JPH04291978A - Manufacture of compound semiconductor device - Google Patents

Abstract

PURPOSE:To manufacture an uneven shape of a compound semiconductor without processing damage on a crystal surface of a base without dry etching and to manufacture the uneven shape in the same accuracy as that of dry etching. CONSTITUTION:A substance 6 having selectivity of etching for first compound semiconductor 10 and second compound semiconductor crystal 7 is formed in an opposite shape of the uneven shape to the uneven shape of the compound semiconductor, a second compound semiconductor 7 is crystalline grown on a part of a window of the compound semiconductor crystal exposed out of patterning, and then the substance 6 is removed by wet etching.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor device, and more specifically, the present invention relates to a method for manufacturing a semiconductor device, and more specifically, it relates to a method for manufacturing a semiconductor device, and more specifically, it relates to a method for manufacturing a semiconductor device. The present invention relates to a method of manufacturing a semiconductor device that improves the method of forming a diffraction grating made of.

[0002] In order to obtain an optical semiconductor device that operates only for a single wavelength, a distributed feedback laser diode (DFB-LD), which has a diffraction grating made of fine concavo-convex shapes of a compound semiconductor inside the element, is used.
Optical semiconductor devices such as ack lasers) and optical waveguide devices have been put into practical use. In order to improve the operating characteristics of such an element, it is essential to strictly control the dimensions of the fine irregularities, such as several tens of nanometers in height.

0003

[Prior art] In the normally used fine unevenness processing technology, two
A striped resist pattern is drawn on the surface of a compound semiconductor in the form of a diffraction grating using beam interference exposure or electron beam exposure, and in the subsequent process, the crystal surface is etched using wet etching to create fine irregularities on the crystal surface. . Here, for example, a DFB that oscillates at 1.55 μm
- The dimensions of the diffraction grating-like fine irregularities used in the LD are very fine, with a period of about 240 nm and a height of about 30 nm. In particular, when the height is much smaller than the period and wet etching is used, fluctuations in the etching rate due to etching solution concentration, temperature, etc. make it difficult to control the height dimension of the fine uneven shape. For this reason, reactive ion etching (RIE) has recently replaced wet etching.
) has come into use. In this type of dry etching, gas in a plasma state is used, and although the accuracy of machining the uneven shape has been improved by using dry etching, there is a problem that machining damage occurs near the surface of the underlying crystal during this machining process. was.

0004

[Problems to be Solved by the Invention] As described above, in the conventional method of applying micro-roughness to the crystal surface using etching technology, the dimensional accuracy of the uneven shape is low in wet etching, and the dimensional accuracy of the uneven shape in dry etching is low. There is a problem that machining damage occurs.

The present invention provides a method for producing fine irregularities on the surface of a compound semiconductor crystal such as InP or InGaAsP without dry etching the compound semiconductor crystal, thereby preventing processing damage from occurring on the underlying crystal surface. The purpose of the present invention is to fabricate the uneven shape without any process, and also to produce the uneven shape with high precision equivalent to dry etching.

[0006]

[Means for Solving the Problems] A method according to the present invention includes forming a mask layer covering the surface of the first compound semiconductor at a predetermined period on the crystal of the first compound semiconductor, and exposing the crystal of the first compound semiconductor. selectively growing crystals of a second compound semiconductor in a window portion of the first compound semiconductor, and then removing the mask layer by wet etching; It is characterized by having etching selectivity with respect to compound semiconductors. 2 and 3 are diagrams explaining the principle of the present invention.

[0007] In the present invention, [1] A substance capable of selectively etching the first compound semiconductor crystal, such as silicon oxide or silicon nitride, is applied to the entire surface of the base crystal 10 made of the first compound semiconductor crystal using plasma. A vapor deposited film 2 is formed by vapor deposition using CVD or the like (see (A) in FIG. 2). The thickness of the deposited film 2 is, for example, approximately 10 nm. Later process (see (D) in Figure 2)
When etching this material, it is necessary to prevent the underlying crystal from being etched.

[2] A resist 3 is applied to the entire surface of the base crystal 10 of the first compound semiconductor substrate that has been vapor-deposited (see FIG. 2B).

[3] A diffraction grating is formed on a crystal substrate by exposing the resist 3 onto the diffraction grating using a two-beam interference exposure method, an electron beam exposure method, or other exposure method, and then developing the exposed resist 3. A resist pattern 4 having a shape is formed (see (C) of FIG. 2).

[4] The base crystal 10 on which the resist pattern 4 has been applied is treated with an acid such as hydrofluoric acid to form the resist pattern 4.
The removed portion of the deposited film 2 of silicon oxide or silicon nitride is removed by etching, and a resist pattern in the form of a diffraction grating is transferred to the deposited film 2 of silicon oxide or silicon nitride (see (D) in FIG. 2). Note that since wet etching is performed in this step, the underlying crystal 1 is not damaged.

[5] The crystal substrate is cleaned with an organic solvent to remove all the resist pattern 4 on the surface (see FIG. 3A).

[6] Next, a crystal consisting of a second compound semiconductor crystal is grown on the crystal substrate on which a vapor deposited film pattern 6 of silicon oxide or silicon nitride has been applied, so that the pattern is formed by crystal growth. It is transferred as a layer to the compound semiconductor growth film 7 (see FIG. 3B). In this step, the height of the compound semiconductor growth film 7 is precisely controlled by the growth time, and a highly accurate uneven structure can be obtained. The general growth rate of MOVPE is 10 nm/min, so in order to form a compound semiconductor growth film of about 30 nm with an accuracy of ±1 nm, it is necessary to control the growth time with an accuracy of 6 seconds. It is fully possible with current technology.

[7] Next, by treatment with hydrofluoric acid,
The deposited film pattern 6 on the surface of the substrate is removed by etching. Therefore, the material of the deposited film 6 must have etching selectivity also with respect to the second compound. Note that the first compound semiconductor and the second compound semiconductor may be of the same type or may be of different types. Through the above steps, a diffraction grating-like finely uneven layer 10 is formed on the surface of the compound semiconductor crystal (see FIG. 3B).

[0014] Preferred embodiments of the present invention will be explained below. As the crystal growth method in [6] above, it is preferable to use metal organic vapor phase epitaxy (MOVPE) or molecular beam epitaxy (MBE), which allows easy control of the thickness of the grown layer. In the present invention, for example, the underlying crystal is an InP crystal substrate, and the finely textured layer is InP or Inx Ga 1-x As 1-y Py (0≦x≦
It can be applied to manufacturing a compound semiconductor device satisfying 1,0≦y≦1).

When forming fine irregularities with InP crystal, MOVPE is used to grow InP crystal on the InP crystal substrate.
In the growth, trimethylindium (TMIn) is used as the growth raw material.
), phosphine (PH3) was used, and the growth pressure was set to about 0.
．． 1 atm, growth temperature about 600℃, growth rate about 1/hour.
The general growth condition is µm. When a crystal is grown under such growth conditions, the shape of the InP or InGaAsP growth layer 7 when viewed from a cross section in the silicon oxide stripe direction (that is, the extension direction of the deposited film 6) as shown in FIG. 1 is such that the side surfaces are (111 ) plane, and the upper flat surface becomes a (100) plane. In the fabrication of InP uneven shapes by this growth, the upper limit of the height of the uneven shapes cannot exceed the height at which the (111) planes intersect, so it is limited by the width of the window of the silicon oxide stripe. Width is 500n
If it is about m, it is a commonly used unevenness height2
A trapezoidal uneven shape with a height of 0-40 nm can be produced.

In the above case, a stripe of InP crystal is transferred onto an InP crystal substrate.
Inx Ga 1-xAs1 substantially lattice matched to P
-y Py (0≦x≦1, 0≦y≦1) crystal, and the fine unevenness layer is InP or the Inx Ga 1-x
As1-y Py Inx Ga 1-x As1-y Py which is substantially lattice matched to InP which has a different composition from the crystal
(0≦x≦1, 0≦y≦1). By employing InGaAsP crystal for the growth layer, the coupling between the light guided within the device and the diffraction grating shape becomes weaker than in the case of InP crystal. Therefore, the growth of InGaAsP crystals is effective in producing devices in which the bond is designed to have a very weak value. In this case, in addition to the above-mentioned raw materials, triethyl gallium (TEGa), arsine (AsH3), etc. are generally used as growth raw materials.

In the present invention, as a deposited film on the surface of a compound semiconductor, a silicon oxide or silicon nitride film has etching selectivity with respect to the compound semiconductor, has good crystallinity and adhesion, and has a second layer on top of it. It is a film-forming material that has the favorable property that compound semiconductors do not grow.

[0018]

[Operation] In the present invention, a diffraction grating-like fine unevenness is formed on the compound semiconductor surface by wet etching of a resist film drawn on the underlying crystal surface and crystal growth on the crystal surface. Therefore, whereas in the past, machining damage occurred to the crystal during etching treatment, by using the present invention, fine irregularities in the form of a diffraction grating can be formed on the surface of a compound semiconductor without causing machining damage. Can be done. In addition, the height of the uneven shape is determined by the film thickness (i.e. growth time) of the crystal grown on the crystal that has been patterned into a diffraction grating with a silicon oxide or silicon nitride film, so the in-plane height is Variations in each unevenness can be suppressed to 3% or less.

As described above, by using the present invention, it becomes possible to fabricate a diffraction grating-like fine uneven shape with high dimensional accuracy without causing processing damage to the underlying crystal surface.

[0020]

[Example] Manufacturing the present invention on an InP crystal substrate 1.
A distributed feedback laser (DFB-LD) that oscillates at 55 μm will be explained as an example. Although silicon oxide is used as an example of the deposited film for patterning, the method of implementing the present invention is the same even if silicon nitride is used. In the case of a DFB-LD (substrate laser) having a diffraction grating on the crystal substrate side of the active layer, [1
] An n-type InP (100)-oriented substrate is used as the base crystal 1, and a vapor deposition film 2 of silicon oxide or the like is deposited on the entire surface thereof to a thickness of 10 to 20 nm by plasma CVD or the like (see (A) in FIG. 2). ).

[2] Vapor-deposited base crystal 1 (hereinafter referred to as InP
A resist 3 ((B) in FIG. 1) is coated on the entire surface of a crystal substrate 1.
(see (B) in Figure 2). [3] The resist 3 is exposed onto the diffraction grating by a two-beam interference exposure method, an electron beam exposure method, or other exposure method (see (C) of FIG. 2). Here, the period of the stripes is about 240 nm, and the stripe direction is (110). After this exposure treatment, the resist 3 is developed, and a diffraction grating pattern is formed on the silicon oxide vapor deposited film 2 on the InP crystal substrate 1 using the resist (see (D) in FIG. 2).
.

[4] The InP crystal substrate 1 patterned with the resist 3 is cleaned with hydrofluoric acid, and the resist 3 is removed.
The silicon oxide in the portion of the window where the was removed is removed by etching, and a resist pattern in the form of a diffraction grating is transferred to the silicon oxide vapor deposited film 2 (see (D) in FIG. 3). [5] After transferring the diffraction grating resist pattern to the silicon oxide vapor deposited film 2, the InP crystal substrate 1 is cleaned with an organic solvent to remove all the resist 3 on the surface (Fig. 3
(See (A)).

[6] Next, I was deposited on the InP crystal substrate which was patterned into a diffraction grating using silicon oxide.
Perform nP crystal growth. [7] After crystal growth is performed on the InP crystal substrate on a diffraction grating, the crystal is washed with hydrofluoric acid and the silicon oxide film on the surface of the substrate is etched away. As described above, a diffraction grating-like finely uneven layer made of a compound semiconductor is formed on the surface of the InP substrate without etching the InP crystal substrate. [8] A base crystal substrate for fabricating a DFB-LD is fabricated as described above, and then a laser structure consisting of an optical waveguide layer and an active layer is grown on the crystal substrate by a conventional method. That is, in the case of a laser, there is an InGaAsP guide layer, an InGaAsP active layer, an InP cladding layer, an InGaAsP guide layer, an InGaAsP active layer, an InP cladding layer, and an InGaAsP guide layer.
A contact layer of GaAsP is sequentially formed. In the case of a waveguide, the above layer structure except the active layer is sequentially formed.

In the above embodiments, the case of a DFB-LD (substrate laser) having a diffraction grating on the crystal substrate side of the active layer has been described, but the present invention is a DFE-LD having a diffraction grating on the upper side of the active layer. (Top laser) is also applied in exactly the same way.

In this case, an active layer and an optical waveguide layer made of InGaAsP crystal are grown on an InP crystal substrate,
Steps [1] to [7] are performed on the InGaAsP optical waveguide layer to form fine irregularities on the diffraction grating. The growth layer forming the uneven layer is InP or a crystal with the same composition as InGaAsP, which is the optical waveguide layer, and after removing the silicon oxide film, InP is grown on the top of the uneven layer.
Grow crystals.

[0026]

As described above, by using the present invention, fine irregularities can be formed on the surface of an InP or InGaAsP crystal without dry etching the compound semiconductor crystal. For this reason, various layers,
The uneven shape can be manufactured with high dimensional accuracy without causing processing damage to the underlying crystal surface. In addition, wet etching is used so as not to affect the precision of the fine irregularities. As described above, the present invention greatly contributes to improving the quality of semiconductor devices.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a step immediately before forming fine irregularities in the method of the present invention.

FIG. 2 is a diagram showing the steps up to forming stripes of a deposited film in the method of the present invention.

FIG. 3 is a diagram illustrating the process from forming stripes of a vapor-deposited film to the final step in the method of the present invention.

[Explanation of sign]

1 Base crystal 2 Vapor deposited film 3 Resist 4 Resist pattern 6 Deposited film pattern 7 Compound semiconductor growth film 10 Fine irregularities

Claims (4)

[Claims] 1. A method for manufacturing a compound semiconductor device having a diffraction grating made of fine concavo-convex shapes of a compound semiconductor therein, wherein a surface of the first compound semiconductor is patterned at a predetermined period on a crystal of the first compound semiconductor. forming a covering mask layer, selectively growing crystals of a second compound semiconductor on the exposed window portion of the first compound semiconductor, and then removing the mask layer by wet etching. . A method for manufacturing a compound semiconductor device, wherein the mask layer has etching selectivity with respect to the first and second compound semiconductors. 2. The method for manufacturing a compound semiconductor according to claim 1, wherein the material having etching selectivity is silicon oxide or silicon nitride. 3. The underlying crystal is an InP crystal substrate, and the finely textured layer is InP or Inx Ga 1-x As 1-y Py (0≦x
3. The method for manufacturing a compound semiconductor device according to claim 1 or 2, characterized in that ≦1, 0≦y≦1). 4. Inx Ga 1-x As 1-y Py (0≦x
≦1,0≦y≦1) crystal, and the fine unevenness layer is InP.
Alternatively, Inx substantially lattice-matched to InP having a different composition from the Inx Ga 1-x As 1-y Py crystal.
Ga1-xAs1-y Py (0≦x≦1,0≦
3. The method for manufacturing a compound semiconductor device according to claim 1, wherein y≦1).