JPH0722645A - Manufacture of nonlinear optical element - Google Patents

Abstract

PURPOSE:To provide a manufacturing method of a nonlinear optical element wherein the side part is made vertical and the working size is uniform without damaging the surface of a semiconductor layer of quantum well structure, and control the quantity of recombination center. CONSTITUTION:A substrate 1, a buffer layer 2, a semiconductor layer 3 of quantum well structure, a semiconductor cap layer 4, and a mask composed of an SiO2 film 5 are formed in order. Dry etching is continuously performed until the cap layer 4, the semiconductor layer 3 and the buffer layer 2, thereby forming a plurality of patterns wherein the thin line type side part is vertical. The buffer layer 2, the semiconductor layer 3 and the semiconductor cap layer 4 are etched by dipping them in chemical etching solution, in the state that the mask of the SiO2 film 5 is fixed.

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 nonlinear optical element using a semiconductor superlattice material applicable to an optical bistable element or the like.

[0002]

2. Description of the Related Art A large non-linear optical effect exhibited by excitons in a quantum well, that is, a phenomenon in which optical constants such as absorptance and refractive index change due to irradiation of light, can be used for optical switching and optical modulators. As a nonlinear optical element utilizing this phenomenon, for example, an optical bistable element as shown in FIG. 4 has been proposed.

FIG. 4 is a schematic sectional view showing an example of a conventional optical bistable element, 41 is a non-linear optical element, 42 is a dielectric reflection film, and 43 is a laser beam introduction direction. However, in such an element, the exciton generated by the introduction of the laser light has a long time of disappearing by recombination of several nanoseconds, and there is a problem that a high speed response cannot be performed.

Therefore, there has been proposed a method in which the quantum well is processed into a plurality of fine line-shaped or dot-shaped patterns to promote the recombination of excitons on the processed side surface, thereby increasing the response time. This utilizes the disappearance of excitons due to the surface states induced on the semiconductor surface and accompanying recombination centers.

Further, in quantum wires and quantum dots in which the quantum well structure is further reduced in size by further miniaturizing the processing size, the degree of freedom of excitons is restricted, and thus the response speed is much faster than that of the quantum well. , High optical nonlinearity is expected.

When the quantum well is processed into a thin wire or a dot, a mask is generally formed on the quantum well structure, and a reactive ion etching (RIE) method, a reactive ion beam etching (RIBE) method or the like is used. This is performed by selectively etching a portion without a mask by using the dry etching method described in (1). According to this method, a large number of recombination centers are formed on the etching surface due to the effect of ion irradiation.

In order to further reduce the size of the fine lines or dots, a method has been proposed in which the quantum well structure under the mask is etched by isotropic etching using an etching solution after processing by dry etching. .

[0008]

However, when the quantum well structure is patterned into a fine line shape or a dot shape, it is difficult to avoid damaging the surface of the quantum well structure during mask formation or dry etching.

Further, in order to reduce the size of the fine lines or dots, the quantum well structure under the mask can be etched by isotropic etching using an etching solution after processing by dry etching. In this case, there is a problem that the quantum well structure immediately below the mask is difficult to be etched, and the size of that portion is increased as shown in FIG.

FIG. 3 is a cross-sectional view of a nonlinear optical element obtained by using dry etching and isotropic etching together by the above conventional method, in which 31 is a substrate and 32 is a quantum well structure. The semiconductor layer 33 which it has shows the mask, and the size of the semiconductor layer 32 which has a quantum well structure of the part just under a mask is large.

Such non-uniformity in size causes fluctuations in the quantization energy, so that the quantization energy has a broad profile, the exciton generation efficiency deteriorates, and the quantum confinement effect decreases. Occurs. In particular, if the size is such that the quantum size effect is a problem, for example, about 50 nm or less, the nonuniformity of the size becomes a serious problem.

The first invention of the present invention has been made in view of the above problem, and a quantum well structure capable of efficiently generating excitons without damaging a semiconductor layer composed of multiple quantum wells. An object of the present invention is to provide a method for manufacturing a non-linear optical element in which the semiconductor layer having a uniform size is formed.

In addition, in the conventional method, the RIE method and the RIBE method are used.
In the method of forming a large number of recombination centers on the surface by the effect of ion irradiation by processing using dry etching method such as the method, since the main purpose is etching, the amount of recombination centers due to ion irradiation is large. Is difficult to control.

The second invention of the present invention has been made in view of the above problems, and provides a manufacturing method capable of controlling the amount of recombination centers formed by ion irradiation formed on the processing side surface. With the goal.

[0015]

In order to solve the above problems, the invention of the first method for manufacturing a nonlinear optical element of the present invention is as follows:
Stacking a semiconductor buffer layer on a semiconductor substrate,
Stacking a semiconductor layer having a superlattice structure having a barrier layer made of a material having the same or a smaller band gap as the semiconductor buffer layer on the semiconductor buffer layer, and the same or larger band gap than the barrier layer Stacking a semiconductor cap layer made of a material on the semiconductor layer having the superlattice structure; forming a thin line-shaped or dot-shaped mask on the semiconductor cap layer; A semiconductor layer having a lattice structure, or a side portion of the semiconductor layer having a superlattice structure remaining under the mask by selectively dry etching the semiconductor cap layer, the semiconductor layer having a superlattice structure, and the semiconductor buffer layer. At least the superlattice is formed by a step of etching in a vertical shape and isotropic etching using an etching solution. Characterized by comprising the step of etching the side of forming the semiconductor layer.

The second invention of the method for manufacturing a non-linear optical element of the present invention has a semiconductor buffer layer on a semiconductor substrate, and a barrier layer made of a material having the same or small band gap as the semiconductor buffer layer. A semiconductor layer having a superlattice structure, a semiconductor cap layer made of a material having the same or larger bandgap as that of the barrier layer are sequentially stacked, and the semiconductor cap layer, a semiconductor layer having a superlattice structure, and a semiconductor buffer layer, or Ions are injected into a nonlinear optical element in which the semiconductor cap layer and the semiconductor layer having a superlattice structure are fine lines or dots, and a mask is further formed on the semiconductor cap layer. Irradiation forms recombination centers in the vicinity of the surface of the semiconductor layer having the superlattice structure. To.

[0017]

According to the first aspect of the present invention, a semiconductor cap layer that absorbs damage during mask formation and dry etching is provided on the semiconductor layer to be processed, and the cap layer and the semiconductor having a superlattice structure are provided. The layer and, if necessary, the buffer layer are dry-etched to form, for example, fine lines or dots. For this reason, all damages during mask formation and dry etching are absorbed by the semiconductor cap layer, so that the surface of the semiconductor layer having multiple quantum wells is not damaged. Furthermore, when the size is reduced by isotropic etching using an etching solution, the portion immediately below the mask is the semiconductor cap layer, so the non-uniform size is absorbed in this portion, and the multiple quantum wells are absorbed. It is possible to prevent the size of the semiconductor layer having a structure from becoming uneven. Therefore, the side portions of the semiconductor layer having the multiple quantum well structure are vertical, and the quantum well structure is confined in a uniform size in the pattern width direction, the fluctuation of the quantization energy is eliminated, and the energy intensity is increased. Become.

According to the second aspect of the present invention, the cap layer and the semiconductor layer having a superlattice structure etched in a fine line shape or a dot shape, and if necessary, the side surface of the buffer layer is ion-implanted, and the ion implantation is performed. By controlling the ion energy and dose, the amount of recombination centers formed by ion irradiation in the vicinity of the surface can be controlled. Since the ion energy and the dose amount can be accurately controlled in the ion implantation, the amount of recombination centers can be controlled with good reproducibility.

[0019]

EXAMPLES Examples of the present invention will be described below. In the present invention, as the semiconductor substrate, for example, GaAs, In
A substrate made of P or the like is a typical example. The buffer layer varies depending on the type of substrate and the type of semiconductor used in the semiconductor layer having a superlattice structure, and is, for example, III-V.
Group semiconductors, II-VI group semiconductors and the like can be mentioned. Examples of the semiconductor used for the semiconductor layer having the superlattice structure include II
I-V group semiconductors and II-VI group semiconductors are preferable. The cap layer may be, for example, a III-V group semiconductor or a II-VI group semiconductor, depending on the type of semiconductor used in the superlattice structure semiconductor layer used.

SiO ₂ , Si ₃ N ₄ and other dielectric materials are preferably used as the material for the thin line or dot mask. The dry etching method is not particularly limited, but reactive ion etching (RI
Dry etching methods such as E) method and reactive ion beam etching (RIBE) method are preferable. In the present invention, the buffer layer may be dry-etched by dry etching, or may be up to the middle of the buffer layer, or the buffer layer is not etched but the semiconductor layer having the superlattice structure is dry-etched. But it's okay.

As the etching liquid for the isotropic etching using the etching liquid, an etching liquid capable of performing the isotropic etching may be appropriately selected and used depending on the material of the target of the isotropic etching. . In particular, sulfuric acid is a relatively frequently used etching solution.

The type of ions used for ion implantation by the ion irradiation used in the second invention is not particularly limited as long as it does not change (change the composition or energy gap) to the inside of the semiconductor layer. However, a material that is difficult to diffuse is preferable as long as it is an element incorporated into the semiconductor layer.

Regarding the energy of the irradiation ions,
Irradiation is performed only near the surface of the semiconductor layer, and lower energy is preferable in order to reduce damage due to ion irradiation. Therefore, the upper limit of ion energy is preferably 500 eV and the lower limit is preferably 1 eV or more. Particularly preferably, it is 100 eV or less and several eV or more. The amount of ion irradiation is determined by how much recombination centers are formed. If it is too small, the effect is small, and if it is too large, the crystal structure may be destroyed. Therefore, it is usually preferable to use a dose amount in the range of 10 ¹⁰ pieces / cm ² to 10 ¹⁷ pieces / cm ² .

FIG. 2 is a sectional view showing an example of a method of forming a recombination center in the vicinity of the surface of the semiconductor layer having a superlattice structure by irradiating with ions. When the ions are irradiated, the direction 8 of the ions to be irradiated is obliquely irradiated as shown in FIG. 2, so that the ions can be uniformly injected into the semiconductor layer. further,
Ions can be uniformly injected into the semiconductor layer by rotating the substrate 1 about the direction of the dry etching, which is preferable.

In the following, further specific examples
Explain the Ming. Example 1 FIG. 1 is a cross section showing a manufacturing process in Example 1 of the present invention.
It is a figure. First, the molecular beam epitaxy method and the organometallic vapor phase
ZnS is grown on the GaAs substrate 1 by using the growth method._ySe
_1-y(y = 0.05) After growing the buffer layer 2, the film thickness is 4 nm
Zn_xCd_1-xS _ySe1-y (x = 0.75, y = 0.05) well
Layers and thickness of 12 nm ZnS_ySe_1-y(y = 0.05) Cross the barrier layer
Worked semiconductor of multi-quantum well structure with 10 layers stacked on each other.
The body layer 3 is formed. Next, ZnS_ySe_1-y(y = 0.05)
The top layer 4 is laminated. (See FIG. 1 (a)).

The buffer layer 2 has a thickness of the substrate 1
And a thickness that can alleviate the lattice mismatch of the semiconductor layer 3 to be processed, and is, for example, 500 nm. In addition, the thickness of the cap layer 4 absorbs surface damage at the time of mask production or dry etching which is necessary in a later step, and absorbs non-uniformity of size at the time of chemical etching. The thickness is set to 100 nm, for example.

Thereafter, a SiO ₂ film 5 is grown on the cap layer 4 by a sputtering method to a thickness of 200 nm, and an aluminum film 6 is grown on the cap layer 4 by a vacuum deposition to a thickness of 100 nm. An electron beam resist is applied on the lever and exposed by a focused ion beam exposure method, for example, a pitch of 250 nm and a line width of 70 n.
Exposing a plurality of fine line-shaped patterns of m. Then, this resist is developed to form a thin line resist pattern 7. (See FIG. 1 (b)).

Next, the aluminum film 6 exposed from the resist pattern 7 is removed by etching by a reactive ion etching method using BCl ₃ gas to form the aluminum film 6 into a plurality of fine line patterns. (See FIG. 1 (c)).

Next, the SiO ₂ film 5 exposed from the pattern of the aluminum 6 is removed by etching by a reactive ion etching method using CF ₄ gas or CHF ₃ gas to form a fine linear pattern of the SiO ₂ film. . (See FIG. 1 (d)).

After that, the cap layer 4, the semiconductor layer 3 to be processed, and the buffer layer are formed by a reactive ion etching (RIE) method using boron trichloride gas, using the pattern of the thin linear SiO ₂ film 5 as a mask. Up to 2 are continuously etched to form a plurality of fine line patterns. in this case,
The etching conditions are such that the side portions of the pattern of the semiconductor layer 3 to be processed have a vertical shape. Although the etching is performed up to the buffer layer 2 here, the etching may be performed up to the middle of the buffer layer 2 or the buffer layer 2 may not be etched. (See (e) of FIG. 1).

Next, the semiconductor buffer layer 2, the semiconductor layer 3 having a multiple quantum well structure, and the semiconductor cap layer 4 are etched by immersing them in a chemical etching solution with the mask of the SiO ₂ film 5 attached. (See (f) in FIG. 1).

The surface of the semiconductor layer 3 having a thin line-shaped multi-quantum well structure thus formed is not damaged during processing, and its side portion has a vertical shape, and has a uniform size. Since it is confined, the fluctuation of the quantization energy becomes small.

In the above-mentioned embodiment, the semiconductor layer to be processed having the quantum well structure is processed into a plurality of fine lines.
It goes without saying that it can be processed into a dot shape having a diameter of m. Also at this time, by providing the semiconductor buffer layer on the semiconductor layer having the quantum well structure, the side portions can be processed into the vertical shape during the chemical etching without damaging the quantum well structure.

The semiconductor having the quantum well structure is not limited to the above materials, and the material used for the semiconductor cap layer is not limited to the above materials. The material of the semiconductor cap layer may be the same material as the barrier layer of the semiconductor layer having the multiple quantum well structure or a material having a large band gap. The conditions such as the line width and pitch of the multiple quantum well structure at the time of processing are not limited to those in the above embodiment.
The number of stacks of the quantum well structure is not particularly limited as long as it is 1 unit or more.

Example 2 In Example 1, the cap layer 4 and the semiconductor to be processed were formed by reactive ion etching (RIE) using boron trichloride gas with the pattern of the thin SiO ₂ film 5 as a mask. The layer 3 and the buffer layer 2 are continuously etched to form a plurality of fine line-shaped patterns (see (e) of FIG. 1) as a sample. Then, the semiconductor buffer layer 2, the semiconductor layer 3 having a multiple quantum well structure, and the semiconductor cap layer 4 are etched by immersing in a chemical etching solution with the SiO ₂ mask 5 attached. Then, the aluminum film 6 is removed by chemical etching.

Next, as shown in FIG. 2, ion implantation is performed. That is, while the substrate is rotated on the nonlinear optical element formed by the above-mentioned etching process, Ar is obliquely tilted.
Ions were implanted at a dose amount of 1 × 10 ¹³ ions / cm ² with an ion energy of 100 ev.

As a result, it was confirmed by the emission lifetime of excitons that the recombination centers could be controlled to an almost desired degree.
Although the sample manufactured in Example 1 was used in the above Example, a thin line-shaped or dot-shaped nonlinear optical obtained by sequentially stacking a semiconductor buffer layer, a semiconductor layer including a quantum well structure, and a semiconductor cap layer. If the material is a mask on the semiconductor cap layer, it can be used as a sample.

[0038]

As described above, according to the first aspect of the present invention, the side portions of the semiconductor layer can be made vertical while the upper portion of the semiconductor layer is not damaged by dry etching. Further, during chemical etching, the quantum well structure is confined in a uniform size in the pattern width direction, fluctuations in quantization energy are eliminated, and a nonlinear optical element having high energy intensity can be manufactured.

Further, according to the second aspect of the present invention, since the amount of recombination centers formed in the vicinity of the surface of the semiconductor layer of the quantum well structure can be controlled, the optimum amount of recombination centers can be estimated. Therefore, a high-speed response optical switching element can be manufactured.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the steps of a manufacturing method in an embodiment of the first invention of the present invention.

FIG. 2 is a cross-sectional view showing a manufacturing method in an embodiment of the second invention of the present invention.

FIG. 3 is a sectional view showing an example of a non-linear optical element obtained by a conventional manufacturing method.

FIG. 4 is a sectional view showing an example of a conventional optical bistable element.

[Explanation of symbols]

1 substrate 2 buffer layer 3 processed semiconductor layer having multiple quantum well structure 4. Cap layer 5 SiO ₂ film 6 Aluminum film 7 Resist pattern 8 Direction of irradiation ions 31 Substrate 32 Semiconductor layer having quantum well structure 33 Mask 41 Non-linear optical element 42 Dielectric reflection film 43 Direction of laser beam introduction

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuneo Mikuro 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A semiconductor layer having a superlattice structure, comprising: a step of stacking a semiconductor buffer layer on a semiconductor substrate; and a superlattice structure semiconductor layer having a barrier layer made of a material having the same band gap or a small band gap as the semiconductor buffer layer. On the semiconductor layer of the superlattice structure, and a thin line on the semiconductor layer of the superlattice structure. Forming a mask in the form of dots or dots, and selectively dry etching the semiconductor cap layer and the semiconductor layer having a superlattice structure, or the semiconductor cap layer, the semiconductor layer having a superlattice structure, and the semiconductor buffer layer. Etching a side portion of the semiconductor layer of the superlattice structure remaining under the mask into a vertical shape; A method for manufacturing a non-linear optical element, comprising the step of etching at least a side portion of the semiconductor layer having the superlattice structure by isotropic etching using an etching solution. 2. A semiconductor buffer layer on a semiconductor substrate,
A semiconductor layer having a superlattice structure having a barrier layer made of a material having the same band gap as or smaller than that of the semiconductor buffer layer, and a semiconductor cap layer made of a material having the same or larger band gap as the barrier layer are sequentially stacked. In the nonlinear optical element, the semiconductor cap layer, the semiconductor layer having a superlattice structure and the semiconductor buffer layer, or the semiconductor cap layer and the semiconductor layer having a superlattice structure are fine lines or dots. A recombination center is formed in the vicinity of the surface of the semiconductor layer having the superlattice structure by irradiating the nonlinear optical element having a mask formed on the semiconductor cap layer with ions. Production method.