Non-volatile memory having nano crystalline silicon hillocks floating gate
A method for making a non-volatile memory device provides a semiconductor substrate including a surface region and a tunnel dielectric layer overlying the surface region. Preferably the tunnel dielectric layer is a high-K dielectric, characterized by a dielectric constant higher than 3.9. The method forms a source region within a first portion and a drain region within a second portion of the semiconductor substrate. The method includes forming a first and second nanocrystalline silicon structures overlying the first and second portions between the source region and the drain region to form a first and second floating gate structures while maintaining a separation between the first and second nanocrystalline silicon structures. The method includes forming a second dielectric layer overlying the first and second floating gate structures. The method also includes forming a control gate structure overlying the first and second floating gate structures.
1. A method for making a non-volatile memory device, the method comprising:
providing a semiconductor substrate including a surface region;
forming a tunnel dielectric layer overlying the surface region;
forming a source region within a first portion of the semiconductor substrate;
forming a drain region within a second portion of the semiconductor substrate;
depositing a first nanocrystalline silicon structure overlying a first portion between the source region and the drain region to form a first floating gate structure;
depositing a second nanocrystalline silicon structure overlying a second portion between the source region and the drain region to form a second floating gate structure, while maintaining separation from the first nanocrystalline silicon structure;
sputtering the deposited first and second nanocrystalline silicon structures to form a pointed top portion and a broad bottom portion;
forming a second dielectric layer overlying the first floating gate structure and the second floating gate structure; and
forming a control gate structure overlying the first floating gate structure and the second floating gate structure.
2. The method of claim 1 , wherein the forming of the first nanocrystalline silicon structure and the forming of the second nanocrystalline silicon structure include using a high density plasma species.
3. The method of claim 1 , wherein the depositing of the first nanocrystalline silicon structure and the depositing of the second nanocrystalline silicon structure comprises:
heating the semiconductor substrate to above 500° C. in an argon ambient with an argon flow of about 50-500 sccm; wherein
the first and second nanocrystalline silicon structures are deposited under a pressure of less than 1.0 torr, argon flow of about 50-500 sccm, and SiH4 flow of about 10-200 sccm; and
the deposited first and second nanocrystalline silicon structures are sputtered in an argon ambient, with an argon flow of about 50-500 sccm and an RF bias power of about 500-3000 Watts.
4. The method of claim 3 , further comprising repeating the heating, depositing, and sputtering steps at least one time.
5. The method of claim 1 , wherein forming a tunnel dielectric layer comprises:
depositing HfO2 layer to a thickness of about 1-20 nm by LPCVD using Hafnium t-butoxide (Hf(OC4H9)4) precursor at about 300-500° C. with a pressure of about 1.0 torr; and
annealing the HfO2 layer at about 600-800° C. in an gas ambient comprising NH3 or N2.
6. The method of claim 1 , wherein the second dielectric layer is selected from the group consisting of HfO2, Al2O3, SiON, and SiN.
7. The method of claim 1 , wherein the second dielectric layer is characterized by a dielectric constant higher than 3.9.
8. The method of claim 1 , wherein the first floating gate structure is less than about 20 nanometers.
9. The method of claim 1 wherein the second floating gate structure is less than about 20 nanometers.
10. The method of claim 1 wherein the first floating gate structure is characterized by a triangular shape.
11. The method of claim 1 wherein the second floating gate structure is characterized by a triangular shape.