JPH098355A - Production of iii-v compound semiconductor - Google Patents

Abstract

PURPOSE: To recover the damage after dry etching by treating a III-V compound semiconductor represented by a specified formula with a specified acid after dry etching. CONSTITUTION: A GaN based semiconductor is deposited on a sapphire substrate 3 by MOVPE through two step growth using a GaN buffer layer 2 and a GaN layer 1 is formed thereon. A p-type GaN layer 1 thus obtained is coated with footrests and dry etched and then it is treated with a solution containing phosphoric acid and sulfuric acid. The volumetric mixing rate is preferably set in the range of 5:1-1:5. The time required for treatment is in the range of 30sec and 60min depending on the size of damage. The temperature is preferably in the range of 200-260 deg.C. This method can recover the damage after dry etching. The III-V compound semiconductor is represented by Inx Gay Alz N (where x+y+z=1, 0<=x<=1, o<=y<=1, 0<=z<=1).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a 3-5 group compound semiconductor.

[0002]

2. Description of the Related Art As a material for a light emitting device such as an ultraviolet or blue light emitting diode (hereinafter, also referred to as an LED) or an ultraviolet or blue laser diode, a general formula In _x Ga _y Al _z N (provided that x + y + z) is used. = 1, 0 ≤
A 3-5 group compound semiconductor represented by x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) is known. Since the Group 3-5 compound semiconductor has a band gap that can be controlled by the composition of the Group 3 element, it can be used for a light emitting device that emits light in the visible light region to the ultraviolet light region. Furthermore, the 3-
Since the group 5 compound semiconductor has a direct transition type band structure, a light emitting device having high luminous efficiency can be obtained by using the group 3-5 compound semiconductor. In particular, an In concentration of 10% or more is particularly important for application to display applications because the emission wavelength can be in the visible region of violet and longer wavelengths.

In order to manufacture a light emitting device using the compound semiconductor, it is generally necessary to perform etching for forming an electrode or for device separation. As etching, so-called wet etching and dry etching are generally known. However, since the compound semiconductor is chemically very stable, no etchant (etchant) having a practical etching rate for the compound semiconductor is known in wet etching.
On the other hand, in the so-called dry etching method of etching the compound semiconductor in an atmosphere containing plasma, 100
High-speed etching of Å / min or more is possible. But,
When dry etching is performed, there has been a problem that electrical or optical properties are deteriorated such that the conductivity is remarkably reduced or the intensity of emission spectrum is weakened after etching. Such deterioration is generally called etching damage, and when a light emitting device is manufactured using the compound semiconductor that has been damaged by etching, there is a problem that the driving voltage becomes high or the light emission efficiency becomes low.

[0004]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a general formula In _x Ga _y Al _z N (where x + y + z = 1,0).
≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) 3-5
An object of the present invention is to provide a method for recovering etching damage when dry etching is performed on a group compound semiconductor to form electrodes and the like, and for manufacturing a group 3-5 compound semiconductor of good quality.

[0005]

Means for Solving the Problems The inventors of the present invention have made earnest studies in view of such circumstances, and as a result, dry etching of the Group 3-5 compound semiconductor, followed by treatment with a specific acid is performed by dry etching. The inventors have found that it has a great effect in recovering damage, and have reached the present invention.

That is, the present invention is the invention described below. [1] general formula In _x Ga _y Al _z N (provided that, x + y +
z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1), and the dry etching is performed on the Group 3-5 compound semiconductor,
A method for producing a Group 3-5 compound semiconductor, comprising a step of treating with a solution containing phosphoric acid and sulfuric acid. [2] the general formula In _x Ga _y Al _z N (provided that, x + y +
z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1), and the dry etching is performed on the Group 3-5 compound semiconductor,
A method for producing a Group 3-5 compound semiconductor, comprising the steps of treating with a solution containing phosphoric acid and sulfuric acid, and then performing heat treatment at 400 ° C. or higher in an inert atmosphere. [3] The method for producing a Group 3-5 compound semiconductor according to [1] or [2], wherein the dry etching uses a rare gas, a molecule containing a halogen element, or a mixed gas thereof.

Next, the present invention will be described in detail. The group III-V compound semiconductor in the present invention, the general formula an In _x Ga _y
Al _z N (where x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦
It is a 3-5 group compound semiconductor represented by y ≦ 1, 0 ≦ z ≦ 1) or a 3-5 group compound semiconductor having a laminated structure thereof. Particularly, a structure in which the compound semiconductor having a smaller band gap is sandwiched between the p-type and n-type compound semiconductors is called a so-called double heterojunction structure and is particularly important because it can emit light with high emission efficiency. Is. The Group 3-5 compound semiconductor crystal in the present invention is usually obtained by growing it on a substrate.
Examples thereof include iC, Si, sapphire, spinel, ZnO and the like. In particular, it is known that a GaN layer with high crystallinity can be grown on sapphire by using a thin film of AlN or the like as a buffer layer, which is preferable.

As the method for producing the 3-5 group compound semiconductor, a molecular beam epitaxy (hereinafter sometimes referred to as MBE) method, a metal organic chemical vapor deposition (hereinafter sometimes referred to as MOVPE) method, Hydride vapor phase growth (hereinafter, HV
Sometimes referred to as PE. ) Method. In addition,
When the MBE method is used, nitrogen gas may be nitrogen gas,
Gas source molecular beam epitaxy (hereinafter referred to as G, which is a method of supplying ammonia and other nitrogen compounds in a gaseous state)
Sometimes referred to as SMBE. ) Method is commonly used. In this case, the nitrogen raw material is chemically inactive, and the nitrogen atom may be difficult to be taken into the crystal. In that case, by exciting the nitrogen raw material by a microwave or the like to supply it in an activated state, it is possible to improve the nitrogen uptake efficiency. Among these manufacturing methods, the MOVPE method is particularly important because it has high uniformity and is suitable for mass production.

Next, examples of the n-type impurities used in the compound semiconductor of the present invention include Si, Ge, Se, S and O. Among them, Si and Ge are preferable, and Si is more preferable. As p-type impurities, Mg, Zn, Cd, B
e, Hg, Mg and Zn are preferable, and M is preferable.
g is more preferred. The 3-5 doped with p-type impurities
The group compound semiconductor may be further reduced in resistance by heat treatment after growth in an inert atmosphere. As a method for doping these impurities, the GSMBE method
When a Group-5 compound semiconductor is manufactured, if the impurities themselves can be controlled to have a vapor pressure that does not interfere with other molecular beams in the growth apparatus, these impurities can be used as they are. In the case of MOVPE, a known compound containing these impurities is introduced into the reaction furnace,
A compound semiconductor doped with impurities can be obtained.

As the dry etching method in the present invention, sputter etching using a rare gas such as Ar, nitrogen or a mixed gas thereof, reactive ion etching using a reactive gas (hereinafter sometimes referred to as RIE),
Alternatively, electron cyclotron resonance plasma etching using a reactive gas (hereinafter sometimes referred to as ECR plasma etching) and the like can be given. Generally, the plasma used in these methods refers to a gas containing charged particles or neutral radical particles.

Each of the above dry etching methods will be described below. Sputter etching is a method in which charged particles are accelerated in an electric field to give kinetic energy and collide with the surface of a substance to be etched to remove constituent atoms on the surface. RIE is a method of reacting plasma with a substance to be etched to form a volatile reaction product and removing the constituent elements on the surface. ECR plasma etching is a method of generating plasma using a microwave and a magnetic field at a place apart from a place where a sample is placed in a dry etching apparatus, and the plasma is generated by an electrostatic field or a high frequency electric field to the place of the etching sample. It is a method of inducing and reacting with a substance to be etched to form a volatile reaction product, and removing the constituent elements on the surface. ECR
Plasma etching can generate a high density plasma in a higher vacuum than the two methods described above,
The feature is that the energy of plasma particles can be controlled over a wide range. The energy of plasma particles decreases in the order of sputter etching, RIE, and ECR plasma etching, and therefore the etching damage also decreases in this order. Therefore, as the etching method with less damage, RIE and ECR plasma etching are preferable, and ECR plasma etching is particularly preferable.

The gas used for dry etching is
A rare gas, a gas composed of molecules containing a halogen element, or a mixed gas thereof is used. He, N as rare gas
e, Ar, Kr, Xe and the like, among which A is
r is preferred. Examples of the halogen element include Cl, Br and I, and examples of the molecule containing the halogen element include X ₂ and H.
_{X, BX 3, CX m X} 'n, SiX m X' n , and the like (wherein, X, X 'are different from each other Cl, Br, I
Where m and n are integers of 0 or more and 4 or less that satisfy m + n = 4. ). Among these, Cl ₂ , BC
It is preferable that l ₃ has a high purity. By mixing these gases with oxygen, hydrogen, or a hydrocarbon compound, surface irregularities caused by etching may be reduced in some cases. Hydrocarbon compounds that can be used for this purpose include those having 1 to 6 carbon atoms.

When the treatment using the solution containing phosphoric acid and sulfuric acid after dry etching in the present invention is performed, the volume mixing ratio of phosphoric acid and sulfuric acid is preferably in the range of 10: 1 to 1:10, and more preferably. 5: 1 to 1: 5.
If the mixing ratio of sulfuric acid is less than 10: 1 or more than 1:10, the surface may be rough and not practical, which is not preferable. The treatment temperature is preferably 180 ° C. or higher and 280 ° C. or lower, more preferably 200 ° C. or higher and 260 ° C. or lower. If the temperature is lower than 180 ° C, the time required for the treatment effect to appear may be extremely long, which is not practical. If the temperature is higher than 280 ° C, the surface may be roughened and the back surface of the substrate may be roughened. Since it is still not practical, it is not preferable.

The treatment time using a solution containing phosphoric acid and sulfuric acid depends on the amount of damage caused by dry etching, but is preferably 30 seconds or more and 60 minutes or less, more preferably 1 minute or more and 30 minutes or less. . If it is shorter than 30 seconds, the treatment effect is not sufficiently exhibited, and if it is longer than 60 minutes, the time required for the process may be long, which is not practical and is not preferable. In the present invention, before or after the treatment using the solution containing phosphoric acid and sulfuric acid, a step of heat treatment at 400 ° C. or higher in an inert atmosphere can be added. In particular, it is preferable that after the treatment with the solution containing phosphoric acid and sulfuric acid, a step of heat treatment at 400 ° C. or higher in an inert atmosphere is further included.

As the inert atmosphere, an inert gas such as Ar, He or nitrogen is used. These gases can be sufficiently purified and used alone or as a mixture. Of these, nitrogen is suitable because nitrogen having a high purity can be obtained relatively easily. The heat treatment temperature in the inert atmosphere is 400 ° C. or higher, preferably 400 ° C. or higher and 1100 ° C. or lower, and more preferably 600 ° C. or higher and 1000 ° C. or lower. When the heat treatment temperature is lower than 400 ° C., the effect of the heat treatment is not sufficient, which is not preferable. Further, if the temperature is higher than 1100 ° C., deterioration may occur due to decomposition of the Group 3-5 compound semiconductor due to heat, which is not preferable. The heat treatment time in the inert atmosphere is preferably 1 minute or more and 3 hours or less, and more preferably 5 minutes or more and 1 hour or less. If the heat treatment time is shorter than 1 minute, the effect of the heat treatment is not sufficient, and if it exceeds 3 hours, the productivity may decrease, which is not preferable.

Usually, when dry etching is performed in the step of manufacturing an element using the compound semiconductor, a mask such as photoresist or SiO ₂ is formed in a portion not to be etched to protect it from plasma. However, even a portion protected from direct contact with plasma may be damaged during dry etching. The method for recovering etching damage according to the present invention is also effective for etching damage that occurs in such a protected portion.

The following can be used for the electrodes used for the Group 3-5 compound semiconductor in the present invention.
Examples of the electrode material having a low contact resistance with the n-type compound semiconductor include Al. Examples of the electrode material having a low contact resistance with the p-type compound semiconductor include Au, or an alloy of Au and another metal. Examples of the metal that forms an excellent electrode with an alloy with Au include Mg, Zn, and Ni. Specifically, Au-Mg, Au-Zn, Au-
Examples thereof include Mg-Zn or Au-Ni alloy. These electrodes can be formed by ordinary vacuum vapor deposition. When the electrode material is an alloy, a method of vapor-depositing the alloy material, a method of sequentially vapor-depositing the metal constituting the alloy and a method of alloying by heat treatment, a method of vapor-depositing the metal constituting the alloy at the same time, etc. are used. Can be formed.

[0018]

The present invention will be described in detail with reference to the following examples.
The present invention is not limited to these. Comparative Example 1 A GaN-based semiconductor was buffered with GaN by the MOVPE method.
It was manufactured by a two-step growth method for forming a layer. Half made
The structure of the conductor is shown in FIG. The raw material used is NH _Three,bird
Methyl gallium (hereinafter sometimes referred to as TMG)
It is. Bismethylcyclopenta as p-type dopant
Mg was doped with dienyl magnesium. growth
Then, the obtained p-type GaN is stored in a nitrogen atmosphere at 800 ° C. for 20 minutes.
Heat treatment was applied to reduce the resistance.

A photoresist was coated on the obtained p-type GaN film by a spinner to a thickness of 1 μm, baked at 90 ° C. for 20 minutes, exposed to ultraviolet rays with an exposure device, and developed to form a desired mask pattern. . The p-type GaN film on which the mask pattern was formed was dry-etched with Cl ₂ gas using an ECR plasma etching apparatus (ECR-510E manufactured by Nichiden Anelva). The dry etching conditions are a pressure of 1.2 mTorr and a Cl ₂ gas flow rate of 30 sc.
cm, RF power 80W, input microwave power 400
W, substrate temperature 20 ° C., etching time 12.5 minutes. After the dry etching, the residual photoresist was removed with an organic solvent, and then the step formed on the p-type GaN film by the dry etching was measured. G obtained from the step
The etching rate of aN was 160Å / min.

Next, when the surface resistance of the p-type semiconductor film after dry etching was measured with a tester, it increased to 50 megohms or more from 200 to 900 kohms before dry etching, and was damaged by etching. . Further, when the p-type GaN semiconductor film before and after the dry etching was irradiated with a helium-cadmium laser having a wavelength of 3250Å and the photoluminescence spectra were compared, the shape was changed from the spectrum before the dry etching shown in FIG. The spectrum is as shown in, and an optical change was observed.

Comparative Example 2 An n-type GaN film was prepared in the same manner as in Comparative Example 1 except that Si was doped using silane as an n-type dopant instead of p-type dopant bismethylcyclopentadienylmagnesium. Grew up. The obtained n-type GaN film was dry-etched with an ECR plasma dry etching device. Dry etching conditions are pressure 0.2m
Torr, Cl ₂ gas flow rate 15 sccm, RF power 1
50W, input microwave power 210W, substrate temperature 0
C., etching time 7 minutes. When the etching rate of GaN was measured by the same method as in Comparative Example 1, it was 360 Å for each.
/ Min. The resistance after dry etching was 50 kOhm, which was higher than the value before dry etching of 10 kOhm, and was damaged by etching. When the photoluminescence spectrum was measured at the liquid nitrogen temperature, the spectrum shape did not change,
The peak intensity of the light emission of 3625Å was reduced to 55% as compared with that before the dry etching, and the GaN crystal was subjected to the optical change.

Example 1 The dry-etched n-type GaN film obtained in Comparative Example 2 was placed in a mixed solution having a volume mixing ratio of phosphoric acid: sulfuric acid of 1: 4 which was previously heated to 240 ° C. A treatment for 1 minute was performed. When the resistance of the n-type GaN film after the mixed acid treatment was measured, it was found to be 10 kOhm and recovered to the value before dry etching. Further, when the photoluminescence spectrum of the n-type GaN film after the mixed acid treatment was measured at the liquid nitrogen temperature, the peak intensity of 3625Å recovered to 90% of the intensity before dry etching.

Comparative Example 3 An n-type GaN film was grown by the same method as in Comparative Example 2. 2000 Å SiO ₂ on the obtained n-type GaN film by vacuum evaporation method.
Was prepared, a photoresist pattern was formed thereon by a usual photolithography method, and then SiO ₂ was treated with buffered hydrofluoric acid, and then the resist was removed with acetone to prepare a SiO ₂ mask. Here, buffered hydrofluoric acid means ammonium fluoride: hydrofluoric acid =
A 20% by weight aqueous solution of a mixture of 6: 1 (weight ratio).
Next, the sample on which the SiO ₂ mask was formed was dry-etched by sputter etching using Ar. As the dry etching condition, Ar gas flow rate 30
sccm, pressure 6.8 mTorr, RF power 400
W, the substrate temperature was room temperature, and the etching time was 30 minutes.
After dry etching, the step difference after removing the SiO ₂ mask was measured and the etching rate of n-type GaN was determined to be 450 Å / min. When the resistance of the sample after dry etching was measured, it was 100 kΩ, which was higher than the resistance value of 10 kΩ of the sample before dry etching.

Example 2 The dry-etched n-type GaN obtained by the same method as in Comparative Example 3 was subjected to mixed acid treatment with phosphoric acid and sulfuric acid under the same conditions as in Example 1, and the resistance was 10 In kilohms,
It recovered to the same value as before dry etching. Next, the sample treated with the mixed solution of phosphoric acid and sulfuric acid in the same manner as described above was subjected to 1 by ordinary photolithography and vacuum deposition.
A sample on which an Al electrode having a thickness of 500 Å was formed was prepared and the current-voltage characteristics were measured. Figure 4 shows the pattern of the Al electrode.
The measurement results are shown in FIG.

Comparative Example 4 A sample having an Al electrode was prepared in the same manner as in Example 2 except that the treatment with a solution containing phosphoric acid and sulfuric acid was not carried out, and the current-voltage characteristics were measured. The measurement result is shown in FIG. Comparing FIG. 5 and FIG. 6, it can be seen that in the sample subjected to the etching damage recovery treatment of the present invention, a large amount of current flows and a good electrode can be formed even at a low voltage as compared with the case not according to the present invention.

[0026]

The method for producing a Group 3-5 compound semiconductor according to the present invention has the general formula In _x Ga _y Al _z N (where x + y +
z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) Etching when dry etching is performed to form an electrode or the like on the 3-5 group compound semiconductor It is possible to recover damage and provide a good quality Group 3-5 compound semiconductor. Since the electrode formed on the surface of the 3-5 group compound semiconductor has excellent current injection characteristics, it is possible to enhance the performance of a light emitting device such as an ultraviolet or blue LED or an ultraviolet or blue laser diode, so that it is of industrial value. Is big.

[Brief description of drawings]

FIG. 1 is a diagram showing a layer structure of a compound semiconductor used in Comparative Example 1 and Example 1.

FIG. 2 is a photoluminescence spectrum of p-type GaN before dry etching.

FIG. 3 is a photoluminescence spectrum of p-type GaN immediately after dry etching.

FIG. 4 is an Al electrode pattern used in Example 2.

FIG. 5 is a diagram showing current-voltage characteristics obtained in Example 2.

FIG. 6 is a diagram showing current-voltage characteristics obtained in Comparative Example 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... GaN layer 2 ... GaN buffer layer 3 ... Sapphire substrate 4 ... Electrode non-deposited portion 5 ... Electrode deposited portion

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01S 3/18 H01L 21/302 FN

Claims (3)

[Claims] 1. A general formula In _x Ga _y Al _z N (where x is
+ Y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1)
The method for producing a Group 3-5 compound semiconductor, comprising the step of dry-etching the Group 3-5 compound semiconductor represented by the following, followed by treatment with a solution containing phosphoric acid and sulfuric acid. 2. The general formula In _x Ga _y Al _z N (where x is
+ Y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1)
After the dry etching of the Group 3-5 compound semiconductor represented by the following, it is treated with a solution containing phosphoric acid and sulfuric acid, and then heat-treated at 400 ° C. or higher in an inert atmosphere. 3-5 Group compound semiconductor manufacturing method. 3. The method for producing a Group 3-5 compound semiconductor according to claim 1, wherein the dry etching uses a rare gas, a molecule containing a halogen element, or a mixed gas thereof.