This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-303281, filed Oct. 18, 2004, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a semiconductor device including MOSFETs.
2. Description of the Related Art
One of the problems which have become obvious accompanying the progress in scaling MOSFETs is deterioration in the reliability of gate oxide film which is brought about due to thermal electrons generated by a concentration of electric fields onto gate electrode edge being poured into the gate oxide film.
In order to avoid this problem, there has been proposed a so-called LDD (Lightly Doped Drain) structure which is formed such that impurities whose concentration is relatively low are implanted into source/drain regions of gate edges, and impurities whose concentration is higher are implanted into regions away from the gate edges in order to decrease the resistance.
The LDD architecture is formed by implanting impurities having relatively low concentration in the source/drain regions of the gate edges after a gate electrode is formed, and thereafter, forming gate sidewall insulating film (spacer) on a sidewall of the gate electrode, and implanting impurities having high concentration. Accordingly, it can be understood that the width of the spacer is extremely important parameter for determining the width of the LDD region.
The spacer is generally formed as follows (Jpn. Pat. Appln. KOKAI Publication No. 2003-163215). That is, the spacer is formed by depositing a silicon oxide film or a silicon nitride film (LPCVD insulating film) on an entire surface by LPCVD process, and thereafter, etching the LPCVD insulating film aeolotropically (anisotropically) by RIE (Reactive Ion Etching) process.
Here, the reason why the LPCVD process is used is as follows. An LPCVD process is excellent in sidewall coverage as compared with plasma CVD process or the like. Therefore, an insulating film suitable for forming spacers is formed by using LPCVD process.
However, in MOSFETs fallen under the realm of nano-order in recent years, the following problem has come to the front with respect to the conventional method for forming the spacer by LPCVD process.
When a film thickness of the spacer (spacer film thickness) is made about several tens of nm, a so-called pattern density difference that the film thicknesses on gate sidewall of an LPCVD insulating film is varied. One of the reasons why the pattern density difference is generated is that an aspect determined by a height of gate electrode and a space between gate electrodes has been made higher. The variation in the film thicknesses on the gate sidewall of the LPCVD insulating film brings about a fluctuation in an LLD structure. Therefore, the variation in the film thicknesses on the gate sidewall has a significant influence on the MOSFET property.
A system LSI has n-channel and p-channel type MOSFETs. An optimum spacer film thickness differs with respect to the n-channel MOSFET and p-channel MOSFET. Moreover, even in MOSFETs of the same channel type, if power supply voltages to be used are different from one another, the thicknesses of the gate oxide films are different from one another. Accordingly, even in MOSFETs of the same channel type, the optimum spacer film thickness is different from each other in some cases. That is, there is a plurality of optimum spacer film thicknesses in a system LSI.
The variation of the spacer film thicknesses depending on the layout (pattern density difference) of the MOSFETs in the system LSI amplifies a fluctuation in the LDD structure of each MOSFET. This has been a factor disturbing the function of the system LSI.
A semiconductor device according to an aspect of the present invention comprises a semiconductor substrate; a first integrated circuit provided on the semiconductor substrate, the first integrated circuit comprising a first MOSFET, a second MOSFET disposed at one side of the first MOSFET, and a third MOSFET disposed at other side of the first MOSFET, the first, second, and third MOSFETs having same channel type, and each of the first, second, and third MOSFETs including gate electrode and gate sidewall insulating film provided on a sidewall of the gate electrode, and a distance between the gate electrodes of the first and second MOSFETs, and a distance between the gate electrodes of the first and third MOSFETs being same first distance; and a second integrated circuit provided on the semiconductor substrate, the second integrated circuit comprising a fourth MOSFET of which at least one of a film thickness of a gate insulating film and a channel type is different from those of the first MOSFET, a fifth MOSFET disposed at one side of the fourth MOSFET, and a sixth MOSFET disposed at other side of the fourth MOSFET, the fourth, fifth, and sixth MOSFETs having the same channel type, and each of the fourth, fifth, and sixth MOSFETs including gate electrode and gate sidewall insulating film provided on sidewall of gate electrode, and a distance between the gate electrodes of the fourth and fifth MOSFETs, and a distance between the gate electrodes of the fourth and sixth MOSFETs being same second distance which is different from the first distance.
A semiconductor device according to another aspect of the present invention comprises a semiconductor substrate; and an integrated circuit provided on the semiconductor substrate, the integrated circuit comprising a first line-up of first MOSFETs each having a first characteristic and a second line of second MOSFETs each having a second characteristic which is different from the first characteristic, each of the first and second MOSFETs includes gate electrode and gate sidewall insulating film provided on a sidewall of the gate electrode, the gate sidewall insulating film of the first MOSFET having a thickness corresponding to the first characteristic, and the gate sidewall insulating film of the second MOSFET having a thickness corresponding to the second characteristic.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In
The nMOS integrated circuit 2 and the pMOS integrated circuit 3 are integrated circuits in, for example, a system LSI, and do not comprises a circuit including gate electrodes repeatedly disposed at intervals of minimum dimension (for example, memory cell circuits in a storage device such as a DRAM or the like) and a peripheral circuit thereof. Or, the nMOS integrated circuit 2 and the pMOS integrated circuit 3 are logic ICs or ASICs, and more specifically, those are CMOS integrated circuits in those integrated circuits. The former logic ICs are circuits in a system LSI in some cases.
The nMOS integrated circuit 2 comprises a first nMOS integrated circuit 21 including a plurality of n-channel type MOSFETs in which the film thicknesses of the gate oxide films are Tox1 and a second nMOS integrated circuit 22 including a plurality of n-channel type MOSFETs in which the film thicknesses of the gate oxide films are Tox2.
The PMOS integrated circuit 3 comprises a first pMOS integrated circuit 31 including a plurality of p-channel type MOSFETs in which the film thicknesses of the gate oxide films are Tox3 and a second pMOS integrated circuit 32 including a plurality of p-channel type MOSFETs in which the film thicknesses of the gate oxide films are Tox4.
In the present embodiment, the description will be carried out supposing that Tox1≠Tox2, Tox3≠Tox4, Tox1=Tox3, Tox2=Tox4. To describe more concretely, that is Tox1=Tox3=15 nm, Tox2=Tox4=4 nm. A power supply voltage of the MOSFETs of Tox1=Tox3=15 nm is 3V, and a power supply voltage of the MOSFETs of Tox2=Tox4=4 nm is 1V.
In
The distance d1 is a distance between the right end of a MOSFET Tri (i=1, 2, 3, 4) 2 and the left end of a MOSFET Tri+1 which is at the right side thereof. In the same way, the distance d2 is a distance between the right end of a MOSFET Trj (j=6, 7, 8, 9) 2 and the left end of a MOSFET Trj+1 which is at the right side thereof.
In the present embodiment, the MOSFET Tr2 is a dummy MOSFET (dummy gate electrode section), and does not carry out transistor operations. The dummy MOSFET is provided so as to make the distances d1 between the respective MOSFETs equal to one another, and the MOSFET Tr2 is not necessarily made a dummy MOSFET. Further, the number of dummy MOSFETs is not limited to one, and may be two or more in some cases. In the same way, the MOSFET Tr7 is a dummy MOSFET provided for making the distances d2 equal to one another.
In
Here, the distances d3 and d4 are defined as in the same way as the distances d1 and d2. The MOSFETs Tr12 and Tr17 are dummy MOSFETs in the same way as the MOSFETs Tr2 and Tr7.
In the present embodiment, distances between the respective gate electrodes in the integrated circuit 21 are d1 which are constant. In the same way, distances between the respective gate electrodes in the integrated circuit 22 are d2 which are constant. Further, as shown in
The distances d1 to d4 between the gate electrodes in the respective integrated circuits 21, 22, 31, and 32 have specific values determined in accordance with a channel type of a MOSFET and a film thickness of a gate oxide film. Generally, a distance between the gate electrodes in a case of an n-channel is shorter than that in a case of a p-channel, and the thinner the film thickness of a gate oxide film is, the shorter the distance between gate electrodes is. Moreover, the film thicknesses T1 to T4 of the spacers 12, 12′, 15, and 15′ in the respective integrated circuit 21, 22, 31, and 32 as well are respectively constant in the same way as the distances d1 to d4 between the gate electrodes. The film thicknesses T1 to T4 are, as shown in
Concretely, that is d1=150 nm, d2=200 nm, d=250 nm, and d4=300 nm. Due to the d1 to d4 being set on the values, optimum spacer film thicknesses which are, for example, T1=20 nm, T2=23 nm, T3=26 nm, and T4=28 nm can be selected. In other words, the spacer film thicknesses T1 and T3 of the MOS integrated circuits 21 and 31 whose power supply voltages are 3V and the spacer film thicknesses T2 and T4 of the MOS integrated circuits 22 and 32 whose power supply voltages are 1V can be respectively set to optimum values.
The cross-sectional views of the comparative example nMOS integrated circuit and pMOS integrated circuit which correspond to
As shown in
Next, a manufacturing method for the semiconductor device of the preset embodiment will be described with reference to FIGS. 6 to 12.
First, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
The n-channel and p-channel type MOSFETs in the integrated circuit 21 and the integrated circuit 31 in which the film thicknesses of the gate oxide films are Tox1(=Tox3) are obtained via the above processes. The n-channel and p-channel type MOSFETs in the integrated circuit 22 and the integrated circuit 32 in which the film thicknesses of the gate oxide films are Tox2(=Tox4) are obtained via the same processes.
The integrated circuits 21, 31 in which the film thicknesses of the gate oxide films are Tox1, and the integrated circuits 22, 32 in which the film thicknesses of the gate oxide films are Tox2 are obtained even by the following process (Multi-Oxied Process).
First, a thick gate insulating film is formed on the silicon substrate 21.
Next, the thick gate insulating film on the region of the integrated circuits 22, 32 is removed by etching the thick gate insulating film in a state that the region of the integrated circuits 21, 31 are covered with resist
Next, a thin gate insulating film is formed on regions including the integrated circuits 21, 22, 31, 32.
The gate insulating film (=the thick gate insulating film+the thin gate insulating film) on the regions of the integrated circuits 21, 31 is thicker than the gate insulating film (=the thin gate insulating film) on the regions of the integrated circuits 22, 32 by the thick gate insulating film).
The thicknesses of the thick gate insulating film and the thin gate insulating film are selected such that the gate insulating films on the integrated circuits 21, 31 are to be Tox1 and the gate insulating films on the integrated circuits 22, 32 are to be Tox2.
Thereafter, the gate electrodes, extensions, and source/drain regions are formed by conventional process.
Thereafter, a process for constructing the circuits by connecting the MOSFETs in the respective integrated circuits with wirings is followed. At this time, the MOSFETs Tr2, 7, 12, and 17 are made dummy MOSFETs by disconnecting the MOSFETs Tr2, 7, 12, and 17 electrically to other MOSFETs. Or, the MOSFETs Tr2, 7, 12, and 17 are made dummy MOSFETs by omitting extensions and source/drain regions in the MOSFETs Tr2, 7, 12, and 17. Such dummy MOSFETs can be easily realized by forming a resist such that the ions are not implanted into the regions of the dummy MOSFETs in the process of ion implantations for forming extensions and source/drain regions.
The plan views of the MOSFETs in the integrated circuits of the present embodiment are shown in
In the drawings, G denote gate electrodes, SP denote spacers, S/D denote source/drain regions, d denote distances between the spacers on the active region (element region), and d′ denote distances between the spacers on the isolation region. In the drawings, the MOSFETs in the integrated circuits 21, 22, 31 and 32 are not discriminated from one another.
Next, another embodiment will be described. The semiconductor device of the present embodiment does not include dummy MOSFETs (dummy gate electrode portion). The spacers provided on sidewalls of the MOSFETs have thickness corresponding to the kind (characteristic) of the MOSFETs.
FIGS. 15 to 18 are cross-sectional views showing the manufacturing method for the semiconductor device of the present embodiment.
In the FIGS. 15 to 18, the left side shows a MOSFET (first MOSFET) in the first nMOS integrated circuit 21, the right side shows a MOSFET (second MOSFET) in the first pMOS integrated circuit 31. Each of the integrated circuits 21, 31 includes a plurality of MOSFET, however, for simplicity, only one MOSFET in the each of the integrated circuits 21, 31 is shown in the FIGS. 15 to 18.
First, the aforementioned steps of
Next, as shown in
Next, as shown in
Next, the resist 33 is removed, thereafter, as shown in
Next, as shown in
Thickness of the spacer 33 of the first MOSFET is T1, thickness of the spacers 32, 33 is T3 (>T1). The thickness of the insulating films 31-33 is selected such that the thickness T1, T2 can be obtained.
Thereafter, source/drain regions are formed as in the same way as the
As in the same way as the present embodiment, the MOSFET in the second nMOS integrated circuit 22 and the MOSFET in the second pMOS integrated circuit 32 can be formed (in a case of different channel types).
Further, the MOSFET in the first nMOS integrated circuit 21 and the MOSFET in the first pMOS integrated circuit 31, or the MOSFET in the second nMOS integrated circuit 22 and the MOSFET in the second pMOS integrated circuit 32 can be formed (in a case of different power supply voltages). In this case, the MOSFET for the higher power supply voltage includes the thicker gate insulating film than the MOSFET for the lower power supply voltage.
Further, the MOSFET in the first nMOS integrated circuit 21 and the MOSFET in the first PMOS integrated circuit 31, and the MOSFET in the second nMOS integrated circuit 22 and the MOSFET in the second pMOS circuit 32 can be formed (in a case of different channel types and power supply voltages).
The present embodiment is not limited to the above specific example. That is, it may be performed, if each of the thicknesses of the spacers is different for each of a plurality of MOSFET line-ups which are subjected to the present invention.
In the embodiments, the present invention is applied to the integrated circuits which do not include a memory and a peripheral circuit thereof, however, the present invention is applicable to an integrated circuit which includes a memory and a peripheral circuit such as a cache memory including a memory (SRAM) and a peripheral circuit, or an embedded DREAM including a DRAM and a peripheral circuit.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
Number | Date | Country | Kind |
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2004-303281 | Oct 2004 | JP | national |