Semiconductor memory cell and driver circuitry with gate oxide formed simultaneously
The present disclosure provides for semiconductor structures and methods for making semiconductor structures. In one embodiment, isolation regions are formed in a substrate, and wells are formed between the isolation regions. The wells include a first low voltage well and a second low voltage well in a logic region of the substrate, and a memory array well in an NVM region of the substrate. A first layer of oxide is formed over the first low voltage well and the memory array well, and a second layer of oxide is formed over the second low voltage well, the second layer being thinner than the first layer. Gates are formed over the wells, including a first gate over the first low voltage well, a second gate over the second low voltage well, and a memory cell gate over the memory array well. Source/drain extension regions are formed around the gates.
1. A method of making a semiconductor structure using a substrate, wherein the semiconductor structure comprises a non-volatile memory (NVM) structure in an NVM region of the substrate, the method comprising:
forming isolation regions in the substrate;
forming wells between the isolation regions, wherein
the wells comprise a first low voltage well and a second low voltage well in a logic region of the substrate, and a memory array well in the NVM region;
forming a first layer of oxide over the first low voltage well and the memory array well;
forming a second layer of oxide over the second low voltage well, wherein the second layer of oxide is thinner than the first layer of oxide;
forming gates over the wells, wherein the gates comprise
a first gate over the first low voltage well, the first gate including the first layer of oxide,
a second gate over the second low voltage well, the second gate including the second layer of oxide, and
a memory cell gate over the memory array well, the memory cell gate including the first layer of oxide; and
forming source/drain extension regions around the gates.
2. The method of claim 1 , wherein the forming the isolation regions comprises:
etching trenches into the substrate;
depositing oxide into the trenches to form the isolation regions; and
polishing a top surface of the substrate.
3. The method of claim 1 , wherein
the first low voltage well and the second low voltage well are formed using a same implant dopant.
4. The method of claim 1 , wherein the forming the first oxide of layer comprises
growing the first layer of oxide over the wells, including the first low voltage well, the second low voltage well, and the memory array well; and
removing the first layer of oxide from over the second low voltage well to leave the first layer of oxide over the first low voltage well and the memory array well.
5. The method of claim 1 , wherein
a first extension region around the first gate and a second extension region around the second gate are formed using a same lightly doped drain (LDD) implant dopant.
6. The method of claim 1 , wherein
the memory cell gate comprises one of a split gate and a floating gate.
7. The method of claim 1 , wherein
the wells further comprise a high voltage well and a dual gate well in the logic region, and
the gates further comprise a third gate over the dual gate well and a fourth gate over the high voltage well.
8. The method of claim 7 , wherein
the first gate, the second gate, the third gate, and the fourth gate are formed using a same gate etch process.
9. The method of claim 7 , wherein
the first gate, the second gate, the third gate, and the fourth gate comprise a conductive layer having a same thickness in each of the first, second, third, and fourth gates.
10. The method of claim 7 , wherein
extension regions around the memory cell gate, the second gate, the third gate, and the fourth gate are formed using different lightly doped drain (LDD) implant dopants.
11. The method of claim 7 , further comprising:
growing a third layer of oxide over the wells, prior to the forming the first layer of oxide;
removing the third layer of oxide from over the dual gate well to leave the third layer over the high voltage well;
growing a fourth layer of oxide over the wells, subsequent to the removing the third layer and prior to the forming the first layer;
removing the fourth layer of oxide from over the first low voltage well and the memory array well to leave the fourth layer over the dual gate well;
growing the first layer of oxide over the wells, subsequent to the removing the fourth layer, wherein the forming the first layer comprises the growing the first layer;
removing the first layer of oxide from over the second low voltage well to leave the first layer over the first low voltage well and the memory array well; and
growing the second layer of oxide over the wells, subsequent to the removing the first layer of oxide, wherein the forming the second layer comprises the growing the second layer.
12. The method of claim 1 , wherein
the first gate in the first low voltage well is included in a semiconductor device that is part of a supra-low voltage circuit in the logic region,
the supra-low voltage circuit comprising one of a column select circuit and a row select driver circuit, and
the supra-low voltage driver circuit operates in a supra-low power domain.
13. The method of claim 12 , wherein
the supra-low power domain has a maximum voltage of 2 volts.