REDUCING BOWING OF MATERIALS BEFORE WAFER-TO-WAFER BONDING FOR LED MANUFACTURING
Disclosed herein are techniques relating to wafer-to-wafer bonding for manufacturing light-emitting diodes (LEDs). In some embodiments, a method includes reducing bowing present in a semiconductor material and a substrate on which the semiconductor material is formed. The reducing involves segmenting the semiconductor material through etching the semiconductor material to form gaps between adjacent segments. The semiconductor material includes an n-type layer, a quantum well layer, and a p-type layer. The method further includes bonding a base wafer to the semiconductor material, removing the substrate from the semiconductor material, and forming a plurality of trenches. The trenches extend through the semiconductor material within each of the segments, thereby singulating the LEDs. In some embodiments, the method is performed in the following order: reducing bowing, bonding the base wafer, removing the substrate, forming the trenches.
1 . A method comprising:
reducing bowing present in a semiconductor material and a substrate on which the semiconductor material is formed, wherein the reducing comprises segmenting the semiconductor material through etching the semiconductor material to form gaps between adjacent segments;
bonding a base wafer to the semiconductor material;
removing the substrate from the semiconductor material; and
forming a plurality of trenches through the semiconductor material within each of the segments to produce a plurality of light-emitting diodes (LEDs).
2 . The method of claim 1 , wherein the semiconductor material comprises, in order, an n-type layer, a quantum well layer, and a p-type layer.
3 . The method of claim 1 , wherein the semiconductor material comprises GaN and the substrate comprises sapphire.
4 . The method of claim 1 , wherein the substrate is removed from the semiconductor material by heating the substrate.
5 . The method of claim 1 , wherein the substrate is removed from the semiconductor material by applying a horizontal force to the substrate.
6 . The method of claim 1 , wherein the substrate is removed after the base wafer has been bonded to the semiconductor material, the removing of the substrate comprising focusing a laser beam at an interface between the semiconductor material and the substrate, at locations that are not vertically aligned with a pixel area of the base wafer.
7 . The method of claim 6 , wherein the locations that are not vertically aligned with the pixel area of the base wafer correspond to wirebond areas.
8 . The method of claim 1 , wherein each LED has an active light emitting area with a linear dimension of less than 50 μm, and wherein each segment has a linear dimension of at least 10 mm.
9 . The method of claim 8 , wherein the active light emitting area of each LED has a linear dimension of less than 10 μm.
10 . The method of claim 8 , wherein each segment has a larger cross-sectional area than an individual LED.
11 . The method of claim 10 , wherein the cross-sectional area of a segment is square.
12 . The method of claim 1 , wherein the semiconductor material comprises a plurality of semiconductor layers, and wherein the etching of the semiconductor material involves etching through the plurality of semiconductor layers until the substrate is reached.
13 . The method of claim 1 , wherein the base wafer is bonded to the semiconductor material after the bowing has been reduced as a result of segmenting the semiconductor material, and wherein the plurality of trenches is formed after the base wafer has been bonded to the semiconductor material.
14 . The method of claim 1 , wherein the base wafer comprises driver circuits configured to control the plurality of LEDs, and wherein the plurality of trenches comprises trenches at locations that are not vertically aligned with the driver circuits.
15 . The method of claim 1 , wherein the plurality of trenches extends partially into the base wafer.
16 . The method of claim 1 , wherein:
the semiconductor material comprises, in order from nearest the substrate to farthest from the substrate, an n-type layer, a quantum well layer, and a p-type layer;
a contact layer is formed on the p-type layer;
a bonding layer is formed on the contact layer;
the etching of the semiconductor material involves etching from the bonding layer toward the substrate; and
the forming of the plurality of trenches involves etching from the n-type layer toward the base wafer, after the substrate has been removed.