JPH03225303A - Production of optical waveguide of semiconductor - Google Patents

Abstract

PURPOSE:To improve the controllability of etching depth by continuously carrying out etching at an increased exhaust speed and an increased flow rate of a gas and etching at a reduced exhaust speed and a reduced flow rate of the gas in an etching stage at the time of forming a rib part. CONSTITUTION:A first clad layer of Al0.5Ga0.5As, a waveguide layer of GaAs and a second clad layer of Al0.5Ga0.5As are successively grown on a GaAs substrate. A photoresist mask 11 having the shape of a waveguide to be formed is then formed on the resulting GaAs/AlGaAs wafer 10. First dry etching in a relatively high physical sputtering state attained by increasing exhaust speed and the flow rate of a gas and second dry etching in a relatively high reactive state attained by reducing exhaust speed and the flow rate of the gas are continuously carried out with the same gas. The controllability of etching depth can be improved independently of the surface state of the wafer.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for manufacturing a semiconductor optical waveguide.

(Prior Art) Along with advances in optoelectronics, research and development into the integration of semiconductor optical devices has been actively progressing in recent years. In particular, semiconductor optical waveguides can be realized on semiconductor substrates by applying microfabrication technology cultivated in semiconductor electronic devices, and can be used for connections between each switch of a semiconductor optical matrix switch, and between semiconductor optical functional elements on the same substrate. It is used for connections between light sources and switches, amplifiers, etc., and is considered to be one of the important components of semiconductor optical integrated circuits. As a method for forming such a semiconductor optical waveguide, after forming a waveguide-shaped mask on a semiconductor substrate by a normal photolithography method, a reactive ion beam etching method (RIBE method) using BCff3 gas is used.
It has been found that a rib-type optical waveguide can be formed by using the following method.Electronics Letters Vol. 22, p. 1243
p, 1243).

(Problem to be Solved by the Invention) Incidentally, when forming a semiconductor optical waveguide, controllability of the height of the rib portion, that is, the etching depth is important.

This is because the depth of etching directly affects the strength of light confinement in the semiconductor optical waveguide. For example, when manufacturing a directional coupler type semiconductor optical switch, the etching depth when forming the rib portion is Unless it is controlled with some degree of precision, the designed operation cannot be obtained. However, in dry etching using the conventional RIBE method, the controllability of the etching depth is affected by the surface condition of the wafer, and the controllability of the etching depth is about ±5% at most. As described above, the conventional semiconductor waveguide manufacturing method has a problem to be solved regarding the controllability of the depth of the rib-type waveguide.

(Means for Solving the Problems) In order to solve the above-mentioned problems, a method for manufacturing a semiconductor optical waveguide according to the present invention includes at least a semiconductor first cladding layer, a semiconductor waveguide layer, and a semiconductor second cladding layer on a semiconductor substrate. a step of stacking to form a stacked structure semiconductor wafer;
A step of providing an etching mask in the shape of an optical waveguide to be formed on the laminated structure semiconductor wafer, and removing the second semiconductor cladding layer other than the portion covered by the mask by etching to form a rib-type optical waveguide. The step of removing the semiconductor second cladding layer other than the portion covered by the mask by etching to form a rib-type optical waveguide is performed by increasing the pumping speed (and increasing the gas flow rate). The first etching step is carried out in a state with relatively strong physical sputtering properties, and the second etching step is carried out in a relatively highly reactive state, which is achieved by slowing down the pumping speed and reducing the gas flow rate. The dry etching process is characterized in that the steps are dry etching steps that are performed consecutively using the same gas.

(Function) Generally, when forming a rib portion of a semiconductor optical waveguide, controllability of etching depth is important. This is because the depth of etching directly affects the strength of light confinement in the semiconductor optical waveguide. For example, when manufacturing a directional coupler type semiconductor optical switch, the depth of etching when forming the rib portion is Unless the temperature is controlled with some degree of precision, the designed operation cannot be achieved. However, in dry etching using the conventional RIBE method, the controllability of the etching depth depends on the surface condition of the wafer, making it impossible to obtain an etching depth with good controllability.

In contrast, in the present invention, in the dry etching process when forming the rib portion, the first etching process is performed in a state with relatively strong physical sputtering properties, which is achieved by increasing the exhaust speed and increasing the gas flow rate. Since this is performed first, the controllability of the etching depth is improved regardless of the surface condition of the wafer. Also, a second etching step due to a relatively more reactive state achieved by slowing the pumping speed and reducing the gas flow rate immediately after the first etching step is also possible.
Since the etching process is performed, a selectivity with respect to the mask is ensured, there is no concern that the perpendicularity will deteriorate due to mask recession, and there is little damage to the etched surface. For this reason,
Compared to etching performed in a highly reactive state from beginning to end, the etching depth can be controlled better, verticality is ensured, and damage to the etched surface is less.

(Example) The present invention will be explained in more detail below with reference to the drawings.

FIG. 1 shows Ga produced by an embodiment of the method of the present invention.
As/A, 1) is a cross-sectional view showing the structure of a GaAs semiconductor optical waveguide. An) 0.5 Ga on the GaAs substrate 1
o,, As first cladding layer 2 is grown, Aff O,
5G a O, 5A s Ga on the first cladding layer 2
An As waveguide layer 3 is formed. The GaAs waveguide layer 3
All O,5G ao5 with a rib part on top
A second cladding layer 4 is formed.

A method for manufacturing the semiconductor optical waveguide shown in FIG. 1 will be described below. On the GaAs substrate 1, a molecular beam epitaxial growth method (MBE method) or a metal organic chemical vapor phase epitaxy method (MO
-CVD method), Ag3.5 Ga o, 5
A S first cladding layer 2, GaAs waveguide layer 3, A, C)
The second cladding layer 4 is sequentially grown. The thickness of each layer is AN o, s Ga
o5A s The first cladding layer 2 is about 1 to 2 μ..., GaA
s waveguide layer 3 is about 0.2 μl, Ag3.5 Ga o
, 5 As, the second cladding layer 4 has a thickness of about 1.2 μm.

After growing the crystal as described above, the waveguide rib part was
R I B E (Reactive
It is formed by the ion beam etching method. An outline of this process is shown in Figure 2. First, as shown in Figure 2(a), GaA
A photoresist mask 11 in the shape of a waveguide to be formed is formed on the s/AΩGaAs wafer 10. Next, as shown in FIG. 2(b), the portions not covered with the photoresist 11 are etched by about 0.1 μm by a first etching process with strong physical sputtering properties. Here, in order to achieve a state with high physical sputtering properties, the opening degree of the valve on the exhaust side of the etching chamber was set to about 60%, and C
The flow rate of the 112 gas is set to about 20 secIm, and the pressure inside the etching chamber is set to about 1 mTorr. At this time, the photoresist mask 11 is etched by at most Q, about 1 μm. Immediately after this, a second etching step, this time in a highly reactive state, etches the portion not covered by the photoresist 11 by an additional 0.9 μm.
■Approximately etching. Here, in order to achieve a highly reactive state, the opening degree of the exhaust side valve is set to about 30%, and Cj
? The flow rate of the two gases was set to about 5 sec, the pressure inside the etching chamber was set to about 1 mTorr, and the
Compared to the etching process described above, the flow rate of CD2 gas is lowered and the exhaust speed of the chamber is lowered. After that, when the photoresist 11 is removed using an organic solvent or the like, the second photoresist 11 is removed.
A semiconductor optical waveguide as shown in Figure (C) is obtained.

The above is an embodiment of the method for manufacturing a semiconductor optical waveguide according to the present invention, and the principle by which the controllability of the etching depth is improved by the above-mentioned manufacturing method will be explained below.

Conventionally, the controllability of the etching depth by dry etching has depended on the surface condition of the wafer being etched, and if dry etching is performed in a highly reactive state from the beginning, the etching depth will vary depending on the surface condition of the wafer. It was put away.

On the other hand, in this example, the wafer surface is first etched by about 0.1 μI in the first etching step with high physical sputtering properties, so the etching depth does not depend on the wafer surface condition. In addition, a clean etched surface can be newly exposed in a vacuum. Therefore, after the first etching process is completed, a clean etching surface that is in the same state is always subjected to the same etching process. This state of high physical sputtering properties is achieved by increasing the pumping speed and increasing the speed of gas molecules introduced within a unit time. In other words, the gas exhaust speed is generally inversely proportional to the square root of the molecular weight of the gas, so if the exhaust speed is increased by increasing the valve opening on the exhaust side, CD2 radicals become more dominant in the chamber than CN radicals. become. Moreover, when the amount of gas molecules introduced per unit time is increased, the energy given per unit time per molecule of CΩ2 gas decreases, and the energy required to dissociate from C, Q2 to C, I7 decreases. decreases, so CΩ2 radicals become even more dominant. Therefore, in the chamber, Cl72 radicals, which have a larger mass than CΩ radicals and have relatively low reactivity, become dominant, so that a state of high physical battering property is obtained. Since the second etching step is performed in a highly reactive state immediately after the first etching step, the controllability of the etching depth is improved compared to etching in a highly reactive state from the beginning. Ru. This state of high reactivity is achieved by reducing the pumping speed and reducing the amount of gas molecules introduced per unit time.

In addition, since the second etching process in a highly reactive state is performed immediately after the first etching process, the selectivity with the mask is ensured, and there is no worry of verticality deterioration due to mask regression. , less damage to the etched surface. Furthermore, after performing a first etching process using a gas with high physical sputtering properties such as Ar, CI? Compared to a dry etching process in which a second etching process is performed using a highly reactive gas such as No. No need to exhaust.

Although the RIBE method was used in this embodiment, the present invention is not limited to this, and the present invention is also applicable to other dry etching methods such as reactive ion etching (RIE).

(Effects of the Invention) As described above, according to the present invention, the controllability of the etching depth is improved in the dry etching step when forming the rib portion, regardless of the surface condition of the wafer. moreover,
The selectivity with respect to the mask is also ensured, there is no concern that the perpendicularity will deteriorate due to mask recession, and there is little damage to the etched surface. Furthermore, since the same gas is used, a gas switching process can be omitted, and vacuum evacuation accompanying gas switching is also unnecessary.

[Brief explanation of drawings]

FIG. 1 shows GaAs/
FIG. 2 is a cross-sectional view showing the structure of an Aj7GaAs semiconductor optical waveguide, and a conceptual diagram showing the etching process in this embodiment. 1-・-G a As substrate, 2 "" I) o,
, Gao, 5A s first cladding layer, 3...
GaAs waveguide, 4-All 0.5 Gao,
s A S second cladding layer, 1O--0GaAs/A (
l GaAs wafer, 11-...photoresist mask.

Claims (1)

[Claims] a step of laminating at least a first semiconductor cladding layer, a semiconductor waveguide layer, and a second semiconductor cladding layer on a semiconductor substrate to form a laminated semiconductor wafer; and a step of laminating an etching mask in the shape of an optical waveguide to be formed. The step of providing the structure on the semiconductor wafer and the step of removing the semiconductor second cladding layer other than the portion covered by the mask by etching to form the rib-type optical waveguide increase the pumping speed and the gas flow rate. The first etching step is carried out in a state with relatively strong physical sputtering properties, which is achieved by etching, and the second etching step is carried out in a state with relatively high reactivity, which is achieved by slowing the pumping speed and reducing the gas flow rate. 1. A method for manufacturing a semiconductor optical waveguide, characterized in that the etching step is a dry etching step performed successively using the same gas.