JPH03181133A - Method for etching compound semiconductor - Google Patents

Abstract

PURPOSE:To improve sizing accuracy of an active layer and prevent a fluctuation in oscillation wavelength by perpendicularly etching an InP layer with mixed solution of hydrochloric acid and phosphoric acid and etching an InGaAsP layer with the above layer as a mask. CONSTITUTION:An SixMy layer 6 is formed on an n-type InP layer 5 of a wafer 1, and this is processed in the 011 direction of a p-type InP substrate 2 to form a mask 6. Then the wafer 1 is soaked in mixed solution of hydrochloric acid and phosphorus acid to have the layer 5 etched then to be washed in pure water and dried. Then the wafer 1 is soaked in mixed solution of sulfuric acid, hydrogen peroxide and water to have an InGaAsP layer 4 to be an active layer etched to be washed in pure water and dried. Further the wafer 1 is soaked in mixed solution of hydrochloric acid and phosphoric acid to have a p-type InP layer 3 etched to be washed and dried. By etching the layer 4 with the layer 5 thus etched perpendicularly by mixed solution of the hydrochloric acid and phosphoric acid as a mask, sizing accuracy of the layer 4 is improved and a fluctuation in oscillation wavelength can be prevented.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a method for etching compound semiconductors.

<Prior Art> Semiconductor laser elements whose emission wavelength is in the near-infrared region are used as light sources for optical communication. In particular, indium gallium arsenide phosphide (hereinafter referred to as 1n
(abbreviated as GaAsP) mixed crystal/indium phosphide (hereinafter 1nP)
)-based semiconductor laser devices have become indispensable as light sources for long-distance optical communications.

The buried portion of the semiconductor laser element is formed by etching. A conventional etching method will be explained with reference to FIG.

As shown in the figure, a P-type InP substrate 2 having a (100) plane on the surface and a p-type InP epitaxially grown on the p-type InP substrate 2 are used to form a buried portion of an InGaAsP mixed crystal/InP semiconductor laser device. Layer 3 and p-type 1nP
InGaAsP layer 4 epitaxially grown on layer 3
and an n-type 1nP layer 5 epitaxially grown on an In aAsP layer 4.
Use.

Said wafer l.

In Step 2, "Formation of Silicon Dioxide Layer", a silicon dioxide (hereinafter abbreviated as 5i02) layer 7 is formed on the n-type 1nP layer 5 of the wafer 1 by low pressure CVD.

In step 2 "forming an etching mask", the 5i02 layer 7 is etched along the (011) direction of the InP substrate 2.
An etching mask is formed by processing the pattern into m stripes.

In the process ■ "Etching", the wafer 1 is coated with 1% bromine.
- Immerse in methanol solution to form an n-type 1nP layer 5, In
GaAsP layer 4. The p-type InP layer 3 is sequentially etched.

In step (2) "cleaning", the wafer 1 is washed with pure water.

In step (2) "Drying", the wafer I is dried by centrifugal drying or the like.

The n-type InP layer 5 and the InGaAsP layer 4 are processed in this order.
and p-type InP layer 3 is formed.

<Problems to be Solved by the Invention> However, in the conventional etching method using the bromine-methanol solution described above, the n-type 1nP layer and the p-type In
Since the etching of the P layer is anisotropic etching in which the etching progresses quickly toward the (111) A plane of each InP layer and slowly toward the (111) B plane, each InP layer has an inverted mesa shape. Therefore, the InGaAsP layer (
It is difficult to control the width of the active layer (active layer), and therefore the dimensions of the InGaAsP layer functioning as a waveguide vary, resulting in variations in the oscillation wavelength of the semiconductor laser device.

Furthermore, if p-type InP is deeply etched to form an inverted mesa shape, it will break at the base of the p-type InP layer.

Furthermore, in the case of a brome-methanol solution, it is difficult to maintain a constant bromine concentration due to the high volatility of bromine, which makes it difficult to maintain a constant etching rate, resulting in low etching accuracy. Means for Solving> The present invention has been made to solve the above problems, and provides a method for etching a compound semiconductor to form a semiconductor laser device with excellent stability of the oscillation wavelength of laser light. The purpose is to provide.

That is, it is a method of etching a compound semiconductor to form a recessed part of an InGaAsP mixed crystal/InP semiconductor laser element, and the process includes forming an SiJv layer on an n-type InP layer of a wafer on which a semiconductor laser element is to be formed. Next, this 5iXNv layer is processed into stripes in the (011> direction of the p-type 1nP substrate to form an etching mask for the Si and Ny layers.Then, the wafer is etched with a mixture of hydrochloric acid and phosphoric acid. The nZJInP layer is anisotropically etched by immersing the wafer in an etching solution containing a mixture of sulfuric acid, hydrogen peroxide, and water, followed by washing with pure water and drying. The wafer is etched with pure water, washed with pure water, and dried.Furthermore, the wafer is immersed in an etching solution containing a mixture of hydrochloric acid and phosphoric acid to anisotropically etch the P-type InP layer, and then washed with pure water and dried. This is the method.

Effect> The above-mentioned compound semiconductor etching method is applicable to InGaA
n-type 1 forming sP mixed crystal/InP semiconductor laser device
InG
Without etching the aAsP layer, (011
) Performs anisotropic etching in which etching progresses along the surface. Therefore, each InP layer is etched substantially perpendicularly to the p-type 1nP substrate, and the etching mask dimensions of the Si, N, and layers are transferred to the n-type InP layer. Also n type 1
The nP layer transfers the etch mask dimensions to the InGaAsP layer.

Furthermore, by using a mixed solution of sulfuric acid, hydrogen peroxide, and water as the etching solution for etching the InGaAsP layer,
Each ■! InGaAs without etching the IP layer
Etch the P layer.

Therefore, n-type InP layer, InGaAsP layer and p-type InP layer
The buried portion formed of the P layer is formed into a substantially rectangular shape with dimensions that are the same as those of the etching mask.

(Example) An example of the present invention will be explained with reference to a process diagram of a compound semiconductor etching method shown in FIG.

As shown in the figure, p-type InP with (Zoo) plane on the surface
A p-type InP layer 3 is formed on the surface of a substrate 2 by epitaxial growth. Furthermore, an epitaxially grown InGaAsP layer 4 is formed on the p-type InP layer 3. Further, an epitaxially grown n-type InP layer 5 is formed on the InGaAsP layer 4 to form a double heterostructure InGaAsP mixed crystal/InP wafer 1.

The epitaxial growth methods include metal organic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE).
) etc. are used.

Using the wafer I, a buried portion of a semiconductor laser is formed through the following steps.

In step ① "formation of silicon nitride layer", the n of the wafer 1 is
A silicon nitride (hereinafter abbreviated as Si, Ny) layer 6 is formed on the InP type layer 5. This Si, Ny layer 6 was formed by low pressure CVD.
Formed by law etc.

■Procedure■ In "etching mask formation", the above Si,
My layer 6 has a predetermined width (0
11 Process into stripes along the direction. In this processing, an etching mask pattern is formed by, for example, photolithography, and 5IXNy M6 is processed by etching.

In step (2) "Etching the n-type InP layer", the wafer 1 is immersed in an etching solution containing a mixture of hydrochloric acid and phosphoric acid to etch the n-type InP layer 5. At this time, the above 5
ixN, layer 6 serves as an etching mask. In the etching solution, it is desirable that the volumetric mixing ratio of hydrochloric acid be 40% to 60%, with the remainder being phosphoric acid.If the volumetric mixing ratio of hydrochloric acid is less than 40%, the etching rate will be slow and n The amount of undercut of the type InP layer 5 increases. On the other hand, if the volumetric mixing ratio of hydrochloric acid exceeds 60%, the etching rate becomes too high and the dimensional accuracy deteriorates.

Furthermore, etch pits are deposited on the etched surface 5a.

The temperature of the etching solution is preferably 0° C. or higher and 25° C. or lower. If the temperature is lower than 0° C., the etching rate becomes too slow and the amount of undercut becomes large. On the other hand, 25℃
If the temperature exceeds 100, the etching rate will be too fast and it will be difficult to control the amount of etching.

Therefore, dimensional accuracy cannot be obtained. Also etching surface 5a
becomes rough.

In Step 2, "Cleaning", the wafer 1 is cleaned with pure water.

In step (2) "Drying", the wafer I is dried by centrifugal drying or the like.

In step ``r Etching of InGaAsP layer,'' the wafer 1 is immersed in an etching solution containing a mixture of sulfuric acid, hydrogen peroxide, and water, and the InGaAsP layer 4 is etched. At this time, the n-type 1nP layer 5 serves as an etching mask. The etching solution used had a volumetric mixing ratio of sulfuric acid, hydrogen peroxide, and water of 10:1:l. Naturally, the volumetric mixing ratio of each liquid is not limited, and it is sufficient if the volumetric mixing ratio of sulfuric acid is higher than the volumetric mixing ratio of hydrogen peroxide or water. On the other hand, when the volumetric mixing ratio of sulfuric acid is lower than the volumetric mixing ratio of hydrogen peroxide, the etching rate becomes faster because the etching rate is determined by the oxidation rate by hydrogen peroxide. Also, since the oxidation rate differs depending on the crystal plane, anisotropic etching occurs. Therefore, InGa
It becomes difficult to control the dimensions of the AsP layer 4.

In step (2) "cleaning", the wafer 1 is washed with pure water.

In step (2) "Drying", the wafer I is dried by centrifugal drying or the like.

In the process ``knee 2ching of p-type InP layer'', the wafer l is fi
Then, the p-type InP layer 3 is etched. At this time, the 1nGaA+P layer 4 serves as an etching mask. Further, since this etching solution is the same as the etching solution explained in step (2) above, detailed explanation will be omitted.

In the process [phase] "cleaning", the wafer 1 is washed with pure water.

In step 0 "drying", the wafer I is dried by centrifugal drying or the like.

As described above, by sequentially performing the steps to step O, the buried portion of the semiconductor laser element consisting of the n-type 1nP layer 5, the InGaAsP layer 4, and the p-type InP layer 3 is formed.

Next, the action of the etching solution, which is a mixture of hydrochloric acid and phosphoric acid, for etching the n-type InP layer 5 and the P-type 1nP layer 3 will be explained.

In this etching solution, each 1nP layer was etched by 3.5 mL with hydrochloric acid.
Since the InP layers 3 and 5 are anisotropically etched along the (011) plane in the (l l 1) plane direction, each InP layer 3, 5 is etched perpendicularly to the InP substrate 2.

Further, each InP layer 3, 5 is etched in the (011) plane direction by the phosphoric acid. However, since the etching rate is extremely slow compared to the etching rate in the direction of the (111) plane using hydrochloric acid, the amount of undercut becomes small, and the etched surface of the (011) plane becomes a mirror or sub-mirror finish.

(Effects of the Invention) As explained above, according to the present invention, an etching solution containing a mixture of hydrochloric acid and phosphoric acid is used to etch an n-type InP layer and a p-type InP layer.
Since the layers are etched, the etched plane of each InP layer can be formed approximately perpendicular to the InP substrate. In addition, I
Since it can be transferred to the nGaAsP layer, the dimensional accuracy of the InGaAsP layer which becomes the active layer can be improved. Therefore, the shape accuracy and dimensional accuracy of the buried portion of the InGaAsP mixed crystal/InP semiconductor laser device can be improved, and variations in the oscillation wavelength of each semiconductor laser device formed on the wafer can be prevented.

Also InP 1f! Since it can be etched vertically, the cross-sectional shape of the embedded part becomes approximately rectangular, so it will not break at the base.

Furthermore, since the etching solution is a non-volatile solution, it is easy to keep the concentration of the etching solution constant, and stable etching performance can always be obtained.

[Brief explanation of drawings]

On the etching method of compound semiconductors Figure 1 shows diagram, Figure 2 shows Ru. l...Wafer. 3...P-type InP layer. 5...n-type InP layer. This is an explanatory diagram of the conventional etching method. 2...p-type InP substrate. 4---InClaAsP layer. 6...Si, Ny layer.

Claims (1)

[Scope of Claims] A p-type indium phosphide substrate having a (100) plane on its surface; a p-type indium phosphide layer epitaxially grown on the p-type indium phosphide substrate; and a p-type indium phosphide layer epitaxially grown on the p-type indium phosphide layer. Etching of a compound semiconductor to form a buried portion of a semiconductor laser element in a wafer having a double heterostructure consisting of an indium gallium arsenide phosphide mixed crystal layer and an n-type indium phosphide layer epitaxially grown on the indium gallium arsenide phosphide mixed crystal layer. The method includes: step (1): forming a silicon nitride layer on the n-type indium phosphide layer of the wafer; step (2): forming the silicon nitride layer into stripes along the <011> direction of the indium phosphide substrate. Step (3): Etching the n-type indium phosphide layer by immersing the wafer in an etching solution containing a mixture of hydrochloric acid and phosphoric acid. Step (4): Etching the n-type indium phosphide layer. The wafer is cleaned with pure water. Step (5): The wafer is dried. Step (6): The wafer is immersed in an etching solution containing a mixture of sulfuric acid, hydrogen peroxide, and water to remove the indium gallium arsenide phosphide layer. etching, step (7): cleaning the wafer with pure water, step (8): drying the wafer, step (9): immersing the wafer in an etching solution containing a mixture of hydrochloric acid and phosphoric acid; Step (10) of etching the p-type indium phosphide layer; Step (11) of cleaning the wafer with pure water;
): A method for etching a compound semiconductor, characterized in that steps (1) to (11) comprising drying the wafer are performed in order.