JP2005217153A - Heat treatment method for group ii-vi compound semiconductor substrate and the semiconductor substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat treatment method for a group II-VI compound semiconductor substrate capable of realizing making the resistance of the substrate low without deteriorating the crystalinity, and to provide the group II-VI compound semiconductor substrate subjected to heat treatment. <P>SOLUTION: The heat treatment method of the group II-VI compound semiconductor substrate includes the steps of preparing a ZnSe substrate 10 having a front side 10a on which a semiconductor film serving as an active layer is formed, and a rear side 10b in contact with an aluminum film 9 and located opposite to the front side 10a; and applying heat treatment to the ZnSe substrate 10 in a processing chamber exposed in an atmosphere comprising Zn of a group II element configuring the ZnSe substrate 10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention generally relates to a heat treatment method for a II-VI group compound semiconductor substrate and a II-VI group compound semiconductor substrate, and more specifically, to a zinc-selenium (ZnSe) substrate having aluminum as a donor impurity ( The present invention relates to a heat treatment method for doping Al) and a ZnSe substrate subjected to the heat treatment.

  Conventionally, ZnSe-based light-emitting elements have attracted attention as light-emitting elements such as short-wavelength lasers such as blue, green, and blue-green, or light-emitting diodes (LEDs). These light emitting elements can also be manufactured on a substrate such as gallium arsenide (GaAs). However, from the viewpoint of improving the device characteristics by improving the crystallinity of the ZnSe thin film formed on the substrate, the ZnSe thin film is formed by homoepitaxial growth on the ZnSe substrate, which is the same material as the thin film. Is desirable.

  When a ZnSe single crystal substrate is used as a substrate for a light emitting element, in order to simplify the element structure and improve the element characteristics, it is indispensable to increase the conductivity of the substrate, that is, to lower the resistance of the substrate. However, a ZnSe bulk single crystal manufactured by a manufacturing method such as a PVT (physical vapor transport) method or a GG (grain growth) method is undoped, that is, not doped with impurities, and thus has high resistance.

  As a method of reducing the resistance of a ZnSe single crystal, a method of obtaining a low-resistance ZnSe single crystal by heat-treating a ZnSe single crystal in a Zn-Al melt is described in, for example, G. Jones and J. Woods, “The electrical properties of zinc selenide ", J. Phys. D: Appl. Phys., Vol. 9, 1976, pp. 799-810 (Non-Patent Document 1). In this method, Al diffuses into the ZnSe crystal and acts as a donor impurity, and at the same time, the concentration of Zn vacancies decreases. Thereby, the activation rate of Al can be increased, and a desired specific resistance value can be obtained by increasing the n-type carrier concentration.

  Further, Al doped in the ZnSe crystal forms complex defects called Zn vacancies and SA centers. From the SA center, light emission from red to yellow called SA light emission occurs. Focusing on this phenomenon, a new concept white LED using ZnSe has been developed in recent years. This white LED mixes the short wavelength light generated from the active layer formed on the ZnSe substrate and the long wavelength light (SA emission) excited by the short wavelength light to obtain white light. It is. Since the white LED uses the substrate itself as a light emitter, it is essential to use a ZnSe substrate.

  Therefore, in order to produce a high-quality light-emitting element, it is important that the crystallinity of the ZnSe substrate is good. However, the method disclosed in Non-Patent Document 1 cannot prevent the melt from adhering to the ZnSe single crystal during cooling. Therefore, the dislocation density of the ZnSe single crystal increases due to the stress due to the difference in thermal expansion between ZnSe and the melt. As a result, the crystallinity is remarkably deteriorated, and there is a problem that the lifetime is reduced when used as a light emitting element.

In order to solve such problems, a method of forming an Al thin film on the surface of a ZnSe single crystal, sealing it in a quartz container and heat-treating it in a Zn atmosphere is disclosed in Japanese Patent Laid-Open No. 10-265299. (Patent Document 1). This method makes it possible to suppress a significant deterioration in crystallinity, and can substantially suppress an increase in the dislocation density for a substrate having a dislocation density before heat treatment of 5 × 10 ⁴ cm ⁻² or more.

However, when a substrate having good crystallinity with a lower dislocation density is heat-treated under the same conditions, there arises a problem that the dislocation density increases as the thickness of the Al thin film increases. That is, in the method disclosed in Patent Document 1, when the thickness of the Al thin film is 40 nm or more, the increase in the dislocation density cannot be sufficiently suppressed at a level of dislocation density of 5 × 10 ⁴ cm ⁻² or less.

The cause of such deterioration in crystallinity is that the Al solution that contacts the substrate surface reacts with the SiO gas released from the quartz container, thereby causing a beryl (Al ₂ SiO ₅ ) or mullite (3Al ₂ O). It is considered that reaction products such as ₃ · 2SiO ₂ ) are formed on the ZnSe substrate. Therefore, a heat treatment method for a II-VI group compound semiconductor aimed at isolating the Al solution and the SiO gas as much as possible is disclosed in Japanese Patent Laid-Open No. 2003-124235 (Patent Document 2).

According to the heat treatment method disclosed in Patent Document 2, first, a ZeSe substrate on which an Al thin film is formed is housed in a container made of a material that does not contain quartz. The container is further accommodated in a quartz container, the inside is evacuated and sealed, and then the ZeSe substrate is heat-treated in a Zn atmosphere. Thereby, the deterioration of the crystallinity of the ZnSe substrate after the heat treatment is further suppressed.
JP-A-10-265299 JP 2003-124235 A G. Jones and J. Woods, `` The electrical properties of zinc selenide '', J.Phys.D: Appl.Phys., Vol.9, 1976, pp.799-810

However, even with the heat treatment method disclosed in Patent Document 2, the reaction between Al and SiO cannot be sufficiently suppressed. Specifically, when the thickness of the Al thin film is 100 nm or more, variation in the crystallinity of the ZnSe substrate is recognized, and when the thickness of the Al thin film is 200 nm or more, the increase in dislocation density of the ZnSe substrate is 5 × 10 ⁴ cm ⁻² or more. For this reason, a substrate having good crystallinity cannot be obtained.

  On the other hand, to increase the brightness of the white LED, it is necessary to increase the emission intensity of the substrate. For this purpose, the concentration of Al contained in the substrate must be increased, and the thickness of the Al thin film formed on the ZnSe substrate must be increased before the heat treatment. However, as described above, when the thickness of the Al thin film is increased, the crystallinity of the substrate is deteriorated. For this reason, a substrate having both good crystallinity and sufficient emission intensity cannot be formed by a conventional heat treatment method.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problem, and a heat treatment method for a II-VI group compound semiconductor substrate capable of realizing low resistance of the substrate without deteriorating crystallinity, and II for which the heat treatment has been performed. -To provide a Group VI compound semiconductor substrate.

  A heat treatment method for a II-VI group compound semiconductor substrate according to the present invention has a surface on which a semiconductor film to be an active layer is formed and a back surface located on the opposite side of the surface, and aluminum is brought into contact with the back surface. Preparing a II-VI group compound semiconductor substrate, and heat-treating the II-VI group compound semiconductor substrate in a processing chamber having a gas atmosphere containing a Group II element constituting the II-VI group compound semiconductor substrate. Prepare.

  According to the heat treatment method for a II-VI group compound semiconductor substrate thus configured, aluminum is brought into contact with the back surface opposite to the surface on which the semiconductor film to be the active layer is formed. For this reason, a reaction product produced by reaction with aluminum during the heat treatment process does not remain on the surface side of the substrate. Thereby, it is possible to prevent the crystallinity on the surface side of the substrate from being deteriorated due to the thermal stress generated due to the reaction product. On the other hand, the diffusion of aluminum into the substrate proceeds from not only the back surface of the substrate in contact with aluminum but also the entire surface including the front surface. For this reason, a sufficient amount of aluminum can be diffused also on the surface side of the substrate. Therefore, according to the present invention, a sufficient amount of aluminum can be diffused into the substrate without deteriorating the crystallinity of the surface on which the semiconductor film to be the active layer is formed, thereby reducing the resistance of the substrate. .

  Preferably, the heat treatment step includes a step of placing the II-VI group compound semiconductor substrate in the treatment chamber so that the surface is exposed in a gas atmosphere. According to the heat treatment method for a II-VI compound semiconductor substrate configured as described above, the surface of the substrate does not come into contact with a member having a coefficient of thermal expansion different from that of the substrate during the heat treatment step. For this reason, it can prevent that the crystallinity on the surface side of a board | substrate is deteriorated by the thermal stress resulting from a thermal expansion coefficient difference with the member which contacts the surface of a board | substrate.

Preferably, the processing chamber has an inner surface surrounding the II-VI group compound semiconductor substrate. Its inner surface was selected from the group consisting of pyrolytic boron nitride (pBN), hexagonal boron nitride (hBN and wBN), sapphire, aluminum oxide (Al ₂ O ₃ ), aluminum nitride (AlN), and polycrystalline diamond. It consists of at least one kind. hBN indicates low-pressure phase boron nitride similar to a hexagonal graphite structure, and wBN indicates boron nitride having a hexagonal wurtzite structure.

  According to the heat treatment method for a II-VI group compound semiconductor substrate thus configured, these materials constituting the inner surface of the processing chamber do not react with the II-VI group compound semiconductor substrate, and the II-VI group It is a substance that does not become a source of impurity contamination for compound semiconductor substrates. Since the substrate is heat-treated in a processing chamber having such an inner surface, even if the amount of aluminum in contact with the substrate increases, crystal defects do not increase in the II-VI group compound semiconductor substrate during the heat treatment. As a result, a large amount of aluminum can be diffused into the substrate without reducing crystallinity. Thereby, the resistance of the substrate can be further reduced.

  Preferably, the heat treatment method for the II-VI group compound semiconductor substrate further includes a step of evacuating the processing chamber substantially before the heat treatment step. According to the heat treatment method for a II-VI group compound semiconductor substrate configured as described above, gaseous impurities in the processing chamber can be removed by evacuating the processing chamber before the heat treatment. Thereby, generation | occurrence | production of the crystal defect of a II-VI group compound semiconductor substrate can further be prevented.

  Preferably, an aluminum thin film is directly formed on the back surface. According to the heat treatment method of the II-VI compound semiconductor substrate thus configured, the contact area between the back surface of the II-VI compound semiconductor substrate and the aluminum is increased, so that a larger amount of aluminum is diffused into the substrate. Can be made.

  Preferably, the aluminum thin film has a thickness of 1 nm to 300 nm.

  Preferably, the heat treatment step includes a heat treatment step at a temperature of 660 ° C. to 1200 ° C.

  Preferably, the heat treatment step includes a heat treatment step of 1 hour to 800 hours.

  Preferably, the II-VI group compound semiconductor substrate heat treatment method further includes a step of cooling the II-VI group compound semiconductor substrate at a cooling rate of 1 ° C./min to 200 ° C./min after the heat treatment step. .

  Preferably, when the first region in which the II-VI group compound semiconductor substrate is positioned and the second region provided separately from the first region are defined in the processing chamber, the cooling step includes the second step. Including a step of setting the temperature in the processing chamber so that the temperature of the region is lower by 1 ° C. or more and 100 ° C. or less than the temperature of the first region.

  The II-VI group compound semiconductor substrate according to the present invention is heat-treated by any of the methods described above. The II-VI group compound semiconductor substrate configured as described above has excellent crystallinity on the surface side of the substrate and a sufficiently low specific resistance value.

  As described above, according to the present invention, a heat treatment method for a II-VI compound semiconductor substrate capable of realizing low resistance of the substrate without deteriorating crystallinity, and a II-VI compound semiconductor subjected to the heat treatment. A substrate can be provided.

  The inventors have completed the present invention by obtaining the following knowledge. First, the knowledge obtained by the inventor will be described with reference to the drawings.

  FIG. 3 is a cross-sectional view showing a conventional heat treatment apparatus. Referring to FIG. 3, a conventional heat treatment apparatus 101 is mounted on a case-shaped quartz ampule 103, a quartz enclosure lid 102 that is fitted into the quartz ampule 103 to form a predetermined space, and the quartz enclosure lid 102. And a quartz container 104 surrounded by the quartz ampule 103 and a quartz spacer 105 placed on the quartz container 104.

  On the quartz spacer 105, ZnSe substrates 106 and 109 are provided, and aluminum films 107 and 108 are positioned so as to be sandwiched between the ZnSe substrates 106 and 109. The quartz container 104 is provided with a notch 104h. A Zn crystal 110 is arranged in the quartz container 104.

  In such an apparatus, the quartz ampoule 103 is once evacuated and evacuated, and then the quartz sealing lid 102 is heated. Thus, the quartz ampoule 103 is hermetically sealed by softening and welding the quartz to produce an airtight container. Thereafter, the sealed quartz ampule 103 is placed in a furnace and kept at a high temperature. As a result, a part of the Zn crystal 110 is sublimated, and the quartz ampule 103 has a Zn atmosphere. At the same time, the aluminum films 107 and 108 are melted, so that aluminum diffuses into the ZnSe crystal constituting the ZnSe substrates 106 and 109. Thereby, the conductive ZnSe substrates 106 and 109 can be obtained.

  This heat treatment process increases the dislocation density of the ZnSe substrates 106 and 109. Some reaction product may be involved in the mechanism. Then, the following points became clear when the reaction state was analyzed by calculating the thermodynamic equilibrium state of the system starting from ZnSe, Zn, Al and quartz.

Al cannot exist stably by itself, and in the temperature range from room temperature to about 990 ° C., it is stabilized by being present as an oxide (Al ₂ SiO ₅ ) called beryl. In the temperature range of about 990 ° C. or higher, the presence of mullite (3Al ₂ O ₃ .2SiO ₂ ) stabilizes. In the gas phase, Zn vapor is the main component, but SiO is also stably present at a considerable partial pressure ratio. The composition ratio is approximately Zn: SiO = 1: 10 ⁻³ at a temperature of 1000 ° C.

  Therefore, when ZnSe, Al and Zn are set in a sealed quartz ampoule 103 and heated to a high temperature, Al volatilizes and reacts with quartz. At the same time, Al reacts with Al on the surface of Al. It can be seen that splenite or mullite continues to be produced. Al diffuses into the ZnSe crystal, but beryl and mullite are thought to remain on the ZnSe surface. It is considered that these reaction products, beryl and mullite, adhere to the surface of ZnSe and give stress to the ZnSe crystal during cooling, thereby deteriorating the crystallinity of the ZnSe crystal.

  Based on such a hypothesis, if it is in a state where Al and quartz coexist, splenite or mullite is surely generated. In order to completely suppress the deterioration of the ZnSe crystallinity during the Al diffusion heat treatment, it is considered that the heat treatment must be carried out in an atmosphere free from quartz.

  In this case, the container containing ZnSe does not contain quartz and silicon (Si), is stable at the heat treatment temperature, does not react with ZnSe, does not react with ZnSe, is not a source of impurity contamination with respect to ZnSe, and has excellent airtightness. Must be of the same material. Moreover, when arrange | positioning members, such as a spacer, in a container, those members also need to be formed with the same property. Examples of the material having such characteristics include pyrolithic boron nitride, hexagonal boron nitride, sapphire, aluminum oxide, aluminum nitride, and polycrystalline diamond.

  Ideally, it is desirable to form a vacuum region with a container made of these materials and encapsulate the ZnSe substrate therein. However, since it is necessary to maintain the entire container at a high temperature, it is difficult to maintain a vacuum only with these materials. Therefore, a quartz ampule is used as the outer container. It is possible to adopt a method in which a container made of the above-described material containing ZnSe is set in a quartz ampule and vacuum sealed with the quartz ampule. In this case, it is necessary to evacuate the container made of the above-described material and to provide the container with a communication hole for eliminating a pressure difference between the inside and the outside of the container when the temperature is maintained. In order to suppress the diffusion of SiO gas into the container through the communication hole as much as possible, it is desirable that the communication hole is a narrow tubular orifice.

  From this point of view, the heat treatment method disclosed in Patent Document 2 to be subsequently described has been devised. FIG. 4 is a cross-sectional view showing the heat treatment apparatus disclosed in Patent Document 2. As shown in FIG. In addition, compared with the member shown in FIG. 3, the same reference number is attached | subjected to the member which is the same or it corresponds.

  Referring to FIG. 4, heat treatment apparatus 30 is provided on quartz ampule 1, quartz enclosure lid 2 fitted to quartz ampule 1, quartz support 3 provided on quartz enclosure lid 2, and quartz support 3. PBN container lid 4, pBN container body 7 in contact with pBN container lid 4, pBN support 5 disposed in a space surrounded by pBN container lid 4 and pBN container body 7, and disposed on pBN support 5 And a sapphire spacer 8 provided on the pBN cup 6.

  The quartz ampule 1 is provided so as to form a predetermined space and has an opening. A quartz sealing lid 2 is fitted into the opening. A quartz support 3 is provided in contact with the quartz sealing lid 2. A Zn crystal 22 is disposed in the quartz support 3.

  A pBN container lid 4 is provided on the quartz support 3. The pBN container lid 4 has an orifice 4n, and the orifice 4n extends in a space surrounded by the quartz support 3 so as to face the Zn crystal 22. A pBN support 5 is provided on the inner surface 4 i of the pBN container lid 4. The pBN support 5 has a notch 5h. By this notch 5h and the orifice 4n, the pressure in the space in the quartz support 3 and the space in the pBN container lid 4 become substantially equal.

  A pBN container body 7 is provided so as to be in contact with the pBN container lid 4. A pBN cup 6 and a sapphire spacer 8 are provided in a region surrounded by the pBN container lid 4 and the pBN container body 7. A Zn crystal 21 is disposed in the pBN cup 6. The pBN cup 6 has a notch 6h. Thereby, the pressure of the space surrounded by the pBN cup 6 and the sapphire spacer 8 and the space surrounded by the pBN container main body 7 are substantially equal.

  Subsequently, in order to evaluate the dependence of the dislocation density on the surface of the ZnSe substrate with respect to the thickness of the aluminum film, the test described below was performed.

  A ZnSe substrate on which aluminum films having different thicknesses were deposited was disposed in the heat treatment apparatus 30 in the form shown in FIG. 4, and the ZnSe substrate was subjected to heat treatment. The heat treatment conditions were 900 ° C. and 168 hours. Next, the surface of the ZnSe substrate on which the aluminum film was formed was removed by polishing by a thickness of 100 μm. Furthermore, the dislocation density of the crystal was evaluated by etching the surface with a Br-methanol solution and measuring the etch pit density (EPD). The heat treatment was performed on a plurality of ZnSe substrates, and the dislocation density was evaluated for each substrate.

  FIG. 5 is a graph showing the relationship between the thickness of the aluminum film and the EPD on the surface of the ZnSe substrate when the ZnSe substrate is arranged in the form shown in FIG. The same mark in FIG. 5 indicates a measurement result of a ZnSe substrate manufactured from the same crystal.

  As can be seen with reference to FIG. 5, the dislocation density in the vicinity of the surface on which the aluminum film was deposited rapidly increased as the thickness of the aluminum film increased. This is presumably because the reaction between Al and SiO could not be completely prevented because quartz was used for the quartz ampule 1 and the quartz enclosure lid 2 as the outer container. For this reason, a reaction product is formed on the surface of the ZnSe substrate, and it is presumed that the deterioration of crystallinity is caused by the thermal stress during cooling.

In a ZnSe-based white LED, when the dislocation density of the substrate exceeds 5 × 10 ⁴ cm ⁻² , the lifetime of the LED is remarkably shortened due to the growth of crystal defects. For this reason, it is necessary to heat-treat the ZnSe substrate so that the dislocation density is 5 × 10 ⁴ cm ⁻² or less. From the results shown in FIG. 5, in the conventional heat treatment method, it is determined that the thickness condition of the aluminum film that can stably produce a ZnSe substrate having good crystallinity is about 100 nm or less. However, from the viewpoint of increasing the brightness of the white LED, it is not sufficient that the thickness of the aluminum film is 100 nm. In order to solve this problem, the inventor further performed a test described below.

  First, a ZnSe substrate on which an aluminum film having a different thickness is deposited is placed in the heat treatment apparatus 30 so that the surface on which the aluminum film is formed faces downward (state shown in FIG. 1 described later), and the ZnSe substrate is subjected to heat treatment. Carried out. The heat treatment conditions were the same as in the above test. Next, the surface of the ZnSe substrate on the side arranged upward in the heat treatment apparatus 30 (the surface on the side where the aluminum film is not formed) was polished and removed by a thickness of 100 μm. Further, in the same manner as in the above test, the EPD on the surface was measured, and the dislocation density of the crystal was evaluated.

  FIG. 6 is a graph showing the relationship between the thickness of the aluminum film and the EPD on the surface of the ZnSe substrate when the surface on which the aluminum film is formed faces downward. The same mark in FIG. 6 indicates a measurement result of a ZnSe substrate manufactured from the same crystal. As can be seen with reference to FIG. 6, the rate of increase in dislocation density accompanying the increase in the thickness of the aluminum film is moderate as compared with the result shown in FIG. 5.

  Next, in order to examine how the dislocation density of the ZeSe substrate is distributed in the depth direction of the substrate, the following test was performed. FIG. 7 is a cross-sectional view showing an arrangement state of a ZnSe substrate in this test.

  Referring to FIG. 7, in this test, a ZnSe substrate on which aluminum films having different thicknesses (140 nm, 200 nm, and 300 nm) are deposited is disposed in heat treatment apparatus 30 so that the surface on which the aluminum film is formed faces upward. Then, a heat treatment was performed on the ZnSe substrate. Next, the surface of the ZnSe substrate on the side arranged upward in the heat treatment apparatus 30 (the surface on the side where the aluminum film was formed) was polished and removed. At this time, it was investigated how dislocation density was distributed in the depth direction from the substrate surface by changing the polishing thickness and measuring EPD at each position. Further, the ZnSe substrate was placed in the heat treatment apparatus 30 so that the surface on which the aluminum film was formed faced downward (state shown in FIG. 1 described later), and the dislocation density distribution in this case was also examined in the same manner.

  FIG. 8 is a graph showing the relationship between the distance from the substrate surface and the EPD on the ZnSe substrate surface when the surface on which the aluminum film is formed faces upward. FIG. 9 is a graph showing the relationship between the distance from the substrate surface and the EPD on the ZnSe substrate surface when the surface on which the aluminum film is formed faces downward. In FIG. 8, the position where the distance from the substrate surface is 0 is the surface on the side arranged upward in the heat treatment apparatus 30, that is, the surface on the side where the aluminum film is formed. In FIG. 9, the position where the distance from the substrate surface is 0 is the surface on the side arranged upward in the heat treatment apparatus 30, that is, the surface on the side where the aluminum film is not formed.

  Referring to FIG. 8, when the surface on which the aluminum film is deposited is arranged upward, the dislocation density increases as the thickness of the aluminum film increases on both the surface on which the aluminum film is deposited and the opposite surface. It turned out to increase. Referring to FIG. 9, when the surface on which the aluminum film is deposited is arranged downward, the dislocation density increases rapidly with the increase in the thickness of the aluminum film in the vicinity of the surface on which the aluminum film is deposited. However, it was found that the increase in dislocation density was very small on the opposite surface (the surface on which the aluminum film was not deposited and placed upward).

  From the above test results, it has been clarified that the dislocation density increases as the thickness of the aluminum film increases on the surface on which the aluminum film is deposited and on the surface in contact with the sapphire spacer 8. Since the aluminum content is large on the surface on which the aluminum film is deposited, a large amount of reaction products of aluminum and Si or O remain. For this reason, it is thought that the thermal stress resulting from a thermal expansion coefficient difference with a ZnSe board | substrate becomes large.

  On the other hand, on the surface in contact with the sapphire spacer 8, the ZnSe substrate and the sapphire spacer 8 are fixed, and it is considered that the dislocation density increases due to the thermal stress caused by the difference in thermal expansion coefficient between them. Also in this case, the dislocation density increases as the thickness of the aluminum film increases. This may be because the amount of aluminum has an influence on the strength of fixing between the ZnSe substrate and the sapphire spacer 8. Presumed. Further, in the rapid cooling process after the heat treatment, the temperature of the substrate is drastically lowered, so that the propagation of dislocations is limited, and the dislocation density may have a distribution in the depth direction.

  FIG. 10 is a graph showing the relationship between the distance from the substrate surface and the PL (photoluminescence) intensity. In FIG. 10, the position where the distance from the substrate surface is 0 is the surface on the side where the aluminum film is formed. Referring to FIG. 10, when the ZnSe substrate is arranged so that the surface on which the aluminum film is formed faces upward or when it is arranged so as to face downward, the PL intensity shown in the figure remains almost unchanged. A distribution was obtained. From this result, it was found that the PL intensity was high on both the surface on which the aluminum film was deposited and the surface on the opposite side, and the PL intensity was low near the center between these surfaces.

  This is presumably because the aluminum deposited on one surface melts at a high temperature and diffuses to the surface, so that the aluminum wraps around to the opposite surface. In general, since the surface diffusion coefficient is several orders of magnitude greater than the bulk diffusion coefficient, aluminum diffuses into the ZnSe substrate not only from the deposited surface, but also from the opposite surface (possibly from the side). It is thought that.

  When an LED is fabricated using an actual ZnSe substrate, a multilayer epitaxial film having an LED structure is formed on one substrate surface. Thereafter, the surface on the opposite side is polished to reduce the thickness of the substrate, and chipped by scribing or braking. Therefore, when producing a white LED using the light emission of the substrate, the substrate needs to emit light sufficiently near the surface on which the multilayer epitaxial film constituting the LED structure is formed. From the results shown in FIG. 10, the light emission intensity of the substrate is sufficiently high even on the surface on which the aluminum film is not formed. For this reason, it has become clear that an LED can be manufactured by forming a multilayer epitaxial film on the surface on which the aluminum film is not formed and polishing the surface on which the aluminum film is formed. It was.

  Based on the knowledge described above, the inventor has completed the II-VI compound semiconductor substrate heat treatment method according to the present invention and the II-VI compound semiconductor substrate heat-treated by the method. Embodiments of the present invention will be described below with reference to the drawings.

  1 and 2 are sectional views showing a heat treatment apparatus used in the heat treatment method according to the embodiment of the present invention. Referring to FIG. 1, in the heat treatment method in the present embodiment, heat treatment apparatus 30 whose structure has been described with reference to FIG. 4 is used.

  First, a ZnSe substrate 10 having a front surface 10a and a back surface 10b is prepared. When a device such as an LED is manufactured using the ZnSe substrate 10, the surface 10a is formed by MBE (molecular beam epitaxy) or MOCVD. It is a surface formed using a technique such as (metal organic chemical vapor deposition). The back surface 10b is a surface located on the opposite side of the front surface 10a. When an LED is manufactured using the ZnSe substrate 10, in general, a semiconductor film is not formed on the back surface 10 b and is polished during the manufacturing process in order to reduce the thickness of the ZnSe substrate 10.

  Next, the aluminum film 9 is vapor-deposited on the back surface 10b, and the ZnSe substrate 10 is stored in a space surrounded by the pBN container body 7 and the pBN container lid 4 as a processing chamber formed of high-purity pBN. At this time, the ZnSe substrate 10 is arranged so that the back surface 10b on which the aluminum film 9 is deposited faces the sapphire spacer 8, and the front surface 10a on which the aluminum film 9 is not deposited faces upward. The surface 10a is held in a state where it does not come into contact with other members, that is, in a state where it is exposed in the accommodated space.

  In FIG. 1, only one ZnSe substrate is accommodated. However, as shown in FIG. 2, a plurality of ZnSe substrates 10 are formed by arranging an appropriate number of sapphire spacers 8 at intervals. You may store it at once.

  The processing chamber is divided into a pBN container body 7 and a pBN container lid 4, and the pBN container lid 4 is provided with an orifice 4 n. The pBN container body 7 and the pBN container lid 4 have a structure in which airtightness is maintained by fitting. The pBN container body 7 and the pBN container lid 4 and the Zn crystal 21 are accommodated in the quartz ampule 1 and the quartz enclosure lid 2 is set. The quartz ampule 1 may contain aluminum crystals. When the inside of the quartz ampule 1 is evacuated, the inside of the pBN container body 7 and the pBN container lid 4 as the pBN container is simultaneously evacuated through the orifice 4n. After evacuating to a predetermined degree of vacuum, the quartz enclosure lid 2 is heated and sealed, and the inside of the quartz ampule 1 is sealed in a vacuum.

  The quartz ampule 1 is set in a heat treatment furnace. In order to suppress the pressure of Zn in the quartz ampule 1 and prevent solid Zn from condensing in a low temperature region, it is desirable that the temperature distribution in the quartz ampule 1 be as uniform as possible. By holding the quartz ampule 1 for a predetermined time at a predetermined temperature, aluminum diffuses into the ZnSe substrate 10. After the step of maintaining the high temperature is completed, the ZnSe substrate 10 is cooled at a predetermined cooling rate. Through the above steps, a ZnSe substrate having excellent conductivity and crystal quality can be manufactured.

  The heat treatment method for a II-VI group compound semiconductor substrate according to the embodiment of the present invention includes a front surface 10a on which a semiconductor film serving as an active layer is formed, and a back surface 10b located on the opposite side of the front surface 10a. A step of preparing a ZnSe substrate 10 as a II-VI group compound semiconductor substrate in which an aluminum film 9 as aluminum is contacted, and a processing chamber in which a gas atmosphere containing Zn as a group II element constituting the ZnSe substrate 10 is used. And a step of heat-treating the ZnSe substrate 10.

  The film thickness of the aluminum film 9 is preferably 1 nm or more and 300 nm or less. If the film thickness is less than 1 nm, the amount of Al diffusion into the ZnSe is small, so that the resistance of the ZnSe crystal cannot be sufficiently reduced. On the other hand, when the film thickness exceeds 300 nm, Al or Al—Zn alloy that cannot be diffused remains on the surface of the ZnSe substrate. This exerts stress on the ZnSe crystal during cooling and causes crystallinity to deteriorate.

  It is preferable that the temperature of heat processing is 660 degreeC or more and 1200 degrees C or less. When the temperature is lower than 660 ° C., Al exists in a solid state, and therefore Al cannot be effectively diffused in ZnSe. On the other hand, when the temperature exceeds 1200 ° C., the crystallinity of ZnSe deteriorates due to the influence of the temperature.

  The heat treatment time is preferably 1 hour or more and 800 hours or less. If it is less than 1 hour, Al cannot completely diffuse into ZnSe and remains on the surface of the ZnSe substrate. As a result, the Al remaining during cooling exerts stress on the ZnSe crystal, causing deterioration of crystallinity. On the other hand, when the heat treatment time exceeds 800 hours, Al completely diffuses into the ZnSe substrate, and conversely, outward diffusion becomes remarkable. Thereby, since the Al concentration in ZnSe decreases with time, it is meaningless to lengthen the heat treatment time.

  The cooling rate after the heat treatment is preferably 1 ° C./min or more and 200 ° C./min or less. When the cooling rate exceeds 200 ° C./min, the temperature distribution inside the ZnSe crystal increases, and the crystallinity deteriorates during the cooling process. Further, in slow cooling at a cooling rate of less than 1 ° C./min, the time for passing through the low temperature region becomes long, so that the characteristics of ZnSe approach a thermal equilibrium state at a low temperature. As a result, the Al activation rate decreases, the carrier density decreases, and the resistivity increases.

  When the first region in which the ZnSe substrate 10 is positioned and the second region provided separately from the first region are defined in the processing chamber, the temperature of the second region is 1 than the temperature of the first region. It is preferable to set the temperature in the processing chamber so that the temperature is lower than or equal to 100 ° C. and lower than or equal to 100 ° C.

  When the ZnSe crystal comes into contact with Zn, Al, or a Zn—Al alloy during cooling, the crystallinity of ZnSe is greatly deteriorated due to the difference in thermal expansion coefficient. During cooling, the temperature is adjusted so that the portion with the lowest temperature exists at the place in the reaction vessel excluding the position where the ZnSe substrate 10 is set, so that Zn, Al, and the Zn—Al alloy are at the lowest temperature portion. Since they are transported and solidified, they can be prevented from contacting with the ZnSe crystal. Thereby, deterioration of crystallinity can be prevented.

  At this time, if the temperature difference is less than 1 ° C., there is no effect of setting the lowest temperature portion. When the temperature difference exceeds 100 ° C., the ZnSe crystal itself is transported to the lowest temperature portion, and the influence of deterioration of crystallinity cannot be ignored. During the high temperature holding, the inside of the reaction vessel may be completely soaked. Further, there may be a multilayer temperature distribution within a range where the transport of the ZnSe crystal itself is not significant.

  The comparative example described below and Examples 1 to 3 were carried out to confirm the effects of the present invention.

(Comparative example)
Heat treatment was performed using a heat treatment apparatus 30 in FIG. 1 on a ZnSe substrate (vertical × horizontal 20 mm × 20 mm, thickness 700 μm) made of ZnSe single crystal having a plane orientation (100). The specific resistance of the crystal before the heat treatment was 10 ⁵ Ωcm or more, which is the upper limit of the measurable range of hole measurement, and was high resistance. Further, the substrate surface was mirror-polished, and the dislocation density of the crystal was measured by etching using a Br-methanol solution. The dislocation density was 5 × 10 ³ cm ⁻² or more and 2 × 10 ⁴ cm ⁻² or less.

On the etched surface, an aluminum film having a thickness of 200 nm was formed by vacuum deposition. In this comparative example, the ZnSe substrate was placed on the sapphire spacer 8 so that the surface on which the aluminum film was deposited faced upward like the ZnSe substrate 106 shown in FIG. Further, Zn crystals 21 and 22 each having a mass of 0.1 g were also set in the quartz ampoule 1 at the same time. The quartz ampule 1 was evacuated until the degree of vacuum (pressure) was 2 × 10 ⁻⁸ Torr (2.7 × 10 ⁻⁶ Pa). Thereafter, the quartz ampule 1 was sealed with a quartz sealing lid 2.

  This quartz ampoule 1 was set in a vertical tubular furnace, heated so that the ZnSe substrate had a uniform temperature (1000 ° C.) and the lower end of the quartz ampoule 1 became 980 ° C., and was heat-treated for 7 days (168 hours). Then, it cooled to room temperature with a cooling rate of 60 degreeC / min. After cooling, Zn had condensed on the lower end of the quartz ampule 1. The ZnSe substrate and the sapphire spacer 8 could be easily separated without sticking to each other. The aluminum film deposited on the ZnSe substrate was not visually observed on the surface due to diffusion into the crystal and dissipation to the outside.

The surface of the heat-treated ZnSe substrate on which the aluminum film was deposited and the surface on the opposite side were re-polished to a depth of 100 μm and evaluated. On the surface on which the aluminum film was deposited, the carrier density was 7 × 10 ¹⁷ cm ⁻³ , and the dislocation density was about 1.8 × 10 ⁵ cm ^{−2 on} average in the substrate surface. On the other hand, on the opposite surface, the carrier density was 7 × 10 ¹⁷ cm ⁻³ , and the dislocation density was about 1.6 × 10 ⁵ cm ⁻² in average on the substrate surface. From the above results, it was confirmed that on any surface, the resistance was reduced by the heat treatment, but on the other hand, the dislocation density of the crystal was increased.

(Example 1)
After measuring the dislocation density of the ZnSe single crystal substrate by the same process as in the comparative example, an aluminum film was formed on the surface of the ZnSe single crystal substrate. The dislocation density of the substrate was in the range of 5 × 10 ³ cm ^{−2 to} 2 × 10 ⁴ cm ⁻² . In this embodiment, as shown in FIG. 1, the surface on which the aluminum film is deposited (back surface 10b in FIG. 1) faces downward, and the surface on which the aluminum film is not deposited (surface 10a in FIG. 1) faces upward. As described above, the ZnSe substrate was placed on the sapphire spacer 8. Further, Zn crystals 21 and 22 each having a mass of 0.1 g were also set in the quartz ampoule 1 at the same time. The quartz ampule 1 was evacuated until the degree of vacuum (pressure) was 2 × 10 ⁻⁸ Torr (2.7 × 10 ⁻⁶ Pa). Thereafter, the quartz ampule 1 was sealed with a quartz sealing lid 2.

  Next, heat treatment was performed on the ZnSe substrate under the same conditions as described in the comparative example. Similar to the result in the comparative example, the ZnSe substrate and the sapphire spacer 8 are not fixed to each other, and the aluminum film deposited on the ZnSe substrate is diffused into the crystal and dissipated to the outside. It was not observed on the surface by visual observation.

The surface of the heat-treated ZnSe substrate on which the aluminum film was deposited and the surface on the opposite side were re-polished to a depth of 100 μm and evaluated. On the surface on which the aluminum film has been deposited (back surface 10b in FIG. 1), the carrier density is 7 × 10 ¹⁷ cm ⁻³ , and the dislocation density is about 4.0 × 10 ⁵ cm as an average value in the substrate surface. ^-2 . On the other hand, on the opposite surface (surface 10a in FIG. 1), the carrier density is 7 × 10 ¹⁷ cm ⁻³ , and the dislocation density is about 3.0 × 10 ⁴ cm ^{−2 on} average in the substrate surface. became.

  From the above results, it was confirmed that resistance was reduced by heat treatment on any surface. Regarding crystallinity, on the surface on the side where the aluminum film is deposited (back surface 10b in FIG. 1), the dislocation density is greatly increased, whereas the surface on the side where the aluminum film is not deposited. In (surface 10a in FIG. 1), it was confirmed that the increase in dislocation density was extremely small.

(Example 2)
A ZnSe substrate (thickness 700 μm) having a plane orientation (100) was produced by slicing a ZnSe single crystal. The ZnSe substrate was organically cleaned, then etched in an aqueous NaOH solution, and then further washed with pure water. Next, an aluminum film having a thickness of 150 nm was formed on one surface of the substrate by vacuum vapor deposition. In this embodiment, using the heat treatment apparatus 30 shown in FIG. 2, the surface on which the aluminum film is deposited (the back surface 10b in FIG. 2) faces downward, and the surface on which the aluminum film is not deposited (the surface 10a in FIG. 2). ) About 30 ZnSe substrates were placed on the sapphire spacer 8 so as to face upward. Further, Zn crystals 21 and 22 each having a mass of 0.1 g were also set in the quartz ampoule 1 at the same time. The quartz ampule 1 was evacuated until the degree of vacuum (pressure) was 2 × 10 ⁻⁸ Torr (2.7 × 10 ⁻⁶ Pa). Thereafter, the quartz ampule 1 was sealed with a quartz sealing lid 2.

  Next, heat treatment was performed on the ZnSe substrate under predetermined conditions. Thereafter, the surface of the heat-treated ZnSe substrate on which the aluminum film was not deposited (surface 10a in FIG. 2) was polished to remove a portion having a thickness of 100 μm from the surface, and the surface was finished by mirror polishing. . Next, the ZnSe substrate was etched with a dichromate solution, and the surface layer of the ZnSe substrate was removed by a thickness of 3 μm. The obtained substrate was set in an MBE (molecular beam epitaxy) apparatus, and a ZnSe thin film having a thickness of 1.5 μm was grown.

The grown ZnSe thin film had good surface morphology. The dislocation density of the epitaxial film was measured by etching with a Br-methanol solution. During the epitaxial growth, dislocations were newly increased by about 3 × 10 ³ cm ⁻² , but the total dislocation density combined with dislocations inherited from the ZnSe substrate was 8 × 10 ³ cm ⁻² or more and 3.5 × 10 ^It was in the range of ⁴ cm ⁻² and good crystallinity was maintained.

Further, the back surface of the epitaxially grown ZnSe substrate was polished so that the thickness of the ZnSe substrate was 250 μm. When the carrier density on the back surface of the ZnSe substrate was measured by CV (capacitance-voltage) measurement, the carrier density was about 7 × 10 ¹⁷ cm ⁻³ , which was high enough to form an n-type electrode. I have confirmed that I have it.

(Example 3)
In the MBE apparatus, a ZnSe substrate according to the present invention obtained by the heat treatment method described in Example 2 and a ZnSe substrate for comparison obtained by heat treatment so that the surface on which the aluminum film was deposited faced upward are formed. The ZnSe thin film which comprises LED structure was grown on each board | substrate.

  Ten LED chips were produced by the same process from each ZnSe substrate on which the ZnSe film was grown, and the emission intensity was measured by the same measuring device and compared. In the LED chip using the ZnSe substrate for comparison, the average value of the emission intensity was 2.9 mW, whereas in the LED chip using the ZnSe substrate according to the present invention, the average value of the emission intensity was 3. This was 2 mW, which was about 10% higher than when a comparative ZnSe substrate was used.

  Further, the chromaticity coordinates of the light emission were x = 0.28 and y = 0.31 in the LED chip using the ZnSe substrate for comparison, whereas the LED using the ZnSe substrate according to the present invention. In the chip, x = 0.30 and y = 0.31, and the x value increased by 0.2 as compared with the case of using a ZnSe substrate for comparison. Thereby, when the ZnSe substrate by this invention was used, it has confirmed that the yellow component, ie, the emitted light intensity from a board | substrate, increased.

  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.

It is sectional drawing which shows the heat processing apparatus used for the heat processing method in embodiment of this invention. It is sectional drawing which shows another heat processing apparatus used for the heat processing method in embodiment of this invention. It is sectional drawing which shows the conventional heat processing apparatus. It is sectional drawing which shows the heat processing apparatus disclosed by patent document 2. FIG. It is a graph which shows the relationship between the thickness of an aluminum film, and the EPD of a ZnSe substrate surface at the time of arrange | positioning a ZnSe substrate to the form shown in FIG. It is a graph which shows the relationship between the thickness of an aluminum film, and the EPD of the surface of a ZnSe board | substrate when the surface in which the aluminum film was formed was made downward. It is sectional drawing which shows the arrangement | positioning state of a ZnSe board | substrate in this test. It is a graph which shows the relationship between the distance from a substrate surface, and EPD of a ZnSe substrate surface when the surface in which the aluminum film was formed was made upward. It is a graph which shows the relationship between the distance from a substrate surface, and the EPD of a ZnSe substrate surface when the surface on which an aluminum film is formed faces downward. It is a graph which shows the relationship between the distance from a substrate surface, and PL intensity.

Explanation of symbols

  4 pBN container lid, 4i inner surface, 7 pBN container body, 9 aluminum film, 10 ZnSe substrate, 10a surface, 10b back surface.

Claims (11)

A step of preparing a II-VI group compound semiconductor substrate having a surface on which a semiconductor film to be an active layer is formed, and a back surface located on the opposite side of the front surface, and contacting the back surface with aluminum;
And a heat treatment method for the II-VI group compound semiconductor substrate, comprising: a step of heat-treating the II-VI group compound semiconductor substrate in a processing chamber having a gas atmosphere containing a Group II element constituting the II-VI group compound semiconductor substrate. .   2. The II-VI according to claim 1, wherein the heat treatment includes placing the II-VI compound semiconductor substrate in the processing chamber such that the surface is exposed to the gas atmosphere. Heat treatment method for group compound semiconductor substrate.   The processing chamber has an inner surface surrounding the II-VI group compound semiconductor substrate, and the inner surface is made of pyrolithic boron nitride, hexagonal boron nitride, sapphire, aluminum oxide, aluminum nitride, and polycrystalline diamond. The heat processing method of the II-VI group compound semiconductor substrate of Claim 1 or 2 which consists of at least 1 sort (s) chosen more.   The method for heat treatment of a II-VI group compound semiconductor substrate according to any one of claims 1 to 3, further comprising a step of evacuating the inside of the processing chamber before the heat treatment step.   The heat treatment method for a II-VI group compound semiconductor substrate according to any one of claims 1 to 4, wherein an aluminum thin film is directly formed on the back surface.   The method for heat treatment of a II-VI group compound semiconductor substrate according to claim 5, wherein the aluminum thin film has a thickness of 1 nm to 300 nm.   The heat treatment method for a II-VI compound semiconductor substrate according to any one of claims 1 to 6, wherein the heat treatment step includes a heat treatment step at a temperature of 660 ° C to 1200 ° C.   The method for heat treatment of a II-VI group compound semiconductor substrate according to any one of claims 1 to 7, wherein the heat treatment step includes a heat treatment step of 1 hour to 800 hours.   9. The method according to claim 1, further comprising a step of cooling the II-VI group compound semiconductor substrate at a cooling rate of 1 ° C./min to 200 ° C./min after the heat treatment step. A heat treatment method for a II-VI group compound semiconductor substrate. When the first region in which the II-VI group compound semiconductor substrate is positioned and the second region provided separately from the first region are defined in the processing chamber,
The step of cooling includes the step of setting the temperature in the processing chamber so that the temperature of the second region is lower by 1 ° C. or more and 100 ° C. or less than the temperature of the first region. The heat processing method of II-VI group compound semiconductor substrate.   The II-VI group compound semiconductor substrate heat-processed by the method of any one of Claim 1 to 10.

Images