Oxygen-free atomic layer deposition of indium sulfide
A method for synthesizing an In(III) N,N′-diisopropylacetamidinate precursor including cooling a mixture comprised of diisopropylcarbodiimide and diethyl ether to approximately −30° C., adding methyllithium drop-wise into the mixture, allowing the mixture to warm to room temperature, adding indium(III) chloride as a solid to the mixture to produce a white solid, dissolving the white solid in pentane to form a clear and colorless solution, filtering the mixture over a celite plug, and evaporating the solution under reduced pressure to obtain a solid In(III) N,N′-diisopropylacetamidinate precursor. This precursor has been further used to develop a novel atomic layer deposition technique for indium sulfide by dosing a reactor with the precursor, purging with nitrogen, dosing with dilute hydrogen sulfide, purging again with nitrogen, and repeating these steps to increase growth.
1. A method of oxygen-free atomic layer deposition of indium sulfide on an atomic layer deposition tool at temperatures ranging from 125° C. to 240° C., the method comprising:
providing an ultra-high purity nitrogen carrier gas through the tool;
delivering a solid In(III) N,N′-diisopropylacetamidinate precursor to the tool;
adding a hydrogen sulfide mixture to the tool; and
conducting at least one growth cycle, wherein one growth cycle comprises the following sequential steps:
delivering a saturating dose of the In(III) N,N′-diisopropylacetamidinate precursor;
purging with the ultra-high purity nitrogen carrier gas;
delivering a saturating dose of the hydrogen sulfide mixture; and
purging with the ultra-high purity nitrogen carrier gas.
2. The method of claim 1 , wherein in the one growth cycle, the In(III) N,N′-diisopropylacetamidinate precursor dose is conducted at approximately a 0.04 Torr partial pressure.
3. The method of claim 1 , wherein in the one growth cycle, the hydrogen sulfide dose is conducted at approximately a 0.45 Torr partial pressure.
4. The method of claim 1 , wherein a constant stream of 10 sccm ultra-high purity nitrogen carrier gas is continuously pumped through the tool.
5. The method of claim 1 , wherein the hydrogen sulfide mixture was stepped down to a pressure of 500 Torr through a two-stage regulator before flowing through a 300 μm pinhole just prior to being added to the tool.
6. The method of claim 1 , further comprising repeating the growth cycle.
7. The method of claim 1 , further comprising synthesizing the solid In(III) N,N′-diisopropylacetamidinate precursor that is delivered to the tool,
wherein synthesizing the solid In(III) N,N′-diisopropylacetamidinate precursor comprises
cooling a mixture comprised of diisopropylcarbodiimide and a first solvent to approximately −30° C.;
adding methyllithium drop-wise into the mixture;
allowing the mixture to warm to room temperature;
adding indium(III) chloride as a solid to the mixture to produce a white solid;
dissolving the white solid in a second solvent to form a clear and colorless solution; and
evaporating the solution under reduced pressure to obtain the solid In(III) N,N′-diisopropylacetamidinate precursor.
8. The method of claim 7 , wherein the first solvent is diethyl ether and the second solvent is pentane.
9. The method of claim 7 , wherein synthesizing the solid In(III) N,N′-diisopropylacetamidinate precursor further comprises allowing a reaction of the mixture comprised of diisopropylcarbodiimide, diethyl ether, methyllithium and indium(III) chloride to take place overnight at room temperature prior to the step of evaporating the solution under reduced pressure to obtain the solid In(III) N,N′-diisopropylacetamidinate precursor.
10. The method of claim 7 , wherein synthesizing the solid In(III) N,N′-diisopropylacetamidinate precursor further comprises removing volatiles under a reduced pressure prior to the step of evaporating the solution under reduced pressure to obtain the solid In(III) N,N′-diisopropylacetamidinate precursor.
11. The method of claim 7 , wherein synthesizing the solid In(III) N,N′-diisopropylacetamidinate precursor further comprises further purifying the solid In(III) N,N′-diisopropylacetamidinate precursor by dissolving the solid In(III) N,N′-diisopropylacetamidinate precursor in pentane to form a second mixture and allowing the second mixture to cool to approximately −30° C.
12. The method of claim 7 , wherein synthesizing the solid In(III) N,N′-diisopropylacetamidinate precursor further comprises purifying the solid In(III) N,N′-diisopropylacetamidinate precursor by sublimation at a temperature of approximately 150° C. and a pressure of approximately 20 mTorr.
13. The method of claim 7 , wherein the mixture comprised of diisopropylcarbodiimide, the first solvent, and methyllithium is stirred for two hours prior to the step of adding indium(III) chloride.
14. The method of claim 7 , wherein the step of dissolving the white solid in the second solvent comprises dissolving the white solid in pentane and filtering through a celite plug in order to form the clear and colorless solution.