Isolation stack for a bipolar transistor and related methods
The disclosure provides an isolation stack for a bipolar transistor (BT), and related methods. A structure of the disclosure includes a first isolation layer on a subcollector. A first air gap is between the first isolation layer and a collector of a BT. A second isolation layer is on the first isolation layer and adjacent an intrinsic base of the BT. A third isolation layer is on the second isolation layer, vertically between the second isolation layer and an extrinsic base of the BT. A second air gap is adjacent the third isolation layer and below the extrinsic base.
1 . A structure comprising:
a first isolation layer on a subcollector, wherein a first air gap is between the first isolation layer and a collector of a bipolar transistor (BT);
a second isolation layer on the first isolation layer and adjacent an intrinsic base of the BT; and
a third isolation layer on the second isolation layer, vertically between the second isolation layer and an extrinsic base of the BT, wherein a second air gap is adjacent the third isolation layer and below the extrinsic base, and wherein the second isolation layer defines a physical boundary between the first air gap and the second air gap.
2 . The structure of claim 1 , wherein the second isolation layer is adjacent a lower portion of the intrinsic base of the BT, and wherein the second air gap is adjacent an upper portion of the intrinsic base of the BT.
3 . The structure of claim 1 , wherein the first isolation layer and the third isolation layer each include a same material.
4 . The structure of claim 1 , wherein the first isolation layer, the second isolation layer, and the third isolation layer form an oxide-nitride-oxide (ONO) stack.
5 . The structure of claim 1 , wherein the first air gap is one of a pair of first air gaps each adjacent a sidewall of the collector, and wherein the second air gap is one of a pair of second air gaps each adjacent a sidewall of the intrinsic base.
6 . The structure of claim 1 , wherein the BT is a vertically-oriented heterojunction bipolar transistor.
7 . A structure comprising:
a bipolar transistor (BT) including a subcollector, a collector on the subcollector, an intrinsic base on the collector, an extrinsic base on a first portion of the intrinsic base, and an emitter on a second portion of the intrinsic base; and
an isolation stack adjacent the BT, the isolation stack including:
a first isolation layer on the subcollector, wherein a first air gap is between the first isolation layer and the collector, and wherein a portion of the first air gap is above a portion of the collector;
a second isolation layer on the first isolation layer and adjacent the intrinsic base of the BT; and
a third isolation layer on the second isolation layer, vertically between the second isolation layer and the extrinsic base of the BT, wherein a second air gap is adjacent the third isolation layer and below the extrinsic base, wherein the second isolation layer defines a physical boundary between the first air gap and the second air gap.
8 . The structure of claim 7 , wherein the second isolation layer of the isolation stack is adjacent a lower portion of the intrinsic base of the BT, and wherein the second air gap is adjacent an upper portion of the intrinsic base of the BT.
9 . The structure of claim 7 , wherein the first isolation layer and the third isolation layer each include a same material.
10 . The structure of claim 7 , wherein the first isolation layer, the second isolation layer, and the third isolation layer form an oxide-nitride-oxide (ONO) stack.
11 . The structure of claim 7 , wherein the emitter of the BT is one of a plurality of emitters on the second portion of the intrinsic base.
12 . A method comprising:
forming a first isolation layer on a subcollector, wherein a first air gap is between the first isolation layer and a collector of a bipolar transistor (BT);
forming a second isolation layer on the first isolation layer and adjacent an intrinsic base of the BT; and
forming a third isolation layer on the second isolation layer, vertically between the second isolation layer and an extrinsic base of the BT, wherein a second air gap is adjacent the third isolation layer and below the extrinsic base, wherein forming the second isolation layer defines a physical boundary between the first air gap and the second air gap.
13 . The method of claim 12 , wherein the second isolation layer is adjacent a lower portion of the intrinsic base of the BT, and wherein the second air gap is adjacent an upper portion of the intrinsic base of the BT.
14 . The method of claim 12 , wherein the first isolation layer and the third isolation layer each include a same material.
15 . The method of claim 12 , wherein forming the first isolation layer, the second isolation layer, and the third isolation layer includes forming an oxide-nitride-oxide (ONO) stack.
16 . The method of claim 12 , wherein the first air gap is one of a pair of first air gaps each adjacent a sidewall of the collector, and wherein the second air gap is one of a pair of second air gaps each adjacent a sidewall of the intrinsic base.
17 . The method of claim 12 , further comprising forming the BT as a vertically-oriented heterojunction bipolar transistor on the subcollector.