CN106207743B

CN106207743B - Laser structure for grating coupling and packaging method

Info

Publication number: CN106207743B
Application number: CN201610727562.5A
Authority: CN
Inventors: 宋琼辉; 杜巍; 马洪勇
Original assignee: Accelink Technologies Co Ltd
Current assignee: Accelink Technologies Co Ltd
Priority date: 2016-08-25
Filing date: 2016-08-25
Publication date: 2020-06-23
Anticipated expiration: 2036-08-25
Also published as: WO2018036161A1; CN106207743A

Abstract

The invention relates to a laser element, which comprises a substrate and a laser chip, wherein the laser chip is provided with an active area for generating and outputting laser and an electrode for supplying power to the laser chip; the laser chip is placed in an etched trench in the substrate with the active region of the laser chip aligned with the optical waveguide on the substrate. The laser element only comprises two parts, namely a substrate integrating the optical waveguide and the electrode and a laser chip, and other discrete elements are not needed, so that the laser element is simple in structural design and low in cost; and the coupling of the laser optical path and the coupling of the grating coupler of the chip formed by the laser and the silicon photonic can be realized by adopting a flip chip alignment process, and the coupling efficiency is high by adopting a passive alignment technology, so that the method is suitable for high-efficiency mass production.

Description

Laser structure for grating coupling and packaging method

Technical Field

The invention relates to a laser element for optical fiber communication, in particular to a laser structure for grating coupling and a packaging method, specifically relates to a method for realizing coupling of a laser light source and a grating coupler in a silicon photonic device, and belongs to the field of communication.

Background

Silicon photonic materials have become a research hotspot in the world at present due to their high integration level, good high-frequency characteristics, low power consumption, and compatibility with existing large-scale integrated circuit processes, and various silicon photonic devices such as high-speed electro-optical modulators, photodetectors, and integrated chips have appeared and become mature gradually.

Because the silicon material belongs to an indirect semiconductor material and the material is difficult to manufacture into a laser element, an external III-IV group laser is generally adopted as a light source, and the input of the light source is realized by epitaxial growth or a coupling alignment mode. The mode of epitaxially growing III-IV group lasers on silicon-based materials has high process requirements and great realization difficulty, and only few manufacturers have related reports internationally, and no completely mature products are sold in the market. Therefore, most manufacturers adopt a method of coupling and aligning the complete laser chip and the silicon photonic chip to realize the coupling of the laser light source.

There are two main types of structures for coupling and aligning the silicon photonic device and the light source, one is an end-face coupling structure, and the other is a grating coupler structure. The grating coupler is one of the main light source input modes of the silicon optical chip because the grating coupler is easy to realize in process. For the light source input of the grating coupler, Luxtera is related in US patent application publication US201414324544a1, and the whole laser light source part is composed of a plurality of discrete parts such as a laser chip, a lens, an isolator, a reflector and the like, and the related parts are more and the structure is complex, so that the production efficiency of the assembly process is difficult to improve.

Disclosure of Invention

The invention aims to provide a laser structure with simple structure and a coupling alignment method thereof, and provides a rapid coupling alignment method of a grating coupler of a chip formed by the laser and silicon photons.

The technical scheme adopted by the invention is as follows:

a laser element comprises a substrate and a laser chip, wherein the laser chip is provided with an active area for generating and outputting laser and an electrode for supplying power to the laser chip, one end of the substrate is provided with an etching groove for at least partially accommodating the laser chip, the other end of the substrate is provided with a light emergent surface, and the substrate is also provided with an optical waveguide extending between the etching groove and the light emergent surface; the laser chip is placed in the etching groove of the substrate, and the active area of the laser chip is aligned with the optical waveguide on the substrate.

The surface of the laser chip comprises an alignment mark, the substrate is provided with the alignment mark, and the alignment mark on the laser chip and the alignment mark on the substrate are used for determining the relative position between the laser chip and the substrate so as to facilitate the alignment of the laser chip and the substrate.

And a height positioning block is arranged in the etching groove of the substrate, and the vertical height difference of the height positioning block from the center of the optical waveguide is consistent with the vertical height difference of the surface of the laser chip from the center of the active area of the laser chip, so that after the laser chip is placed in place in the etching groove of the substrate, the active area of the laser chip is aligned with the center of the optical waveguide.

The light-emitting surface of the substrate is a reflecting surface, and the reflecting surface and the surface of the substrate form an angle of 30-50 degrees, so that the light-emitting direction of the optical waveguide is changed in a total reflection mode.

The substrate is also provided with an electrode, and the electrode on the substrate is electrically connected with an electrode for supplying power to the laser chip.

The method for coupling and aligning the laser chip and the substrate of the laser element comprises the following steps: respectively arranging alignment marks on the surface of the laser chip and the substrate, and determining the relative position relationship between the alignment mark on the surface of the laser chip and the alignment mark on the substrate as a preset relative position relationship when the active region of the laser chip is aligned with the optical waveguide of the substrate; respectively identifying an alignment mark on the surface of the laser chip and an alignment mark on the substrate in an image identification mode so as to accurately determine the relative positions of the laser chip and the substrate, and accurately adjusting the position of the laser chip so that the alignment mark of the laser chip and the alignment mark on the substrate meet a preset mutual position relationship so as to align the laser chip with an optical waveguide on the substrate in the horizontal direction of the substrate; and the surface of the laser chip is completely contacted with the height positioning block on the substrate by controlling the pressure of the laser chip, so that the laser chip is accurately aligned with the optical waveguide of the substrate in the vertical direction.

High precision flip chip equipment is used to image recognize alignment marks on the laser chip surface and the substrate, fine tune the laser chip position, and pressure control the laser chip.

A laser assembly, comprising: a silicon photonic integrated chip and a laser component as claimed in claims 1 to 5, the electrodes on the substrate of the laser component electrically connecting the electrodes on the silicon photonic integrated chip and the electrodes of the laser chip of the laser component, the reflective surface of the substrate where the optical waveguide is located being aligned with the grating coupler on the silicon photonic integrated chip.

The alignment precision error between the reflection region of the optical waveguide and the grating coupler is less than or equal to 5 microns, and the alignment error between the electrode on the substrate and the electrode on the silicon photonic integrated chip and the electrode of the laser chip is less than or equal to 20 microns.

A method for manufacturing a laser assembly, comprising the steps of: aligning electrodes on a substrate of the laser element with electrodes on the silicon photonic integrated chip; aligning a local area where a reflecting surface optical waveguide of a substrate of the laser element is located with a grating coupler on the silicon photonic integrated chip; electrically connecting electrodes on a substrate of the laser element with electrodes on the silicon photonic integrated chip using a conductive paste; and arranging matching glue between the local area where the optical waveguide of the reflecting surface of the substrate of the laser element is positioned and the grating coupler on the silicon photonic integrated chip.

The invention has the advantages that:

1. the laser only comprises two parts, namely a substrate integrating the optical waveguide and the electrode and a laser chip, and has no other discrete elements, simple structural design and low cost.

2. In the packaging process, coupling of the laser optical path is realized by adopting a high-precision flip-chip bonding alignment process; the coupling of the laser and the grating coupler of the silicon photonic integrated chip can be realized by adopting the conventional chip mounting technology. The whole packaging process is a passive alignment technology, the coupling efficiency is high, and the packaging method is suitable for high-efficiency mass production.

Drawings

FIG. 1 is a schematic diagram of a laser according to the present invention;

FIG. 2 is a schematic cross-sectional view of a laser according to the present invention;

FIG. 3 is a schematic diagram of a substrate structure of a laser according to the present invention;

FIG. 4 is a schematic diagram of a chip coupling structure of a laser and a silicon photonic device according to the present invention;

FIG. 5 is a schematic cross-sectional view of a laser and a silicon photonic integrated chip provided by the present invention;

FIG. 6 is a schematic diagram of a silicon photonic integrated chip structure provided by the present invention;

FIG. 7 is a schematic diagram of the optical path of a laser provided by the present invention;

the labels in the figure are:

1: substrate 2: laser chip

3: gold wire bonding wire 4: silicon photon integrated chip

5: gold-tin solder 6: conductive adhesive

7: matching glue 11: optical waveguide

12, 13: electrode 14: etching groove

15: alignment mark 16: height positioning block

17: coupling surface 18: reflecting surface

21: laser chip active region 41: grating coupler

42, 43: silicon photonics chip upper electrode

Detailed Description

The invention is described in further detail below with reference to the accompanying drawings and detailed description, in order to facilitate the understanding and implementation of the invention by those skilled in the art.

The structure of the laser provided by the invention is shown in fig. 1-3, and comprises a substrate 1 and a laser chip 2; the substrate 1 includes an optical waveguide 11, an electrode 12, an electrode 13, an etching groove 14, an alignment mark 15, a height positioning block 16 (not shown in fig. 1), a coupling surface 17, and a reflection surface 18, where one end of the substrate 1 is provided with the etching groove 14 for at least partially accommodating the laser chip 2, the other end of the substrate 1 is provided with the reflection surface 18 (i.e., a light exit surface), the optical waveguide 11 extends between the etching groove 14 and the reflection surface 18, and the reflection surface 18 is used for changing the light exit direction of the optical waveguide 11 in a total reflection manner; the laser chip 2 has an active region 21 that generates and outputs laser light and electrodes (anode and cathode) that supply power to the laser chip 2, and the surface of the laser chip 2 contains alignment marks. The laser chip 2 is placed in the etched trench 14 of the substrate 1 with the active region 21 of the laser chip aligned with the optical waveguide 11 on the substrate.

The structural section of the laser provided by the invention is shown in fig. 2, in order to realize the precise alignment of the active area of the laser chip 2 and the optical waveguide 11 on the substrate 1, an alignment mark 15 and a height positioning block 16 are designed in an etching groove 14 on the substrate 1, wherein the vertical height difference of the height positioning block 16 from the center of the optical waveguide 11 is consistent with the vertical height difference of the surface of the laser chip 2 from the center of the active area 21 of the laser chip 2, so that the active area 21 of the laser chip 2 is aligned with the center of the optical waveguide 11 after the laser chip 2 is placed in place in the etching groove 14 of the substrate 1. The alignment mark 15 may be provided at any position on the substrate 1 that facilitates determination of the relative positional relationship between the substrate 1 and the laser chip 2.

The invention also provides a method for quickly coupling and aligning the laser chip 2 and the optical waveguide 11 of the substrate 1, which can respectively identify the alignment mark of the laser chip 2 and the alignment mark 15 on the substrate 1 in an automatic or manual image identification mode by utilizing high-precision flip chip welding equipment so as to accurately determine the relative position relationship between the laser chip 2 and the substrate 1, and accurately adjust the position of the laser chip 2 by utilizing the high-precision flip chip welding equipment so that the alignment mark of the laser chip 2 and the alignment mark 15 on the substrate 1 meet the preset mutual position relationship, thereby aligning the laser chip 2 with the optical waveguide 11 on the substrate 1 in the horizontal direction of the substrate 1; the pressure control provided to the laser chip 2 by the flip chip bonding apparatus brings the surface of the laser chip 2 into full contact with the height positioning blocks 16 on the substrate 1, thereby accurately aligning the laser chip 2 with the optical waveguide 11 of the substrate 1 in the vertical direction, as shown in fig. 2. The precision alignment here requires that the alignment precision error between the laser chip 2 and the optical waveguide 11 is 1 μm or less.

The left end of the electrode 13 on the substrate 1 is located at the bottom of the etching groove 14 and contacts with the electrode on the upper surface (i.e. the surface falling into the etching groove 14 and facing the substrate 1) of the laser chip 2, and the gold-tin solder 5 is required to be plated on the contact part, as shown in fig. 3. In the flip chip bonding process, the gold-tin solder is heated and melted, so that the electrode 13 on the substrate 1 and the electrode on the upper surface of the laser chip 2 are electrically connected, as shown in fig. 2. The electrode on the back side (i.e. the lower surface, the surface opposite to the substrate 1) of the laser chip 2 can be electrically connected by means of gold wire bonding, that is, the electrode on the back side of the laser chip 2 and the electrode 12 on the substrate 1 are electrically connected by the gold wire bonding wire 3, as shown in fig. 1. When the cathode and the anode of the laser chip 2 are both on the upper surface of the laser chip 2, the

electrodes

12 and 13 on the substrate 1 are both located on the bottom surface of the etching groove 14 and are connected with the cathode and the anode of the laser chip 2 by the gold-tin solder 5.

The coupling surface 17 of the optical waveguide 11 on the substrate 1, which is located on the side wall of the etching groove 14, is designed to form an angle of 6 to 10 degrees with the laser emitting end surface of the active region 21 of the laser chip 2, so as to reduce the reflection of light between the laser chip 2 and the coupling end surface 17 of the optical waveguide 11, thereby reducing the influence of the reflected light on the power and mode stability of the laser chip 2.

The right end (emitting end face) of the substrate 1 is polished to form an angle of 30 to 50 degrees with the surface (horizontal plane) of the substrate 1 to form a reflecting surface of the emitted light, and the purpose is to enable the laser to be transmitted to the right end (emitting end face) of the substrate 1 through the optical waveguide 11, then to be totally reflected and output in a direction perpendicular to the surface (vertical to the horizontal plane) of the substrate 1.

The relative positions of the

electrodes

12 and 13 on the substrate 1 and the waveguide reflection area are consistent with the relative positions of the

electrodes

42 and 43 and the grating coupler 41 on the silicon photonic integrated chip 4.

Fig. 4-5 are schematic diagrams of a chip coupling structure formed by a laser and a silicon photonic chip. Except for the left end region where the laser chip 2 is located, the other part of the laser substrate 1 is bonded to the upper surface of the silicon photonic integrated chip 4. The upper surface of the silicon photonic integrated chip 4 is designed with a grating coupler 41 and

electrodes

42, 43 as shown in fig. 6.

By the patch technology, the right end part of the electrode 13 on the laser substrate 1 is aligned with the electrode 43 on the silicon photonic integrated chip 4, the right end part of the electrode 12 on the laser substrate 1 is aligned with the electrode 42 on the silicon photonic integrated chip 4, and the local area where the waveguide of the reflecting surface of the laser substrate 1 is positioned is aligned with the grating coupler 41 on the silicon photonic integrated chip 4. The

electrodes

12 and 13 on the laser substrate 1 and the

electrodes

42 and 43 on the silicon photonic integrated chip 4 are electrically connected by using the conductive adhesive 6, and the reflection on the grating surface is reduced by using the matching adhesive 7 between the laser substrate 1 and the grating coupler 41 on the silicon photonic integrated chip 4. As shown in fig. 5, the alignment here requires that the alignment precision error between the reflection region of the optical waveguide 11 and the grating coupler 7 is 5 microns or less, and the alignment error between the electrodes is 20 microns or less.

The conductive adhesive 6 and the matching adhesive 7 are both thermal curing adhesives, the curing temperature is 150-200 ℃, the curing temperature is lower than the welding temperature of the gold-tin solder of 250-350 ℃, the bonding reliability of the laser chip cannot be influenced, and the performance of other areas on the silicon photonic integrated chip 4 cannot be influenced.

When the laser module constituted by the above-mentioned manner works, the driving current output by the

electrodes

42 and 43 on the silicon photonic integrated chip 4 is loaded to the cathode and the anode of the laser chip 2 through the conductive adhesive 6 and the

electrodes

12 and 13 on the laser substrate 1, so that the laser chip 2 works to emit light, the light emitted from the active region 21 of the laser chip 2 enters the optical waveguide 11 of the substrate 1, is reflected to the reflecting surface 18 at the right end of the substrate 1 and then is output from the lower surface of the substrate 1, and finally enters the grating coupler 41 on the silicon photonic integrated chip 4 through the matching adhesive 7, thereby realizing the whole process of outputting the light from the laser chip 2 to inputting the silicon photonic integrated chip 4, as shown in fig. 7.

Although the present invention has been illustrated and described in detail with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes in the details of fabrication of the laser structure and packaging methods may be made therein without departing from the spirit and scope of the invention upon reading and understanding the specification and the drawings. Such modifications are intended to fall within the scope of the invention as claimed.

Claims

1. A laser assembly comprising a silicon photonic integrated chip, a substrate and a laser chip, the silicon photonic integrated chip having a grating coupler and an electrode on an upper surface thereof, the laser chip having an active region for generating and outputting laser light and an electrode for supplying power to the laser chip, wherein: one end of the substrate is provided with an etching groove at least partially accommodating the laser chip, the other end of the substrate is provided with a light-emitting surface, and the substrate is also provided with an optical waveguide extending between the etching groove and the light-emitting surface; the laser chip is placed in an etching groove of the substrate, and an active area of the laser chip is aligned with the optical waveguide on the substrate;

the substrate is also provided with an electrode, and the electrode on the substrate is electrically connected with an electrode powered by the laser chip; the other end part of the electrode on the substrate is aligned with the electrode on the silicon photonic integrated chip and is electrically connected with the electrode; the silicon photons form a driving current output by an on-chip electrode, and the driving current is loaded to a cathode and an anode of the laser chip through the electrode on the substrate, so that the laser chip works and emits light;

the waveguide reflection region on the substrate is aligned with the grating coupler on the silicon photonic integrated chip; and light emitted from the active region of the laser chip enters the optical waveguide of the substrate, is transmitted to the reflecting surface at the right end of the substrate, is reflected and is output from the lower surface of the substrate, and finally enters the grating coupler on the silicon photonic integrated chip.

2. A laser assembly as claimed in claim 1, wherein: the surface of the laser chip comprises an alignment mark, the substrate is provided with the alignment mark, and the alignment mark on the laser chip and the alignment mark on the substrate are used for determining the relative position between the laser chip and the substrate so as to facilitate the alignment of the laser chip and the substrate.

3. A laser assembly as claimed in claim 2, wherein: and a height positioning block is arranged in the etching groove of the substrate, and the vertical height difference of the height positioning block from the center of the optical waveguide is consistent with the vertical height difference of the surface of the laser chip from the center of the active area of the laser chip, so that after the laser chip is placed in place in the etching groove of the substrate, the active area of the laser chip is aligned with the center of the optical waveguide.

4. A laser assembly according to claim 3, wherein: the light-emitting surface of the substrate is a reflecting surface, and the reflecting surface and the surface of the substrate form an angle of 30-50 degrees, so that the light-emitting direction of the optical waveguide is changed in a total reflection mode.

5. A laser assembly as claimed in claim 1, wherein: the alignment precision error between the reflection region of the optical waveguide and the grating coupler is less than or equal to 5 microns, and the alignment error between the electrode on the substrate and the electrode on the silicon photonic integrated chip and the electrode of the laser chip is less than or equal to 20 microns.

6. A method for coupling alignment of a laser chip and a substrate of a laser assembly according to any of claims 3-5, comprising the steps of:

respectively arranging alignment marks on the surface of the laser chip and the substrate, and determining the relative position relationship between the alignment mark on the surface of the laser chip and the alignment mark on the substrate as a preset relative position relationship when the active region of the laser chip is aligned with the optical waveguide of the substrate;

respectively identifying an alignment mark on the surface of the laser chip and an alignment mark on the substrate in an image identification mode by using high-precision flip chip welding equipment so as to accurately determine the relative positions of the laser chip and the substrate, and accurately adjusting the position of the laser chip so that the alignment mark of the laser chip and the alignment mark on the substrate meet a preset mutual position relation, thereby aligning the laser chip with an optical waveguide on the substrate in the horizontal direction of the substrate;

by using high-precision flip chip bonding equipment, the surface of the laser chip is completely contacted with the height positioning block on the substrate by controlling the pressure of the laser chip, so that the laser chip is accurately aligned with the optical waveguide of the substrate in the vertical direction.

7. The method of claim 6, wherein: high precision flip chip equipment is used to image recognize alignment marks on the laser chip surface and the substrate, fine tune the laser chip position, and pressure control the laser chip.

8. A method for manufacturing a laser assembly according to any of claims 1-5, characterized in that it comprises the steps of:

aligning electrodes on a substrate of the laser element with electrodes on the silicon photonic integrated chip by a chip mounting technique;

aligning a local area where a reflecting surface optical waveguide of a substrate of the laser element is located with a grating coupler on the silicon photonic integrated chip;

electrically connecting electrodes on a substrate of the laser element with electrodes on the silicon photonic integrated chip using a conductive paste;

and arranging matching glue between the local area where the optical waveguide of the reflecting surface of the substrate of the laser element is positioned and the grating coupler on the silicon photonic integrated chip.