JP6236753B2 - Manufacturing method of semiconductor substrate - Google Patents

Description

  In this specification, the technique regarding the manufacturing method of a semiconductor substrate using the support substrate for semiconductor layer bonding is disclosed.

  A so-called SOI (Silicon on Insulator) substrate in which an insulating layer is formed on a supporting substrate and a Si single crystal layer is formed on the insulating layer is known. Further, it has been studied to use various semiconductor layers such as a SiC single crystal layer in place of the Si single crystal layer. Moreover, as related literature, patent document 1 is mentioned, for example.

JP 2003-37253 A

  When a void exists in the support substrate or when the surface roughness of the support substrate is large, it may be preferable to planarize the support substrate or the formed insulating film surface by polishing or the like. In addition, when a SiC single crystal layer is bonded to the insulating layer to form a bonded substrate, the bonded substrate may be annealed at a high temperature of 1600 ° C. or higher after ion implantation into the SiC single crystal layer. Needed. As described above, the insulating layer is required to have reflow properties and high-temperature resistance that can withstand high-temperature processes.

  The present specification discloses a method for manufacturing a semiconductor substrate. The method for manufacturing a semiconductor substrate includes a first layer forming step of forming a first layer having a melting point lower than that of the support substrate on the surface of the support substrate. There is provided a heating step of heating the support substrate on which the first layer is formed to a predetermined temperature not lower than the melting point of the first layer in an oxygen-free atmosphere. An oxidation step is provided in which the support substrate is exposed to an oxygen-containing atmosphere in a state where the support substrate is heated to the melting point of the first layer or higher. A bonding step of bonding the second layer formed of a semiconductor single crystal to the surface of the first layer after the oxidation step is performed is provided. The first layer after the oxidation step has a lower conductivity and a higher melting point than the first layer before the oxidation step.

  In the above method, the first layer can be reflowed in the heating step. Therefore, when a void exists in a support substrate, or when the surface roughness of a support substrate is large, it can planarize with the reflowed 1st layer. In the oxidation step, the first layer can be oxidized. Therefore, the electrical conductivity of the first layer can be reduced and the first layer can function as an insulating layer. In addition, the melting point of the first layer can be increased. As described above, since the melting point of the first layer can be lowered before the oxidation step, the first layer can function as a planarization film. In addition, after the oxidation step, the first layer can be modified so as to increase the melting point of the first layer and decrease the conductivity, so that the first layer functions as an insulating layer having high temperature resistance. be able to.

  According to the technique disclosed in this specification, a method for manufacturing a bonded substrate having high-temperature resistance can be provided.

It is a figure which shows an insulating layer film-forming apparatus. It is a perspective view of a bonded substrate. It is the elements on larger scale of the surface of a support substrate. It is the elements on larger scale of the surface of a support substrate. It is the elements on larger scale of the surface of a support substrate.

  Hereinafter, some technical features of the embodiments disclosed in this specification will be described. The items described below have technical usefulness independently.

(Characteristic 1) In the semiconductor substrate manufacturing method, the melting point of the first layer after the oxidation step is performed is higher than the maximum temperature of various semiconductor manufacturing processes used when a semiconductor device is formed in the second layer. May be higher. Thereby, it becomes possible to produce various semiconductor devices in the second layer using the substrate in which the first layer and the second layer are bonded together.

(Feature 2) In the semiconductor substrate manufacturing method described above, the hydrogen concentration contained in the first layer after the oxidation step is performed is the same as the hydrogen concentration contained in the layer having the same composition formed by the CVD method. May be lower. When a layer having the same composition as the oxidized first layer is formed using the CVD method, hydrogen gas or a gas containing hydrogen may be used as a source gas. In this case, hydrogen is contained in the formed film. When the second layer is bonded onto the film containing hydrogen, when the bonded substrate is annealed, the hydrogen contained in the film may be degassed as a gas. The first layer and the second layer may peel off. In the above method, since the unoxidized first layer is formed and the first layer is oxidized in the oxidation step, the concentration of hydrogen contained in the oxidized first layer is reduced as compared with the case of using the CVD method. Can be lowered. Thereby, it can be made difficult to peel the first layer and the second layer.

(Feature 3) In the semiconductor substrate manufacturing method, the first layer may be a layer containing aluminum. Thereby, the 1st layer after an oxidation process can be made into the layer of aluminum oxide. Since the melting point of aluminum oxide is as high as about 2073 ° C., high temperature resistance can be obtained.

(Feature 4) In the semiconductor substrate manufacturing method, the support substrate may be a sintered body of a ceramic material. Since the sintered body is a porous body, many voids appear on the surface of the support substrate. In the above method, since the first layer can function as a planarizing film by reflowing the first layer in the heating step, the voids on the surface of the support substrate can be embedded and planarized. Thereby, since the contact area of a 1st layer and a 2nd layer can be increased, it becomes possible to stick both layers and to bond.

(Feature 5) In the semiconductor substrate manufacturing method, the second layer may be formed of a SiC single crystal. The melting point of the first layer after the oxidation process may be higher than the maximum temperature of the annealing process performed after ions are implanted into the second layer. After ion implantation into the SiC single crystal layer, an annealing process at a high temperature (eg, 1600 ° C. or higher) is required to remove crystal defects and the like. In the above method, the first layer can have high temperature resistance that can withstand the annealing step. Thereby, it becomes possible to produce various semiconductor devices in the second layer using the substrate in which the first layer and the second layer are bonded together.

(Characteristic 6) In the semiconductor substrate manufacturing method, in the heating step and the oxidation step, the heating of the first layer may be performed by irradiating the surface of the first layer with laser scanning. By irradiating the laser, the vicinity of the surface of the first layer can be instantaneously heated and melted. Thereby, since only the surface of the first layer can be annealed, it is possible to prevent a situation where the support substrate is affected by heat. Moreover, since it is a local annealing process, processing time can be shortened compared with the case where the whole support substrate is annealed.

<Structure of insulating layer deposition apparatus>
FIG. 1 shows an insulating layer film forming apparatus 100. The insulating layer deposition apparatus 100 includes a chamber 110, a substrate holding unit 111, a heating unit 112, a target 113, a DC power supply unit 114, a gas supply line 120, an oxygen supply unit 121, an argon supply unit 122, an MFC (mass flow controller) 131, and 132 and the vacuum exhaust device 140. A substrate holding unit 111 and a heating unit 112 are stored in the chamber 110. The substrate holding part 111 is a part that holds the support substrate 11. The substrate holding part 111 is provided with a clamp (not shown) for fixing the support substrate 11 at its peripheral edge so that the support substrate 11 does not move. The heating unit 112 is disposed below the substrate holding unit 111. The heating unit 112 is a device that heats the support substrate 11 to a desired temperature. The target 113 is a part used for forming an aluminum layer on the support substrate 11 by sputtering. The target 113 is made of aluminum. The target 113 is disposed so as to face the substrate holding unit 111. The DC power supply unit 114 is a part that applies a DC high voltage between the substrate holding unit 111 and the target 113. The gas supply line 120 is a line for introducing oxygen gas and argon gas supplied from the oxygen supply unit 121 and the argon supply unit 122 into the chamber 110. The oxygen gas supplied from the oxygen supply part 121 may contain components other than oxygen. The MFC 31 is a controller that controls the supply amount of oxygen gas supplied from the oxygen supply unit 121. The MFC 32 is a controller that controls the supply amount of argon gas supplied from the argon supply unit 122. The vacuum exhaust device 140 is a device for bringing the inside of the chamber 110 into a desired vacuum state.

<Configuration of bonded substrate>
FIG. 2 is a perspective view of the bonded substrate 10 according to the present embodiment. The bonded substrate 10 is formed in a substantially disk shape. The bonded substrate 10 includes a support substrate 11 disposed on the lower side, an insulating layer 12 disposed on the upper surface of the support substrate 11, and a semiconductor layer 13 bonded to the upper surface of the insulating layer 12. The semiconductor layer 13 may be formed of a single crystal of a compound semiconductor (eg, 6H—SiC, 4H—SiC, GaN, AlN), for example. For example, it may be formed of a single crystal of a single element semiconductor (eg, Si, C).

The support substrate 11 is a sintered body made of a mixed material of ceramic materials. The ceramic material to be used may be various materials, for example, at least one of SiC, Si, AlN, Al ₂ O ₃ , GaN, SiN, SiO ₂ , TaO, and the like. Specifically, the mixed powder material is subjected to CIP (cold isostatic pressing) to produce a molded body of the support substrate 11. And the produced molded object is baked in nitrogen atmosphere. A discharge plasma sintering apparatus or a hot press apparatus may be used for firing the compact.

  The support substrate 11 on which the insulating layer 12 is formed and the semiconductor layer 13 are separately manufactured. Then, by bonding the semiconductor layer 13 to the insulating layer 12 by room temperature bonding, plasma bonding, hydroxyl bonding, or the like, a bonded substrate 10 having a so-called SOI structure is formed. The bonding surface of the insulating layer 12 may be bonded to the semiconductor layer 13 after being flattened by polishing or the like. The thickness T11 of the support substrate 11 may be determined so as to obtain mechanical strength that can withstand post-processing. For example, when the diameter of the support substrate 11 is 100 mm, the thickness T11 may be about 100 μm. The thickness T12 of the insulating layer 12 may be determined based on a required specification (eg, withstand voltage) of a device created in the semiconductor layer 13. The thickness T13 of the semiconductor layer 13 may be about 5 μm, for example. In the present embodiment, as an example, a case will be described in which the support substrate 11 is formed by a sintered body of a powder material containing SiC powder. A case where the insulating layer 12 is made of aluminum oxide and the semiconductor layer 13 is made of SiC single crystal will be described.

<Method for manufacturing bonded substrate>
The manufacturing method of the bonded substrate 10 according to the present embodiment includes an aluminum layer forming step, a heating step, an oxidation step, and a bonding step. The aluminum layer forming step is a step of forming an aluminum layer on the surface of the support substrate 11. The heating step is a step of heating the support substrate 11 on which the aluminum layer is formed in an oxygen-free atmosphere to reflow the aluminum layer. The oxidation process is a process of modifying the aluminum layer to the insulating layer 12 by exposing the support substrate 11 on which the aluminum layer is formed in an atmosphere containing oxygen while the support substrate 11 is heated. The bonding step is a step of bonding the semiconductor layer 13 formed of SiC single crystal to the surface of the insulating layer 12.

<Aluminum layer forming step>
The aluminum layer forming step will be described. The support substrate 11 is placed on the substrate holder 111 in the chamber 110 of the insulating layer deposition apparatus 100. And the peripheral part of the support substrate 11 is fixed with a clamp not shown. The inside of the chamber 110 is put into a high vacuum state using the vacuum exhaust device 140. The degree of vacuum may be, for example, about 1 × 10 ⁻⁹ Torr. Next, supply of argon gas from the argon supply unit 122 is started. The flow rate of the argon gas is set so as to maintain a high vacuum state in the chamber 110.

  A DC high voltage is applied between the substrate holding unit 111 and the target 113 by the DC power supply unit 114 to cause glow discharge, thereby generating argon gas plasma. By attracting argon gas positively ionized by arc discharge to the negative electrode side (target 113), argon ions collide with the target 113, and aluminum particles are sputtered. Thereby, as shown in the partial enlarged view of the surface of the support substrate 11 in FIG. 3, the aluminum layer 12 a is formed on the surface of the support substrate 11. Since the support substrate 11 is a sintered body and a porous body, a large number of voids 14 are exposed on the surface of the support substrate. Therefore, since the aluminum layer 12a is embedded in the void 14, the shape of the void is transferred to the surface of the aluminum layer 12a, and the recess 15 is formed. The arithmetic average roughness Ra of the surface of the aluminum layer 12a is often several μm or more before the heating step.

<Heating process>
When the aluminum layer forming process is completed, the process proceeds to the heating process. In the heating step, the support substrate 11 is heated to a predetermined temperature using the heating unit 112 while the chamber 110 is maintained in a high vacuum state. The predetermined temperature is a temperature equal to or higher than the melting point of the aluminum layer 12a. Thereby, it can be made to reflow by fuse | melting the aluminum layer 12a and giving fluidity | liquidity. Therefore, as shown in the partially enlarged view of FIG. 4, since the recess 15 can be erased, the surface of the aluminum layer 12a can be planarized. In addition, predetermined | prescribed temperature shall be in the range of 700-1000 degreeC, for example.

  In the method for manufacturing the bonded substrate 10 of this example, the aluminum layer forming step and the heating step are continuously performed in a high vacuum. Thereby, it is possible to prevent a film of aluminum oxide, which is a hard substance having a high melting point (about 2073 ° C.), from being formed on the surface of the aluminum layer 12a. Therefore, good reflow characteristics of the aluminum layer 12a can be obtained in the heating step.

<Oxidation process>
When the heating process ends, the supply of oxygen gas from the oxygen supply unit 121 is started, and the process proceeds to the oxidation process. An oxidation process is performed in the state which heated the support substrate 11 more than melting | fusing point of the aluminum layer 12a. Thereby, since the aluminum layer 12a can be oxidized in a state in which the aluminum layer 12a is melted, it is possible to oxidize the inside of the aluminum layer 12a. The heating temperature in the oxidation step is, for example, in the range of 700 to 1000 ° C.

By the oxidation step, as shown in the partially enlarged view of FIG. 5, the aluminum layer 12a can be modified into the insulating layer 12 formed of aluminum oxide (Al ₂ O ₃ ). That is, the aluminum layer 12a which is a conductor (the electrical resistivity is about 28.2 nΩ · m) is modified to the insulating layer 12 (aluminum oxide) which is an insulator. In addition, the melting point (about 660 ° C.) of the aluminum layer 12a is modified to the melting point (2073 ° C.) of the insulating layer 12 (aluminum oxide).

<Lamination process>
A bonding process will be described. As an example, a case where room temperature bonding is performed will be described. The semiconductor layer 13 and the support substrate 11 are set in a chamber of a room temperature bonding apparatus (not shown). After the chamber is evacuated, the back surface of the semiconductor layer 13 and the bonding surface of the insulating layer 12 are irradiated with an ion beam. Accordingly, the oxide film and the adsorption layer on the surface of the material can be removed to expose the bond, so that the surface can be activated. Thereafter, the back surface of the semiconductor layer 13 and the bonding surface of the insulating layer 12 are brought into contact with each other, whereby both layers can be bonded. The pressure at the time of joining may be in the range of 10 to 50 MPa. Thereby, the bonded substrate 10 is completed. The bonded substrate 10 has a thickness and strength for handling with a normal semiconductor device. Therefore, various known semiconductor processes such as photolithography and etching can be performed on the bonded substrate 10, and various devices can be formed on the surface of the semiconductor layer 13.

<Effect>
In the aluminum layer forming step, an aluminum layer 12a having a melting point lower than that of the support substrate 11 is formed. Thereby, since the aluminum layer 12a can be reflowed in the heating step, the surface of the support substrate 11 can be planarized by the reflowed aluminum layer 12a. In the oxidation step, the aluminum layer 12a can be modified to an aluminum oxide layer. Since the aluminum oxide layer is an insulator, the aluminum oxide layer can function as the insulating layer 12. Further, by modifying the aluminum oxide layer, the melting point of the insulating layer 12 can be made higher than the melting point of the aluminum layer 12a. As described above, it is possible to provide an insulating layer having both reflow properties and high temperature resistance.

  Many voids may appear on the surface of the support substrate 11. In the manufacturing method of the semiconductor substrate of this example, the voids on the surface of the support substrate 11 can be embedded by reflowing the aluminum layer 12a in the heating step, so that the surface of the aluminum layer 12a can be planarized. Thereby, since the surface of the insulating layer 12 can be planarized, the contact area between the insulating layer 12 and the semiconductor layer 13 can be increased. Therefore, both layers can be bonded together.

After ion implantation is performed on the semiconductor layer 13 formed of SiC single crystal, a high temperature annealing step (eg, 1600 ° C. or higher) is required to remove crystal defects and the like. In the manufacturing method of the semiconductor substrate of this example, the melting point (Al ₂ O ₃ : about 2073 ° C.) of the insulating layer 12 can be made higher than the annealing temperature (1600 ° C.) of the high temperature annealing step. Can be carried out. As a result, various semiconductor devices can be formed on the semiconductor layer 13 using the bonded substrate 10.

In order to form a layer having the same composition as that of the insulating layer 12 (that is, an aluminum oxide layer) by using the CVD method, hydrogen gas or a gas containing hydrogen may be used as a source gas. For example, an aluminum oxide film by a CVD method can be formed based on a chemical formula of “2AlCl ₃ + 3 / 2CO ₂ + H ₂ → Al ₂ O ₃ + 3CO + 6HCl”. In this case, since the source gas contains hydrogen, the aluminum oxide layer after film formation contains hydrogen. When a semiconductor layer is bonded onto an aluminum oxide layer containing hydrogen, hydrogen contained in the aluminum oxide layer may be degassed when the bonded substrate is annealed Therefore, the aluminum oxide layer and the semiconductor layer may be peeled off. On the other hand, in the manufacturing method of the semiconductor substrate of this embodiment, the insulating layer 12 (aluminum oxide) is formed by oxidizing the aluminum layer 12a formed by the sputtering method in the oxidation step. Since hydrogen is not required as a raw material for forming the aluminum layer 12a, it can be prevented that the aluminum layer 12a after film formation contains hydrogen. Further, in the oxidation step, even when hydrogen is included in the gas used for oxidation, hydrogen hardly enters the layer to be oxidized. Thereby, it can prevent that hydrogen is contained in the aluminum oxide layer (insulating layer 12) after film-forming. As described above, the hydrogen concentration contained in the insulating layer 12 can be reduced as compared with the case where the CVD method is used. Therefore, since generation | occurrence | production of deaeration of hydrogen gas can be suppressed, it becomes possible to make it difficult to peel the insulating layer 12 and the semiconductor layer 13 from.

  In the case where an insulating layer is formed on a wafer using the CVD method, it is necessary to periodically clean the film deposit attached to the inner wall of the chamber. For example, plasma cleaning is performed in which a film-like deposit is removed by introducing a cleaning gas and generating plasma in a chamber. However, film deposits that adhere when a hard insulating layer having a high melting point, such as aluminum oxide, is difficult to remove by plasma cleaning, so the chamber is disassembled and removed using a cleaning solution or the like. There is a need. Then, since the operating rate of the CVD apparatus is lowered, it is difficult to efficiently form the insulating layer. However, since the insulating layer film forming apparatus 100 of this embodiment can form the insulating layer 12 made of aluminum oxide without using the CVD method, the frequency of performing cleaning by dismantling the chamber can be reduced. . Therefore, since the operating rate of the insulating layer film forming apparatus 100 can be increased as compared with the CVD apparatus, it is possible to efficiently form the insulating layer of aluminum oxide.

  As mentioned above, although the Example of this invention was described in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

<Modification>
In the heating step and the oxidation step, the aluminum layer 12a may be heated by so-called laser annealing. Laser annealing is a method in which a surface of a processed surface is scanned after a pulse laser beam such as an excimer laser is processed by an optical system so that the shape on the irradiated surface becomes a spot or a line of several cm square. By irradiating the laser, the vicinity of the surface of the aluminum layer 12a can be instantaneously heated and melted, so that the aluminum layer 12a can be reflowed or oxidized. Since only the surface of the aluminum layer 12a can be annealed, it is possible to prevent a situation where the support substrate 11 is affected by heat. Moreover, since it is a local annealing process, processing time can be shortened compared with the case where the whole support substrate 11 is annealed.

  Although the heating step is performed after the aluminum layer forming step, the heating step is not limited to this mode, and the aluminum layer forming step and the heating step may be performed simultaneously. For example, in forming the aluminum layer, the aluminum layer 12a may be formed by sputtering while heating the support substrate 11 to a predetermined temperature.

  In the heating process, the inside of the chamber 110 is maintained in a high vacuum state, but this is not a limitation. The heating step can also be performed in an atmosphere of a non-oxidizing gas (eg, argon gas) that does not react with the aluminum layer 12a.

Although the form which modify | reforms the aluminum layer 12a to aluminum oxide was demonstrated, it is not restricted to this form. For example, the aluminum layer 12a may be modified to aluminum nitride (AlN) (melting point: about 2200 ° C.). In this case, a nitriding process may be introduced instead of the oxidizing process. In the nitriding process, a gas containing nitrogen may be introduced into the chamber 110 in a state where the support substrate 11 is heated to the melting point of the aluminum layer 12a or higher. As the gas containing nitrogen, a hydrogen-containing gas is preferably used. For example, ammonia (NH ₃ ) gas may be used.

The gas used in the oxidation step is not limited to oxygen gas, and various gases can be used. For example, water vapor (H ₂ O) gas may be used. In this case, a burner that burns hydrogen and generates water may be connected to the gas supply line 120. Then, hydrogen gas and oxygen gas may be supplied to the burner, and a gas containing water vapor in oxygen may be generated and supplied to the chamber 110. In the oxidation step, oxygen gas and hydrogen gas may be mixed and supplied to the chamber 110.

  The material used for the support substrate 11 is not limited to a sintered body of a ceramic material. Any material may be used as long as it is resistant to various thermal processes applied to the semiconductor layer 13. For example, it is possible to use polycrystalline SiC. In addition, various polytypes of SiC crystals may be mixed in the polycrystalline SiC. Since polycrystalline SiC in which various polytypes are mixed can be manufactured without performing strict temperature control, the cost for manufacturing the support substrate can be reduced.

  The layer formed on the surface of the support substrate 11 is not limited to the aluminum layer 12a. For example, a polycrystalline silicon layer can be formed. In this case, in the oxidation step, the polycrystalline silicon layer (melting point: about 1410 ° C.) may be modified to a silicon oxide layer (melting point: about 1650 ° C.). Alternatively, a nitriding process may be introduced instead of the oxidizing process, and the polycrystalline silicon layer may be modified to a silicon nitride layer (melting point: about 1900 ° C.).

  An element that improves fluidity may be added to the aluminum layer 12a. For example, at least one of elements such as Ge, Sn, Ga, Zn, Pb, In, and Sb may be added. Thereby, the aluminum layer 12a can be reflowed at a temperature of about 450 ° C.

  In the bonding step, the semiconductor layer 13 bonded to the insulating layer 12 is not limited to one type. For example, the bonding surface of the insulating layer 12 may be divided into a plurality of areas, and a different semiconductor layer 13 may be bonded to each area.

  The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

  10: Bonded substrate, 11: Support substrate, 12: Insulating layer, 12a: Aluminum layer, 13: Semiconductor layer, 100: Insulating layer deposition apparatus, 110: Chamber

Claims (5)

A method for manufacturing a semiconductor substrate, comprising:
The surface of the support substrate of the sintered body of ceramic material, a first layer forming step of forming a first layer of aluminum having a lower melting point than the support substrate,
A heating step of heating the support substrate on which the first layer is formed to a predetermined temperature equal to or higher than the melting point of the first layer in an oxygen-free atmosphere;
An oxidation step of exposing the support substrate to an oxygen-containing atmosphere in a state where the support substrate is heated to a temperature equal to or higher than the melting point of the first layer;
A bonding step of bonding a second layer formed of a semiconductor single crystal to the surface of the first layer after the oxidation step;
With
Wherein the first layer after the oxidation process is performed, the oxidation process is the first layer to the conductivity is lower than before to be performed, a manufacturing method of a semiconductor substrate, wherein the higher melting point. 2. The method of manufacturing a semiconductor substrate according to claim 1, wherein a melting point of the first layer after the oxidation process is 2073 ° C. 3. In the first layer forming step, the first layer is formed by sputtering ,
The hydrogen concentration contained in the first layer after the oxidation step is performed is lower than the hydrogen concentration contained in a layer having the same composition formed by a CVD method. Or the manufacturing method of the semiconductor substrate of 2 . The second layer is formed of SiC single crystal;
The melting point of the first layer after the oxidation step is performed, any one of claims 1-3, characterized in that higher than the highest temperature of the annealing step performed after implanting ions into the second layer 2. A method for manufacturing a semiconductor substrate according to item 1. Wherein in the heating step and the oxidation step, the heating of the first layer, any one of claim 1 to 4, characterized in that is carried out by irradiating by scanning a laser on the surface of the first layer A method for producing a semiconductor substrate as described in 1.

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