JPS60222819A - Optical integrated circuit and its production - Google Patents

Abstract

PURPOSE:To improve the life and reliability of an optical element by providing an insulating layer under an electrode which impresses a driving voltage thereby obviating generation of the breakdown of the electrode. CONSTITUTION:An insulating film 7 which flattens the shape of a ridge is formed on one surface of a substrate 4 after a ridge type waveguide 2 having the metallic electrode 1 is formed thereon. The tentire surface of the film 7 is thereafter uniformly etched and the film 7 on the ridge is thinner than the film 7 except on the ridge and therefor only the electrode 1 on the waveguide can be exposed. The layer 7 is formed under a bonding pad 6 when the pad 6 is formed by lift-off, etc. The easy formation of the layer 7 only under the pad 6 is thus made possible without using a mask.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an optical integrated circuit used in the fields of optical communications and optical information processing, and a method for manufacturing the same, and in particular to a compound semiconductor optical integrated circuit that utilizes electro-optic effects. This is related to.

[Background of the invention]

In recent years, the practical application of optical communications has progressed rapidly, and research and development are actively being carried out to make optical components smaller and more reliable. Waveguide-type optical devices using the electro-optic effect are capable of high-speed operation, and have conventionally mainly been used with L, which has a large electro-optic coefficient.
Dielectric materials such as iNbOi have been used. However, from the perspective of integrating individual optical elements such as light sources, isolators, and modulators, and aiming for high-density integration, active research is also being conducted into optical integrated circuits using compound semiconductor materials such as GaAs and InP. ing. Optical devices made of such compound semiconductor materials are ridge-shaped.

The basic component is an optical waveguide, such as an embedded type or a loaded type. Among these three-dimensional optical waveguides, ridge-type optical waveguides have a good optical energy confinement rate, can form curved waveguides with a curvature as small as 71%, and are relatively easy to form. .

FIG. 1 shows an example of a directional coupler consisting of a ridge-shaped optical waveguide. Light is mainly confined in the n-GaAs layer directly under the electrode. The AQ on the optical waveguide has Schottky contact with the n''-GaAs layer, and applying a reverse voltage changes the refractive index directly under the electrode.Generally, in such a structure, light confinement depends on the thickness. The intensity in the optical waveguide is stronger in the direction than in the transverse direction, and has an elliptical distribution.Therefore, the intensity is stronger in the optical fiber.

When considering coupling, it is necessary to make the ridge high and make the intensity distribution close to a circular shape to obtain a high coupling efficiency. It also occurs due to radiation caused by bending.

In order to prevent crosstalk between optical waveguides, it is desirable that the slab mode is near the cutoff outside the optical waveguide. The width of the leading waveguide is extremely narrow, approximately 10 μm or less, so that only a single mode is excited. Therefore, it is necessary to form a bonding pad on the outside of the optical waveguide for connection with an external electrode.

The optical waveguide layer under this bonding butt has a thickness such that the slab mode is close to the cutoff, and the wavelength is, for example, 1.
3 pm, and the refractive index of n GaAs and n 10 GaAs are 3.44 and 3.43, respectively, then approximately 1.2 μm
The thickness will be . Therefore, breakdown may occur at the bonding butt at a relatively low driving voltage, which extremely deteriorates the life and reliability of the optical device.

[Purpose of the invention]

An object of the present invention is to provide a highly reliable optical integrated circuit and a method for manufacturing the same, which has been made to prevent electrode destruction due to the breakdown described above.

[Summary of the invention]

The structure of the optical device according to the present invention is shown in FIG.

That is, a bonding pad is formed on the epitaxial film outside the optical waveguide with an insulating layer interposed therebetween.

The manufacturing method will be explained below using FIG. 3. First, after forming a ridge-shaped optical waveguide with metal electrodes, an insulating film is formed on the substrate surface to flatten the ridge shape (3-1), and then the entire surface of the insulating film is uniformly etched. Since the insulating film on the ridge is thinner than the insulating film outside the ridge, only the metal electrode on the optical waveguide can be exposed (3-2). Finally, if a bonding butt is formed by lift-off or the like, an insulating layer is formed under the bonding pad (3-3). Note that when removing an unnecessary insulating film for reasons such as cleavage, the unnecessary insulating film can be selectively etched using the bonding pad as a mask. After forming an insulating film on the ridge, it is possible to form a through hole on the ridge and connect it to an external electrode, but forming a through hole on an extremely thin waveguide requires high manufacturing precision. It takes. According to the present invention, without using a mask,
The insulating layer can be formed only under the bonding bat very easily.

[Embodiments of the invention]

Examples according to the present invention will be described below.

3μ thick by MOCVD method on GaAs substrate.
An epitaxial layer of m n GaAs was formed. After AQ was deposited on this substrate, an optical waveguide was patterned using photoresist, and a ridge-shaped optical waveguide was formed by ion milling. The width of the optical waveguide is 5 μm and the height is 2 μm. Select polyimide isoindoquinazolinedione resin or polyimide resin as an insulating film to flatten the shape of this ridge-shaped optical waveguide, and apply it to the entire surface with a spinner to form a resin layer on the entire surface. was 0.7 μm outside the optical waveguide, while it was 0.2 μm on the optical waveguide. next,
The substrate coated with the resin layer is etched again by ion milling. As shown in Figure 4, acceleration voltage 600V
, when the ion current density is 0.35 mA/cmZ and the initial vacuum level is 10-''ton or less, the etching rate of the resin layer and AQ is 130 people/win p.
150 people/win, and etching with good reproducibility is possible. Furthermore, even when the initial achieved vacuum level is 10" tons or more, the etching rate of the resin layer increases with respect to the achieved vacuum level, whereas the etching rate of AQ decreases, whereas the etching rate of AQ decreases. On the contrary, it decreases.

Therefore, the risk of disconnection of AQ on the optical waveguide due to excessive etching is small, and even if the thickness of the resin layer (insulating layer) on the optical waveguide is slightly different, it is possible to expose only AQ on the optical waveguide. It's easy. Finally, a bonding pad is formed by lift-off. Since there is a resin layer on the outside of the optical waveguide, even an optical waveguide with a high ridge can be easily lifted off. The present invention is applied to a directional coupler-type optical switch, and ultimately relates to input and output end faces of the optical switch. At this time, if there is a resin layer, a good cracking surface cannot be obtained, so the resin layer other than the one under the bonding pad is etched away using a plastic atsher. 1
Breakdown due to breakdown occurred at around 7V, but by intervening the resin layer, the dielectric breakdown was improved to 30V.

〔Effect of the invention〕

As explained in the above embodiments, according to the present invention, the electrodes do not break even when a large driving voltage is applied, and the life and reliability of the optical device is improved due to the easy manufacturing method. The effect is great.

[Brief explanation of drawings]

FIG. 1 is an example of a cross section of a ridge-type directional coupler using a compound semiconductor. FIG. 2 is a sectional view of an optical element with a resin layer (insulating layer) interposed below a bonding pad to which a driving voltage is applied. FIG. 3 shows a manufacturing process for an optical device having the structure shown in FIG. FIG. 4 shows the etching rate of PIQ and AQ by ion milling with respect to the ultimate vacuum degree. 1 metal electrode, 2... ridge type optical waveguide, 3... high resistance epitaxial film, 4... substrate, 5... back electrode, 6 bonding pad, 7... resin layer (insulating layer).

Claims (1)

[Claims] (1) In order to improve electrode destruction due to breakdown in a compound semiconductor optical integrated circuit using the electro-optic effect,
An optical integrated circuit characterized in that an insulating layer is provided under an electrode to which a driving voltage is applied. 2. Forming a planarizable insulating film on the substrate surface of the compound semiconductor that constitutes the ridge-type optical waveguide with metal electrodes,
By uniformly etching this insulating film, only the upper part of the ridge-type optical waveguide is exposed, and the metal electrode on the optical waveguide is connected to the bonding pad formed on the I@edge film. Method of manufacturing Th optical integrated circuit.