Method of manufacturing CMOS integrated circuit
In a method of manufacturing a CMOS integrated circuit according to the present invention, a PSD step (step of forming P-type source/drain regions) is first carried out, and an NSD step (step of forming N-type source/drain regions) is thereafter carried out, in order to create a mixed structure of a silicide transistor and a non-silicide transistor. Thus, a step of depositing an oxide film on a substrate surface may be carried out only once, the oxide film can be removed by a single step of etching with hydrofluoric acid, and the operating characteristics of formed devices can be excellently maintained.
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1. Field of the Invention
The present invention relates to a method of manufacturing a CMOS integrated circuit, and more particularly, it relates to a method of manufacturing a CMOS integrated circuit mixedly provided with a silicified transistor and a non-silicified transistor.
2. Description of Related Art
A CMOS (Complementary Metal Oxide Semiconductor) integrated circuit has advantages such as small power consumption and a stable operation, and is widely applied to a VLSI (Very Large Scale Integrated Circuit). In recent years, a CMOS integrated circuit mixedly provided with transistors of different types has also been implemented.
For example, a CMOS integrated circuit in which part of transistors are silicide transistors and the other transistors are non-silicide transistors is implemented. In this integrated circuit, the silicide transistors exhibiting low gate, source and drain resistance values of about 15Ω can be utilized as transistors for high-speed operations, while the non-silicide transistors having excellent withstand voltage characteristics against external surge voltages, for example, can be utilized as input/output circuits to which high electrostatic withstand voltages are required. Therefore, a semiconductor integrated circuit chip mixedly provided with the different types of silicide transistors and non-silicide transistors can be used for various applications.
A conventional method of manufacturing a CMOS integrated circuit mixedly provided with silicide transistors and non-silicide transistors generally performs first an NSD step of forming source and drain regions for N-type transistors after forming gate electrodes on the surface of a silicon substrate, then a PSD step of forming source and drain regions for P-type transistors, and thereafter a step of covering the non-silicide transistors with oxide films and forming silicide films on the gate electrodes, the source regions and the drain regions of silicified transistors.
In this case, As+ (arsenic) ions are implanted in the NDS step in order to form the N-type source and drain regions, while the implanted As+ ions may punch through the gate electrodes. In order to prevent this, an oxide film (TEOS film, for example) having a thickness of about 180 Å must be deposited in advance of the NSD step, and the deposited TEOS film is removed with hydrofluoric acid after the NSD step.
When the transistors are selectively silicified, the non-silicified transistors must be covered with protective oxide films (TEOS films, for example). The silicifying step is carried out while depositing TEOS films having a thickness of about 500 Å, for example, on the non-silicide transistors. Therefore, the TEOS films must be removed by etching with hydrofluoric acid after the silicifying step.
As hereinabove described, the conventional method inevitably includes two steps of removing oxide films with hydrofluoric acid. In the steps of removing the oxide films by etching with hydrofluoric acid, isolation oxide films (STI oxide films, for example) are excessively scraped off due to overetching, to result in increase in borderless contact leakage.
The present invention has been proposed under the aforementioned circumstances, and a main object of the present invention is to provide a method of manufacturing a CMOS integrated circuit capable of ensuring a leakage margin for preventing increase in borderless contact leakage.
Another object of the present invention is to provide an improved method of manufacturing a CMOS integrated circuit mixedly provided with a silicide transistor and a non-silicide transistor.
Further another object of the present invention is to provide a method of manufacturing a CMOS integrated circuit reducing a hydrofluoric acid treatment step for removing an oxide film.
SUMMARY OF THE INVENTIONIn the method of manufacturing a CMOS integrated circuit according to the present invention, a P well and an N well are formed, a PSD step of forming P-type source and drain regions in the N well is first carried out, and an NSD step of forming N-type source and drain regions in the P well is thereafter carried out, whereby an oxide film is deposited on the surface of a semiconductor substrate only once, and can be removed by a single step of etching with hydrofluoric acid. Therefore, the operating characteristics of formed devices can be desiredly maintained.
Particularly in a case of manufacturing an integrated circuit mixedly provided with a silicide transistor and a non-silicide transistor, increase in borderless contact leakage is suppressed in each transistor, and a semiconductor integrated circuit having excellent characteristics can be manufactured.
The foregoing and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.
N− diffusion layers 18 are thinly formed on the surface layer regions of the P wells 11, to be bridged by the corresponding gate oxide films 14. On the other hand, P+ diffusion layers 18 are thinly formed on the surface layer regions of the N wells 12, to be bridged by the corresponding gate oxide films 14. The diffusion layers 18, also referred to as extensions, are so provided as to prevent generation of hot electrons or the like by forming source and drain diffusion regions located under the sidewalls 17 so as to have the so-called double diffusion structures, as shown in
The gate electrodes 15, the sidewalls 17 and the extensions 18 are formed through well-known steps. In other words, oxide films and polysilicon films are deposited on the surfaces of the P wells 11 and the N wells 12 respectively, and parts of the oxide films and the polysilicon films other than the gate oxide films 14 and the gate electrodes 15 are removed by photolithography. The gate electrodes 15 are employed as masks to form the extensions 18 in a self-aligned manner. The extensions 18 are individually formed on the P wells 11 and the N wells 12 respectively. Thereafter an oxide film made of TEOS is thinly formed on the surface of the structure, and a film of SiN to form sidewalls is deposited and etched back to complete the sidewalls 17. Thus, the structure shown in
Referring to
Then, an oxide film 22 made of TEOS is deposited on the entire upper surface of the substrate, as shown in
Then, an NSD step is carried out, as shown in
Then, a non-silicide transistor region is covered with a resist film 25 (protective resist film 25) in order to selectively form silicide transistors, as shown in
After the oxide film 22 is removed from the upper surface of the silicide transistor region, cobalt is deposited on the entire surface of the substrate by sputtering and annealed at a temperature of about 800° C., thereby forming silicide films 26 and 27 of CoSi2 on the surface layer portions of the gate electrodes 15 and the surface layer portions of the source regions 23 and the drain regions 24 respectively, as shown in
This embodiment includes the aforementioned steps described with reference to
In other words, the NSD step is carried out after the PSD step according to this embodiment, reversely to the prior art, while the oxide film is deposited on the surface of the substrate only once and removed by the single hydrofluoric acid etching step, whereby the operating characteristics of formed devices can be desiredly maintained.
While the oxide film 22 is made of TEOS (the so-called TEOS film) in the aforementioned embodiment, the oxide film 22 is not necessarily be made of TEOS but may be prepared from another material, so far as the oxide film 22 is removable with hydrofluoric acid and capable of preventing the implanted As+ ions from punching through the gate electrodes 15.
The STI oxide film 13 functioning as isolation film is not scraped off (removed) by etching, and an end surface of the source region 23 opposite to the gate electrode 15 is opposed to the corresponding STI oxide film 13. An edge of the drain region 24 opposite to the gate electrode 15 is similarly sufficiently in contact with the corresponding STI oxide film 13. Even if a contact 30 formed on the source region 23 and the STI oxide film 13 are in borderless contact with each other (the contact 30 is so provided as to come into contact with the STI oxide film 13), therefore, a leakage current can be prevented from flowing from the contact 30 into the substrate (well).
Assuming that two hydrofluoric acid etching steps are carried out in order to manufacture the transistor, the STI oxide film 13 may be scraped off up to a degree shown by a broken line L1. If the STI oxide film 13 is scraped off by etching, electrons may transfer as shown by thick arrow in
Further, the oxide film 22 removed by hydrofluoric acid is formed only once, whereby no heat treatment is required for depositing the oxide film 22, and spreading of the extensions (diffusion layers) 18 is suppressed. Referring to
The flow of the conventional steps shown in
In the flow of the steps according to the embodiment of the present invention, on the other hand, the oxide film is deposited only once and removed only once.
The present invention is not limited to the aforementioned embodiment, but can be modified in various ways in the range of the scope of claims for patent.
For example, while the embodiment is described with reference to the transistors each having the gate electrode sandwiched between the pair of sidewalls, the manufacturing method of the present invention is also applicable to a transistor having a sidewall only on one side or a transistor having no sidewall.
While the present invention has been described in detail by way of the embodiments thereof, it should be understood that these embodiments are merely illustrative of the technical principles of the present invention but not limitative of the invention. The spirit and scope of the present invention are to be limited only by the appended claims.
This application corresponds to Japanese Patent Application No. 2007-173962 filed with the Japanese Patent Office on Jul. 2, 2007, the disclosure of which is incorporated herein by reference.
Claims
1. A method of manufacturing a CMOS integrated circuit by forming isolated P and N wells on a surface layer region of a semiconductor substrate, forming gate electrodes on the respective wells, and thereafter sequentially carrying out:
- (1) a PSD step of forming P-type source and drain regions on the N well;
- (2) an NSD step of forming N-type source and drain regions on the P well by depositing an oxide film on a surface of the substrate and selectively covering the N well with a resist film;
- (3) a step of selectively removing the resist film, thereafter selectively covering the N well and the P well for a non-silicide transistor not subjected to silicide formation with a resist film, and then removing the oxide film from the N well and the P well constituting a silicide transistor; and
- (4) forming a silicide on the gate electrodes and the source and drain regions of the N well and the P well from which the oxide film is removed.
2. The method of manufacturing a CMOS integrated circuit according to claim 1, wherein
- the NSD step includes a step of implanting As ions for forming the N-type source and drain regions.
3. The method of manufacturing a CMOS integrated circuit according to claim 2, employing hydrofluoric acid for selectively removing the oxide film.
4. The method of manufacturing a CMOS integrated circuit according to claim 1, employing hydrofluoric acid for selectively removing the oxide film.
Type: Application
Filed: Jul 1, 2008
Publication Date: Jan 8, 2009
Applicant: ROHM CO., LTD. (Kyoto)
Inventor: Hiroshi Oji (Kyoto)
Application Number: 12/216,215
International Classification: H01L 21/8238 (20060101);