Method for forming staircase word lines in a 3D non-volatile memory having vertical bit lines
AssigneeSanDisk 3D LLC
InventorsRaul Adrian Cernea, Henry Chien
Life of this patent
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Abstract
A 3D nonvolatile memory has memory elements arranged in a three-dimensional pattern defined by rectangular coordinates having x, y and z-directions and with a plurality of parallel planes stacked in the z-direction over a semiconductor substrate. It has vertical local bit lines and a plurality of staircase word lines. Each staircase word line has a series of alternating segments and risers elongated respectively in the x-direction and z-direction traversing across the plurality of planes in the z-direction with a segment in each plane. Methods of forming a slab of multi-plane memory with staircase word lines include processes with one masking and with two maskings for forming each plane.
Claims14
A method of forming a staircase word line in a 3D memory for accessing memory elements arranged in a three-dimensional pattern defined by rectangular coordinates having x, y and z-directions and with a plurality of parallel planes stacked in the z-direction, said method includes forming plane by plane a slab of the plurality of parallel planes, comprising:
- (a) depositing a layer of word line material in an x-y plane;
- (b) cutting a pattern of trenches in the layer of word line material with a first mask, the trenches extending along the y-direction and are spaced apart in the x-direction for isolating the layer of word line material into word line segments;
- (c) filling the trenches with oxide;
- (d) depositing a layer of oxide above the layer of word line material followed by planarization;
- (e) cutting a second pattern of trenches in the layer of oxide with a second mask for isolating the layer of oxide into oxide segments, the second mask being identical to the first mask but offset from the first mask in the x-direction by a predetermined offset such that the one end of each word line segment is exposed for connection to a layer of word line material to be formed in the next plane;
- and
- repeating (a)-(e) for the next plane except the first mask is offset by the predetermined offset from the second mask of a previous plane such that one end of each oxide segment is exposed for connection to a layer of oxide material to be formed in the next plane.
A method of forming a staircase word line in a 3D memory for accessing memory elements arranged in a three-dimensional pattern defined by rectangular coordinates having x, y and z-directions and with a plurality of parallel planes stacked in the z-direction, said method includes forming plane by plane a slab of the plurality of parallel planes, comprising:
- (a) depositing a base layer serving as a stop etching through layer in an x-y plane;
- (b) depositing a layer of oxide for a first plane of two adjacent planes;
- (c) cutting a pattern of trenches in the layer of oxide with a first mask down to the base layer, the trenches extending along the y-direction and are spaced apart in the x-direction for isolating the layer of oxide into oxide segments;
- (d) depositing a layer of word line material to form word lines in the two adjacent planes so that a section of the layer of word line material at a base of each trench belongs to the first plane and a section of the layer of word line material at the top of each trench belongs to the second plane and two corner portions are formed around a top of each trench;
- (e) filling the trenches with oxide;
- (f) depositing a layer of oxide for the second plane above the layer of word line material followed by planarization;
- (g) cutting a pattern of trenches in the layer of oxide for the second plane with a second mask until the layer of word line material is reached, the second mask being identical to the first mask but offset from the first mask in the x-direction by a predetermined offset less than a width of the trench to expose an horizontal portion of a corner of the word line layer in the x-y plane;
- (h) removing selectively the corner of the word line layer including the horizontal portion as well as an adjoining vertical portion buried in the first oxide layer along the z-direction;
- (i) replacing the removed corner of the word line layer with oxide by deposition;
- (j) etching the layer of oxide to expose a stub of the word line layer in each trench for connection to a next layer of word line material to be deposited in the trench;
- and
- repeating (d)-(j) for the next two adjacent planes except the mask is offset by the predetermined offset from the second mask of a previous plane such that the one end of each oxide segment is exposed for connection to a layer of oxide material to be formed in the next plane.
Dependencies are inferred from the claim text.