JP4969926B2 - Heat treatment apparatus, oxidation treatment system, and heat treatment method - Google Patents

Description

  The present invention relates to a heat treatment method and a heat treatment apparatus suitable for treating an object to be treated such as a semiconductor substrate by steam oxidation, and more particularly to an apparatus for performing the oxidation treatment in a state where the progress of the oxidation treatment can be monitored. Is.

  Conventionally, the current confinement layer of the surface emitting laser element has been formed through the following steam oxidation process. That is, the current confinement layer having an opening with a desired diameter is formed by gradually oxidizing the AlAs layer of the mesa post from the surroundings in a water vapor atmosphere to change it into an oxide insulating layer.

  In such a steam oxidation process, a heat treatment apparatus for heating a semiconductor substrate provided with an AlAs layer in a steam atmosphere is used. In the steam oxidation process, since the oxidation progress rate is very sensitive to temperature, it is strongly desired to keep the temperature constant at the start of oxidation and during oxidation. For this reason, in a conventional heat treatment apparatus, for example, nitrogen gas is introduced into a heating furnace, the substrate is heated, and after the temperature in the heating furnace is stabilized, water vapor is introduced to form the above-described oxide insulating layer. (See Patent Document 1).

  In addition, there is an apparatus in which the entire water vapor gas system is placed in a thermostatic bath to prevent condensation of water in the piping and to eliminate fluctuations in gas temperature due to gas switching (see Patent Document 2).

  Furthermore, since the oxide insulating layer is selectively grown to a desired size, there is one that can monitor the growing oxide insulating layer from the outside of the heating furnace through a window (see Patent Document 3).

JP-A-10-144682 JP 2004-228335 A JP 2003-179309 A

  However, in the heat treatment apparatus described in Patent Document 1, vaporized high-temperature water vapor is mixed in a stable state where normal-temperature nitrogen gas flows, so that the gas temperature in the furnace fluctuates during gas switching. However, it is difficult to control the temperature field in the furnace, and in particular, the initial growth rate of the oxide insulating layer fluctuates, which makes it difficult to control the growth of the oxide insulating layer.

  In the heat treatment apparatus described in Patent Document 2, the apparatus is arranged in a thermostatic chamber so that there is no temperature fluctuation of the introduced gas. However, even in this apparatus, the substrate temperature fluctuates. Therefore, this apparatus also has a problem that it is difficult to control the growth of the oxide insulating layer.

  In particular, when the wafer (substrate) is warped (the crystal-grown substrate is often slightly warped), and the contact state between the surface of the tray (mounting table) and the wafer is uneven, In many cases, a uniform heat treatment cannot be performed because a temperature distribution is generated in the wafer surface direction between a poor contact state and a good contact state with the tray.

  Incidentally, since the oxidation rate varies greatly depending on the processing state of the previous process, there is an apparatus in which an observation window is provided to monitor the growth of the oxide insulating layer (Patent Document 3). The observation window is provided in a processing unit (reaction unit) where the object to be processed is oxidized. However, in an apparatus provided with such an observation window, the temperature field in the furnace becomes non-uniform and unstable due to heat radiation from the window. For this reason, when the oxide insulating layer of the surface emitting laser element is formed, there is a problem that it is difficult to control the growth of the oxide insulating layer stably.

  The present invention has been made in view of the above, and an object of the present invention is to provide a heat treatment method and a heat treatment apparatus capable of performing a steam oxidation treatment or the like in a stable temperature field. In particular, it is an object of the present invention to provide a heat treatment method and apparatus capable of more stably controlling the growth of an oxide insulating layer when forming a current confinement layer of a surface emitting laser element.

  In order to solve the above-described problems and achieve the object, a heat treatment method according to the present invention is a heat treatment method in which a preheated gas is introduced into a treatment unit in which a heated object to be processed is set and processed. The temperature of the gas introduced into the processing unit is adjusted in advance by the preheating unit to the same temperature as the temperature of the workpiece set in the processing unit, and then the gas is introduced into the processing unit. .

  The heat treatment apparatus according to the present invention is a heat treatment apparatus for processing an object to be processed in a heated atmosphere, and a mounting table on which the object to be processed is set and an object to be processed set on the mounting table. A heating furnace having a processing unit having a heating means for heating an object and a preheating unit for preheating gas sent to the processing unit is provided.

  In the heat treatment apparatus according to the present invention, in the above invention, the preheating part has a cylindrical flow path whose temperature is controlled by the heating means, and the gas sent to the treatment part is in the flow path. It is characterized by being preheated through the flow.

  Moreover, the heat treatment apparatus according to the present invention is characterized in that, in the above invention, the treatment unit functions as a reaction unit that oxidizes the workpiece set on the mounting table with steam in a heated atmosphere. To do.

  Moreover, in the heat treatment apparatus according to the present invention, in the above invention, the processing unit has an observation window for directly observing the workpiece set on the mounting table from the outside of the processing unit, and the observation window The reflector is provided inside, and the reflector is movable so that the object to be processed can be observed from the observation window.

  In the heat treatment apparatus of the present invention, the temperature of the gas introduced into the processing unit is adjusted in advance by the preheating unit to the same temperature as the temperature of the workpiece set in the processing unit, and then the gas is introduced into the processing unit. Therefore, heat transfer between the introduced gas and the object to be processed can be suppressed. As a result, a stable temperature field can always be formed, the in-plane surface of the workpiece can be processed uniformly, and even between different batches, the processing can always be stably performed.

  In particular, fluctuations in the amount of heat transferred between the object to be treated and the introduced gas, which are likely to occur when the type of the introduced gas is changed, due to the difference in specific heat of the introduced gas, can be suppressed. In addition, the temperature of the entire surface of the object to be processed can be kept more uniform, and variations in heat treatment can be suppressed.

  Further, the heat treatment apparatus according to the present invention can introduce the introduction gas sent to the reaction section by preheating to the same temperature as the substrate temperature in the preheating section provided on the upstream side of the heating furnace. Therefore, there is an effect that a stable temperature field can always be formed, the in-plane processing can be performed uniformly, and even between different batches, the processing can always be performed stably. In particular, in a heat treatment apparatus provided with a reflector inside the observation window, temperature changes in the reaction part (treatment part) due to observation from the observation window can be minimized, and a more stable temperature field in the reaction part. Can be formed.

  Hereinafter, a heat treatment apparatus which is the best mode for carrying out the present invention will be described with reference to the drawings.

(Embodiment 1)
1 is a cross-sectional view schematically showing a schematic configuration of a heating furnace portion of a heat treatment apparatus according to Embodiment 1 of the present invention. The heating furnace 1 includes a processing unit 2 provided with a heating unit, and a preheating unit 3 provided in the previous stage of the processing unit 2. The processing unit 2 is a part that functions as a reactor (hereinafter referred to as “reaction unit 2”). ). The preheating unit 3 is a part for preheating the gas introduced into the reaction unit 2.

  The reaction unit 2 includes a turntable 4a that rotates around the rotation shaft 4 as a mounting table on which an object to be processed is set. In the turntable 4a, a wafer 6 which is a semiconductor substrate to be processed is placed on a tray 5 placed thereon, and the wafer 6 being processed is rotated by a rotating shaft 4. A heater 7 is provided below the rotary table 4a. The inside of the reaction unit 2 is heated by the heater 7 and is kept at a predetermined temperature. As a result, the wafer 6 that is the object to be processed is also heated and maintained at a constant temperature. High-temperature water vapor is introduced into the reaction unit 2 at an appropriate timing, and the AlAs layer provided on the wafer 6 is oxidized by the water vapor to form an oxide insulating layer. This state of selective growth is observed by the monitor 9 through the observation window 8. The observation window 8 is made of heat-resistant glass, and is provided on the furnace wall directly above the wafer 6 in the reaction unit 2. The monitor 9 observes the progress of processing. The monitor is a microscope mechanism for optical observation and direct observation, and uses a visible light or infrared sensor.

  The preheating unit 3 functions as a flow path 11 for introducing the introduced gas into the reaction unit 2. The gas introduced into the reaction unit 2 is introduced into the preheating unit 3 from the gas introduction unit 3 a and flows into the reaction unit 2 after passing through the preheating unit 3. In the preheating unit 3, a heater 10 is provided along the flow path 11.

  In the heat treatment method using this apparatus, the gas flowing in the flow path 11 by the heater 10 is preheated so as to be the same temperature as the temperature of the wafer 6 on the turntable 4a in the reaction unit 2 (note that Here, the same temperature means that the temperature is the same within the controllable range of the apparatus.)

  In this way, even if the gas species is switched, the temperature in the reaction unit 2 and the temperature of the wafer 6 do not change, and a stable temperature field can always be formed.

  A diffusion plate 12 is provided on the outlet side (reaction part 2 side) of the flow path 11 of the preheating part 3. The diffusion plate 12 is a plate-like member provided with a plurality of holes, and diffuses the gas heated in the flow path 12 and introduces it into the reaction section 2, thereby having a uniform temperature distribution. A gas is introduced into the reaction unit 2, and disturbance of the temperature distribution in the reaction unit 2 can be prevented. Instead of the diffusing plate 12, various mechanisms can be used as long as the gas can be diffused and supplied to the reaction unit 2. For example, you may make it provide the member which disturbs the flow of gas in the gas introduction part 3a side. Moreover, a better effect may be acquired by installing two or more diffusion plates. Note that the gas in the reaction unit 2 is exhausted through the flow path 13. A heater 14 is also provided in the lower part of the flow path 13 to prevent a temperature change in the reaction unit 2 from occurring.

  A wafer 6 which is an example of an object to be processed is one in which a plurality of surface emitting laser elements shown in FIG. 2 are finally formed. FIG. 2 is a cross-sectional view of the configuration of the surface emitting laser element formed on the wafer 6 as viewed obliquely. In the surface emitting laser element 20, a buffer layer 31, a lower multilayer reflector 22, an active region 23, an upper multilayer reflector 26 including a current confinement layer 25, and a contact layer 27 are sequentially stacked on a GaAs substrate 21, An n-side electrode 33 is provided below the GaAs substrate 21, and a ring-shaped p-side electrode 28 and an electrode pad 30 for drawing out the electrode of the p-side electrode 28 are provided above the contact layer 27. . The active region 23, the upper multilayer reflector 26 and the p-side electrode 28 form a cylindrical mesa post with the periphery removed, and the side walls of the mesa post and the upper part of the lower multilayer reflector 22 are covered with a silicon nitride film 29. It has been broken. The periphery of the mesa post is filled with polyimide 32 with the silicon nitride film 29 interposed therebetween.

  Here, a manufacturing method of the surface emitting laser element 20 will be described. First, a GaAs buffer layer 31, a lower multilayer reflector 22, an active region 23, an upper multilayer reflector 26, and a contact layer 27 are sequentially stacked on the above-described GaAs substrate 21 by MOCVD. A current confinement layer 25 made of AlAs is laminated on the lowermost layer of the upper multilayer mirror 22.

  Thereafter, a silicon nitride film is formed on the growth surface of the contact layer 27 by plasma CVD, and the circular pattern is transferred using a photolithographic technique using a photoresist. The silicon nitride film is etched using the transferred circular resist mask. Further, etching is performed until the lower multilayer film reflecting mirror 22 is reached, thereby forming a mesa post having a columnar structure. The etching depth is stopped at the position of the lower multilayer film reflecting mirror 22.

The wafer 6 in this state is heated to 250 to 450 ° C. in a water vapor atmosphere in the reaction section 2 and left to stand, thereby selectively oxidizing the current confinement layer 25 at the lowermost layer of the upper multilayer reflector 26. An oxidation process is performed. The gas at this time is nitrogen gas containing water vapor, and the gas pressure is from 10 Torr to normal pressure. AlAs current blocking layer 25 generates Al ₂ O ₃ reacts with H ₂ O, oxidation proceeds by the in this Al ₂ O ₃ H ₂ O to produce a further Al ₂ O ₃ diffuses To go. As a result, the oxide insulating layer 24 is selectively formed.

  When the selective oxidation step is performed, as shown in the monitor image shown in FIG. 3 and FIG. 4, oxidation proceeds from the periphery of the AlAs layer 50, and finally, an oxidation aperture OA that is a rectangular current injection region is formed. . The shape of the oxidized aperture OA should be circular when the oxidation rate is constant. However, due to the influence of the crystal structure of the AlAs layer 50, the oblique oxidation amount L1 and the lateral oxidation amount L2 are different. It becomes a different value and becomes the substantially rectangular shape mentioned above.

  In general, in the CVD method, as shown in FIG. 5, the gases react with each other, and the species after the reaction are chemically adsorbed on the wafer. In the CVD method, the wafer temperature is higher than the gas temperature in the reaction furnace. This prevents pre-reaction where gases react before reaching the wafer surface, and the gas reacts immediately before deposition (chemical adsorption) on the wafer, so that only reactive species can be chemically adsorbed. The merit that the purity of the film to be increased becomes high.

  On the other hand, in the above-described selective oxidation step, as shown in FIG. 6, the reaction gas is physically adsorbed, and further, the reaction proceeds and the oxidation reaction proceeds. Here, when the temperature of the wafer 6 is higher than the gas temperature of the reaction unit 2, the reaction gas is difficult to physically adsorb to the wafer 6, and the selective oxidation process may be limited by the adsorption process. Furthermore, a slight temperature difference between the gas temperature and the temperature of the wafer 6 greatly affects physical adsorption, resulting in fluctuations in the oxidation rate, leading to destabilization of the oxidation rate.

  Thus, the influence of the temperature difference between the wafer and the gas is completely different between the deposition by the CVD method and the selective oxidation step. In the selective oxidation step, it is desirable that the temperature field in the reaction unit 2 is uniform, and the gas temperature in the reaction unit 2 and the temperature of the object to be processed (wafer 6) are substantially the same.

  Here, in the heat treatment apparatus of the first embodiment, the preheating unit 3 is provided, and the temperature of the gas is heated in advance to the same temperature as the temperature of the wafer 6 on the mounting table, which is the object to be processed, and then in the reaction unit 2. Therefore, the temperature of the wafer 6 does not change, the gas temperature in the furnace does not change, and the temperature field in the furnace is kept uniform. As a result, even when the selective oxidation step described above is performed, the oxidation rate can be accurately controlled.

  In the heat treatment method of the first embodiment, since the temperature of the introduced gas is the same as that of the tray 5 (and thus the wafer 6), the heat transfer between the wafer 6, the tray 6 and the introduced gas can be suppressed. Therefore, in the heat treatment method of this embodiment, the entire surface of the wafer 6 can be uniformly heat treated. That is, the oxidation rate of the selective oxidation process can be controlled with high accuracy, and the oxide insulating layer 24 can be formed more uniformly.

  FIG. 7 shows the entire oxidation processing apparatus provided with the heating furnace 1. In the figure, 51 is a nitrogen gas cylinder. The nitrogen gas supplied from the nitrogen gas cylinder 51 is adjusted as a purge gas by a mass flow controller (MFC) 54 and then supplied to a heat exchanger 56. It is supplied to the reaction unit 2. The nitrogen gas is supplied to the vaporizer 63 via the MFC 57 as a carrier gas.

  On the other hand, reference numeral 61 in the figure denotes a helium gas cylinder. From the helium gas cylinder 61, helium gas having a lower solubility in water than other gases is supplied. The helium gas is supplied to a gas portion in the pressure vessel 62 in which water is stored, and pumps the water in the pressure vessel 62. The pumped water is introduced into the vaporizer 63 via the MFC 64, becomes steam while being controlled in temperature, and is supplied to the reaction unit 2 side.

  Nitrogen gas sent from the MFC 54 and water vapor sent from the vaporizer 63 are mixed at the confluence P, and the temperature is controlled by the heat exchanger 56 so that the temperature is substantially the same as that of the wafer to be processed. Part 2 is introduced. A rotary pump 71 is connected to the downstream side of the reaction unit 2 to perform exhaust processing. Further, a part of nitrogen gas sent to the heat exchanger 56 and water vapor sent from the vaporizer 63 can be discharged through valves 72 and 73, respectively.

  Here, heaters are provided between a predetermined position downstream of the MFC 54 and the junction P, between a predetermined position downstream of the vaporizer 63 and the junction P, and between the junction P and the reaction unit 2, respectively. P1 to P3 are provided to heat the gas flowing through the flow paths in the heaters P1 to P3. The flow path in which these heaters P1 to P3 are provided corresponds to the flow path 11 shown in FIG. That is, the portion including the junction P constitutes the preheating unit 3. In addition, what is necessary is just to provide the heat exchanger 56 as needed. Moreover, the gas type to be used is not limited to nitrogen or helium gas.

  In the first embodiment, the preheating unit 3 is provided, the temperature of the introduced gas is preheated to substantially the same temperature as the substrate temperature of the wafer 6, and the preheated gas is introduced into the reaction unit 2. Since the temperature difference between the substrate temperature and the gas temperature is always eliminated and the gas temperature is always uniform, the variation in oxidation within the wafer surface can be reduced, and the variation in oxidation treatment between batches can be reduced. This control can be performed with high accuracy.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. In Embodiment 2 of the present invention, reflectors are provided in the preheating part and the reaction part.

  8 and 9 are cross-sectional views schematically showing a schematic configuration of the heating furnace 81 of the heat treatment apparatus according to Embodiment 2 of the present invention. In the heating furnace 81, a fixed reflector 82 is provided in the preheating unit 3, and a movable reflector 83 is provided in the reaction unit 2. Examples of the material of the reflectors 82 and 83 include stainless steel, copper, and silicon carbide sintered body.

  The reflector 82 has a substantially cylindrical shape and is disposed on the preheating portion 3. The reflector 82 is heated by a heater 84 provided on the lower side of the preheating unit 3. The internal space of the reflector 82 forms a flow path 11 through which gas flows. As a result, the gas flows through the reflector 82 without being in contact with the furnace wall 3b and is preheated. As a result, the gas in the preheating unit 3 is heated more efficiently, and the temperature field can be kept more uniform. The upper wall of the reflector 82 is heated by radiant heat from the heater 84.

  In addition, a movable reflector 83 is provided in the reaction section 2 of the heating furnace 81. This movable reflector 83 is substantially plate-shaped. The movable reflector 83 is for suppressing heat in the reaction unit 2 from escaping from the observation window 8 to the outside. The movable reflector 83 is provided so that the observation window 8 can be opened and closed. That is, the movable reflector 83 is disposed at a position between the observation window 8 provided on the wall immediately above the wafer 6 set in the reaction unit 2 and the wafer 6, and is selected by the monitor 9. When monitoring the progress of the oxidation process, the heat in the reaction unit 2 is located between the observation window 8 and the wafer 6 so that it can be retracted outside the observation range of the monitor 9. Escape from the observation window 8 to the outside is suppressed.

  In this Embodiment 2, since the reflector 82 was provided, the uniformity of the gas temperature in the cross section orthogonal to the gas distribution direction of the flow path 11 of the preheating part 3 can be improved more. As a result, a gas with increased temperature uniformity is sent to the reaction unit 2, and a more uniform temperature field can be formed in the reaction unit 2.

  Further, in the apparatus according to the second embodiment, since the movable reflector 83 is provided in the reaction unit 2, the heat radiation from the observation window 8 can be suppressed, and the wafer 6 can be oxidized under a more stable temperature field.

(Embodiment 3)
Next, a third embodiment of the present invention will be described. In the third embodiment of the present invention, a heater is also provided on the preheating portion.

  10 and 11 are cross-sectional views schematically showing a schematic configuration of a portion of the heating furnace 91 of the heat treatment apparatus according to Embodiment 3 of the present invention. As shown in FIG. 9, a substantially cylindrical reflector 82 is also provided in the preheating portion of the heating furnace 91. In the third embodiment, a heater 85 is further provided between the reflector 82 and the furnace wall 3b. Thereby, the preheating of the introduced gas is performed uniformly from the periphery including the top and bottom of the preheating unit 3. In addition, since the gas flows through the reflector 82 without being in contact with the furnace wall 3b and is preheated, the preheating temperature field in the preheating unit 3 is further uniformed.

  In the first to third embodiments described above, the wafer 6 is processed in the face-up state. However, the heat treatment apparatus of the present invention is not limited to this and is a face-down heat treatment apparatus. May be.

  In Embodiments 1 to 3 described above, the apparatus that oxidizes the object to be processed using water vapor has been described. However, the heat treatment apparatus of the present invention is not limited to these, and can be applied to an apparatus that oxidizes using oxygen. . Furthermore, it can be applied to an annealing apparatus. In the case of the annealing apparatus, the upstream and downstream temperature fields of the object to be processed can be made constant in the processing section to be annealed, and in particular, variations in the surface of the object to be processed can be reduced.

It is sectional drawing which shows typically the schematic structure of the heat processing apparatus which is Embodiment 1 of this invention. It is sectional drawing which looked at the surface emitting laser element as a device in which a selective oxidation layer is formed from the diagonal. It is a figure which shows the image of the oxidation aperture observed with the oxidation monitor. It is a figure which shows the structure of the selective oxidation layer formed in a mesa post. It is a figure which shows the principle of deposition by CVD method. It is a figure which shows the principle of a selective oxidation process. It is a figure which shows the system configuration | structure at the time of applying a heat processing apparatus to a gas type circuit. It is sectional drawing which shows typically the schematic structure of the heat processing apparatus which is Embodiment 2 of this invention. It is an AA partial fragmentary sectional view of the direction orthogonal to a flow path which shows the reflector part of embodiment shown in FIG. It is sectional drawing which shows typically schematic structure of the heat processing apparatus which is Embodiment 3 of this invention. It is a BB line partial sectional view of a direction which intersects perpendicularly with a channel showing a reflector part of an embodiment shown in FIG.

Explanation of symbols

1,81,91 Heating furnace 2,53 Reaction section (processing section)
DESCRIPTION OF SYMBOLS 3 Preheating part 3a Gas introducing | transducing part 4 Rotating shaft 4a Rotating table 5 Tray 6 Wafer 7, 10, 14, 84, 85 Heater 8 Observation window 9 Oxidation monitor 11, 13 Flow path 12 Diffusion plate 20 Surface emitting laser element 51 Nitrogen gas cylinder 61 Helium gas cylinder 56 heat exchanger 62 pressure vessel 63 vaporizer 82 reflector 83 movable reflector

Claims (9)

A heat treatment apparatus for treating an object to be processed in a heated atmosphere,
A processing unit having a mounting table on which the processing object is set and a heating unit that heats the processing object set on the mounting table;
A preheating unit having a flow path for preheating the gas sent to the processing unit, and provided with a fixed reflector ;
A heating furnace having
The processing unit has an observation window for directly observing the workpiece set on the mounting table from the outside of the processing unit, and a reflector is provided inside the observation window, and the reflector extends from the observation window. A heat treatment apparatus which is movable so that the object to be treated can be observed. The preheating unit has the cylindrical flow path whose temperature is controlled by a heating unit provided in the preheating part, and the gas sent to the processing unit flows through the flow path and is preheated. The heat treatment apparatus according to claim 1 . Heat treatment according to claim 1 or 2, characterized in that it comprises the diffusing plate provided on the outlet side of the gas or member for disturbing the flow of gas provided in the introduction side of the gas in the flow path apparatus. Heat treatment apparatus according to any one of claims 1 to 3, characterized in that the mounting base is in the rotary table. Second flow path is provided in the exhaust side of the processing section rear, either of claims 1 to 4, characterized in that the second heating means relative to said second flow path is provided 1 The heat processing apparatus as described in. The preheating gas flows through the straight of the flow path, directly, the heat treatment apparatus according to be introduced into the mounting table to any one of claims 1 to 5, characterized. The heat treatment apparatus according to any one of claims 1 to 6 , wherein the processing unit functions as a reaction unit that oxidizes the workpiece set on the mounting table with water vapor in a heated atmosphere. . Oxidation system heat treatment apparatus according to any one of claims 1 to 7, characterized in that it is used in the oxidation of the selective oxidation semiconductor layer made of AlAs of the surface-emitting laser element. A heat treatment method in which a preheated gas is introduced into a processing unit in which a heated object to be processed is set and processed.
The temperature of the gas introduced into the processing unit, with reflector preheating unit provided stationary, since the preconditioned Me at the same temperature as the temperature of the object to be processed is set to the processing unit, the said gas In addition, the processing unit is provided with an observation window for directly observing the workpiece set on the mounting table from the outside of the processing unit, and a movable type is provided inside the observation window . reflector is provided, said movable reflector, wherein has the observation window is the movable as can be observed the object to be processed, when monitoring the progress of the process, the movable reflector from observation range A heat treatment method, wherein the object to be treated is monitored by evacuation.