JPH118438A - Manufacture of semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor laser device, which can easily predict a distribution in device characteristics with a high accuracy at an earlier stage of its manufacturing process, to thereby eliminate a defective device and increase the manufacturing yield. SOLUTION: After an active layer has been formed by a sequential epitaxial growth process as disposed between a pair of cladding layers on a semiconductor substrate, the active layer is photo-excited at a stage where having formed a ridge to the epitaxial layer for measuring a photoluminescence in the active layer and for selecting a good element formation region on the basis of its measured result. The selected element formation region is subjected to subsequent manufacturing processes, including electrode formation to manufacture a semiconductor laser device. In particular, the intensity of the photoluminescence and spectrum in the active layer after the ridge formation are measured by scanning a plurality of points on the epitaxial layer or the entire surface thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a semiconductor laser device capable of manufacturing a semiconductor laser device suitable for use as a light source in optical communication and the like with a high yield.

[0002]

2. Related Background Art A semiconductor laser device having a small size and low power consumption is used as a light source of an optical information recording / reproducing device or a light source in optical communication, and plays an important role in industry. This type of semiconductor laser device is, for example, such that an active layer sandwiched between a pair of cladding layers is epitaxially grown on a single crystal substrate of a III-V compound semiconductor such as InP or GaAs, and a ridge is formed on the epitaxial layer. Manufactured by subjecting to fine processing.

[0003] Incidentally, the manufacture of the above-mentioned semiconductor laser device is as follows.
For example, as shown in FIG. 1, a 2 μm thick n-Al substrate is first formed on an n-GaAs substrate 1 having a thickness of several hundred μm by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).
_{The process is started} by growing a _0.3 Ga _0.7 As clad layer 2 and then epitaxially growing an active layer 3 and then a 2 μm thick p-Al _0.3 Ga _0.7 As clad layer 4 and a p-GaAs contact layer 5 thereon.

As the n-GaAs substrate 1, for example, a wafer having a diameter of 50 to 100 mm is used. The active layer 3 is formed between a pair of optical confinement layers (SHC layers) 3a and 3b made of, for example, Al _0.1 Ga _0.9 As having a thickness of 100 nm.
Although it has a structure in which an In _0.15 Ga _0.85 As quantum well layer 3c having a thickness of nm is interposed, a structure in which a plurality of quantum well layers are provided, or a structure in which layers having other functions are also formed. Is also good. Further, the composition and thickness of each layer are not limited to the examples described above, and are determined according to specifications such as the oscillation wavelength and oscillation intensity.

[0005] Conventionally, generally, after an epitaxial wafer having the above-mentioned layer structure is formed, a part thereof is cleaved as shown in FIG. 2 and cut out as an evaluation sample 10. The characteristics of the epitaxial wafer are inspected. This inspection is performed by examining the surface state (morphology), the thickness of each layer, the composition of the cladding layers 2 and 4, the emission wavelength of the active layer 3, the carrier concentration, the transition density, and the like. Especially the active layer 3
Is an important inspection item because it affects the oscillation wavelength of the semiconductor laser device finally manufactured.

Incidentally, the inspection of the emission wavelength of the active layer 3 is performed, for example, as shown in FIG.
Is irradiated with an excitation light 11 such as a HeNe laser beam, the photoluminescence (PL) light 12 emitted from the active layer 3 is detected, and the emission spectrum is measured. At this time, in order to sufficiently excite the active layer 3 with the excitation light 11, the p-GaAs contact layer 5 and the p-GaAs contact layer 5 are etched using an etching solution such as an aqueous solution of hydrogen peroxide and sulfuric acid.
A part of the Al _0.3 Ga _0.7 As clad layer 4 is etched,
The PL measurement is performed in a state where the thickness of the p-Al _0.3 Ga _0.7 As clad layer 4 is reduced to about 1 μm to increase the PL light emission intensity.

By performing a PL measurement or the like of the evaluation sample 10 as described above and confirming that the characteristics such as the emission wavelength are good, if the remaining regions 13 and 14 of the epitaxial wafer shown in FIG. The overall characteristics are considered to be good. That is, the characteristics of the entire epitaxial wafer are evaluated using a part (evaluation sample 10).

Thereafter, in this case, the remaining regions 13 and 14 of the epitaxial wafer are
A ridge 6 having a height of about 2 μm and a width of about 4 μm as shown in FIG.
Is formed in a stripe shape at a pitch period of 250 to 350 μm, and an insulating oxide film 7 such as SiNx or SiO ₂ is formed thereon as shown in FIG. Next, as shown in FIG. 4C, the insulating oxide film 7 on the ridge 6 is locally removed by lithography or the like to form a contact portion. afterwards,
As shown in FIG. 4D, the back surface of the n-GaAs substrate 1 is
Polishing is performed to about 0 μm, and a P electrode 8 of Ti / Pt / Au is formed on the upper surface by vapor deposition, and an N electrode 9 of AuGeNi is formed on the lower surface of the substrate 1 by vapor deposition. After that, the wafer is cleaved, scribed, etc. to separate elements,
A semiconductor laser device (element) as shown in FIG. 5 is obtained. The semiconductor laser thus separated from the device is packaged in a can package or incorporated in a module to which an optical fiber is connected.

[0009]

However, in the semiconductor laser device manufactured as described above, the manufacturing processes such as film thickness control (control) of each layer in the epitaxial growth and fine processing of the ridge are complicated. There is a problem that the production yield is low. In particular, a semiconductor laser device for optical communication, for example, a ridge waveguide type semiconductor laser device in the 0.98 μm band is used as an excitation light source in an erbium-doped optical fiber amplifier, and is an important device for long-distance optical communication. It is. Therefore, the specifications for the characteristics are very strict, and high reliability and oscillation wavelength accuracy are required. Therefore, the production yield may be less than 10%.

In particular, in the prior art, the evaluation sample 10 is cut out from a part of the epitaxial wafer, and the evaluation sample 10 is tested to evaluate the overall characteristics. Therefore, the reliability is poor and the production yield is improved. I couldn't hope. For example, even if the crystallinity of the epitaxial layer is poor and the PL wavelength in the entire epitaxial wafer varies, it cannot be detected from the evaluation sample 10, so that the oscillation wavelength of the manufactured semiconductor laser device varies. As a result, the yield and the reliability of the final device characteristics are reduced.

The present invention has been made in view of such circumstances, and an object of the present invention is to make it possible to easily and accurately predict the distribution of device characteristics at an early stage of a manufacturing process. It is an object of the present invention to provide a simple and practical method for manufacturing a semiconductor laser device capable of increasing the manufacturing yield by eliminating defective products.

[0012]

In order to achieve the above-mentioned object, a method of manufacturing a semiconductor laser device according to the present invention comprises the steps of: sequentially growing an active layer sandwiched between a pair of cladding layers on a semiconductor substrate; When manufacturing a semiconductor laser device by forming a ridge on the epitaxial layer and then forming an electrode, etc., after forming the ridge, the active layer is optically excited to measure photoluminescence in the active layer. It is characterized in that good element formation regions are selected based on the results.

In particular, the intensity of the photoluminescence in the active layer after the formation of the ridge, or the spectrum thereof, is measured at a plurality of points on the epitaxial layer or by scanning the entire surface thereof, and a defect out of specifications is determined based on the measurement result. The method is characterized in that a region is predicted in advance, and a manufacturing yield is predicted based on the region.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a semiconductor laser device according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 6 shows a processing (step) procedure of the method for manufacturing a semiconductor laser device according to this embodiment. The manufacturing process itself of the semiconductor laser device is basically the same as the above-described conventional procedure, and is started by sequentially epitaxially growing an active layer sandwiched between a pair of clad layers on a predetermined semiconductor substrate [ Step S1].

That is, this epitaxial growth is performed by using the MOCVD method as described above, for example, an n-Al _0.3 Ga _0.7 As clad layer (2 μm thickness) on a n-GaAs substrate (300 μm thickness), and a pair of Al _0.1 Ga _0.9 As Active layer consisting of an In _0.15 Ga _0.85 As quantum well layer (7 nm thick) sandwiched between optical confinement layers (100 nm thick), p-Al _0.3 Ga _0.7 As
This is performed by sequentially growing a cladding layer (2 μm thick) and a p-GaAs contact layer.

Thereafter, a predetermined ridge is formed on the epitaxial wafer composed of the above layers by lithography, etching or the like [Step S2]. As described above, the formation of the ridge is about 2 μm in height and about 4 μm in width.
This is done by forming m ridges in a stripe pattern at a pitch period of 250 to 350 μm. At this time, by setting the off-ridge height to 1.5 μm or less, the thickness of the cladding layer beside the ridge is sufficiently reduced to 1 μm or less. Next, including the above-mentioned ridge region, SiNx and SiO ₂ are formed thereon.
Forming an insulating oxide film (insulating film) such as [Step S]
3].

The feature of the present invention is that, in the state where the ridge is thus formed (including the formation of the insulating film), the epitaxial wafer after the ridge is formed is
The step is to examine the emission wavelength characteristics and the like from the photoluminescence in the active layer for the measurement [Step S
4]. At this time, the formation of the ridge removes the contact layer on its side and the thickness of the cladding layer is sufficiently thin, so that it is not necessary to perform an etching process as in the related art. Therefore, after the ridge is formed, the epitaxial wafer having the insulating oxide film formed thereon can be directly used for PL measurement.

In this PL measurement, for example, as shown in FIG. 7, the epitaxial wafer 21 is placed on a table 22, and the active layer of the epitaxial wafer 21 is irradiated with excitation light from an obliquely upper side by a laser device 23. The detection is performed by detecting the photoluminescence light generated in the active layer by the irradiation of the excitation light by the PL detector 24 provided thereabove. Incidentally, the excitation light has a wavelength characteristic shorter than the emission wavelength of the active layer, and has a spectral characteristic that does not overlap with the spectrum of the photoluminescence light.
Further, a HeNe laser, an Ar laser, a Kr laser or the like is used as a device capable of exciting a photoluminescence light of 1 W / cm ² or more. Therefore, as the laser device 23, a solid-state laser device or a gas laser device for obtaining the high-power laser light is used.

The PL detector 24 measures not only the intensity but also the peak wavelength of the spectral component and further the half width from the spectral distribution of the photoluminescence detected as shown in FIG. . Incidentally, the peak wavelength in the photoluminescence spectrum substantially corresponds to the oscillation wavelength in the final semiconductor laser device. In addition, the half width reflects the crystallinity (crystal quality) of the epitaxial layer. Therefore, when the half width is, for example, 30 meV or less, or more, it is possible to determine that the crystal characteristics of the epitaxial layer are poor or the reliability is poor. The strength reflects the doping concentration of the epitaxial layer, crystal quality, off-ridge height, and the like. Therefore,
For example, by setting upper and lower limits in advance based on the average intensity and evaluating the detected intensity, it is possible to predict the degree of influence on the characteristics and reliability of the final device (semiconductor laser device) Becomes

The laser device 23 and the PL
PL of epitaxial wafer 21 using detector 24
The measurement is performed over a plurality of points of the epitaxial wafer 21 under the control of the scanning mechanism 25 or over the entire surface thereof by 600 μm.
Scanning is performed in m steps while avoiding the ridge portion. The information (intensity, peak wavelength, half width) of the photoluminescence at these measurement points is provided to the spectrum measurement unit 26 and recorded (mapped) in association with each measurement site. At this time, as described above, even if the ridge portion is not intentionally avoided, since the photoluminescence cannot be detected at the ridge portion, it is possible to scan the entire area of the epitaxial wafer 21 without avoiding the ridge portion.

Thus, when the PL measurement of the active layer of the epitaxial wafer 21 is performed at a plurality of points in this manner, for example, as shown in FIG. Can be obtained. For example, by mapping the peak wavelength at each measurement point as a measurement image in which the color is changed every 1 nm, the distribution of the peak wavelength characteristics of the photoluminescence of the active layer in the entire epitaxial wafer 21 can be obtained.

Therefore, from such mapping data,
For example, it is determined that a region having a peak wavelength of 978 to 981 nm (for example, a dot region in FIG. 9) is an element formation region capable of realizing a semiconductor laser device having an oscillation wavelength intended for manufacturing (conforming to specifications). Can be. In other words, in the other regions (the hatched regions and the cross-line regions in FIG. 9), even if the subsequent manufacturing process is advanced to manufacture the semiconductor laser device, the oscillation wavelength is shifted to the short wavelength side or the super wavelength side. It can be predicted that a shift will occur and that it must eventually be eliminated.

Therefore, in the present invention, an element formation region that satisfies the specifications is determined from the PL measurement result (peak wavelength distribution) of the epitaxial wafer 21 measured as described above [Step S5]. Then, the epitaxial wafer 21 in which the element formation region does not reach a predetermined ratio.
Is removed from the subsequent manufacturing process, and the epitaxial wafer 2 having an element formation region expected to satisfy the specifications
Only one is sent to the subsequent manufacturing process.

For example, in the example shown in FIG. 9, for the two upper left wafers, the element formation region indicated by the halftone dot region is less than half, and it is determined that most of them do not satisfy the specifications. Is not sent to the manufacturing process. That is, it is excluded. In the lower left wafer, although the element formation region indicated by the halftone dot region is small, a somewhat good element formation region is recognized, so that the wafer is sent to the subsequent manufacturing process. However, as will be described later, after element isolation, only chips required from good element formation regions are extracted based on the mapping information. In addition, since the good element formation region occupies a large portion of the two upper right wafers, the subsequent manufacturing process is advanced to complete the semiconductor laser device. However, also in this case, only the chips cut out from the favorable element formation region after element isolation are extracted according to the mapping information.

In the subsequent manufacturing process for the epitaxial wafer 21 selected as described above, first, the insulating oxide film on the ridge is removed to start exposing the contact portion [Step S6]. Next, after polishing the back surface of the n-GaAs substrate as described above, a P electrode of Ti / Pt / Au is formed on the upper surface including the contact portion by vapor deposition. An N electrode made of AuGeNi is formed on the back surface of the substrate by vapor deposition [Step S7]. After that, the wafer is cleaved, scribed, etc. to separate elements [Step S8]. At this stage, chips formed in the defective area indicated by the above-described mapping data are excluded.

Thereafter, the chip (semiconductor laser device) separated and separated is provided with electrode wiring to form a can package, or as a module together with an optical fiber to be incorporated as a final product [Step S].
9]. In this state, a final inspection of the element characteristics is performed, the quality and characteristics are checked, and defective products are eliminated.

According to the present manufacturing method for manufacturing a semiconductor laser device as described above, the distribution of device characteristics, particularly the activity, is measured by PL measurement at the stage when the ridge is formed on the epitaxial wafer, that is, at the initial stage of the manufacturing process. Since the PL peak wavelength and the like in the layer are evaluated and the oscillation wavelength characteristics of the finally manufactured semiconductor laser device are predicted with high accuracy, the element formation region determined to not satisfy the specifications is excluded from the subsequent manufacturing process. be able to. Moreover, the reliability and the like can be evaluated in advance from the intensity of PL (photoluminescence) and the half width, and the subsequent manufacturing process can be performed. Therefore, the element characteristics are good,
In addition, a semiconductor laser device with high operation reliability can be manufactured with good yield.

In particular, since the distribution characteristics of PL over the entire surface of the epitaxial wafer are evaluated and the element formation region to be advanced to the subsequent manufacturing process is selected, the characteristics of the finally manufactured semiconductor laser device do not greatly differ. It is possible to increase the production yield. In other words,
Since the manufacturing process does not proceed for the device formation region where the device characteristics remain unknown, that is, based on the device characteristics of the epitaxial wafer only represented by the evaluation sample, it depends on the film thickness distribution of the epitaxial layer, etc. The occurrence of defective products can be greatly reduced. Therefore, since a semiconductor laser device having undesired characteristics is not manufactured without necessity, effects such as reduction in manufacturing cost can be obtained.

As described above, since the epitaxial wafer after the ridge formation is subjected to PL measurement, a secondary operation such as etching the wafer is not required. That is, in the process of forming the ridge, the contact layer on the side of the ridge is removed, and the cladding layer is also thinned to a certain extent. No pre-processing is required. Therefore, also in this respect, effects such as simplification of the PL measurement work and simplification of the whole manufacturing process can be obtained.

The present invention is not limited to the above embodiment. For example, the present invention can be similarly applied to a semiconductor laser device having a buried ridge waveguide structure, that is, it can be applied to a semiconductor laser device having an element structure manufactured and processed while an active layer remains flat. Further, it is of course possible to obtain the intensity distribution of the PL light and evaluate its characteristics. In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0031]

As described above, according to the present invention, after an active layer sandwiched between a pair of cladding layers is sequentially epitaxially grown on a semiconductor substrate, the active layer is formed at the stage of forming a ridge in the epitaxial layer. Photoexcitation of the layer is performed to measure photoluminescence in the active layer, a good element formation region is selected based on the measurement result, and a subsequent manufacturing process including the electrode formation is performed on the selected element formation region. The semiconductor laser device will be manufactured. In particular, the intensity of the photoluminescence in the active layer after the formation of the ridge, or the spectrum thereof, is measured at a plurality of points on the epitaxial layer or by scanning the entire surface thereof, and based on the measurement result, a defective region out of specifications is determined in advance. I try to eliminate it.

Therefore, according to the present invention, at the initial stage of the manufacturing process, the distribution of device characteristics, particularly the PL peak wavelength in the active layer, etc. can be easily and accurately evaluated by PL measurement. Since the oscillation wavelength characteristic of the semiconductor laser device to be manufactured is predicted with high accuracy and the defective element formation region is eliminated, the manufacturing yield can be improved without wasting the manufacturing process. Therefore, it is possible to produce a semiconductor laser device having good element characteristics and high operation reliability with a good yield, and it is possible to efficiently manufacture the semiconductor laser device. It is suitable.

[Brief description of the drawings]

FIG. 1 is a diagram showing a layer structure of an epitaxial wafer forming a semiconductor laser device.

FIG. 2 is a view showing the concept of cutting out an evaluation sample from an epitaxial wafer.

FIG. 3 is a diagram showing the principle of photoluminescence measurement on an active layer.

FIG. 4 is a view showing step by step a manufacturing process of a semiconductor laser device including ridge formation and electrode formation on an epitaxial wafer.

FIG. 5 is a diagram showing an element shape of a semiconductor laser device (chip).

FIG. 6 is a flowchart showing a manufacturing process of the semiconductor laser device according to one embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of a PL measurement device.

FIG. 8 is a view showing spectral characteristics of PL light.

FIG. 9 is a diagram showing an example of a measurement image obtained by mapping a peak wavelength distribution of an epitaxial wafer subjected to PL measurement.

[Explanation of symbols]

Reference Signs List 1 n-GaAs substrate 2 n-Al _0.3 Ga _0.7 As cladding layer 3 active layer 3 a, 3 b Al _0.1 Ga _0.9 As light confinement layer (SHC layer) 3 c In _0.15 Ga _0.85 As quantum well layer 4 p-Al _0.3 Ga _0.7 As Cladding layer 5 p-GaAs contact layer 6 ridge 7 insulating oxide film (SiNx, SiO2) 8 P electrode (AuGeNi) 9 N electrode (Ti / Pt / Au) 10 evaluation sample 11 excitation light 12 photoluminescence (PL) light 21 Epitaxial wafer 22 Table 23 Laser device 24 PL detector 25 Scanning mechanism 26 Spectrum measurement unit

Claims (3)

[Claims] An active layer sandwiched between a pair of cladding layers is epitaxially grown on a semiconductor substrate, a ridge is formed on the epitaxial layer, an electrode is formed, and then an element is separated. In manufacturing, after the formation of the ridge, the active layer is photoexcited to measure photoluminescence in the active layer, and a semiconductor substrate or an element formation region is selected based on the measurement result. A method of manufacturing a semiconductor laser device, wherein a subsequent manufacturing process including formation of the electrode is performed on a formation region. 2. The method for manufacturing a semiconductor laser device according to claim 1, wherein the photoluminescence measurement is performed by measuring the intensity of the photoluminescence or the spectrum thereof. 3. The method according to claim 1, wherein the measurement of the photoluminescence is performed by scanning a plurality of points or the entire surface of the epitaxial layer after the ridge is formed.