JP7221347B1 - Semiconductor device manufacturing method and data analysis system - Google Patents

Abstract

An object of the present invention is to improve the uniformity of the oscillation wavelength and the optical output power of a DFB laser within a wafer, and suppress the variation in the characteristics of each chip. A method of manufacturing a semiconductor device according to the present invention includes preparing a substrate on which a semiconductor layer including a laser active layer is formed, and fabricating the semiconductor layer, a dielectric film formed on the semiconductor layer, or both. Estimate the in-wafer distribution of the electro-optical structure including film thickness or refractive index by a measurement means, correct the design variables of the diffraction grating of the distributed feedback laser using the estimation result and the correction means, and perform diffraction reflecting the parameter correction. It is characterized by forming a lattice and dividing it into chips. [Selection drawing] Fig. 3

Description

The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a distributed feedback semiconductor laser.

In the Internet of Things (IOT) society, where the amount of information is rapidly increasing, wavelength division multiplexing (WDM), which has a large communication capacity per fiber, is widely used. In such a wavelength division multiplexing (WDM) system, a distributed feedback semiconductor laser (DFB laser), which has a periodic diffraction grating structure around the active layer, is characterized by its high single-wavelength selectivity. Used as a light source. Surface-emitting lasers, which have been conventionally used for short-distance communications, tend to oscillate in multiple modes due to their structure and are not suitable for WDM. Mode thin film type DFB lasers are desired and research and development are being advanced.

In the manufacture of thin-film DFB lasers, the thin-film formation process between different materials is an important technology, and high reproducibility is required for various thin-film structures to be formed. Thermally oxidized SiO ₂ with a low refractive index and spin-coated benzocyclobutene (BCB) film are used as the cladding layer to enhance the interaction between light and injected carriers, resulting in further miniaturization and lower power consumption. It is done. On the other hand, the compound semiconductor thin film layer to be the core region is once laminated on the surface of the compound semiconductor substrate by metal-organic vapor phase epitaxy or the like, and then connected to the cladding layer by wafer bonding technology or the like. By adaptively combining wafer bonding technology and conventional thin film growth technology, the degree of freedom in selecting thin film materials has been improved. In bonding dissimilar materials, depending on the film thickness and bonding conditions, crystal defects can easily occur due to stress. In addition, due to the structure in which the semiconductor thin film is sandwiched between materials with a large difference in refractive index, a slight change in layer thickness has a greater effect on the equivalent refractive index than in conventional lasers made only of semiconductors.

Since the oscillation wavelength of the DFB laser depends on the temperature of the active layer, the thermal resistance around the active layer affects the control of the oscillation wavelength. The SiO ₂ and BCB films used for the clad layer have lower thermal conductivity than semiconductors (InP _: 50 W/(mK), Si: 150 W/(mK)). 1.38 W/(m·K) and 0.2 W/(m·K) for BCB. In other words, the heat escaping from the core region does not pass through the upper and lower clad layers, but first passes through the semiconductor layer in the same plane as the active layer. From this, it can be seen that high reproducibility is required for the film thickness and film quality of the thin film structure also in the thermal design of the active layer temperature.

The design parameters used in the design of the DFB laser diffraction grating include the material of the clad layer, the thickness of the clad layer, the overall length of the diffraction grating, the spacing of the diffraction grating, the width of the diffraction grating, the depth of the recesses of the diffraction grating, and the depth of the diffraction grating. The number of iterations of the lattice can be increased. In the prior art, for example, a crystal growth method capable of improving the film quality during film formation for making a diffraction grating (Patent Document 1, Semiconductor device manufacturing method), an improvement method using diffraction gratings having two different periodic structures (Patent Document 2) , a semiconductor laser element and an optical semiconductor device), a method of optimizing the bandgap of the cladding layer and stabilizing the coupling coefficient κ (Patent Document 3, Distributed Feedback Semiconductor Laser Manufacturing Method), a sub-diffraction grating parallel to the main diffraction grating There is a method of providing a grating to improve mode stability (Patent Document 4; semiconductor laser device). In these conventional diffraction grating manufacturing processes, attempts have mainly been made to improve the accuracy of reflecting design variables in actual devices and, as a result, to stabilize the oscillation wavelength and output of the DFB laser.

On the other hand, in the optical interconnection technology using lasers, there has been a demand for lasers that can be highly integrated and have low power consumption. In particular, inter-board or inter-chip optical interconnection technology requires fusion with Si photonics technology and a degree of laser array integration comparable to the number of Si-LSI chip I/Os (Non-Patent Document 3). Due to the above-mentioned situation, it is necessary to improve the uniformity of characteristics, especially within the wafer surface during manufacturing, in order to improve the degree of integration of DFB lasers. .

Japanese Patent Application No. 9-265941 JP 2014-150145 A JP 2008-227185 A JP 2015-179783 A

T. Okamoto, N. Nunoya, Y. Onodera, S. Tamura and S. Arai, "Continuous wave operation of optically pumped membrane DFB laser", Ellectron. Lett., Nov. 2001, vol. 37, no. 24, pp. 1455-1456. T. Fujii, K. Takeda, N-P. Diamantopoulos, E. Kanno, K. Hasebe, H. Nishi, R. Nakao, T. Kakitsuka, and S. Matsuo: "Heterogeneously Integrated Membrane Lasers on Si Substrate for Low Operating Energy Optical Links, "IEEE Journal of Selected Topics in Quantum Electronics, 2016, Vol. 24. No. 1, 1500408. Optical Circuit Implementation Technology Roadmap 2016 Edition - Issues and Forecasts for the Second Popularization Generation of Optical Interconnection -, The 31st Spring Conference of the Institute of Electronics Packaging, JIEP Optical Circuit Implementation Technology Committee, 2017.2, p.340- 343 STIMULATED EMISSION IN A PERIODIC STRUCTURE, H. Kogelnik and C. V. Shank, Appl. Phys. Letters, 1971, 18, 152

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing a distributed feedback semiconductor laser that can improve the uniformity of the oscillation wavelength and optical output power of a DFB laser within a wafer, and suppress variations in the characteristics of each chip. do.

A method of manufacturing a semiconductor device according to the present invention includes preparing a substrate on which a semiconductor layer including a laser active layer is formed, and determining the thickness or refractive index of the semiconductor layer, the dielectric film formed on the semiconductor layer, or both. In-wafer distribution of the electro-optical structure including the index is estimated by a measuring means, the design variables of the diffraction grating of the distributed feedback laser are corrected using the estimation result and the correction means, and a diffraction grating reflecting the parameter correction is formed. , is divided for each chip.

The DFB laser manufacturing method of the present invention can improve the uniformity of the oscillation wavelength and the optical output power of the DFB laser within the wafer, and suppress the variation in the characteristics of each chip.

FIG. 4 is a diagram showing a manufacturing process of the distributed feedback laser according to the embodiment of the present invention; FIG. 4 is a diagram showing a correlation diagram for design variable correction of the diffraction grating of the distributed feedback laser according to the embodiment of the present invention; FIG. 4 is a diagram showing a manufacturing process flowchart of the distributed feedback laser according to the embodiment of the present invention;

An embodiment of a method for manufacturing a DFB laser according to the present invention will be described below with reference to the drawings.

1(a) to (e) are diagrams showing an example of the manufacturing process of a DFB laser on a Si substrate according to one embodiment of the present invention. FIG. 3 is a flow chart showing the above manufacturing process.

FIG. 1(a) shows a step of preparing a support substrate in the manufacturing process. In this embodiment, a silicon (Si) substrate 1 on which a silicon (Si) oxide film 2 is formed is used as the supporting substrate. The silicon oxide film 2 may be formed by thermal oxidation, wet oxidation, vapor deposition, or SOI technology. Here, the thickness of the silicon oxide film 2 is preferably 0.01 μm or more, more preferably 0.5 μm or more. SiC, sapphire, GaP, GaAs, InP, GaN, benzocyclobutene, polymethyl methacrylate, etc. can also be used as the support substrate other than the silicon oxide film 2 . FIG. 1(b) shows a step of forming a semiconductor layer (hereinafter referred to as LD layer 3) including a laser active layer on a support substrate using a wafer bonding technique (S1 in FIG. 3). In the process of forming the LD layer 3, first, an InP substrate serving as a base is prepared, and the InP layer, quantum well structure, and separate confinement heterostructure (SCH) included in the LD layer 3 are formed thereon by metal-organic chemical vapor deposition. Layers are grown sequentially. Next, the LD layer 3 of the InP substrate and the silicon oxide film on the surface of the support substrate are bonded by wafer bonding technology, and unnecessary InP substrate is removed by dry etching, wet etching, wafer polishing technology, or a combination of these technologies. . At this time, in order to increase the stability of the finished film thickness of the LD layer 3, it is preferable to previously provide a thin etch stop layer between the LD layer 3 and the InP substrate.

Next, FIG. 1(c) shows the step of measuring the electro-optical structure of the formed LD layer 3 (S2 in FIG. 3). Specifically, on-wafer mapping 4 is used to measure the thickness of each layer constituting the LD layer 3 and the presence of an interface layer in each of a plurality of shots 5 on the LD layer 3 . Here, the "shot" is a region that occurs due to the convenience of the manufacturing process and is mainly derived from mask exposure using a stepper. At least one wafer chip (final product) corresponds to one shot in this embodiment. The shot is determined within a feasible range considering the spatial resolution of the ellipsometer (spot size of about several millimeters) and the measurement time, etc. , is divided into chips to form finished products (final products).

By performing the above wafer mapping 4, the film thickness of each shot of the LD layer 3 within the wafer surface can be measured in-line. Similarly, by performing wafer mapping 4 inline, it is also possible to measure the refractive index of each layer and the average refractive index for each shot of the LD layer 3 . That is, in this step S1, it is possible to obtain information for each shot 5 necessary for matching the oscillation wavelength of the DFB laser from the evaluation of the LD layer 3 using the spectroscopic ellipsometer. As another measurement method, in addition to spectroscopic ellipsometry, for example, photoluminescence measurement is used as an auxiliary method to analyze light emission caused by the quantum well structure in the LD layer 3, and the quantum well structure in the wafer plane. Information can be obtained about the distribution for each shot 5 . In addition, if the X-ray diffraction method is added to the evaluation of the LD layer 3, the crystallinity of the LD layer 3 and the underlying substrate can be analyzed. effective for After the above measurements, the formation of the mesa region of the LD layer 3 (region for laser oscillation) and the re-growth of the waveguide layer and the contact layer are carried out.

By measuring the electro-optical structure for each shot of the wafer as described above, it is possible to estimate the in-wafer distribution of the electro-optical structure.

Next FIG. 1(d) shows the steps of forming a diffraction grating (including steps S3, S4, and S5 in FIG. 3). First, the exposed region 6 formed by electron beam exposure is developed, and the concave portion of the diffraction grating 10 is etched using the resist film 8 in which this region is developed as an etching mask. The exposure area 6 formed by electron beam exposure corresponds to the drawing pattern of electron beam exposure.

Next, the contact layer formed in the process shown in FIG. 1(c) is doped with impurities and activated. The contact layer and the LD layer 3 are joined by impurity doping, and a bias current can be applied to the LD layer 3 . Further, an electrode 9 containing metal is formed on the contact layer. In this embodiment, a passivation layer (not shown) is formed to further improve reliability (S5 in FIG. 3).

In the above process shown in FIG. 1(d), the pattern of the diffraction grating 10 is formed by electron beam exposure. At this time, in the estimation step (S2 in FIG. 3) described above, the design variables of the diffraction grating 10 are determined using the film thickness of the LD layer 3 and the refractive index of each layer, which are found from the results of the spectroscopic ellipsometry acquired for each shot 5. A correction value is obtained for each shot 5 (S3 in FIG. 3).

The following relational expression (1) holds among the oscillation wavelength (λ) of the thinned DFB laser, the equivalent refractive index (n _eff ) of the active layer, and the lattice spacing (Λ) of the diffraction grating.

where m is an integer giving the order of the Bragg reflection of the grating (Non-Patent Document 4). As can be understood from equation (1), when the equivalent refractive index n _eff obtained from the results of spectroscopic ellipsometry is lower than the target equivalent refractive index, the oscillation wavelength λ can be kept constant. That is, in the embodiment of the present invention, the value of the grating spacing Λ is determined according to the value of the equivalent refractive index n _eff obtained for each shot, and the design parameters of the diffraction grating are corrected to keep the oscillation wavelength constant.

As a result, the oscillation wavelength between shots can be made equal, and the uniformity of the laser oscillation wavelength and the optical output power within the wafer can be improved. As described above, since the oscillation wavelengths can be substantially the same between shots, the oscillation wavelengths can be made uniform between the finally obtained chips. In the above example, the in-wafer distribution is estimated for each shot, and the design variables (correction values) of the diffraction grating are obtained. Of course, the in-wafer distribution may be estimated for each chip area, and the correction value of the diffraction grating may be obtained.

According to the present embodiment described above, the pattern change of the diffraction grating 10 can be completed only by correcting the electron beam exposure data. Therefore, no additional process is required to adjust the design variables of the diffraction grating 10, and the in-wafer distribution of device characteristics can be made uniform.

In this embodiment, a correlation diagram between the electro-optical structure of the LD layer 3 and the design variables of the diffraction grating 10 created based on experimental results is used in order to further improve the correction accuracy of the design variables of the diffraction grating 10 described above. .

The oscillation wavelength of the distributed feedback laser depends not only on the equivalent refractive index of the active layer, but also on the temperature of the LD layer 3 in operation. Therefore, even when the same operating bias current or voltage is applied, the oscillation wavelength varies depending on the Joule heat generated in the LD layer 3 . Furthermore, fluctuations in oscillation wavelength due to Joule heat depend on the film thickness of the LD layer 3 . The reason for this is that the thermal resistance of the LD layer 3 depends on the thickness of the LD layer 3, and even if the same amount of heat is generated, the oscillation wavelength will differ if the LD layer thickness is different. Also, regarding the spacing of the grating 10 and the width of the grating, their lengths may differ between different shots. Here, the diffraction grating interval is the interval between adjacent diffraction gratings in the shot 5, and the diffraction grating width is the width of the diffraction grating in the shot. In order to suppress the decrease in accuracy due to these temperature dependencies and shot-to-shot variations, distributed feedback lasers having different thicknesses of the LD layer 3 and different periods of the diffraction gratings were prepared. By checking beforehand the correlation of , and performing correction based on this, it is possible to perform correction with higher accuracy.

FIG. 2 is a diagram showing an example of a correlation diagram created for the above correction. When this correlation was examined, the environmental temperature was 25° C. and the LD drive current was 10 mA. FIG. 2 corresponds to data a to d acquired after device formation from four wafers having different LD layer 3 film thicknesses after the dicing process. The horizontal axis is the normalized diffraction grating interval, and the vertical axis is the normalized oscillation wavelength λ. Normalization is the rate of change with respect to the target film thickness. The uppermost data a corresponds to the film thickness of the LD layer 3 which is 0.8 times the target film thickness, the lowermost data d corresponds to the data when it matches the target film thickness, and the data b and c are It corresponds to a predetermined film thickness between them. Normally, if the film thickness is determined, the (effective) refractive index is also almost uniquely determined, so it is only necessary to pay attention to either the film thickness or the refractive index. As an extreme example, if the epitaxial growth of the LD layer 3 has not progressed completely, the relation between the film thickness and the refractive index is also different from the previously acquired data, and in this case it is necessary to judge whether the wafer is good or bad. be.

From FIG. 2 above, the correlation between the oscillation wavelength and the spacing of the diffraction grating 10 for each film thickness of the active layer can be understood. can be corrected (adjustment 7 of the period of the diffraction grating). As a result, the oscillation wavelength λ can be accurately adjusted to the target value for each shot (S4 in FIG. 3).

To acquire the correlation shown in FIG. 2, the design variables of the analysis grating are given with some width in advance, and the oscillation wavelength is measured after the manufacturing process according to the present invention is performed. By comparing the measurement result with the film thickness and dielectric constant obtained by spectroscopic ellipsometry and the design variable data of the diffraction grating 10, the correlation between them can be obtained. Further, since the correlation must be created with high accuracy, the accuracy can be improved by combining direct cross-sectional TEM measurement with film thickness measurement. Further, as described in the prior art of Non-Patent Document 2, it is easily conjectured that the modification of the design parameters of the diffraction grating 10 according to the present invention can also be applied to the diffraction grating of the distributed Bragg reflector used in the DFB laser. be.

After completing the steps described above, next, a dividing step is performed for each chip ((S6) dividing for each chip in FIG. 3). This step can be performed by, for example, using a dicing saw to divide the wafer into chips.

In this embodiment, the pattern of the diffraction grating is formed by electron beam exposure, but it may be formed by mechanically marking grooves in the metal film with a diamond cutter or the like, or by photolithography.

The method of manufacturing a DFB laser according to this embodiment can suppress variations in characteristics between chips. The method for manufacturing the DFB laser of this embodiment is suitable for mass production.

In this embodiment, the method of forming a diffraction grating in the LD layer bonded to the supporting substrate by the steps (S1) to (S6) shown in FIG. ₃ has been described. It is also possible to deposit a dielectric layer such as SiON and form a diffraction grating on the dielectric layer. In this case, by obtaining information on the dielectric layer in addition to the information on the LD layer by spectroscopic ellipsometry, it is possible to uniform the device characteristics as in the first embodiment.

Furthermore, when the above-described methods are widely applied, in addition to spectroscopic ellipsometry, measurement of the intra-wafer distribution of the electro-optical structure including film thickness or refractive index and oscillation wavelength measurement, as well as high-definition Appearance inspection of the device by image, measurement of one or more of optical S parameter measurement and current-voltage characteristic measurement or acquisition of in-plane distribution data of device electro-optical characteristics by inspection together, correction of design variables of the diffraction grating By confirming whether the results are good or bad, and confirming whether the results are good or bad for a plurality of devices, the correlation data of each measurement result is accumulated in a data analysis system (not shown). It is preferable to check the quality of many devices. By accumulating the correlation data in a data analysis system such as a server, centrally managing and comparatively analyzing it, it becomes easier to predict device characteristics, including external features, oscillation wavelength, and high-frequency response. As a result, it becomes possible to improve the yield during mass production and to speed up and improve the quality judgment, and to manufacture a distributed feedback laser array with a higher degree of integration.

INDUSTRIAL APPLICABILITY The present invention is applicable to technical fields related to optical communication technology.

1 Si (silicon) substrate 2 silicon oxide film 3 LD layer 4 mapping 5 shot 6 exposure region 7 period adjustment of diffraction grating 8 resist film 9 electrode 10 diffraction grating

Claims (4)

preparing a substrate on which a semiconductor layer including a laser active layer is formed;
estimating an in-wafer distribution of an electro-optical structure including a film thickness or a refractive index of the semiconductor layer, a dielectric film formed on the semiconductor layer, or both, by a measuring means;
A method of manufacturing a semiconductor device, comprising the steps of correcting design variables of a diffraction grating of a distributed feedback laser using the estimation result and correction means, forming a diffraction grating reflecting parameter correction, and dividing into chips. The semiconductor manufactured on the basis of experimental results using a substrate having an oxide film formed on a silicon wafer as a support substrate, using spectroscopic ellipsometry as the measuring means, and using the correction means for the design variables of the diffraction grating. 2. The method of manufacturing a semiconductor device according to claim 1, wherein a correlation diagram between the electro-optical structure of the layer and the design variables of the diffraction grating is used. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the diffraction grating design parameters include at least the diffraction grating interval and the diffraction grating width of the distributed feedback laser. 3. The method of manufacturing a semiconductor device according to claim 1, wherein in addition to the measurement of the in-wafer distribution of the electro-optical structure including the film thickness or the refractive index and the measurement of the oscillation wavelength, an outline inspection using an image and an optical S By using a combination of in-plane distribution data of the electro-optical characteristics of the device obtained by one or more of parameter measurement and current-voltage characteristic measurement or inspection, the correctness of the correction result of the design variables of the diffraction grating is confirmed. 7. A data analysis system, wherein correlation data of each measurement result is accumulated by confirming the pass/fail for a plurality of the devices.

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