Insulated-gate field-effect thin film transistors

1. A method of fabricating a semiconductor Insulated-Gate Field-Effect Transistor (Gated-FET), comprising:

depositing a semiconductor thin film layer on a thick insulator; and

forming a substantially rectangular channel region in said semiconductor thin film layer, said channel region lightly doped to form a resistive channel, wherein the height of the channel region comprising the entire thin film thickness; and

depositing a gate insulator layer above said channel region; and

depositing a gate material above said gate insulator layer, said material forming a gate region above said channel region;

wherein optimizing said thin film properties, gate insulator properties and gate material properties such that said gate region further comprises:

a first voltage level that modulates said channel resistance to a substantially non-conductive state by fully depleting majority carriers from said channel region; and

a second voltage level that modulates said channel resistance to a substantially conductive state by at least partially accumulating majority carriers near the gate insulator surface in said channel region; and

wherein depositing said semiconductor thin film layer further comprises:

defining a surface voltage as Φ S =V D −V FB −T G *Q S /∈ G ; and

defining a surface dopant level as N S =D*exp(qΦ S /kT); and

defining a first thickness as L D =[∈ S *kT/(q 2 N S )] 0.5 ; and

defining a second thickness as X A =√2*L D *[(N S /D) 0.5 −1]; and

defining a surface charge as Q S =q*N S *X A /(1+X A /(√2*L D )]; and

iteratively identifying the consistent set of values that satisfies said definitions; and

depositing a substantially uniform thickness T S of said semiconductor thin film layer, wherein said thickness T S is greater than said second thickness X A ;

where, V D is power supply voltage level, ∈ S is channel semiconductor permittivity, ∈ G is gate insulator permittivity, T G is gate insulator thickness, V FB is gate material to semiconductor channel absolute flat band voltage, k is the Boltzmann's constant, T is the absolute temperature, q is electron charge and D is channel region doping level.

2. The method of claim 1 , wherein depositing said semiconductor thin film layer further comprises:

defining a third thickness as X=∈ S *T G /∈ G ; and

defining a fourth thickness as Y=[(2*∈ S *(V FB −V T ))/(q*D)] 0.5 ; and

defining a fifth thickness as Z=(X 2 +Y 2 ) 0.5 −X; and

depositing said substantially uniform thickness T S of said semiconductor thin film layer, wherein said thickness T S satisfies a thickness range approximately 0.8*Z to 1.2*Z;

where, ∈ S is channel semiconductor permittivity, ∈ G is gate insulator permittivity, T G is gate insulator thickness, V FB is gate material to semiconductor channel absolute flat band voltage, V T is channel region absolute threshold voltage, q is electron charge and D is channel region doping level.

3. The method of claim 1 , wherein said gate insulator material comprises an oxide, said gate material comprises a heavily doped poly Silicon material with opposite type dopant to said channel region, and depositing said semiconductor thin film layer further comprises:

defining a third thickness as X=3*T OX (Angstroms); and

defining a fourth thickness as Y=0.28/√D (Angstroms); and

defining a fifth thickness as Z=(X 2 +Y 2 ) 0.5 −X (Angstroms); and

depositing said substantially uniform thickness T S of said semiconductor thin film layer, wherein said thickness T S further satisfies a thickness range approximately 0.8*Z to 1.2*Z;

where, T OX is gate oxide thickness in Angstroms, D is channel doping level in atoms/(Angstroms) 3 and T S is channel semiconductor layer thickness in Angstroms.

4. The method of claim 1 , comprised of forming one of N channel or P channel Gated-FET thin film transistor consisting a process sequence comprised of:

depositing one of amorphous or crystalline poly-1 (P1);

performing P1 mask & etching P1;

applying blanket Gated-NFET V T N− implant;

applying Gated-PFET V T mask & P− implant;

depositing Gox;

depositing one of amorphous or crystalline poly-2 (P2);

applying blanket P+ implantation of Gated-NFET Gate;

applying N+ mask & implanting Gated-PFET Gate;

applying P2 mask & etching P2;

applying blanket LDN N implant (Gated-NFET LDD);

applying LDP mask & P implant (Gated-PFET LDD);

depositing a spacer oxide and etching the spacer oxide;

depositing Nickel;

salicidizing the Nickel on exposed P1 and P2;

salicidizing P1 completely;

performing RTA anneal, P1 and P2 re-crystallization and dopant anneal;

depositing ILD oxide & CMP;

applying C2 mask & etch;

forming a W plug & CMP; and

depositing M1.

5. The method of claim 1 , comprised of forming one of N channel or P channel thinned down SOI Gated-FET thin film transistor consisting a process sequence comprised of:

forming SOI substrate wafer;

performing Shallow Trench isolation: Trench Etch, Trench Fill and CMP;

depositing Sacrificial oxide;

applying Periphery PMOS V T mask & implant;

applying Periphery NMOS V T mask & implant;

applying Gated-FET mask and Silicon etch;

performing Gated-FET blanket V T N implant;

applying Gated-FET V T P mask and P implant;

performing Dopant activation and anneal;

performing Sacrificial oxide etch;

depositing Gate oxide/Dual gate oxide option;

depositing Gate poly (GP);

applying Gated-FET N+ mask and N+ implant;

applying Gated-FET P+ mask and P+ implant;

applying GP mask & etch;

applying LDN mask & N− implant;

applying LDP mask & P− implant;

depositing Spacer oxide & spacer etch;

applying Periphery N+ mask and N+ implant;

applying Periphery P+ mask and P+ implant;

depositing Ni;

performing RTA anneal—Ni salicidation (S/D/G regions & interconnect);

performing Dopant activation;

performing Unreacted Ni etch;

depositing ILD oxide & CMP; and

applying contact mask and etch.

6. The method of claim 1 , comprising forming a source region and a drain region on opposite sides of said substantially rectangular channel region in said semiconductor thin film layer, further comprised of:

doping said source region to a higher level than said channel region, said dopant type same as said channel region; and

doping said drain region to a higher level than said channel region, said dopant type same as said channel region; and

providing a conducting path from said source region to said drain region through said resistive channel region in the middle, said conducting path comprising the entire thickness of the thin film layer;

wherein the absolute value of said channel region threshold voltage V T comprises a value in the range from 0.10 to 0.40 times a system power voltage level, and preferably in the range 0.15 to 0.30 times a system power voltage level, and more preferably in the range 0.18 to 0.22 times a system power voltage level.

7. A method of fabricating a semiconductor N channel Gated-FET transistor, comprising:

depositing a semiconductor thin film layer on a thick insulator; and

forming a substantially rectangular channel region in said semiconductor thin film layer, said channel region lightly doped with N type dopant to form a resistive channel, wherein the height of the channel region comprising the entire thin film thickness; and

forming a source region and a drain region on opposite sides of said rectangular channel region in said semiconductor thin film layer, said source and drain regions heavily doped with N type dopant; and

depositing a gate insulator layer above said channel region; and

depositing a heavily P type doped poly-silicon gate material above said gate insulator layer, said gate material forming a gate region above said channel region; and

optimizing said thin film properties, gate insulator properties and gate material properties such that said gate region further comprises:

a first voltage level that modulates said channel resistance to a substantially non-conductive state by fully depleting majority carriers from said channel region, said state disconnecting said source from said drain region; and

a second voltage level that modulates said channel resistance to a substantially conductive state by at least partially accumulating majority carriers near the gate insulator surface of said channel region, said state connecting said source to said drain region;

wherein said first voltage level comprises a voltage in the range from system ground voltage level to a threshold voltage level, wherein:

said thin film channel is fully depleted of majority carriers; and

said source region is decoupled from said drain region for a drain to source differential bias voltage ranging from zero to a system power supply voltage.

8. The method of claim 7 , wherein said second voltage level comprises a voltage in the range from said threshold voltage level to a flat band voltage level, wherein:

said thin film channel is not fully depleted, said channel comprising majority carriers; and

said source region is coupled to said drain region for a differential bias voltage ranging from zero to a system power supply voltage.

9. The method of claim 7 , wherein said second voltage level comprises a voltage in the range from said flat band voltage level to a system power voltage level, wherein:

said thin film channel majority carrier concentration is substantially enhanced above said channel doping level by an accumulation near the gate insulator surface; and

said source region is coupled to said drain region for a differential bias voltage ranging from zero to a system power supply voltage.

10. A method of fabricating a semiconductor P-channel Gated-FET transistor, comprising:

depositing a semiconductor thin film layer on a thick insulator; and

forming a substantially rectangular channel region in said semiconductor thin film layer, said channel region lightly doped with P type dopant to form a resistive channel, wherein the height of the channel region comprising the entire thin film thickness; and

forming a source region and a drain region on opposite sides of said rectangular channel region in said semiconductor thin film layer, said source and drain regions heavily doped with P type dopant; and

depositing a gate insulator layer above said channel region; and

depositing a heavily N type doped poly-silicon gate material above said gate insulator layer, said gate material forming a gate region above said channel region; and

optimizing said thin film properties, gate insulator properties and gate material properties such that said gate region further comprises:

a first voltage level that modulates said channel resistance to a substantially non-conductive state by fully depleting majority carriers from said channel region, said state disconnecting said source from said drain region; and

a second voltage level that modulates said channel resistance to a substantially conductive state by at least partially accumulating majority carriers near the gate insulator surface of said channel region, said state connecting said source to said drain region;

wherein said first voltage level comprises a voltage in the range from a system power voltage level to a threshold voltage below system power voltage level, wherein:

said thin film channel is fully depleted of majority carriers; and

said source region is decoupled from said drain region for a source to drain differential bias voltage ranging from zero to said system power supply voltage.

11. The method of claim 10 , wherein said second voltage level comprises a voltage in the range from a flat band voltage level below system power voltage level to said threshold voltage below system power voltage level, wherein:

said thin film channel is not fully depleted, said channel comprising majority carriers; and

said source region is coupled to said drain region for a differential bias voltage ranging from zero to said system power supply voltage.

12. The method of claim 10 , wherein said second voltage level comprises a voltage range from a system ground voltage level to said flat band voltage level below system power voltage level, wherein:

said thin film channel majority carrier concentration is substantially enhanced above said channel doping level by an accumulation near the gate insulator surface; and

said source region is coupled to said drain region for a differential bias voltage ranging from zero to said system power supply voltage.