Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of...
Reexamination Certificate
2001-08-28
2003-03-11
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
C438S492000, C438S493000, C438S478000, C438S022000, C257S079000, C372S043010
Reexamination Certificate
active
06531408
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for growing a ZnO based oxide semiconductor layer, and a method for manufacturing a semiconductor light emitting device using the same. More specifically, the present invention relates to a method for growing a ZnO based oxide semiconductor layer in which the ZnO based oxide layer grown has the excellent flatness and has little crystal defects.
BACKGROUND OF THE INVENTION
Recently, it has become possible to obtain a light emitting diode (hereinafter, referred to as LED) in blue-based color (which means the wavelength range from ultraviolet to yellow, herein after, indicating the same meaning) used for a full-color display and a signal light, and a blue-based color laser for use in next-generation high-definition DVD light source which continuously emits light at room temperature (hereinafter, referred to as an LD), by depositing GaN based compound semiconductor layers onto a sapphire substrate, and there is a growing interest in them. As light emitting devices with short wavelength such as described above, GaN based compound semiconductor is in the mainstream. Besides the GaN based compound semiconductor, the use of, for example, Groups II-VI compound semiconductor such as ZnSe/ZnMgSSe based or ZnO based compound semiconductor has been studied.
A ZnO based oxide has been conventionally utilized only in the form of amorphous and polycrystalline. In recent years, however, plasma technology for making a gas such as nitrogen into plasma has been advanced. Accordingly, the thin film crystal growth technology where the above-mentioned plasma technology is applied using a radical source molecular beam epitaxy (RS-MBE) apparatus has made significant advancement. Moreover, studies on ZnO single crystal have been proceeded by employing PLD and a vapor phase transporting method, and have reached to the level at which the laser oscillation can be observed by a laser beam excitation (see Solid Stat. Commun., by P. Yu et al., vol. 103, No. 8 issue, on pages 459 to 466, in 1977, or Appl. Phys. Lett., by D. M. Bagnall et al, vol. 170, No. 17 issue, on pages 2230 to 2232, in 1977).
As described above, studies on ZnO based oxide semiconductor have made advancement. However, ZnO based oxide semiconductor has disadvantage in that, as compared with GaN, ZnO has high concentration of residual carriers, and the value thereof reaches to 10
18
cm
−3
of n-type. The simplest method for lowering the concentration of the residual carriers is to elevate the high growth temperature. However, the present inventors have confirmed that, if simply elevating the growth temperature on the substrate, Zn which has reached on the substrate revaporizes from the surface of the substrate at high rate, and the growth does not proceed. This is because the deposition coefficient of ZnO onto the sapphire substrate having the different characteristics from ZnO is small, and in the case of ZnO, the vapor pressure of Zn is high (for example, see The 8th SiC and related wide gap semiconductor workshop P-83, or The 47th Applied Physics related association party, articles for lecture, 29a-YL-3). For the above reason, the growth temperature on the substrate is set to as low as at approximately 300° C. in many cases. However, at a low growth temperature, the concentration of the residual carries cannot be lowered, and the low concentration of the residual carriers, which is an essential condition for a semiconductor material, is not be attained.
Thus, it is considerable that a ZnO based oxide layer is once grown as a buffer layer at a low temperature, and after that, the temperature is elevated to high value at which an predetermined ZnO based oxide semiconductor layer such as a light emitting layer forming portion is grown. However, even in this method, the flatness of the buffer layer is degraded during elevating the temperature on the substrate. In this case, the ZnO based oxide semiconductor layer which constitutes the light emitting layer forming section has poor flatness accordingly, making it impossible to obtain improved light emitting characteristics.
SUMMARY OF THE INVENTION
The present invention has been made to solve the problems such as described above, and an object thereof is to provide a method for growing a ZnO based oxide semiconductor layer with excellent crystallinity and low concentration of residual carriers.
Another object of the present invention is to provide a method for manufacturing a semiconductor light emitting device with excellent light emitting characteristics such as a light emitting diode with excellent light emitting efficiency and a laser diode with low threshold current value by growing a ZnO based oxide semiconductor layer with excellent crystallinity.
The prevent inventors have conducted intensive studies to attain the growth of ZnO based oxide semiconductor layer without crystal defects, and with low concentration of residual carries. As a result of the studies, it was found out that the crystal defects and high concentration of the residual carries are resulted from the roughness on a surface of the growing ZnO based oxide semiconductor layer.
Specifically, as described above, if it is attempted to grow ZnO directly on a sapphire substrate at high temperature, ZnO is not sufficiently deposited onto the surface of the sapphire substrate, because the sapphire substrate has the different characteristics from those of ZnO. In addition, the vapor pressure of Zn is high. As a result, the growth of ZnO onto the sapphire substrate does not proceed, and the surface of the substrate becomes rough. The ZnO based oxide semiconductor layer which is grown thereon also has a rough surface resulted from the roughness of the surface of the substrate, and accordingly, has poor crystallinity. Even if the buffer layer is formed at a temperature as low as approximately 300° C., and then, the temperature is elevated to approximately 600° C. and an predetermined ZnO based oxide semiconductor layer is grown, thus-formed ZnO based oxide semiconductor layer still has poor flatness. It is also impossible to obtain a semiconductor layer with excellent crystallinity.
The present inventors have made intensive studies on the reason why excellent flatness cannot be attained even if a buffer layer is formed at a low temperature, and then, the temperature of the substrate is elevated to high temperature and an predetermined ZnO based oxide semiconductor layer is grown thereon. As a result of the studies, it was found the following. At the time when the temperature of the substrate is elevated to high temperature after the buffer layer is deposited, if the temperature is elevated in the state of supplying oxygen as is the case of a conventional material gas of Group V elements such as GaAs and GaN, etching effect occurs by the supplied oxygen during the elevation of the temperature. As a result, the flatness of the surface of the buffer layer is degraded, and the roughness is formed thereon.
Due to the roughness on the surface of the buffer layer, an predetermined ZnO based oxide semiconductor layer which is grown thereon at high temperature also has roughness because of the roughness of the buffer layer, and has poor crystallinity. To overcome this problem, the present inventors have reached the following finding. In the temperature elevating step, the supply of oxygen is stopped to eliminate the influence of oxygen. Then, the temperature of the substrate is elevated to a predetermined temperature and a necessary raw materials such as plasma oxygen and Zn is irradiated onto the buffer layer. In this manner, a semiconductor layer with excellent crystallinity can be obtained.
According to the present invention, a method for growing a ZnO based semiconductor layer includes the steps of: supplying raw materials containing oxygen onto a substrate at a temperature lower than a temperature at which a function layer made of a predetermined ZnO based oxide semiconductor is grown, so as to grow a buffer layer made of ZnO based oxide semiconductor; stopping the
Fons Paul
Iwata Kakuya
Matsubara Koji
Nakahara Ken
Niki Shigeru
Arent Fox Kintner & Plotkin & Kahn, PLLC
Lee Granvill D
National Institute of Advanced Industrial Science and Technology
Smith Matthew
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