JP6572118B2 - Optical component structure - Google Patents

Description

  The present invention relates to an optical component for optical communication. More specifically, for example, a semiconductor substrate provided with an optical semiconductor element such as a photodiode (PD) and an optical component substrate provided with an optical component such as a lens are provided. The present invention relates to a bonded optical component structure.

  Conventionally, for example, in a receiver module for optical communication, a photodiode (PD: Photo Diode) is used as an optical semiconductor element for optical-electrical conversion, but a high-speed response corresponding to an increase in communication capacity in recent years. Characteristics are required.

  As one of means for dealing with the high-speed response, a technique of reducing the junction capacitance by reducing the junction area of the PD is generally used.

  However, since the junction area is synonymous with the area that can absorb light as a PD (light-receiving area), reducing the junction area is a reduction in the efficiency of optical coupling between the signal light and the PD, and mounting when mounted as a receiving module. There has been a problem that tolerance (allowable error range such as component mounting position and direction) is reduced.

  In order to solve this problem, by integrating, for example, lenses as optical components on the back surface of a PD substrate (semiconductor substrate) having a PD formed on the front surface, and condensing signal light from the back surface of the PD substrate, An optical component structure has been realized that can reduce the reduction in coupling sensitivity and tolerance even when the junction area is small (see Non-Patent Document 1).

(Conventional example 1)
FIG. 1 shows a cross-sectional structure of such an optical component as Conventional Example 1.
In FIG. 1, an optical semiconductor element is formed on the surface (upper surface) of a PD substrate 1 which is a semiconductor substrate by a laminated structure of an n-type semiconductor layer 2, a light absorption layer 3 formed of an i-type semiconductor, and a p-type semiconductor layer 4. This photodiode (PD) is configured. Wiring electrodes 5 and 6 are formed on the left and right ends of the n-type semiconductor layer 2 and on the p-type semiconductor layer 4 via contact electrodes, respectively, and incident light incident from the back surface (lower surface) side of the PD substrate 1. An electrical signal obtained by photoelectrically converting 7 is taken out.

  As described above, the lens 8 is formed as an optical component at a position corresponding to the optical axis of the PD on the back surface (lower surface) side of the PD substrate 1 on which the incident light 7 is incident, and at least the surface of the lens 8 ( In order to prevent reflection at the interface of incident light (signal light), an antireflection film (AR film: Anti-Reflection) 9 made of a dielectric multilayer film or the like is provided on the lower surface.

  Such a lens 8 can be formed by etching the PD substrate 1 as described in Non-Patent Document 1 below.

  However, this method of directly integrating the lens on the back surface of the semiconductor substrate of the PD is high in controlling the etching conditions and controlling the etching amount according to the in-plane thickness distribution of the lens shape for processing the back surface of the semiconductor substrate. There was a problem that accuracy was required.

  In addition to forming the optical components such as mirrors and prisms in addition to the lens, it is necessary to process the semiconductor substrate into a shape different from that of the lens, so etching conditions (processing conditions) different from lens formation are required. Further, there is a problem that the process becomes more complicated.

  In order to cope with these problems, a semiconductor wafer (semiconductor substrate) on which an optical semiconductor element such as PD is formed and a wafer (optical component substrate) on which optical components such as lenses, mirrors, and prisms are formed are manufactured separately. It is conceivable to form an optical component having a composite function by bonding the wafers to each other.

(Conventional example 2)
In the conventional example 2 shown in FIG. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, but the fundamental difference is that in FIG. 2, the optical component different from the PD substrate 1 which is a semiconductor substrate on which the PD is configured. The lens 8 is formed on the lower surface (back surface) side of the substrate 21. The material of the optical component substrate 21 is not required to be a semiconductor as long as it is transparent to the incident light 7 (signal light). For example, it can be glass or transparent plastic.

  As in FIG. 1, an antireflection film (AR film) 9 is provided on at least the surface of the lens 8 on the lower surface side of the optical component substrate 21. 2 is also provided with an antireflection film (AR film) 22 for preventing reflection at the joint with the PD substrate 1 on the upper surface side, and is formed by curing an adhesive or the like. It is bonded to the lower surface of the PD substrate 1 through the bonding layer 23.

  Thus, if the optical component substrate can be formed separately from the semiconductor wafer, there is an advantage that the optical component function can be added to the light receiving component at a low cost, such as using a molding technique for processing the optical component.

  In the case of such a configuration, in order to make the signal light incident from the lower side of FIG. 2 and absorbed by the light absorbing portion of the upper photodiode, at least a path portion (optical path) through which the incident light passes through the bonding layer 23. Needs to be transparent to the signal light, and it is necessary to use an adhesive having a high transmittance at the time of curing with respect to the wavelength of the signal light.

S.R.Cho et al, Enhanced Optical Coupling Performance in an InGaAs Photodiode Integrated With Wet-Etched Microlens, IEEE PTL (2002) Vol.14, No.3, p.378

  In the structure of the joining type optical component as shown in FIG. 2, the method of using an adhesive for wafer joining is generally used as described above. However, in the wafer joining using an adhesive, the adhesive is applied to the wafer joining surface. Then, since a bonding layer is formed by pressure bonding and curing, there is a problem that voids (bubbles) due to air may be formed at the wafer bonding interface.

  The generation of voids at such joints, their density, shape, and generation position are involved in delicate conditions during manufacturing, and it is difficult to completely control them.

  However, if a void is formed on the optical path of the signal light that connects the optical semiconductor element and the optical component across the inter-substrate junction, the light is refracted according to its shape and position, for example, optical coupling efficiency to PD This causes a problem of lowering.

  Since fluctuations in the optical coupling efficiency of the PD are directly related to fluctuations in the performance of the optical communication receiver module, it is desirable to inspect and sort at the chip stage and exclude defective ones.

  However, in order to inspect the presence or absence of voids and to sort out and eliminate defective ones, it is necessary to test and evaluate the light receiving sensitivity of the completed optical component, which increases the manufacturing cost for inspection and sorting There is a problem.

  The problem of void generation on the optical path of the joint is not limited to the light receiving part in which the PD and the lens are joined, but is a problem that occurs in common if it is a joint type optical part having a substrate joint with an adhesive. In addition to a PD as a light receiving element, a light emitting element such as an LED or a laser, a semiconductor substrate provided with a device, and an optical component substrate having an optical component such as a mirror or a prism other than a lens are bonded. The same applies to the optical component structure.

  The present invention has been made in view of such problems, and the object of the present invention is to eliminate the possibility of void generation on the joint optical path due to the adhesive in the joint type optical component, and at a low cost. The object is to provide an optical component structure with stable performance.

  In order to achieve such an object, the present invention is characterized by having the following configuration.

(Structure 1 of the invention)
An optical component comprising a semiconductor substrate provided with an optical semiconductor element on the front surface and an optical component substrate provided with an optical component on the back surface, wherein the back surface of the semiconductor substrate and the surface of the optical component substrate are bonded using an adhesive. In structure
The semiconductor substrate and the adhesive on the portion corresponding to the optical path between the optical semiconductor element of the joint the signal light forming an optical component between optical component substrate rather name
A weir body structure is formed so as to at least partially surround a portion corresponding to the optical path of the signal light of the joint portion, and the adhesive does not flow into the optical path;
The weir structure is
A weir body comprising another antireflection film formed on the surface of the optical component substrate or the semiconductor substrate on the side of the bonding portion and separated from the antireflection film formed in the portion corresponding to the optical path of the signal light An optical component structure formed from a film .

(Structure 2 of the invention)
In the optical component structure according to Configuration 1 of the invention,
The optical semiconductor element is one or more of a photodiode (PD), an LED, and a laser,
The optical component structure is one or more of a lens, a mirror, a prism, an optical waveguide, and a diffraction grating (grating).

(Structure 3 of the invention)
Forming an optical semiconductor element on a surface of a semiconductor substrate;
Forming an optical component on the back surface of the optical component substrate;
Forming an antireflection film on the front surface of the optical component substrate or the back surface of the semiconductor substrate;
The surface of the optical component substrate or the back surface of the semiconductor substrate is at least partially surrounded by a portion corresponding to the optical path of the signal light connecting the optical component and the optical semiconductor element to prevent the adhesive for bonding the substrate from flowing into the optical path. a step that form the Sekitai structure, wherein the anti-reflection film as a separate anti-reflection film that is spaced apart from,
Forming an adhesive pattern on the front surface of the optical component substrate or the back surface of the semiconductor substrate, spaced from the weir structure;
A method of manufacturing an optical component structure comprising the steps of pressure bonding the optical component substrate and the semiconductor substrate, and curing the adhesive to form a substrate bonded portion.

  According to the present invention described above, it is possible to provide an optical component structure with stable performance at low cost by eliminating the possibility of voids on the optical path of the junction in the junction type optical component.

It is a figure which shows the cross-section of the optical component of the prior art example 1. It is a figure which shows the cross-section of the optical component of the prior art example 2. It is a figure which shows the cross-sectional structure before and behind wafer joining of the optical component of Example 1 of this invention. It is a figure which shows PD board | substrate (surface) of the optical component of Example 1 of this invention. It is a figure which shows the optical component board | substrate (surface = joining surface) of the optical component of Example 1 of this invention. It is a figure which shows the cross-sectional structure before and behind wafer joining of the optical component of Example 2 of this invention. It is a figure which shows the optical component board | substrate (surface = joining surface) of the optical component of Example 2 of this invention. It is a figure which shows another example of the optical component board | substrate (surface = joining surface) of the optical component of Example 2 of this invention.

(Overview)
As described above, the optical component using wafer bonding has a problem that the void of the adhesive is generated on the optical path of the bonding portion between the substrates and the optical coupling efficiency is lowered.

  Although it is necessary to use an adhesive for wafer bonding, this problem does not occur unless the void of the adhesive is on the optical path. Therefore, a structure in which there is no adhesive on the optical path of the bonded portion may be adopted.

  Therefore, the adhesive is patterned by photolithography or the like, and the optical path portion is removed and the adhesive is applied so that the portion corresponding to the optical path of the bonded substrate joint has no adhesive.

  In addition, if there is no adhesive at the time of application, the adhesive may protrude from the optical path part due to a substrate pressing operation at the time of bonding. In order not to flow in, a structure (weir structure) is formed that blocks the sticking out of the adhesive around the optical path of the joint.

  As such a dam body structure, for example, an optical component structure that prevents the adhesive from protruding into the optical path can be realized by performing uneven processing on the wafer bonding surface of the optical component substrate or the semiconductor substrate provided with the optical component.

  As such concavo-convex processing, the concavo-convex processing can be performed directly on the substrate itself to form a weir body structure, but the surface on the bonding portion side of the substrate usually reduces the reflection loss of signal light at the bonding surface. Therefore, since an antireflection (AR) film is provided, the weir structure can be configured using this.

  Hereinafter, as a dam structure that prevents the adhesive from protruding into the optical path, an antireflection (AR) film is patterned to form a dam body film, and a dam body film such as a metal patterned on the AR film is formed. An embodiment is shown.

Example 1
FIG. 3 shows a cross-sectional structure of the optical component of Example 1 of the present invention before and after wafer bonding.
FIG. 3A shows a state before wafer bonding, and FIG. 3B shows a state after wafer bonding in which the wafer is pressed up and down. As for the PD substrate 1, a PD using an InP-based semiconductor is taken as an example. This PD can be formed by the following method.

  First, an n-type InP layer 2, a non-doped (i-type) InGaAs layer 3, and a p are formed on the surface of an InP substrate 1 made of high-resistance InP by using an epitaxial growth method such as metal organic chemical vapor deposition (MOVPE). A type InGaAs layer 4 is formed.

  Next, the p-type InGaAs 4, the non-doped InGaAs 3, and the n-type InP layer 2 are processed into a mesa type by a known photolithography and etching technique, and then the n-type InP layer 2 and the p-type InGaAs layer 4 are respectively ohmic-processed. A contact electrode is formed in contact.

  Further, as shown in FIG. 4, wiring electrodes 5 and 6 made of a metal plate made of Au or the like are formed on the surface of the PD substrate 1 on which PD is formed by photolithography, lift-off technology, vacuum deposition technology, or the like. To do.

  Finally, the back surface of the PD substrate is polished and adjusted to a desired thickness, and the PD substrate 1 is completed.

  On the other hand, for the optical component substrate 21, for example, an optical component is manufactured by processing the back surface (lower surface) of the glass substrate into a desired shape (the shape of the lens 8 in FIG. 3) using a known glass mold technique or the like. Is done.

  Glass mold technology is a technology for processing glass materials into arbitrary shapes by putting glass materials (preforms) into molds made of metal, etc., softening them by heating, and then pressing them. is there. If the material of the optical component substrate 21 is plastic, processing is easier.

  In the optical component substrate 21 formed in this way, the surface opposite to the bonding surface (back surface, bottom surface) is prevented from being reflected as much as possible when signal light is incident as in the conventional case. It is desirable to form an antireflection (AR) film 9 on at least a portion including the surface of the lens 8.

  In the first embodiment, when the InP, which is the material of the PD substrate 1, and the glass, which is the material of the optical component substrate 21, are bonded, the optical component substrate is designed so that reflection is not generated as much as possible on the bonding surface. An AR film 39 (on the process, not shown) is also formed on the upper surface (surface, bonding surface) of 21.

  The AR film 39 can be formed by a known method, for example, by sputtering a dielectric multilayer film using a sputtering apparatus.

  Further, in the first embodiment, the AR film 39 on the upper surface (surface, bonding surface) of the optical component substrate 21 formed as described above is circularly formed around the lens optical axis as shown in FIG. 5 by known photolithography and etching. The anti-reflection AR film 39a formed on the substrate and the AR film 39b which is a weir body film as a weir body structure formed in an annular shape spaced apart from the outside are patterned.

  By patterning in this way, an air layer 30 is provided in an annular shape outside the circular AR film 39a on the optical path directly under the PD, as shown in the state after wafer bonding in FIG. The AR film 39b is left in an annular shape as a weir body film on the outside, and a weir body structure can be formed.

  In this way, even if the adhesive 23a flows over the outermost annular AR film 39b at the time of joining, the air layer 30 becomes a buffer zone, and the central circular AR film 39a that is the optical path of the signal light is formed. It is possible to realize a dam structure that can prevent the adhesive from flowing in, and to prevent voids due to the adhesive from being generated on the optical path of the substrate bonding portion.

  Further, as shown in FIG. 5, a resin (adhesive 23a) that can be patterned by photolithography such as photosensitive polyimide is patterned on the upper surface (surface, bonding surface) of the optical component substrate 21 before bonding. Keep it. At this time, a pattern is provided in the portion directly under the PD which is the optical path so that there is no adhesive.

  As shown in FIGS. 3A and 5, the pattern of the adhesive 23 a surrounds the optical path portion, but reaches the outer periphery of the annular AR film 39 b (weir body film) in consideration of the protrusion due to the joining operation. In order to avoid this, it is desirable to perform patterning at intervals and to adjust the amount.

  Since there is no adhesive in the optical path part of the bonding layer through which the signal light beam passes, there is no restriction on the transparency of the adhesive after curing as before, and it can be used even if the transparency of the adhesive after curing is low The degree of freedom of the adhesive that can be used is also great.

  Further, on the premise that the cross-sectional shape of the optical path of the signal light 7 at the substrate bonding portion is circular, the shape of the antireflection film (AR film) is expressed as circular or annular according to the figure, but the light beam of the optical path Since the cross-sectional shape is not necessarily circular, it is obvious that the shapes of the AR film 39a and the AR film 39b may be adapted to the cross-sectional shape of the light beam in the optical path.

  Furthermore, since the weir body film as the weir body structure only needs to prevent the inflow of the adhesive to the optical path portion, it is not necessary to have an annular shape completely surrounding the optical path portion of the signal light. Even if it is a weir body structure formed of a weir body film composed of one or a plurality of parts that at least partially surround the optical path part to such an extent that an adhesive can be prevented from flowing into the optical path part in consideration of the agent pattern, etc. good.

  The PD substrate 1 thus formed and the optical component substrate 21 are coated by patterning an adhesive by a known wafer bonding technique, and then bonded and cured to form a bonding layer 23 to be integrated (FIG. 3 ( b)).

  Thereafter, chipping is performed by dicing to complete a light receiving component including an optical component and a PD.

  In the structure of the first embodiment, since there is no adhesive in the portion that becomes the optical path of the signal light, in principle there is no void generation that affects the signal light, and overcoming the AR film 39b that is a weir body film. Even if the adhesive flows, the air layer 30 as a buffer layer is prevented from reaching the AR film 39a which is an antireflection film for signal light, so that the possibility of generation of voids can be made almost zero. Inspection that assumes a decrease in coupling efficiency is no longer necessary, contributing to cost reduction in optical component manufacturing.

(Example 2)
FIG. 6 shows a cross-sectional structure of the optical component according to the second embodiment of the present invention before and after wafer bonding.

  In Example 2 of FIG. 6 as well, PD is produced on the PD substrate 1 as in Example 1 of FIG. 3 (FIG. 6A). However, an AR film 69a is also formed on the lower surface of the PD substrate 1 so that reflection does not occur as much as possible even if signal light enters the PD substrate from the air layer 60 below the PD substrate after polishing (FIG. 6 ( b)).

  On the other hand, for the optical component substrate 21, as in the first embodiment, for example, a glass substrate is used, and the lens 8 and the AR film 9 are formed on the lower surface thereof, but the upper surface (surface, bonding surface) of the optical component substrate 21 is formed. Also, when the signal light 7 is transmitted from the optical component substrate 21 to the air layer 60, the AR film 69b is provided so that reflection is not generated as much as possible. Further, unlike the first embodiment, the AR film 69b on the bonding surface is provided on the entire upper surface of the optical component substrate 21 as shown in FIGS. 6 and 7, and the pattern processing as shown in FIG. 5 is not performed.

  In Example 2 of FIG. 6, patterning is performed on the surface of the AR film 69b at the joint surface in a ring shape with the optical axis as the center, as shown in FIG. 7, by known photolithography and lift-off technology or plating technology. An annular weir body film 70 made of a metal or the like is formed as a weir structure.

  The weir body film 70 functions as the same weir body structure as the outermost annular AR film 39b described in the first embodiment, and prevents the adhesive 23a from flowing into the center portion of the optical path due to the protrusion during bonding. .

  The weir body film (annular AR film 39b) having the weir body structure of Example 1 was formed by the same process as the circular AR film 39a on the optical path as the antireflection film, and therefore the antireflection effect was taken into consideration. However, since the thickness of the weir body film 70 is limited, the weir body film 70 according to the second embodiment is a single-layer film different from the AR film. It is possible to easily form the structure of the optimum thickness and material in order to prevent the protrusion.

  As shown in the cross-sectional view after wafer bonding in FIG. 6B, in the second embodiment, unlike the first embodiment, an air layer 60 is provided at the center of the optical path of the signal light 7 directly under the PD. Since both the PD substrate 1 and the optical component substrate 21 have the AR films 69a and 69b formed on the bonding surface side, it may be considered that the reflection of the signal light 7 by the air layer 60 is negligible.

  Since the air layer 60 immediately below the PD in Example 2 has a larger volume than the air layer 30 in Example 1, even if the adhesive 23a protrudes beyond the weir body film 70, there is no influence on the optical path. Although the volume is relatively small, on the contrary, since the volume is large, expansion / contraction of the air in the air layer 60 due to a temperature change or the like may be a problem.

  In this case, as shown in FIG. 8, a part of the circumference of the annular weir body film 70 is cut out so that an air passage is secured from the air layer 60 directly under the PD to the outer periphery of the chip. Thus, the weir body film 80 formed in a hairpin shape and extending to the outside of the substrate and drawn out and communicated with the outside of the optical component structure as an air passage of the air layer 60 may be used.

  Also in the structure of the second embodiment, as in the first embodiment, the basic shape of the weir body film is not limited to the annular shape, and one or more portions that at least partially surround the portion corresponding to the optical path of the signal light. A dam body structure formed of a dam body film may be used.

  Also in the structure of the second embodiment, as in the first embodiment, since there is no adhesive in the portion that becomes the optical path of the signal light, in principle there is no void generation that affects the signal light. Even if the adhesive flows over the film 70 or 80, the air layer 60 is wide, so that it can be prevented from reaching the optical path portion of the signal light, and the possibility of void generation can be almost zero. This eliminates the need for inspections that assume a decrease in optical coupling efficiency due to, thereby contributing to cost reduction in optical component manufacturing.

(Other examples)
As described above, in the first and second embodiments, the light receiving component in which the semiconductor substrate on which the PD is formed and the optical component substrate on which the lens is bonded is described. However, the optical component structure of the present invention is bonded with an adhesive. The present invention can be applied to any optical component having a joint. As another example, in addition to a PD as a light receiving element, a semiconductor substrate provided with an optical semiconductor element that is a light emitting element such as an LED or a laser can be used. In addition to the lens, an optical component substrate provided with optical components such as a mirror, a prism, an optical waveguide, and a diffraction grating (grating) may be used.

  These optical semiconductor elements and optical components are not limited to one on the substrate, and a plurality of the same or different types may be provided on both substrates, and the optical path of signal light connecting these elements and components. It is also clear that the present invention can be applied even if there are a plurality of them.

  In addition, the structure of the weir body structure and the weir body film is described as being formed on the surface (upper surface, bonding surface) of the optical component substrate, but the surface on the bonding portion side (back surface, lower surface, bonding surface) of the semiconductor substrate. It is also clear that it may be formed.

  The surface on which the adhesive is applied is not necessarily the same as the surface on which the dam body structure and the dam body film are formed, and accuracy of alignment at the time of substrate bonding (wafer bonding) is required. It is also possible to divide the surface to be coated and the surface on which the weir body structure and the weir body film are formed into the surface on the optical component substrate side, the surface on the semiconductor substrate side, or vice versa.

  As described above, according to the present invention, it is possible to provide a low-cost and stable performance optical component structure by eliminating the possibility of voids on the optical path of the junction in the junction-type optical component. It becomes.

1 PD substrate (semiconductor substrate)
2 n-type semiconductor layer, n-type InP layer 3 i-type light absorption layer, non-doped (i-type) InGaAs layer 4 p-type semiconductor layer, p-type InGaAs layer 5, 6 wiring electrode 7 incident light, signal light 8 lens 9, 22 , 39, 39a, 39b, 69a, 69b Antireflection film (AR film)
21 Optical component substrate 23 Bonding layer 23a Adhesive 30, 60 Air layer 70, 80 Weir body film

Claims (3)

An optical component comprising a semiconductor substrate provided with an optical semiconductor element on the front surface and an optical component substrate provided with an optical component on the back surface, wherein the back surface of the semiconductor substrate and the surface of the optical component substrate are bonded using an adhesive. In structure
There is no adhesive in the portion corresponding to the optical path of the signal light connecting the optical semiconductor element and the optical component at the joint between the semiconductor substrate and the optical component substrate,
A weir body structure is formed so as to at least partially surround a portion corresponding to the optical path of the signal light of the joint portion, and the adhesive does not flow into the optical path;
The weir structure is
A weir body comprising another antireflection film formed on the surface of the optical component substrate or the semiconductor substrate on the side of the bonding portion and separated from the antireflection film formed in the portion corresponding to the optical path of the signal light An optical component structure formed of a film. The optical component structure according to claim 1 ,
The optical semiconductor element is one or more of a photodiode (PD), an LED, and a laser,
The optical component structure is one or more of a lens, a mirror, a prism, an optical waveguide, and a diffraction grating (grating). Forming an optical semiconductor element on a surface of a semiconductor substrate;
Forming an optical component on the back surface of the optical component substrate;
Forming an antireflection film on the front surface of the optical component substrate or the back surface of the semiconductor substrate;
The surface of the optical component substrate or the back surface of the semiconductor substrate is at least partially surrounded by a portion corresponding to the optical path of the signal light connecting the optical component and the optical semiconductor element to prevent the adhesive for bonding the substrate from flowing into the optical path. a step that form the Sekitai structure, wherein the anti-reflection film as a separate anti-reflection film that is spaced apart from,
Forming an adhesive pattern on the front surface of the optical component substrate or the back surface of the semiconductor substrate, spaced from the weir structure;
A method of manufacturing an optical component structure comprising the steps of pressure bonding the optical component substrate and the semiconductor substrate, and curing the adhesive to form a substrate bonded portion.