Group III Nitride Semiconductor Crystal Substrate and Semiconductor Device

Abstract

A group III nitride semiconductor crystal substrate has a diameter of at least 25 mm and not more than 160 mm. The resistivity of the group III nitride semiconductor crystal substrate is at least 1×10−4 Ω·cm and not more than 0.1 Ω·cm. The resistivity distribution in the diameter direction of the group III nitride semiconductor crystal is at least −30% and not more than 30%. The resistivity distribution in the thickness direction of the group III nitride semiconductor crystal is at least −16% and not more than 16%.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a group III nitride semiconductor crystal substrate and a semiconductor device.[0003]2. Description of the Background Art[0004]Gallium nitride (GaN) type semiconductor materials are known to have superior properties such as a large bandgap that is approximately 3 times that of silicon (Si), a high breakdown electric field that is approximately 10 times that of silicon, and also a high saturation electron velocity. Research and development of the gallium nitride type semiconductor material for use in devices of high frequency and high power output in the field of radio communication are actively in progress, and has already come to the stage of practical use in devices directed to base stations for cellular phones. Moreover, the expectation of covering the two competing demands of high breakdown voltage and low loss, i.e. low ON-state resistance, that was difficult in conventional Si powe...

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Benefits of technology

[0014]In view of the foregoing, an object of the present invention is to provide a group III nitride semiconductor crystal substrate, allowing the resistivity to be reduced and preventing degradation in the resistivity in-plane distribution.

[0015]Another object of the present invention is to provide a semiconductor device that can have degradation in properties prevented and the yield improved.

[0016]As a result of diligent research on the doping conditions of silicon, the inventors found that, by employing silicon tetrafluoride gas as the doping gas, or by setting the growth rate of a group III nitride semiconductor crystal substrate to at least 200 μm / h and not more than 2000 μm / h based on the usage of silicon tetrachloride gas as the doping gas, decomposition of the doping gas can be prevented and reaction per se of the doping gas with another gas can be suppressed or the effect of the reaction reduced, at the stage of doping silicon. Thus, there was obtained a group III nitride semiconductor crystal substrate allowing the resistivity to be reduced by readily controlling the resistivity and preventing degradation in the resistivity in-plane distribution.

Problems solved by technology

Moreover, the expectation of covering the two competing demands of high breakdown voltage and low loss, i.e. low ON-state resistance, that was difficult in conventional Si power devices, has attracted attention in the application to power devices.

It was difficult to control the concentration of silicon in the doping gas if the doping gas directed to supplying silicon was decomposed or caused reaction prior to arriving at the underlying substrate.

Therefore, it was difficult to control the resistivity of the group III nitride semiconductor crystal with silicon as a dopant.

Particularly, this problem was further noticeable when HVPE was employed since the decomposition of the doping gas and / or reaction with another gas was significant due to the entire heating of the reaction tube.

However, the concentration distribution of the doping gas supplied to the underlying substrate will be degraded if the doping gas is supplied at high rate, leading to significant degradation in the in-plane distribution of the resistivity in the group III nitride semiconductor crystal.

Thus, there was a problem that the property such as the ON-resistance is degraded in the case where the resistivity is not regulated and a semiconductor device is fabricated employing a group III nitride semiconductor crystal substrate of high resistivity.

Further, in the case where a semiconductor device is fabricated employing a group III nitride semiconductor crystal substrate having poor resistivity in-plane distribution, the yield was degraded since the property such as the ON-resistance of the semiconductor device will vary.

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