Method and system for providing a polysilicon stringer monitor

Information

  • Patent Grant
  • 6602776
  • Patent Number
    6,602,776
  • Date Filed
    Thursday, May 23, 2002
    22 years ago
  • Date Issued
    Tuesday, August 5, 2003
    21 years ago
Abstract
A system and method detecting the presence of polysilicon stringers on a memory array using a polysilicon stringer monitor. The polysilicon stringer monitor includes a continuous type-2 layer of polysilicon forming a first row and a second row across the active region and covering the active region in-between the first and second rows. The polysilicon stringer monitor further includes a continuous type-1 layer of polysilicon extending under the first row, wherein the type-1 layer also covers the active area in-between the first and second rows as well as covers the active area under the second row.
Description




FIELD OF THE INVENTION




The present invention relates to memory arrays, and more particularly to a method and system for providing a polysilicon stringer monitor.




BACKGROUND OF THE INVENTION




Achieving higher yields continues to be a desired goal during memory chip fabrication. The various processes and techniques used to manufacture chips have therefore become increasingly important. Part of the process involved in manufacturing a flash memory array, for example, requires creating an array of CMOS (Complementary MOS) transistors using layers of polysilicon.




The flash memory array includes columns of active regions that are separated by columns of insulating field oxide regions. The transistors are spaced apart in the active regions and each a row of transistors are bits in a memory word. The transistors are formed with various materials including a type-1 layer of polysilicon, and transistors forming a row in the array are connected by a word-line comprising a type-2 layer of polysilicon.





FIGS. 1-4

are diagrams illustrating the process of creating such a memory array.

FIG. 1A

is a top view of a portion of a substrate


10


and

FIG. 1B

is a cross-sectional view of the substrate


10


along line A. The first step of the process is creating the columns of active regions


12


and insulating field oxide regions (FOX)


14


.





FIGS. 2A and 2B

are top and cross-sectional views of the substrate


10


, respectively, showing that a layer of tunnel oxide


16


is then deposited over the active regions


12


followed by the deposition of a type-1 layer of polysilicon


18


, which is referred to as a poly1 layer. The poly1 layer


18


is then masked and etched as shown.





FIG. 3A

is a top view of the substrate


10


showing that a layer of oxide nitride (ONO)


20


is then deposited over the poly1 layer


18


, and that a type-2 layer of polysilicon


22


(poly2 ) is patterned over the ONO


20


to form word lines.

FIG. 3B

is a cross-sectional view of the substrate


10


along line B, and

FIG. 3B

is a cross-sectional view of the substrate


10


along line C.




In

FIG. 4A

, after the poly2 layer is deposited, an etch is performed on the ONO


20


and the poly1 layer


18


between the rows of the poly2 layer


22


, which is also shown in the cross-sectional view of FIG.


4


B.





FIG. 4C

is a cross-sectional perspective view of the substrate along line E after the etching of the ONO


20


and the poly1 layer


18


. The etching process is anisotropic, meaning that it removes material directionally to a predetermined depth. But due to the shape of the FOX regions


14


, the thickness of the ONO


20


and the poly1 layer


18


at the vertical edges of the poly1 layer


18


is greater than their average thicknesses. Therefore, the etching process sometimes fails to remove all of the ONO


20


and the poly1


18


from the active regions


12


between the rows of poly2


22


, leaving what is called a poly1 stringer


26


. The presence of a poly1 stringer


26


provides a contact between the two adjacent transistors, which causes problems in the memory array.




Accordingly, what is needed is a system and method for detecting the presence of poly1 stringers on a memory array. The present invention addresses such a need.




SUMMARY OF THE INVENTION




The present invention provides a system and method for detecting the presence of poly1 stringers on a memory array. The polysilicon stringer monitor includes a continuous type-2 layer of polysilicon forming a first row and a second row across the active region and covering the active region in-between the first and second rows. The polysilicon stringer monitor further includes a continuous type-1 layer of polysilicon extending under the first row, wherein the type-1 layer also covers the active area in-between the first and second rows as well as covers the active area under the second row.




According to the present invention, extending the type-1 and type-2 layers of polysilicon in this manner effectively enables the detection of poly1 stringers in the active areas of the memory array.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1A

is a top view of a portion of a substrate.





FIG. 1B

is a cross-sectional view of the substrate along line A.





FIGS. 2A and 2B

are top and cross-sectional views of the substrate along line .





FIG. 3A

is a top view of the substrate showing the deposition of poly1 layer.





FIG. 3B

is a cross-sectional view of the substrate along line B.





FIG. 3C

is a cross-sectional view of the substrate along line C.





FIG. 4A

is a top view of the substrate showing the etching of the poly1 layer between the rows of a poly2 layer





FIG. 4B

is a cross-section view of the substrate along line D.





FIG. 4C

is a cross-sectional perspective view of the substrate along line E after the etching the poly1 layer.





FIG. 5

is a top view of the substrate illustrating the beginning of the process for creating a poly 1 stinger monitor in accordance with the present invention.





FIG. 6

is a top view of the substrate showing a continuous poly1 layer over the active region.





FIG. 7A

is a top view of the substrate


10


showing a continuous layer of poly2 .





FIG. 7B

is a cross-sectional view of the substrate along line F showing the width of the connected poly2 layer over the poly1 layer.





FIG. 8A

is a top view of the substrate showing the poly1 stringer monitor of the present invention.





FIG. 8B

is a cross-sectional view of the substrate along line G.











DETAILED DESCRIPTION




The present invention relates to the detection of type-1 polysilicon stringers along the active region of a memory array between two transistor areas. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein.




The present invention provides a poly1 stringer monitor that is capable of detecting poly 1 stringers along the active region of a memory array between two transistor areas. The poly1 stringer monitor comprises a continuous layer of type-2 polysilicon that extends along word lines and along the active region in-between each pair of word lines. The poly1 stringer monitor also includes a continuous layer of type-1 polysilicon that extends under one word line in a pair, over the active area in-between the pair of word lines, and extends over the active region under the second word line in the pair.




To more particularly describe the present invention, refer now to FIG.


5


- illustrating the process of creating the poly 1 stringer monitor in accordance with the present invention.





FIG. 5

is a top view of the substrate illustrating that the process for creating the poly 1 stinger monitor begins with creating active regions


12


and insulating FOX regions


14


.





FIG. 6

is a top view of the substrate showing that after formation of the active regions


12


, a tunnel oxide layer (not shown) and a poly1 layer


30


are deposited and etched over the active region


12


. As, shown, the tunnel oxide layer and the poly1


30


are etched such that the tunnel oxide layer and the poly1


30


also cover the area of the substrate where a word line will be located.





FIGS. 7A

is a top view of the substrate


10


and

FIG. 7B

is a cross-sectional view of the substrate


10


along line F. After the poly1 layer


30


is etched, a layer of oxide nitride (ONO)


32


is then deposited over the poly1


30


followed by a type-2 layer of polysilicon


34


(poly2 ) to form the word lines. The ONO


32


and the poly2 are etched such that the ONO


32


and the poly2


34


extend between each pair of word lines over the active area


12


. This effectively connects the poly2 lines


34


over the active regions


12


between two transistor areas.




In

FIG. 8A

, after the poly2 layer


34


is deposited, an etch is performed on the ONO


32


and the poly1 layer


30


outside each pair of word lines over the active area


12


, which is also shown in the cross-sectional view of

FIG. 4B

, to provide the poly 1 stringer monitor of the present invention.




For each pair of word lines in the poly 1 stringer monitor, one of the word lines in the pair will include a layer of poly1


30


. Each word line poly 1 stringer monitor having a layer of poly1


30


is then connected to an external pad


36


so that any poly1 stringers present on the memory array may be detected.




A method and system for providing a poly 1 stringer monitor has been disclosed. Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one or ordinary skill in the art without departing from the spirit and scope of the appended claims.



Claims
  • 1. A method for creating a poly 1 stringer monitor, comprising the steps of:(a) creating active regions over a substrate; (b) patterning a poly1 layer over the active region such that the poly1 layer also covers the area of the substrate where one word line in a pair of word lines will be located; (c) patterning a continuous poly2 layer over the substrate to form the word lines such that the poly2 layer extends between each pair of word lines over the active area; (d) etching the poly1 layer outside each pair of word lines over the active area; and for each pair of word lines, connecting the word line having a layer of poly1 to an external pad so that any poly1 stringers that occur after etching may be detected.
  • 2. The method of claim 1 wherein step (c) includes the step of patterning the poly2 over the active region such that the poly 2 connects lines two transistor areas.
CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. Ser. No. 09/429,244, filed Oct. 28, 1999, now U.S. Pat. No. 6,448,609, and assigned of record to Advanced Micro Devices, Inc., of Sunnyvale, Calif.

US Referenced Citations (4)
Number Name Date Kind
4180826 Shappir Dec 1979 A
6030868 Early et al. Feb 2000 A
6057193 Wag et al. May 2000 A
6266264 Proebsting Jul 2001 B1