JPS6286884A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To perform crystal growth by forming a layer of a composition which is hardly thermally deformed and melt-back at epitaxially growing time at the end of a projection of irregular portion formed on a main surface to allow the irregular portion to faithfully remain. CONSTITUTION:After an N-type InGaAsP layer 2, a P-type InGaAsP layer 101, and a P-type InP layer 102 are formed on an N-type InP substrate 1, diffraction gratings 103 are formed on the layers 101, 102. Then, when a P-type InP layer 104 is formed by a liquid-phase epitaxially growing method on the gratings 103, since the layers 102 remaining on the ends of the projections are hardly thermally deformed or melt-back, the shape of the layer 101 does not alter. Then, the shape of the diffraction grating 103' after crystal growing can faithfully remain in the irregular shape of the layer 101. A semiconductor laser having preferable characteristics can be manufactured by this method.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a semiconductor device in which a semiconductor layer is grown by Evitakin cell growth on a compound semiconductor crystal substrate having an uneven portion on its main surface.

Conventional technology Conventionally, for applications in distributed feedback semiconductor laser devices, distributed reflection semiconductor laser devices, and optical integrated circuits, it has been necessary to grow crystals on compound semiconductor substrates on which fine irregularities of several micrometers have been formed. It is said that Particularly in the case of semiconductor laser devices, the uneven portion consists of an extremely fine periodic structure of 1 μm or less called a diffraction grating, and the device characteristics are determined by the depth of this diffraction grating. The challenge was whether to grow the crystal while maintaining the

However, with GZLAS-based and InGaAsP-based compound semiconductor substrates, the shape of the uneven portions becomes rounded or disappears due to thermal deformation and meltback during epitaxial growth on the substrate, resulting in a problem in which device characteristics cannot be improved beyond a certain level. Met.

A conventional example will be explained using a cross-sectional structural diagram shown in FIG. In Figure 2, 1 is an N-type InP substrate, 2 is an N-type InG4
ASP layer (λg=1.3 μm), 3 is P-type InGaAs
P layer (λg=1.1 μm), 4 is a diffraction grating with a period of 4000 formed on the P-type InGaAsP layer 3, 4' is a diffraction grating after crystal growth, 6 is a P-type InP layer, 6 is a P-type grating nG
It is an aAsP layer (λg=1.1 μl!l). Second
Figure (a) shows gold before crystal growth, and Figure 2 (b) shows gold after crystal growth. FIG. 3 is an example of a conventional liquid phase epitaxial growth method. In FIG. 3, 1o is a compound semiconductor crystal substrate consisting of an InP substrate 1 with a diffraction grating 4 formed on its main surface, an InG4ASP layer 2, and an InGaAsP layer;
11 is an eaAs substrate, the next is a protective cover made of an InP substrate, 12 is a P-type InP metal/V metal, and 13 is a P-type InGa.
14 is a carbon substrate support port, 16 is a sliding rod, and 16 is a carbon crystal growth port.

In this liquid phase epitaxial growth method, the dissociation pressure is compensated by a PH5 atmosphere and a protective cover so that the compound semiconductor crystal substrate does not thermally dissociate while the temperature of the furnace increases. However, due to the mass transport phenomenon, the crystal collapses from the sharp parts where the bonding force of Si atoms is weak, and the depth of the diffraction grating 4 becomes shallow.

Furthermore, when the xncraAsp layer 3 contacts the InP melt 12 during crystal growth, the surface of the InGaAsP layer 3 melts back because the InP melt 12 is unsaturated with As. For this reason, the unevenness of the diffraction grating 4' after crystal growth became extremely small, and device characteristics could not be improved.

Problems to be Solved by the Invention In such conventional semiconductor device manufacturing methods, it is difficult to grow crystals while faithfully leaving the uneven shape on the main surface of a compound semiconductor substrate before crystal growth. Particularly in semiconductor laser devices having a diffraction grating, there is a problem in that good characteristics cannot be obtained if the depth of the diffraction grating becomes shallow.

The present invention has been made in view of the above points, and an object of the present invention is to provide a method for manufacturing a semiconductor device with a simple configuration, which allows crystal growth while faithfully preserving the uneven shape on the main surface of a compound semiconductor substrate.

Means for Solving the Problems The present invention provides that when a new first semiconductor layer is epitaxially grown on a compound semiconductor crystal substrate having an uneven portion on its main surface, the semiconductor layer on the uneven portion touches the tip of the convex portion. It has a two-layer structure of a second semiconductor layer to be formed and a third semiconductor layer to form the base of the convex portion.

By making the composition of the second semiconductor layer less susceptible to thermal deformation at the temperature during epitaxial growth and less susceptible to meltback during epitaxial growth of the first semiconductor layer than the composition of the third semiconductor layer. This solves the above problems.

As is clear from the above structure, the present invention focuses on the fact that the collapse of the uneven portions of the crystal due to heat occurs from the sharp corners at the tips of the uneven portions. This structure eliminates the possibility of collapse. At the same time, we focused on the meltback phenomenon during crystal growth, and by bringing the crystal composition at the tips of the uneven parts closer to the crystal composition growing on the uneven parts, we obtained crystals that do not collapse.

Example An embodiment of the present invention will be described with reference to FIG.

FIGS. 1(fL) and (b) respectively show the cross-sectional structure before and after crystal growth for an InP/InGaAsP DFB laser having an oscillation wavelength of 1.3 μm. In Figure 1, 1 is an N-type InP substrate, 2 is an N-type InG4ASP
layer (λg=1.3 μm), 101 is P-type I n (ra
AsP layer (λg=1.1μm), 102 is P-type InP
layer 103 is an InGaAsP layer 101 and an InP layer 102
103' is a diffraction grating formed on the InGaAsP layer 101 after crystal growth;
104 is a P-type InP layer, and 105 is a P-type InGaASP layer (λg = 1.1 μm).

When the crystal growth explained in FIG. 3 is performed with this structure, In
Since the P layer 102 is less susceptible to thermal deformation than the InGaAsP layer 101, the shape of the diffraction grating 103 is preserved during heating of the furnace. Further, the InP layer 102 grows crystals without causing meltback because the phosphorus pressure in the melt is supersaturated with respect to the melt used to grow the crystals of the InP layer 104. At this time, the shape of the InGaAIP layer 101 does not change,
The shape of the diffraction grating 1Q3' after crystal growth maintains the shape of the InGaAsP layer 101 of the diffraction grating 103 before crystal growth. If the thickness of the InP layer 102 is made thin, the diffraction gratings 103 and 103' can be approximately equal. In this embodiment, the depth of the diffraction grating 103 is '12'.
When the thickness of the InP layer 102 was selected as SOO, the depth of the diffraction grating was 2000. This results in a large grating coupling coefficient (K > 1o, o
The characteristics of the element, which can uniformly and reproducibly obtain cm-'), have been significantly improved.

Although this example describes a diffraction grating made of a combination of InP and InGaAgP, this composition combination is not limited to this, and G4AS and A
The same applies to combinations of lGaAs and other crystals. This can be applied not only to a wide range of <IV group compound semiconductors but also to compound semiconductors such as [1-Vl group compound semiconductors. The conductivity type of each layer is not limited to the structure of this embodiment.

Further, although a liquid phase epitaxial method is shown as an example of a crystal growth method, the same effect can be obtained by a vapor phase epitaxial method.

Effects of the Invention As described above, according to the present invention, it is easy to grow a crystal while faithfully leaving the uneven shape of the uneven portion on the main surface of a compound semiconductor substrate before crystal growth. In the semiconductor laser device having the above structure, the depth of the diffraction grating can be increased, and the device characteristics can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a manufacturing method for a semiconductor device according to an embodiment of the present invention, FIG. 2 is a diagram showing a conventional method for manufacturing a semiconductor device, and FIG. 3 is a configuration of a conventional crystal growth apparatus. It is a diagram. 101--InGaAsP layer, 102----
-InP layer, 103... Diffraction grating before crystal growth, 103'... Diffraction grating after crystal growth, 10
4...InP layer. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure Iθ3 Figure 2: Il'' (

Claims (3)

[Claims] (1) When newly epitaxially growing a first semiconductor layer on a compound semiconductor crystal substrate having an uneven portion on its main surface, the semiconductor layer of the uneven portion forms a second
2 of the semiconductor layer and the third semiconductor layer forming the base of the convex portion.
The second semiconductor layer has a layered structure, and the composition of the second semiconductor layer is less susceptible to thermal deformation at the temperature during epitaxial growth than the composition of the third semiconductor layer, and prevents meltback during epitaxial growth of the first semiconductor layer. A method for manufacturing a semiconductor device made of a composition that is not susceptible to susceptibility. (2) The uneven portion on the main surface is a diffraction grating with a constant period,
2. The method of manufacturing a semiconductor device according to claim 1, wherein the semiconductor device is a distributed feedback semiconductor laser device or a distributed reflection semiconductor laser device. (3) The first semiconductor layer is InP crystal, the second semiconductor layer is In_xGa_(_1_-_x_)AS_yP_(_1
____y_) crystal, the third semiconductor layer is In_x_'Ga
＿(＿１＿−＿x＿′＿)As＿y＿′P＿(＿１＿−
_y_'_) crystal, and x>x' and y<y'.