DE4226421A1 - MASK READ MEMORY ONLY - Google Patents

Description

The invention relates to a semiconductor memory device and in particular a mask read only memory (mask ROM).

In general, to reduce a dwell time (turn Around Time, TAT) of a mask ROM a method for Programming data shown after metal etching.

Fig. 2 shows a design of a known NAND mask ROM in which a plurality of MOS transistors are connected in series. A diffusion region 3 is separated from a further diffusion region by an insulation region 1 , which is formed from a field oxide. The diffusion regions are arranged parallel to one another in a first direction. The insulation region 1 extends in the first direction. A word line 5 made of a polysilicon layer extends in a second direction, which is arranged at a right angle to the first direction, and is arranged parallel to other word lines. Bit lines 11 and 13 made of a metal layer extend in the first direction over the insulation region 1 and the diffusion region 3 adjacent thereto and contact the word line 5 through first and second contact regions 7 and 9 . The word line 5 and the diffusion area 3 adjacent to it form a program area 15 into which impurities are implanted when given data are programmed into the mask ROM.

In this case, data will be formed prior to the formation of the word line programmed polysilicon layer or after an n-type (or p-type) diffusion region with high  Concentration is formed, the desired data be programmed. In the case, however, in the data after forming the bit line by structuring one Metal layer by a photolithographic process can be programmed, the impurities with one the bit line and the diffusion area overlapped Area not happen. Therefore, the desired data cannot be programmed in the program area.

The invention is therefore based on the object Provide mask ROM, in which even after formation of a Bit line data are programmable.

According to an aspect of the present invention a bit line only on an isolation area between Diffusion areas formed.

For a better understanding of the invention, the following is an advantageous embodiment based on the Drawing attached figures explained in more detail and described.

Show it:

Fig. 1 is a schematic view of a draft of an example of a mask ROM according to the invention, and

Fig. 2 is a schematic view of a design of a known mask ROM.

According to FIG. 1, a diffusion region 23 extends in a first direction parallel to a further diffusion region 23 and separated from it by an insulation region 21 and separated by a field oxide. The insulation region 21 extends in the first direction. A word line 25 made of a polysilicon layer extends in a second direction, which is arranged at a right angle to the first direction, and is arranged parallel to further word lines. Bit lines 31 and 33 made of a metal layer extend in the first direction within a region corresponding to the insulation region 21 and above the arrangement of the word line. The bit lines are connected to the word lines 25 through first and second contact areas 27 and 29 .

The word line 25 and the diffusion area 23 adjacent to it form a programming area 35 in which impurities are implanted when data is programmed into the mask ROM. Since the bit line is separated from the diffusion region by a predetermined interval, contaminants for programming the data can also be implanted in the bottom of the word line.

As described above, in a mask ROM desired data easily in a program area be programmed in which a bit line above a upper portion of an isolation area without overlap is formed with a diffusion region.

Therefore, a TAT of a memory array can be significant be reduced. Since there is still an interval between the Bit lines is enlarged, the capacity can be between the bit lines can be reduced.

While a preferred embodiment of the invention has been shown and described, it is for a person skilled in the art evident that further changes in form and details possible without leaving the scope of the invention are.

Claims (1)

Mask read-only memory, characterized by :
a diffusion region ( 23 ) of a first conductivity type which extends in a first direction and is separated from a further diffusion region ( 23 ) by an insulation region ( 21 );
a word line ( 25 ) extending in a second direction perpendicular to the first direction and arranged parallel to a spaced apart further word line ( 25 ); and
a bit line ( 31 , 33 ) extending in the first direction within an area corresponding to the isolation area ( 21 ) and in contact with the word line ( 25 ) through a given contact area ( 27 , 29 ), this area is arranged above an arrangement of the word line ( 25 ).