1. Field of the Invention
The present invention relates to an optical device composed of a substrate and a light emitting layer formed on the front surface of the substrate and also to a manufacturing method for the optical device.
1. Description of the Related Art
In a fabrication process for an optical device such as a laser diode (LD) and a light emitting diode (LED), a light emitting layer (epitaxial layer) is formed by epitaxial growth, for example, on the upper surface (front surface) of a crystal growing substrate of sapphire, SiC, or the like, thereby manufacturing an optical device wafer for forming a plurality of optical devices. The light emitting layer formed on the crystal growing substrate of the optical device wafer is partitioned by a plurality of crossing division lines to define a plurality of separate regions where the plural optical devices such as LDs and LEDs are respectively formed. The optical device wafer is divided along these division lines to obtain the individual optical devices as chips.
As a method of dividing the optical device wafer along the division lines, there are known methods as described in Japanese Patent Laid-open Nos. Hei 10-305420 and 2008-006492. The dividing method described in Japanese Patent Laid-open No. Hei 10-305420 includes the steps of applying a pulsed laser beam having an absorption wavelength to the wafer along the division lines to form a laser processed groove along each division line and next applying an external force to the wafer to thereby break the wafer along each division line where the laser processed groove is formed as a division start point.
On the other hand, the dividing method described in Japanese Patent Laid-open No. 2008-006492 is intended to improve the luminance of the optical device and it includes the steps of applying a pulsed laser beam having a transmission wavelength to the wafer along the division lines in the condition where the focal point of the pulsed laser beam is set inside the wafer, thereby forming a modified layer inside the wafer along each division line and next applying an external force to each division line where the modified layer is formed to be reduced in strength, thereby dividing the wafer along each division line.
In each of the dividing methods described in Japanese Patent Laid-open Nos. Hei 10-305420 and 2008-006492, the laser beam is directed to the optical device wafer substantially perpendicularly thereto to form the laser processed groove or the modified layer and then divide the optical device wafer along the laser processed groove or the modified layer as a division start point, thereby obtaining the individual optical devices. Each optical device has a rectangular boxlike shape such that each side surface is substantially perpendicular to the light emitting layer formed on the front surface of the substrate. Accordingly, of the light emitted from the light emitting layer of the optical device and reflected on the back surface of the optical device, the proportion of the light striking each side surface at an incident angle greater than the critical angle is large. As a result, the proportion of the light totally reflected on each side surface is large, so that there is a possibility that the light repeating the internal total reflection in the substrate may finally become extinct in the substrate. Accordingly, the light extraction efficiency of the optical device is reduced to cause a reduction in luminance.
It is therefore an object of the present invention to provide an optical device and a manufacturing method therefor which can improve the light extraction efficiency.
In accordance with an aspect of the present invention, there is provided an optical device including a substrate and a light emitting layer formed on the front surface of the substrate, wherein the back surface of the substrate is formed with a concave portion.
With this configuration, the concave portion is formed on the back surface of the substrate. Accordingly, the light striking the inner surface of the concave portion can be irregularly reflected on the inner surface of the concave portion. Further, of the light irregularly reflected on the inner surface of the concave portion and striking each side surface of the substrate, the proportion of the light striking each side surface at an incident angle less than or equal to the critical angle can be increased. As a result, the proportion of the light totally reflected on each side surface and returned to the light emitting layer can be reduced to thereby increase the proportion of the light emerging from each side surface. That is, the light extraction efficiency can be improved.
In accordance with another aspect of the present invention, there is provided a manufacturing method for optical devices each including a substrate and a light emitting layer formed on the front surface of the substrate, wherein the back surface of the substrate is formed with a concave portion, the manufacturing method including an attaching step of attaching a protective tape to the front side of an optical device wafer having a light emitting layer on the front side, the light emitting layer of the optical device wafer being partitioned by a plurality of crossing division lines to define a plurality of separate regions where the optical devices are respectively formed; a division start point forming step of forming a division start point where division is started along each division line of the optical device wafer after performing the attaching step; a dividing step of applying an external force to the optical device wafer along each division line after performing the division start point forming step, thereby dividing the optical device wafer along each division line to obtain the individual optical devices; and a concave portion forming step of applying a laser beam having an absorption wavelength to the optical device wafer before or after performing the dividing step, thereby forming a plurality of concave portions on the back side of the optical device wafer at the positions respectively corresponding to the optical devices. According to this method, the optical device having the concave portion on the back surface can be manufactured without complication of each step and elongation of the time of each step.
Preferably, the concave portion forming step includes an etching step of etching the inner surface of the concave portion formed on the back side of the optical device wafer.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention.
A preferred embodiment of the optical device and the manufacturing method therefor according to the present invention will now be described in detail with reference to the attached drawings. There will first be described a preferred embodiment of the optical device according to the present invention with reference to
As shown in
The light emitting layer 22 is formed by the epitaxial growth of an n-type semiconductor layer (e.g., n-type GaN layer) in which electrons function as majority carrier, a semiconductor layer (e.g., InGaN layer), and a p-type semiconductor layer (e.g., p-type GaN layer) in which holes function as majority carrier. These layers are epitaxially grown in this order on the front surface 21a of the substrate 21. The light emitting layer 22 is formed with two electrodes (not shown) respectively connected to the n-type semiconductor layer and the p-type semiconductor layer. A voltage from an external power source is applied to the two electrodes to thereby emit light from the light emitting layer 22.
Both the front surface 21a and the back surface 21b of the substrate 21 have substantially the same rectangular shape as viewed in plan and they are parallel to each other. The substrate 21 has four side surfaces 21c respectively connecting the four sides of the front surface 21a and the four sides of the back surface 21b. Each side surface 21c is a flat surface perpendicular to both the front surface 21a and the back surface 21b. The back surface 21b of the substrate 21 is formed with a concave portion 23. The concave portion 23 has a curved inner surface like a crater and it is substantially circular as viewed in bottom plan. The inner surface of the concave portion 23 is treated with etching to remove debris inside the concave portion 23, thereby improving the luminance. Wet etching may be adopted as the etching. The proportion of the area where the concave portion 23 is formed to the total area of the back surface 21b is set to 40 to 80%. While the single concave portion 23 is formed on the back surface 21b of the substrate 21 in this preferred embodiment, a plurality of concave portions may be formed on the back surface 21b of the substrate 21.
The luminance improving effect by the optical device 1 shown in
As shown in
The light propagating along the optical path A3 strikes the light emitting layer 22 and is absorbed by the light emitting layer 22, so that the light cannot be extracted to the outside. The light propagating along the optical path A4 strikes the interface between one of the side surfaces 21c of the substrate 21 and an air layer at an incident angle θ1. Similarly, the light propagating along the optical path A5 strikes the interface between another one of the side surfaces 21c of the substrate 21 and an air layer at an incident angle θ2. When each of the incident angles θ1 and θ2 is less than or equal to the critical angle of the substrate 21, at least part of the incident light is allowed to emerge from the side surfaces 21c.
In contrast thereto, the light is emitted from the optical device 3 as a comparison shown in
According to the optical device 1 shown in
There will now be described a preferred embodiment of the optical device manufacturing method according to the present invention. The optical device manufacturing method in this preferred embodiment includes an attaching step, a division start point forming step, a concave portion forming step by a laser processing apparatus, and a dividing step by a dividing apparatus. In the attaching step, an adhesive sheet (protective tape) is attached to the front side of an optical device wafer on which a light emitting layer is formed. In the division start point forming step, a division start point where division is started is formed along each division line of the optical device wafer. In the concave portion forming step, a plurality of concave portions are formed on the back side of the optical device wafer. In the dividing step, the optical device wafer is divided along each division line where the division start point is formed, thereby obtaining a plurality of individual optical devices. These steps of the manufacturing method will now be described in more detail.
Referring to
As shown in
The laser processing apparatus 100 has a boxlike base 101. There is provided on the upper surface of the base 101 a chuck table moving mechanism 104 for feeding the chuck table 103 in the X direction extending along an X axis shown in
The chuck table moving mechanism 104 includes a pair of parallel guide rails 115 provided on the upper surface of the base 101 so as to extend in the X direction and a motor-driven X table 116 slidably supported to the guide rails 115. The chuck table moving mechanism 104 further includes a pair of parallel guide rails 117 provided on the upper surface of the X table 116 so as to extend in the Y direction and a motor-driven Y table 118 slidably supported to the guide rails 117.
The chuck table 103 is provided on the upper surface of the Y table 118. Nut portions (not shown) are formed on the lower surfaces of the X table 116 and the Y table 118, and ball screws 121 and 122 are threadedly engaged with these nut portions of the X table 116 and the Y table 118, respectively. Drive motors 123 and 124 are connected to the end portions of the ball screws 121 and 122, respectively. Accordingly, when the ball screws 121 and 122 are rotationally driven by the drive motors 123 and 124, respectively, the chuck table 103 is moved in the X direction and the Y direction along the guide rails 115 and 117, respectively.
The chuck table 103 is a circular member and it is rotatably provided on the upper surface of the Y table 118 through a θ table 125. A suction holding member (not shown) of a porous ceramic material is formed on the upper surface of the chuck table 103. Four clamps 126 are provided on the outer circumference of the chuck table 103, wherein each clamp 126 is supported through a pair of arms to the chuck table 103. The four clamps 126 are driven by an air actuator (not shown) to thereby fix a ring frame F supporting the optical device wafer W through an adhesive sheet S.
The laser processing unit 102 has a processing head 127 provided at the front end of the arm portion 112. An optical system is provided in the arm portion 112 and the processing head 127 to constitute the laser processing unit 102. More specifically, a laser oscillator (not shown) is provided in the arm portion 112, and the processing head 127 includes a focusing lens (not shown) for focusing a laser beam oscillated from the laser oscillator to the optical device wafer W held on the chuck table 103, thereby processing the optical device wafer W. In this case, the laser beam has an absorption wavelength to the optical device wafer W, and the focal point of the laser beam is adjusted by the optical system so that the laser beam is focused on the back side of the optical device wafer W (the upper surface as viewed in
By the application of the laser beam to the optical device wafer W, ablation occurs on the back side of the optical device wafer W to partially etch the back side of the wafer W, thereby forming a plurality of concave portions 23 (see
The optical device wafer W is a substantially disk-shaped member. As shown in
The optical device manufacturing method by processing the optical device wafer W according to this preferred embodiment will now be described with reference to
The attaching step shown in
After performing the attaching step, the division start point forming step shown in
In this case, the plural modified layers R along each division line ST are formed by changing the vertical position of the focal point of the laser beam along the thickness of the substrate W1. More specifically, the first modified layer R is formed by setting the vertical position of the focal point to a position near the light emitting layer W2 of the optical device wafer W and then applying the laser beam along the predetermined division line ST. The formation of the first modified layer R is repeated for all of the division lines ST. Thereafter, the focal point is shifted upward by a predetermined amount to form the second modified layer R along each division line ST. Thereafter, the laser processing is similarly performed along all of the division lines ST until the total thickness of the plural modified layers R along each division line ST becomes a predetermined thickness. Thusly, a division start point where division is started is formed by the plural modified layers R along each division line ST. Each modified layer R is a region different from its ambient region in density, refractive index, mechanical strength, or any other physical properties in the optical device wafer W irradiated with the laser beam, causing a reduction in strength as compared with the ambient region. Examples of each modified layer R include a melted and rehardened region, cracked region, breakdown region, and refractive index changed region. These regions may be mixed.
After performing the division start point forming step, the concave portion forming step shown in
After performing the concave portion forming step, the dividing step shown in
A pressure blade 49 for pressing the optical device wafer W from the upper side thereof is provided above the support beds 45 at a horizontal position therebetween. That is, an external force is applied from the pressure blade 49 to the optical device wafer W held on the support beds 45. The pressure blade 49 extends in one direction (perpendicular to the sheet plane of
An example of the laser processing conditions in the concave portion forming step is shown below.
Light source: CO2 laser
Wavelength: 9.4 μm (infrared radiation)
Power: 5 W
Repetition frequency: 1 kHz
Pulse width: 20 μsec
Focused spot diameter: 200 μm
Work feed speed: 600 mm/s
By using the optical device 1 obtained in Example, the total intensity (power) of light radiated was measured (total radiant flux measurement). As compared with the conventional optical device having the flat back surface as shown in
According to the optical device manufacturing method in this preferred embodiment, the concave portions 23 can be quickly formed by ablation. Further, the concave portions 23 can be successively formed on the back surfaces of the plural optical devices 1 of the optical device wafer W. As a result, complication of the concave portion forming step and elongation of the time of this step can be suppressed to thereby effect efficient manufacture of the optical devices 1. Furthermore, since the inner surface of each concave portion 23 is treated with etching to thereby remove debris after performing the ablation, the luminance of each optical device 1 can be further improved.
The present invention is not limited to the above preferred embodiment, but various modifications may be made. The size, shape, etc. of the parts in the above preferred embodiment shown in the attached drawings are merely illustrative and they may be suitably changed within the scope where the effect of the present invention can be exhibited. Further, the above preferred embodiment may be suitably modified without departing from the scope of the object of the present invention. For example, while the concave portion forming step is performed before performing the dividing step in the above preferred embodiment, the concave portion forming step may be performed after performing the dividing step or may be performed between the attaching step and the division start point forming step.
Further, while the optical device wafer W is divided by combining the division start point forming step and the breaking operation in the above preferred embodiment, the dividing step in the present invention is not limited to this configuration. That is, the dividing step in the present invention may be performed by using any apparatus capable of dividing the optical device wafer W along the division lines ST to obtain the individual optical devices 1. For example, the optical device wafer W may be divided by combining the division start point forming step and an expanding operation of expanding the adhesive sheet S to thereby apply an external force to the modified layers R formed along the division lines ST.
Further, a division groove may be formed along each division line ST on the optical device wafer W by ablation in the division start point forming step. As a modification, this division groove may be formed as a half-cut groove by using a cutting blade. In any case, the breaking operation as the dividing step may be replaced by the expanding operation. In the case of performing the concave portion forming step after performing the dividing step, a DBG (Dicing Before Grinding) operation may be performed to grind the back side of the optical device wafer W after forming a half-cut groove along each division line ST on the front side of the optical device wafer W, thereby dividing the optical device wafer W into the individual optical devices 1. As a modification, a full-cut groove may be formed along each division line ST by using a cutting blade to thereby divide the optical device wafer W.
Further, the steps of the optical device manufacturing method in the above preferred embodiment may be performed by using separate apparatuses or by using the same apparatus.
The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.
Number | Date | Country | Kind |
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2014-012519 | Jan 2014 | JP | national |