Method for forming transistor with high breakdown voltage using pitch multiplication technique
Transistors are formed using pitch multiplication. Each transistor includes a source region and a drain region connected by strips of active area material separated by shallow trench isolaton structures. The shallow trench isolaton structures are formed by dielectric material filling trenches that are formed by pitch multiplication. During pitch multiplication, rows of spaced-apart mandrels are formed and spacer material is blanket deposited over the mandrels. The spacer material is etched to define spacers on sidewalls of the mandrels and the mandrels are subsequently removed, thereby leaving free-standing spacers. The spacers constitute a mask, through which an underlying substrate is etched to form the trenches and strips of active area material. The trenches are filled to form the shallow trench isolaton structures. The substrate is doped to form source, drain and channel regions and a gate is formed over the channel region. In some embodiments, the shallow trench isolaton structures and the strips of material facilitate the formation of transistors having a high breakdown voltage.
1. A method for forming a transistor, comprising:
providing a plurality of mandrels overlying a semiconductor substrate;
blanket depositing a layer of spacer material on the mandrels;
selectively etching the spacer material to form spacers on sidewalls of the mandrels;
forming a spacer mask overlying the substrate by selectively removing the mandrels to leave a plurality of spacers, the spacers formed of elongated loops of spacer material;
etching the substrate through the spacer mask to define a plurality of trenches in the substrate, the trenches defined between strips of semiconductor material, wherein etching the substrate comprises:
providing a protective mask material over ends of the loops; and
transferring a pattern formed by exposed portions of the loops to the substrate while the protective mask material simultaneously prevents transfer of a shape defined by the ends of the loop to the substrate;
filling the trenches with an dielectric material;
providing a source for the transistor proximate an end of the trenches;
providing a drain for the transistor proximate an opposite end of the trenches, the strips of semiconductor material extending between the drain and the source; and
providing a gate overlying a channel region between the source and the drain.
2. The method of claim 1 , wherein providing the plurality of mandrels comprises defining a pattern in a photoresist layer.
3. The method of claim 2 , wherein the mandrels comprise photoresist.
4. The method of claim 2 , further comprising transferring the pattern in the photoresist to a sacrificial layer formed of sacrificial material, wherein the mandrels are formed of the sacrificial material.
5. The method of claim 1 , wherein providing the gate comprises forming a gate at least partially overlapping the plurality of trenches.
6. The method of claim 1 , wherein providing the source comprises doping the substrate to form an N-doped region after etching the substrate.
7. The method of claim 6 , wherein providing the drain comprises doping the substrate to form an N-doped region after etching the substrate.
8. The method of claim 7 , wherein the strips of semiconductor material are formed of N-doped silicon.
9. The method of claim 8 , wherein the channel region is a P-type region formed by doping the substrate to form the P-type region after etching the substrate.
10. A method for integration circuit fabrication, comprising:
providing a plurality of elongated loops of masking material over the substrate, the loops having loop ends and central portions disposed between the loop ends;
providing a protective mask material over the loop ends;
transferring a pattern defined by exposed central portions to the substrate to form a plurality of trenches in the substrate, wherein the trenches separate strips of material in the substrate to define a transistor extension region in the substrate;
blocking transfer of a shape defined by the loop ends to the substrate while transferring the pattern defined by exposed central portions;
forming a transistor source region contiguous with the transistor extension region; and
forming a transistor drain region contiguous with the transistor extension region.
11. The method of claim 10 , further comprising selectively etching the loop ends before transferring the pattern defined by the central portions to the substrate.
12. The method of claim 10 , wherein the plurality of elongated loops is formed of silicon oxide.
13. The method of claim 10 , wherein the transistor source region, the transistor drain region and the transistor extension region are disposed on a same level, further comprising forming a transistor gate over that level.
14. The method of claim 13 , wherein the transistor gate is disposed at least partially overlapping the transistor drain extension.
15. The method of claim 13 , wherein the transistor gate is formed without overlapping the trenches.
16. The method of claim 15 , wherein the trenches are filled with dielectric material before forming the transistor gate.
17. The method of claim 10 , further comprising forming electrical contacts to each of the transistor source region and the transistor drain region.
18. The method of claim 17 , wherein forming electrical contacts comprises forming a plurality of electrical contacts to each of the transistor source region and the transistor drain region.
19. The method of claim 18 , wherein a transistor drain region is disposed at separated ends of the strips, wherein the electrical contacts contact ends of each of the strips.
20. The method of claim 10 , wherein the transistor drain region extends across and connects each of the strips of substrate material.
21. The method of claim 10 , wherein the transistor source region extends across and connects each of the strips of substrate material.
22. A method for fabricating a transistor, comprising:
photolithographically defining a plurality of spaced-apart photoresist rows in a photoresist layer;
deriving a mask pattern from the photoresist rows, the mask pattern comprising loops of mask material formed by elongated portions connected at ends of the loops, the elongated portions having a pitch two times or more a pitch of the photoresist rows;
transferring the mask pattern to an underlying substrate, thereby defining a plurality of spaced apart rows in the substrate, wherein transferring the mask pattern to the underlying substrate comprises transferring a pattern formed by exposed portions of the loops to the substrate while a protective mask material overlies the ends of the loops;
preventing transfer of a shape defined by the ends of the loops to the substrate while transferring the mask pattern to the underlying substrate;
providing a transistor source region contiguous with one end of the rows in the substrate; and
providing a transistor drain region contiguous with an other end of the rows in the substrate.
23. The method of claim 22 , wherein deriving the mask pattern comprises:
blanket depositing a spacer material on the spaced-apart photoresist rows;
etching the spacer material to form spacers on sidewalls of the photoresist rows; and
selectively removing the photoresist rows.
24. The method of claim 22 , wherein the plurality of spaced apart rows have a row width and the rows are separated by a row separation width, wherein a ratio of row width to row separation is about 1:1 or more.
25. The method of claim 22 , further comprising providing a gate overlying the substrate and disposed between the source and drain regions, wherein the spaced apart rows are disposed on one side of the substrate.
26. The method of claim 22 , wherein the substrate comprises a N-type region overlying a P-type region, wherein transferring the mask pattern defines trenches extending through the N-type region into the P-type region.
27. The method of claim 26 , wherein providing the transistor source region and providing the transistor drain region comprises performing a doping process to form the N-type region.
28. The method of claim 22 , wherein the rows in the substrate extend substantially parallel to one another, each row in the substrate extending in a substantially straight line.