JP2607191B2 - Method for measuring deep impurity levels in semiconductors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a deep impurity level in a semiconductor.

[0002]

2. Description of the Related Art Deep impurity levels in a semiconductor greatly affect the characteristics, reliability and deterioration of the semiconductor. In recent years, with the increase in the density of semiconductor integrated circuits, very high sensitivity has been achieved regarding the electrical characteristics of various defects generated during the semiconductor manufacturing process due to ion implantation, thermal neutron doping, etc. or defects present in crystals themselves. In addition, there is a need to easily and accurately measure dynamic properties.

As one of those requirements, there is a method for measuring a deep impurity level of a semiconductor (hereinafter, referred to as a DLTS measurement method) proposed by Lang. FIG.
1 shows an apparatus for performing a DLTS measurement method. In this figure, reference numeral 1 denotes a cryostat, in which a semiconductor 2 as a sample is provided. Reference numeral 3 denotes a temperature sensor for detecting the temperature near the semiconductor 2 in the cryostat 1. The output of the sensor 3 is input to a temperature controller 4, and the temperature in the cryostat 1 is set to a desired temperature based on the output. Reference numeral 5 denotes a transient capacitance meter for measuring a change in the capacitance of the semiconductor 2, and has a built-in transient converter. 6 is a computer as a signal processing device, and 7 is an output device.

According to the Lang's method for measuring DLTS, a bias pulse as shown in FIG. 3A is applied to the semiconductor 2 using the above-described apparatus, and the semiconductor 2 is filled with a large number of carriers.
With the falling of the bias pulse, a transient change output of the semiconductor junction capacitance as shown in FIG. Then, in the computer 6, the transient change output is multiplied by a weighting function signal having a narrow pulse width t ₁ , t ₂ called a double boxcar type as shown in FIG. , And a product thereof to obtain a deep impurity level signal (hereinafter, referred to as a DLTS signal).

In FIG. 3, V ₀ is the bias pulse voltage, V _R is the reverse bias voltage, T ₁ is the bias pulse application time (pulse width), C ₁ is the junction capacitance when the bias pulse is applied, ∞ is the junction capacitance in the steady state achieved after application of the reverse bias voltage, and C ₀ is from V ₀ to V
The junction capacitance immediately after the application of the reverse bias voltage to _R , C ₀ ′, is the minimum junction capacitance obtained from the response characteristics of the capacitance meter relay.

[0006] Such a Lang's DLTS measurement method is different from other conventional methods in that detection sensitivity, measurement speed, ease of analysis, and measurement by separating two or more deep impurity levels. There are excellent advantages such as being able to. However, in this measurement method, if the device is constituted only by analog, the temperature of the device becomes extremely high because a double box car is used. Further, there is a disadvantage that the S / N of the DLTS signal is not sufficient.

On the other hand, Kimerling
Has proposed a DLTS measurement method using a lock-in amplifier. In this method, one cycle of the bias pulse as shown in FIG. 3 (D) is defined as one cycle T ′, and a rectangular wave weighting function signal which rises when the bias pulse rises is used and obtained from the transient capacitance meter 5. This is a method of obtaining a DLTS signal output by multiplying a transient change output of the semiconductor junction capacitance by a weighting function as shown in FIG.

In such a method for measuring chimering, the equipment is relatively inexpensive and the S / N of the DLTS signal output is improved. However, in this measurement method, a procedure such as determination of a certain constant is required in order to obtain data such as a trap level obtained from the obtained DLTS signal, which complicates data analysis and makes the transient capacitance meter 5 There is a drawback that an error due to responsiveness is mixed in and the error is not easily separated.

[0009] To solve the above-mentioned drawbacks of the conventional measuring method, a DLTS disclosed in Japanese Patent Publication No. 58-10853 is disclosed.
There is a measurement method. According to this method, as a weighting function signal, a continuous time (T ₁ + T _d ) of the sum of the application time T ₁ of the bias pulse and the expected response time T _d of the transient capacitance meter 5 as shown in FIG. A signal that rises to zero and rises after the expected response time _Td and changes in a rectangular waveform, and changes from the expected response time _Td to the rising of the next bias pulse in one cycle is used.

However, in the method described in this publication, the weighting function needs to be determined so that the definite integration becomes zero. When applying the weighting function to discrete data, the measurement procedure is complicated and the measurement accuracy is not good, for example, extremely complicated operation is required to make the definite integral zero. There is such a disadvantage.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned matters, and an object of the present invention is to provide a method for measuring a deep impurity level of a semiconductor which has an excellent numerical integration accuracy and a simple measurement procedure. Is to do.

[0012]

In order to achieve the above object, in the present invention, a bias pulse is applied to a semiconductor, and a transient capacitance meter measures a transient change in a semiconductor junction capacitance caused by a fall of the bias pulse. In a method of measuring a deep impurity level of a semiconductor by obtaining a deep impurity level signal by multiplying the transient change output obtained from this transient capacitance meter by a weighting function signal, the weighting function signal, After the transient capacitance meter response time,
A signal that changes in a triangular wave shape that can be defined by defining a point is used.

[0013]

In the semiconductor deep impurity level measuring method according to the present invention, a triangular wave signal changing as shown in FIG. 1B is used as a weighting function signal to be multiplied by a transient change output obtained from a transient capacitance meter. Used. Therefore, the place where the weight is applied becomes the largest in absolute value at both ends of the area of the weighting function, so that the waveform separation is performed well. Also, since the area of definite integration at the time of waveform processing is determined only by the points at both ends of the weighting function, it is not necessary to perform integration by dividing the integration interval as in the method described in the above-mentioned publication. Is easy. The accuracy of numerical integration is good, and the area of definite integration of the square of the weighting function is large, so that the S / N is greatly improved.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

The method for measuring the deep impurity level of a semiconductor according to the present invention uses the same apparatus as that shown in FIG. 2, but uses a transient function as a weighting function to be multiplied by the transient output obtained from the transient capacitance meter 5. The difference from the conventional method is that a signal that changes in a triangular waveform, which can be defined by defining any two different points after the response time of the capacitance meter 5, is used.

In the measurement, a transient capacitance waveform of the semiconductor 2 is collected while changing the temperature of the semiconductor 2 at a constant rate.
FIG. 1A is a diagram showing an example of a waveform of the transient capacitance obtained at this time. In this figure, the horizontal axis represents time t, and the vertical axis represents transient capacitance C (t). Since the transient capacity meter 5 has a built-in transient converter, a digitized transient waveform is sent to the computer 6 and stored in the memory. Then, the computer 6 multiplies the digitized transient waveform by a weighting function w (t) that changes like a triangular wave, as shown in FIG.

[0017] That is, a plurality of transient waveforms stored inside the computer 6 data C _1, C _2, with respect ... C _n,
The following calculations are performed respectively.

[0018]

(Equation 1)

[0019] Thus, rate window t _r at a certain temperature T, DLTS signal at t _j (hereinafter, DLTS
(Referred to as (T)) is calculated. By performing this for a plurality of rate windows, a plurality of DLTS (T)
Is obtained. By plotting this data against the temperature T to be swept, a DLTS waveform can be obtained.

[0020]

As described above, in the method of the present invention, since a signal that changes in a triangular wave shape is used as the weighting function, the place where the weight is applied is the absolute value at both ends of the area of the weighting function. Since it is the largest, waveform separation is performed well. In addition, since the area of definite integration at the time of waveform processing is determined only by the points at both ends of the weighting function, it is not necessary to divide the integration section and perform integration, thereby simplifying the procedure. The accuracy of the numerical integration is good, and the area of the definite integral of the square of the weighting function is large.
Is greatly improved. As a result, highly accurate measurement can be easily performed.

The method of the present invention can be applied not only to DLTS measurement but also to ICTS (isothermal transient capacitance measurement) method.

[Brief description of the drawings]

FIG. 1A is a diagram showing an example of a waveform of a transient capacitance, and FIG. 1B is a diagram showing a weighting function used in the present invention.

FIG. 2 is a diagram showing a configuration of an apparatus for implementing a method for measuring a deep impurity level of a semiconductor.

FIGS. 3A to 3E are diagrams for explaining a conventional technique.

[Explanation of symbols]

 w (t): weighting function.

Claims (1)

(57) [Claims] 1. A bias pulse is applied to a semiconductor, and a transient change in a semiconductor junction capacitance caused by a fall of the bias pulse is measured by a transient capacitance meter, and a weight is assigned to a transient change output obtained from the transient capacitance meter. In a method of measuring a deep impurity level of a semiconductor by obtaining a deep impurity level signal by multiplying a weighting function signal, as the weighting function signal,
A method for measuring a deep impurity level in a semiconductor, comprising using a signal that changes in a triangular wave shape that can be defined by defining any two different points after the response time of the transient capacitance meter.