JP2596023B2 - Evaluation method of semiconductor photo detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for evaluating the output characteristics of a semiconductor light-receiving element. The object of the present invention is to evaluate the linearity of the output characteristics in a state of a wafer or a chip and to reduce the manufacturing cost. Determining in advance the correlation between the output characteristic of the photocurrent with respect to the incident light intensity and the relationship between the capacitance value of the element and the reverse bias voltage between the P electrode and the N electrode of the element; Measuring a capacitance value for a specific value of the reverse bias voltage, and evaluating the measured capacitance value by referring to the correlation to determine whether the output characteristic of the semiconductor light receiving element is linear or non-linear. And a step of determining

A step of obtaining in advance a correlation between a photocurrent output characteristic with respect to an incident light intensity of the semiconductor light receiving element and a relation of a series resistance value of the element with respect to a reverse bias voltage between a P electrode and an N electrode of the element; Measuring a series resistance value of the target semiconductor light receiving element with respect to a specific value of the reverse bias voltage; and evaluating the measured series resistance value by referring to the correlation to obtain the output of the semiconductor light receiving element. The method is characterized by including a step of determining whether the linearity of characteristics is good or bad.

[Industrial applications]

The present invention relates to a method for evaluating output characteristics of a semiconductor light receiving element.

Recently, optical fiber communication has been put to practical use, and a semiconductor light receiving element (photodiode) used for the optical fiber communication has been developed.
Are expected to further improve quality and reduce costs.

[Conventional technology]

Various semiconductor light-receiving elements (photodiodes) made of silicon, germanium, compound semiconductors, etc. are used. For example, an InGaAs-based light-receiving element is known as a semiconductor light-receiving element having high light-receiving efficiency for light in a wavelength of 1.3 μm band. Have been. FIG. 4 is a cross-sectional view of the PIN type InGaAs light receiving element, wherein 1 is an n-InP substrate, 2 is an n-InP buffer layer, 3
Is an n-InGaAs light absorbing layer, 4 is an n-InP cap layer, and 5 is a p-
The light receiving region, 6 is a p-electrode, 7 is an n-electrode, and when light is incident on the p-light receiving region 5 by applying a reverse bias voltage between the electrodes,
The structure is such that electrons and holes are excited in the n-InGaAs light absorbing layer 3, photocurrent flows through the pn junction, and the output is detected.

Now, one of the important characteristics of the light receiving element as described above,
The linearity of light output (linearity; lin) to determine whether a photocurrent output proportional to the intensity of the incident light is obtained.
earity). FIG. 5 is a diagram showing the conventional linearity measurement method, in which 11 is a light receiving element, 12 is a temperature controller, 13 is a light emitting element, 14 is an attenuator, 15 is an optical fiber, 16
Is an output meter. For example, assuming that the light receiving element is used at a low temperature, the temperature of the temperature controller 12 is set to −40 ° C., and light from the light emitting element 13 is transmitted through the optical fiber 15 via the attenuator 14 to the light receiving element 11. When it is incident on the light emitting element
The current output of the light receiving element 11 with respect to the light energy from 13 is obtained. In general, a current output is represented by electric power as a product of a photocurrent and a bias voltage.

The light energy of such a light emitting element 13 is attenuated.
Switch with 14 to change the amount of light incident on the light receiving element 11,
FIG. 6 shows output characteristics in which the current output (watt) of the light receiving element 11 is plotted against the incident light power (watt). In FIG. 6, when the current output increases in proportion to the incident light power, it means that the linearity is good. Curve I shown by a solid line is a light receiving element (good product) having good linearity, and curve II shown by a dotted line Is a light receiving element (defective product) with poor linearity because the linearity is broken at low incident light power. Conventionally, since detecting a curve as shown in FIG. 6 requires a lot of man-hour, a method of measuring three specified points on the curve is usually employed. And the light receiving element 11
Since the linearity changes depending on the temperature of the light-receiving element, the temperature controller 12
11 are stored.

[Problems to be solved by the invention]

By the way, the conventional measuring method shown in FIG. 5 is a completed product in which the light receiving element 11 to be measured is incorporated in a package. If the linearity is measured and the product is defective, the assembled product is discarded. In such a case, the number of assembling steps is wasted, and the manufacturing cost increases accordingly.

Accordingly, the present invention proposes an evaluation method for solving such a problem and evaluating linearity in a state of a wafer or a chip to reduce manufacturing cost.

[Means for solving the problem]

The object is to obtain in advance a correlation between the output characteristic of the photocurrent with respect to the intensity of the incident light of the semiconductor light receiving element and the relationship between the capacitance value of the element and the reverse bias voltage between the P electrode and the N electrode of the element. Measuring a capacitance value of the semiconductor light receiving element to be evaluated with respect to a specific value of the reverse bias voltage; and evaluating the measured capacitance value by referring to the correlation to obtain the output characteristic of the semiconductor light receiving element. This is achieved by a method for evaluating a semiconductor light receiving element having a step of determining whether the linearity is good or bad.

In addition, the purpose is to obtain in advance the correlation between the output characteristic of the photocurrent with respect to the incident light intensity of the semiconductor light receiving element and the series resistance of the element with respect to the reverse bias voltage between the P electrode and the N electrode of the element. A step of measuring a series resistance value of the semiconductor light receiving element to be evaluated with respect to a specific value of the reverse bias voltage; and evaluating the measured series resistance value by referring to the correlation. This is achieved by a method for evaluating a semiconductor light receiving element, which comprises a step of determining whether the linearity of the output characteristic of the element is good or bad.

(Operation)

That is, the output characteristic of the photocurrent with respect to the incident light intensity of the semiconductor light receiving element is previously obtained from the reverse bias voltage dependency of the capacitance, and the capacitance value for the specific value of the reverse bias voltage of the semiconductor light receiving element is obtained. It is possible to evaluate the linearity of the output characteristics of the semiconductor light receiving element, and to obtain the output characteristics of the photocurrent with respect to the incident light intensity of the semiconductor light receiving element in advance from the dependence of the series resistance on the reverse bias voltage. By determining the value of the series resistance for a specific value of the reverse bias voltage of the device, it is possible to evaluate the linearity of the output characteristics of the semiconductor photo detector.

〔Example〕

Hereinafter, embodiments will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a method for measuring the bias voltage dependency of the capacitance or the bias voltage dependency of the series resistance according to the present invention, wherein 21 is a wafer, 22 is a substrate stage, 23 is an LCR meter, 24 is a computer, 25 is a plotter. Then, the prober 26 is brought into contact with the p-electrode of one chip (element) in the wafer 25, and a bias is applied between the prober 26 and the substrate stage 22 (which is in contact with the n-electrode on the back surface of the wafer). Apply voltage.

Then, the bias voltage dependency of the capacitance measured by adding the signal current modulated at the frequency of 1 MHz and the amplitude voltage of 10 mV is processed by the computer 24 and recorded on the plotter 25. 2 (a) and 2 (b) exemplify the measurement results of the dependence of the capacitance on the bias voltage. FIG. 2 (a) shows a light receiving element with poor linearity, and FIG. 2 (b) shows good linearity. It is an example of a light receiving element. From Figure 2,
When the values of the capacitance (PF) at a reverse bias voltage of 1 V are listed, the capacitance of the light receiving element having poor linearity in FIG. In FIG. 2B, the capacitance of the light receiving element having good linearity is 42.15PF, 44.12PF, 41.74PF, 44.62PF, 44.66PF.

Therefore, in the above embodiment, if the capacitance at a reverse bias voltage of 1 V is detected, the light receiving element having a small capacitance has good linearity, the light receiving element having a large capacitance has poor linearity, and the linearity of output characteristics (linearity) It is possible to evaluate It should be noted that the linearity amount / defectiveness is detected by the conventional measuring method for the assembled product after the above-described measurement.

Next, the bias voltage dependence of the series resistance measured under the same measurement conditions will be described.
3B shows a measurement result of the bias voltage dependence of the series resistance. FIG. 3A shows an example of a light receiving element having good linearity, and FIG. 3B shows an example of a light receiving element having poor linearity. From FIG. 3, when the value of the series resistance (Ω) at the forward bias voltage (V) is described, in the case of a light receiving element having good linearity, On the other hand, in the case of a light receiving element with poor linearity, Therefore, a significant difference is clearly seen, and the light receiving element having a large series resistance has poor linearity, and the light receiving element having a small series resistance has good linearity.

Therefore, according to the present invention, it is possible to evaluate the linearity of the output characteristics in the state of a wafer at room temperature without using a temperature controller, so that only a non-defective product of linearity can be evaluated without assembling a defective product of linearity. It can be assembled into a finished product to reduce manufacturing costs.

Although the above is an example in which the evaluation is performed in the state of the wafer, it goes without saying that the evaluation can be similarly performed even after the wafer is cut into chips.

〔The invention's effect〕

As is clear from the above description, according to the present invention, the linearity of the output characteristics can be evaluated in the state of a wafer or a chip, which has a remarkable effect in reducing the manufacturing cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a measuring method according to the present invention, FIGS. 2 (a) and 2 (b) are diagrams showing a bias voltage dependency of capacitance, and FIGS. 3 (a) and 3 (b) are biases of a series resistor. FIG. 4 is a diagram showing voltage dependency, FIG. 4 is a cross-sectional view of an InGaAs light receiving device, FIG. 5 is a diagram showing a conventional measuring method, and FIG. 6 is a diagram showing output characteristics of the light receiving device. In the figure, 21 indicates a wafer, 22 indicates a substrate stage, 23 indicates an LCR meter, 24 indicates a computer, 25 indicates a plotter, and 26 indicates a prober.

Claims (2)

(57) [Claims] A step of obtaining in advance a correlation between an output characteristic of a photocurrent with respect to an incident light intensity of a semiconductor light receiving element and a relation of a capacitance value of the element with respect to a reverse bias voltage between a P electrode and an N electrode of the element. Measuring a capacitance value of the semiconductor light receiving element to be evaluated with respect to a specific value of the reverse bias voltage; and evaluating the measured capacitance value by referring to the correlation, and outputting the output of the semiconductor light receiving element. A method for evaluating a semiconductor light receiving element, comprising a step of determining whether the linearity of characteristics is good or bad. 2. A method of obtaining a correlation between output characteristics of a photocurrent with respect to an incident light intensity of a semiconductor light receiving element and a series resistance of the element with respect to a reverse bias voltage between a P electrode and an N electrode of the element. Measuring a series resistance value for a specific value of the reverse bias voltage of the semiconductor light receiving element to be evaluated; and evaluating the measured series resistance value by referring to the correlation to evaluate the semiconductor light receiving element. Determining whether the linearity of the output characteristics is good or bad.