JPH09288241A - Film optical waveguide device and production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an optical waveguide device on a semiconductor wafer by using a standard stage. SOLUTION: An upper cladding layer 110 is partly removed from above a waveguide 106 and a temporary spacer layer 114 is deposited in place of the removed upper cladding 110 as this method. A metallic film 116 is deposited and patterned on the temporary spacer 114. The temporary spacer 114 is removed and the metallic film 116 is suspended on the waveguide 106. When a difference of voltage is applied between the metallic film 116 and an electrode 108 formed on the lower cladding 102, the metallic film 116 collapses and leans on the waveguide 106. The waveguide 106 attenuates the arbitrary light propagated therein.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to the field of optical processing, and in particular to the manufacture of optical waveguide devices such as switches and attenuators.

[0002]

Optical fiber waveguides are widely used in communication systems due to their small size and extremely high bandwidth. Although the optical fiber itself is very small and relatively inexpensive, it is difficult to produce related optical devices such as modulators, switches and attenuators so cheaply that the available output of fiber optics can be fully utilized.

[0003]

In order to develop a method for manufacturing an optical device on a semiconductor wafer such as silicon or gallium arsenide using a standard semiconductor wafer manufacturing process,
Many efforts have been made. For example, resistive heat or control of free carriers can be used to add impurities to silicon to form electronic devices that modulate light passing through the device. If standard devices could be used to form optical devices on semiconductor wafers, the devices would be much easier to integrate into existing semiconductor waveguides,
It will increase the number of practical applications of fiber optic devices.

[0004]

Means for Solving the Problems One aspect of the present invention is:
A method of manufacturing an optical waveguide, such as a switch or an attenuator, using a temporary spacing layer to support a metal film above the waveguide during the manufacturing process. This temporary spacing layer is removed, allowing the metal film to be deflected towards the electrodes formed in the lower cladding. When deflected, the metal film defeats the entire internal reflection of the waveguide, attenuating the light carried in the waveguide. This manufacturing process produces a new optical device that can be easily manufactured.

[0005]

DETAILED DESCRIPTION OF THE INVENTION Optical waveguides are characterized by the fact that light is completely reflected by the interface between its inner core and the surrounding material called cladding.
It works by allowing light to pass freely through the inner core. The ratio between the index of refraction of the inner core and the index of refraction of the cladding determines the maximum angle at which the transmitted light is completely reflected when it strikes the interface. The larger this angle, the more modes the waveguide supports and the larger the admittance angle to the fiber. Larger admittance angles result in larger tolerances in aligning the waveguide with adjacent optical devices.

Although air is a suitable cladding, it does not prevent an object, such as an adjacent optical fiber, from contacting the optical fiber. If the adjacent optical fiber contacts the first optical fiber, the adjacent optical fiber acts as a cladding for the first optical fiber, thus defeating the total internal reflection. In order to prevent internal reflections from being defeated by nearby objects, glass or the like with impurities is used to prevent other objects or optical fibers from contacting the optical fibers and defeating internal reflections.

Semiconductor waveguides can be formed using a two-piece oxide cladding surrounding a nitride inner core. Semiconductor waveguides are typically deposited by first depositing a lower cladding of silicon dioxide and then depositing and patterning a waveguide of silicon nitride on the lower cladding. Then another layer of oxide is deposited over the nitride and bottom cladding to form the top cladding.

Some types of optical waveguide devices, such as taught in US Pat. No. 5,278,925, "Integrated Optical Waveguide Devices and Methods," issued Jan. 11, 1994, have been placed in proximity to or in contact with a waveguide. The light transmitted to the waveguide is modulated by deflecting the metal film to a position with an air gap. This metal film modifies the effective index of refraction of the waveguide to attenuate the light transmitted in the waveguide. As the attenuation effect of the optical device increases, the optical device acts like a switch, effectively blocking all light transmitted in the waveguide.

Ideally, the metal film may be formed on the planar surface of the upper cladding and the upper cladding is removed from underneath a portion of the metal film so that the metal film is directed toward the waveguide core. Deflection is possible. This manufacturing method is
What is needed is an upper cladding material with a refractive index of about 1.45 that can be undercut or removed from underneath selected areas of the metal film. Unfortunately, the development of suitable materials is very difficult and most of the existing low index materials contain fluorine, which complicates the deposition and etching of aluminum metal films over the cladding. I have to.

The lack of a suitable upper cladding that can be easily undercut after depositing an overlying metal film has prompted research into alternative device designs and manufacturing processes. One promising solution is to remove some of the upper cladding and replace it with a planarizing spacer layer that can be easily undercut. The metal film is deposited on top of the planarizing spacer layer. After depositing the film, the planarizing spacer layer is removed, leaving the film suspended above the waveguide. This two-material method does not require an ideal single material that has a suitable index of refraction and can be easily undercut, but instead an oxide cladding layer that provides a suitable index of refraction,
Two materials are used, with a temporary planarizing layer that can be easily undercut.

1 to 7 show an optical device according to the invention at several steps of the manufacturing process. FIG.
In, a substrate 100 such as a semiconductor wafer is prepared,
A lower cladding layer 102 and a waveguide core layer 104 are deposited on the prepared substrate 100. The lower cladding layer 102 is typically silicon oxide, while the core layer 1
04 is typically silicon nitride. Silicon wafers
It typically has an electronic device formed on the surface of a silicon wafer, which includes electrodes 103 formed on the surface of the silicon wafer. These electronic devices are used to control the operation of optical devices.

After the core layer 104 is deposited, it can be patterned to form a waveguide. In FIG. 2, the core layer 104 is patterned to form two parallel waveguides 106. Although two waveguides 106 are shown in FIG. 2, any number of waveguides 106 can be used. Waveguide 106 is typically two waveguides 1.
It is formed close enough to form crosstalk between 06. After the waveguide is formed, the wafer 10
The 0's are heated to reflow the waveguide, giving it a rounded top surface.

Next, a thin metal layer is deposited on the lower cladding layer 102 near the waveguide 106 and the electrode 108.
Is patterned to form a. The cross-sections of FIGS. 1 through 7 pass through each half of the device at different points, as shown in FIG. This allows FIGS. 1 to 7 to show as much detail as possible.

In order that the insulator can protrude above the electrodes,
The electrodes are typically comb-shaped. The insulator prevents the subsequently formed metal film from contacting the electrodes and shorting the device. Although a comb shape is shown, many other configurations can be used. For example, as an alternative,
A hole is formed in the electrode to allow an insulating post to be formed above the electrode to insulate the electrode from the deflected metal film. Alternatively, the insulating post is formed directly on top of the solid electrode.

After the electrodes have been formed, an upper cladding layer 110, typically silicon oxide, is formed on top of the lower cladding layer 102, waveguide 106, and electrodes 108. As discussed previously, this upper cladding layer 110 ensures that all light passing through the waveguide is internally reflected and that adjacent objects constrain the core of the waveguide and cause Prevents the entire reflection from beating.

The upper cladding layer 110 is removed from the area above the electrodes where the metal film will deflect. FIG. 3 shows the partially completed device after the top cladding has been removed, and the patterned electrode 1
08 and the waveguide 106 are exposed. If the upper cladding 110 is removed, the electrodes 108 can be used to indicate when to stop etching the upper cladding. Ideally, the etching of the upper cladding is stopped as soon as the bottom of the pit formed in the upper cladding is flush with the top surface of the electrode 108. The electrodes 108 are then etched back so that the oxide remaining from the upper cladding projects between the comb teeth of the electrodes. As discussed above, this protrusion prevents the metal film from contacting the electrode 108.

The upper cladding layer 110 is replaced with a temporary planarizing spacer that can be easily undercut or etched away. One useful material to temporarily replace the upper cladding layer 110 is FUTURREX, the upper cladding layer 1
It is a photoresist particularly suitable for planarizing the large steps formed by the removal of 10. Any compound that can be applied to the device with a planar layer and that can be easily removed will be useful. To planarize the surface, the compound is preferably spun into a thick layer on a silicon wafer. The weaker the photosensitivity of the compound, the more likely it is to have a flat surface on which to form the metal film.

FUTURREX or other temporary spacer 114, typically 10 to 15 micrometers
Are rotatably formed on the wafer, covering the pits 112. Ideally, the temporary spacer 114 has a top surface that only fills the pits and is flush with the top surface of the surrounding upper cladding 110. However, in practice, the temporary spacer 114 covers the entire wafer,
As shown in, the upper surface of the temporary spacer 114 is located above the upper surface of the upper cladding 110. The upper surface of the temporary spacer 114 will typically not be perfectly flat, but will have a sloped region 116 at the edge of the pit 112. These slope regions 116 form the waveguide 106.
It is acceptable as long as the area covering is approximately flat.

The temporary spacers 114 are applied and then cured to be stable during future processing. The temporary spacers 114 are then patterned to form areas that can be mechanically contacted with the upper cladding 110 layer for support, allowing electrical contact with electrodes on the wafer 100. Since the ideal temporary spacer material is not photosensitive, an oxide layer is created over the temporary spacers, and a hard etch mask is formed and used to pattern the temporary spacer material.

The mechanical coupling between the metal film and the upper cladding supports the metal film as it deflects downwards with respect to the waveguide 106. According to the first embodiment, this mechanical connection is formed by a series of paths between the metal film and the upper cladding, as shown in the left half of FIGS. 5 and 8B. In another embodiment shown in the right half of FIGS. 5 and 8B, the metal film is simply a temporary spacer layer 114.
Of the metal film to form a continuous bond between the metal film and the upper cladding layer along the two edges of the metal film.

The electrical connection between the metal film on the surface of the wafer and the electrode uses a single via, or wafer 100 and lower cladding 102.
Lower cladding 102 and upper cladding 11
0, and finally through an indirect connection with the upper cladding 110 and a metal film.

The method of electrical connection is selected by the range of path steps between the two layers. If the vias are wide enough, the metal from the film layer is kept with sufficient force on both sides of the via, and a single via connects the metal film to the electrodes on the wafer. If a structurally good path cannot be formed between the metal film and the wafer surface, then multiple paths between the layers must be used indirectly. Most devices require multiple paths to connect the electrodes on the wafer surface to the metal film due to the poor range of steps that can be obtained when depositing metal in the paths.

After the temporary spacer layer is patterned, a metal layer is deposited over the wafer and patterned to form a metal film 116. Metal film 116 is typically a 0.5 micrometer thick layer of aluminum.
After the metal film 116 is formed, the temporary spacer layer is removed, leaving the film suspended over the exposed waveguides and electrodes as shown in FIG.

To activate the device, a voltage potential is created between the metal film and the electrode at the bottom of the pit. As shown in FIG. 7, this voltage potential creates an electrostatic force between the membrane and the electrode, causing the membrane to collapse towards the electrode. The elevated oxide insulator keeps the film from touching the electrodes, but allows the film to touch the waveguide along most of the exposed length of the waveguide. The contact between the membrane and the waveguide defeats the internal refraction of the waveguide and prevents light from propagating through the waveguide. To use the device as a switch, the light transmitted from the first waveguide is coupled into the second waveguide by the narrow gap between the two waveguides. The metal film associated with the first waveguide is deflected at this time,
Attenuate or block light passing through the first waveguide. The metal film associated with the second waveguide does not deflect and light coupled into the second waveguide can pass through the second waveguide.

While we have disclosed above specific embodiments for optical waveguide devices and methods of making such devices, such detailed references, except as set forth in the following claims, are of this invention. It is not intended to limit the scope. Furthermore, it is to be understood that, with respect to some of the detailed embodiments described herein, further modifications are now apparent to those skilled in the art and are all within the scope of the appended claims. It is intended to include modifications.

With regard to the above description, the following items will be further disclosed.

(1) forming a lower cladding layer on a substrate, forming a waveguide on the cladding layer, and depositing an upper cladding layer on the lower cladding layer and the waveguide; Removing a portion of the upper cladding layer from a region adjacent to the waveguide, depositing a temporary spacer layer on the waveguide in the region, depositing a metal layer on the spacer layer, A method of manufacturing an optical device comprising removing a spacer layer.

(2) The method according to claim 1, wherein the lower cladding is an oxide.

(3) The method according to claim 1, wherein the upper cladding is an oxide.

(4) The temporary spacer layer is FUTU
The method of paragraph 1 which is RREX.

(5) The method according to item 1, wherein the metal layer is an aluminum alloy.

(6) The method according to claim 1, further comprising the step of forming an electrode layer on the lower cladding layer.

(7) A substrate, a lower cladding supported by the substrate, at least one electrode on the lower cladding, a waveguide supported by the lower cladding, and a waveguide of the waveguide. An upper cladding that covers the first portion and does not cover the second portion of the waveguide, and extends over the second portion of the waveguide that is spaced over the upper cladding. An optical device comprising a metal film being formed.

(8) The optical device according to item 7, further including an electronic device formed in the substrate.

(9) The optical device according to item 7, wherein the upper cladding is an oxide.

(10) The optical device according to item 7, wherein the lower cladding is an oxide.

(11) The waveguide is a nitride of the seventh
The optical device according to the item.

(12) A method of manufacturing an optical waveguide device, wherein the upper cladding layer 110 is formed from above the waveguide.
Of the upper cladding 11 by removing a part of the
Including a temporary spacer layer 114 instead of zero. A metal film 116 is deposited and patterned on the temporary spacer 114, the temporary spacer 114 is removed, and the metal film 116 is suspended on the waveguide 106. When a voltage difference is applied between the metal film 116 and the electrode 108 formed on the lower cladding 102,
The metal film 116 is crushed and leans against the waveguide 106,
Attenuate any light propagating in the waveguide 106.

[Brief description of drawings]

For a more complete understanding of the present invention and its advantages, the drawings accompanying the above description are as follows.

FIG. 1 is a cross-sectional view of an optical device according to one embodiment of the present invention, prior to patterning the waveguide on the lower cladding.

2 is a cross-sectional view of the optical device of FIG. 1, showing the upper cladding.

FIG. 3 shows a cross-sectional view of the optical device of FIG. 2 after the upper cladding has been etched to form pits.

FIG. 4 is a cross-sectional view of the optical device of FIG. 3 after the temporary planarizing spacers have been deposited in the etched pits.

5 is a cross-sectional view of the optical device of FIG. 4 after a metal film is formed on the temporary planarizing spacer.

FIG. 6 is a cross-sectional view of the optical device of FIG. 5 after the temporary planarizing spacers have been removed.

7 is a cross-sectional view of the optical device of FIG. 6 showing the deflection of a portion of the metal film.

FIG. 8A is a plan view of the optical device of FIGS. 1-7, showing electrodes formed on a lower cladding layer.
B is a plan view of the optical device shown in FIGS. 1 to 7, showing a completed metal film.

[Explanation of symbols]

 100 Substrate 102 Lower Cladding Layer 104 Core Layer 106 Waveguide 108 Electrode 110 Upper Cladding Layer 112 Pit 114 Temporary Spacer Layer 116 Metal Film

Claims (2)

[Claims] 1. A lower cladding layer is formed on a substrate, a waveguide is formed on the cladding layer, and an upper cladding layer is deposited on the lower cladding layer and the waveguide. Removing a portion of the upper cladding layer from a region adjacent to the waveguide, depositing a temporary spacer layer on the waveguide in the region, depositing a metal layer on the spacer layer, A method of manufacturing an optical device comprising removing a layer. 2. A substrate, a lower cladding supported by the substrate, at least one electrode on the lower cladding, a waveguide supported by the lower cladding, and a first waveguide of the waveguide. An upper cladding that covers one portion and does not cover the second portion of the waveguide, and extends over the second portion of the waveguide that is spaced over the upper cladding. An optical device having a metal film.