JPS5948542B2 - Method for measuring deep impurity levels in semiconductors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for measuring deep impurity levels contained in a semiconductor, and the present invention relates to improving a method for measuring deep impurity levels contained in a semiconductor.
And it is designed to be easily obtained.

To measure deep impurity levels, there is a method of examining the time change in capacitance based on the depletion layer in a pn junction or Schottky barrier.Recently, various measurement methods based on this principle have been proposed, and semiconductor evaluation technology has improved. is being run as.

In these measurement methods, the time constant of the temporal change in capacitance is directly determined by the thermal radiation rate (emission) of deep impurity levels.
It is based on the assumption that it corresponds to the reciprocal of the rate), and therefore, in reality, the time change in capacitance, dC, is directly converted into the time change in voltage, and a signal is measured and analyzed. Measurements are made by As a specific example of this type of conventional measurement method, the case of a pn junction will be described.

The electric capacitance Co due to the depletion layer of the p''n junction when applying the reverse bias VR is C''←゜■qksε.

A″N, O/ 2 (VD + VR) (1) where q is the amount of charge, and ε is the dielectric constant of the semiconductor forming the p″’n junction. A is the cross-sectional area of the joint,
N and O are the net ionized impurity concentrations in the depletion layer, and qVD is the diffusion potential. Now, if we apply an injection pulse of minority carriers or majority carriers to the junction in this state and then calculate the change in capacitance Δc() in seconds, we get ΔC()■Co((1+ΔN
, (wo)/N, O)”-1)・・・・・・・・・・・・
(2) Or, if ΔNi()<Nlo, approximately ΔC()■ -ΣΔN2() 2N, oi =-ΣΔN, O(O)exp(--)...・
...(3) Given by 2N10iτ1.

Here, ΔNi(O) is the value of ΔN, () when = 0, and τ is the thermal radiation rate at the i-th impurity level (this value for electrons and holes is en and ep, respectively). is given by the time constant (defined by ).

In this way, Equation (2) or Equation (3) shows that the time constant of the change in capacitance over time is directly the reciprocal of the heat radiation rate of the deep impurity level τ''.

Therefore, conventionally, first, the time change in capacitance Δc (t)
This was directly extracted as a signal converted into a voltage change over time, and this was used to determine the heat radiation rate of deep impurity levels using an appropriate analysis device. At this time, the following two methods, which are broadly classified, have been adopted as signal analysis methods. First, the analog signal ΔC(t
) is analyzed in an analog manner by selecting only the values of certain times T and T2, and is an analysis method generally called the DLTS method.

Another method is to obtain information by converting an analog signal into a digital signal through an A/D converter, storing this value in a computer, and analyzing it. This method is called the ICTS method. It is being

A major feature of the DLTS method is that the distribution profile within the energy gap of deep impurity levels is determined by continuously changing the temperature of the sample, which makes it easy to obtain the desired profile. There is an advantage.

However, continuously changing the temperature is a big problem in terms of measurement accuracy, and it is also difficult to automate the measurement. On the other hand, the ICTS method is a method proposed to improve the shortcomings of the above-mentioned DLTS method.
This method obtains the profile of the impurity level in the gap at a constant temperature without continuously changing the temperature, but although it has many advantages, it is not possible to use a wide range of methods such as the DLTS method due to the capabilities of current measuring instruments. Not suitable for measuring energy distribution.

As described above, at present, the DLTS method is suitable for simply determining the energy distribution, and the ICTS method is suitable for accurately determining parameters of deep impurity levels.

In view of the above points, it is an object of the present invention to provide a novel measuring method in which both methods can be performed simultaneously.

The present invention will be explained below. The attached drawings show an example of an apparatus for carrying out the present invention, in which S is a sample, 1 is a pulse generator that generates a voltage pulse or a light pulse and applies it to the sample S, 2 is a transient capacitance meter, and 3 is a signal aperture. 4 is an X-Y plotter that records the output of the amplifier 3 relative to the temperature of the sample S.

The measuring section I using the conventional DLTS method is configured as described above.
Also, 5 is a high-speed A/D converter, 6 is an interface, 7 is an electronic computer, 8J is a display device, and 9 is an A/D converter.
/D converter, and these constitute a measuring section 11 based on the conventional ICTS method. Next, the operation will be explained.

First, let Δc (t) on the left side of equation (2) be
A light pulse or a voltage pulse is extracted from the pn junction or shot barrier to which the reverse bias voltage VR is applied by applying it from the pulse generator 1.

This itself can be used with the conventional transient capacitance meter 2 or other Δc (t
) or c (t) by using a capacitance meter. By using an amplifier 3 such as a signal averager or a locking amplifier for the analog signal c(t) taken out from the transient capacitance meter 2, a certain predetermined time T and T are obtained.

The signals of capacitances c(T,) and C(T.) at The signal is recorded on the X-Y plotter 4 to obtain a so-called DLTS signal. This is the same as the conventional DLTS method, but in the present invention, the above DLTS method is the same as the conventional DLTS method.
By analog method, the time-varying signal of capacitance is processed using temperature as a parameter to measure the number of types of impurity levels, and from this we can grasp the outline of deep impurity levels in the semiconductor, and then The temperature of the semiconductor sample is maintained at a temperature at which the type of impurity level that is desired to be precisely measured among the number of types of impurity levels is maintained, and at the same time, the analog signal from the transient capacitance meter 2 is passed through the high-speed A/D converter 5. The digital signal is converted into a digital signal, which is recorded in an electronic computer 7 capable of waveform analysis via an interface 6 with a built-in microcomputer, and the parameters of the deep impurity level are calculated based on equation (4). The result is displayed on the display device 8.

This is the ICTS signal obtained by the ICTS analysis method. The dotted line in the figure is a control line. In addition, in Figure 1, DL
To facilitate analysis using the TS method, an X-Y plotter 4
It is also possible to simultaneously input the signals input to the electronic computer 7 via the A/D converter 9 and analyze them digitally.

In the above 1CTS method, it is possible to accurately obtain information on the impurity level determined by two conditions: the set temperature and the transient response speed of the transient capacitance meter 2, but usually there is only one type of impurity level information determined by the response speed of the transient capacitance meter 2. It is difficult to measure two or more types of impurity levels at the same time.

However, a measurement in which information on impurity levels is obtained by changing the set temperature requires a huge number of measurements and a huge amount of time for one sample. Therefore, in the present invention, DLTS
ICT method is used to measure the number of types of impurity levels by changing the set temperature of the sample, and after understanding the outline of the impurity levels.
Since the S method is applied, the set temperature is already determined when the ICTS method is applied, so the measurement time is significantly shortened.

As described above, the present invention first uses temperature as a parameter for an unknown sample using the DLTS method, which handles the change signal of the capacitance of the depletion layer of a semiconductor Pn junction or shot barrier junction in an analog manner. An IC that measures the number of types of deep impurity levels and then digitally handles the capacitance change signal and makes full use of an electronic computer.
Using the TS method, the sample is kept at a temperature at which the required impurity level can be measured among the number of types of impurity levels determined above, and the concentration, energy position, and capture cross section of that impurity level are determined. Therefore, it is possible to effectively use the features of each, and compensate for the weaknesses of each.
Compared to the case where both methods are used alone, there is an advantage that the desired measurement can be carried out in a much shorter time and with higher precision.

[Brief explanation of the drawing]

The drawing is a plotter diagram showing an example of an apparatus for carrying out the present invention. In the figure, S is the sample, 1 is the pulse generator, 2 is the transient capacitance meter,
3 is an amplifier, 4 is an X-Y plotter, 5 is a 7 high-speed A/D converter, 6 is an interface, 7 is a computer, 8
is the display device, 9 is the A/D converter, and I is the DL.
11 is a measuring section based on the TS method; and 11 is a measuring section based on the ICTS method.

Claims (1)

[Claims] 1. When measuring information about deep impurity levels in a semiconductor from changes in the capacitance of the depletion layer of a pn junction or Schottky barrier junction of a semiconductor, first, the capacitance is measured using temperature as a parameter using the DLTS method. The time-varying signal is processed in an analog manner to measure the number of types of impurity levels, and then the ICTS method is used to measure the required impurity level among the number of types of impurity levels determined above. A method for measuring deep impurity levels in semiconductors, which is characterized by determining the temperature, energy position, and capture cross section of the impurity levels.