Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2002-06-10
2004-06-29
Pham, Long (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S411000, C257S637000, C257S638000, C257S639000
Reexamination Certificate
active
06756635
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device including a plurality of types of transistors different in required characteristics, and a method for manufacturing this semiconductor device, and in particular, it relates to a semiconductor device having a plurality of types of gate dielectric films different in film thickness and nitrogen concentration, and a method for efficiently manufacturing this semiconductor device.
2. Description of the Related Art
A few types of transistors are selectively produced according to required performance in a semiconductor device. When a gate dielectric film of a transistor is made thin, an on-current of the transistor increases, and high speed performance increases. However, when the gate dielectric film is thin, a tunnel current flows between a gate electrode and a substrate, a gate leak current increases, and a power consumption of the transistor increases. To the contrary, when the gate dielectric film is made thick, though the gate leak current decreases, the on-current decreases, and the high speed performance decreases. Thus, when the high speed performance is required for a transistor, its gate dielectric film is manufactured as thin. When it is necessary to reduce the power consumption of a transistor by restraining the gate leak current, its gate dielectric film is manufactured as thick. A silicon oxide or oxynitride film is generally used as the gate dielectric film.
A high performance transistor (an HP transistor) is used in a core unit of a conventional semiconductor device. The core unit is a part where a circuit for executing high speed arithmetic and logic processing is provided. The film thickness and a threshold voltage of the gate dielectric film of the HP transistor are set to lower than those of transistors provided in other parts. The HP transistor has a structure for giving priority to securing the on-current which determines the high speed capability of the transistor over restraining the gate leak current which increases as the film thickness of the gate dielectric film becomes lower, and restraining the off-current which increases as the threshold voltage decreases. The off-current is also referred to as a sub-threshold current in general, and is a leak current which flows between the source and the drain when the gate electric potential and the source electric potential is equal in a transistor, namely when the transistor is tuned off.
A transistor (an I/O transistor), whose gate withstand voltage is prioritized, is used in an I/O unit. The I/O unit is a part where a circuit for providing data for and receiving data from other semiconductor devices is provided. The film thickness of the gate dielectric film of the I/O transistor is set to be higher than that of the transistor in other parts, and its threshold voltage is set to be higher than that of the transistors in the core.
A lower power transistor (an LP transistor) is used in a low power unit. The low power unit is a part where a circuit whose leak current is restrained as low as possible is provided to control power consumption in a standby state. The film thickness of the gate dielectric film of the LP transistor is set to a value between the film thickness of the gate dielectric film in the core unit, and the film thickness of the gate dielectric film in the I/O unit. With this constitution, the gate leak current is restrained.
Further, a middle performance transistor (an MP transistor) whose characteristics are between those of the HP transistor and the LP transistor is formed on the same chip in some cases. Generally, the film thickness of the gate dielectric film of the MP transistor is set to equal to the film thickness of the gate dielectric film of the HP transistor. The off-current of the MP transistor is set to be lower than the one of the HP transistor by setting the threshold voltage thereof. The MP transistor is used in a core unit of a conventional semiconductor device.
As described above, a common gate dielectric film is generally used both for the HP transistor and the MP transistor. And, the film thickness of the gate dielectric film of the LP transistor is set to be higher than the film thickness of the gate dielectric film of the HP (MP) transistor, the film thickness of the gate dielectric film of the I/O transistor is set to be higher than the film thickness of the gate dielectric film of the LP transistor. Namely, three types of transistors, which are the core transistor (the HP transistor and the MP transistor), the LP transistor, and the I/O transistor, are used for a semiconductor device. The off-current of the LP transistor is about 1 to 50 pA/&mgr;m, and the LP transistor is used for a circuit for which low power consumption is required. It is preferable to scale the gate dielectric film of the LP transistor, and to make it common with the gate dielectric film of the core transistor for simplifying a manufacturing step of the semiconductor device. However, when the gate dielectric films are made common, the gate leak current exceeds the off-current in a circuit where a low power consumption is prioritized, and the gate leak current determines the power consumption of the transistor. Because of the foregoing, the film thickness of the gate dielectric film of the LP transistor is not scaled, and is set to a film thickness different from that of the gate dielectric film of the core transistor (the HP transistor and the MP transistor). In this way, the film thicknesses of the gate dielectric films of the core transistor and the LP transistor are reduced almost to their limits in terms of the gate leak current.
A technique of introducing nitrogen (N) into the gate dielectric film that consists silicon oxide, and increasing the dielectric constant has been applied for simultaneously increasing the high speed performance and restraining the gate leak current of a transistor. Increasing the dielectric constant of the gate dielectric film allows decreasing an electrical film thickness of the gate dielectric film. As a result, the on-current of the transistor increases, and the speed of the transistor increases. Alternatively, the thickness of the gate dielectric film can be increased by an amount corresponding to the increase of the dielectric constant, and the gate leak current can be reduced.
As a method for introducing nitrogen into the gate dielectric film, heat treatment is applied to a silicon substrate in an NO atmosphere, for example. As another method, silane gas, O
2
gas, and N
2
gas are simultaneously supplied when the dielectric film is formed on the silicon substrate. Also, as another method, a silicon oxide film is annealed in an ammonia atmosphere. As yet another method, nitrogen is directly implanted into the silicon oxide film. However, the amount of nitrogen introduced into the silicon oxide film is about 2 to 3 atom %, and there is such a problem as the dielectric constant is not sufficiently increased in these methods.
Japanese Patent Publication Laid-Open No. Hei. 6-140392 discloses a method for radical-nitriding a silicon oxide film. With the method disclosed in Japanese Patent Publication Laid-Open No. Hei. 6-140392, a wafer on which a silicon oxide film is formed is loaded in a chamber, and is heated to 700 to 900° C. Then, NH
3
gas is introduced into the chamber, VUV plasma light emitting disc lamp is used to form Ar plasma, and nitrogen radical is generated. The generated nitrogen radical is used to directly nitride the silicon oxide film, and a silicon oxynitride film is formed. As a result, the silicon oxynitride film with a nitrogen concentration exceeding 10 atom % is formed. Nitrogen radical is nitrogen having one unpaired electron, and has larger energy and higher reactivity compared with non-radical nitrogen. Radical nitriding is also called as remote plasma nitriding.
However, the prior art has the following problems. Namely, when radical nitriding is simultaneously applied to a plurality of types of silicon oxide films having a film thicknes
Kimizuka Naohiko
Yasuda Yuri
Katten Muchin Zavis & Rosenman
NEC Electronics Corporation
Pizarro-Crespo Marcos D.
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