Method of verifying a mask for a mask ROM

Details Method of verifying a mask for a mask ROM Method of verifying a mask for a mask ROM

2003-09-15

2004-08-10

Tsai, H. Jey (Department: 2812)

Semiconductor device manufacturing: process

With measuring or testing

C438S275000

Reexamination Certificate

active

06773937

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to a mask read-only memory (ROM), and, more particularly, to a method to verify the mask for a mask ROM.
BACKGROUND OF THE INVENTION
Conventionally, the verification for mask ROMs applies ion implantation of binary random code, i.e., “0” and “1”, to the memory cells of each memory chip and then reads the implanted code out from the memory cells one by one to be further compared with the original implantation pattern so as to determine the chip is perfect or defective. As shown in
FIG. 1
, for example, a memory chip
10
includes a plurality of memory cells implanted with a “0” or “1” code, a plurality of buried diffusion layers
12
, and a plurality of polysilicon layers
14
, in which the region highlighted with a dotted line indicates a defective memory cell
16
. Unfortunately, there can be only one, “0” or “1”, to be verified in a verification system. For instance, in a system capable of verifying code “0” to be defective, a defective cell implanted with code “1” may be read a “0” out and thus is supposed to be a perfect cell. Particularly, In
FIG. 1
, the random code implanted into the defective memory cell
16
is “1”, and in this case, if the cell implanted with code “1” can be verified to be defective, then the defect of the cell
16
can be verified, and thus the mask for the process to manufacture the memory chip
10
can be further determined to be defective. However, in another case that only the cell with implanted code “0”, can be verified to be defective, the cell
16
cannot be verified to have a defect, and therefore the mask used to produce the chip
10
cannot be verified defective as well. Since conventional verification method cannot completely verify each memory cell to determine if there is a defect, the photomask used for the process cannot be subsequently accurately verified defective or not.
Accordingly, it is desired a method to completely verify the photomask for mask ROMs.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method that can completely verify the photomask for mask ROMs.
In an embodiment according to the present invention, a verification of the mask for a mask ROM includes implanting a binary random code and its reverse tone into two chips that are manufactured by the same process with the mask, and then testing the two chips and comparing their test results. The two chips used for the verification can be selected from different wafers that are manufactured by the same process with the mask, or from two die regions of a single wafer manufactured by a process with the mask under verified.
For verification of a mask for a mask ROM according to another embodiment, several exclusive random codes are implanted into a plurality of chips, respectively, and the coded chips are then tested for comparison of their test results to determine if the mask is perfect or defective. Likewise, the chips to carry out the verification can be selected from different wafers manufactured by the same process with the mask, or from two die regions of a single wafer with the verified mask.


REFERENCES:
patent: 2003/0134478 (2003-07-01), Lai et al.

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