Process for preparing mask-type ROM

Abstract

A manufacturing method of a mask-type read-only memory. First, a buried bit line is formed on a base, and then a gate dielectric layer and a word line are formed on the base. The word line is perpendicular to the buried bit line. At this time, the part of the substrate located between a pair of buried bit lines and below a word line serves as a memory cell. Then cover the base with a first dielectric layer, and then form several coding windows in the first dielectric layer, which are located above part of the memory cells. Then an ion is implanted into the memory unit under the encoding window, and a second dielectric layer is formed on the substrate to fill up all the encoding windows.

Description

technical field [0001] The present invention relates to a semiconductor process method (Semiconductor Process), and in particular to a mask-type read-only memory (MaskROM) manufacturing method. Background technique [0002] Among all kinds of read-only memories, the mask-type read-only memory is the simplest in structure and process. The basic structure of its memory cell (MemoryCell) is a metal oxide semiconductor transistor (MOSTransistor), and when it is programmed, it is in its gate. Ions are implanted into the channel region (Channel) below the pole (Gate) to change its threshold voltage (Threshold Voltage, VT). The mask ROM is to use the initial voltage of the storage unit to represent the data value in it, and the data value is determined by the channel opening and closing of the storage unit under a certain gate voltage when reading, and the channel’s On and off are determined by the starting voltage of the memory cell itself. [0003] Please refer to the manufactu...

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Problems solved by technology

[0006] Though above-mentioned known method is often adopted, has its shortcoming to exist

Please refer to Figure 1B Since the width of the coding window 153 of the photoresist layer 150 is greater than the width of the memory cell 144 to be implanted, the implanted ions 160 are easily diffused into the memory cell 144 that does not need to be implanted, and affect its starting voltage and channel opening current, Then affect the accuracy of data storage and retrieval

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