JPH10256236A - Dry etching method and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a vertical working sectional form by making a mixture gas as etchant to form a step at a work by dry etching method contain the mixture gas, which has at least one nitrogen atoms of nitrogen gas, ammonium gas, nitrogen dioxide gas, or the like. SOLUTION: The pattern of an SiO2 mask 1 is made on an n-type lnP substrate 2, using a heat CVD method and a lithography technique. Next, this water is placed on the cathode electrode of an etching device which has parallel board type of electrode structure, and the mixture gas of methane and hydrogen is introduced into an etching processor, and it is supplied with high-frequency power, where an electrode on which a sample is placed is a cathode to cause glow discharge, whereby reactive ion etching is performed to make a step at the substrate. Since the reactive gas contains nitrogen gas, a nitride 3 accumulates on the sidewall of etching, and side etching does not occur, and vertical sectional form is obtained. As compared with the case where nitrogen is not added, superior dimensional controllability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a compound semiconductor device, and more particularly to a dry etching technique suitable for manufacturing a compound semiconductor element and a semiconductor element structure characterized by the dry etching technique.

[0002]

2. Description of the Related Art Techniques for forming a waveguide structure of a compound semiconductor device by etching are used for various compound semiconductor devices such as a semiconductor laser and an optical modulator. The wet etching has long been used for the etching of compound semiconductors. However, in recent years, there has been an increasing demand for improving the processing dimension uniformity within the wafer surface, and research on dry etching technology has been advanced. Conventional dry etching techniques for compound semiconductors are described systematically and in detail in Integrated Circuit Process Technology Series Semiconductor Dry Etching Techniques, edited by Wei Tokuyama and Sangyo Tosho Co., Ltd. As described in detail in this document, two systems of a hydrocarbon-based gas and a chlorine-based gas have been studied as a dry etching method for a compound semiconductor. Of these, etching with a hydrocarbon-based gas is widely used for etching InP-based materials. This is because it is difficult to remove the In chloride, and it is difficult to obtain a good processed shape by etching the InP-based material with the chlorine-based gas. As a known example of a compound semiconductor device manufactured by dry etching of a hydrocarbon-based gas, for example, the reliability test result of an InGaAsP embedded semiconductor laser in which an optical waveguide is formed by reactive ion etching of a methane / hydrogen mixed gas is described in 1996. It was reported in the 57th Autumn Meeting of the Japan Society of Applied Physics 8a-KH-8.

[0003]

The above-mentioned conventional dry etching technology of hydrocarbon gas has the following problems.
In dry etching using methane gas or a mixed gas of ethane gas and hydrogen, side etching by hydrocarbon radicals proceeds simultaneously with etching in the vertical direction.
As a result, the perpendicularity of the processed cross-sectional shape is impaired. In particular, when the object to be etched has a multilayer structure of different materials, the side etching rates are different between the different materials, so that the perpendicularity of the cross-sectional shape is significantly impaired. However, in order to enhance the processing dimension controllability, it is desirable to obtain a vertical processing sectional shape without side etching. This is because if the processed cross-sectional shape is vertical, the mask pattern dimensions can be transferred with high accuracy, and thus high dimensional controllability is obtained.

A first object of the present invention is to provide a method for dry-etching a hydrocarbon-based gas which can obtain a vertical processed sectional shape without side etching. A second object of the present invention is to provide a semiconductor device manufactured by using the dry etching method of the present invention.

[0005]

SUMMARY OF THE INVENTION A first object of the present invention is to provide:
In a dry etching method for forming a step on a workpiece such as a semiconductor substrate on which a mask pattern has been formed in advance by using a plasma of a mixed gas containing a hydrocarbon gas as an etchant, the mixed gas may be a nitrogen gas or an ammonia gas.
Alternatively, it is achieved by including a gas (gas molecule) of a compound having at least one nitrogen atom such as nitrogen dioxide gas. Further, in the above dry etching method, the above is achieved by using methane gas or ethane gas as the hydrocarbon gas. Further, in the above dry etching method, it is achieved by including hydrogen gas in the mixed gas. Further, in the above dry etching method, the above is achieved when the mask pattern is silicon oxide or silicon nitride. Further, in the above dry etching method, the object is achieved in that the workpiece includes a III-V compound semiconductor or a III-V mixed crystal semiconductor. Here, the group III-V compound semiconductor refers to a compound semiconductor material composed of a group III element such as Al, Ga, and In and a group V element such as N, P, As, and Sb. The mixed crystal semiconductor particularly refers to a compound semiconductor material having three or more constituent elements (three or more elements).

A second object of the present invention is attained by providing a semiconductor device manufactured by using the above dry etching method.

The operation of the present invention will be described below with reference to FIG.

FIG. 1 is a structural diagram showing a cross-sectional shape of a sample in which a step is formed on an InP substrate 2 on which an SiO ₂ mask pattern 1 has been formed in advance by reactive ion etching of a methane / hydrogen / nitrogen mixed gas of the present invention. It is. In the present invention, since a gas containing nitrogen is mixed in the reactive gas, nitride is deposited on the etching side wall. Since the nitride has the effect of protecting the side wall from radical attack, the etched cross section is vertical. More specifically, the nitride tends to deposit on the etched bottom, but the nitride does not deposit on the etched bottom due to ion bombardment. On the other hand, since the sidewalls are hardly subjected to ion bombardment, nitride is deposited and acts as a sidewall protective film.

Therefore, the dry etching method of the present invention,
In other words, as an example of an element formed by applying the method of manufacturing a semiconductor element, in a semiconductor element having a step (convex portion) formed in a substrate or a semiconductor layer laminated thereon, a region along a step side surface is formed. A structural feature that the nitrogen content is higher than the region along the etching bottom surface (upper surface of the concave portion) which is a shoulder with respect to the step (convex portion) can be found. At the bottom of the etch, the nitride is removed shortly after deposition by ion bombardment, but traces of nitrogen atoms may remain. However, the nitride is likely to adhere to the side walls of the convex portions that are not subjected to ion bombardment, and local diffusion of nitrogen atoms during the adhesion may occur. Therefore, there is a clear difference in the amount of nitrogen contained in both regions as described above. In each region, the nitrogen atom replaces the lattice site of the same group V element in the group III-V compound semiconductor crystal, enters between lattices, and the mode differs depending on the process conditions. Further, the degree of remaining in the semiconductor element also depends on the process conditions.
However, in any case, since the distribution of nitrogen atoms is biased toward the so-called interface of the side surface of the convex portion or the bottom surface of the etching portion, there is almost no possibility that the nitrogen atoms diffuse to the center of the convex portion and impair the original characteristics of the semiconductor element. Rather, nitrogen atoms may be biased toward the interface to improve the electrical insulation.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to Examples 1 and 2 and specific examples disclosed in FIGS.

<First Embodiment> First, a first embodiment of the present invention will be described in detail with reference to FIG.

An SiO ₂ mask pattern (width 1.5 μm, thickness 500 nm) was formed on a 2-inch n-type InP substrate 2 by using a thermal CVD method and a lithography technique (FIG. 2A). Next, the wafer is placed on the cathode electrode of an etching apparatus having a parallel plate electrode structure, and a mixed gas of methane, hydrogen, and nitrogen is mixed at 100 sccm (mixing ratio).
5: 20: 1, sccm is the flow rate per minute under atmospheric pressure (cc unit)
Is introduced into the etching apparatus, and at a gas pressure of 50 mT, a high-frequency power of 300 W is supplied using the electrode on which the sample is placed as a cathode to cause glow discharge, thereby performing reactive ion etching to form a 3 μm step on the substrate. Formed (Fig. 2
(b)). In the present etching step, since the reaction gas contained nitrogen gas, the nitride 3 was deposited on the etching side wall, no side etching occurred, and a vertical cross-sectional shape was obtained.

At this time, the angle between the etching side wall and the etching bottom was 90 °. In addition, reflecting the high processing dimension controllability of the dry etching method in which side etching does not occur according to the present invention, the mesa width distribution in the 2-inch wafer surface is 1.5 μm ± 0.05 μm, and the surface when no nitrogen is added is provided. Excellent dimensional controllability was obtained as compared with the internal distribution of 1.5 μm ± 0.1 μm. Further, in the present embodiment, an example using nitrogen gas was described, but the same effect was obtained by using ammonia gas or nitrogen dioxide gas.

<Embodiment 2> Next, a second embodiment will be described in detail with reference to FIG.

An n-type InP buffer layer (thickness 0.3 μm) 4, an undoped multiple quantum well active layer 5 and a p-type InP cladding layer (thickness 2.0 μm) are formed on an n-type InP substrate 2 by metal organic chemical vapor deposition. 6, p
InGaAs contact layers (thickness: 0.2 μm) 7 were sequentially formed.
The multiple quantum well active layer 5 is formed by sandwiching five InGaAs well layers (thickness: 60 nm) with six InGaAsP barrier layers (thickness: 100 nm, composition wavelength: 1.15 μm). Next, 300 nm thick Si is deposited by thermal CVD.
O ₂ film is formed using conventional lithography techniques width 1.5
Micron SiO ₂ stripes 1 were formed (FIG. 3A).

Next, this wafer is loaded on the cathode electrode of an etching apparatus having a parallel plate electrode structure, and a mixed gas of ethane, hydrogen and nitrogen, 50 sccm (mixing ratio: 4: 10: 1), is introduced into the etching apparatus. Then, at a gas pressure of 80 mT, reactive ion etching was performed by supplying glow discharge by supplying high frequency power of 13.56 MHz and 200 W using the electrode on which the sample was placed as a cathode, thereby forming a 3 micron step on the substrate. At this time, since the reaction gas contained nitrogen, the cross-sectional shape after etching became vertical (FIG. 3B). Thereafter, the polymer deposited on the SiO ₂ pattern 1 during the etching was removed by oxygen plasma ashing, and then carried into a metal organic chemical vapor deposition furnace. Next, a phosphine gas, trimethylindium, ferrocene, and methyl chloride were introduced at a growth temperature of 600 ° C. to grow an Fe-doped semi-insulating InP current confinement layer (thickness: 3 μm) 8 (FIG. 3C). ). Since compound semiconductors such as InP do not grow on SiO ₂ stripes, InP
The layer exposes the semiconductor exposed surface selectively. However,
A semiconductor may be deposited in an amorphous or polycrystalline state on the SiO ₂ stripe, but such a precipitation can be suppressed by adding a small amount of methyl chloride as in this example, and the embedded surface is flattened. Can be

After the buried growth, the SiO ₂ stripe 1 was removed with dilute hydrofluoric acid to form a p-side electrode 9, the back surface of the substrate was thinned by polishing, and an n-side electrode 10 was formed on the back surface (FIG. 3 (d)). )). Finally, by dividing and cleaving, a semiconductor laser having an emission wavelength of 1.55 μm (μm) was manufactured.

The fabricated laser device had a low threshold voltage and a high efficiency of 0.45 W / A under a continuous condition at room temperature with a threshold current of 10 mA and high efficiency. In addition, as a result of conducting a constant light output energization test at 50 ° C and 5 mW, the estimated life was 20
10,000 hours were obtained. In addition, reflecting the high processing dimension controllability without side etching of the present invention, the oscillation wavelength yield is
The device could be manufactured at a low cost, as high as 95%.
In this embodiment, the case where the present invention is applied to a semiconductor laser in the 1.55 μm band is described, but the present invention is also applicable to a semiconductor laser in the 1.3 μm band and other wavelength bands. Further, in this embodiment, the case where the reactive ion etching is used has been described, but it goes without saying that the same effect can be obtained even when applied to other dry etching such as reactive ion beam etching and ion beam etching. Further, although this embodiment described the case of using SiO ₂ as a mask material, Si ₃ N
Other materials such as ₄ may be used. In the present embodiment, the case where the present invention is applied to a semiconductor laser has been described.
It could also be applied to other optical devices such as optical modulators, photodiodes, and optical waveguide devices. Further, in this embodiment, an example using a mixed gas of ethane / hydrogen / nitrogen has been described, but methane may be used as the hydrocarbon gas. Further, another gas such as argon or oxygen may be added to the mixed gas.

The buried hetero (BH) type structure of this embodiment, that is, the upper part of the n-type InP substrate 2, the n-type InP buffer layer 4, the undoped multiple quantum well active layer 5, the p-type InP clad layer 6, and the p-type InGaA
In a structure in which both sides of a ridge-shaped structure (simply protruding from the InP substrate 2) composed of the s contact layer 7 are embedded with a semi-insulating InP current confinement layer 8, both sides of the ridge portion are formed. Is a semi-insulating InP current confinement layer 8 of the InP substrate 2
It was confirmed that nitrogen atoms were present at a higher concentration along the bonding interface with. However, even if the concentration was high, the absolute value was small, and did not penetrate into the ridge where the light emitting region was located. Therefore, no adverse effect on the laser diode characteristics was observed.

[0020]

According to the present invention, dry etching with excellent perpendicular anisotropy of a compound semiconductor can be realized. The use of the present invention is effective in lowering the cost by improving the yield in manufacturing compound semiconductor devices.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the operation of the present invention.

FIG. 2 is a diagram illustrating an embodiment of the present invention.

FIG. 3 is a diagram illustrating an embodiment of the present invention.

[Explanation of symbols]

1 ... SiO ₂ mask, 2 ... InP substrate, 3 ... nitride, 4 ... n-type InP
Buffer layer, 5 ... undoped multiple quantum well active layer, 6 ... p
-Type InP cladding layer, 7 ... p-type InGaAs contact layer, 8 ... Fe
Doped semi-insulating InP current confinement layer, 9 ... p-side electrode, 10 ... n-side electrode.

Claims (12)

[Claims] 1. A dry etching method for forming a step on a workpiece on which a mask pattern has been previously formed by using a plasma of a mixed gas containing a hydrocarbon gas as an etchant, wherein the compound having at least one nitrogen atom in the mixed gas is used. A dry etching method characterized by mixing the above gases. 2. The dry etching method according to claim 1, wherein said hydrocarbon gas is methane gas. 3. The dry etching method according to claim 1, wherein said hydrocarbon gas is ethane gas. 4. The dry etching method according to claim 1, wherein said mixed gas contains a hydrogen gas. 5. The dry etching method according to claim 1, wherein said mask pattern is silicon oxide. 6. The dry etching method according to claim 1, wherein said mask pattern is silicon nitride. 7. The dry etching method according to claim 1, wherein the workpiece includes a III-V compound semiconductor. 8. The dry etching method according to claim 1, wherein the workpiece includes a group III-V mixed crystal semiconductor. 9. The dry etching method according to claim 1, wherein the gas of the compound having at least one nitrogen atom is a nitrogen gas. 10. The dry etching method according to claim 1, wherein the gas of the compound having at least one nitrogen atom is ammonia gas. 11. The dry etching method according to claim 1, wherein the gas of the compound having at least one nitrogen atom is a nitrogen dioxide gas. 12. A semiconductor device manufactured by using the dry etching method according to claim 1.