The present invention relates to techniques for scribing a wafer of semiconductor light emitting devices formed on a transparent substrate.
Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
Individual devices or groups of devices are often separated from a wafer by scribing and breaking the wafer along streets between rows of devices.
It is an object of the invention to provide a technique for scribing a wafer of semiconductor light emitting devices.
Embodiments of the invention include a method for separating a wafer including a growth substrate and a plurality of devices formed on the growth substrate and arranged in a plurality of rows separated by at least one street. The wafer includes a front side on which the plurality of devices are formed and a back side, which is a surface of the growth substrate. The method includes scribing a first scribe line aligned with the street on the front side, scribing a second scribe line aligned with the street on the back side, and scribing a third scribe line aligned with the street on the back side.
Embodiments of the invention include a method for separating a wafer including a growth substrate and a plurality of devices formed on the growth substrate and arranged in a plurality of rows separated by at least one street. The wafer includes a front side on which the plurality of devices are formed and a back side, which is a surface of the growth substrate. The method includes scribing a first scribe line aligned with the street on the front side and scribing a second scribe line aligned with the street on the back side. The growth substrate has a thickness greater than 100 microns. The street has a width less than 50 microns.
Embodiments of the invention include a method for separating a wafer including a growth substrate and a plurality of devices formed on the growth substrate and arranged in a plurality of rows separated by at least one street. The wafer has a front side on which the plurality of devices are formed and a back side, which is a surface of the growth substrate. The method includes scribing a first scribe line aligned with the street and scribing a second scribe line aligned with the street. The first and second scribe lines are both formed on the same side of the wafer.
In the technique illustrated in
In some light emitting devices, it is desirable to leave a thick growth substrate attached to the light emitting device, for example to space a wavelength converting layer or other structure formed on the growth substrate apart from the light emitting layer of the device. Embodiments of the invention are directed to techniques for scribing and breaking a wafer of light emitting devices with a thick growth substrate.
Though in the examples below the semiconductor light emitting devices are III-nitride LEDs that emit blue or UV light, semiconductor light emitting devices besides LEDs such as laser diodes and semiconductor light emitting devices made from other materials systems such as other III-V materials, III-phosphide, III-arsenide, II-VI materials, ZnO, or Si-based materials may be used.
The semiconductor structure 12 includes a light emitting or active region sandwiched between n- and p-type regions. An n-type region 16 may be grown first and may include multiple layers of different compositions and dopant concentration including, for example, preparation layers such as buffer layers or nucleation layers, which may be n-type or not intentionally doped, and device layers that are not intentionally doped, n- or even p-type, designed for particular optical, material, or electrical properties desirable for the light emitting region to efficiently emit light. A light emitting or active region 18 is grown over the n-type region. Examples of suitable light emitting regions include a single thick or thin light emitting layer, or a multiple quantum well light emitting region including multiple thin or thick light emitting layers separated by barrier layers. A p-type region 20 may then be grown over the light emitting region. Like the n-type region, the p-type region may include multiple layers of different composition, thickness, and dopant concentration, including layers that are not intentionally doped, or n-type layers.
After growth, a p-contact is formed on the surface of the p-type region. The p-contact 21 often includes multiple conductive layers such as a reflective metal and a guard metal which may prevent or reduce electromigration of the reflective metal. The reflective metal is often silver but any suitable material or materials may be used. After forming the p-contact 21, a portion of the p-contact 21, the p-type region 20, and the active region 18 is removed to expose a portion of the n-type region 16 on which an n-contact 22 is formed. The n- and p-contacts 22 and 21 are electrically isolated from each other by a gap 25 which may be filled with a dielectric such as an oxide of silicon or any other suitable material. Multiple n-contact vias may be formed; the n- and p-contacts 22 and 21 are not limited to the arrangement illustrated in
In order to form electrical connections to the LED, one or more interconnects 26 and 28 are formed on or electrically connected to the n- and p-contacts 22 and 21. Interconnect 26 is electrically connected to n-contact 22 in
Many individual LEDs are formed on a single wafer then diced from the wafer by scribing and breaking, as described below. The growth substrate is often thinned before scribing and breaking. The growth substrate may be thinned by any suitable technique including etching or mechanical techniques such as grinding, polishing, or lapping. After thinning, the growth substrate 10 may be at least 100 μm thick in some embodiments, at least 180 μm thick in some embodiments, at least 200 μm thick in some embodiments, no more than 360 μm thick in some embodiments, at least 220 μm thick in some embodiments, and no more than 260 μm thick in some embodiments. After thinning, the surface of the growth substrate opposite the growth surface (i.e. the surface through which a majority of light is extracted in a flip chip configuration) may be patterned, roughened or textured, which may improve light extraction from the device.
The device illustrated in
The individual LEDs including the epitaxially grown structure 12, the n- and p-contacts 22 and 21, and the interconnects 26 and 28 are represented in the following figure by block 1.
The scribe line 40 formed on the front side 48 of the wafer extends through the entire thickness 34 of the semiconductor material 33 remaining in the street 32, which was epitaxially grown on the growth substrate as part of the semiconductor structure that forms the LEDs 1, and into growth substrate 10. The depth of the scribe line 40 in the growth substrate 10 is at least the thickness of material 33 in some embodiments and no more than three times the thickness of material 33 in some embodiments. The epitaxially grown material 33 is no more than 16 μm thick in some embodiments and no more than 8 μm thick in some embodiments.
The street 32 is also scribed from the back side 50 to form at least one scribe line. Two scribe lines 42 and 44 are illustrated in
The first back side scribe line 42 is located at a different depth within the growth substrate 10 than the second back side scribe line 44. The defected regions 42 and 44 may be at least 10 μm wide in some embodiments and no more than 50 μm wide in some embodiments. In some embodiments the defected regions 42 and 44 may be at least 20 μm and no more than 120 μm long. In some embodiments the shallow defected region 44 may be at least 10 μm and no more than 50 μm from the surface 30 of growth substrate 10. In some embodiments the deep defected region 42 may be at least 40 μm and no more than 120 μm from the surface 30 of growth substrate 10. The depth of scribe lines 42 and 44 relative to the surface 30 of growth substrate 10 may be selected by adjusting the optics on a commercially available stealth scribing tool.
In some embodiments, the shallow back side scribe line 44 may be formed by quasi-stealth scribing, where a portion of the scribe line at the surface 30 of substrate 10 is formed by laser ablation scribing and a portion of the scribe line within substrate 10 is formed by focusing the laser beam to form a defected region. In some embodiments, the shallow back side scribe line 44 may be formed by ablation scribing. Ablation scribing is described above in reference to front side scribe line 40.
The scribed lines 40, 42, and 44 may be formed in any order. In some embodiments, the front side scribe line 40 is formed first, then the wafer is flipped over and the back side scribe lines 42 and 44 are formed. In some embodiments, the back side scribe lines 42 and 44 are formed first, then the wafer is flipped over and the front side scribe line 40 is formed. The deeper back side scribe line 42 may be formed before shallower scribe line 44, or the shallower back side scribe line 44 may be formed before deeper scribe line 42.
In some embodiments, more than three scribe lines may be formed before breaking. Additional scribe lines may be formed on a thicker substrate as needed to facilitate breaking. In some embodiments, one or more additional back side scribe lines formed by stealth scribing at different depths may be added. In particular, fourth and fifth scribe lines may be formed by stealth scribing from the back side.
At least one of the scribe lines 42 is formed fairly deeply within the growth substrate, as compared to the shallow scribe lines described in
The front side and back side scribe lines are all aligned in substantially the same plane, for example using visual alignment as is known in the art.
In some embodiments, the front side scribe line 40 is omitted, and the wafer is broken after forming at least two scribe lines at different depths from the back side 50 of the wafer. In some embodiments, first, second, and third scribe lines are formed from the back side 50 of the wafer, for example using stealth scribing. One of the first, second, and third scribe lines is formed in an area close to the front side 48 surface of substrate 10, such that this scribe line effectively replaces front side scribe line 40. In some embodiments the scribe line formed closest to the front side surface of substrate 10 may be formed within 20 μm of the front side surface of substrate 10.
In some embodiments, the wafer is broken after forming at least two scribe lines at different depths from the front side 48 of the wafer, and the back side scribe lines are omitted. For example, the wafer may be broken after forming a front side ablation scribed line, and a front side stealth scribed line.
In a first example, the substrate is scribed with one front side scribe line and two back side scribe lines, as illustrated in
In a second example, the substrate is scribed with one front side scribe line and four back side scribe lines. The substrate is 350 microns thick, the front side scribe extends 6 microns into the substrate, the first back side scribe (the back side scribe line closest to the front side 48 of the wafer) is between depths 15 microns and 35 microns in the substrate, the second back side scribe is between depths 45 microns and 75 microns in the substrate, the third back side scribe is between depths 80 and 110 microns in the substrate, and the fourth back side scribe (the back side scribe line closest to the back side 50 of the wafer) is between depths 115 and 150 microns on the substrate.
After the wafer is scribed as described above, the wafer may be broken along the scribe lines by a Guillotine-like die breaker, which is known in the art and commercially available. The wafer is placed on a support. A gap in the support is aligned with the scribe line to be broken. The wafer may be protected by a cover disposed between the wafer and the support. A breaker blade is aligned with the scribe line to be broken and a force is applied to a blade. The force on the blade causes fracture propagation between the scribed lines, resulting in separation.
Having described the invention in detail, those skilled in the art will appreciate that, given the present disclosure, modifications may be made to the invention without departing from the spirit of the inventive concept described herein. Therefore, it is not intended that the scope of the invention be limited to the specific embodiments illustrated and described.
Filing Document | Filing Date | Country | Kind |
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PCT/IB2014/065251 | 10/13/2014 | WO | 00 |
Number | Date | Country | |
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61896842 | Oct 2013 | US |