Memory block with separately driven source regions to improve performance
Apparatuses and techniques are described for providing separate source regions in the substrate below a block of memory cells. The source regions can be separately driven by respective voltage drivers to provide benefits such as more uniform program and erase speeds and narrower threshold voltage distributions. In one approach, a single source region is provided and divided into multiple source regions by etching trenches and filling the trenches with an insulating material. Contacts to the source regions can include post-shaped contacts which extend through the block for each source region. In another approach, one or more planar contacts extend through the block for each source region. In another aspect, a program operation applies different voltages to the respective source regions during a verify test of a program operation.
1. An apparatus, comprising:
a substrate;
separate source regions in the substrate including at least a first source region and a second source region;
an insulating region in the substrate between the first source region and the second source region to electrically isolate the first source from the second source region; and
a block on the substrate, the block comprising a set of NAND strings arranged vertically, different subsets of the set of NAND strings are in contact with different source regions of the separate source regions including at least a first subset of the NAND strings in contact with the first source region and a second subset of the NAND strings in contact with the second source region.
2. The apparatus of claim 1 , further comprising:
a set of bit lines, wherein the different subsets of the set of NAND strings are in contact with different subsets of the set of bit lines.
3. The apparatus of claim 1 , wherein:
each source region comprises a diffusion region in the substrate extending at least a width of the block.
4. The apparatus of claim 1 , wherein the first subset of NAND strings are located above the first source region and the second subset of NAND strings are located above the second source region.
5. The apparatus of claim 4 , further comprising:
a set of bit lines extending in a bit line direction, wherein the insulating region extends in the bit line direction.
6. The apparatus of claim 1 , further comprising:
contacts extending vertically in the block, each contact is connected to a respective source region of the separate source regions.
7. The apparatus of claim 6 , wherein:
the contacts comprise post-shaped contacts.
8. The apparatus of claim 6 , wherein:
the contacts comprise a plurality of planar contacts.
9. The apparatus of claim 8 , further comprising:
an insulating post which separates adjacent planar contacts of the plurality of planar contacts.
10. The apparatus of claim 9 , wherein:
the adjacent planar contacts each comprise a conductive material; and
the insulating post has a width which is greater than a width of the conductive material.
11. The apparatus of claim 1 , further comprising:
separate voltage drivers for the separate source regions including at least a first voltage driver connected to the first source region and a second voltage driver connected to the second source region.
12. A method, comprising:
forming a source region in a substrate;
forming one or more insulating regions in the source region to divide the source region into a plurality of separate source regions including at least a first source region that is separated from a second source region by an insulating region; and
forming a block on the substrate over the first source region and the second source region, the block comprising a set of NAND strings arranged vertically, the set of NAND strings including at least a first subset of NAND strings overlying and in contact with the first source region and a second subset of NAND strings overlying and in contact with the second source region.
13. The method of claim 12 , further comprising:
etching a trench in a stack that includes the set of NAND strings of the block, the trench extending a height and length of the stack;
depositing conductive material in the trench, the conductive material extending the height and length of the block; and
separating the conductive material into separate contacts, where each contact is connected to a respective source region of the separate source regions including at least a first contact connected to the first source region and a second contact connected to the second source region.
14. The method of claim 13 , wherein:
the separating the conductive material comprises etching a post-shaped void in the conductive material.
15. The method of claim 14 , wherein:
the post-shaped void has a width which is greater than a width of the conductive material.
16. The method of claim 15 , wherein: the post-shaped void is etched in a widened region of the trench.
17. An apparatus, comprising:
a control circuit configured to connect to a plurality of source region voltage drivers for a plurality of source regions that are located in an area of a substrate under a block, the plurality of source region voltage drivers including at least a first source region voltage driver connected to a first source region and a second source region voltage driver connected to a second source region; and
a memory interface connected to the control circuit, the control circuit is configured to issue a command via the memory interface to instruct each source region voltage driver of the plurality of source region voltage drivers to provide a respective voltage signal to a respective source region among a plurality of source regions including providing a first voltage signal to the first source region and a second voltage signal to the second source region, the second voltage signal is different to the first voltage signal.
18. The apparatus of claim 17 , wherein:
the control circuit is configured to instruct each source region voltage driver to provide the respective voltage signal to the respective source region during a verify phase of a program loop of a program operation.
19. The apparatus of claim 17 , wherein:
the control circuit is configured to instruct each source region voltage driver to provide the respective voltage signal to the respective source region during a sensing operation.
20. The apparatus of claim 17 , wherein
during a sensing operation for memory cells associated with one of the source regions, the control circuit is configured to instruct a respective source region voltage driver to set a voltage of the respective voltage signal as a function of a distance of the one of the source regions from a word line driver.