Nonvolatile semiconductor memory device and method of fabricating the same
View Patent ↗According to an embodiment, in a method of fabricating a nonvolatile semiconductor memory device, second trenches penetrating the first and second conductive layers above the first trenches are formed to reach the stack, and a second insulating layer is formed on the second trenches and the first insulating layer so as to fill the second trenches. A part of the second insulating layer in a first region extending in a direction orthogonal to a direction that the first and second semiconductor pillars extend in a plane parallel to the back gate layer is removed while a part of the second insulating layer in a second region adjacent to the first region is left. The first sacrificial layer is selectively removed, and the first conductive layers and second conductive layers exposed in the first and second trenches are silicidized.
1. A method of fabricating a nonvolatile semiconductor memory device including:
a plurality of stacks arranged side by side in a first direction, and extending in a second direction orthogonal to the first direction, in a plane in parallel with a substrate, each stack including a plurality of first conductive layers stacked above the substrate with insulating layers interposed between the first conductive layers;
a second conductive layer provided on the stack; and
a plurality of first memory strings including a first semiconductor pillar, a second semiconductor pillar and a first connection portion, respectively, the first and second semiconductor pillars penetrating each stack in a way to reach a back gate layer above the substrate, the first connection portion being provided in a surface of the back gate layer, one end of the first connection portion being connected to a lower end of the first semiconductor pillar, the other end of the first connection portion being connected to a lower end of the second semiconductor pillar, a memory layer being provided in an outer side portion of the first semiconductor pillar, the second semiconductor pillar and the first connection portion, a first semiconductor layer being provided in an inner side portion of the first semiconductor pillar, the second semiconductor pillar and the first connection portion, and the first memory strings being arranged side by side in the second direction,
the method comprising the steps of:
burying a first sacrificial layer in each of a plurality of first trenches penetrating to the first conductive layer at the lowest layer of the stack;
forming the second conductive layer and a first insulating layer on the stack and the first sacrificial layers;
forming the first semiconductor pillar and second semiconductor pillar alternately arranged between the pairs of two first trenches adjacent to each other and forming the first connection portion connecting the first and second semiconductor pillars;
forming second trenches penetrating the first insulating layer and the second conductive layer above the first trenches to reach the stack and forming a second insulating layer on the second trenches and the first insulating layer to fill the second trenches;
removing a part of the second insulating layer in a first region extending in the first direction orthogonal to a third direction that the first and second semiconductor pillars extend while leaving a part of the second insulating layer in a second region adjacent to the first region in the second direction; and
selectively removing the first sacrificial layer to silicidize the first and second conductive layers exposed in the first and second trenches.
2. The method according to claim 1 , further comprising a step of:
after the silicidization, embedding a third insulating layer in the exposed first and second trenches.
3. The method according to claim 1 , wherein
the back gate layer is provided on an underlying layer including a substrate and an interlayer insulating layer.
4. The method according to claim 1 , wherein
the first and second semiconductor pillars are linearly-arranged side by side in the second direction.
5. The method according to claim 1 , wherein
the first semiconductor layer is composed of a polycrystalline silicon.
6. The method according to claim 1 , wherein
the first and second conductive layers are composed of a polycrystalline silicon.
7. The method according to claim 6 , wherein
the silicidization is performed using any one of nickel (Ni), cobalt (Co), titanium (Ti), tantalum (Ta), and tungsten (W).
8. The method according to claim 1 , wherein
the first sacrificial layer is composed of a silicon nitride (Si 3 N 4 ) film, the first insulating layer is composed of a tantalum oxide film (TaO x film) or a stacked film which is stacked a tantalum oxide film (TaO x film) on a silicon dioxide film (SiO 2 film), and the second insulating layer is composed of a silicon oxide film (SiO 2 ).
9. The method according to claim 8 , wherein
the first sacrificial layer is selectively removed using phosphoric acid (H 3 PO 4 ) solution.
10. The method according to claim 1 , wherein
the nonvolatile semiconductor memory device is a three-dimensional NAND flash memory.