Strain relief trenches for epitaxial growth
Strain relief trenches may be formed in a substrate prior to growth of an epitaxial layer on the substrate. The trenches may reduce the stresses and strains on the epitaxial layer that occur during the epitaxial growth process due to differences in material properties (e.g., lattice mismatches, differences in thermal expansion coefficients, and/or the like) between the epitaxial layer material and the substrate material. The stress and strain relief provided by the trenches may reduce or eliminate cracks and/or other types of defects in the epitaxial layer and the substrate, may reduce and/or eliminate bowing and warping of the substrate, may reduce breakage of the substrate, and/or the like. This may increase the center-to-edge quality of the epitaxial layer, may permit epitaxial layers to be grown on larger substrates, and/or the like.
1 . A method, comprising:
forming a plurality of trenches in a substrate,
wherein a first trench, of the plurality of trenches, is formed to have a different width-to-height aspect ratio than a second trench of the plurality of trenches,
wherein the first trench is formed to have a different width than the second trench,
wherein the plurality of trenches are formed to have tapered walls,
wherein a first tapered wall, of the tapered walls, associated with the first trench has a different wall angle from a second tapered wall of the tapered walls, associated with the second trench, and
wherein a location of the first tapered wall relative to the first trench corresponds to a location of the second tapered wall relative to the second trench; and
growing a gallium nitride (GaN) epitaxial layer in the plurality of trenches,
wherein a first portion of the GaN epitaxial layer is grown in the first trench and a second portion of the GaN epitaxial layer is grown in the second trench, and
wherein the first portion and the second portion are grown to form isolated islands of epitaxial growth.
2 . The method of claim 1 , wherein forming the plurality of trenches in the substrate comprises:
forming a photoresist layer on the substrate;
exposing portions of the photoresist layer to a radiation source;
removing the exposed portions of the photoresist layer from the substrate; and
etching the substrate using a pattern formed based on removing the exposed portions of the photoresist layer from the substrate.
3 . The method of claim 2 , further comprising:
removing remaining portions of the photoresist layer from the substrate.
4 . The method of claim 1 , wherein, when growing the GaN epitaxial layer in the plurality of trenches, the GaN epitaxial layer is not grown between the first portion and the second portion.
5 . The method of claim 1 , wherein the plurality of trenches are formed to have a grid pattern of perpendicular and intersecting trenches.
6 . The method of claim 5 , wherein a first subset of the plurality of trenches are formed to be spaced more closely together than a second subset of the plurality of trenches.
7 . A method, comprising:
forming a photoresist layer over a substrate;
exposing the photoresist layer to form a pattern in the photoresist layer;
forming, using the pattern in the photoresist layer, a plurality of trenches in the substrate,
wherein a first trench, of the plurality of trenches, is formed to have a different width-to-height aspect ratio than a second trench of the plurality of trenches,
wherein the first trench is formed to have a different width than the second trench,
wherein the plurality of trenches are formed to have tapered walls,
wherein a first tapered wall, of the tapered walls, associated with the first trench has a different wall angle from a second tapered wall of the tapered walls, associated with the second trench, and
wherein a location of the first tapered wall relative to the first trench corresponds to a location of the second tapered wall relative to the second trench; and
growing an epitaxial layer in the plurality of trenches,
wherein a first portion of the epitaxial layer is grown in the first trench and a second portion of the epitaxial layer is grown in the second trench, and
wherein the first portion of the epitaxial layer and the second portion of the epitaxial layer are grown to form isolated islands of epitaxial growth.
8 . The method of claim 7 , wherein forming, using the pattern in the photoresist layer, the plurality of trenches in the substrate comprises:
removing exposed portions of the photoresist layer from the substrate to expose the pattern in the photoresist layer; and
etching the substrate using the pattern in the photoresist layer.
9 . The method of claim 8 , further comprising:
removing remaining portions of the photoresist layer after etching the substrate using the pattern in the photoresist layer.
10 . The method of claim 7 , wherein growing the epitaxial layer in the plurality of trenches comprises:
growing the first portion of the epitaxial layer in the first trench and the second portion of the epitaxial layer in the second trench such that an epitaxial region is not grown between the first portion of the epitaxial layer and the second portion of the epitaxial layer.
11 . The method of claim 7 , wherein growing the epitaxial layer in the plurality of trenches comprises:
growing the first portion of the epitaxial layer in the first trench such that a height of the first portion of the epitaxial layer is greater than a width of the first portion of the epitaxial layer.
12 . The method of claim 7 , wherein growing the epitaxial layer in the plurality of trenches comprises:
growing the first portion of the epitaxial layer in the first trench such that a width-to-height aspect ratio of the first portion of the epitaxial layer is in a range from 0.1 to 0.8.
13 . The method of claim 7 , wherein the plurality of trenches are formed to have a grid pattern of perpendicular and intersecting trenches.