Epitaxial strontium titanate on silicon
A method for processing a substrate includes positioning a silicon substrate in a deposition chamber. One or more intermediate layers are deposited on a surface of the silicon. The one or more intermediate layers can include strontium, which combines with the silicon to form strontium silicide. Alternatively, the one or more intermediate layers comprise germanium. A layer of amorphous strontium titanate is deposited on the one or more intermediate layers in a transient environment in which oxygen pressure is reduced while temperature is increased. The substrate is then exposed to an oxidizing and annealing atmosphere that oxidizes the one or more intermediate layers and converts the layer of amorphous strontium titanate to crystalline strontium titanate.
1 . A method for processing a substrate, the method comprising:
positioning the substrate in a deposition chamber, wherein the substrate comprises a wafer of single crystal silicon having a top surface;
forming one or more intermediate layers on the top surface of the wafer of single crystal silicon;
forming an amorphous strontium titanium oxide layer on the one or more intermediate layers using molecular-beam epitaxy (MBE) in an environment in which oxygen pressure is reduced while temperature is increased;
converting the amorphous strontium titanium oxide layer to a crystalline strontium titanium oxide layer;
after converting the amorphous strontium titanium oxide layer to a crystalline strontium titanium oxide layer, oxidizing the one or more intermediate layers to form a transition layer disposed between the substrate and the crystalline strontium titanium oxide layer; and
increasing a thickness of the crystalline strontium titanium oxide layer.
2 . The method of claim 1 wherein the one or more intermediate layers comprise germanium.
3 . The method of claim 2 wherein the one or more intermediate layers comprise atomic deposits of germanium randomly dispersed on the top surface of the wafer of single crystal silicon, and wherein the transition layer comprises germanium oxide.
4 . The method of claim 1 wherein the one or more intermediate layers comprise silicon germanium and wherein the transition layer comprises silicon germanium oxide.
5 . The method of claim 4 wherein the one or more intermediate layers comprises a graded silicon germanium layer that transitions from a composition greater in silicon than germanium at the wafer of single crystal silicon to a composition greater in germanium than silicon at a top surface of the one or more intermediate layers.
6 . The method of claim 1 wherein the one or more intermediate layers comprise a combination of strontium and silicon.
7 . The method of claim 6 wherein the one or more intermediate layers comprise a layer of strontium silicide (SrSi) deposited on the top surface of the wafer of single crystal silicon and wherein the transition layer comprises strontium silicate (SrSiO).
8 . The method of claim 1 wherein the transition layer is amorphous.
9 . A method comprising:
providing a silicon-based substrate;
depositing a layer containing strontium on the silicon-based substrate;
providing an oxygen environment;
performing molecular-beam epitaxy (MBE) in the oxygen environment to form an amorphous strontium titanium oxide layer on the layer containing strontium, wherein performing MBE in the oxygen environment comprises:
reducing oxygen pressure of the oxygen environment; and
increasing temperature of the oxygen environment;
converting the amorphous strontium titanium oxide layer to a crystalline strontium titanium oxide layer;
after converting the amorphous strontium titanium oxide layer to the crystalline strontium titanium oxide layer, oxidizing the layer containing strontium to form an amorphous strontium oxide layer disposed between the silicon-based substrate and the crystalline strontium titanium oxide layer; and
increasing a thickness of the crystalline strontium titanium oxide layer.
10 . The method of claim 9 wherein atomic deposits of germanium are randomly dispersed on the silicon-based substrate before the depositing the strontium containing layer.
11 . The method of claim 9 further comprising depositing a silicon germanium layer on the silicon-based substrate before the depositing the strontium containing layer.
12 . The method of claim 11 wherein the silicon germanium layer is a graded silicon germanium layer that transitions from a composition greater in silicon than germanium at the silicon substrate to a composition greater in germanium than silicon at a top surface of the graded silicon germanium layer.
13 . The method of claim 9 wherein the silicon-based substrate is characterized by a clean top surface.
14 . The method of claim 9 wherein a layer of strontium silicide is formed when depositing the layer containing strontium on the silicon-based substrate.
15 . A method for processing a substrate, the method comprising:
positioning the substrate in a deposition chamber, wherein the substrate comprises a top layer of silicon having a top surface;
forming one or more intermediate layers on the top surface of the top layer of silicon;
forming an amorphous layer of strontium titanium oxide on the one or more intermediate layers using molecular-beam epitaxy (MBE) in an environment in which oxygen pressure is reduced while temperature is increased;
converting the amorphous layer of strontium titanium oxide to a crystalline layer of strontium titanium oxide; and
after converting the amorphous layer of strontium titanium oxide to the crystalline layer of strontium titanium oxide, oxidizing the one or more intermediate layers to form a transition layer disposed between the substrate and the crystalline layer of strontium titanium oxide.
16 . The method of claim 15 wherein converting the amorphous layer of strontium titanium oxide to the crystalline layer of strontium titanium oxide is performed by heating the substrate.
17 . The method of claim 16 wherein the substrate is heated to a temperature above 500° C.
18 . The method of claim 15 wherein the one or more intermediate layers comprise atomic deposits of germanium randomly dispersed on the top surface of the top layer of silicon and the transition layer comprises amorphous germanium oxide.
19 . The method of claim 15 wherein the transition layer comprises a graded silicon germanium layer that transitions from a composition greater in silicon than germanium at the top layer of silicon to a composition greater in germanium than silicon at a top surface of the transition layer.
20 . The method of claim 15 wherein the top surface of the top layer of silicon is a clean top surface.