Anti-fuse memory cell
An anti-fuse memory cell having a variable thickness gate oxide. The variable thickness gate oxide is formed by depositing a first oxide over a channel region of the anti-fuse memory cell, removing the first oxide in a thin oxide area of the channel region, and then thermally growing a second oxide in the thin oxide area. The remaining first oxide defines a thick oxide area of the channel region. The second oxide growth occurs under the remaining first oxide, but at a rate less than thermal oxide growth in the thin oxide area. This results in a combined thickness of the first oxide and the second oxide in the thick oxide area being greater than second oxide in the thin oxide area.
1. A method of forming a variable thickness gate oxide for an anti-fuse transistor, comprising the steps of:
growing a first oxide in a channel region of the anti-fuse transistor;
removing the first oxide from a thin oxide area of the channel region;
thermally growing a second oxide in the thin oxide area and in a thick gate oxide area of the channel region under the first oxide, and a combination of the first oxide and the second oxide in the thick gate oxide area has a thickness greater than the second oxide in the thin oxide area; and
forming a diffusion region adjacent the thick oxide area for receiving current from the channel region.
2. The method of claim 1 , wherein thermally growing includes growing the second oxide in the thin oxide area at a first rate and growing the second oxide in the thick gate oxide area at a second rate less than the first rate.
3. The method of claim 2 , wherein growing the second oxide in the thin oxide area at a first rate includes consuming a substrate surface of the thin oxide area to a first depth, and growing the second oxide in the thick gate oxide area includes consuming a substrate surface of the thick gate oxide area to a second depth less than the first depth.
4. The method of claim 3 , wherein thermally growing includes forming an angled oxide area between the thick gate oxide area and the thin gate oxide area, the angled oxide area having a thickness different from the combination of the first oxide and the second oxide in the thick gate oxide area, and different from the second oxide in the thin oxide area.
5. The method of claim 4 , further including forming a common gate over the first oxide the second oxide, and the angled oxide area.
6. The method of claim 1 , wherein the second oxide under the first oxide is thinner than the second oxide in the thin oxide area.
7. The method of claim 1 , further including forming a bitline contact in electrical contact with the diffusion region for sensing a current from the common gate when a conductive link is formed between the channel and the common gate.
8. An anti-fuse memory cell having a variable thickness gate oxide comprising:
a channel region in a substrate;
a first oxide in a thick oxide area of the channel region; and,
a second oxide thermally grown in a thin oxide area of the channel region and in the thick oxide area underneath the first oxide;
a diffusion region adjacent to the thick oxide area for receiving current from the channel region;
isolation adjacent to the thin gate oxide area; and
a gate over the first oxide and the second oxide.
9. The anti-fuse memory cell of claim 8 , wherein the second oxide under the first oxide is thinner than the second oxide in the thin oxide area.
10. The anti-fuse memory cell of claim 9 , wherein a combination of the first oxide and the second oxide in the thick oxide area has a thickness greater than the second oxide in the thin oxide area.
11. The anti-fuse memory cell of claim 10 , wherein the second oxide in the thin oxide area extends into the substrate to a first depth, and the second oxide in the thick oxide area extends into the substrate to a second depth less than the first depth.
12. The anti-fuse memory cell of claim 8 , further including an angled oxide area between the thick gate oxide area and the thin gate oxide area, the angled oxide area having a thickness different from the combination of the first oxide and the second oxide in the thick gate oxide area, and different from the second oxide in the thin oxide area.
13. The anti-fuse memory cell of claim 8 , wherein the gate is connected to a wordline.
14. The anti-fuse memory cell of claim 13 , wherein the diffusion region is connected to a bitline.
15. The anti-fuse memory cell of claim 13 , further including an access transistor adjacent to the diffusion region, and another diffusion region adjacent to the access transistor.
16. The anti-fuse memory cell of claim 15 , wherein the another diffusion region is connected to a bitline.
17. The anti-fuse memory cell of claim 16 , wherein the access transistor has a gate oxide thickness corresponding to the combination of the first oxide and the second oxide in the thick gate oxide area.