Method of manufacturing a memory device
A memory device comprises an active area comprising a source and at least two drains defining a first axis. At least two substantially parallel word lines are defined by a first pitch, with one word line located between each drain and the source. Digit lines are defined by a second pitch, one of the digit lines being coupled to the source and forming a second axis. The active areas of the memory array are tilted at 45° to the grid defined by the word lines and digit lines. The word line pitch is about 1.5F, while the digit line pitch is about 3F.
1. A method of manufacturing a memory device, the method comprising:
providing a substrate;
defining at least one active area within the substrate, said active area comprising a source and two drains, the source and at least one of the drains forming a line along which a first axis is defined;
defining at least one pair of word lines within the substrate by a pitch-doubling technique, the word lines of the pair being parallel one another over the active area along a word line axis; and
defining at least two digit lines above the substrate, at least a portion of one of the at least two digit lines extending above the source and defining a second axis that forms an acute angle with the first axis, the second axis running perpendicular to the word line axis, the at least two digit lines having a pitch of between 2.75 and 3.25 times a minimum resolution (F) of a photolithographic technique used to form the memory device.
2. The method of claim 1 , wherein defining the word lines further comprises recessing the word lines into the substrate.
3. The method of claim 1 , wherein defining the word lines further comprises:
forming a pattern of lines in a photoresist layer by photolithography;
etching the pattern of lines through the photoresist layer onto a hard mask layer;
stripping the photoresist layer;
depositing spacer material over the hard mask layer;
etching the spacer material to remove the spacer material from horizontal surfaces of the hard mask layer and form spacers on sidewalls of the hard mask layer;
depositing a material between the spacers and which is different composition from the spacers;
stripping the spacer material to form at least one pair of trenches;
etching into the substrate to deepen the at least one pair of trenches; and
partially filling the at least one pair of trenches with an electrode material.
4. The method of claim 3 , wherein the step of depositing an electrode material further comprises:
depositing polysilicon to fill the at least one pair of trenches;
etching back the polysilicon within the at least one pair of trenches;
depositing a metal layer to substantially cover the etched back polysilicon; and
siliciding the polysilicon by an annealing step.
5. The method of claim 3 , wherein partially filling comprises filling the at least one pair of trenches with a metallic material and recessing the metallic material in the trenches.
6. The method of claim 1 , wherein defining the word lines comprises simultaneously defining logic gates in another region of the memory device.
7. A method of forming a memory device, the method comprising:
providing a substrate;
defining at least one active area within the substrate, said active area comprising a source and two drains, the source and at least one of the drains forming a line along which a first axis is defined;
defining at least one pair of word lines within the substrate, the pair of word lines intersecting the at least one active area and the pair of word lines having a pitch of less than two times a minimum resolution (F) of a photolithographic technique used to form the memory device, the word lines of the pair being parallel one another over the active area along a word line axis; and
defining at least two digit lines above the substrate along a second axis generally perpendicular to the at least one pair of word lines, at least a portion of one of the at least two digit lines extending above the source and defining a bit line axis above the source, the bit line axis running perpendicular to the word line axis, the at least two digit lines having a pitch of between 2.75 and 3.25 times the minimum resolution.
8. The method of claim 7 , wherein an acute angle between the first and second axes is within the range of 10 to 80 degrees.
9. The method of claim 8 , wherein the acute angle between the first and second axes is within the range of 40 to 50 degrees.
10. The method of claim 9 , wherein the acute angle between the first and second axes is about 45 degrees.
11. The method of claim 7 , wherein the word lines are defined by a width that is less than the minimum resolution.
12. The method of claim 7 , wherein the word lines are fully recessed.
13. The method of claim 7 , wherein the step of defining the at least one pair of word lines further comprises:
defining the at least one pair of word lines according to a pitch-doubling technique.
14. A method of manufacturing a memory device, comprising:
providing a substrate;
defining at least two rows of active areas within the substrate, said active areas individually comprising a source and two drains, the source and drains of individual active areas forming a line along which a first axis is defined, the first axes within each row being parallel one another, the first axes within adjacent of the two rows being parallel one another;
defining at least two pairs of word lines within the substrate, the word lines within each pair being parallel one another along a word line axis, one of the two pairs of word lines extending along one of the two rows of active areas, another of the two pairs of word lines extending along an adjacent of the two rows of active areas; and
defining at least two digit lines above the substrate, at least a portion of one of the at least two digit lines extending above the source and defining a second axis that forms an acute angle with the first axis, the at least two digit lines having a pitch of between 2.75 and 3.25 times a minimum resolution (F) of a photolithographic technique used to form the memory device.