Dense arrays and charge storage devices
There is provided a monolithic three dimensional array of charge storage devices which includes a plurality of device levels, wherein at least one surface between two successive device levels is planarized by chemical mechanical polishing.
1. An array of nonvolatile memory cells, comprising a monolithic three dimensional memory array that comprises N device levels that are vertically stacked and separated from each other, wherein N is an integer greater than 1;
wherein each device level of the N device levels includes a respective two-dimensional array of memory cells, and N two-dimensional arrays of memory cells are vertically stacked within the array; and
wherein each memory cell comprises a semiconductor device and each memory cell size per bit is about (2f 2 )/N, where f is a minimum feature size.
2. The array of claim 1 , wherein
the semiconductor device comprises a TFT EEPROM comprising a channel, source and drain regions, and a charge storage region.
3. The array of claim 2 , further comprising:
a plurality of bit lines arranged in columns in each of the N device levels, each bit line contacting the source or the drain regions of the TFT EEPROMs, wherein the bit lines extend substantially perpendicular to a source-channel-drain direction of the TFT EEPROMs within a respective device level;
a plurality of word lines arranged in rows in each of the N device levels, and the words lines extend substantially parallel to the source-channel-drain direction of the TFT EEPROMs within a respective device level; and
at least one interlayer insulating layer located between the device levels.
4. The array of claim 3 , wherein:
the TFT EEPROMs further comprise control gates; and
the plurality of word lines are self aligned to the control gates of the respective TFT EEPROMs, to the channel regions of the respective TFT EEPROMs, and to the charge storage regions of the respective TFT EEPROMs located below the respective word lines.
5. The array of claim 4 , wherein the TFT EEPROMs further comprise:
sidewall spacers located adjacent to sidewalls of the gates of the TFT EEPROMs, wherein the sidewall spacers have approximately the same height as the gates; and
an intergate insulating layer which is located between the sidewall spacers, and above the source and the drain regions of the TFT EEPROMs in each device layer, and wherein the intergate insulating layer has approximately the same height as the sidewall spacers.
6. The array of claim 5 , wherein:
the word lines are located on the sidewall spacers and on the intergate insulating layer in each device level; and
the word lines contact the respective TFT EEPROM control gates through an opening between the sidewall spacers.
7. The array of claim 3 , wherein the TFT EEPROMs further comprise:
floating gates located in the charge storage regions;
sidewall spacers located adjacent to sidewalls of the floating gates of the TFT EEPROMs;
an intergate insulating layer which is located between the sidewall spacers, and above the source and the drain regions of the TFT EEPROMs in each device layer, and wherein the intergate insulating layer has approximately the same height as the sidewall spacers; and
a control gate dielectric located above the sidewall spacers and the intergate insulating layer and below the word lines.
8. The array of claim 7 , wherein the floating gates extend vertically and laterally above the sidewall spacers, such that the floating gates have a “T” shape.
9. The array of claim 3 , further comprising word line contacts and bit line contacts which connect the word lines and the bit lines with peripheral circuits located in a semiconductor substrate below the first device level of the array; and
wherein the bit line contacts extend between plural device layers.
10. The array of claim 1 , wherein each device level includes a two-dimensional array of charge storage regions, a plurality of bit lines extending below bottom surfaces of the two-dimensional array of charge storage regions, and a plurality of word lines located above top surfaces of the two-dimensional array of charge storage regions.
11. The array of claim 10 , wherein:
each device level includes a two-dimensional array of channel regions; and
each channel region contacts a bottom surface of a respective charge storage region of the two-dimensional array of charge storage regions.
12. The array of claim 11 , wherein each charge storage region of the two-dimensional array of charge storage regions contacts a pair of bit lines within the plurality of bit lines.
13. The array of claim 12 , wherein each bit line comprises a vertical stack including, from top to bottom, a silicide region and a transistor source and drain region.
14. The array of claim 13 , wherein:
the silicide region contacts a sidewall of a respective charge storage region within the two-dimensional array of charge storage regions; and
the transistor source and drain region contacts a bottom surface of the respective charge storage region within the two-dimensional array of charge storage regions.
15. The array of claim 10 , wherein the plurality of bit lines overlies, and is vertically spaced from, the plurality of word lines.
16. The array of claim 15 , wherein each device level includes a two-dimensional array of gate electrodes that overlies the two-dimensional array of charge storage regions.
17. The array of claim 16 , wherein:
each device level includes a two-dimensional array of pairs of gate stack sidewall spacers that contact sidewalls of a respective gate electrode within the two-dimensional array of gate electrodes; and
the plurality of bit lines contacts top surfaces of the two-dimensional array of pairs of gate stack sidewall spacers.
18. The array of claim 17 , wherein each gate stack sidewall spacer includes a sidewall that contacts an insulating material portion which contacts a top surface of a respective bit line and a bottom surface of a respective word line.
19. The array of claim 16 , wherein each gate electrode within the two-dimensional array of gate electrodes contacts, or is electrically shorted to, a respective one of the plurality of word lines.
20. The array of claim 16 , wherein each device level includes a two-dimensional array of control gate dielectrics that contacts a respective gate electrode within the two-dimensional array of gate dielectrics and underlies the plurality of word lines.