Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1998-03-20
2001-03-27
Chaundhuri, Olik (Department: 2514)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C438S201000, C438S211000, C438S258000
Reexamination Certificate
active
06207991
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to semiconductor memory devices generally, and more particularly, to methods and structures providing both non-volatile memory (such as an electrically erasable and programmable read-only memory or EEPROM) and CMOS circuity (such as a Random Access Memory or RAM) on a single integrated circuit.
BACKGROUND OF THE INVENTION
EEPROMs are non-volatile memory devices which are erased and programmed using electrical signals. In general, an EEPROM cell, such as a FLOTOX (floating gate-tunnel oxide) cell, includes a floating gate transistor and a select transistor. The select transistor generally selects which individual cells of the EEPROM device are erased and programmed at a particular time.
CMOS devices may be used to implement a variety of discrete logic components and other digital devices, such as various types of RAMS, microprocessors, shift registers, sense amplifiers, etc. Generally, however, many of the processing steps for making an EEPROM device differ from the processing steps for making CMOS devices.
Conventional approaches to forming both EEPROM devices and CMOS devices on a single die generally comprise forming the EEPROM devices while masking the area(s) for the CMOS devices, then masking the EEPROM devices and forming the CMOS devices separately, or vice versa. This approach requires a total number of steps generally equal to the steps required to form each device on separate dice. While some basic steps may be performed simultaneously, it is generally difficult to integrate the steps of the EEPROM and CMOS processes.
SUMMARY OF THE INVENTION
The present invention concerns a method of forming non-volatile memory (e.g., an EEPROM device) and a CMOS device (e.g., a RAM), on a single die or chip, and a structure formed by the method. In one embodiment, the control gate of the storage transistor as well as the gate of the select transistor may be formed during the same manufacturing process step, and thus may be formed of the same gate poly material and may have a similar thickness.
One aspect of the invention includes a two transistor EEPROM cell with source/drain junctions and channel implants formed independent (e.g., custom junctions) of CMOS source/drain junctions and channel implants. Another aspect of the invention includes forming a channel stop structure and a tunnel oxide with a high voltage gate oxide using a single photolithographic step. Yet another aspect of the present invention includes a structure comprising (i) a two transistor EEPROM cell, and (ii) an NMOS transistor select transistor. Such a structure can be made by the present method with the addition of three photolithographic steps to a conventional CMOS process.
Another aspect of the invention includes a two transistor EEPROM cell having a high voltage intrinsic transistor, a high voltage PMOS transistor and a high voltage NMOS transistor with independently formed (i.e., separate from the CMOS junctions) junctions, while using only three additional photo steps.
The objects, features and advantages of the present invention include a method providing a non-volatile memory device and a CMOS device on a single integrated circuit while combining similar steps of each process, and a single-chip structure comprising a non-volatile memory device structure and a CMOS device structure made by such a method. The present invention may provide the combination of processes without significantly interrupting the flow of either process (e.g., the EEPROM process or the SRAM/CMOS process).
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Wei-Hua Liu et al., A 2-Transistor Source-Select (2TS) Flash EEPROM for 1.8v-Only Applications, pp. 1-3.
Chaundhuri Olik
Christopher P. Maiorana P.C.
Cypress Semiconductor Corp.
Weiss Howard
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