KR0169837B1 - Method for precise alignment of optical device and optical fiber - Google Patents

Abstract

The present invention relates to a precise manual alignment method of optical elements and optical fibers.

Precise manual alignment method of the light emitting device and the optical fiber according to a preferred embodiment of the present invention, in the precision manual alignment method of the optical device and the optical fiber using the V-groove, when the optical fiber is aligned when manufacturing the V-groove A marker for measuring V-groove width is formed on the substrate for manual alignment for accurate measurement of the groove width, and in order to increase the alignment accuracy with the optical fiber when flip chip bonding the optical device to the substrate for manual alignment. An alignment code for flip chip bonding is formed.

Description

Precise manual alignment of optical element and optical fiber

1 is a cross-sectional view showing a manufacturing process diagram of a manual alignment substrate according to the present invention and a process of aligning an optical element and an optical fiber to the prepared substrate.

Figure 2 (a) is a plan view showing an example of the use of the marker for measuring the V-groove width in accordance with the present invention.

Figure 2 (b) is a perspective view showing an example of the use of flip chip bonding alignment code according to the present invention.

Figure 2 (c) is a plan view showing an example of the use of the fine ruler for optical fiber alignment according to the present invention.

Figure 2 (d) is a plan view showing an example of the use of the optical fiber traveling origin according to the present invention.

Figure 3 (a) is a perspective view of a substrate for a light emitting device manufactured according to the present invention.

Figure 3 (b) is a perspective view of a substrate for a light receiving element manufactured according to the present invention.

* Explanation of symbols for main parts of the drawings

1: silicon wafer 2: silicon nitride

3: photoresist for metal deposition

4: under-bump metallurgy (UBM)

5: UBM pad 5 ': Redefined UBM pattern

6: silicon nitride 7: V-groove

8: photoresist for forming V-groove opening 9: V-groove opening

10: thick film photoresist 11: deposited solder bumps

12: reflowed solder bump 13: light emitting device waveguide

14 substrate for manual alignment 15 light emitting element

16: optical fiber arranged on substrate for light emitting element

17: optical fiber core 18: light receiving element

19: light receiving window

20: optical fiber arranged on substrate for light receiving element

21: Alignment code for flip chip bonding 22: Marker for measuring V-groove width

23: fine ruler for optical fiber alignment 24: optical fiber progress origin

25: fiber progress check marker 26: (111) reflective surface

27: light emitting element position on the substrate 28: light receiving element position on the substrate

29: light receiving window position

The present invention relates to a precise manual alignment method of optical elements and optical fibers.

More specifically, the present invention provides a V-groove to achieve precise optical coupling by enabling the position control of the optical device and the optical fiber when optical coupling between the optical device and the optical fiber using the V-groove on the silicon substrate. It relates to a precise manual alignment method of the optical device and the optical fiber used.

There are two ways to combine optical fiber that transmits light with optical devices. There are two types of optical alignment methods: active alignment and passive alignment.

In general, unlike the active alignment method of aligning optical fibers while observing an electrical signal from a lens-attached TO package, in the manual alignment method, optical devices such as a light emitting device are fixed on a silicon substrate by flip chip bonding or the like, and then on the same substrate. The bonding process is completed by aligning the optical fiber in a V-shaped groove (V-groove) which is designed and formed so that the center core of the optical fiber is aligned with the waveguide of the flip chip bonded optical element adjacent thereto.

Therefore, in the manual sorting method, wire bonding can be eliminated, and it has the advantage of not only excellent electrical characteristics but also simple packaging operation, so that mass production is easy. The positional correlation of the optical devices must be maintained very accurately. Particularly, in the case of a light emitting device, alignment accuracy of about ± 2 μm in the left and right directions (x direction) and ± 1 μm in the height direction (y direction) should be maintained in a plane perpendicular to the optical waveguide, and aligned in the V-groove. The distance between the cut surface of the optical fiber and the optical waveguide (z direction) should also be adjusted to about 20 μm to obtain practical optical coupling efficiency.

Of these, the alignment of the optical element and the optical fiber in the x direction is to align the waveguide of the optical element with the central axis of the optical fiber placed on the V-groove. For this purpose, the optical element is placed on a flip chip bonding pad formed in accordance with the position of the V-groove. It must be aligned and bonded. When flip chip bonding of solder-based optical devices, the self-alignment property due to the surface tension of the molten solder can be used to achieve the x-direction alignment at the desired position without precisely aligning the optical devices before bonding. Is the basis of the optical element manual alignment method. However, in practice, it is very difficult to obtain the alignment accuracy of the error range within 2 μm only by the restoring force by the surface tension of the solder, and in practice, the time required for bonding may be very long. It is desirable to be as precise as possible. Bonding pads are typically used as a pattern for aligning chips such as optical elements on a substrate. However, since the size reaches about 100 μm, the alignment precision necessary for optical coupling cannot be obtained with such an alignment pattern.

On the other hand, the alignment in the y-direction, that is, the height of the optical element can be adjusted by adjusting the size of the solder bumps or forming a stage for controlling the height of the optical element between the optical element and the substrate, but the central core of the optical fiber It is important to control the size of the V-groove because the height of is determined purely by the width of the V-groove. However, since the width of the V-groove for manual alignment of the optical fiber is usually 140 μm or more, to adjust it to an error range of about 1 μm, there must be a means for measuring the reproducibility of the process and the reality. When measuring the V-groove width using a conventional optical microscope, it is very difficult to measure the accuracy within 1μm due to the problem of resolution and measurement error, and it is possible to measure using the latest measuring equipment of 2D or 3D method. Even though special equipment is required and time-consuming, it is difficult to reflect the result in the process immediately.

In addition, the optical fiber is aligned on the V-groove (z-axis alignment) to achieve optical coupling with the optical device in which the flip chip bonding is completed, in which the spacing between the center core and the optical device active region on the optical fiber cutting surface is important. In the case of simple cutting of the optical fiber, the closer this interval is, the better, but considering the process margin in the process for fixing the aligned optical fiber, about 20 ± 10 μm is sufficient. However, in the case of making the end of the cut optical fiber lenticular in order to increase the optical coupling efficiency, this spacing varies depending on the diameter of the lens and usually requires an alignment error within 3 m. Particularly, in the case of the light emitting device, the optical fibers can be aligned while observing the distance. However, in the optical coupling of the light receiving device, since the light receiving device is flip chip bonded and the light receiving window exists underneath, the position of the optical fiber cannot be seen. Difficult to achieve the desired spacing.

Therefore, the manual alignment method may determine the z-axis spacing while observing the light output by driving the optical device during the process, but this method is a factor of cost increase due to the trouble of connecting the electrodes and the need for additional equipment. do.

After all, the present invention is to solve the above problems, an object of the present invention is to facilitate the alignment for flip chip bonding of the optical device when the optical device and the optical fiber is coupled by the manual alignment method, the optical fiber and optical device escape The precise manual alignment method of optical devices and optical fibers that enables precise manual alignment of optical devices and optical fibers for optical coupling by precisely controlling the distance between them and enabling the width control of the V-groove to determine the height of the optical fibers. In providing.

Precision manual alignment method of the light emitting device and the optical fiber according to the preferred embodiment of the present invention to achieve the above object, in the precision manual alignment method of the optical device and the optical fiber using the V-groove, when manufacturing the V-groove In order to accurately measure the V-groove width at which the optical fiber is aligned, a marker for measuring V-groove width is formed on the passive alignment substrate, and the alignment accuracy with the optical fiber is increased when flip-chip bonding the optical element to the passive alignment substrate. A flip chip bonding alignment code is formed on a passive alignment substrate.

At this time, in order to precisely adjust the distance between the light emitting element and the optical fiber in the direction of the optical fiber axis, it is preferable to further form a fine ruler for optical fiber alignment on the manual alignment substrate.

In addition, in order to precisely control the position of the optical fiber during optical coupling between the flip chip bonded light-receiving element and the optical fiber, the optical fiber traveling origin is further added to the exposed point on the passive alignment substrate at a certain distance away from the point where the end surface of the optical fiber should finally be located. It is preferable to form.

In addition, in order to confirm the progress accuracy of the optical fiber during optical coupling between the light receiving element and the optical fiber, it is preferable to further form an optical fiber progress check marker at the front end of the optical fiber traveling origin.

In order to fabricate a substrate for passive alignment to achieve the above object, an under-bump metallurgy (UBM) for the formation of silicon nitride, the formation of V-grooves, the pads and the alignment codes for insulation and silicon etching prevention ), And solder deposition for flip chip bonding are required, followed by bonding of the optical device and alignment of the optical fiber, which will be described in more detail with reference to the accompanying drawings.

1 is a cross-sectional view showing a manufacturing process diagram of a manual alignment substrate according to the present invention and a process of aligning an optical element and an optical fiber to the manufactured substrate.

In the first process, silicon nitride 2 (or silicon oxide) is deposited on the silicon wafer 1, which is a substrate for optical element and optical fiber alignment, for electrical insulation and V-groove formation. ) Is shown.

In the second process, a pad 5 called a UMB (for example, Ti / Ni / Au) capable of solder bonding for solder bonding, an optical element alignment code 21, and a marker for measuring V-groove width 22 are used. And a fine ruler 2 for optical fiber alignment (in the case of a light emitting device), an optical fiber advancing origin 24, and an optical fiber progress check marker 25 (in the case of a light receiving device) as necessary. ), An exposure process is performed to form an opening defining a pattern, and then the metal layer 4 is deposited on the entire surface as shown in FIG. 1 (b), and as shown in FIG. The lift-off process is used to form special patterns such as UBM pads 5 and markers. In this case, an electroplating method may be used to form the UBM. If the transmission line is connected to the UBM pad 5, the silicon nitride 6 may be used to prevent the solder from sticking along the transmission line. The pattern 5 'is redefined, and the cross section through this process is shown in FIG. 1 (d).

In the third process, the photoresist 8 is first applied to form the calculated V-groove 7 pattern, the pattern is defined through an exposure process, and the silicon nitride 2 is dry etched to dry the V-groove 7. Opening 9 is made. The cross-sectional view after this process is shown in FIG. 1 (e).

In the fourth step, after the photoresist 8 is removed in the third step, the etching process is performed in the opening 9 for forming the V-groove 7 by using the silicon nitride 2 as an etch stopper. KOH or the like is used.

In this case, using the V-groove width measuring marker 22 formed in the photolithography and the deposition process of the second process, misregistration of the etching pattern or misregistration occurring in the photo transfer operation is performed. Not only can it easily determine the expansion of the width due to the error, but also the process of controlling the V-groove to a desired width, it is possible to prevent excessive etching. The V-groove thus formed is shown in FIG. 1 (f), and an example of use of the V-groove width measuring marker is shown in FIG. 2 (a).

The fifth process is a process for forming solder bumps, and as shown in FIG. 1 (g), a lift-off process is used as in the process of forming the UBM pad 5 in the second process. To this end, after the thick film photoresist 10 is applied and exposed to define a pattern for solder deposition, the solder 11 is deposited on the entire surface, and the thick film photoresist 10 is removed from the acetone solution to remove the UBM. Only the solder bumps on the pad 7 are left. At this time, the solder bumps are usually formed on one side of the substrate or optical element, and sometimes both of them are necessary.

In the sixth process, a reflow process is performed in an oven of nitrogen (or hydrogen) atmosphere to uniformize the composition of the deposited solder. When the solder reflows, the shape of the solder 12 is due to the surface tension of the molten solder. Is rounded and is shown in FIG. 1 (h).

In the seventh process, the chip 15 of the optical element 15 having the UBM pattern corresponding to the solder bump pad pattern on the passive alignment substrate 14 having the above-described process is flip-chip bonded, and the direction of the optical waveguide 13 is The result of bonding completed to match the direction is shown in FIG. 1 (i). The alignment is achieved by matching the alignment code 21 of the optical device having the corresponding pattern with the alignment code 21 formed on the substrate 14 during the alignment for bonding. In this case, as the alignment code 21, a simple cross or a vernier form, or various shapes for increasing convenience and accuracy of alignment may be used. In addition, by forming two or more of these symbols in different positions, it is possible to accurately correct the rotational alignment error of the device and the substrate during the alignment for bonding. An example of the use of the flip chip bonding alignment code 21 is shown in FIG. 2 (b).

The eighth step is to align the optical fiber to the optical element flip-chip bonded on the substrate 14, the optical fiber core 17 and the light emitting element by aligning the optical fiber 16 to the first (j) or the light emitting element 15 The state where the alignment is completed so that the optical waveguide 13 in (15) coincides.

In order to align the optical fiber 16 to the light emitting device 15, it is important not only to align the xy direction but also to adjust the distance (z-direction) between the optical waveguide 13 and the optical fiber cutting surface of the optical device. The use of the fine ruler 23 for aligning the optical fiber not only makes the measurement of this distance very accurate, but also makes the alignment easy because of the easy reading. The fine ruler 23 for aligning the optical fiber is formed to the front and rear of the cut surface to which the optical waveguide 13 is exposed in consideration of the inaccuracy of the size of the optical device and the bonding process error, and the fine ruler 23 of FIG. An example of use is shown.

On the other hand, as shown in Figure 1 (k), in the optical coupling of the light receiving element 18, as described above, the optical fiber 20 is located below the flip chip bonded light receiving element 18, the optical fiber ( 20 is transmitted to the light-receiving window 19 using the (111) slope of the V-groove 7 coated with a metal film as a reflecting surface, so that the optical signal aligned on the V-groove 7 20) should be pushed to the lower point of the light receiving element 18. Since the progress of the optical fiber 20 cannot be seen from the bottom of the flip chip bonded chip, the cut surface of the optical fiber 20 is positioned to the point most suitable for optical coupling. It becomes difficult to do it. Therefore, in this process, the optical fiber cutting plane is aligned with the optical fiber traveling origin 24 set outside of the light receiving element bonding position 28, and then the optical fiber 20 is moved in the -z-direction by using a micropositioner for a predetermined distance. By proceeding with, the optical fiber 20 can be precisely aligned to a desired point under the bonded light receiving element 18. Furthermore, when the optical fiber progress confirmation marker 25 having a different length or shape is set so as to be distinguished from the optical fiber progress origin marker 24 at a predetermined distance in the direction of the optical fiber 20 traveling from the origin, the progress of the optical fiber 20 You can check the accuracy on the way. An example in which the optical fiber progressing point 24 and the optical fiber 20 are aligned by using the same is shown in FIG. 2 (d).

In addition, the light-emitting device substrate and the light-receiving device substrate manufactured according to the present invention described above are shown in FIGS. 3 (a) and 3 (b), respectively.

As described in detail above, in the present invention, when the optical devices are aligned by flip chip bonding to achieve optical coupling with the optical fiber, an alignment code for flip chip bonding is formed on the optical device and the substrate, and the width of the V-groove is increased. Forming a marker for measuring the optical density, forming a fine ruler for adjusting the alignment gap when the light emitting device and the optical fiber are coupled, and setting an optical fiber progression point for optical coupling with the light receiving device, respectively. While reducing the time required for self-alignment, the error is small, and the exact width of the V-groove can be easily measured and immediately reflected in the process, and the distance between the light emitting element and the optical fiber can be adjusted constantly in a short time. In addition, the optical fiber can be aligned in the correct position even in the invisible position under the light receiving element.

Claims (4)

In the precision manual alignment method of the optical device and the optical fiber using the V-groove, the V-groove width is measured on the passive alignment substrate for accurate measurement of the V-groove width in which the optical fiber is aligned when the V-groove is manufactured. The precision of optical devices and optical fibers, characterized in that the formation of the yaw marker, the flip chip bonding alignment code is formed on the manual alignment substrate in order to increase the alignment accuracy with the optical fiber when flip-chip bonding the optical device to the substrate for manual alignment. Manual sorting method. According to claim 1, Fine alignment of the optical element and the optical fiber, characterized in that further forming a fine ruler for optical fiber alignment on the manual alignment substrate in order to precisely control the distance between the light emitting element and the optical fiber in the direction of the optical fiber axis Way. 2. The optical fiber of claim 1, wherein the optical fiber proceeds to an exposed point on the passive alignment substrate at a distance from the point where the cut surface of the optical fiber should be finally positioned for accurate control of the position of the optical fiber during optical coupling between the flip chip bonded light receiving element and the optical fiber. Precision manual alignment method of the optical element and the optical fiber, characterized in that further forming the origin. The optical device and the optical fiber according to claim 3, wherein an optical fiber progress check marker is further formed at the front end of the optical fiber progressing point in order to confirm the accuracy of the optical fiber upon optical coupling between the light receiving element and the optical fiber. Precision manual alignment.