Methods of formation of a SiGe/Si superlattice
A method and apparatus for forming a super-lattice structure on a substrate is described herein. The super-lattice structure includes a plurality of silicon-germanium layers and a plurality of silicon layers disposed in a stacked pattern. The methods described herein produce a super-lattice structure with transition width of less than about 1.4 nm between each of the silicon-germanium layers and an adjacent silicon layer. The methods described herein include flowing one or a combination of a silicon containing gas, a germanium containing gas, and a halogenated species.
1 . A method of forming a semiconductor device, comprising:
(a) introducing a first silicon containing gas at a first flow rate and a germanium containing gas at a second flow rate into a deposition chamber to form a silicon-germanium layer on a substrate within the deposition chamber;
(b) stopping the flow of the first silicon containing gas and the germanium containing gas into the deposition chamber after forming the silicon-germanium layer;
(c) flowing a halogenated species into the deposition chamber; and
(d) flowing a second silicon containing gas at a third flow rate greater than the first flow rate into the deposition chamber to form a silicon layer on the substrate within the deposition chamber.
2 . The method of claim 1 , further comprising repeating (a)-(d).
3 . The method of claim 2 , wherein (a)-(d) are repeated greater than 20 times.
4 . The method of claim 1 , wherein the halogenated species includes one or a combination of H x SiY (4-x) , H x GeY (4-x) , or HY, where x is equal to an integer between 0-3 and y is equal to one of chlorine (Cl), bromine (Br), or iodine (I).
5 . The method of claim 1 , wherein (c) is performed between (b) and (d), and flowing the halogenated species is stopped in (d).
6 . The method of claim 5 , wherein (c) is performed during (a) and (d).
7 . The method of claim 1 , wherein the silicon-germanium layer and the silicon layer are grown at a growth rate of greater than 150 nm/min.
8 . The method of claim 7 , wherein (c) is performed between (b) and (d), and the transition width between the silicon-germanium layer and the silicon layer is less than 1.4 nm.
9 . The method of claim 1 , wherein the silicon-germanium layer comprises 12% to 30% germanium.
10 . A method of forming a semiconductor device, comprising:
forming a unit cell comprising:
introducing a silicon containing gas and a germanium containing gas into a deposition chamber to form a silicon-germanium layer on a substrate within the deposition chamber;
stopping the flow of the germanium containing gas into the deposition chamber after forming the silicon-germanium layer;
flowing a halogenated species into the deposition chamber; and
forming a silicon layer on the substrate within the deposition chamber from the silicon containing gas, the halogenated species flowing at a first flow rate during the introducing of the silicon containing gas and the germanium containing gas, the first flow rate of the halogenated species is increased to a second flow rate prior to the forming of the silicon layer, and the first flow rate is increased to the second flow rate simultaneously to or after the stopping of the flow of the germanium containing gas; and
repeating the forming the unit cell to form a stack of unit cells.
11 . The method of claim 10 , wherein the repeating the forming the unit cell comprises forming greater than 25 unit cells.
12 . The method of claim 10 , wherein the halogenated species is introduced during each of the formation of the silicon-germanium layer, the formation of the silicon layer, and between the formation of the silicon-germanium layer and the formation of the silicon layer.
13 . The method of claim 10 , wherein the silicon layer is disposed directly on the silicon-germanium layer.
14 . The method of claim 10 , wherein:
the halogenated species is flowed into the deposition chamber during each of formation of the silicon-germanium layer, formation of the silicon layer, and between the formation of the silicon-germanium layer and the silicon layer; and
the flow of the halogenated species is reduced from the second flow rate back to the first flow rate for the forming of the silicon layer.
15 . The method of claim 10 , wherein the halogenated species is flowed into the deposition chamber between the formation of the silicon-germanium layer and the silicon layer, the silicon containing gas flows at a third flow rate during the forming of the silicon-germanium layer, the silicon containing gas continues to flow during the stopping of the flow of the germanium containing gas and during the flowing of the halogenated species, the silicon containing gas flows at a second flow rate during the forming of the silicon layer, and the second flow rate is increased relative to the first flow rate.
16 . A super-lattice device structure, comprising:
a first unit cell comprising:
a first silicon-germanium layer; and
a first silicon layer disposed on the first silicon-germanium layer, wherein a transition width between the first silicon-germanium layer and the first silicon layer is less than 1.4 nm; and
a second unit cell comprising:
a second silicon-germanium layer; and
a second silicon layer disposed on the second silicon-germanium layer, wherein the transition width between the second silicon-germanium layer and the second silicon layer is less than 1.4 nm.
17 . The super-lattice device structure of claim 16 , wherein the silicon-germanium layer includes 12% to 30% germanium.
18 . The super-lattice device structure of claim 16 , wherein the silicon layer includes less than 1% germanium.
19 . The super-lattice device structure of claim 16 , wherein each of the first unit cell and the second unit cell further comprise an additional silicon-germanium layer and an additional silicon layer.
20 . The super-lattice device structure of claim 16 , wherein the first silicon-germanium layer, the second silicon-germanium layer, the first silicon layer, and the second silicon layer have varying thicknesses.