Method for forming flash memory cell

Abstract

The invention discloses a forming method of a flash memory storage unit. The forming method comprises the following steps of: providing a plurality of batches of semiconductor structures, wherein each semiconductor structure comprises a substrate; the substrate comprises a plurality of floating gate areas and isolation areas, which are arranged in parallel; a tunneling oxidization layer and a floating gate layer are formed at the surface of each floating gate area of the substrate; each isolation area of the substrate has an isolation structure; the surface of the isolation structure is equal to or higher than the surface of the floating gate layer; the isolation structure has a first area and a second area, which are adjacent; orderly etching the second areas o the isolation structures of the plurality of batches of semiconductor structures, so that the surface of the second area of each isolation structure is lower than the surface of the first area, wherein the method for determining the etching time of each batch to be etched comprises the following steps: testing the etching rate of the previous batch of isolation structure of the batch to be etched; testing the thickness of the isolation structure before the batch to be etched is etched; obtaining the etching time of the batch to be etched by combining with the preset thickness of the second area of each isolation structure after the batch to be etched is etched, wherein the formed isolation structure is accurate in thickness; the formed flash memory storage unit is stable in performance.

Description

Technical field [0001] The present invention relates to the field of semiconductor storage devices, in particular to a method for forming a flash memory storage unit. Background technique [0002] In the current semiconductor industry, integrated circuit products can be divided into three main types: analog circuits, digital circuits and digital / analog hybrid circuits. Among them, storage devices are an important device type in digital circuits. In recent years, flash memory in storage devices has developed particularly rapidly. The main feature of flash memory is that it can maintain stored information for a long time without power; and flash memory has the advantages of high integration, fast access speed, easy erasing and rewriting, etc., so it is used in many fields such as microcomputers and automatic control. Has been widely used. [0003] figure 1 It is a schematic cross-sectional structure diagram of a flash memory cell in the prior art, including: a substrate 10; a tunne...

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Problems solved by technology

[0006] However, when the second region B of the isolation structure 24 is formed in the prior art, the thickness of the second region B is difficult to control accurately. When the thickness of the second region B of the isolation structure 24 is too thin, the isolation structure 24 of the second region B is more It is easy to be broken down, and the threshold voltage of the second region B of the isolation structure 24 drops, which will cause program disturbance, or cause the word line layer 15 (such as figure 1 shown) the turn-off capability becomes worse; when the thickness of the second region B of the isolation structure 24 is too thick, it will cause the formed floating gate 12 (such as figure 1 Shown) the data retention capacity is reduced, and the performance of the flash storage unit is unstable

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