Semiconductor device with a metal insulator semiconductor transistor

Abstract

It is an object to provide a semiconductor device capable of holding multibit information in one memory cell also when scaling for a nonvolatile memory progresses, and a method of manufacturing the semiconductor device. A trench (TR1) is formed in a channel portion of an MONOS transistor. Then, a source side portion and a drain side portion in a silicon nitride film (122) of a gate insulating film (120) which interpose the trench (TR1) are caused to function as first and second electric charge holding portions capable of holding electric charges (CH1) and (CH2). In the case in which the electric charges (CH1) are trapped and the electric charges (CH2) are then trapped, thus, a portion (130a) of a gate electrode (130) in the trench (TR1) functions as a shield. If a fixed potential is given to the gate electrode (130), the second electric charge holding portion is not influenced by an electric field (EF1) induced by the electric charges (CH1) so that the trapping of the electric charges (CH2) is not inhibited.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a semiconductor device to be utilized for a memory cell of a nonvolatile memory and a method of manufacturing the semiconductor device. [0003] 2. Description of the Background Art [0004] Examples of a semiconductor device to be utilized for a memory cell of a nonvolatile memory include an MONOS (Metal Oxide Nitride Oxide Semiconductor) transistor having a structure shown in FIG. 35. The MONOS transistor comprises a source region 111s and a drain region 111d which are formed in a semiconductor substrate 110, a gate insulating film 120 formed on the semiconductor substrate 110, and a gate electrode 130 formed on the gate insulating film 120. [0005] The gate insulating film 120 is a laminated film (an ONO film) in which a silicon oxide film 121, a silicon nitride film 122 and a silicon oxide film 123 are sequentially provided. When the MONOS transistor is to be under a programming (writ...

AI Technical Summary

Benefits of technology

[0025] In the MIS transistor, the gate electrode is formed on the gate insulating film to enter the trench. The first and second electric charge holding portions are formed in the gate insulating film to interpose the trench therebetween. In the case in which an electric charge is trapped into the first electric charge holding portion and another electric charge is then trapped into the second electric charge holding portion, accordingly, the gate electrode in the trench functions as a shield. More specifically, the second electric charge holding portion is not influenced by an electric field induced by the electric charge of the first electric charge holding portion, and the trapping of the electric charge into the second electric charge holding portion is not inhibited even if scaling progresses. If the MIS transistor is applied to a memory cell of a nonvolatile memory, therefore, a semiconductor device capable of holding multibit information in one memory cell can be implemented also when scaling for the nonvolatile memory progresses. Moreover, the trench is formed between the source region and the drain region. Consequently, an effective channel length can be increased and a tolerance to a punch-through can also be enhanced.

Problems solved by technology

With a structure of a conventional semiconductor device, therefore, it is harder to hold multibit information in one memory cell when the scaling progresses.

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