FIELD

The described embodiments relate generally to silicon-based wafers for photonic circuits. More particularly, the present embodiments relate to silicon wafers that include an epitaxial layer of SrTiO3.

BACKGROUND

Currently there are a wide variety of methods to remove the native oxide, SiO2, from the surface of a silicon wafer and form an epitaxial layer of SrTiO3on the wafer. Some methods use thermal desorption at high temperatures of nearly 900° C. or above to remove the amorphous SiO2layer on the silicon before depositing one or more layers that terminate in SrTiO3. The use of high temperatures often results in excessive wafer bowing that can be on the order of 100 microns or greater for an 12 inch wafer. Other methods use one or more hazardous chemicals such as HF to etch the SiO2, however in addition to being dangerous, this method often results in the formation of SiC on the silicon surface which is very difficult to remove and is undesirable for epitaxial growth of SrTiO3. In addition, semiconductor industry has developed processes that use remote plasma of NH3and NF3gas to etch native oxide to form silicate salts that can be thermal desorbed at low-temperatures. Additionally, NH3and HF vapor phase reactions have been used to etch native oxide. However, both these methods are challenged to leave atomically clean surface of silicon. Further methods use Sr mediated de-oxidation to remove the SiO2, however there is still an undesirably large lattice mismatch between the silicon and the epitaxial SrTiO3layer.

New methods for removing the native oxide from a silicon wafer and for forming an epitaxial SrTiO3layer on a silicon wafer are needed that result in reduced bow of the wafer, increased safety, reduction of the formation of undesirable species on the silicon surface (e.g., SiC) and an improved lattice match between silicon and epitaxial SrTiO3.

SUMMARY

In some embodiments a method for processing a substrate comprises positioning the substrate in a deposition chamber, wherein the substrate comprises a wafer of single crystal silicon covered with a layer of amorphous silicon oxide. A layer of germanium is deposited on the layer of amorphous silicon oxide and the substrate is heated to a temperature below 850° C. causing at least a portion of the layer of amorphous silicon oxide to react with the layer of germanium to form germanium oxide.

In some embodiments the method further comprises repeating the depositing the layer of germanium and the heating the substrate until the layer of amorphous silicon oxide is removed from the wafer of single crystal silicon. In various embodiments after the amorphous silicon oxide is removed from the wafer of single crystal silicon, residual germanium from the depositing the layer of germanium is distributed on the wafer of single crystal silicon. In some embodiments an epitaxial layer of strontium titanate is deposited on the wafer of single crystal silicon and on the residual germanium.

In some embodiments the method further comprises exposing the wafer of single crystal silicon to oxygen after the depositing the epitaxial layer of strontium titanate, causing the silicon and the residual germanium to react forming a silicon germanium oxide layer between the layer of strontium titanate and the wafer of single crystal silicon. In various embodiments the method further comprises depositing a layer of germanium on the wafer of single crystal silicon after the layer of amorphous silicon oxide is removed. In some embodiments the method further comprises exposing the layer of germanium and the wafer of single crystal silicon to a temperature sufficient to cause the layer of germanium to inter-diffuse with the wafer of single crystal silicon to create a graded layer having a composition higher in silicon than germanium at the wafer of single crystal silicon and a composition that is higher in germanium than silicon at a top of the graded layer.

In some embodiments the method further comprises depositing a graded layer on the wafer of single crystal silicon after the layer of amorphous silicon oxide is removed, wherein the graded layer has a composition higher in silicon than germanium at the wafer of single crystal silicon and a composition that is higher in germanium than silicon at a top of the graded layer.

In some embodiments a method for removing an oxide layer from a substrate comprises depositing a layer of germanium on the oxide layer and heating the substrate to a temperature below 850° C. to cause the layer of germanium to react with the oxide layer and generate germanium oxide. In various embodiments the substrate comprises silicon and the oxide layer comprises silicon dioxide. In some embodiments the substrate comprises silicon germanium and the oxide layer comprises silicon germanium dioxide. In various embodiments the temperature is between 700° C. and 750° C. In some embodiments the method further comprises repetitively depositing the layer of germanium and heating the substrate until the oxide layer is removed.

In some embodiments the method further comprises depositing germanium on a surface of the substrate after the oxide layer is removed. In various embodiments the method further comprises depositing an epitaxial layer of strontium titanate after the depositing the germanium. In some embodiments the method further comprises exposing the substrate to oxygen after the depositing the epitaxial layer of strontium titanate, the oxygen causing the germanium to form a layer of silicon germanium oxide between the substrate and the epitaxial layer of strontium titanate.

In some embodiments a method for processing a substrate comprises positioning the substrate in a deposition chamber, wherein the substrate comprises a top layer of silicon germanium oxide, a middle layer of silicon germanium and a bottom layer of silicon. A layer of germanium is deposited on the layer of silicon germanium oxide and the substrate is heated to a temperature below 850° C. causing at least a portion of the layer of silicon germanium oxide to react with the layer of germanium to form germanium oxide. In various embodiments the method comprises repeating the depositing the layer of germanium and the heating the substrate until the layer of silicon germanium oxide is removed from the layer of silicon germanium.

In some embodiments the method further comprises depositing an epitaxial layer of strontium titanate on the layer of silicon germanium. In various embodiments the method of comprises exposing the layer of strontium titanate to oxygen causing the layer of silicon germanium to react with the oxygen forming a layer of silicon germanium oxide between the layer of strontium titanate and the layer of silicon.

To better understand the nature and advantages of the present disclosure, reference should be made to the following description and the accompanying figures. It is to be understood, however, that each of the figures is provided for the purpose of illustration only and is not intended as a definition of the limits of the scope of the present disclosure. Also, as a general rule, and unless it is evident to the contrary from the description, where elements in different figures use identical reference numbers, the elements are generally either identical or at least similar in function or purpose.

