JPS61281570A - Inspection method for semiconductor laser - Google Patents

Abstract

PURPOSE:To decide the nondefectives or defectives of semiconductor-laser wafers by detecting discharge currents generated from the semiconductor-laser wafers by applying pulse-shaped voltage between electrodes. CONSTITUTION:A whole surface electrode is formed onto the surface of a substrate as a semiconductor-laser wafer 5 and partial electrodes 3 onto the surface on the side reverse to the substrate in a striped manner, and the wafer 5 prepared in this manner is connected to an external circuit through a prober 4. The external circuit consists of a power supply 1 and a current detector 2 connected in series with the power supply 1. Pulse voltage is applied to the semiconductor-laser wafer by the power supply 1, and an optical output is detected by a photodiode composed of Ge. When a threshold current value is increased, discharge currents are reduced, and negative correlation is generated. Accordingly, the threshold current values of laser oscillations can be determined under the state of wafers without cleavage by measuring the discharge currents of the semiconductor-laser wafers, thus deciding nondefectives or defectives by the threshold currents values at the step of the wafer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an inspection method for semiconductor lasers, and particularly to an inspection method suitable for determining the quality of a wafer.
1. [Background of the Invention] Conventionally, when investigating the optical characteristics of a semiconductor laser, especially the threshold current value of laser oscillation, a direct current or an alternating current is passed through the semiconductor laser, the emitted light is captured by a detector, and the optical output is measured. The threshold current value for bead oscillation was set at a current of 2.1 current, which rapidly increases. Therefore, unless the laser beam can be extracted, that is, the wafer is expanded and opened to form a reflective surface, the threshold current value of laser oscillation cannot be investigated, and detection at the wafer stage is impossible. Ta.

As a result, even if there are defective parts within the wafer, there is a drawback that it is impossible to determine whether the wafer is good or bad until the process has progressed to a considerably later stage.

[[Physics Op Semiconductor Devices; J.W. Willey & Sons (1981) 75
1 * J (S, M, Sze, Physics of
Sem1conductor 'Devices
+ John Wiley & 8ons+ (198
1) P2S5) ) [Object of the Invention] An object of the present invention is to improve the above-mentioned disadvantages of the prior art and to provide a semiconductor laser inspection method.

[Summary of invention Q]

The present invention is an inspection method for determining the quality of a semiconductor laser wafer based on its size by measuring the discharge current that flows when the charge charged when a pulse voltage is applied to the semiconductor laser wafer is discharged.

[Embodiments of the invention]

Embodiments of the semiconductor laser wafer inspection method of the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit for measuring discharge current. Full-surface electrode 6 on the semiconductor laser wafer 50 substrate surface
, partial electrodes 3 are formed in stripes on the surface opposite to the substrate. The wafer thus produced is connected to an external circuit through the prober 4 □. The external circuit consists of a power supply 1 and a current detector 2 connected in series with the power supply 1. When a pulse voltage indicated by a solid line 7 in FIG. 2 is applied to the semiconductor laser wafer by the power source 1, a current as indicated by a solid line 8 flows. At this time, the negative '#L current indicated by 9 is the discharge current.

Now, the time when the discharge current reaches its minimum value is defined as time zero second. FIG. 3 shows actual measured values of the discharge current of an In, Ga, As, and P buried semiconductor laser at a wavelength of t3μya. The conditions for one pulse of the applied voltage are a frequency of IMHz, a pulse width of 05μ, and 1...Svo is ■. was set to be 10 mA. Figure 4 shows that by changing the partial electrodes contacted by the prober 4,
The discharge currents as shown in Fig. 3 were measured, and the discharge current at time 0 seconds was taken as the vertical axis. After the semiconductor laser wafer was expanded and assembled on the stem, and bonded and bonded, the semiconductor was stored at room temperature. The horizontal axis represents the threshold current value for laser oscillation when a current is passed through the laser and its optical output is detected by a Ge photodiode. The measurement conditions for the discharge current are a frequency of I MHz, a pulse width of 05μ, and a voltage of V. ■. Set so that the current is 10mA. As is clear from FIG. 4, as the threshold current value increases, the discharge current decreases as shown by the solid line 10, and a negative correlation exists. Therefore, by measuring the discharge current, the threshold current value for laser oscillation after the valve is opened can be determined without folding the semiconductor laser wafer, that is, in the wafer state. It can be used as a law. For example, if the semiconductor laser wafer has a threshold current value of 30 or less at room temperature, and if more than 50% of the chips satisfying the above 1 degree condition can be obtained from the semiconductor laser wafer, the semiconductor laser wafer When using the pass/fail judgment criteria, semiconductor laser wafers in which the discharge current at time zero is 8 mA or more at a rate of 50% or more may be accepted.
11 (In the above example, the applied voltage and current conditions were set to a frequency of IFJHz and a pulse width of 0.5/j
Formula r I (1-10 mA, but the applied voltage is v, (v
) state where the current is constant ■. The applied voltage pulse conditions may be arbitrary as long as the voltage appears within the range. Regarding the discharge current, the relationship between the value at time zero and the threshold current value was taken, but the time may be arbitrary as long as it is greater than zero and before the time when the next voltage pulse is generated.

〔Effect of the invention〕

As explained above, according to the present invention, by measuring the discharge current of the laser wafer of the semiconductor 11, laser oscillation can be detected in the wafer state without any difficulty.

Since the threshold current value can be known, pass/fail judgment can be made based on the threshold current value at the wafer stage, making it possible to detect defective products in the previous process compared to conventional technology.1. .

This has the effect of preventing defective products from entering subsequent processes and reducing man-hours.

[Brief explanation of drawings]

FIG. 1 shows a discharge current measurement circuit according to an embodiment of the present invention. Schematic diagram of the circuit, Figure 2 shows the applied voltage, first flow time, 1°4
・The chart, FIG. 6 is a diagram showing the time change of the discharge current, and FIG. 4 is a diagram showing the relationship between the discharge current and the threshold current value of laser oscillation. 1...Power supply, 2...Current detector, 3.
...Partial electrode, 4...Prober, 5...Semiconductor laser wafer 1. 6...Full surface electrode. 1 is represented by patent attorney Katsuo Ogawa, 1.

Claims (1)

[Claims] 1. After multilayer epitaxial growth, in a semiconductor laser wafer before cleavage with electrodes formed on the substrate surface and the surface opposite to the substrate, a pulsed voltage is applied between the electrodes, and as a result, a discharge current generated from the semiconductor laser wafer is detected. A semiconductor laser inspection method characterized by determining the quality of a semiconductor laser wafer.