JP2016174014A - Substrate processing method, and manufacturing method of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the deposition of a foreign material to a GaN substrate.SOLUTION: A substrate processing method comprises: supplying a carrier gas used in crystalline growth into a MOCVD apparatus before placing a substrate 10 for crystalline growth in the MOCVD apparatus, provided that the flow rate of the carrier gas is periodically pulsated in such a way that the flow rate is made 10 m/s and 0 m/s alternately and repeatedly (step S10); subsequently, stopping the supply of the carrier gas into the MOCVD apparatus and placing the substrate 10 in the MOCVD apparatus (step S20); then, evacuating the MOCVD apparatus to 2 Pa at a rate of 4×10Pa/min or less and further, evacuating to 2×10Pa or less (step S30); and then, supplying a carrier gas at a flow rate of 0.5 cm/s to return a pressure back to a pressure for growth of Group III nitride semiconductor in the subsequent step (step S40).SELECTED DRAWING: Figure 2

Description

  The present invention relates to a substrate processing method for preventing foreign matter from adhering to a substrate made of a group III nitride semiconductor before crystal growth. Further, the present invention is a method for manufacturing a semiconductor element made of a group III nitride semiconductor capable of improving the breakdown voltage yield.

  In recent years, power devices and high-frequency devices made of a group III nitride semiconductor using a GaN substrate have been actively researched and developed.

  When a group III nitride semiconductor is grown on a GaN substrate to produce a semiconductor element, a large number of pits are generated, and the pits become a leak path, so that a leak current is large. It is considered that the cause of the generation of pits is a foreign matter adhering to the GaN substrate (for example, a by-product generated by crystal growth such as a miscellaneous crystal or carbide of a group III nitride semiconductor). Therefore, in order to suppress the leakage current of a semiconductor element made of a group III nitride semiconductor using a GaN substrate and improve the breakdown voltage yield, it is necessary to reduce foreign matter on the GaN substrate.

  Patent Document 1 describes that an inert gas is allowed to flow in parallel to the wafer surface to remove foreign substances adhering to the wafer surface.

  Patent Document 2 describes that an inert gas is allowed to flow at a flow rate of 10 m / s or more and a foreign substance in the MOCVD apparatus is blown away before the substrate is placed in the MOCVD apparatus. This prevents foreign matter in the MOCVD apparatus from adhering to the substrate.

JP 2006-140492 A JP 2006-318959 A

  However, when a GaN substrate is used as the growth substrate, there has been a problem that it is difficult to remove foreign substances adhering to the GaN substrate by the conventional cleaning method.

  Accordingly, an object of the present invention is to reduce the adhesion of foreign matter to a substrate made of a group III nitride semiconductor.

  The first invention is the first step of introducing an inert gas into the vapor phase growth apparatus and pulsating the flow rate of the inert gas before placing the substrate made of the group III nitride semiconductor in the vapor phase growth apparatus. And after the substrate is placed in the vapor phase growth apparatus, before the group III nitride semiconductor is crystal-grown on the substrate, the inside of the vapor phase growth apparatus is evacuated, and then an inert gas is supplied to supply the group III And a second step of returning to the growth pressure for growing the nitride semiconductor.

  The first step may be performed while heating the inside of the vapor phase growth apparatus. It is possible to further reduce the adhesion of foreign matter on the substrate.

  The pulsation of the flow rate of the inert gas in the first step can be made to pulsate periodically by alternately repeating the first flow rate and the second flow rate slower than the first flow rate. At this time, the number of repetitions is preferably 5 to 50 times. The difference between the first flow rate and the second flow rate is preferably 1 to 50 m / s. The first flow rate is preferably 50 m / s or less. In either case, it is effective to further reduce the adhesion of foreign matter on the substrate.

The vacuuming in the second step is preferably performed at a reduced pressure rate of 4 × 10 ³ Pa / min or less. Moreover, it is good to carry out until the pressure in a vapor phase growth apparatus becomes 2 * 10 < ^-3 > Pa or less. In either case, the foreign matter adhering to the substrate can be removed more efficiently.

  In the second step, the flow rate of the inert gas when returning to the growth pressure after evacuation is preferably 50 cm / s or less. This is because foreign matters can be prevented from scattering and adhering to the substrate.

  The second step may be performed at a temperature lower than the growth temperature of the group III nitride semiconductor in the vapor phase growth apparatus. This is because when the temperature is higher than the growth temperature, the foreign matter is hardened and difficult to remove.

  It is preferable to have a third step of heat-treating the substrate in an inert gas atmosphere after the first step and before the second step. This is because foreign substances adhering to the substrate can be further removed.

  According to a second aspect of the present invention, there is provided a method for manufacturing a semiconductor device, wherein a semiconductor layer made of a group III nitride semiconductor is formed on a substrate after the substrate processing method according to the first aspect of the present invention.

  According to the present invention, the foreign substance on the inner wall of the crystal growth apparatus can be peeled off by the pressure difference caused by the pulsation of the inert gas, and the foreign substance floating in the crystal growth apparatus can be removed. Therefore, it is possible to prevent foreign matters from adhering to the substrate when the substrate is disposed in the crystal growth apparatus.

  Further, the foreign matter deposited on the substrate can be removed from the substrate by the subsequent evacuation.

  Therefore, according to the present invention, a group III nitride semiconductor can be grown in a state in which foreign matter adhering to the substrate is reduced. In addition, when a semiconductor element made of a group III nitride semiconductor is manufactured using the substrate, foreign substances on the substrate are reduced, so that the breakdown voltage yield can be improved.

FIG. 3 is a diagram illustrating a configuration of a Schottky barrier diode according to the first embodiment. The flowchart which showed the substrate processing process. The graph which showed the relationship between the flow velocity of carrier gas and time. A graph showing the relationship between the number of pits and the number of repetitions. A graph showing the relationship between the number of pits and the decompression speed. The graph which showed the relationship between the number of pits and the flow velocity of carrier gas. FIG. 5 is a diagram showing a configuration of a MOSFET according to Example 2. FIG. 6 is a diagram showing a manufacturing process of the MOSFET of Example 2. 9 is a flowchart showing a substrate processing process of Example 3.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples.

  FIG. 1 is a diagram illustrating a configuration of the Schottky barrier diode according to the first embodiment. As shown in FIG. 1, the Schottky barrier diode of Example 1 includes a substrate 10, an n layer 11 positioned in contact with the substrate 10, a Schottky electrode 12 positioned in contact with the n layer 11, and a substrate 10. , And an ohmic electrode 13 located in contact with the back surface (the surface opposite to the n-GaN layer 11 formation side). This is a vertical element that conducts in a direction perpendicular to the main surface of the substrate 10.

The substrate 10 is obtained by dividing a substrate having a main surface of c-plane and having a diameter of 2 inches or more for each element, and is, for example, 3 mm square. The substrate 10 is made of n-GaN having a Si concentration of 1 × 10 ¹⁸ / cm ³ or more and has a thickness of 300 to 500 μm.

The n layer 11 is positioned in contact with the substrate 10. The n layer 11 is a layer having a thickness of 10 to 15 μm made of n-GaN having a Si concentration of 1 × 10 ¹⁶ / cm ³ or less and a C (carbon) concentration of 1 × 10 ¹⁶ / cm ³ or less.

  Schottky electrode 12 is positioned on and in contact with n layer 11. The Schottky electrode 12 is made of a conductive material that forms a Schottky junction with the n layer 11 and is, for example, Ni.

  The ohmic electrode 13 is positioned in contact with the back surface of the substrate 10. The ohmic electrode 13 is made of a conductive material that makes ohmic contact with the substrate 10, and is, for example, a material in which Ti and Al are laminated in order from the back side of the substrate 10.

  Next, the manufacturing process of the Schottky barrier diode of Example 1 will be described.

  First, before forming the n-GaN layer 11 on the substrate 10, substrate processing is performed as follows. FIG. 2 is a flowchart showing the substrate processing process. The substrate processing process will be described based on the flowchart of FIG.

[Step S10]
First, before the substrate 10 for crystal growth is placed in the MOCVD apparatus, a carrier gas used for crystal growth is supplied into the MOCVD apparatus. In crystal growth of a group III nitride semiconductor, H ₂ and N ₂ are used as carrier gases, and either one or a mixed gas is used. In addition, what is necessary is just not only carrier gas but inert gas. For example, a rare gas such as Ar, Ne, or Kr may be used, or a mixed gas of a rare gas and a carrier gas may be used. However, it is preferable to use a carrier gas in terms of consistency with the semiconductor element manufacturing process.

  The pressure (static pressure) in the MOCVD apparatus is normal pressure. However, the pressure may be reduced or increased. The temperature in the MOCVD apparatus (temperature of the susceptor) may be room temperature, but it is preferable to heat it to a temperature higher than room temperature, for example, the growth temperature of the group III nitride semiconductor (approximately 1050 ° C.) or higher. Is desirable. More desirable is 1100 to 1200 ° C.

  Here, the flow velocity of the carrier gas is periodically pulsated as shown in FIG. 3 (step S10). More specifically, the period during which the flow velocity is maintained at 10 m / s (the period during which the flow velocity takes the maximum value Vmax) is T1, then the period during which the flow velocity is decreased from 10 m / s to 0 m / s is T2, and then the flow velocity is 0 m / s. The period to maintain at (the period when the flow velocity takes the minimum value Vmin) is T3, then the period during which the flow velocity is increased from 0 m / s to 10 m / s is T4, and the period from T1 to T4 is one cycle T. Repeat a predetermined number of times. The flow rate is a value at the gas inlet to the MOCVD apparatus (value in the gas supply pipe).

  As described above, in step S10, the carrier gas is introduced into the MOCVD apparatus before the substrate 10 is placed in the MOCVD apparatus, and the pressure in the MOCVD apparatus is changed by pulsating the flow velocity of the carrier gas. ing. And the foreign material which exists in the inner wall of a MOCVD apparatus can be peeled with the pressure difference by the pressure fluctuation. The separated foreign matter or the foreign matter floating in the MOCVD apparatus is discharged from the MOCVD apparatus together with the carrier gas, and some foreign matter is deposited on the bottom of the MOCVD apparatus. Therefore, when the substrate 10 is placed in the MOCVD apparatus, foreign substances are peeled off from the inner wall (other than the bottom) of the MOCVD apparatus and adhered to the substrate 10, or foreign substances floating in the atmosphere in the MOCVD apparatus dropped. Adhesion on the substrate 10 is reduced. In particular, if the inside of the MOCVD apparatus is heated in step S10, it is desirable that adhesion of foreign matters can be further reduced.

  In order to further reduce the accumulation of foreign matter on the substrate 10, it is desirable that the conditions regarding the pulsation of the carrier gas are as follows.

  The periods T1 to T4 are preferably set to 1 to 10 s, respectively. The periods T1 to T4 may not be equal to each other. It is more preferably 1 to 5 s, and further preferably 1 to 2 s.

  The periods T2 and T4 are preferably as short as possible, and are preferably set to a minimum value within a range that can be set in the MOCVD apparatus to be used. This is because the rate of change in pressure becomes larger and foreign substances are more easily separated from the inner wall of the MOCVD apparatus. In the periods T2 and T4, the flow velocity is not necessarily changed linearly. Further, it is desirable that the periods T1 and T3 be equal. One or both of the periods T1 and T3 may be set to 0 s. That is, the flow velocity may be decreased as soon as the flow velocity reaches 10 m / s, and the flow velocity may be increased as soon as the flow velocity reaches 0 m / s.

  The number of repetitions is preferably 5 to 50 times. If it is less than 5 times, it is not possible to sufficiently reduce the accumulation of foreign substances on the substrate 10 after the substrate 10 is placed in the MOCVD apparatus, and the yield cannot be improved. Moreover, if it exceeds 50 times, the reduction effect is saturated, and 50 times or less is good considering the manufacturing time and raw material cost. More desirably, it is 5 to 20 times, and further desirably 7 to 15 times.

  In the first embodiment, the maximum value Vmax of the flow velocity is 10 m / s, but the present invention is not limited to this. The maximum value Vmax of the flow velocity is desirably 50 m / s or less. If it is faster than 50 m / s, foreign matter may be scattered in the MOCVD apparatus, which is not desirable. A more desirable range of the maximum value Vmax of the flow velocity is 10 to 50 m / s, and further desirably 30 to 50 m / s. In Example 1, the minimum value Vmin of the flow velocity is set to 0 m / s, but the minimum value Vmin of the flow velocity is 0 m / s or more, and the flow rate difference ΔV (difference between the maximum value Vmax and the minimum value Vmin of the flow rate). Should be within the following range.

  The flow rate difference ΔV is preferably 1 to 50 m / s. This is because as the flow rate difference ΔV is larger, the pressure difference in the MOCVD apparatus (difference between the maximum value and the minimum value of the pressure) is also increased, and foreign substances adhering to the inner wall of the MOCVD apparatus can be efficiently separated. More preferably, it is 10-50 m / s, More preferably, it is 40-50 m / s.

  In the first embodiment, the carrier gas is periodically pulsated by alternately switching between a fast flow rate and a slow flow rate, but may be periodic or aperiodic as long as the pulsation is performed. For example, it may be a periodic pulsation in which an intermediate flow rate is sandwiched between a fast flow rate and a slow flow rate. Further, for example, in the time waveform of the flow velocity in FIG. 3, it is possible to make a non-periodic pulsation by changing the period T1 and the period T3 for each repetition, or to make a non-periodic pulsation by making Vmax and Vmin different. . As shown in FIG. 3, in Example 1, the initial supply of carrier gas is constant at 5 m / s and the flow rate is pulsated thereafter, but it may be periodically pulsated from the beginning.

[Step S20]
Next, the supply of the carrier gas into the MOCVD apparatus is stopped, and the substrate 10 is placed in the MOCVD apparatus (step S20). In addition, when performing the process of step S10, heating, arrangement | positioning of the board | substrate 10 is performed after temperature-falling to normal temperature.

[Step S30]
Next, the inside of the MOCVD apparatus is evacuated to 2 Pa at a speed of 4 × 10 ³ Pa / min or less using a dry pump, and then further evacuated to 2 × 10 ⁻³ Pa or less using a turbo molecular pump (step) S30). And the state of 2 * 10 < ^-3 > Pa or less is maintained for 1 to 10 minutes. Thereby, the foreign material adhering to the board | substrate 10 is peeled and removed.

  Note that the evacuation may not be performed at room temperature, and may be performed at a temperature not higher than the growth temperature of the group III nitride semiconductor (approximately 1050 ° C.). If the temperature is higher than the growth temperature of the group III nitride semiconductor, foreign matter adhering to the substrate 10 is hardened and cannot be removed.

Further, in evacuation, it is desirable that the speed (pressure reduction speed) at which the pressure is reduced to reduce foreign matter on the substrate 10 is as slow as possible. Therefore, in Example 1, vacuuming is performed at a speed of 4 × 10 ³ Pa / min or less. Moreover, since it will take too much time to reach the target pressure if the pressure reduction rate is too slow, it is desirable to set it to 1 × 10 ³ Pa / min or more. More desirably, it is 1 × 10 ³ Pa / min or more and 3 × 10 ³ Pa / min or less.

In step S30, the vacuum is evacuated to 2 × 10 ⁻³ Pa or less. The lower the pressure, the more desirable, and the pressure is desirably 1 × 10 ⁻³ Pa or less. Foreign matter on the substrate 10 can be further reduced. More desirably, it is 5 × 10 ⁻⁴ Pa or less. In view of labor and cost, it is desirable that the pressure be 4 × 10 ⁻⁴ Pa or more.

The time for maintaining the state of 2 × 10 ⁻³ Pa or less is more preferably 5 to 10 minutes. Foreign substances on the substrate 10 can be reduced more efficiently.

[Step S40]
Next, the carrier gas is supplied at a flow rate of 0.5 cm / s to return to the growth pressure of the group III nitride semiconductor in the next process (step S40). This prevents foreign matters remaining in the MOCVD apparatus from scattering and adhering to the substrate 10.

  The flow rate of the carrier gas when returning to the growth pressure is not limited to 0.5 cm / s, but is desirably as slow as possible. This is because the number of foreign substances adhering to the substrate 10 can be further reduced. In order to reduce the number of foreign substances as compared with the conventional case, the flow rate of the carrier gas needs to be 50 cm / s or less. In order to sufficiently improve the yield, it is preferably 1 cm / s or less, and more preferably 0.5 cm / s or less.

  According to the above substrate processing, before the substrate 10 is placed in the MOCVD apparatus, the carrier gas is introduced into the MOCVD apparatus and the gas flow is pulsated, so that the pressure difference due to the pulsation causes the inner wall of the MOCVD apparatus to be pulsated. The adhered foreign matter can be peeled off and removed, and foreign matter floating in the MOCVD apparatus can be removed. As a result, it is possible to prevent foreign matter from adhering to the substrate 10 when the substrate 10 is disposed in the MOCVD apparatus. Further, even if foreign matter has already adhered on the substrate 10 when the substrate 10 is placed in the MOCVD apparatus, the foreign matter deposited on the substrate 10 can be removed by evacuation.

  Specifically, conventionally, when a group III nitride semiconductor is formed on the substrate 10, about 100 pits are generated per wafer in the group III nitride semiconductor due to the foreign matter. It can be reduced to about one.

Subsequently, the source gas and the dopant gas are supplied into the MOCVD apparatus, and the n layer 11 is formed on the substrate 10. The source gases used in the MOCVD method are ammonia (NH ₃ ) as a nitrogen source, trimethylgallium (Ga (CH ₃ ) ₃ ) as a Ga source, silane (SiH ₄ ) as an n-type dopant gas, and H ₂ as a carrier gas. It is.

In forming the n layer 11, the pressure was 25 to 100 kPa, the temperature was 900 to 1050 ° C., and the V / III ratio (ratio of the ammonia supply amount to the trimethylgallium supply amount) was 2500 to 10,000. By growing under such conditions, the C concentration can be reduced to 1 × 10 ¹⁶ / cm ³ or less, and the breakdown voltage performance can be improved. Further, the supply amount of silane is adjusted so that the Si concentration is 1 × 10 ¹⁶ / cm ³ or less.

  Next, the wafer is taken out from the MOCVD apparatus and placed in the vapor deposition apparatus, and the Schottky electrode 12 is formed on the n layer 11 and the ohmic electrode 13 is formed on the back surface of the substrate 10 by vapor deposition. Thus, the Schottky barrier diode of Example 1 shown in FIG. 1 is manufactured.

  In the Schottky barrier diode of Example 1 manufactured by the above manufacturing method, since the n layer 11 is formed in a state where the foreign matter on the substrate 10 is reduced, pits are generated in the n layer 11 due to the foreign matter. Can be reduced. As a result, uniform pressure resistance can be obtained with all elements obtained from one wafer, and the breakdown voltage yield can be improved.

[Experiment 1]
In step S10 of the substrate processing of Example 1, the number of repetitions when the carrier gas is periodically pulsated is changed, and when the n layer 11 is formed on the substrate 10 after the substrate processing of Example 1, per wafer The number of pits in the n layer 11 was measured.

  FIG. 4 is a graph showing the relationship between the number of pits and the number of repetitions. As can be seen from FIG. 4, the number of pits decreases hyperbolically as the number of repetitions increases. The number of pits decreases greatly with the increase in the number of repetitions until the number of repetitions is 5, and the number of pits gradually decreases until the number of repetitions exceeds 5, and the number of pits decreases significantly after 20 times. It was gentle. Therefore, it was found that the number of repetitions should be 5 or more in order to efficiently reduce the number of pits. In addition, as shown in FIG. 4, when the number of repetitions increases, the effect of reducing the number of pits is saturated. Therefore, it was found that the number of repetitions should be 50 or less in consideration of manufacturing time and raw material cost.

[Experiment 2]
In step S30 of the substrate processing of Example 1, the pressure reduction rate when evacuating was changed, and the number of pits was measured in the same manner as in Experimental Example 1.

FIG. 5 is a graph showing the relationship between the number of pits and the decompression speed. The depressurization rate is the amount of change in pressure per minute, and the unit is Pa / min. The decompression speed is an average value, which is a value obtained by dividing the pressure change from normal pressure to 2 Pa by the time required for it. As shown in FIG. 5, it was found that the number of pits decreases as the decompression speed decreases. From this result, it was found that it is desirable that the pressure reduction rate when evacuating is as small as possible. For example, the pressure reduction rate may be 4 × 10 ³ Pa / min or less.

[Experiment 3]
In step S40 of the substrate processing in Example 1, the number of pits was measured in the same manner as in Experimental Example 1 by changing the flow rate of the carrier gas when returning to the growth pressure.

  FIG. 6 is a graph showing the relationship between the number of pits and the flow rate of the carrier gas. As shown in FIG. 6, it was found that the number of pits increased as the flow rate increased. When the chip size is 3 mm square with a 2-inch substrate, the number of pits needs to be 2 or less in order to obtain a yield of 90% or more. From FIG. 6, the carrier gas flow rate is 0.5 cm / s. It turned out that it should be the following.

  FIG. 7 is a diagram illustrating the configuration of the power MOSFET according to the second embodiment. The power MOSFET according to the second embodiment includes a substrate 10, a first n layer 21, a p layer 22, a second n layer 23, and a drain electrode 24, a gate electrode 25, and a source electrode 26 that are sequentially stacked on the substrate 10. , P body electrode 27 and gate insulating film 28. The substrate 10 is the same as that in the first embodiment.

The first n layer 21 is a layer made of n-GaN having a thickness of 10 to 15 μm located on the substrate 10. The Si concentration is 1 × 10 ¹⁶ / cm ³ or less, and the C (carbon) concentration is 1 × 10 ¹⁶ / cm ³ or less.

The p layer 22 is a layer made of p-GaN having a thickness of 0.5 to 1 μm located on and in contact with the first n layer 21. The Mg concentration is 1 × 10 ¹⁸ to 1 × 10 ²⁰ / cm ³ .

The second n layer 23 is a layer made of n-GaN having a thickness of 0.1 to 0.5 μm located in contact with a partial region on the p layer 22. The Si concentration is 1 × 10 ¹⁸ / cm ³ or more, and the C (carbon) concentration is 1 × 10 ¹⁶ / cm ³ or less. Further, a groove 29 having a depth reaching the first n layer 21 is formed in a partial region of the second n layer 23, and the first n layer 21 is exposed on the bottom surface 29 a of the groove 29. The first n layer 21, the p layer 22, and the second n layer 23 are exposed on the side surface 29b.

  The drain electrode 24 is located in contact with the back surface of the substrate 10 (the surface opposite to the first n layer 21 side), and is made of, for example, a material in which Ti and Al are laminated in order from the back surface side of the substrate 10.

The gate insulating film 28 is provided in a film shape continuously from the surface of the second n layer 23 to the side surface 29b of the groove 29 and the bottom surface 29a of the groove 29. The gate insulating film 28 is made of, for example, SiO ₂ , Al ₂ O ₃ , AlN, SiN or the like.

  The gate electrode 25 is provided continuously from the surface of the second n layer 23 to the side surface 29b of the groove 29 and further to the bottom surface 29a of the groove 29 via the gate insulating film 28. The gate electrode 25 is made of, for example, Al.

  The p body electrode 27 is located in contact with the exposed area of the surface of the p layer 22 (the surface on the first n layer 21 side) where the second n layer 23 is not formed. The p body electrode 27 is made of, for example, a material in which V and Al are stacked in this order from the p body electrode 27 side.

  The source electrode 26 is located on the second n layer 23. The source electrode 26 is made of the same material as the drain electrode 24, for example.

The power MOSFET according to the second embodiment operates using the side surface of the p layer 22 exposed on the side surface 29b of the groove 29 as a channel, and controls the current between the drain electrode 24 and the source electrode 26 by applying a voltage to the gate electrode 25. The structure of the mold. In the power MOSFET of the second embodiment, the breakdown voltage performance is improved by setting the C concentration of the first n layer 21 and the second n layer 23 to 1 × 10 ¹⁶ / cm ³ or less.

  Next, the manufacturing process of the MOSFET of Example 2 will be described with reference to FIG.

  First, substrate processing is performed in the same manner as in Example 1 before forming a semiconductor layer on the substrate 10. That is, the process shown in the flowchart of FIG. 2 is performed. Thereby, the foreign matter on the substrate 10 is sufficiently reduced before the group III nitride semiconductor is grown on the substrate 10.

Subsequently, the source gas and the dopant gas are supplied into the MOCVD apparatus, and the first n layer 21, the p layer 22, and the second n layer 23 are sequentially stacked on the substrate 10 (see FIG. 8A). . The source gases used in the MOCVD method are ammonia (NH ₃ ) as a nitrogen source, trimethyl gallium (Ga (CH ₃ ) ₃ ) as a Ga source, silane (SiH ₄ ) as an n-type dopant gas, and p-type dopant gas. Cyclopentadienyl magnesium (Mg (C ₅ H ₅ ) ₂ ) and H ₂ as a carrier gas.

In the formation of the first n layer 21 and the second n layer 23, the pressure is 25 to 100 kPa, the temperature is 900 to 1050 ° C., and the V / III ratio (ratio of the ammonia supply amount to the trimethylgallium supply amount) is 2500. -10000. By growing under such conditions, the C concentration can be reduced to 1 × 10 ¹⁶ / cm ³ or less, and the breakdown voltage performance can be improved. Further, in the formation of the first n layer 21, the Si concentration is 1 × 10 ¹⁸ / cm ³ or more in the formation of the second n layer 23 so that the Si concentration is 1 × 10 ¹⁶ / cm ³ or less. The supply amount of silane is adjusted so that

In forming the p layer 22, the pressure is preferably 25 to 100 kPa, the temperature is 900 to 1050 ° C., and the V / III ratio is preferably 1 to 500. By growing under such conditions, the C concentration can be 5 × 10 ¹⁶ / cm ³ or more, and the channel mobility can be improved. Further, the supply amount of cyclopentadienyl magnesium is adjusted so that the Mg concentration becomes 1 × 10 ¹⁸ to 1 × 10 ²⁰ / cm ³ .

  Next, the wafer is taken out from the MOCVD apparatus and placed in a dry etching apparatus, and a part of the second n layer 23 is dry etched to partially expose the surface of the p layer 22. Further, a partial region of the second n layer 23 is etched to a depth reaching the first n layer 21 to form a groove 29 (see FIG. 8B).

  Next, the wafer is taken out from the dry etching apparatus and placed in the annealing apparatus, and heat treatment is performed at 700 to 900 ° C. for 5 to 60 minutes in a nitrogen atmosphere. This activates Mg in the p layer 22 to make the p layer 22 p-type.

  Next, the wafer is taken out from the annealing apparatus and placed in the vapor deposition apparatus, and the gate insulating film 28 is vapor deposited continuously on the bottom surface 29a, the side surface 29b of the groove 29, and the region near the groove 29 on the surface of the second n layer 23. Then, the drain electrode 24, the p body electrode 27, and the source electrode 26 are formed on the back surface of the substrate 10, the p layer 22, and the second n layer 23. Further, the gate electrode 25 is formed continuously on the bottom surface 29 a and the side surface 29 b of the groove 29 and the region near the groove 29 on the surface of the second n layer 23 with the gate insulating film 28 interposed therebetween. As described above, the power MOSFET of Example 2 shown in FIG. 7 is manufactured.

  In the power MOSFET according to the second embodiment, the substrate processing is performed in the same manner as the first embodiment before the first n layer 21 is formed on the substrate 10. Therefore, the first n layer 21 can be formed in a state in which foreign matter on the substrate 10 is reduced, and pits are formed in the first n layer 21, the p layer 22, and the second n layer 23 due to the foreign matter. Can be reduced. As a result, uniform pressure resistance can be obtained with all elements obtained from one wafer, and the breakdown voltage yield can be improved.

  In the third embodiment, as shown in FIG. 9, a step of heating and heat-treating the substrate 10 between step S20 and step S30 in the substrate processing of FIG. 2 of the first and second embodiments is added (step S25). ). The heat treatment is performed in a carrier gas atmosphere, a pressure of 10 k to 101 kPa, and 200 to 1050 ° C. for 0.5 to 5 minutes. You may carry out by inert gas not only in carrier gas atmosphere.

  By performing this substrate heat treatment, it is possible to further suppress the adhesion of foreign matters on the substrate 10, and thus the breakdown voltage yield of the semiconductor element can be further improved.

  More preferable heat treatment conditions for the substrate 10 are as follows. The pressure is more preferably 30 to 50 kPa, and even more preferably 30 to 40 kPa. The temperature is more preferably 500 to 1050 ° C, and still more preferably 800 to 1050 ° C. The heat treatment time is more preferably 1 to 5 minutes, and further preferably 3 to 5 minutes.

[Variations]
In Examples 1 to 3, a substrate made of GaN was used as the growth substrate for the group III nitride semiconductor. However, the present invention is not limited to this, and any substrate made of a group III nitride semiconductor may be used. In addition to GaN, for example, a substrate such as AlN, InN, AlGaN, InGaN, or AlGaInN may be used. In the embodiment, the substrate is doped with n-type impurities, but may be non-doped or p-type impurity doped.

  In Examples 1 to 3, a group III nitride semiconductor is crystal-grown using an MOCVD apparatus as a vapor phase growth apparatus, but other conventionally known as a group III nitride semiconductor vapor phase growth apparatus. The present invention can also be applied to the case of using one. For example, an HVPE apparatus.

  Moreover, although the example of the Schottky barrier diode is shown in Example 1 and the example of the power MOSFET is shown in Example 2, the present invention can be applied to any semiconductor element. For example, the present invention can be applied to light-emitting elements such as LEDs and LDs, bipolar transistors, and the like, and uniform breakdown voltage can be obtained with all elements obtained from one wafer as in Examples 1 and 2. And withstand voltage yield can be improved.

  According to the present invention, the breakdown voltage yield of the group III nitride semiconductor device can be improved, which is effective for power devices and the like.

10: substrate 11: n layer 12: Schottky electrode 13: ohmic electrode 21: first n layer 22: p layer 23: second n layer 24: drain electrode 25: gate electrode 26: source electrode 27: p body Electrode 28: Gate insulating film 29: Groove

Claims (12)

A first step of introducing an inert gas into the vapor phase growth apparatus and pulsating the flow rate of the inert gas before placing the substrate made of a group III nitride semiconductor in the vapor phase growth apparatus;
After the substrate is placed in the vapor phase growth apparatus, before the group III nitride semiconductor is crystal-grown on the substrate, the inside of the vapor phase growth apparatus is evacuated, and then an inert gas is supplied. A second step of returning to the growth pressure for growing the group nitride semiconductor;
A substrate processing method comprising:   The substrate processing method according to claim 1, wherein the first step is performed while heating the inside of the vapor phase growth apparatus.   2. The first step is characterized in that the flow rate of the inert gas is periodically pulsated by alternately repeating a first flow rate and a second flow rate slower than the first flow rate. Alternatively, the substrate processing method according to claim 2.   4. The substrate processing method according to claim 1, wherein the periodic pulsation of the flow rate of the inert gas in the first step is repeated 5 to 50 times. 5. .   The substrate processing method according to claim 1, wherein a difference between the first flow velocity and the second flow velocity is 1 to 50 m / s.   The substrate processing method according to claim 1, wherein the first flow velocity is 50 m / s or less. The substrate processing method according to claim 1, wherein the vacuuming in the second step is performed at a reduced pressure rate of 4 × 10 ³ Pa / min or less. The evacuation in the second step is performed until the pressure in the vapor phase growth apparatus becomes 2 × 10 ⁻³ Pa or less. 8. Substrate processing method.   9. The substrate processing according to claim 1, wherein the flow rate of the inert gas when returning to the growth pressure after evacuation in the second step is 50 cm / s or less. Method.   10. The substrate processing method according to claim 1, wherein the second step is performed at a temperature equal to or lower than a growth temperature of the group III nitride semiconductor in the vapor phase growth apparatus. 11.   11. The method according to claim 1, further comprising a third step of heat-treating the substrate in an inert gas atmosphere after the first step and before the second step. Substrate processing method.   A method for manufacturing a semiconductor device, comprising: forming a semiconductor layer made of a group III nitride semiconductor on the substrate after the substrate processing method according to claim 1.

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