: Integral. 1997.390 s.

2. USSR author's certificate N1347050, G01R 31/28.

3. Van der Zeal "Noise (sources, description, measurement)." M .: Sov. radio. 1973.- 229 p.

4. Copyright certificate of the USSR N490047, G01R 31/26.

Claims (1)

A method for determining potentially unreliable bipolar transistors, namely, that bipolar transistors measure the low-frequency noise of the emitter-base (E-B) and collector-base (K-B) junctions at two operating currents, characterized in that the potential reliability of the device judged by the value of the rejection criterion B, which is defined as

where I ₁ , I ₂ - current strength values, U ² _ШЭ1 , U ² _ШЭ2 - squared noise voltage of transition E-B with current strength, respectively, for the first and second values; U ² _ШК2 is the square of the noise voltage of the K-B transition for the second value of the current strength, while the critical value In _{cr is} set experimentally for each type of device.