JPH10163576A - Method for manufacturing compound semiconductor device - Google Patents

Abstract

(57) [Summary] One object of the present invention is to provide a technique for forming a mask on a compound semiconductor. SOLUTION: A mask 6 made of a conductive material is formed on a surface 4 of the nitride compound semiconductor 2 after the dry etching,
Using the mask 6, an impurity is selectively introduced into the nitride compound semiconductor 2. Since a conductive material is used as a mask for introducing impurities, even if a mask component remains on the surface of the compound semiconductor, it does not cause a decrease in conductivity. Therefore, the electric characteristics of the compound semiconductor element are not adversely affected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a compound semiconductor device, and more particularly to a method for manufacturing a nitride compound semiconductor device such as GaN.

[0002]

BACKGROUND ART Nitride compound semiconductors are used for manufacturing light emitting diodes and semiconductor lasers.
Semiconductor lasers in the blue to ultraviolet region using a group III-V nitride compound semiconductor have been developed and are receiving attention.

[0003]

SUMMARY OF THE INVENTION The inventor of the present invention has
Research on impurity doping technology for compound semiconductors by ion implantation.

As a result, when a photoresist mask is formed on the surface of the compound semiconductor after the dry etching and ion implantation is performed, the photoresist remains on the surface even though the photoresist mask is removed, even though the photoresist mask is removed.
It has been found that the remaining photoresist may adversely affect the electrical characteristics of the compound semiconductor device.

The present invention has been made based on the above-described novel findings, and one of its objects is to provide a more improved technique for impurity doping of compound semiconductors.

[0006]

SUMMARY OF THE INVENTION The present invention comprises a step of forming a mask on a surface of a nitride compound semiconductor after dry etching, at least a portion in contact with the surface is made of a conductive material. It is characterized by.

Since a conductive material is used at least in a portion of the mask that comes into contact with the compound semiconductor, even if a mask component remains on the surface of the compound semiconductor, it does not cause a decrease in conductivity. Therefore, the electrical characteristics of the compound semiconductor element are not adversely affected.

As the “conductive material”, it is preferable to use the same material as the metal used for the electrode. This is because, if it is a component of the electrode, even if it remains, it does not affect the current / voltage characteristics of the element and has good compatibility with the compound semiconductor. The “metal used for the electrode” refers to a metal including at least a portion of the metal material in contact with the surface of the compound semiconductor.

The present invention can be applied when a mask needs to be formed on a processing surface such as dry etching.
Short wavelength (blue to blue) using III-V group nitride compound semiconductor
(Ultraviolet region). That is, in a semiconductor laser using a group III-V nitride compound semiconductor, sapphire (Al ₂
O ₃ ) on an insulating substrate, for example, n-type AlGa
An InN-based semiconductor and a p-type AlGaInN-based semiconductor are sequentially grown.

In this case, since the insulating substrate is used, a structure (sandwich structure) in which the growth layer is sandwiched between the p-electrode and the n-electrode is different from the case of the II-VI compound semiconductor such as ZnSe. It cannot be used, and inevitably takes a planar type electrode structure in which either electrode is formed on an insulating substrate. In order to obtain this planar type electrode structure, the compound semiconductor substrate after crystal growth must be processed by dry etching, and ions are selectively implanted into a part of the surface appearing as a result of the dry etching to form the surface. The present invention is applicable to a case where a part is made nonconductive.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

(1) Matters Revealed by the Inventor of the Present Invention First, novel findings discovered by the present inventors will be described.

(A) Description of Phenomenon A semiconductor laser using an AlGaInN-based semiconductor is obtained by sequentially growing an n-type AlGaInN-based semiconductor and a p-type AlGaInN-based semiconductor on an insulating substrate such as sapphire and forming a p-type layer. A part is removed by a dry etching method such as RIE to expose an n-type layer, and electrodes are formed on an unetched p-type surface and an etched n-type surface,
The structure is such that current flows between both electrodes.

In this manufacturing process, a current confinement structure is formed below the p-type electrode so that a current flows only in a part of the active layer before the electrode is formed. Since a conductive AlGaInN-based semiconductor becomes nonconductive when ion-implanted, a method in which a part of the surface of the p-type layer is left as a current constriction structure and made nonconductive by ion implantation is taken as an effective method.

On the other hand, by implanting ions into a part of the surface of the n-type layer and rendering the part nonconductive, foreign matter is temporarily present, and the side wall is exposed by dry etching and the surface of the n-type layer. It is desirable to prevent an electrical short-circuit from occurring even when the active layer or the like in contact with the foreign substance via the foreign matter.

Therefore, a mask pattern is formed on the surface of both the p-type layer and the n-type layer. Conventionally, a photoresist having a thickness of about 1 μm is used as a mask.

When ion implantation is performed using a photoresist as a mask, the current confinement structure corresponding to the mask pattern is formed in the p-type layer because the ion element capability of the mask is sufficient.

However, when the current / voltage characteristics of a laser device manufactured using a photoresist as a mask are measured,
It was found that the voltage at which the current began to flow was about 5 V, which was higher than the voltage expected from the band gap of about 3.5 V. This means that the driving voltage of the laser increases.

That is, in order to flow a predetermined current, it is necessary to apply a voltage higher than the theoretical value, which causes a significant decrease in the luminous efficiency and reliability of the laser. In order to lower the driving voltage, it is necessary to bring this rising voltage closer to a voltage of a theoretical value determined by the band gap.

The above phenomena (defects) have been clarified by the study of the present inventors.

(B) Phenomenon analysis results (and experimental results)
The inventors of the present invention have studied the causes of the above-described problems (causes of high rise voltage). One of the main causes is that the mask material is present on the dry-etched n-type layer surface (interface). It was found that the photoresist was to remain, albeit in trace amounts (by Auger analysis).

That is, when the surface of a dry-etched compound semiconductor is observed with a scanning electron microscope (SEM), although there are some differences depending on the etching conditions, a columnar structure having a height of about 10 nm to 100 nm is formed on the surface. Very dense formation was observed (FIGS. 10 and 11).

Therefore, when a photoresist for a mask is applied to this surface, the photoresist enters between the fine columnar structures and remains after the removal of the mask, and the photoresist forms a barrier, which raises a rising voltage. It turned out to be the cause of the rise. The photoresist barrier causes an increase in contact resistance between the electrode and the compound semiconductor.

FIG. 11 shows dry etching (RI) on the entire surface of AlGaN.
The cross section of the surface after the application of E) is 5000
It is an electron micrograph observed at the magnification of 0 times.

The lower part of FIG. 11 is a cross section of AlGaN.
A columnar structure (cross section near the interface) is seen in the middle. It can be seen that the shape is such that thin columns are bundled.

The height of the columns is about 100 angstroms, and the distance between the columns (width of the groove) is about 10 to 30 angstroms. The upper part of FIG. 11 shows the form of the surface when the columnar structure is viewed obliquely from above, and it can be seen that the surface is not a mirror surface and many voids exist.

It should be noted that when the above sample was manufactured, Al
GaN dry etching conditions were as follows.

Etching gas Cl ₂ Flow rate of etching gas Cl ₂ (1.48 cm ³ / mi)
n) BCl ₃ (50 cm ³ / min) Pressure 2.7 × 10 ⁻⁴ Pa RF power 160 W Substrate temperature 28 ° C. FIG. 10 is a diagram schematically showing the state of the interface of AlGaN. At the interface of the GaN-based compound semiconductor 20 formed on the substrate 10 after the dry etching, many columnar structures are formed. The photoresist, which is an insulator, remains in the gaps of the columnar structure, causing deterioration of the electrical characteristics of the device.

The above phenomenon is caused by GaN, AlGa
Group III (Ga, Al, In) such as N, AlInGaN
It was also confirmed that the compound was commonly found in nitride compound semiconductors of -V group (N).

The same experiment was conducted when not only N (nitrogen) but also As (arsenic) and P (phosphorus) were added as group V elements, and it was found that a similar phenomenon occurs in this case. Was.

(C) Consideration Consideration of Formation of Columnar Structure The main factors for formation of a columnar structure after dry etching are the ease of chemical reaction during RIE (reactive ion etching) and compound semiconductors. Hardness (density)
And so on.

Group III (Ga, Al, In) -V (N) nitride compound semiconductors such as GaN, AlGaN, and AlInGaN are dense and hard, and have a high growth temperature. Further, the chemical reactivity at the time of RIE is considerably lower than that of non-nitride-based compound semiconductors such as GaAs and InP.

The present inventor also performed dry etching on GaAs, InP and the like while changing the conditions, and observed the state of the interface. In this case, although some columnar structures may be observed, it has been found that the columnar structures can be prevented from appearing by setting the optimum etching conditions.

Compounds containing As (arsenic) and P (phosphorus) as group V elements in addition to N (nitrogen) are also:
Focusing on the fact that, like AlGaN and the like, a large number of columnar structures having a considerable height are formed, and the fact that increasing the nitrogen content tends to decrease the chemical reactivity of the nitride compound semiconductor, When a photoresist is used as a mask, the formation of a barrier made of a photoresist material due to the formation of a columnar structure can be considered to be a phenomenon particularly noticeable in a nitride compound semiconductor containing nitrogen.

Countermeasures In consideration of the above phenomena, a mask for ion implantation which does not leave the photoresist and does not affect the rising voltage of the laser device was studied.

An experiment was conducted using a mask structure in which at least the first layer of the mask in contact with the semiconductor surface was made of the same metal as the electrodes formed on the etched surface. As a result, it was confirmed that good current-voltage characteristics of the laser element were obtained (FIG. 9A, this point will be described later).

In the mask having this structure, the electrode metal penetrates into the gaps between the columnar structures. Therefore, even if the electrode metal remains on the surface in the mask removing step, a barrier is formed at the interface between the electrode and the semiconductor as in the case of a photoresist. Without forming
Also, the adverse effect on the contact resistance can be eliminated.

It should be noted that, in addition to the dry-etched surface, when a mask is formed on a surface that has been processed (eg, polished) to form a similar surface with voids,
A similar problem may occur, and it is considered that a similar measure is effective in such a case.

(2) First Embodiment A first embodiment of the present invention will be described below with reference to FIGS. 1 (a) to 1 (c).

In the method of manufacturing a compound semiconductor device of the present embodiment, as shown in FIG. 1A, the surface 4 of the nitride-based compound semiconductor 2 is subjected to dry etching.

Next, as shown in FIG. 1B, a conductive film 6 made of a metal or another conductive material is selectively formed.
This conductive film 6 needs to have the ability to prevent impurity introduction and to be easily processed on the compound semiconductor 2.
For example, a metal electrode material can be used.

Next, as shown in FIG.
Is used as a mask to ion-implant impurities (eg, nitrogen or hydrogen). In the case of a nitride-based compound semiconductor, the region into which impurities are implanted becomes a nonconductor. This makes it possible to narrow down the current (current constriction) and prevent short-circuiting due to foreign matter.

The conductive film 6 may be removed, or may be left as it is and used as an electrode. That is, as described above, the conductive film 6 can be the same as the metal used for the electrode. In this case, the conductive film 6 serves as both the mask and the electrode. That is, the impurity is introduced by self-alignment using the electrode as a mask. Note that the “metal used for the electrode” refers to a metal including at least a part of the metal material in contact with the surface of the compound semiconductor.

The conductive film 6 as the impurity introduction mask is
Since it has conductivity, it does not hinder the electrical characteristics of the element.

(3) Second Embodiment A method of manufacturing a short wavelength laser device having a current confinement structure using an AlGaInN-based compound semiconductor will be described with reference to FIGS.

(A) Step 1 As shown in FIG. 2, a sapphire (Al ₂ O ₃ ) A-plane substrate 40
Each layer of the laser is grown thereon by MOCVD.

That is, first, aluminum nitride (Al)
N) The layer 50 is grown at a growth temperature of 500 ° C. with a thickness of about 500 Å. This aluminum nitride (AlN) layer 50 is made of a sapphire substrate 40 and n-type GaN.
This layer is inserted in order to alleviate the mismatch of the lattice constant with the layer 60 to enable good epitaxial growth of the GaN crystal.

Next, an n-type GaN layer 60 of about 1 μm is grown (growth temperature: 1000 ° C., growth time: about 15 minutes). The surface is a (0001) plane.

[0048] Subsequently, n-type Al _0.15 Ga0. ₈₅ N layer 70
Is grown to about 5000 angstroms. This layer becomes the cladding layer.

Next, an In _0.08 Ga _0.92 layer (active layer) 80
Is grown to about 1000 angstroms. At this time, many layers having slightly different mixed crystal ratios are stacked,
A QW structure is also possible.

Subsequently, a p-type Al _0.15 Ga _0.85 N layer (cladding layer) 90 is grown to about 5000 angstroms.

Next, a p-type GaN layer 100 is grown to about 1 μm.

(B) Step 2 As shown in FIG. 3, etching is performed to the middle of the n-AlGaN layer 70 by dry etching (RIE) (FIG. 3).

(C) Step 3 Next, as shown in FIG. 4, a metal (Ni) layer 110 (thickness of about 0.1 to 0.5 μm) serving as a mask for ion implantation.
Is formed by an electron beam evaporation method or the like. Then, a photoresist 120 is applied thereon. Nickel (Ni)
Is also the material of both the p and n electrodes (at least the constituent components of the electrode portion in contact with the compound semiconductor) to be formed in a later step.

(D) Step 4 Next, as shown in FIG. 5, the photoresist is patterned to form a layer 120 serving as a mask for processing the Ni layer 110.
a, 120b are formed.

(E) Step 5 Next, as shown in FIG.
The Ni layer 110 is etched with acid using Oa and 120b as a mask to form a Ni / resist two-layer mask for ion implantation. Mask (120b, 1) on p-type layer
The width of 10b) is about 2 to 10 μm.

(F) Step 6 Next, the mask (110A, 120a, 110b,
120b), nitrogen ions (N ⁺ ) are ion-implanted. The dopant is not limited to N ⁺ .

As a result, the ion-implanted portion changes to a non-conductor. Reference numbers 130a, 130b, 130
c and 130d denote a non-conductive region. On the other hand, the masked portion is kept on the conductor.

Mask on p-type layer (110b, 120b)
Is set to a width of 2 to 10 μm, the flowing current is also limited to that region, and as a result, current constriction is performed. That is, the non-conductive region 130
c and 130d work to narrow the current.

On the other hand, the non-conductive region 130 in the n-type layer
a and 130b prevent short-circuit between the n-type AlGaN layer 70 and the active layer 80 or the like due to adhesion of foreign matter, or prevent current from flowing on the surface of the n-type AlGaN layer 70 (that is, an unexpected route). This prevents current flow from adversely affecting the laser oscillation, and improves the reliability of the device.

(G) Step 7 The mask layer (110a, 1a) is etched by acid.
20a, 110b, and 120b) are removed, and an n-electrode 150 and a p-electrode 140 made of Ni are formed on the surface. Thus, the semiconductor laser is completed.

In this example, Ni is used for both the p and n electrodes.
Although (single layer) is used, a multilayer film can be used, and different materials and structures can be used for the p electrode and the n electrode.

For example, as the p electrode, Ni (first layer) /
Au (second layer) was used, and Ti (first layer) was used as the n-electrode.
/ Al (second layer) can also be used. In this case, as the conductive material constituting the ion implantation mask in the above step 3, Ni or Ti itself, which is a component of the first layer of the electrode, or an alloy containing at least those components can be used.

FIG. 9A shows the current-voltage characteristics of the semiconductor laser manufactured through the above-described steps. On the other hand, FIG.
(B) shows, as a comparative example, the current-voltage characteristics of the semiconductor laser when a photoresist is used as an ion implantation mask (the other steps are the same).

Even though the steps are substantially the same, the current-voltage characteristics of the semiconductor laser manufactured without using the Ni layer as a mask in the ion implantation step (FIG. 9B)
Means that the rising voltage is high (about 4 V in the case of (a)),
It can be seen that the slope of the rise of the characteristic curve is gentle (that is, the element resistance is high).

That is, comparing the two characteristics, FIG.
It can be seen that the characteristic of (a) is lower than the characteristic of (b) in the same figure, the rising voltage is lower, the slope is steep, the element resistance is lower, and the current / voltage characteristics are excellent.

If the present invention is used for manufacturing a semiconductor laser,
A semiconductor laser with high luminous efficiency and high reliability can be obtained. The present invention is not limited to the manufacture of semiconductor lasers, but can be used for the manufacture of other optical elements such as light-emitting diodes and the manufacture of other semiconductor devices (FETs and the like).

The present invention is not limited to the formation of a mask for selectively introducing impurities, but can be applied to the formation of a light-shielding mask or an etching mask.

[0068]

[Brief description of the drawings]

FIGS. 1A to 1C are cross-sectional views of a device in each step of a method for manufacturing a compound semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a device in a first step of a method for manufacturing a compound semiconductor device according to a second embodiment of the present invention.

FIG. 3 is a sectional view of a device in a second step of the method for manufacturing a compound semiconductor device according to the second embodiment of the present invention.

FIG. 4 is a sectional view of a device in a third step of the method for manufacturing a compound semiconductor device according to the second embodiment of the present invention.

FIG. 5 is a sectional view of a device in a fourth step of the method for manufacturing a compound semiconductor device according to the second embodiment of the present invention.

FIG. 6 is a sectional view of a device in a fifth step of the method for manufacturing a compound semiconductor device according to the second embodiment of the present invention.

FIG. 7 is a sectional view of a device in a sixth step of the method for manufacturing a compound semiconductor device according to the second embodiment of the present invention.

FIG. 8 is a sectional view of a device in a seventh step of the method for manufacturing a compound semiconductor device according to the second embodiment of the present invention.

9A is a diagram showing current-voltage characteristics of a semiconductor laser manufactured by a method according to a second embodiment of the present invention, and FIG. 9B is a diagram showing a comparative example (impurity using a photoresist mask). It is a figure which shows the current-voltage characteristic of the example which introduced.

FIG. 10 is a cross-sectional view of a device schematically showing a surface state when a nitride-based compound semiconductor is subjected to dry etching (RIE).

FIG. 11 shows dry etching (RI) on the entire surface of AlGaN.
The cross section of the surface after the application of E) is 5000
It is an electron micrograph observed at the magnification of 0 times.

[Explanation of symbols]

 Reference Signs List 2 compound semiconductor element 4 processed surface (dry etching processed surface) 6 conductive film 40 sapphire substrate 50 AlN layer 60 n-GaN layer 70 n-AlGaN layer 80 InGaN layer 90 P-AlGaN layer 100 P-GaN 110 Ni electrode layer 120 photo Resist

Claims (1)

[Claims] 1. A compound semiconductor device according to claim 1, further comprising a step of forming a mask on a surface of the nitride compound semiconductor after the dry etching, at least a portion in contact with the surface is made of a conductive material. Production method.