Flash memory and method of manufacturing the same
A flash memory structure includes a memory gate on a substrate, a select gate adjacent to the memory gate, and an oxide-nitride spacer between the memory gate and the select gate, where the oxide-nitride spacer further includes an oxide layer and a nitride layer having an upper nitride portion and a lower nitride portion, and the upper nitride portion is thinner than the lower nitride portion.
1. A flash memory, comprising:
a memory gate on a substrate;
a select gate adjacent to said memory gate, wherein said select gate comprises an upper portion and a lower portion; and
an oxide-nitride spacer between said memory gate and said select gate, wherein said oxide-nitride spacer comprises an oxide layer directly contacting said memory gate and a nitride layer having an upper nitride portion corresponding to said upper portion and a lower nitride portion corresponding to said lower portion, wherein said upper portion covers, and is in direct contact with, a topmost surface of said lower nitride portion with respect to said substrate, and a topmost surface of said upper nitride portion is higher than a topmost surface of said oxide layer with respect to said substrate, and a conformal thickness of said upper nitride portion is thinner than a conformal thickness of said lower nitride portion.
2. The flash memory of claim 1 , further comprising a plane interface between said upper nitride portion and said lower nitride portion, wherein said plane is higher than the top surface of said memory gate.
3. The flash memory of claim 1 , wherein a height of said oxide layer of said oxide-nitride spacer is flush with a top surface of said memory gate.
4. The flash memory of claim 1 , wherein a thickness of said upper nitride portion is smaller than 60% of a thickness of said lower nitride portion.
5. The flash memory of claim 1 , wherein a thickness of said upper nitride portion is smaller than 30 Angstroms.
6. The flash memory of claim 1 , wherein a thickness of said lower nitride portion is larger than 40 Angstroms.
7. The flash memory of claim 1 , wherein a height of said select gate is higher than a height of said memory gate.
8. The flash memory of claim 1 , further comprising a gate dielectric layer between said memory gate and said substrate and between said select gate and said substrate.
9. The flash memory of claim 8 , wherein said gate dielectric layer between said memory gate and said substrate is oxide/nitride/oxide tri-layer.
10. The flash memory of claim 1 , wherein said nitride layer comprises silicon nitride (SiN) or silicon carbide nitride (SiCN).
11. The flash memory of claim 1 , wherein said memory gate and said select gate comprise polysilicon.
12. A flash memory, comprising:
a memory gate on a substrate;
a select gate adjacent to said memory gate; and
an oxide-nitride spacer between said memory gate and said select gate, wherein said oxide-nitride spacer comprises an oxide layer directly contacting said memory gate and a nitride layer having an upper nitride portion and a lower nitride portion, wherein a topmost surface of said upper nitride portion is higher than a topmost surface of said oxide layer with respect to said substrate and is flushed with a top surface of said select gate with respect to said substrate, and a conformal thickness of said upper nitride portion is thinner than a conformal thickness of said lower nitride portion.