JP7744663B2 - High-temperature vapor phase growth apparatus and method for growing semiconductor crystal film - Google Patents

Description

The present invention relates to a high-temperature vapor phase growth apparatus and a method for growing semiconductor crystal films that are ideal for growing nitride semiconductor crystal films such as aluminum nitride and aluminum gallium nitride.

Generally, when growing a crystalline film of a compound semiconductor on a substrate, vapor phase growth methods such as metalorganic chemical vapor deposition and molecular beam epitaxy are used.

As shown in Figure 4, when a first conventional vapor phase growth apparatus 600 (see, for example, Patent Document 1) is used to grow a nitride semiconductor crystal film such as aluminum nitride and aluminum gallium nitride on a substrate 610 made of sapphire or the like using metal organic chemical vapor deposition, the substrate 610 is heated to a predetermined temperature while held on a substrate holder 615, and a source gas 620 is brought into contact with the substrate 610 to deposit and form a nitride semiconductor crystal film on the substrate 610.

The vapor phase growth apparatus 600 includes a substrate holder 615 for holding a substrate 610, a flow channel 625 for efficiently directing a source gas 620 onto the substrate 610, a susceptor 630 as a heat source, and an RF coil 635 for heating the susceptor 630.

In the vapor phase growth apparatus 600 configured as described above, source gas 620 flows parallel to the substrate 610 from the gas supply port toward the gas exhaust port within the flow channel 625. Then, with the substrate 610, made of sapphire or the like, heated to a predetermined temperature, the upper surface of the substrate 610 comes into contact with the source gas 620 flowing within the flow channel 625. This results in the formation of a nitride semiconductor crystal film, such as aluminum nitride or aluminum gallium nitride, on the upper surface of the substrate 620.

The source gas 620 is supplied from a gas supply port, flows through a flow channel 625, and contributes to the growth of a crystal film on the upper surface of the substrate 610, while the source gas 620 that does not contribute to the growth of the nitride semiconductor crystal film is discharged from a gas exhaust port.

It is generally known that defects in nitride semiconductor crystals such as aluminum nitride and aluminum gallium nitride are inversely proportional to the crystal growth temperature. In other words, to obtain a high-quality crystal film with few crystal defects, the temperature of the top surface of the substrate 620 must be at least 1200°C or higher. It has also been suggested that a temperature as high as 1800°C is necessary (see, for example, Patent Document 2).

However, when a conventional vapor phase growth apparatus 600 is heated to such high temperatures, the source gas 620 supplied from the horizontal direction of the flow channel 625 reacts with itself before reaching the substrate 620 unless the gas flow rate is increased, reducing the amount of source gas 620 that reaches the upper surface of the substrate 610. This results in a problem of low utilization efficiency of the source gas 620.

Furthermore, when the substrate 610 is heated to a high temperature of 1200°C or higher, strong thermal convection occurs on the upper surface of the substrate 610 on which the crystalline film is grown. This thermal convection caused by the highly heated substrate 620 causes the source gas 620 to rise and diffuse into the flow channel 625. Components produced by the reaction of the diffused source gas 620 adhere to the walls of the flow channel 625 as well as to the observation window (not shown). This causes problems such as the generation of dust and the incorporation of impurities into the crystalline film formed on the substrate 620. Furthermore, because the interior of the vapor phase growth apparatus 600 is exposed to high temperatures, there is also the problem of rapid deterioration of each component of the apparatus, significantly reducing the apparatus's durability.

To suppress the occurrence of this thermal convection, a second conventional vapor phase growth apparatus 700 (see, for example, Patent Document 3) has been proposed, as shown in Figure 5. This vapor phase growth apparatus 700 comprises a reaction vessel 710, a susceptor 715, a heater 720, a source gas injection pipe 725, and an auxiliary injection pipe 730.

In the vapor phase growth apparatus 700 configured as described above, the substrate 705 is placed on the susceptor 715 and heated by the heater 720 to the temperature required for crystal growth. To ensure uniform crystal growth, the susceptor 715 is rotated by a shaft 735 attached to the bottom of the susceptor 715. The reactant gas, which is the raw material, is introduced through a raw material gas injection pipe 725 located laterally of the vapor phase growth apparatus 700. The pressurized gas, which is an inert gas, is introduced through a secondary injection pipe 730 above the substrate 705 .

In other words, the reactive gas is supplied to the surface of the heated substrate 705 in a direction parallel to the substrate 705, and at the same time, a pressurizing gas is blown downward from above the substrate 705 perpendicularly toward the substrate 705 to pressurize the reactive gas.

JP 2010-080614 A JP 2006-70325 A Patent No. 2628404

When such a conventional vapor phase growth apparatus 700 is used to grow a nitride semiconductor crystal film, such as aluminum nitride or aluminum gallium nitride, on the upper surface of a substrate 705 made of sapphire or the like at a high temperature exceeding 1200°C, if the reactive gas and the pressurizing gas are flowed from different directions and collide, turbulence or vortex flows are generated, resulting in the formation of non-uniform crystals within the surface of the substrate 705. In other words, there is a problem that unevenness occurs in the film thickness, and crystals with different compositions are formed in parts of the upper surface of the substrate 705 , making it difficult to ensure stable quality of the crystal film.

Furthermore, with this configuration, although the pressurized gas blown down from vertically above the substrate can suppress the upward movement of the reactant gas due to convection, the pressurized gas slows down the flow of the reactant gas, causing the reactant gas to react with itself before it reaches the top surface of the substrate 705 , resulting in a drastic reduction in the amount of reactant gas that reaches the substrate 705. As a result, the proportion of the reactant gas that contributes to crystal growth decreases, and there is also the problem of a decrease in the efficiency of raw material use.

This aspect of the present invention is a horizontal vapor phase growth apparatus capable of heating to 1200°C or higher, in which a source gas injection unit that injects source gas and a susceptor surface that heats the substrate are arranged in parallel, and at least one first gas injection member having multiple holes for injecting an inert gas toward the source gas is arranged between the source gas injection unit and the susceptor.

In this aspect of the present invention, in addition to the first gas injection member, at least one second gas injection member having a plurality of approximately cylindrical holes for injecting the inert gas toward the susceptor may be disposed above the susceptor.

In one aspect of the present invention, the first gas injection member and the second gas injection member may be arranged consecutively.

In one aspect of the present invention, the first gas injection member and the second gas injection member may be arranged consecutively.

In one aspect of the present invention, the holes of the first gas injection member may be inclined toward the source gas injection portion with respect to the vertical direction so that the flow lines of the source gas and the inert gas form an acute angle.

In one aspect of the present invention, the holes in the first gas injection member may be nozzle-shaped, with the cross-sectional area of the holes on the gas outflow side being smaller than the cross-sectional area of the holes on the gas inflow side.

In one aspect of the present invention, the sum of the cross-sectional areas of the multiple holes in the one or more second gas injection members provided on the gas outlet side may be smaller than the sum of the cross-sectional areas of the multiple holes in the second gas injection member provided on the gas inlet side.

In consideration of the above-mentioned problems, the present invention provides a vapor phase growth apparatus that makes it possible to obtain uniform crystal films of nitride semiconductors such as aluminum nitride and aluminum gallium nitride, even when growing crystals at high temperatures exceeding 1200°C, improves the efficiency of use of the source gas 50, and suppresses temperature increases in each component of the apparatus even at high temperatures.

1 is a schematic cross-sectional view showing the structure of a vapor phase growth apparatus according to a first embodiment of the present invention. FIG. 2 is a partial cross-sectional view of a first gas injection portion according to the first embodiment of the present invention. FIG. 10 is a partial cross-sectional view of a first gas injection portion in a second embodiment of the present invention. FIG. 1 is a schematic cross-sectional view of a first conventional vapor phase growth apparatus. FIG. 10 is a schematic cross-sectional view of a second conventional vapor phase growth apparatus.

Next, the first embodiment of the present invention will be described with reference to the drawings.

Figure 1 shows the schematic configuration of a vapor phase growth apparatus 1000 according to this embodiment. This vapor phase growth apparatus 1000 is used to grow a Group III nitride semiconductor layer containing aluminum or boron on the upper surface of a substrate 111 made of sapphire or the like.

The vapor phase growth apparatus 1000 is equipped with a TaC-coated carbon susceptor 112 for holding and heating the substrate 111, a resistance heating heater 115 for heating the susceptor 112, and a current introduction bar 142 for applying current to the heater 115 for heating. While the heater 115 is a resistance heating type in this embodiment, it may also be a high-frequency electromagnetic induction type heater or a lamp-based heater.

The source gas 50 reacts and crystallizes, depositing and adhering not only on the upper surface of the substrate 111 but also on the upper surface of the susceptor 112 that holds the substrate 111. When the heating process is repeated during the manufacture of nitride semiconductors, repeated stress is applied to the susceptor 112 due to the difference in thermal expansion coefficients between the crystallized deposits and the susceptor, which may result in damage to the susceptor 112. To prevent this, a TaC-coated carbon peripheral ring 116 is provided around the periphery of the susceptor 112 to prevent crystallized deposits from adhering to the susceptor 112.

This vapor phase growth apparatus 1000 has a plurality of roughly cylindrical holes 120 for injecting cooling inert gas 55, a first gas injection member 121 positioned opposite the substrate 111, a base plate 113 positioned on the susceptor 112 side, and a flow path lid 114 to prevent the atmosphere and surrounding area from being contaminated by reaction deposits.

As shown in the partial cross-sectional view of the first gas injection section in the first embodiment of the present invention in Figure 2, the multiple, approximately cylindrical holes 120 in the first gas injection member 121 are inclined toward the source gas injection section 150 with respect to the vertical direction so that the angle θ between the flow line of the source gas 50 and the flow line of the inert gas 55 is an acute angle.

The rotation shaft 145 provided at the bottom of the susceptor 112 and the susceptor 112 are configured to rotate together by a rotation means (not shown).

The vapor phase growth apparatus 1000 of this embodiment is further equipped with a reflector 141 to reduce the downward transmission of heat from the heater 115 and heat from the susceptor 112 heated by the heater 115 through the rotation shaft 145. To prevent the heater 115 from corroding due to ammonia, which is one of the source gases 50 heated to high temperatures, the heater 115 is made of, for example, TaC-coated carbon or pBN-coated carbon. Alternatively, a SiC or high-melting-point metal heater may also be used.

Even if the heater 115 is resistant to highly corrosive ammonia, it is necessary to prevent ammonia from coming into contact with the heater 115 to prevent deterioration of the heater 115. Therefore, a heater cover 143 is provided to create positive pressure around the heater 115, and nitrogen or hydrogen gas is supplied from below inside the rotating shaft 145. In addition, a thermocouple 144 is provided below the susceptor 112, in the center of the heater 115, to measure the temperature of the backside of the susceptor 112.

In the vapor phase growth apparatus 1000 of this embodiment, the source gas injection unit 150 consists of an upper gas inlet 153, a middle gas inlet 152, and a lower gas inlet 151. The source gas 50 supplied from the source gas injection unit 150 flows through the upstream flow channel 131 and reacts on the upper surface of the substrate 111, growing a crystalline film. The source gas 50 that does not contribute to the growth of the crystalline film passes through the downstream flow channel 132 and is exhausted from the exhaust port 155.

An inert gas inlet 125 for supplying inert gas 55 for air cooling is provided vertically above the susceptor 112, and multiple second gas injection members 122a, 122b are provided between the inert gas inlet 125 and the first gas injection member 121. In this embodiment, two second gas injection members are provided.

In order to distribute the inert gas 55 uniformly and increase the flow rate of the inert gas 55 in these second gas injection members 122a, 122b, the sum of the cross-sectional areas of the multiple, approximately cylindrical holes in the second gas injection member 122a provided on the outlet side of the inert gas 55 is configured to be smaller than the sum of the cross-sectional areas of the multiple, approximately cylindrical holes in the second gas injection member 122b provided on the inlet side of the inert gas 55.

The lower gas inlet 151 introduces ammonia gas, which is a nitrogen source, and hydrogen, or ammonia and nitrogen, while the middle gas inlet 152 supplies hydrogen containing an organometallic source, or nitrogen containing an organometallic source, and hydrogen or nitrogen. The upper gas inlet 153 supplies hydrogen or nitrogen, but the functions and effects of the present invention are not impaired even if nothing is supplied from the upper gas inlet 153.

Organometallic raw materials include trimethylaluminum, trimethylgallium, triethylgallium, and tetraethylboron.

The inert gas 55 for air cooling supplied through the inert gas inlet 125 may be nitrogen, hydrogen, argon, fluorine, or helium.

The crystal growth method in this example will be described. To grow a nitride semiconductor crystal film such as aluminum nitride or aluminum gallium nitride using the vapor phase growth apparatus 1000 of this embodiment, a source gas 50 is introduced from the source gas injection unit 150. A substrate 111 such as sapphire is heated to a predetermined temperature via a susceptor 112 by a heater 115. The rotation shaft 145 and the susceptor 112 are rotated integrally at a predetermined speed by a rotation means (not shown), thereby growing a nitride semiconductor crystal film uniformly on the upper surface of the substrate 111.

Inert gas 55 for air cooling is supplied from the inert gas inlet 125, passes through the second gas injection members 122b and 122a, and the first gas injection member 121 before flowing into the upstream flow channel 131. Since the sum of the cross-sectional areas of the multiple holes in the second gas injection member 122a is configured to be smaller than the sum of the cross-sectional areas of the multiple holes in the second gas injection member 122b, in accordance with the law of continuity of fluids, the flow rate of the inert gas 55 increases after passing through the second gas injection member 122b and further increases after passing through the second gas injection member 122a.

As shown in the partial cross-sectional view of the first gas injection unit in the first embodiment of the present invention in FIG. 2 , the inert gas 55 is inclined toward the source gas injection unit 150 with respect to the vertical direction so that when the inert gas 55 passes through a plurality of substantially cylindrical holes 120 provided in the first gas injection member 121, the angle θ between the flow line of the source gas 50 and the flow line of the inert gas 55 becomes an acute angle.

Therefore, the velocity vector v2 of the inert gas 55 has a horizontal component v2x in addition to a vertical component v2y. The vertical component v2y of the velocity of the inert gas 55 acts to suppress the source gas 50 from convecting vertically upward, allowing the source gas 50 to react efficiently on the upper surface of the substrate 111. On the other hand, the horizontal component v2x of the velocity of the inert gas 55 is added to the horizontal velocity vector v1 of the source gas 50, accelerating the flow rate of the source gas 50.

As a result, even in an atmosphere where the vapor phase growth temperature exceeds 1200°C, reaction between the source gas 50 molecules before it reaches the substrate 111 can be suppressed, and the source gas 50 can be efficiently delivered to the substrate 111 heated to a predetermined temperature by the susceptor 112, allowing it to react on the upper surface of the substrate 111. This significantly improves the efficiency of use of the source gas 50, making it possible to provide an inexpensive crystal film.

While the substrate 111 is maintained at a high temperature of 1200°C or higher to promote crystal growth on the top surface of the substrate 111, areas other than the top surface of the substrate 111 do not need to be at high temperatures. It is desirable to maintain the vapor phase growth apparatus 1000 at as low a temperature as possible to prevent thermal degradation of the components of the vapor phase growth apparatus 1000 and to prevent reactions in areas other than the top surface of the substrate 111 that do not contribute to the crystal growth of the source gas 50.

In order to cool the vapor phase growth apparatus 1000, it is necessary to maximize the heat transfer coefficient between the inert gas 55 and each component of the vapor phase growth apparatus 1000. The heat transfer coefficient is inversely proportional to the thickness of the thermal boundary layer that forms between the inert gas 55 and each component of the vapor phase growth apparatus 1000. Therefore, the cooling effect can be enhanced by thinning the thermal boundary layer. This thermal boundary layer and the velocity boundary layer that forms between the inert gas 55 and each component of the vapor phase growth apparatus 1000 are in a similar relationship according to Newton's law of cooling, and when the Prandtl number is 1, the two are approximately equal. Therefore, increasing the flow velocity of the inert gas 55 prevents the temperature of each component of the vapor phase growth apparatus 1000 from rising.

As described above, the inert gas 55 flowing in through the inert gas inlet 125 is accelerated after passing through the second gas injection members 122b and 122a, and is further accelerated when it passes through the first gas injection member 121 and flows into the upstream flow channel 131. Therefore, the velocity boundary layer generated between the inert gas 55 and each component of the vapor phase growth apparatus 1000 becomes thinner as the flow velocity of the inert gas 55 increases; in other words, the temperature boundary layer becomes thinner. As a result, the heat transfer coefficient increases, allowing each component of the vapor phase growth apparatus 1000 that has been heated to a high temperature to be cooled, and preventing deterioration of each component.

Figure 3 shows a partial cross-sectional view of the first gas injection section in the second embodiment of the present invention. The difference from the first embodiment is the shape of the multiple holes 220 provided in the first gas injection section 221 of the second embodiment. The rest of the configuration is exactly the same as the first embodiment.

In other words, this hole 220 has a nozzle shape in which the cross-sectional area of the inert gas 55 outlet side is smaller than the cross-sectional area of the inert gas 55 inlet side. When the inert gas 55 flows into the hole 220 at flow velocity v3, the hole 220 has a nozzle shape in which the cross-section narrows in the gas outflow direction. Therefore, according to the law of continuity of fluids, as the cross-sectional area of the hole 220 becomes smaller, the flow velocity of the inert gas 55 increases, and the inert gas 55 flows out at flow velocity v4. Therefore, the flow velocity of the source gas 50 is increased and a cooling effect is obtained for each component of the vapor phase growth apparatus 1000.

1000 Metal-organic chemical vapor deposition apparatus 50 Source gas 55 Inert gas 111 Substrate 112 Susceptor 113 Base plate 114 Flow path cover 115 Heater 116 Outer ring 120 Hole 121 First gas injection member 122a, 122b Second gas injection member 124 Gas diffusion plate cap 125 Inert gas inlet 131 Upstream flow channel 132 Downstream flow channel 141 Reflector 142 Current introduction bar 143 Heater cover 144 Thermocouple 145 Rotating shaft 150 Source gas injection unit 151 Lower gas inlet 152 Intermediate gas inlet 153 Upper gas inlet 155 Exhaust port
220 Vacancy
221 Gas injection unit
600 Vapor phase growth apparatus
610 substrate
615 Substrate holder
620 Raw material gas
620 substrate
625 Flow Channel
630 susceptor
635 coil
700 Vapor phase growth equipment
705 Substrate
710 Reaction vessel
715 susceptor
720 heater
725 Raw material gas injection pipe
725 Reaction gas injection tube
730 Sub-injection pipe
735 shaft

Claims (5)

A horizontal vapor phase growth apparatus in which a source gas injection unit that injects a source gas in a horizontal direction and a susceptor surface that heats a substrate are arranged in parallel, and the apparatus can heat an upper surface of the substrate to a temperature of 1200°C or higher,
at least one first gas injection member having a plurality of holes for injecting an inert gas toward the source gas is disposed between the source gas injection unit and the susceptor in a horizontal plane so as to overlap with the source gas injection unit,
a base plate is disposed between the susceptor, which supports the substrate on its upper surface, and the source gas injection unit;
a region where the inert gas is injected onto the base plate from the first gas injection member is provided before the source gas reaches the susceptor;
a horizontal vapor phase growth apparatus, wherein the holes of the first gas injection member are inclined with respect to a vertical direction in a direction of travel of the source gas so that a flow line of the source gas and a flow line of the inert gas form an acute angle. The horizontal vapor phase growth apparatus of claim 1, characterized in that, in addition to the first gas injection member, at least one second gas injection member having a plurality of approximately cylindrical holes for injecting the inert gas toward the susceptor is also provided above the susceptor. 3. The horizontal vapor phase growth apparatus according to claim 2 , wherein the first gas injection member and the second gas injection member are arranged in series. The horizontal vapor phase growth apparatus described in claim 1, characterized in that the holes of the first gas injection member have a nozzle shape in which the cross-sectional area of the holes on the gas outflow side is smaller than the cross-sectional area of the holes on the gas inflow side. The horizontal vapor phase growth apparatus described in claim 2, characterized in that, in the one or more second gas injection members, the sum of the cross-sectional areas of the multiple holes in the second gas injection member provided on the gas outlet side is smaller than the sum of the cross-sectional areas of the multiple holes in the second gas injection member provided on the gas inlet side.