Seed layer processes for MOCVD of ferroelectric thin films on high-k gate oxides

1. A method of forming a ferroelectric thin film on a high-k layer, comprising:

preparing a silicon substrate;

forming a high-k layer on the substrate and annealing the high-k layer to form an oxide layer;

preparing a PGO precursor solution;

depositing a seed layer of ferroelectric material on the high-k oxide layer, wherein said depositing a seed layer includes depositing a layer of c-axis oriented PGO thin film at a temperatures of between about 500° C. to 540° C., at a pressure of between about 1 torr to 5 torr, in an atmosphere having an oxygen partial pressures of between about 20% to 30%, at a vaporizer temperature of between about 180° C. to 200° C.; wherein the precursor solution has a delivery rate of between about 0.05 ml/min to 0.1 ml/min, for a deposition time of between about 5 minutes to 20 minutes;

depositing a top layer of ferroelectric material on the seed layer at a relatively low temperature, wherein said depositing a top ferroelectric layer includes depositing a PGO thin film at a deposition temperatures of between about 380° C. and 420° C., wherein the deposition pressure is between about 5 torr to 10 torr, in an atmosphere having an oxygen partial pressure of between about 30% to 40%, at a vaporizer temperature of between about 200° C. to 240° C., wherein the precursor solution delivery rate is between about 0.1 ml/min to 0.2 ml/min; and wherein the deposition time is between about one hour to three hours; and

annealing the substrate, the high-k layer and the ferroelectric layers to form a ferroelectric thin film, wherein said annealing includes annealing at a temperature of between about 520° C. to 560° C. for between about thirty minutes and one hour in a pure oxygen atmosphere.

2. The method of claim 1 wherein said preparing a ferroelectric precursor solution for deposition by MOCVD, includes preparing a solution of [Pb(thd) 2 ] and [Ge(ETO) 4 ], where thd is C 11 H 19 O 2 and ETO is OC 2 H 5 , in a molar ratio of about 5.0:3 to 5.5:3, are dissolved in a mixed solvent, consisting of solvents taken from the group of solvents consisting of butyl ether, and tetrahydrofuran, isopropanol and tetraglyme, in the molar ratio of about 8:2:1, wherein the solution has a concentration of about 0.1 M/L of PGO, and wherein the solution is injected into a vaporizer at temperature in the range of between about 180° C. to 240° C., by a pump at a flow rate of between about 0.05 ml/min to 0.20 ml/min, to form the precursor gas, and wherein a MOCVD feed line is maintained at a temperature of between about 185° C. to 245° C.

3. The method of claim 1 wherein said forming a high-k layer includes forming a layer of material taken from the group of material consisting of HfO 2 and (Zr 0.5 , Hf 0.5 )O 2 , to a thickness of between about 3.5 nm to 15 nm.

4. The method of claim 1 wherein said preparing the silicon substrate includes cleaning the substrate using SC1+SC2; where SC1 is a mixture of 5500 ml of deionized water, 1100 ml of NH 4 OH and 1 100 ml of H 2 O 2 , and where SC2 is a mixture of 6000 ml of deionized water, 1000 ml of HCl and 1000 ml of H 2 O 2 ; and which further includes removing any surface oxide by an HF dip etch.