JP2007123638A - Manufacturing method of nitride semiconductor and thin film working device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a nitride semiconductor capable of working a desired surface shape on the surface of the nitride semiconductor, regardless of a surface rugged shape before working. <P>SOLUTION: An etching object A is mounted on an XY stage 6, the XY stage 6 is scanned while performing measurement irradiation with a laser beam whose intensity is weakened by an attenuator 4, a transmitted light quantity is detected by a power meter 11, and a film thickness distribution is measured. Then, the XY stage 6 is scanned while irradiating it with the laser beam whose intensity is increased so as to dissolve the crystal structure of the etching object A, and the working irradiation of the etching object A is performed. The intensity of the laser beam is modulated to the intensity corresponding to the film thickness distribution by using the attenuator 4, and the working irradiation is performed. The etching object A for which the working irradiation is completed is detached from the thin film working device 100, acid treatment is performed, and the damage layer of a surface is removed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor manufacturing method for processing the surface shape of a nitride semiconductor such as a blue light emitting diode by irradiating a laser beam, and a thin film processing apparatus suitable for use in the implementation of this method.

  Nitride semiconductors typified by gallium nitride GaN are attracting attention as materials for high-intensity light-emitting devices with short wavelengths such as blue and green. For practical application of laser diodes and optical integrated circuits using gallium nitride GaN, etc. Various production methods have been studied.

  When manufacturing a laser diode or an optical integrated circuit, it is necessary to form a flat crystal plane. A group III-V nitride semiconductor such as gallium nitride GaN has a hexagonal crystal structure, and each axis Since the growth rates in the directions are greatly different, it is difficult to form a flat crystal growth surface by conventional techniques such as sputtering growth and vapor phase growth.

  Further, when manufacturing a laser diode or an optical integrated circuit, it is necessary to strictly control the thickness of the semiconductor layer, but a group III-V nitride semiconductor such as gallium nitride GaN has an etching rate in each axial direction of the crystal structure. Therefore, when dry etching is performed, the flatness and roughness of the surface are greatly deteriorated. In dry etching, there is also a problem that the crystal structure is damaged by ion bombardment.

  Patent Document 1 discloses a nitride semiconductor etching method that can control the thickness of a semiconductor layer while planarizing the surface of a nitride semiconductor such as gallium nitride GaN without using dry etching.

  Here, the surface of the gallium nitride GaN thin film layer is irradiated with a laser beam at a time to dissolve the crystal structure, expelling nitrogen and liquefying the gallium, thereby depending on the cumulative irradiation dose (intensity and number of pulses) of the laser beam. Thick gallium nitride GaN is removed. In addition, the gallium nitride GaN thin film layer irradiated with laser light is immersed in hydrochloric acid, and the crystal layer that has been damaged by the laser light is selectively removed by etching, so that a crystal plane with improved flatness appears on the surface. I am letting.

JP 2000-260742 A

  In the nitride semiconductor etching method disclosed in Patent Document 1, laser light having a uniform intensity distribution is collectively irradiated to a wide irradiation region of the nitride semiconductor etching target. Even though the unevenness difference is somewhat reduced, the uneven shape following the original uneven shape remains (see FIG. 7).

  An object of the present invention is to provide a method for manufacturing a nitride semiconductor, in which the surface of the nitride semiconductor can be subjected to surface processing with reduced dependency on the surface irregularities before processing.

  The method for manufacturing a nitride semiconductor of the present invention is a method for manufacturing a nitride semiconductor in which the surface shape of the nitride semiconductor thin film is processed by irradiating a laser beam, and the film thickness distribution before the processing of the nitride semiconductor thin film is measured. A measuring step, a processing step of scanning the surface of the nitride semiconductor thin film with a focused laser beam spot, and applying a different irradiation amount to each scanning point of the surface according to the measured film thickness distribution; And an acid treatment step of acid-treating the surface of the nitride semiconductor thin film that has undergone a processing step.

  The thin film processing apparatus of the present invention is a thin film processing apparatus for processing the surface shape of a thin film layer formed on a translucent substrate, a light source means for generating laser light, and a laser beam by guiding the generated laser light to a processing point. Optical system means for forming a spot, scanning stage means for moving the translucent substrate to position each scanning point on the thin film layer at the processing point, and transmitted through the thin film layer and the translucent substrate Detecting means for detecting the transmitted light intensity of the laser beam spot; intensity modulating means for changing the intensity of the laser beam spot; and controlling the intensity modulating means based on the transmitted light intensity detected at the scanning point. And a control means for processing and irradiating the scanning point with the laser beam spot having an intensity corresponding to the transmitted light intensity.

  In the method for manufacturing a nitride semiconductor according to the present invention, a processing amount (depth) required for each scanning point in a processing range with a converged laser beam spot instead of collectively irradiating a planar laser beam on the processing range. Inject light energy according to. By doing so, surface processing with little dependency on the uneven shape of the substrate surface before surface processing is realized.

  Hereinafter, the processing method of the gallium nitride semiconductor thin film of this embodiment and the thin film processing apparatus of this embodiment will be described in detail with reference to the drawings. In the present embodiment, processing of the gallium nitride thin film layer 9 formed on the sapphire transparent substrate 8 will be described. However, the thin film processing apparatus of the present invention can also be used for surface processing of III-V nitride semiconductors such as GaN, InGaN, and AlGaN, other semiconductor thin films, and these semiconductor thin films formed on an opaque substrate.

  In this embodiment, as an example of a nitride semiconductor etching method, a processing method is described in which a nitride semiconductor is etched by a three-step process of measuring transmittance at a laser beam wavelength, laser irradiation treatment, and hydrochloric acid treatment. However, the thin film processing apparatus of the present embodiment irradiates a group III-V nitride semiconductor as a processing target with a laser beam for measuring the amount of transmitted light of an etching laser or a monitoring laser and laser irradiation processing. Since the apparatus performs the processing, it can be used for processing other than the processing method described below.

  The thin film processing apparatus of the present invention is not limited to the constituent members of the embodiments described below, and can be implemented in various embodiments in which some or all of the constituent members are replaced with other constituent members having equivalent functions. is there. This embodiment has a feature in the process of irradiating a thin film layer with laser light, and there is a difference from the present invention regarding acid treatment, semiconductor physical properties, laser light properties, modulation, optical design, generation method, and the like. Therefore, a detailed description of such matters described in Patent Document 1 is omitted to avoid complications.

  In this embodiment, instead of collectively irradiating a planar laser beam on the processing range, light energy corresponding to a required processing amount (depth) is applied to each scanning point in the processing range with a converged laser beam spot. Injecting and causing dissolution and damage of the crystal structure concentrated in the surface layer. Therefore, at a scanning point where the required processing amount is large, the cumulative irradiation amount (irradiation intensity, irradiation time, number of irradiations, or a combination thereof) is increased to increase the removal depth, and at a scanning point where the required processing amount is small, By reducing the cumulative irradiation amount and reducing the removal depth, a desired surface shape can be processed regardless of the surface uneven shape before processing.

  In this embodiment, scanning point thickness detection and processing irradiation are performed through the same optical system means. And a detection means detects the thickness of the thin film layer before a process by detecting the transmitted light quantity of the thin film layer by the laser beam spot as film thickness detection light. The control means sets the irradiation intensity of the laser beam spot at the same processing point by the intensity modulation means according to the required processing amount obtained from the thickness before processing and the target thickness obtained by the detection means. Accordingly, it is possible to accurately remove the crystal layer by precisely matching the thickness detection position and the processing irradiation position.

  Therefore, when etching a nitride semiconductor, it is possible to realize a thin film processing apparatus capable of performing high-speed processing, having a highly flat processed surface, and capable of controlling the remaining film thickness on the nano order. Become.

  The conventional dry etching method can solve the problem of under-etching and over-etching (see FIG. 10). That is, when a part of the thin film layer reaches the etch stop film thickness (just etching part), a film thickness distribution is formed such that the other part is under-etched or over-etched (see FIG. 12). is there. In other words, what is necessary for a semiconductor element or an optical integrated circuit is not “a portion removed by etching” but “a thin film layer left by etching”. It can be performed more precisely than the device.

<Thin Film Processing Apparatus of First Embodiment>
FIG. 1 is an explanatory diagram of the configuration of the thin film processing apparatus according to the first embodiment, and FIG. 2 is a flowchart of control of the thin film processing apparatus. FIG. 1 shows an example of an apparatus configuration for realizing a group III-V nitride semiconductor etching method according to the present invention, in which the intensity of the same laser is modulated by an attenuator as a light source for transmittance measurement and etching. FIG.

  As shown in FIG. 1, the thin film processing apparatus 100 of the first embodiment converges the laser light generated by the laser generator 1 with an optical system 3, guides it to a processing point K with a mirror 5, and A laser beam spot is formed on the surface.

  The laser generator 1 is a YAG quadruple laser generator that converts the wavelength of a laser beam having a wavelength of about 1 μm generated by using a YAG crystal and outputs a laser beam having a wavelength of 266 nm. The wavelength of 266 nm is selected as a wavelength that can be absorbed by a gallium nitride GaN crystal to excite electrons, as will be described later.

  A homogenizer 2 disposed downstream of the laser generator 1 receives the laser beam emitted from the laser generator 1 to shape the beam profile of the laser beam and uniformize the spatial intensity distribution in the beam profile. Exit.

  The optical system 3 condenses the laser light emitted from the homogenizer 2 to form a 10 μm square laser beam. The total reflection mirror 5 bends the laser beam whose diameter is reduced / shaped by the optical system 3 so as to be directed toward the etching object A, and forms a laser beam spot at the processing point K. The attenuator 4 disposed between the optical system 3 and the total reflection mirror 5 adjusts the intensity of the incident laser light and emits it.

  The XY stage 6 performs two-dimensional scanning while holding the etching object A on a transparent sample stage. The etching target A has a gallium nitride thin film layer 9 formed on the surface of a transparent substrate 8 made of sapphire. The XY stage 6 is stepped at a pitch of 10 μm matched to the laser beam spot size, and sequentially positions each scanning point S of the etching target A to the processing point K.

  A laser beam that has passed through the etching object A is incident on the power meter 11 disposed under the etching object A of the XY stage 6. The power meter 11 monitors the intensity of the laser beam that has passed through the etching object A, and inputs the monitoring result to the control unit 10.

  The controller 10 calculates the transmittance of the etching object A from the intensity of the laser beam measured by the power meter 11 and calculates the film thickness of the thin film layer 9 from the extinction coefficient or the like. Then, various corrections are applied to calculate the optimum etching laser output, and the modulation amount by the attenuator 4 for each scanning point S is calculated. The calculation result is stored in the control unit 10 as map data, and in the processing irradiation executed after the film thickness measurement, the attenuator 4 is controlled based on the calculation result, and the etching target is controlled by the intensity-modulated laser beam. A is exposed. At this time, the control unit 10 controls the XY stage 6 to move the etching target A as the etching target so that the laser beam hits the entire etching site.

  In addition, since the irradiation of the laser beam to the etching target A (gallium nitride GaN) is performed in a nitrogen gas atmosphere, the XY stage 6 is installed in an airtight processing chamber (chamber) (not shown). The optical path of the laser beam is divided into the inside and outside of the hermetic treatment chamber by a transparent window (not shown). A vacuum pump system (not shown) and a nitrogen gas supply system are connected to the hermetic treatment chamber.

  Referring to FIG. 1, as shown in FIG. 2, the setting of the etching object A to the XY stage 6 is completed (YES in S11), and the necessary setting operation for the control unit 10 is completed (YES in S12). Then, an operation for starting machining is performed on the control unit 10 (YES in S13). Then, the control part 10 starts film thickness measurement (S15).

  That is, the control unit 10 starts the laser generator 1 and stops the movement of the XY stage 6 at a pitch of 10 μm equal to the laser beam spot size in a state where the intensity of the laser beam spot can be lowered to a predetermined value by the attenuator 4. Then, one pulse of laser beam pulse is output from the laser generator 1 in a state where it is stopped at every scanning position S of the etching object A. At the same time, the control unit 10 detects the transmitted light amount of the etching object A from the output of the power meter 11, and forms the transmitted light amount map data of the etching object A in combination with the coordinate position of the XY stage 6 (S15). . This process is repeated until the XY stage 6 is moved by scanning to cover all the scanning points S of the etching target A (YES in S15).

  Then, when the XY stage 6 is scanned and moved to complete the creation of the transmitted light amount map (YES in S15), the control unit 10 calculates the film thickness distribution before processing based on the transmitted light amount map (S16), and the monitor Display on the screen. Further, the processing target value input in advance in step 12 is subtracted from the film thickness before processing at each scanning point S to obtain a required processing amount for each scanning point S and a scanning point for realizing this processing amount. A processing condition map is formed by calculating the laser beam intensity for each S (S17).

  Then, the control unit 10 controls the attenuator 4 so that the intensity of the laser beam spot can be raised from the measurement level to the processing level, and adjusts the intensity according to the processing condition map while moving the XY stage 6 to each scanning position. Is moved while being positioned (S18). Then, each scanning point S of the etching object A is irradiated with a laser beam having an intensity corresponding to the required processing amount by one pulse (S18).

  When the processing irradiation is completed by scanning and moving the XY stage 6 (YES in S19), the control unit 10 stops the laser generator 1 and performs system termination / initialization processing including storage of various data. (S20).

<Description of processing principle>
Figure 3 is a phase transition diagram of gallium nitride, 4 diagram of the temperature distribution simulation result of the film thickness direction in the laser output 35 mJ / cm ^2, Figure 5 is a temperature distribution simulation result in the thickness direction in the laser output 100 mJ / cm ² FIG. FIG. 6 is a diagram of a temperature distribution simulation in the film thickness direction at a laser output of 50 mJ / cm ² , and FIG. 7 is an explanatory diagram of an etching result by the thin film processing method of the present embodiment.

  The group III-V nitride semiconductor, which is the etching target A in the present embodiment, is a wide bandgap compound, and has a large extinction coefficient mainly at ultraviolet wavelengths. Therefore, in addition to YAG fourth harmonic 266 nm, YAG third harmonic 355 nm, KrF 248 nm, ArF 193 nm, and the like can be used.

  Group III-V nitride semiconductors have different film qualities depending on film forming conditions and the like, and the extinction coefficient is not constant, but is in the range of 10 4 to 5 5. Therefore, when the group III-V nitride semiconductor is irradiated with the laser beam in the above wavelength range, the electrons in the crystal structure of the group III-V nitride are excited and the irradiation energy is absorbed.

  However, when the excited electrons return to the ground state, most of the absorbed energy other than that deactivated by fluorescence or phosphorescence such as photoluminescence (hereinafter referred to as PL) is converted into heat, so the crystal structure rapidly increases in temperature. cause. Accordingly, the amount of heat generated on the surface layer by the laser light having a wavelength having an energy density larger than the band gap is proportional to the extinction coefficient ε and the laser energy density J.

  Etching to dissolve the crystal structure is started when the temperature of the group III-V nitride semiconductor heated by the laser beam exceeds the melting point. The phase transition diagram of gallium nitride shown in FIG. 3 shows that the crystal structure causes an irreversible decomposition reaction between gallium metal and nitrogen when the temperature exceeds the melting point at 1 atmosphere. The depth of pyrolysis depends on the calorific value and the thermophysical properties of the III-V nitride, and is mainly influenced by the heat capacity. From the molar specific heat and the latent heat of fusion (enthalpy) required for raising the temperature of the object to be etched from the initial temperature to the melting point, the meltable (thermally decomposable) volume, the density of the III-V nitride semiconductor and the laser beam spot diameter Can be calculated in consideration of

  In the region where the crystal structure is thermally decomposed, only gallium metal remains as a residue, and the etching is completed by removing this by acid treatment. On the other hand, even if the temperature rises, the crystal structure of gallium nitride is stable unless the amount of heat exceeding the melting point is supplied. This can be easily imagined from the fact that the deposition temperature during vapor phase growth (epitaxial) is close to the melting point. The vapor-grown III-V nitride semiconductor has a stable crystal structure up to the melting point, which is supported by DSC (Differential Thermal Scanning Calorimetry) measurement results.

  In the first step (S14: FIG. 2) in the manufacturing method of the present embodiment, as shown in FIG. 4, the entire processing region of the etching object A is obtained using laser light having an energy density not exceeding the melting point even on the surface. The transmittance is measured for each scanning position S. A laser beam generator dedicated to transmittance measurement may be provided separately. However, if the intensity of the etching laser light is adjusted by the attenuator 4 and the etching laser light is also used as the film thickness monitoring light, the thin film processing apparatus 100 can be made compact. In addition, adjustment to match the optical axes of the monitor light and the etching laser light becomes unnecessary.

  In the manufacturing method of this embodiment, the film thickness of the etching object A before processing is obtained from the transmittance of the etching object A. The transmittance of the etching object A is obtained by dividing the intensity of the monitored laser light by the intensity of the laser light when there is no etching object A.

  From the film thickness monitored in the first step of measuring the film thickness distribution, the calorific value for making the film thickness after processing is calculated, and based on this, the laser light intensity of the second condition adjusted by the attenuator 4 is used. Exposure is a second step (S18: FIG. 2). In the second step of performing the processing irradiation, as shown in FIGS. 5 and 6, a laser beam having a high energy density such that the temperature exceeds the melting point in a region having a required processing depth is used. Then, processing irradiation for each scanning position S is performed over the entire processing region of the etching target A. As shown in FIG. 5, since the intensity distribution of the laser beam in the film thickness direction is exponentially attenuated from the surface by absorption, the surface temperature becomes the highest, the temperature distribution is generated in the film thickness direction, and reaches the melting point. The part up to the depth is etched.

  The etching object A that has completed the second step of the processing irradiation is taken out from the thin film processing apparatus 100 and treated with an acid in the third step, so that the gallium residue and nitrogen forming the crystal structure are removed. The portion damaged in the crystal structure is selectively removed. As a result, as shown in FIG. 7, the surface of the object to be etched that has undergone the third step has a flat crystal with a surface roughness that does not depend on the unevenness before processing and that depends on the processing accuracy of the thin film processing apparatus 100. The surface is exposed.

<Details of processing method>
In the first step of measuring the film thickness distribution (S14: FIG. 2), first, the surface reflectance and transmittance of the etching target A at the laser wavelength to be used, and the laser of the sample stage on which the etching target A is placed. The transmittance at the wavelength is measured as the background. Depending on the etching accuracy, the XY stage 6 is scanned if necessary, and the background is also measured as mapping data.

  After the measurement, the etching object A is set on the sample stage of the XY stage 6, and the transmittance of the etching object A is measured in a non-destructive state without thermal decomposition under the first condition not exceeding the melting point. The extinction coefficient of the etching object A can be accurately obtained from the transmittance measured at the initial film thickness on the order of several microns.

  Subsequently, the film thickness is obtained from the laser transmittance of the etching target A actually measured in consideration of the background. The film thickness is expressed as a function obtained by dividing the logarithm of transmittance by the extinction coefficient. In the first cycle, it matches the initial film thickness set for calculating the extinction coefficient, but after the second cycle, the etching residual film thickness of the etching object A is obtained from the transmittance and monitored.

Next, a laser output for setting the remaining film thickness to a predetermined value is calculated from the heat capacity of the etching object A and the temperature profile in the film thickness direction (FIGS. 5, 6, etc.). The second condition in the processing irradiation is, for example, an absorption coefficient ε of gallium nitride at 266 nm ε = 100000 C = 0.87 [J / g · K], d = 6.1 [g / cm 3]. Further, the transmittance T% of the sapphire transparent substrate 8 is 80%, and the laser energy density is 50 mJ / cm ² . As a result of simulation under such conditions, a depth profile as shown in FIG. 6 can be drawn. Further, error diffusion coefficient correction in consideration of the film thickness of the adjacent region and correction in consideration of thermal conductivity are added, and time and place are integrated by XY scanning of the XY stage 6. The simulation is summarized as follows.

Considering a segment with an area of 1 cm ² and a thickness of 1 nm, the light intensity density I at a position of depth dnm is
I = I0 · 10 (−ε · d)
I: light intensity density at a position of depth dnm [J / cm ² ], I0: exposure energy density [J / cm ² ],
ε: extinction coefficient [cm−1], d: thickness [cm].

Further, the temperature Td at the position of depth dnm (thickness 1 nm) is
Td = ΔI / C · ρ
Td: temperature at the position of depth dnm (thickness 1 nm) [K], ΔI: intensity attenuation for each thickness of 1 nm [J / cm ² ],
C: specific heat [J / g · K], ρ: density [g / cm ³ ].

The heat flow rate q is
q = λ · ΔT / t
q: thermal flow velocity [W / cm ² ], λ: thermal conductivity [W / m · K], ΔT: temperature difference of each segment [K], t: thickness [m].

In this embodiment, the extinction coefficient ε = 100000 C = 0.87 [J / g · K], d = 6.1 [g / cm ³ ], and the transmittance T% = 80% of the transparent substrate 8 made of sapphire. is there.

According to the simulation result calculated in this way, as shown in FIG. 6, when the laser energy density is 50 mJ / cm ² , the melting point of gallium nitride is 1200 ° C. or more in the range of 15 nm from the surface. As shown in FIG. 5, when the laser energy density is 100 mJ / cm ² , the melting point of gallium nitride is 1200 ° C. or higher in the range of 45 nm. As shown in FIG. 4, if the laser energy density is 35 mJ / cm ² or less, the melting point is not reached even at the surface below 1200 ° C. In the present embodiment, since the pulse repetition period is sufficiently short, no correction is made approximately.

The exposure energy density I0 is
I0: exposure energy density [J / cm ² ] ≦ maximum laser energy density [J / cm ² ] × number of pulses [1 / sec] × v [sec]
v: Time [sec] required to scan an area of 1 cm ² .

Accordingly, the exposure energy density I0 [J / cm ² ] for each scanning position S is determined by referring to the lookup table created in this way, and the thickness position d from the surface is the melting point 1200 ° C. of gallium nitride. Ask to be. When d = 0, the laser output is set below the threshold or zero.

In this way, the exposure energy density I0 [J / cm ² ] for each scanning position S of the etching target A and the control amount of the attenuator 4 for the simulation calculation are calculated. Thereafter, as a second step of the present embodiment, the etching object A is actually laser-exposed while the energy density is modulated by the attenuator 4 based on the simulation result.

  In the case of pulse exposure, if it is predicted that the exposure will be less than a predetermined remaining film thickness by exposure with one pulse of the pulse laser, the low energy is divided into several pulses for etching. In the case of pulse exposure, it is desirable to keep the time lag within the light-heat conversion time and chemical reaction time in the III-V nitride semiconductor. In addition, the CW laser can be exposed by being divided into several cycles.

  When the second step is completed, the etching object A is taken out from the thin film processing apparatus 100, and as a third step of the present embodiment, acid treatment with hydrochloric acid, sulfuric acid, etc. and rinse treatment with pure water, alcohol, etc. are performed.

  The above-described method for etching a group III-V nitride semiconductor according to the present embodiment is a cycle in which laser transmittance measurement, laser processing irradiation, and hydrochloric acid treatment are performed once each. Then, the above process is repeated for a plurality of cycles until the entire processing area of the thin film layer 9 (all scanning points S) reaches a predetermined remaining film thickness.

  Thus, according to the method for etching a group III-V nitride semiconductor of the present embodiment, the group III-V nitride semiconductor can be etched at a high speed, and the processing surface can be highly planarized. .

  Even if the group III-V nitride semiconductor, which is the etching target A, is irradiated with laser light with strong energy, the group III-V nitride semiconductor, which is the processing target, is not seriously damaged.

  Furthermore, the adjustment of the remaining film thickness in the group III-V nitride semiconductor that is the etching object A can be performed by changing the film thickness monitor by laser, the laser energy density, and the number of irradiation pulses.

  As the laser beam to be used, laser beams having a plurality of wavelengths shorter than the wavelength of the absorption edge of the material to be processed are used. Then, the spatial intensity distribution of the laser beam is made uniform using the homogenizer 2 and condensed to about several tens of microns to several microns using the optical system 3.

  As is apparent from the above, the III-V nitride semiconductor etching method according to the present embodiment solves the problem of obtaining a smooth film controlled with a nano-order residual film thickness of the prior art. be able to.

  Furthermore, according to the group III-V nitride semiconductor etching method of the present invention, when performing photonic crystal processing of an optical integrated circuit using a group III-V nitride semiconductor, the group III-V nitridation of the present invention is performed. An etching method of a physical semiconductor can be used.

  In the scanning of the surface to be processed with the laser beam spot, the etching target A is generally moved two-dimensionally by the XY stage 6. However, the etching object A may be fixed and the laser beam spot and the power meter 11 of the transmittance measuring device may be scanned.

  Further, the attenuator 4 may be arranged at another position on the laser optical path, such as between the laser light generator 1 and the homogenizer 2, and an intensity modulation device other than the attenuator 4, for example, a beam whose distribution rate can be changed. It may be replaced with a splitter, an ND filter, or the like. Further, the processing irradiation may be performed in a semiconductor stepper system by replacing the optical system 3 with a reduction projection optical system disposed between the mirror 5 and the etching object A.

  Further, the shape of the laser beam spot is not limited to a square, and may be an elongated slit shape. Further, one-pulse irradiation for each step feed may be replaced with continuous feed pulse irradiation, continuous feed continuous irradiation, or the like. As described above, the cumulative irradiation amount for each scanning point can be set not only by controlling the pulse intensity using the modulation means, but also by the cumulative number of irradiations of the same output pulse, the pulse exposure time, and a combination thereof.

<Example of etching process>
An etching object A was obtained in which a 2 μm gallium nitride thin film layer 9 was epitaxially grown on a polished 430 μm sapphire transparent substrate 8. When the surface smoothness of the etching target A was measured, the flat portion had a roughness of about 80 nm in an area of 100 μm ² , but there were some protrusions of 100 nm to 400 nm partially. According to the transmittance measurement using a spectroscope, the extinction coefficient at 266 nm was 8 × 10 ⁴ . The transmittance of the polished 430-micrometer sapphire substrate is 85%, and this extinction coefficient is a value converted from gallium nitride alone corrected for this.

  It is used with reference to the basic physical properties of the etching object A obtained above. As constants of the thin film processing apparatus 100 shown in FIG. 1, the transmittance loss due to quartz on the sample stage of the etching target A in the XY stage 6 is 8% on average, and a transmittance map at each point was obtained by XY scanning. .

Subsequently, the energy density of the 266 nm YAG fourth harmonic wave beam-formed to 10 μm □ via the optical system 3 shown in FIG. Then, the attenuator 4 was set so that the maximum irradiation energy density to gallium nitride was 50 mJ / cm ² in consideration of the transmittance loss at the mounting table.

  Based on these data, the temperature profile in the gallium nitride film thickness direction at a single pulse was estimated for a plurality of irradiation energy densities, and a lookup table was created.

The etching object A diced to 1 cm ² □ was placed on the sample stage of the XY stage 6, and the transmittance was measured as the first step. The thickness of the gallium nitride thin film layer 9 was estimated to be 2 microns from the value obtained by correcting the transmittance loss of the sapphire substrate and the mounting table and the extinction coefficient. Since the extinction coefficient is obtained from the transmittance on the premise of the initial film thickness, it is natural that the initial film thickness is obtained by using the extinction coefficient and the transmittance.

  Since the transmittance is low when the film thickness is thick, the film thickness measurement accuracy by transmitted light is low. However, referring to the lookup table, the influence is small because the maximum irradiation energy density is obtained.

Next, as a second step, the etching object A was irradiated at a maximum irradiation energy density of 50 mJ / cm ² . The same first step (transmittance measurement / film thickness calculation / irradiation energy density calculation) was performed by scanning 10 μm steps in the X direction. Except for the scanning position S at the origin, the target remaining film thickness was calculated by correcting the film thickness at the adjacent scanning position S by error diffusion, and reflected in the irradiation energy density.

  In this way, the second step (irradiation / step scanning) was sequentially repeated to scan the gallium nitride in a line. Next, 10 μm step scanning was performed in the Y direction, and scanning in the line shape in the negative X direction was repeated. When the entire exposed gallium nitride was observed, metallic luster was observed, and as a third step, it was immersed in 35% hydrochloric acid for 1 minute and then washed with distilled water.

  Similarly, one cycle of processing from the first step to the third step is repeated for several cycles to several tens of cycles. A case where the end point is set to a remaining film thickness of, for example, 400 nm will be described. When the film thickness reaches about 400 nm, the transmittance becomes close to 50%, so that the film thickness measurement accuracy increases.

  When a look-up table was referred to for this film thickness, it was found that 400 nm was over-etched at the maximum irradiation energy density, so that exposure was performed at the optimum irradiation energy density obtained by calculation. Under the conditions of this processing example, etching up to approximately 20 nm on an average per cycle was possible.

  The processing method described in the present embodiment is a single crystal such as a III-V nitride semiconductor, GaN (gallium nitride), InN (indium nitride) or AlN (aluminum nitride), or a mixed crystal thereof (InGaN, AlGaN, etc.). When high-speed etching is performed, the processing surface can be highly planarized. Since crystals such as GaN, InN, and AlN have the same structure, mixed crystals (InGaN, AlGaN, etc.) can also be created, and these mixed crystals are also included in III-V group nitride semiconductors.

  The processing method described in this embodiment can provide a group III-V nitride semiconductor in which the remaining film thickness is controlled on the nano order. In particular, since the film thickness measurement accuracy is improved as the remaining film thickness with a high transmittance is increased, the nano-order remaining film thickness can be etched accurately. And since the film thickness of an adjacent area | region is considered by error diffusion, the etching process excellent in smoothness without a level | step difference can be performed.

<Thin Film Processing Apparatus of Second Embodiment>
FIG. 8 is an explanatory diagram of the configuration of the thin film processing apparatus of the second embodiment, FIG. 9 is an explanatory diagram of the relationship between the wavelength of the laser beam and the amount of heat generation, and FIG. 10 is an explanation of the processing result by two types of laser beams having different wavelengths. FIG. The thin film processing apparatus 200 of the second embodiment is obtained by adding a YAG third harmonic laser irradiation optical system in parallel to the YAG fourth harmonic laser irradiation optical system to the thin film processing apparatus 100 of the first embodiment shown in FIG. It is. Therefore, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 8, the thin film processing apparatus 200 of the second embodiment branches a laser beam having a wavelength of about 1 μm generated by the laser generator 1A using a YAG crystal into two optical paths by the half mirror 17. Then, laser light traveling in one optical path is made incident on the FHG conversion element 1C by the mirror 19. The FHG conversion element 1C converts the wavelength of the incident YAG laser light into ¼ to generate laser light with a wavelength of 266 nm. The YAG fourth harmonic laser converted by the FHG conversion element 1C is converged by the optical system 3 and guided to the processing point K by the beam combiner 16 to form a laser beam spot on the surface of the etching object A.

  Further, the laser light traveling on the other optical path branched by the half mirror 17 is incident on the THG conversion element 1B by the mirror 18. The THG conversion element 1B converts the wavelength of the incident YAG laser light into ３ and generates laser light with a wavelength of 355 nm. The third harmonic laser beam converted by the THG conversion element 1B is converged by the optical system 13, guided by the mirror 15 and the beam combiner 16 to the same processing point K as the fourth harmonic laser beam, and is applied to the surface of the etching object A. A laser beam spot is formed. As described above, the wavelengths of 266 nm and 355 nm are selected as wavelengths that can be absorbed by the crystal structure of gallium nitride GaN to excite electrons.

  The homogenizer 12 disposed downstream of the THG conversion element 1B shapes the beam profile of the laser beam and emits it with a uniform spatial intensity distribution in the beam profile. The optical system 13 condenses the laser light emitted from the homogenizer 12 to form a 10 μm square laser beam. The mirror 15 bends the laser beam whose diameter is reduced / shaped by the optical system 13 and directs the laser beam toward the etching object A. The attenuator 14 disposed between the optical system 13 and the mirror 15 adjusts the intensity of the incident laser light and emits it.

  The control unit 10 calculates the transmittance of the etching object A from the intensities of the two types of laser beams having wavelengths of 266 nm and 355 nm measured by the power meter 11, and calculates the film thickness of the thin film layer 9 from the extinction coefficient or the like. Then, various corrections are applied to calculate the optimum etching laser output, a combination of laser beams having two wavelengths is selected, and the modulation amounts by the attenuators 4 and 14 for each scanning point S are calculated.

  This calculation result is stored in the control unit 10 as map data, and in the processing irradiation executed after the film thickness measurement, the attenuators 4 and 14 are controlled based on the calculation result, and the object to be etched with the intensity-modulated laser beam. Object A is exposed. At this time, the control unit 10 controls the XY stage 6 to scan and move the etching target A so that the laser beam hits the entire etching site.

  Therefore, the adjustment of the remaining film thickness in the group III-V nitride semiconductor that is the etching object A is performed by changing at least one of the laser energy density and the number of irradiation pulses according to the film thickness monitoring result by the laser beam. .

  As a laser beam to be used, a laser beam having a wavelength shorter than the wavelength of the absorption edge of the material to be processed is used. Then, the spatial intensity distribution of the laser light is made uniform using the homogenizers 2 and 12 and condensed by the optical systems 3 and 13 to about several tens of micrometers to several micrometers.

  The thin film processing apparatus 200 includes a chamber chamber for controlling the etching atmosphere by installing an XY stage 6 for placing the etching object A inside, or a nitrogen gas spraying apparatus for the processing point K. May be.

  The group III-V nitride, which is the etching target A, exhibits a larger extinction coefficient for YAG fourth harmonic 266 nm than for YAG third harmonic 355 nm. Therefore, even if the film thickness cannot be measured accurately because the transmitted light is too weak at YAG fourth harmonic 266 nm, the film thickness can be measured more accurately by using YAG third harmonic 355 nm.

  As shown in FIGS. 9A and 9B, irradiation with a laser beam having such a wavelength that is equal to or greater than the band gap of the III-V nitride causes the III-V nitride to be excited. Then, when returning from the excited state to the ground state, the band gap energy is converted into heat or passes through two paths, which emit light as photoluminescence (hereinafter referred to as PL) such as fluorescence or phosphorescence.

At this time, as shown in FIG. 9A, when the wavelength λ _{1 of the} laser light is close to the band gap λ _PL , PL is observed strongly, but the wavelength λ having energy larger than the band gap λ _{PL. In} the light of ₂ , the shorter the wavelength, the higher the conversion efficiency to heat. This phenomenon is excited in level of the upper including the vibrational level shorter wavelength, to thermal radiation with the transition to the impurity level or PL level of the lowest level and the band gap lambda _PL bandgap lambda _PL It is explained that.

Therefore, the heat conversion efficiency of the laser light in a short wavelength having a larger energy than the band gap lambda _PL is proportional to the extinction coefficient epsilon, calorific value is proportional to the extinction coefficient epsilon and laser energy density J, it depends on the wavelength lambda. Here, since the wavelength energy and the laser intensity energy are not confused, the latter is described as energy density or laser output.

  Therefore, by calculating the film thickness from the transmittance and the extinction coefficient at a plurality of laser wavelengths, the film thickness can be obtained more accurately than a single wavelength. The transmittance can be obtained by dividing the actually measured laser light intensity by the laser light intensity when there is no etching object A.

  In the thin film processing apparatus 200 of the second embodiment, the calorific value for obtaining a predetermined film thickness is calculated from the film thickness monitored using two types of laser light in the first step of measuring the film thickness distribution, Based on this, the second step is to process and irradiate with a plurality of laser wavelength lights under the second condition adjusted by the attenuator.

  As described above, the intensity distribution of the laser beam in the film thickness direction during exposure attenuates exponentially from the surface, so the surface temperature becomes the highest, the temperature distribution occurs in the film thickness direction, and the part that has reached the melting point Is etched. Therefore, it is preferable that the processing irradiation with a plurality of laser wavelength lights is simultaneously exposed with a plurality of laser wavelength lights. Further, even when a plurality of laser wavelength lights are separately exposed alternately, it is desirable to keep the time lag within the light-heat conversion time and the chemical reaction time in the group III-V nitride semiconductor.

  In the thin film processing apparatus 200 according to the second embodiment, both the YAG fourth harmonic and the YAG third harmonic perform wavelength conversion on the YAG fundamental wave generated by the laser light generator 1A using the nonlinear optical crystal of the THG conversion element 1B and the FHG conversion element 1C. . Then, the YAG fundamental wave is branched by the half mirror 17 of the beam splitter, wavelength-converted by the THG conversion element 1B and the FHG conversion element 1C, and then condensed by the beam combiner 16, so that pulse emission can be easily synchronized.

  However, even when separate laser light generators are used, it is easy to keep within the chemical reaction time by performing pulsed emission in synchronization with the trigger signal transmitted from the control unit.

<Details of processing method>
First, the surface reflectance and transmittance of the etching target A and the transmittance of the sample stage of the XY stage 6 on which the etching target A is placed are measured as backgrounds for YAG third harmonic 355 nm and YAG fourth harmonic 266 nm, respectively. Keep it. At this time, as described above, the transmittance of the etching object A is measured in a non-destructive state without thermal decomposition under the first condition not exceeding the melting point. The extinction coefficient of the etching object A can be accurately obtained from the transmittance measured at the initial film thickness on the order of several microns.

  Subsequently, as the first step of the present invention, the film thickness is obtained from the laser transmittance of the etching object A measured in consideration of the background. The film thickness is expressed as a function obtained by dividing the logarithm of transmittance by the extinction coefficient. The film thickness coincides with the initial film thickness set for calculating the extinction coefficient only in the first cycle, but after the second cycle, the remaining film thickness is obtained from the transmittance and monitored.

  Next, the laser output for setting the remaining film thickness to a predetermined value is calculated from the heat capacity and the temperature profile in the film thickness direction. The YAG fourth harmonic 266 nm is as described above. The same temperature increase simulation in the depth direction is performed for the YAG third harmonic 355 nm by performing the same thermal conversion efficiency correction for a plurality of wavelengths. Thereby, the simulation result of the temperature profile in the film thickness direction at each wavelength is obtained.

  In the second step of processing irradiation, a combination of a plurality of wavelength energy densities with an optimum etching film thickness is selected based on the simulation result, and each wavelength light is intensity-modulated by the attenuators 4 and 14 and laser exposure is performed. . At this time, in the pulse laser, when it is predicted that the exposure will be less than a predetermined remaining film thickness by one pulse of exposure, the low energy is divided into several pulses for etching.

  Even in the case of pulse exposure, it is desirable to keep the time lag within the light-heat conversion time and the chemical reaction time in the group III-V nitride semiconductor. With a CW laser, exposure can be performed in several cycles.

  Subsequently, as described in the first embodiment, the etching object A processed and irradiated with the laser beam is removed from the thin film processing apparatus 200. Then, the III-V group nitride semiconductor is subjected to a third step of treating with an acid, and the gallium residue and damage layer on the surface are removed by the acid treatment. In the third step, acid treatment with hydrochloric acid or sulfuric acid and rinsing treatment with pure water or alcohol are performed.

  The entire processing region of the thin film layer 9 is defined as a cycle in which the laser transmittance measurement, the laser irradiation treatment, and the hydrochloric acid treatment, which are the III-V group nitride semiconductor etching method of this embodiment, are performed once each (Cycle). The above process is repeated for a plurality of cycles until becomes a predetermined remaining film thickness.

Thus, according to the III-V nitride semiconductor etching method of the present invention, as shown in FIG. 10, the laser beam reaches a position deeper than the case of only YAG fourth harmonic 266 nm, and the film thickness is accurately measured. Measurements can be made. This is because two types of wavelengths λ ₁ and λ ₂ , that is, YAG fourth harmonic 266 nm and YAG third harmonic 355 nm are used in combination.

  Further, in the processing irradiation, the high temperature region can be extended to a deep position, and the III-V nitride semiconductor can be etched at a high speed to a predetermined processing target film thickness, and the processing surface can be highly planarized. it can.

  Similarly to the case of only YAG fourth harmonic 266 nm, even if the III-V nitride semiconductor that is the etching target A is irradiated with laser light with strong energy, the etching target A is III-V. There is no serious damage to the group nitride semiconductor.

<Example of etching process>
A sample was obtained by epitaxially growing 2 μm gallium nitride on a polished 430 μm sapphire substrate. When the surface smoothness of the sample was measured, the flat portion had a roughness of about 80 nm in an area of 100 μm ² , but there were some protrusions of 100 nm to 400 nm partially. According to the transmittance measurement using a spectroscope, the extinction coefficient at 266 nm was 8 × 10 ⁴ , and the extinction coefficient at 355 nm was 7.5 × 10 ⁴ . The transmittance of the polished 430-micrometer sapphire substrate is 85% at 266 nm and 87% at 355 nm, which is a value converted to an extinction coefficient of gallium nitride alone corrected for this.

  The extinction coefficient indicates the rate of excitation, and the heat generation efficiency from the excited state was obtained by measuring in advance the etching depth at a specified energy density at each wavelength for a sampled piece of the same sample. It is used with reference to the basic physical properties of the etching target obtained above.

  As an apparatus constant of the thin film processing apparatus 200 shown in FIG. 8, the transmittance loss at both wavelengths due to quartz of the sample stage on which the etching object A is placed is 8% on average, and a transmittance map at each point is obtained by XY scanning. Obtained.

Subsequently, the energy density of a 266 nm YAG fourth harmonic wave beam-formed to 10 μm square via the optical system 3 in FIG. 8 is measured by the power meter 11, and the loss of transmittance at the sample stage is taken into consideration to gallium nitride. The maximum irradiation energy density was set to 50 mJ / cm ² .

Similarly, the energy density of the 355 nm YAG triple wave beam-formed to 10 μm square via the optical system 13 of FIG. Then, in consideration of the transmittance loss at the sample stage, the maximum irradiation energy density to gallium nitride was similarly set to 50 mJ / cm ² .

Two small pieces of gallium nitride are sampled, exposed to an etching at a wavelength of 266 nm maximum irradiation energy density of 50 mJ / cm ² and a wavelength of 355 nm maximum irradiation energy density of 50 mJ / cm ² , and treated with hydrochloric acid to measure the etching depth. did. 20 nm and 15 nm, respectively, and the difference is probably due to the difference in heat generation efficiency.

  Based on these data, the temperature profile in the gallium nitride film thickness direction at a single pulse was estimated for a plurality of irradiation energy densities, and a lookup table was created.

The etching object A diced to 1 cm ² □ was placed on the sample stage of the XY stage 6 of the thin film processing apparatus 200 of the second embodiment. And as a 1st process, the film thickness was estimated to be 2 microns from the value which measured the transmittance | permeability, and corrected the transmittance | permeability loss of the sapphire substrate and the sample stand, and the light absorption coefficient. Since the extinction coefficient is obtained from the transmittance on the premise of the initial film thickness, it is natural that the initial film thickness is obtained by using the extinction coefficient and the transmittance.

  Since the transmittance is low when the film thickness is thick, the film thickness measurement accuracy is poor. However, when the lookup table is referenced, the influence is small because the maximum irradiation energy density is obtained. It was decided to use 100% of a 266 nm laser having an etching depth of 20 nm.

Next, as a second step, the sample was processed and irradiated with a laser beam having a wavelength of 266 nm at a maximum irradiation energy density of 50 mJ / cm ² . The same first process (transmittance measurement, film thickness calculation, irradiation energy density calculation) was performed by scanning 10 μm steps in the X direction. Other than the origin, the target remaining film thickness was calculated by correcting the film thickness at the adjacent scanning position by error diffusion, and reflected in the irradiation energy density.

  Then, the second step (processing irradiation / step scanning) was sequentially repeated to scan the surface of the gallium nitride thin film layer of the etching target A in a line shape. Next, 10 μm step scanning was performed in the Y direction, and scanning in the line shape in the negative X direction was repeated. When the etching target A after the scanning exposure was observed, a metallic luster was observed, and as a third step, it was immersed in 35% hydrochloric acid for 1 minute and then washed with distilled water. Similarly, the processes from the first process to the third process are repeated several to several tens of cycles.

A case where the end point is set to a remaining film thickness of, for example, 400 nm will be described. When the film thickness reaches about 400 nm, the transmittance becomes close to 50%, so that the film thickness measurement accuracy increases. When a look-up table was referred to for this film thickness, it was found that 400 nm was over-etched at the maximum irradiation energy density, and therefore, exposure was performed at optimum irradiation energy densities of 266 nm, 20 mJ / cm ² and 355 nm, 30 mJ / cm ² .

Although the total is 50 mJ / cm ^2, since the heating efficiency and temperature profiles are different, the etching depth is different from 266nm50mJ / cm ² alone at. This is probably because the longer the wavelength, the smaller the attenuation (and the smaller the extinction coefficient), and the different temperature profiles. Further, by performing exposure with only a 355 nm laser near the end point, it is possible to control the film thickness with high accuracy by shallow etching.

  Note that, in the conditions of this example, etching up to about 30 nm on an average of one cycle was possible.

Further, the energy density of the YAG third harmonic wave having a wavelength of 355 nm has a maximum output of 200 mJ / cm ² unless intensity modulation is performed by the attenuator 14, and etching of about 100 nm is possible in one cycle. Shortening can be achieved. When the initial thickness of promoting etching at a wavelength 355nm energy density 200 mJ / cm ^2, the advancing etching range residual film thickness of 266nm50mJ / cm ² and 355nm50mJ / cm ² at approaching the set value. As a result, high-speed and high-precision etching can be achieved with a single thin film processing apparatus 200 by a continuous etching method.

  In the thin film processing apparatus 200 of the second embodiment, when the III-V group nitride semiconductor is subjected to high-speed etching, the processed surface can be highly planarized and the remaining film thickness is controlled in the nano order. A group V nitride semiconductor can be obtained. In particular, since the film thickness measurement accuracy is improved as the remaining film thickness with a high transmittance is increased, the nano-order remaining film thickness can be etched accurately.

  In addition, by selectively using laser beams of a plurality of wavelengths, precise etching can be performed with a combination of temperature profiles in the film thickness direction, which is impossible by intensity modulation of a single wavelength laser beam.

<Processing method of comparative example>
FIG. 11 is an explanatory diagram of a processing result by the processing method of the comparative example, and FIG. 12 is an explanatory diagram of etching processing using an end marker. The group III-V nitride semiconductor is indispensable for realizing a high-intensity light-emitting element with a short wavelength such as a blue light-emitting solid-state element such as a blue light-emitting diode, a high-intensity green light-emitting diode, or a blue laser diode, or an ultraviolet light-emitting solid-state element. The group III-V nitride semiconductor includes a single crystal such as GaN (gallium nitride), InN (indium nitride) or AlN (aluminum nitride) or a mixed crystal thereof (InGaN, AlGaN, etc.). With the recent progress of research, it has become impossible to obtain a high-quality thin film crystal (epitaxial layer) that can be used as a material for such a device using these III-V nitride semiconductors.

  However, as a main factor hindering the practical use of such blue light-emitting solid-state devices and ultraviolet light-emitting solid-state devices, III-V group nitride semiconductors such as GaN, InGaN, and AlGaN as the material of the devices will be described below. There were significant manufacturing problems.

(1) Difficulties in smoothing an epitaxially grown film When epitaxially growing sapphire or silicon carbide (SiC) that has been polished and smoothed as a substrate, III-V nitride semiconductors such as GaN, InGaN, and AlGaN are hexagonal crystals. Therefore, the growth rate in the axial direction is greatly different. Therefore, there is a problem that the obtained growth film has poor surface smoothness.

  Therefore, it is necessary to first perform a smoothing process before dry etching, but there is a problem that scratches are easily caused by polishing. Further, local unevenness can be smoothed by conventional means such as GCIB (gas cluster ion beam) and CMP (Chemical Mechanical Planarization), but there is a problem that the film thickness unevenness cannot be corrected over the entire substrate.

(2) Difficulties in etching processing While process technologies such as crystal growth methods and device fabrication technologies are being established, etching processing of III-V group nitride semiconductors such as GaN-based crystals is performed using III-based such as GaN-based crystals. It is extremely difficult due to the high chemical stability and high hardness of the group V nitride semiconductor.

  For example, when a III-V nitride semiconductor is etched by plasma etching or reactive ion etching (RIE), which is generally used, the processing speed is extremely slow. Moreover, damage to the crystal is introduced by collision of plasma or active ions with the crystal structure.

  Therefore, at present, a dry etching technique for III-V nitride semiconductors has not been established, and development of a low-damage high-speed etching technique capable of obtaining a flat plane is strongly demanded.

(3) Difficulties in manufacturing a parallel plane resonator in laser diode fabrication In order to oscillate a semiconductor laser, it is necessary to cleave the laminated structure to bring out end faces of perfectly parallel mirror surfaces. For example, a cubic semiconductor crystal is used for an element structure such as a red laser diode, and in this crystal system, a resonator can be easily manufactured by cleavage. However, group III-V nitride semiconductors such as GaN, InGaN, and AlGaN, which are the closest element materials for practical use of short wavelength lasers, are hexagonal crystals. For this reason, the flatness of the cleaved surface is low, and the decrease in flatness on the cleaved surface significantly affects the laser oscillation performance.

  In other words, because the hexagonal cleavage technology has its limitations, this causes deterioration of the laser oscillation performance and low yield, and development of flattening technology for the surface obtained by cleavage is strong. It has been demanded.

  Further, in the processing of laser diodes and photonic crystals, a technique for controlling the nano-order film thickness is required. However, as shown in FIG. 12, a conventional film thickness monitor using an end marker can monitor the film thickness distribution at a pinpoint in parallel with dry etching, but cannot monitor the film thickness distribution. Alternatively, in order to measure the film thickness distribution, a separate scanning means is required, and it is difficult to monitor the film thickness distribution in real time while etching, resulting in a complicated apparatus configuration.

  And in the pinpoint residual film thickness monitor using end markers, the film thickness outside the pinpoint is not detected, so local over-etching and under-etching often occur, and nano-order residual film It was difficult to just etch with a thickness.

In contrast, Patent Document 1 discloses a method for planarizing a nitride semiconductor by combining laser light irradiation and hydrochloric acid etching. Here, for the purpose of controlling the etching depth from the surface and smoothing the surface, etching is performed for only one pulse while changing the energy density of the pulse laser beam between 0.3 and 3.5 J / cm ² by an attenuator. Irradiate the substrate on which the thin film layer of the object is formed.

However, in III-V nitride semiconductors,
(1) Etching proceeds with surface irregularities reflected (2) Etching rate is anisotropic depending on crystal orientation (3) Sufficient solution to the problem that there is no means to monitor film thickness distribution during etching It cannot be said to have aimed at. In addition, since the flattening method of Patent Document 1 is based on the etching depth from the surface and the in-plane smoothness, it is difficult to keep the film thickness on the basis of the substrate constant and smooth. .

  Patent Document 1 describes that “the adjustment of the etching depth can be performed by changing the laser energy and the number of irradiation pulses” in the group III-V nitride semiconductor which is an object to be etched. Further, it is described that when the energy density of the pulse laser beam irradiated in the laser irradiation treatment is increased, the etching depth on the surface of the substrate immediately after the laser irradiation and the etching depth on the surface of the substrate after the hydrochloric acid treatment are increased. Has been.

  However, in the planarization method in which the etching depth is simply changed according to the laser energy and the number of pulses, as shown in FIG. 11, if the smoothness of the surface before processing is poor, it is reflected in the GCIB. It is the same as the conventional etching method.

Patent Document 1 discloses that the energy density of the pulsed laser light irradiated in the laser irradiation processing is 3.3 than that in the case where the energy density of the pulsed laser light irradiated in the laser irradiation processing is as low as 0.7 J / cm ² . It is described that the state of the surface of the substrate is further flattened when it is as high as 5 J / cm ² . However, since it is a batch exposure of the entire processed surface, as described above, there is a limit to flattening because “the etching depth changes according to the laser energy”. Therefore, as shown in FIG. 11, when there is a large film thickness distribution over the entire transparent substrate, it is difficult to flatten it.

  Further, in order to leave a nano-order residual film thickness, as shown in FIG. 12, when even a part of the film is etched to the just-etched film thickness, local under-etched portions and over-etched portions are generated in the film surface. There was a problem.

As described above, in order to put a blue light-emitting diode, a high-intensity green light-emitting diode, or a blue laser diode into practical use by using a group III-V nitride semiconductor such as GaN, InGaN, and AlGaN as a material,
(A) Providing a low-damage high-speed etching device capable of obtaining a flat surface (b) Providing an etching device that controls the accuracy of nano-order and leaves a residual film thickness (c) Strong development of etching surface flattening technology It has been demanded. Since it is difficult to process III-V nitride semiconductors with conventional technology, a processing apparatus and processing that can perform high-speed processing, have a highly flattened processing surface, and can control the remaining film thickness on the nano order. Technical proposals are desired.

<Correspondence with Invention>
The nitride semiconductor manufacturing method described in this embodiment processes the surface shape of a nitride semiconductor thin film by irradiating laser light. Then, the first step of measuring the film thickness distribution before the processing of the nitride semiconductor thin film and the surface of the nitride semiconductor thin film are scanned with the focused laser beam spot, and the thickness distribution differs depending on the measured film thickness distribution. And a third step of acid-treating the surface of the nitride semiconductor thin film that has undergone the second step.

  In other words, instead of irradiating the processing area with planar laser light at once, light energy corresponding to the required processing amount (depth) is injected into each scanning point in the processing area with a focused laser beam spot. Causes dissolution and damage of the crystal structure concentrated in the surface layer. Therefore, at a scanning point where the required processing amount is large, the cumulative irradiation amount (irradiation intensity, irradiation time, number of irradiations, or a combination thereof) is increased to increase the removal depth, and at a scanning point where the required processing amount is small, By reducing the cumulative irradiation amount and reducing the removal depth, a desired surface shape can be processed regardless of the surface uneven shape before processing.

  In the nitride semiconductor manufacturing method described in the present embodiment, the nitride semiconductor thin film is irradiated with the film thickness detection light by using the optical system 3 and the mirror 5 that guide the laser beam spot to the surface, and is nitrided by the film thickness detection light. The film thickness distribution is measured by detecting the transmission amount of the physical semiconductor thin film. Therefore, the processing irradiation position by the laser beam spot and the film thickness measurement position by the film thickness detection light coincide precisely, and a processing error due to the positional deviation between them does not occur.

  The film thickness detection light in the nitride semiconductor manufacturing method described in the present embodiment is a laser beam spot having a lower intensity than that used in the second step. Therefore, a light source dedicated to film thickness detection light is not necessary.

  In the nitride semiconductor manufacturing method described in this embodiment, the laser beam spot is intensity-modulated to vary the accumulated irradiation amount at each scanning point. Therefore, the processing irradiation at each scanning position S can be performed in one pulse emission time, and the processing time required for the entire processing region is shortened as compared with the case of adding a small constant output pulse.

  In the nitride semiconductor manufacturing method described in this embodiment, the laser beam spot is formed by overlapping a plurality of laser beams having different wavelengths. Therefore, compared to the case of using laser light of one kind of wavelength, it is possible to take a fine response to measurement of film thickness distribution and processing irradiation by making use of the characteristics of each wavelength.

  In the nitride semiconductor manufacturing method described in the present embodiment, the surface of the nitride semiconductor film is processed by irradiating laser light. Then, a first step of measuring the film thickness distribution before processing of the nitride semiconductor film, and a step of affecting the surface of the nitride semiconductor film with a different laser light irradiation amount for each region according to the measured film thickness distribution. And a third step of removing a material constituting the nitride semiconductor on the surface of the nitride semiconductor film after the second step.

  However, the third step can be replaced with another method as long as it is a removal step for removing the material constituting the nitride semiconductor on the surface of the nitride semiconductor film. That is, the “removal step” includes (1) treatment with an acid, (2) dissolution by heating, volatilization, (3) removal by physical sweep, or ( 1) to (3) may be combined and removed. Incidentally, since the melting point of Ga is approximately 30 ° C., dissolution by heating is not difficult.

  The thin film processing apparatus 100 of the first embodiment processes the surface shape of the thin film layer 9 formed on the transparent substrate 8. Then, the laser beam generator 1 that generates laser beam, the optical system 3 that forms the laser beam spot by guiding the generated laser beam to the processing point, the mirror 5, and the transparent substrate 8 are moved to move the laser beam on the thin film layer 9. An XY stage 6 that positions each scanning point S at a processing point K, a power meter 11 that detects the transmitted light intensity of the laser beam spot that has passed through the thin film layer 9 and the transparent substrate 8, and an attenuator that changes the intensity of the laser beam spot. 4 and a control unit 10 for controlling the attenuator 7 based on the transmitted light intensity detected at the scanning point S and processing and irradiating the scanning point S with a laser beam spot having an intensity corresponding to the transmitted light intensity.

  That is, the thickness detection and processing irradiation of the scanning point S are performed through the same optical system 3 and mirror 5. And the power meter 11 detects the thickness of the thin film layer 9 before a process by detecting the transmitted light quantity of the thin film layer 9 by the laser beam spot as film thickness detection light. The control unit 10 sets the irradiation intensity of the laser beam spot at the same processing point K by the attenuator 11 according to the required processing amount obtained from the thickness before processing and the target thickness obtained by the power meter 11. Accordingly, it is possible to accurately remove the crystal layer by precisely matching the thickness detection position and the processing irradiation position.

  The control unit 10 of the thin film processing apparatus 100 according to the first embodiment uses the laser beam spot whose intensity is decreased by controlling the attenuator 11 to detect the transmitted light intensity at all the scanning points S, and then scans each scanning point. Processing irradiation with intensity corresponding to the transmitted light intensity with respect to S is started. Therefore, the map data of the film thickness distribution is formed prior to the processing irradiation, and the error compression of the measurement result can be performed using a comprehensive method such as error diffusion. Further, it is possible to execute processing irradiation at once according to the completed map data.

  The control unit 10 of the thin film processing apparatus 100 of the first embodiment uses the laser beam spot whose intensity has been reduced by controlling the attenuator 11 to detect the transmitted light intensity at all the scanning points S, and then scan points S. Start processing irradiation for. Therefore, a dedicated light source for film thickness detection is not necessary.

  The laser light generator 1A, the THC conversion element 1B, and the FHG conversion element 1C of the thin film processing apparatus 200 according to the second embodiment output a plurality of laser lights having different wavelengths. Each laser beam is guided to a processing point K to form a superimposed laser beam spot. Therefore, it is possible to meticulously cope with each scanning point S by combining a plurality of laser beams having different wavelengths and exhibiting the respective characteristics.

  In the thin film processing apparatus 200 according to the second embodiment, laser light having a single wavelength generated by the laser light generator 1A is wavelength-converted in a plurality of ways by the THC conversion element 1B and the FHG conversion element 1C, and a plurality of types of wavelengths are converted. Of laser light. Accordingly, only one laser beam generator 1A is required, and the component cost and power consumption of the device can be reduced.

It is explanatory drawing of a structure of the thin film processing apparatus of 1st Embodiment. It is a flowchart of control of a thin film processing apparatus. It is a phase transition diagram of gallium nitride. It is a diagram of a temperature distribution simulation result in the film thickness direction at a laser output of 35 mJ / cm ² . It is a diagram of a temperature distribution simulation result in the film thickness direction at a laser output of 100 mJ / cm ² . It is a diagram of a temperature distribution simulation result in the film thickness direction at a laser output of 50 mJ / cm ² . It is explanatory drawing of the etching result by the thin film processing method of this embodiment. It is explanatory drawing of a structure of the thin film processing apparatus of 2nd Embodiment. It is explanatory drawing of the relationship between the wavelength of a laser beam, and the emitted-heat amount. It is explanatory drawing of the processing result by two types of laser beams from which a wavelength differs. It is explanatory drawing of the processing result by the processing method of a comparative example. It is explanatory drawing of the etching process using an end marker.

Explanation of symbols

1, 1A Light source means (laser light generator)
2, 12 Homogenizer 3, 13, 5, 15 Optical system means (optical system, mirror)
4, 14 Intensity modulation means (attenuator)
5, 15, 18, 19 Mirror 6 Scanning stage means (XY stage)
8 Translucent substrate (transparent substrate)
9 Thin film layer 10 Control means (control part)
11 Detection means (power meter)
16 Beam combiner 17 Half mirror 1B, 1C Wavelength conversion means (THC conversion element, FHG conversion element)
A Etching object K Processing point S Scanning point 100, 200 Thin film processing apparatus

Claims (11)

In a method for manufacturing a nitride semiconductor in which a surface shape of a nitride semiconductor thin film is processed by irradiating a laser beam,
A measuring step of measuring a film thickness distribution before processing of the nitride semiconductor thin film;
Scanning the surface of the nitride semiconductor thin film with a focused laser beam spot, and applying a different irradiation amount to each scanning point of the surface according to the measured film thickness distribution,
And an acid treatment step of treating the surface of the nitride semiconductor thin film that has undergone the processing step with an acid treatment.   The film thickness detection light is irradiated to the nitride semiconductor thin film using optical system means for guiding the laser beam spot to the surface, and the film thickness is detected by detecting the transmission amount of the nitride semiconductor thin film by the film thickness detection light. The nitride semiconductor manufacturing method according to claim 1, wherein the distribution is measured.   3. The method of manufacturing a nitride semiconductor according to claim 2, wherein the film thickness detection light is the laser beam spot having a lower intensity than when used in the processing step.   4. The method for manufacturing a nitride semiconductor according to claim 1, wherein intensity of the laser beam spot is modulated to vary the irradiation amount at each scanning point. 5.   The method for manufacturing a nitride semiconductor according to claim 1, wherein the laser beam spot is formed by overlapping a plurality of laser beams having different wavelengths. In a method for manufacturing a nitride semiconductor in which a surface of a nitride semiconductor film is processed by irradiating a laser beam,
A measuring step of measuring a film thickness distribution before processing the nitride semiconductor film;
According to the film thickness distribution, a processing step that affects the surface of the nitride semiconductor film with a different amount of laser light irradiation for each region;
A method for producing a nitride semiconductor comprising: a removal step of removing a material constituting the nitride semiconductor on the surface of the nitride semiconductor film after the processing step. In a thin film processing apparatus for processing the surface shape of a thin film layer formed on a translucent substrate,
Light source means for generating laser light;
Optical system means for guiding the generated laser beam to a processing point to form a laser beam spot;
Scanning stage means for moving the translucent substrate to position each scanning point on the thin film layer at the processing point;
Detecting means for detecting the transmitted light intensity of the laser beam spot transmitted through the thin film layer and the translucent substrate;
Intensity modulation means for changing the intensity of the laser beam spot;
Control means for controlling the intensity modulation means based on the transmitted light intensity detected at the scanning point, and processing and irradiating the scanning point with the laser beam spot having an intensity corresponding to the transmitted light intensity. A thin film processing apparatus characterized by that.   The control means detects the transmitted light intensity at all the scanning points using the laser beam spot whose intensity has been reduced by controlling the intensity modulating means, and then transmits the transmitted light intensity for each scanning point. The thin-film processing apparatus according to claim 7, wherein processing irradiation with an intensity corresponding to is started.   The control means detects the transmitted light intensity at all the scanning points using the laser beam spot whose intensity has been reduced by controlling the intensity modulating means, and then starts the processing irradiation on the scanning points. The thin film processing apparatus according to claim 7. The light source means outputs a plurality of laser beams having different wavelengths,
10. The thin film processing apparatus according to claim 7, wherein the optical system means forms the laser beam spot by superimposing the plurality of laser beams respectively on the processing points. 11. The thin film processing according to claim 10, wherein the light source means includes wavelength conversion means for converting the generated single-wavelength laser light into a plurality of wavelengths to form laser lights having a plurality of types of wavelengths. apparatus.

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