Semiconductor device and method of fabricating the same
View Patent ↗A semiconductor device and a method of fabricating the same are disclosed. A reference direction for a substrate is parallel to a first or second crystallographic direction, and a patterned hard mask layer is distributed along the first crystallographic direction. For substrates with notches oriented in different crystallographic directions, the patterned mask layer may be used as a mask for forming trenches in the substrate surface. When viewed normal to a cross-section perpendicular to the substrate, each trench has a cross-sectional width decreasing from the substrate surface toward the inside of the substrate. This allows the semiconductor device to have increased light absorption and conversion efficiency. Forming the trenches by wet etching can avoid increased dark current due to damage to the trenches' side surfaces that may be caused by the use of a dry etching process. Thus, an effective improvement in terms of dark current can be achieved.
1 . A method of fabricating a semiconductor device, comprising:
providing a substrate, the substrate being formed with a locating notch in an edge thereof, wherein a line connecting a center of the substrate and the locating notch defines a reference direction, wherein across a surface of the substrate, regions oriented in first and second crystallographic directions belonging to different families of crystallographic directions are periodically distributed around the center, and wherein the reference direction is parallel to the first crystallographic direction or the second crystallographic direction;
forming a patterned mask layer on the surface of the substrate, the patterned mask layer defining a pattern distributed in parallel to the first crystallographic direction; and
forming a plurality of trenches by performing a wet etching process on the surface of the substrate using the patterned mask layer as a mask, the plurality of trenches each having a cross-sectional width decreasing from the surface of the substrate to the inside of the substrate, when viewed normal to a cross-section perpendicular to the substrate, and the plurality of trenches forming a finely roughened surface structure for extending an optical path length in an optoelectronic device,
wherein the patterned mask layer comprises a first set of elongate pattern elements and a second set of elongate pattern elements, and wherein the second set of elongate pattern elements is arranged on both sides of the first set of elongate pattern elements, or the first set of elongate pattern elements is arranged on both sides of the second set of elongate pattern elements,
wherein the wet etching process employs at least one of a tetramethyl ammonium hydroxide (TMAH) solution, an ammonia solution, a potassium hydroxide (KOH) solution and a sodium hydroxide (NaOH) solution, and
wherein the plurality of trenches are at least one of inverted quadrilateral pyramid-shaped trenches and inverted truncated quadrilateral pyramid-shaped trenches.
2 . The method of claim 1 , wherein the surface of the substrate is oriented in a (100) plane, wherein the first crystallographic direction belongs to the <110> family of crystallographic directions, wherein the second crystallographic direction belongs to the <100> family of crystallographic directions, and wherein the (100) plane includes mutually perpendicular crystallographic direction I and II in the <110> family of crystallographic directions.
3 . The method of claim 2 , wherein the patterned mask layer comprises a first set of elongate pattern elements spaced apart from one another and extending in parallel to the crystallographic direction I and/or a second set of elongate pattern elements spaced apart from one another and extending in parallel to the crystallographic direction II.
4 . The method of claim 2 , wherein the patterned hard mask layer comprises first rectangular annular pattern elements and second rectangular annular pattern elements within the respective first rectangular annular pattern elements, and wherein adjacent sides of the first and second rectangular annular pattern elements are respective parallel to the crystallographic directions I and II.
5 . The method of claim 1 , wherein the first set of elongate pattern elements and the second set of elongate pattern elements in the patterned hard mask layer cross each other to form a lattice pattern.
6 . The method of claim 1 , wherein the inverted quadrilateral pyramid-shaped trenches have side surfaces oriented in the {111} families of crystallographic planes and surface openings oriented in the (100) plane, or wherein the inverted truncated quadrilateral pyramid-shaped trenches have side surfaces oriented in the {111} families of crystallographic planes and surface openings oriented in the (100) plane.
7 . The method of claim 1 , wherein
the formation of the patterned mask layer on the surface of the substrate comprises:
successively forming a hard mask layer and a photoresist layer over the surface of the substrate; exposing and developing the photoresist layer; patterning the hard mask layer by etching the hard mask layer, with the patterned photoresist layer serving as a mask.
8 . The method of claim 7 , further comprising:
removing the patterned hard mask layer; and
forming a filler layer, which fills the plurality of trenches.
9 . The method of claim 1 , wherein when viewed normal to the cross-section perpendicular to the substrate, each trench has an inverted trapezoidal or inverted triangular cross-sectional shape.