JP5019913B2 - Method of manufacturing nitride semiconductor device - Google Patents

Description

  The present invention relates to a method for manufacturing a nitride semiconductor device, and more particularly to a method for manufacturing a nitride semiconductor device having a mesa structure formed by dry etching.

  In recent years, nitride-based (GaN-based) semiconductor materials have been researched and developed as light-emitting element materials for short wavelengths such as semiconductor lasers and LEDs (light-emitting diodes), and nitride-based LEDs have already been mass-produced. . In addition, since nitride semiconductors have high dielectric breakdown voltage and high electron velocity, it is considered that high-temperature operation, high-speed switching operation, high-power operation, etc. are possible, and application to electronic devices is also expected.

  Since nitride semiconductors are chemically very stable, it is difficult to perform wet etching. For this reason, when forming a mesa structure or the like, dry etching is used for etching the nitride semiconductor. Since dry etching is performed using a plasma dry etching apparatus such as ICP or RIE using a highly reactive gas such as chlorine as a reactive gas, a damage layer is formed on the nitride semiconductor surface after etching. It is formed. This damaged layer has been found to adversely affect the characteristics of the nitride semiconductor device.

  For example, in a semiconductor laser having a ridge structure formed by dry etching, a damaged layer generated by dry etching becomes a light absorption layer, which causes deterioration of light output characteristics. In addition, in an electronic device using a nitride semiconductor, when an electrode is formed by depositing a metal on a surface subjected to dry etching, it is favorable due to the influence of a damaged layer formed by dry etching. There arises a problem that it is difficult to form an ohmic electrode.

Conventionally, various etching methods, pre-treatments, and post-treatments have been studied for nitride semiconductor dry etching methods. For example, Patent Document 1 discloses that dry etching is performed using a mixed gas of a gas containing chlorine and an inert gas for the purpose of improving dry etching speed, improving ohmic properties, and reducing contact resistance. In addition, as post-processing after dry etching, it is described that the surface is cleaned using an inert gas such as Ar or oxygen gas. However, in any of the methods including the method described in Patent Document 1, the damaged layer generated by dry etching cannot be completely removed. In particular, in a blue-violet semiconductor laser using a nitride semiconductor, it has been found that the influence of a damaged layer caused by dry etching appears more conspicuously as the output increases. In a nitride semiconductor laser, a damage layer is generated by dry etching, resulting in a decrease in slope efficiency, an increase in drive current value during high output drive, and adverse effects such as an increase in drive voltage and a decrease in device life. So far, the details of the cause of the damaged layer caused by dry etching have not been clarified.
JP-A-10-27783

  The present invention has been made to solve the above-described problems, and an object thereof is a nitride semiconductor device having a mesa structure formed by dry etching and removing a damaged layer caused by dry etching. Thus, it is an object to provide a method for manufacturing a nitride semiconductor device having improved electrical characteristics and optical characteristics.

  The inventors first conducted elemental analysis on the dry etching surface to investigate the cause of the damage layer. As a result, it was found that there are two characteristic differences between the surface where dry etching was performed and the surface where dry etching was not performed. The first point is that a larger amount of impurity elements such as C, O, Si, and Cl were detected on the surface where dry etching was performed than on the surface where dry etching was not performed. The second point is that the amount of nitrogen detected on the surface subjected to dry etching was smaller than that on the surface not subjected to dry etching.

  FIG. 1 shows the result of investigating the elemental ratio of Ga and N by AES (Auger Electron Spectroscopy) when dry etching is performed and when dry etching is not performed. The vertical axis represents the amount of N relative to Ga, and the horizontal axis represents sputter etching time (minutes). The sputter etching time on the horizontal axis corresponds to the depth from the surface. Specifically, a sputter etching time of 1 minute corresponds to a depth of about 3 nm. It can be seen from FIG. 1 that the amount of nitrogen is reduced when dry etching is performed on the outermost surface (the point at 0 minutes on the horizontal axis in the figure) as compared with the case where dry etching is not performed. This is considered to be because nitrogen was separated from the surface of the nitride semiconductor layer by the energy of plasma by performing dry etching. Thus, it can be seen that a large amount of nitrogen detachment, that is, nitrogen vacancies are generated in the vicinity of the dry etching surface due to damage of dry etching.

In addition, the reason why impurity elements such as C, O, Si, and Cl are detected from the dry etching surface is that the elements decomposed from SiO ₂ or resist used as a mask material and the residual elements of the etching gas at the time of dry etching However, it is considered that the impurity layer was formed on the etched surface due to the redeposition on the etched surface, or the formation of a natural oxide film on the surface after the etching or the adhering of contaminants, moisture or the like. As described above, since a large amount of nitrogen vacancies exist in the vicinity of the dry etching surface, it is very easy to bond with the impurity element. Is considered.

  As described above, nitrogen vacancies are generated on the dry etching surface due to nitrogen loss caused by damage due to dry etching, and impurity elements are recombined in the nitrogen vacancies to form an impurity layer. It was found that a damage layer was formed due to the combined factors. It is considered that these damaged layers cause light absorption on the dry etching surface, abnormal electrical characteristics, and the like.

  Based on the above findings, the present inventors have performed the cleaning by removing the impurity element recombined with the etched surface in order to recover the damaged layer caused by the dry etching, and further on the cleaned surface. The idea of eliminating nitrogen vacancies by recombining nitrogen with existing nitrogen vacancies was obtained. In addition, since nitrogen molecules are stable molecules, even if nitrogen molecules are brought into contact with the surface where nitrogen vacancies exist, nitrogen vacancies and nitrogen molecules do not easily recombine, but nitrogen It has been found that by making it into plasma, nitrogen can be excited to a more active state, and the recombination rate of the nitrogen leaving surface to the nitrogen vacancy can be dramatically improved. That is, the present invention is as follows.

  The present invention relates to a method of manufacturing a nitride semiconductor device having a mesa structure formed by dry etching, and the surface exposed by the dry etching is plasma-treated in an atmosphere containing nitrogen plasma (hereinafter simply referred to as nitrogen). It is also characterized by including a step (A) (also called plasma treatment).

  Here, the nitride semiconductor device may be a nitride semiconductor light emitting device having a current path limiting structure formed by dry etching, or a nitride semiconductor laser device having a ridge structure formed by dry etching. There may be.

  The atmosphere containing nitrogen plasma is preferably generated from a gas containing substantially only nitrogen.

  The plasma treatment may be performed under a condition where the substrate temperature of the nitride semiconductor element is 100 ° C. or higher and 800 ° C. or lower.

  The atmosphere containing nitrogen plasma is preferably generated by electron cyclotron resonance from a gas containing nitrogen, and the plasma generation microwave power in the electron cyclotron resonance is preferably 200 W or more and 800 W or less.

  Moreover, it is preferable that the plasma processing time of the said plasma processing is 30 second or more and 20 minutes or less.

  In the method for manufacturing a nitride semiconductor device of the present invention, an ashing step (B) for cleaning the surface exposed by dry etching may be provided before the step (A).

  The ashing in the step (B) may be plasma ashing, photoexcitation ashing, or wet processing.

  The plasma ashing is preferably performed in an atmosphere containing at least one of rare gas plasma and nitrogen plasma. The rare gas is preferably argon.

  According to the present invention, in the atmosphere containing nitrogen plasma, the surface exposed by dry etching is subjected to plasma treatment, whereby nitrogen is re-applied to nitrogen vacancies existing in a large amount in the damaged layer formed by dry etching. By bonding, the crystallinity of the damaged layer can be improved, and the electrical characteristics and optical characteristics of the nitride semiconductor element can be improved. When the present invention is applied to a nitride semiconductor laser device, the differential efficiency of the semiconductor laser is increased and the light output characteristics are improved. In addition, when the present invention is applied to a nitride semiconductor electronic device, an electrode having good ohmic characteristics can be formed even on a nitride semiconductor layer subjected to dry etching.

  The method for manufacturing a nitride semiconductor device according to the present invention is a dry etching method in which a nitride semiconductor is dry-etched using a plasma dry etching apparatus such as ICP or RIE using a halogen-based reactive gas such as chlorine. It is characterized by having a step (hereinafter referred to as step (A)) of performing a plasma treatment in an atmosphere containing nitrogen plasma on the damaged layer containing nitrogen vacancies formed on the etched surface. In general, since nitrogen molecules are stable, even if nitrogen molecules are brought into contact with nitrogen vacancies, nitrogen vacancies and nitrogen molecules do not easily recombine. According to the method of irradiating the damaged layer, since nitrogen is excited to a more active state, recombination of nitrogen vacancies and nitrogen is promoted, and the crystallinity of the damaged layer can be recovered. . Thereby, the optical characteristics and electrical characteristics of the nitride semiconductor device are improved.

Here, the nitride semiconductor element according to the present invention is not particularly limited as long as it is a nitride semiconductor element having a partial structure formed by dry etching. An example of the partial structure formed by dry etching is a mesa structure. In this specification, the mesa structure means a stepped structure formed by dry etching, and includes a reverse mesa structure and a ridge structure in a semiconductor laser element. Further, a current path limiting structure such as a current confinement structure for limiting a current path in a nitride semiconductor light emitting device (LED or the like) is also a kind of mesa structure in the present invention. The basic structure (multilayer structure) itself of the nitride semiconductor device according to the present invention may be produced by any conventionally known method, and examples thereof include MOCVD. Further, the material of each layer constituting the nitride semiconductor device according to the present invention is not particularly limited, and conventionally known materials can be used. For example, as the nitride semiconductor substrate, in addition to an n-type GaN substrate, a semi-insulating GaN substrate, an Al _1-x Ga _x N (0 ≦ x ≦ 1) substrate, or the like may be used. In addition to the nitride semiconductor substrate, a pseudo-GaN substrate in which the defect density is controlled by a method such as ELOG (Epitaxial Lateral Over Growth) on a substrate such as sapphire can be used.

  In the method for manufacturing a nitride semiconductor device of the present invention, preferably, before the step (A), an ashing step (B) for cleaning the surface exposed by dry etching is provided. Hereinafter, the step (A) and the ashing step (B) will be described in detail.

<Ashing process (B)>
In the present invention, it is preferable to perform an ashing process (ashing process (B)) for cleaning the surface exposed by dry etching before the plasma process (process (A)). As a result, an impurity layer composed of an element separated from the mask material used during dry etching, an etching residue, a surface oxide film, moisture, and the like is removed, and a clean dry etching surface is exposed. ) Can be efficiently performed. In particular, when an organic substance or the like is used as a mask material, it is preferable to perform an ashing process in order to more efficiently prevent deterioration in device characteristics due to impurity residues after dry etching. Regardless of the type of mask material used, when dry etching processing is performed at a mass production level (in large quantities), there are variations in the state of impurity formation after dry etching, which greatly increases device characteristics. Therefore, it is preferable to provide an ashing process in order to reduce such variation. Furthermore, when a dielectric or an electrode is formed on the dry etched surface, it is preferable to perform an ashing process in order to clean the etched surface and improve the adhesion strength of the dielectric and the electrode.

  In addition, the said process (B) is arbitrarily performed in the manufacturing method of the nitride semiconductor element of this invention, Comprising: It is not an essential process. For example, since a certain amount of impurities can be removed also by the following step (A), depending on the kind of attached impurities, etc., the removal of the impurity layer and recombination of nitrogen into the nitrogen vacancies only by the following step (A) It is also possible to recover the damaged layer at the same time.

  As a method of ashing (ashing) for cleaning the surface exposed by dry etching, a plasma ashing method for removing and treating an impurity layer in a plasma such as a rare gas plasma such as Ar and / or nitrogen plasma, Examples include a photo-excited ashing method in which ozone gas is excited with UV light to remove and treat the impurity layer, and a wet process (wet treatment) method in which the impurity layer is dissolved and removed with a solvent. One method is preferably used. In addition, the ashing method is an appropriate method for removing impurities depending on the material used as a mask for dry etching when forming the mesa structure, and the type of contaminants, moisture, etc. reattached to the etched surface. Since they are different, it is necessary to select them appropriately.

  For example, when a metal, dielectric, or the like is used as the mask material, it is preferable to use a plasma ashing method. When a resist or the like is used as the mask material, it is preferable to use a photoexcited ashing method. In addition, when organic substances adhere as impurities, the wet process method is effective.

  The plasma atmosphere in the plasma ashing process may be, for example, a rare gas plasma such as Ar or He, or may be a mixed plasma of the rare gas plasma and nitrogen plasma. The rare gas plasma may be composed of a plurality of types of rare gases, and may include other plasmas such as oxygen plasma in addition to the rare gas plasma and nitrogen plasma.

  As described above, since the elements constituting the impurity layer formed on the etched surface are diverse, such as the elements detached from the mask material used during dry etching, etching residues, surface oxide films, moisture, etc., some ashing It is also effective to combine methods. For example, the plasma ashing treatment may be performed after the dry etching surface treatment by a wet process and / or the photoexcited ashing treatment of the dry etching surface by UV irradiation. When specific impurities are formed on the dry etching surface, it is more effective to perform plasma ashing after removing the specific impurities efficiently by wet process or UV ashing. Is cleaned and the effect is increased. In the case where impurities and residues formed on the dry etching surface can be completely removed by the wet process and / or the photoexcited ashing method, the plasma ashing process is not necessarily required. In order to remove a natural oxide film or the like formed after the photoexcited ashing, it is preferable to perform a plasma ashing process.

  Further, when the step (B) is performed, even if the surface is cleaned by ashing, a natural oxide film is formed again on the cleaned ashing surface when exposed to the atmosphere again. Then, after the ashing process, it is desirable to perform a process (step (A)) for eliminating nitrogen vacancies after the ashing process.

  For example, when the nitrogen plasma treatment in the next step (A) is performed using an ECR (Electron Cyclotron Resonance) sputtering apparatus, the impurity layer is removed in a rare gas such as Ar and / or a nitrogen plasma atmosphere. It is possible to continuously perform a plasma ashing process for the purpose of the above and a nitrogen plasma process (step (A)) for the purpose of recombination of nitrogen into the damaged layer in the same apparatus. In addition, even when the plasma dry etching apparatus itself used for dry etching has a function of generating plasma such as Ar and nitrogen, after performing dry etching, plasma ashing treatment and nitrogen plasma treatment are continuously performed. It is possible to do.

  In addition, when the wet process method is necessary for removing the impurity layer, after removing the impurity layer using the wet process method, it is introduced into an apparatus capable of continuously performing plasma ashing treatment and nitrogen plasma treatment, It is desirable to recover the damaged layer by cleaning the surface and recombining nitrogen vacancies. Even in the case of using the photoexcited ashing method, when exposing to the atmosphere after ashing, after the photoexcited ashing treatment, it is introduced into an apparatus capable of performing plasma ashing treatment and nitrogen plasma treatment in the same manner as described above. It is desirable to recover the damaged layer by cleaning and recombination of nitrogen vacancies.

<Process (A)>
In this step, the dry etching surface that has been ashed or not ashed is subjected to plasma treatment in an atmosphere containing nitrogen plasma to recover the damaged layer. Here, the atmosphere containing nitrogen plasma may be an atmosphere consisting essentially of nitrogen plasma, or may be a mixed plasma atmosphere further containing plasma other than nitrogen plasma. In the latter case, the mixed plasma atmosphere is preferably an atmosphere containing nitrogen plasma as a main component, and the mixed gas used for plasma generation contains nitrogen at a rate of 10% or more in terms of gas flow rate (volume). It is preferable to include. Examples of plasma other than nitrogen plasma include oxygen plasma, chlorine plasma, and the like, in addition to rare gas plasma such as Ar.

  The plasma generation method is not particularly limited as long as nitrogen plasma can be generated. For example, a generation method by ECR can be used. At this time, the plasma generation microwave power is desirably 200 W or more and 800 W or less. If it is less than 200 W, the natural oxide film, moisture, contaminants, etc. on the dry etched surface may not be completely removed. On the other hand, if it is larger than 800 W, the power of the plasma treatment is too strong, so that not only recombination of nitrogen into the nitrogen vacancies is inhibited, but conversely, there is a possibility of causing detachment of nitrogen from the dry etching surface. . The exposure time (plasma treatment time) to the atmosphere containing nitrogen plasma is preferably 30 seconds or more and 20 minutes or less. If it is less than 30 seconds, the natural oxide film, moisture, contaminants, etc. on the resonator end face cannot be completely removed. Further, if the treatment time is longer than 20 minutes, reactions other than recombination of nitrogen into the nitrogen vacancies, for example, detachment of elements from the mask material, etc. are promoted, which may cause adverse effects.

  The plasma treatment of the dry etching surface in an atmosphere containing nitrogen plasma may be performed at any temperature including a temperature of about room temperature, or may be performed in a heated state. When performed in a heated state, for example, the substrate temperature of the nitride semiconductor element is preferably 100 ° C. or higher and 800 ° C. or lower, more preferably 500 ° C. or lower. By performing plasma treatment at a substrate temperature of 100 ° C. or higher, recombination of nitrogen is promoted, and the damage layer recovery effect can be enhanced. When processing is performed at a substrate temperature of 800 ° C. or higher, damage to the element structure of the nitride semiconductor due to heat may occur. In addition, when processing is performed at a substrate temperature of 500 ° C. or higher, the electrode structure may be affected by heat depending on the electrode structure. In addition, by performing plasma treatment in such a high temperature region, when a dielectric is formed on the dry etching surface, the adhesion of the dielectric can be further improved. The substrate temperature can be measured by reading an instruction temperature such as a thermocouple installed in the vicinity of the substrate.

  When performing the nitrogen plasma treatment, it is necessary to carry out so that a new impurity layer is not formed on the dry etching surface. For example, when nitrogen plasma treatment is performed using an ECR sputtering apparatus, substances deposited so far adhere to the wall surface of the ECR sputtering apparatus as impurities. It is necessary to prevent adhesion. These impurities are mainly target materials and their oxides, nitrides, etc. Among these, metallic impurities made of the target material have a self-potential formed during nitrogen plasma treatment, Sputtered from the wall. For this reason, there is a possibility that these impurities re-adhere to the dry etching surface as impurities. Therefore, when performing nitrogen plasma treatment using an ECR sputtering apparatus, in order to prevent such reattachment of impurities, means such as oxidizing the wall surface and target surface in the film forming furnace in advance are provided. It is preferable to take. This is because the metal target material attached to the wall surface is sufficiently oxidized to become a dielectric or an insulator, so that the self-generated potential is reduced or the amount of reverse sputtering is significantly reduced. There are two methods for performing oxidation. One is a method of generating a plasma consisting only of oxygen in a film forming furnace. Thereby, the metal in the film forming furnace and the target surface is oxidized. Another method is a method of applying RF of an ECR apparatus after flowing an oxygen gas having a flow rate that allows sputtering in an oxide state from a target. When sputtering is performed from the target in an oxide state, not only the vicinity of the sample surface but also the entire film forming furnace can be covered with the oxide. The oxygen flow rate in such a state can be easily determined by monitoring the potential on the target surface when the flow rate of oxygen gas is increased while applying RF of constant power. As the oxygen gas flow rate is increased, the potential rapidly decreases at a certain flow rate. This means that the target is sufficiently oxidized. Therefore, when oxygen is supplied at an amount higher than this flow rate and RF is applied, the target is sputtered in an oxide state, and the target and the deposition furnace are made of oxide. Will be covered. These operations must be performed before the nitride semiconductor element is introduced, or after the introduction, with the shutter closed. Note that the in-furnace oxidation is not necessarily required if the apparatus has a dedicated processing chamber for performing exposure to a plasma atmosphere independently of the film forming furnace.

  In the case where a dielectric, electrode metal, or the like is formed on the dry etching surface after performing the above-described nitrogen plasma treatment, it can be continuously formed without opening to the atmosphere after the nitrogen plasma treatment. desirable. This is because the dielectric and electrode metal are formed again on the dry etched surface that has been cleaned by ashing and nitrogen plasma treatment and has no nitrogen vacancies, without causing the deposition of natural oxide films or impurities. This is because it is possible to dramatically improve the adhesion of the dielectric and the characteristics of the electrode metal. When nitrogen plasma treatment is performed using an ECR sputtering apparatus, it is possible to form a dielectric such as a nitride film or an oxide film or an electrode metal without performing exposure to the atmosphere after the nitrogen plasma treatment.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Examples 1 and 2 and Comparative Examples 1 and 2>
A semiconductor laser device having a semiconductor multilayer structure shown in FIG. 2 was produced. Hereinafter, a method for manufacturing the semiconductor laser element will be described with reference to FIG. First, the nitride semiconductor substrate 201 was introduced into the MOCVD apparatus, and the temperature was raised to 1050 ° C. while flowing N ₂ and NH ₃ each at 5 L / min. After the temperature increase, the carrier gas was changed from N ₂ to H ₂ , TMG was introduced at 100 μmol / min, SiH ₄ was introduced at 10 nmol / min, and the n-type GaN layer 202 shown in FIG. 2 was grown by 3 μm. Thereafter, the flow rate of TMG was adjusted to 50 μmol / min, TMA was introduced at 40 μmol / min, and the n-type Al _0.1 Ga _0.9 N cladding layer 203 was grown to a thickness of 0.5 μm. After the growth of Al _0.1 Ga _0.9 N was completed, the supply of TMA was stopped, TMG was adjusted to 100 μmol / min, and the n-type GaN light guide layer 204 was grown to a thickness of 0.1 μm. . Thereafter, the supply of TMG and SiH ₄ is stopped, the carrier gas is changed from H ₂ to N ₂ again, the temperature is lowered to 700 ° C., trimethylindium (TMI) as an indium raw material is 10 μmol / min, and TMG is 15 μmol / min. Min was introduced, and an 8 nm thick barrier layer made of In _0.01 Ga _0.99 N was grown. Thereafter, the supply amount of TMI was increased to 50 μmol / min, and a 4 nm thick well layer made of In _0.10 Ga _0.90 N was grown. A well layer was grown in a similar manner for a total of three layers, and a light emitting layer 205 of a multiple quantum well (MQW) having a total of four barrier layers between and on both sides of the well layer was grown. . After the growth of MQW is completed, the supply of TMI and TMG is stopped, the temperature is raised again to 1050 ° C., the carrier gas is changed from N ₂ to H ₂ again, TMG is 50 μmol / min, TMA is 30 μmol / min. Min, p-type doping raw material bisethylcyclopentadienylmagnesium (EtCp ₂ Mg) was flowed at 10 nmol / min to grow a 20 nm thick p-type Al _0.3 Ga _0.7 N carrier blocking layer 206. After the growth of the carrier block layer 206 was completed, the supply of TMA was stopped, the supply amount of TMG was adjusted to 100 μmol / min, and a p-type GaN light guide layer 207 having a thickness of 0.1 μm was grown. Thereafter, the supply of TMG is adjusted to 50 μmol / min, 40 μmol / min of TMA is introduced, a 0.4 μm thick p-type Al _0.1 Ga _0.9 N cladding layer 208 is grown, and finally, the supply of TMG is 100 μmol / min. Then, the supply of TMA was stopped, the p-type GaN contact layer 209 having a thickness of 0.1 μm was grown, and the growth of the light emitting device structure was completed. When the growth was completed, the supply of TMG and EtCp ₂ Mg was stopped and the temperature was lowered, and the substrate was taken out from the MOCVD apparatus at room temperature.

Next, a laser structure having a ridge stripe structure was fabricated on the element taken out from the MOCVD apparatus. The laser structure was formed as follows. SiO ₂ was formed on the wafer taken out from the MOCVD apparatus using the CVD apparatus. Next, a resist stripe was formed using a photolithography technique. Then, the resist stripe as a mask, dry-etched using the SiO _2, was performed in the formation of SiO ₂ stripe of about 1.5 [mu] m. The dry etching of SiO ₂ was performed by an RIE apparatus using Ar as a reactive gas.

Next, using the SiO ₂ stripe as a mask, the nitride semiconductor layer was dry etched to form a ridge stripe. In the present invention, the nitride semiconductor layer is dry etched using an ICP apparatus using chlorine (Cl) as a reactive gas. The etching depth of the nitride semiconductor layer was about 550 nm. Next, a nitrogen plasma treatment step (step (A)) was performed on the etched surface after dry etching for the purpose of recovering the damaged layer. The procedure of the nitrogen plasma treatment step (step (A)) will be described in detail below.

(Introduction to equipment)
FIG. 3 is a diagram schematically showing an ECR (Electron Cyclotron Resonance) sputtering apparatus used in the nitrogen plasma treatment of this example. The apparatus is roughly divided into a film formation furnace 300 and a plasma generation chamber 309. The film formation furnace 300 is provided with a gas inlet 301, a target 304, a heater 305, a sample stage 307, and a shutter 310, and is vacuum-controlled. It is exhausted by a pump. An RF power source 308 is connected to the target 304. The plasma generation chamber 309 includes a gas introduction port 301, a microwave introduction window 302, and a magnetic coil 303, and plasma is generated when the microwave is introduced from the microwave introduction window 302. The dry-etched semiconductor laser bar attached to the holder was placed at the position of the sample 306 in FIG. 3 so that the etching surface was irradiated with plasma.

(Nitrogen plasma treatment)
Under the following conditions, gas was introduced to generate plasma, the shutter 310 was opened, and nitrogen plasma treatment was performed. Table 1 shows the nitrogen plasma treatment conditions of Examples 1 and 2 and Comparative Examples 1 and 2. Comparative Example 1 is a case where only Ar is used as the plasma gas, and Comparative Example 2 is a case where nitrogen plasma treatment is not performed.

After the nitrogen plasma treatment, a ZrO ₂ layer 210 as an insulating layer and a TiO ₂ layer 211 as an adhesion layer were formed on the nitride semiconductor layer portion excluding the upper portion of the ridge stripe. The formation of the ZrO ₂ layer 210 and the TiO ₂ layer 211 was continuously performed by an ECR sputtering apparatus without being exposed to the air atmosphere. Next, after the wafer is taken out of the ECR sputtering apparatus, SiO ₂ is removed by etching with a buffered hydrofluoric acid solution, thereby simultaneously removing ZrO ₂ and TiO ₂ on the upper part of the ridge stripe. Exposed. Next, a p-type pad electrode 112 made of palladium (Pd), molybdenum (Mo), and gold (Au) was formed as shown in FIG.

  Subsequently, the nitride semiconductor substrate 201 was polished and polished from the back surface so that it could be easily cleaved. An n-type electrode 213 made of hafnium (Hf) and aluminum (Al) was formed on the back surface of the nitride semiconductor substrate 201 that had been polished and polished, and electrode alloying was performed. Subsequently, a metallized layer 214 made of Mo, platinum (Pt), and Au was formed on the n-type electrode 213.

The semiconductor wafer thus formed was divided into bars having a resonator length of 600 μm by a scribing device, and then the end surfaces of the divided bars were coated. First, alumina was formed on the end face on one side of the bar using an ECR apparatus. Alumina was formed by adjusting the optical film thickness so as to function as a 5% low reflection coating (Anti Reflection Coating). Next, 50 nm of alumina was formed on the opposite end face by the same method. Next, a nine-layer dielectric multilayer film composed of SiO ₂ and TiO ₂ that functions as a high reflection coating of about 95% was formed. Next, the bar on which the front and rear end face coating was finished was divided into chips by a scribe and break device. Thereafter, the divided chip was mounted on an AlN submount and mounted on the stem together with the submount. Thereafter, the pin of the stem was wire-bonded and capped with air sealing.

The current-light output characteristics of the semiconductor laser device fabricated as described above were measured. The measurement results are shown in FIG. Table 2 summarizes the characteristics of the semiconductor laser elements of the examples and comparative examples. The current-light output characteristics were measured under the following measurement conditions using the following apparatus.
Measuring device: Pulse IL measuring instrument,
Measurement conditions: Pulse measurement with a pulse width of 100 nsec, a duty of 30%, a current Max of 300 mA, and an optical output Max of 250 mW.

  In the element (Example 1) subjected to plasma treatment in nitrogen gas, the slope efficiency was significantly increased as compared with Comparative Example 2, and the light output characteristics of the semiconductor laser were significantly improved. . In addition, with respect to Example 2 in which the treatment was performed in an Ar gas and nitrogen gas plasma atmosphere, although not as much as Example 1, an improvement in slope efficiency was observed. On the other hand, in Comparative Example 1 in which the plasma treatment was performed in an atmosphere containing only Ar, the characteristics were worse than those in Comparative Example 2 in which the treatment was not performed. This is considered to be because the etched surface was further damaged by Ar plasma, and nitrogen separation was promoted.

<Example 3>
A semiconductor laser device was fabricated in the same manner as in Example 1 except that the nitrogen plasma treatment conditions were changed to those shown in Table 3, and the current-light output characteristics of the obtained semiconductor laser device were measured. The measurement results are shown in FIG. Table 3 summarizes the characteristics of the semiconductor laser elements. 5 and Table 3 also show the data of Comparative Example 2 for comparison.

  Even when the nitrogen plasma treatment was performed in a heated state, the light output characteristics of the semiconductor laser were also significantly improved.

<Example 4>
A semiconductor laser device was fabricated in the same manner as in Example 1 except that a plasma ashing treatment with Ar plasma was performed before the nitrogen plasma treatment, and current-light output characteristics of the obtained semiconductor laser device were measured. The measurement results are shown in FIG. Table 4 summarizes the conditions of the plasma ashing treatment using Ar plasma and the nitrogen plasma treatment, and the characteristics of the semiconductor laser device. In FIG. 6, the data of Comparative Examples 1 and 2 are also shown for comparison. The plasma ashing treatment using Ar plasma and the nitrogen plasma treatment were continuously performed using the same ECR sputtering apparatus without being exposed to the air atmosphere.

  Thus, the effect of the present invention was confirmed even when the treatment was performed in two stages of an Ar gas atmosphere and a nitrogen gas atmosphere. In this embodiment, the process is performed in two stages of an Ar gas atmosphere and a nitrogen gas atmosphere. In the first stage process, plasma ashing is performed for the purpose of cleaning the dry etching surface. It is. By this treatment, it is possible to remove residues, impurities, and the like attached to the etched surface during dry etching, and as a result, the adhesion strength of a dielectric formed later on the etched surface is dramatically improved. Nitrogen plasma treatment, which is the second stage treatment, is intended to reduce etching damage by recombining nitrogen with nitrogen vacancies on the etched surface. As described above, by performing the first stage and second stage plasma treatments, it is possible to form a dielectric layer having high adhesion to the dry etched surface, and etching damage on the etched surface is reduced. Thus, the device characteristics can be improved.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The nitride semiconductor device manufacturing method of the present invention can be applied to nitride semiconductor light emitting devices such as semiconductor lasers and light emitting diodes, or nitride semiconductor electronic devices. Equipped with hologram laser device, optoelectronic IC device integrated with IC chip for processing such as driving or signal detection, compound optical device integrated with waveguide or micro optical element, or high-frequency transistor , Etc. Further, the present invention can be applied to an optical recording system, an optical disc system, an ultraviolet to green light source system, a high frequency system, and the like provided with these devices.

It is a graph which shows the result of having investigated the element amount ratio of Ga and N by AES (Auger Electron Spectroscopy) measurement when not performing dry etching. It is a schematic sectional drawing of the semiconductor laser element produced in the Example. It is a figure which shows typically the ECR sputtering apparatus used for nitrogen plasma processing. 6 is a graph showing current-light output characteristics of the semiconductor laser elements of Examples 1 and 2 and Comparative Examples 1 and 2. 6 is a graph showing current-light output characteristics of the semiconductor laser device of Example 3. 6 is a graph showing current-light output characteristics of the semiconductor laser device of Example 4.

Explanation of symbols

201 Nitride semiconductor substrate, 202 n-type GaN layer, 203 n-type Al _0.1 Ga _0.9 N clad layer, 204 n-type GaN light guide layer, 205 multiple quantum well (MQW) light emitting layer, 206 p-type Al _0.3 Ga _0.7 N carrier Block layer, 207 p-type GaN light guide layer, 208 p-type Al _0.1 Ga _0.9 N cladding layer, 209 p-type GaN contact layer, 210 ZrO ₂ layer, 211 TiO ₂ layer, 212 p-type pad electrode, 213 n-type electrode, 214 Metallized layer, 300 Deposition furnace, 301 Gas inlet, 302 Microwave inlet window, 303 Magnetic coil, 304 Target, 305 Heater, 306 Sample, 307 Sample stand, 308 RF power supply, 309 Plasma generation chamber, 310 Shutter .

Claims (12)

A method for manufacturing a nitride semiconductor device having a mesa structure formed by dry etching,
A cleaning step of removing impurities present on the surface exposed by the dry etching in an atmosphere of a rare gas plasma;
In an atmosphere containing nitrogen plasma, the surface exposed by dry etching which is subjected to the cleaning step, as engineering for plasma processing,
Without exposing the plasma-treated surface in an atmosphere including a nitrogen plasma atmosphere, forming a dielectric layer on the surface,
A method for manufacturing a nitride semiconductor device comprising:   The method for manufacturing a nitride semiconductor device according to claim 1, wherein the nitride semiconductor device is a nitride semiconductor light emitting device having a current path limiting structure formed by dry etching.   2. The method for manufacturing a nitride semiconductor device according to claim 1, wherein the nitride semiconductor device is a nitride semiconductor laser device having a ridge structure formed by dry etching.   The method for manufacturing a nitride semiconductor device according to claim 1, wherein the atmosphere containing nitrogen plasma is generated from a gas containing 10% by volume or more of nitrogen. 5. The plasma treatment in an atmosphere containing nitrogen plasma is performed under a condition that a substrate temperature of the nitride semiconductor element is 100 ° C. or higher and 800 ° C. or lower. Of manufacturing a nitride semiconductor device.   The method for manufacturing a nitride semiconductor device according to claim 1, wherein the atmosphere containing nitrogen plasma is generated by electron cyclotron resonance from a gas containing nitrogen.   The method for manufacturing a nitride semiconductor device according to claim 6, wherein a plasma-generated microwave power in the electron cyclotron resonance is 200 W or more and 800 W or less. The method of manufacturing a nitride semiconductor device according to any one of claims 1 to 7, wherein a plasma processing time of the plasma processing in an atmosphere containing nitrogen plasma is not less than 30 seconds and not more than 20 minutes. The nitriding according to claim 1 , further comprising a step of removing impurities present on the surface exposed by the dry etching by photoexcited ashing before the step of performing the plasma treatment in an atmosphere containing nitrogen plasma. Method for manufacturing a semiconductor device. 2. The nitriding according to claim 1 , further comprising a step of removing impurities existing on a surface exposed by the dry etching by a wet treatment before the step of performing the plasma treatment in an atmosphere containing the nitrogen plasma. Method for manufacturing a semiconductor device. The method of manufacturing a nitride semiconductor device according to claim 1 , wherein the rare gas is argon. The dielectric layer, the manufacturing method of the nitride semiconductor device according to any one of claims 1 to 11, characterized in that zirconium oxide.

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