Controlling trap formation to improve memory window in one-time program devices
In some embodiments, the present disclosure relates to a one-time program (OTP) memory cell. The OTP memory cell includes a read transistor and a program transistor neighboring the read transistor. The read transistor includes a read dielectric layer and a read gate electrode overlying the read dielectric layer. The program transistor includes a program dielectric layer and a program gate electrode overlying the program dielectric layer. The program transistor has a smaller breakdown voltage than the read transistor.
1 . A one-time program (OTP) memory cell, comprising:
a read transistor coupled in series with a program transistor over a substrate; and
a pair of source/drain regions in the substrate;
wherein the read transistor comprises a read gate electrode and a read dielectric layer between the read gate electrode and the substrate;
wherein the program transistor comprises a program gate electrode and a program dielectric layer between the program gate electrode and the substrate;
wherein the program gate electrode is between and borders the pair of source/drain regions;
wherein a top surface of the program dielectric layer has a first portion and a second portion that are at a same elevation and that underlie the program gate electrode;
wherein the first and second portions are closer respectively to the pair of source/drain regions than to a center between the pair of source/drain regions;
wherein the read dielectric layer has a first average surface roughness; and
wherein the first and second portions of the program dielectric layer at the same elevation have a second average surface roughness that is greater than the first average surface roughness.
2 . The OTP memory cell of claim 1 , wherein the read transistor has a greater breakdown voltage than the program transistor.
3 . The OTP memory cell of claim 1 , wherein the read and program gate electrodes are different conductive materials, and wherein the first and second portions of the program dielectric layer at the same elevation have a first indent density and a top surface of the read dielectric layer has a second indent density less than the first indent density.
4 . The OTP memory cell of claim 1 , wherein the read dielectric layer comprises a first concentration of defects, and wherein the first and second portions of the program dielectric layer at the same elevation comprise a second concentration of defects greater than the first concentration of defects.
5 . The OTP memory cell of claim 1 , wherein the first and second portions of the program dielectric layer are level with a top surface of the read dielectric layer.
6 . The OTP memory cell of claim 1 , further comprising:
a program interfacial layer underlying the program dielectric layer and contacting the program dielectric layer at a planar interface that extends continuously from a first location overlying one of the pair of source/drain regions to a second location overlying another one of the pair of source/drain regions.
7 . The OTP memory cell of claim 1 , wherein a bottom surface of the program dielectric layer has a single elevation underlying the first and second portions.
8 . A memory device comprising a one-time program (OTP) memory cell, wherein the OTP memory cell comprises:
a semiconductor substrate;
a read gate dielectric layer overlying the semiconductor substrate;
a read gate electrode overlying the read gate dielectric layer;
an interfacial layer overlying the semiconductor substrate;
a program gate dielectric layer overlying the interfacial layer;
a program gate electrode overlying the program gate dielectric layer and having a first sidewall and a second sidewall on opposite sides of the program gate electrode; and
a source/drain region in the semiconductor substrate, between and bordering the read and program gate electrodes;
wherein the read and program gate dielectric layers share a common material, wherein the program gate dielectric layer is thinner than the read gate dielectric layer, wherein the read and program gate dielectric layers have individual top surfaces with plasma etch damage, wherein the individual top surface of the program gate dielectric layer at a single elevation over the interfacial layer has a greater amount of plasma etch damage than the individual top surface of the read gate dielectric layer, and wherein the program gate dielectric layer and the interfacial layer extend along the read and program sidewalls of the program gate electrode and arm continuous from the read sidewall to the program sidewall.
9 . The memory device according to claim 8 , wherein the read gate dielectric layer is on sidewalls of the read gate electrode.
10 . The memory device according to claim 9 , wherein the individual top surface of the program gate dielectric layer at the same elevation has a greater average surface roughness than a sidewall surface of the program gate dielectric layer facing the second gate electrode.
11 . The memory device according to claim 8 ,
wherein a width of the interfacial layer is greater than the program gate dielectric layer.
12 . The memory device according to claim 11 , wherein the interfacial layer has a U-shaped profile.
13 . The memory device according to claim 8 , wherein the OTP memory cell repeats in a plurality of rows and a plurality of columns, and wherein repetitions of the OTP memory cell are independent of each other.
14 . The memory device according to claim 8 , wherein the OTP memory cell further comprises:
a pair of source/drain regions, wherein the second gate electrode is between and borders the pair of source/drain regions, and wherein the first and second sidewalls of the second gate electrode respectively overlie the pair of source/drain regions, laterally offset from sidewalls of the pair of source/drain regions.
15 . The OTP memory cell of claim 8 , wherein a bottom surface of the program dielectric layer has a second single elevation underlying the individual top surface of the program gate dielectric layer and overlying the interfacial layer.
16 . A one-time program (OTP) memory cell, comprising:
a read transistor over a substrate, and comprising a read gate electrode and a read dielectric layer between the read gate electrode and the substrate; and
a program transistor over the substrate and coupled in series with the program transistor, and comprising a program gate electrode and a program dielectric layer between the program gate electrode and the substrate,
wherein a top surface of the program dielectric layer has a first portion and a second portion at a same elevation and underlying the program gate electrode,
wherein the read dielectric layer has a first average surface roughness, and
wherein the first and second portions of the top surface of the program dielectric layer at the same elevation have a second average surface roughness that is greater than the first average surface roughness of the read dielectric layer.
17 . The OTP memory cell of claim 16 , further comprising:
a pair of source/drain regions in the substrate, wherein the program gate electrode is between and borders the pair of source/drain regions, wherein the first and second portions are closer respectively to the pair of source/drain regions than to a center between the pair of source/drain regions, and wherein a breakdown voltage of the program transistor is smaller than a breakdown voltage of the read transistor.
18 . The OTP memory cell of claim 16 , wherein a bottom surface of the program dielectric layer underlying the first and second portions has a single elevation.
19 . The OTP memory cell of claim 16 , wherein the read dielectric layer comprises a first concentration of defects, wherein the first and second portions of the program dielectric layer at the same elevation comprise a second concentration of defects different from the first concentration of defects, and wherein the second concentration of defects is greater than the first concentration of defects.
20 . The OTP memory cell of claim 16 , wherein the read dielectric layer has a first average thickness, and wherein the first and second portions of the program dielectric layer at the same elevation have a second average thickness that is less than the first average thickness.