# Patent

## Title
Method of manufacturing non-volatile memory

## Abstract

A method of manufacturing a non-volatile memory including the following steps is provided. First, a dielectric layer, a first conductive layer and a patterned mask layer are sequentially formed on a substrate. A portion of the first conductive layer is removed using the patterned mask layer as a mask to form a plurality of first gates. An oxidation process is performed to form an oxide layer on the sidewalls of the first gates. The patterned mask layer is removed. A plurality of second gates is formed between two adjacent first gates so that the first gates and the second gates co-exist to form a memory cell column. A doped region is formed in the substrate adjacent to the memory cell column.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a method of manufacturing a non-volatile memory.
2. Description of Related Art
As the name implies, memory is a semiconductor device designed specially for storing data or codes. As the functions provided by a computer microprocessor are increasingly powerful and the amount of programming and computation in most computer software continues to increase, memory with larger storage capacity is urgently needed. In order to fabricate cheaper and larger capacity memory, the techniques and processes of fabricating memory devices is the driving force behind the challenge of pushing semiconductor technologies toward a higher level of integration.
Non-volatile memory is a type of memory device that allows multiple data writing, reading and erasing operations. Furthermore, the stored data will be retained even after power to the device is removed. With these advantages, non-volatile memory has been broadly applied in personal computer and electronic equipment.
At present, one of the more commonly used memory array structures includes the NAND type array structure. Because the NAND type array structure mainly contains a serially connected memory cells whose programming and erasing operations are carried out together, a memory cell array fabricated as a NAND type array structure is able to increase the packing density of devices and ultimately their level of integration.
With the rapid development of fabrication processes and the continuous reduction of device dimensions, the space between the NAND type array structure and various memory cells is being shrink correspondingly. However, due to the limitation of the process window in photolithographic and etching processes, it is very difficult to fabricate a product that meets the required memory cell size and spatial separation between memory cells. Furthermore, in a subsequent process, the slight shrinkage of size that leads to a relative shrinkage of the space between the memory cells can lead to additional problems. For example, when filling the space between various memory cells with an insulating material, the insulating material layer inside the space may form voids or the insulating material may be prevented from filling up the space. Consequently, the reliability of the process is questionable.
SUMMARY OF THE INVENTION
Accordingly, at least one objective of the present invention is to provide a method of manufacturing a non-volatile memory capable for avoiding voids or missing the space altogether during the process of filling the space between memory cells using an insulating material and thereby increase the level of device integration.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method of manufacturing a non-volatile memory including the following steps. First, a dielectric layer, a first conductive layer and a patterned mask layer are sequentially formed on a substrate. Next, a portion of the first conductive layer is removed using the patterned mask layer as a mask to form a plurality of first gates. An oxidation process is performed to form an oxide layer on the sidewalls of the first gates. Thereafter, the patterned mask layer is removed. A plurality of second gates is formed between two adjacent first gates so that the first gates and the second gates co-exist to form a memory cell column. After that, a doped region is formed in the substrate adjacent to the memory cell column.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the foregoing oxidation process is, for example, an in situ steam generation (ISSG) oxidation process or a thermal oxidation process.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the material constituting the foregoing oxide layer includes silicon dioxide, for example.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the method of forming the second gates includes, for example, forming a second conductive layer over the substrate to cover the first gates, the oxide layer and the dielectric layer. Next, a portion of the second conductive layer is removed to expose the surface of the first gates.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the method of removing a portion of the second conductive layer to expose the surface of the first gates includes, for example, performing a chemical-mechanical polishing or a back etching process.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the first and the second gates are fabricated using an identical material such as doped polysilicon.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the foregoing dielectric layer is, for example, a silicon oxide layer or a composite dielectric layer. The composite dielectric layer is an oxide-nitride-oxide (ONO) layer or an oxide-nitride-oxide-nitride-oxide (ONONO) layer, for example.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the material constituting the foregoing patterned mask layer includes silicon nitride, for example.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the method of forming the foregoing doped region includes, for example, the following steps. First, a photoresist layer is formed over the memory cell column. Next, an ion implantation is performed using the photoresist layer as a mask. Finally, the photoresist layer is removed.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the method of removing the foregoing patterned mask layer includes, for example, performing an etching process or a lift-off process.
The present invention also provides an alternative method of manufacturing a non-volatile memory including the following steps. First, a dielectric layer, a first conductive layer and a patterned mask layer are sequentially formed on a substrate. Next, a portion of the first conductive layer is removed using the patterned mask layer as a mask to form a plurality of first gates. An oxidation process is performed to form an oxide layer on the sidewalls of the first gates. Thereafter, a second conductive layer is formed above the substrate. A portion of the second conductive layer is removed to expose the surface of the oxide layer. Next, the patterned mask layer is removed to form a plurality of second gates between two adjacent first gates so that the first gates and the second gates co-exist to form a memory cell column. Next, a doped region is formed in the substrate adjacent to the memory cell column.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the foregoing oxidation process is, for example, an in situ steam generation (ISSG) oxidation process or a thermal oxidation process.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the material constituting the foregoing oxide layer includes silicon dioxide, for example.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the method of removing a portion of the second conductive layer to expose the surface of the oxide layer includes, for example, performing a etching back process.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the first and the second gates are fabricated using an identical material such as doped polysilicon.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the foregoing dielectric layer is, for example, a silicon oxide layer or a composite dielectric layer. The composite dielectric layer is an oxide-nitride-oxide (ONO) layer or an oxide-nitride-oxide-nitride-oxide (ONONO) layer, for example.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the material constituting the foregoing patterned mask layer includes silicon nitride, for example.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the method of forming the foregoing doped region includes, for example, the following steps. First, a photoresist layer is formed over the memory cell column. Next, an ion implantation is performed using the photoresist layer as a mask. Finally, the photoresist layer is removed.
According to the method of manufacturing non-volatile memory in one embodiment of the present invention, the method of removing the foregoing patterned mask layer includes, for example, performing an etching process or a lift-off process.
In the present invention, an oxide layer is formed on the sidewalls of the first gates to serve as a dielectric material layer that fills the space between the memory cells of a conventional memory cell column before forming the second gates and completing the memory cell column. Therefore, the possibility of formation of voids in the insulation material layer or some missing space the insulation material may be effectively reduced. Furthermore, the oxide layer is formed in an oxidation process in the present invention. Hence, by adjusting the processing condition of the oxidation process, thickness of the oxide layer can be controlled so that the smallest possible spatial separation between adjacent memory cells in a memory cell column constrained by the photolithographic and etching process can be relaxed.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
FIGS. 1A through 1F are schematic cross-sectional views showing the steps for fabricating a non-volatile memory according to one embodiment of the present invention.
FIGS. 2A through 2D are schematic cross-sectional views showing the steps for fabricating a non-volatile memory according to another embodiment of the present invention.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
FIGS. 1A through 1F are schematic cross-sectional views showing the steps for fabricating a non-volatile memory according to one embodiment of the present invention.
First, as shown in FIG. 1A, a substrate 100 is provided. The substrate 100 is, for example, a silicon substrate or other semiconductor substrate. Next, a dielectric layer 102 is formed on the substrate 100. The dielectric layer 102 is, for example, a silicon oxide layer formed by performing a chemical vapor deposition process. Obviously, the dielectric layer 102 can be, for example, a composite dielectric layer comprising a multiple of layers. The composite dielectric layer can be an oxide-nitride-oxide (ONO) layer or an oxide-nitride-oxide-nitride-oxide (ONONO) layer, for example.
After forming the dielectric layer 102, a conductive layer 104 is formed on the dielectric layer 102. The conductive layer 104 is, for example, a doped polysilicon formed by performing a chemical vapor deposition process. Next, a patterned mask layer 106 is formed on the conductive layer 104. The patterned mask layer 106 is, for example, a silicon nitride layer formed by performing a chemical vapor deposition process.
Next, as shown in FIG. 1B, a portion of the conductive layer 104 is removed using the patterned mask layer 106 as a mask to form a plurality of gates 108. The method of removing a portion of the conductive layer 104 includes, for example, performing an etching process.
As shown in FIG. 1C, an oxidation process is performed to form an oxide layer 110 on the sidewalls of the gates 108. The foregoing oxidation process can be, for example, an in situ steam generation (ISSG) oxidation process or a thermal oxidation process. The material constituting the oxide layer 110 is silicon dioxide, for example.
It should be noted that the oxide layer 110 formed on the sidewalls of the gates 108 serves as an insulating material layer that fills the space between the memory cells of a conventional memory cell column before forming the second gates and completing the memory cell column. Furthermore, the oxide layer 110 is formed in an oxidation process in the present invention. Hence, by adjusting the processing condition of the oxidation process, thickness of the oxide layer 110 can be controlled so that the smallest possible spatial separation between adjacent memory cells in a memory cell column constrained by the photolithographic and etching process can be relaxed.
In addition, the early formation of the oxide layer 110 on the sidewalls of the gates 108, compared with the conventional process, prevents the insulating material layer that fills the space between neighboring memory cells with voids or some missing space in insulating material layer. Thus, the reliability of the entire process may be effectively improved.
As shown in FIG. 1D, the patterned mask layer 106 above the gates 108 is removed after forming the oxide layer 110. The method of removing the mask layer 106 includes, for example, performing an etching process or a lift-off process. After that, a conductive layer 112 is formed over the substrate 100 to cover the gates 108, the oxide layer 110 and the dielectric layer 102. The conductive layer 112 is, for example, a doped polysilicon formed by performing a chemical vapor deposition process.
As shown in FIG. 1E, a portion of the conductive layer 112 is removed to expose the surface of the gates 108 so that a plurality of gates 114 is formed between two adjacent gates 108. The method of removing a portion of the conductive layer 112 to expose the surface of the gates 108 includes, for example, performing a chemical-mechanical polishing process or an etching back process.
The gates 114 and the gates 108 co-exist to form a memory cell column. Next, a photoresist layer 116 is formed over the memory cell column. Thereafter, an ion implant process 118 is performed using the photoresist layer 116 as a mask to form a doped region 120 in the substrate 100 on the sides of the memory cell column.
As shown in FIG. 1F, the photoresist layer 116 is removed after forming the doped regions 120. Thus, the fabrication of a non-volatile memory in the present embodiment is complete.
Aside from the foregoing embodiment, the present invention also provides another embodiment for fabricating the non-volatile memory. FIGS. 2A through 2D are schematic cross-sectional views showing the steps for fabricating a non-volatile memory according to another embodiment of the present invention. FIG. 2A is a continuation of the steps in FIG. 1C carried out in the foregoing embodiment. Moreover, the elements in FIGS. 1A through 1F identical to the ones in FIGS. 2A through 2D are labeled identically.
First, as shown in FIG. 2A, the main difference from the previous embodiment shown in FIGS. 1A through 1F is that the patterned mask layer 106 is not removed after forming the oxide layer 110 in the present embodiment. Instead, a conductive layer 202 is directly formed over the substrate 100. The conductive layer 202 is, for example, a doped polysilicon layer formed by performing a chemical vapor deposition process.
Next, as shown in FIG. 2B, after forming the conductive layer 202, a portion of the conductive layer 202 is removed to expose the surface of the oxide layer 110 and form a conductive layer 203. The method of removing a portion of the conductive layer 202 includes, for example, performing an etching back process. A portion of the residual conductive layer 203 remains on the upper surface of the patterned mask layer 106.
Next, as shown in FIG. 2C, the patterned mask layer 106 is removed. The method of removing the patterned mask layer 106 includes, for example, performing an etching process or a lift-off process. After removing the patterned mask layer 106, the residual conductive layer 203 on the upper surface of the patterned mask layer 106 is also removed, thereby forming a plurality of gates 204 between two adjacent gates 108.
The gates 204 and the gates 108 co-exist to form a memory cell column. Next, a photoresist layer 116 is formed over the memory cell column. Thereafter, an ion implant process 118 is performed using the photoresist layer 116 as a mask to form a doped region 120 in the substrate 100 on the sides of the memory cell column.
As shown in FIG. 2D, the photoresist layer 116 is removed after forming the doped regions 120. Thus, the fabrication of a non-volatile memory in the present embodiment is complete.
In summary, the method in the present invention has at least the following advantages.
1. The present invention can avoid the problem of having voids in the insulating material layer filling the space between neighboring memory cells of a conventional memory cell column or missing some insulating material in some of the space between neighboring memory cells, which can significantly affect process reliability.
2. The present invention can provide a breakthrough in the minimum distance of separation between neighboring memory cells in a memory cell column due to the processing restrictions of a photolithographic and etching process.
3. The applications of the present invention are not limited to the fabrication of a non-volatile memory. It can be applied to any process requiring a reduction of device separation.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.

## Claims

1. A method of fabricating a non-volatile memory, comprising:
sequentially forming a dielectric charge trapping layer, a first conductive layer and a patterned mask layer on a substrate;
removing a portion of the first conductive layer using the patterned mask layer as a mask to expose portions of the dielectric charge trapping layer and form a first plurality of gates having sidewalls and top surfaces, the exposed portions extending between adjacent gates in the first plurality of gates;
performing an oxidation process to form an oxide layer on the sidewalls of the gates in the first plurality of gates while protecting the top surfaces of the gates in the first plurality of gates from the oxidation process;
removing the patterned mask layer after performing the oxidation process;
forming a second plurality of gates, after removing the patterned mask layer, on the exposed portions of the dielectric charge trapping layer, the gates in the second plurality of gates interleaved with the gates in the first plurality of gates to define a plurality of respective memory cells in a NAND string, wherein the plurality of memory cells include data storage sites in the dielectric charge trapping layer beneath each gate in the first and second pluralities of gates; and
forming a doped region in the substrate adjacent to the NAND string.

2. The method of claim 1, wherein the oxidation process comprises an in situ steam generation (ISSG) oxidation process or a thermal oxidation process.

3. The method of claim 1, wherein the oxide layer comprises silicon dioxide.

4. The method of claim 1, wherein the method of forming the second plurality of gates comprises:
forming a second conductive layer over the substrate to cover the first plurality of gates, the oxide layer on the sidewalls and the exposed portions of the dielectric charge trapping layer; and
removing a portion of the second conductive layer to expose the top surface of the first plurality of gates.

5. The method of claim 4, wherein the method of removing a portion of the second conductive layer to expose the top surface of the first plurality of gates comprises performing a chemical-mechanical polishing process or an etching back process.

6. The method of claim 1, wherein the material constituting the first gates and the second gates are identical and comprises doped polysilicon.

7. The method of claim 1, wherein the dielectric layer comprises a composite dielectric layer.

8. The method of claim 1, wherein the dielectric layer comprises an oxide-nitride-oxide (ONO) layer or an oxide-nitride-oxide-nitride-oxide (ONONO) layer.

9. The method of claim 1, wherein the patterned mask layer comprises silicon nitride.

10. The method of claim 1, wherein the method of forming the doped region comprises:
forming a photoresist layer on the memory cell column;
performing an ion implant process using the photoresist layer as a mask; and
removing the photoresist layer.

11. The method of claim 1, wherein the method of removing the patterned mask layer comprises performing an etching process or a lift-off process.

12. The method of claim 1, wherein:
the substrate has one of an n-type or p-type conductivity; and
the memory cells in the plurality of memory cells include respective channel regions in the substrate beneath corresponding gates in the pluralities of gates, without intervening terminals between the channel regions of adjacent memory cells having a different conductivity type.

13. A method of fabricating a non-volatile memory, comprising:
forming a dielectric charge trapping layer and a first conductive layer over a substrate;
forming a mask layer over the first conductive layer;
removing a portion of the first conductive layer using the mask layer to expose portions of the dielectric charge trapping layer and form a first plurality of gates having sidewalls and top surfaces, the exposed portions of the dielectric charge trapping layer extending between adjacent first gates;
applying a process to form an insulating layer on the sidewalls of the first plurality of gates while protecting the top surfaces of the first plurality of gates from the process;
removing the mask layer after applying the process;
forming a second conductive layer, after removing the mask layer, to cover the first plurality of gates, the insulating layer and the dielectric charge trapping layer; and
removing a portion of the second conductive layer to expose the top surface of the first gates to form a plurality of second gates, the gates in the second plurality of gates interleaved with the gates in the first plurality of gates to define a plurality of memory cells in a NAND string, wherein the plurality of memory cells include data storage sites in the dielectric charge trapping layer beneath each gate in the first and second pluralities of gates.