HYBRID HIGH-VOLTAGE LOW-VOLTAGE FINFET DEVICE

Abstract

An integrated circuit includes a plurality of low-voltage FinFET transistors each having a channel length l and a channel width w, the low-voltage FinFET transistors having a first threshold voltage channel implant and a first gate dielectric thickness. The integrated circuit also includes a plurality of high-voltage FinFET transistors each having the channel length l and the channel width w, the high-voltage FinFET transistors having a second threshold voltage channel implant greater than the first threshold voltage channel implant and second gate dielectric thickness greater than the first gate dielectric thickness.

Claims

1. An integrated circuit comprising: a plurality of low-voltage FinFET transistors each having a channel length l and a channel width w, the low-voltage FinFET transistors having a first threshold voltage channel implant and a first gate dielectric thickness; and a plurality of hybrid FinFET transistors each having the channel length l and the channel width w, the hybrid FinFET transistors having a second threshold voltage channel implant greater than the first threshold voltage channel implant and second gate dielectric thickness greater than the first gate dielectric thickness.

2. The integrated circuit of claim 1 wherein: the plurality of low-voltage FinFET transistors are n-channel FinFET transistors; and the plurality of hybrid FinFET transistors are n-channel FinFET transistors.

3. The integrated circuit of claim 1 wherein: the plurality of low-voltage FinFET transistors are p-channel FinFET transistors; and the plurality of hybrid FinFET transistors are p-channel FinFET transistors.

4. The integrated circuit of claim 1 wherein: the plurality of low-voltage FinFET transistors include both n-channel FinFET transistors and p-channel FinFET transistors; and the plurality of hybrid FinFET transistors include both n-channel FinFET transistors an p-channel FinFET transistors.

5. A method for fabricating gate dielectric regions for both low-voltage FinFET transistors and hybrid FinFET transistors, the method comprising: forming a first layer of first dielectric material over fin structures in both low-voltage FinFET transistors and hybrid FinFET transistors; applying a gate masking layer over the first layer of dielectric material for the hybrid FinFET transistors; removing the first layer of dielectric material from the fin structures of the low-voltage FinFET transistors; removing the hybrid gate masking layer; forming a second layer of the first dielectric material over the fin structures in both the low-voltage FinFET transistors and hybrid FinFET transistors; and forming a layer of a second dielectric layer over the fin structures of all low-voltage and hybrid FinFET transistors.

6. The method of claim 5 wherein: the first dielectric material is SiO.sub.2; and the second dielectric material is HfO.sub.2.

7. A method for implanting threshold channel implants for both low-voltage FinFET transistors and hybrid FinFET transistors, the method comprising: performing a low-voltage threshold implant in the channel regions of both the low-voltage FinFET transistors and the hybrid FinFET transistors; applying an implant masking layer covering the channel regions of the low-voltage FinFET transistors; performing a hybrid channel threshold implant in the channel regions of the hybrid FinFET transistors; and removing the voltage implant masking layer.

8. The method of claim 7 wherein: the low-voltage FinFET transistors and the hybrid FinFET transistors are re-channel transistors; and performing the low-voltage and the hybrid channel threshold implants comprises implanting arsenic.

9. The method of claim 7 wherein: the low-voltage FinFET transistors and the hybrid FinFET transistors are p-channel transistors; and performing the low-voltage and the hybrid channel threshold implants comprises implanting boron.

10. The method of claim 7 wherein: performing the low-voltage threshold implant in the channel regions of both the low-voltage FinFET transistors and the hybrid FinFET transistors comprises implanting to a level of about 3e18 atoms/cm.sup.3; and performing the hybrid channel threshold implant in the channel regions of the hybrid FinFET transistors comprises implanting to a total level of about 5e18 atoms/cm.sup.3.

11. A method for implanting threshold channel implants for both low-voltage FinFET transistors and hybrid FinFET transistors, the method comprising: performing a low-voltage threshold implant in the channel regions of both the low-voltage n-channel FinFET transistors and the hybrid n-channel FinFET transistors; applying an n-channel implant masking layer covering the channel regions of the low-voltage n-channel FinFET transistors; performing a hybrid channel threshold implant in the channel regions of the hybrid n-channel FinFET transistors; removing the n-channel implant masking layer; performing a low-voltage threshold implant in the channel regions of both the low-voltage p-channel FinFET transistors and the hybrid p-channel FinFET transistors; applying a p-channel implant masking layer covering the channel regions of the low-voltage p-channel FinFET transistors; performing a hybrid channel threshold implant in the channel regions of the hybrid p-channel FinFET transistors; and removing the p-channel implant masking layer.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0016] The invention will be explained in more detail in the following with reference to embodiments and to the drawing in which are shown:

[0017] FIG. 1 is a diagram depicting the layout of a prior-art FinFET transistor in a direction along the channel of the device;

[0018] FIG. 2 is a diagram depicting a cross sectional view of the layout of the prior-art FinFET device of FIG. 1 across the channel at the lines 2-2;

[0019] FIG. 3 is a diagram depicting the top view of the layout of the prior-art FinFET device of FIG. 1;

[0020] FIG. 4 is a diagram depicting the layout of a hybrid FinFET transistor in accordance with the present invention in a direction along the channel of the device;

[0021] FIG. 5 is a diagram depicting a cross sectional view of the layout of the hybrid FinFET transistor device of FIG. 4 across the channel at the lines 2-2; and

[0022] FIG. 6 is a diagram depicting the top view of the layout of the hybrid FinFET transistor device of FIG. 3.

[0023] FIG. 7 is a flow diagram showing an illustrative gate dielectric processing sequence used to fabricate the hybrid FinFET transistor devices of the present invention along with low-voltage and high-voltage FinFET transistor devices.

[0024] FIG. 8 is a flow diagram showing an illustrative threshold implant processing sequence used to fabricate the hybrid FinFET transistor devices of the present invention along with low-voltage and high-voltage FinFET transistor devices.

DETAILED DESCRIPTION

[0025] Persons of ordinary skill in the art will realize that the following description of the present invention is illustrative only and not in any way limiting. Other embodiments of the invention will readily suggest themselves to such skilled persons.

[0026] Referring now to FIGS. 4, 5, and 6, side and top views show a hybrid FinFET transistor device 30 in accordance with one aspect of the present invention, where: FIG. 4 is a diagram depicting the layout of the hybrid FinFET transistor device 30 in a direction along the channel of the device; FIG. 5 is a diagram depicting a cross sectional view of the layout of the hybrid FinFET transistor device 30 of FIG. 4 across the channel at the lines 5-5; and FIG. 6 is a diagram depicting the top view of the layout of the hybrid FinFET transistor device 30 of FIG. 4. Some features of hybrid FinFET transistor device 30 are common to FinFET transistor device 10, and these features will be identified in FIGS. 4-6 using the same reference numerals used in FIGS. 1-3.

[0027] Like the prior-art FinFET transistor device 10 of FIGS. 1-3, the hybrid FinFET transistor device 30 of FIGS. 4 through 6 is fabricated on substrate 12 and includes a thin fin of silicon body 14 extending vertically upward from the surface of the substrate 12. In a channel region 16 of the fin 14 a multi-layer gate dielectric formed from a first dielectric layer 32a formed from, for example, thermal SiO.sub.2, and a second dielectric layer 32b formed from a high-k material, for example HfO.sub.2, surrounds the fin 14. Gate dielectric layers 32a and 32b together have a thickness, such as 30 ? and 36 ? in one particular embodiment, respectively, sufficient to withstand the high-voltage gate potential that will be applied to the device. Gate 20 is formed from a metal such as titanium and/or tantalum, e.g., titanium nitride and/or tantalum nitride.

[0028] Persons of ordinary skill in the art will appreciate that in hybrid FinFET transistor device 30 the gate is wrapped around the fin 14 on three sides to define the channel, which has the same width w and length l as the low-voltage FinFET transistor device 10 depicted in FIGS. 1 through 3, providing excellent control from the three sides (left, right, and top) of the channel as seen in FIG. 5. The portion of the fin 14 extending to the left of the gate 20 in FIG. 4 is the source 22 of the hybrid FinFET transistor device 30 and the portion of the fin 14 extending to the right of the gate 18 in FIG. 1 is the drain 24 of the hybrid FinFET transistor device 30. Where the hybrid FinFET transistor device 30 is an n-channel transistor, the source and drain regions 22 and 24 are implanted with a dopant such as arsenic. Where the hybrid FinFET transistor device 30 is a p-channel transistor, the source and drain regions 22 and 24 are implanted with a dopant such as boron.

[0029] According to another aspect of the present invention illustrated in FIGS. 7 and 8, the n-channel and p-channel FinFET transistor devices according to the present invention may be fabricated using conventional processing steps currently employed in semiconductor foundries, with a few variations that are compatible with these processes.

[0030] Referring now to FIG. 7, a flow diagram shows an illustrative gate dielectric processing sequence 40 that may be used to fabricate the hybrid FinFET transistor device 30 of the present invention along with conventional low-voltage and high-voltage FinFET transistor devices. The process sequence begins at reference numeral 42.

[0031] At reference numeral 44, processing steps that precede gate dielectric formation are performed as is known in the art. At reference numeral 46, a layer of dielectric material such as SiO.sub.2 is formed over the fin. In one particular embodiment of the invention, this layer is formed to a thickness of about 22 ?. Then, at reference numeral 48 a gate masking layer is applied to the gate regions of both the hybrid FinFET transistors and the high-voltage FinFET transistors being fabricated. The gate oxide layer is then dipped back in the unmasked low-voltage transistors at reference numeral 50. At reference numeral 52, the gate masking layer is removed.

[0032] At reference numeral 54 an additional layer of a dielectric such as SiO.sub.2 is formed in the gate regions of all low-voltage, hybrid, and high-voltage FinFET transistors. In one particular embodiment of the invention, this layer is formed to a thickness of about 8 ?. Because the initial layer of dielectric material remains on the hybrid FinFET transistors and the high-voltage FinFET transistors, the total thickness of the combination of layers on the hybrid FinFET transistors and on the high-voltage FinFET transistors increases to about 30 ?, while the thickness of the single layer on the low-voltage FinFET transistors is about 8 ?.

[0033] At reference numeral 56, a second dielectric layer formed from, for example, HfO.sub.2, is formed over of the gate regions of all low-voltage, hybrid, and high-voltage FinFET transistors. In one particular embodiment of the invention, this HfO.sub.2 layer is formed to a thickness of about 36 ?. At reference numeral 58, subsequent processing steps are performed to further fabricate the integrated circuit containing the low-voltage, hybrid, and high-voltage FinFET transistors of the present invention. The process ends at reference numeral 60.

[0034] As will be appreciated by persons of ordinary skill in the art, the total thickness of the gate dielectric layers in the low-voltage FinFET transistors is about 44 ? and the total thickness of the gate dielectric layers in the hybrid FinFET transistors and the high-voltage FinFET transistors is about 66 ?. There is no additional processing that needs to be performed in the process to form gate dielectric regions for the hybrid FinFET transistors of the present invention. The only change to the process involves altering the geometry of the gate masking layer used to protect the high-voltage transistor gate regions from the dip back of the first dielectric region in the exposed low-voltage transistor gate regions at reference numeral 50 by also covering the gate regions of low-voltage form factor FinFET transistor structures that are going to be hybrid FinFET transistors. This simple change in the geometry of an existing mask already used in the fabrication in the process does not affect, and thus is compatible with, the basic fabrication process.

[0035] Referring now to FIG. 8, a flow diagram shows an illustrative threshold implant processing sequence 70 that may be used to fabricate the FinFET transistor devices of the present invention along with low-voltage FinFET transistor devices. The process sequence begins at reference numeral 72.

[0036] At reference numeral 74, processing steps that precede threshold channel implant formation are performed as is known in the art. At reference numeral 76, a low-voltage threshold implant is performed for all FinFET transistors in the integrated circuit. Then, at reference numeral 78 an implant masking layer is applied to the substrate to cover the channel regions of the low-voltage and the high-voltage FinFET transistors. The channel regions of the hybrid FinFET transistors remain exposed. At reference numeral 80, an additional channel threshold implant is performed in the exposed channel regions of the hybrid FinFET transistors. At reference numeral 82, the implant masking layer is removed. At reference numeral 84, subsequent processing steps are performed to further fabricate the integrated circuit containing the low-voltage, hybrid, and high-voltage FinFET transistors. The process ends at reference numeral 86.

[0037] The process sequence shown in FIG. 8 is generic to a channel threshold implant sequence for both n-channel FinFET and p-channel hybrid FinFET transistors. In a process for fabricating integrated circuits having both n-channel and p-channel hybrid FinFET transistor devices, the channel threshold implant process sequence shown in FIG. 8 is simply performed twice, once for n-channel hybrid transistors and once for p-channel hybrid transistors. In the case of n-channel hybrid transistors, according to one exemplary embodiment of the invention, the channel doping is performed using arsenic to about 3e18 atoms/cm.sup.3 in both low-voltage and high-voltage transistor channels and to about 5e18 atoms/cm.sup.3 in hybrid transistor channels. In the case of p-channel hybrid transistors, according to one exemplary embodiment of the invention, the channel doping is performed using boron to about 3e18 atoms/cm.sup.3 in low-voltage and high-voltage transistor channels and to about 5e18 atoms/cm.sup.3 in hybrid transistor channels.

[0038] As will be appreciated by persons of ordinary skill in the art, the only modification to the process that needs to be made in the channel threshold process sequence to implant low-voltage, hybrid, and high-voltage channel threshold implants for FinFET transistors is the application of the implant masking layer to cover the low-voltage and high-voltage transistor channel regions at reference numeral 78, the additional hybrid channel threshold implant performed in the exposed hybrid transistor channel regions at reference numeral 80, and the removal of the implant masking layer at reference numeral 82. As with the high-voltage gate dielectric formation process sequence, this additional processing does not materially affect and thus is compatible with the basic fabrication process. These are acceptable process modifications in that they do not affect other devices and may be implemented at a minimum cost.

[0039] According to one exemplary embodiment of the present invention, the channel implant doping levels result in VtLin=0.457V, Vtsat=0.363V, Sub-Threshold Slope=87 mV/Dec, and Ioff=200 pA@0.8V for the low-voltage transistors and VtLin=0.622V, Vtsat=0.511V, Sub-Threshold Slope=82 mV/Dec, and Ioff=2 pA@0.8V for the high-voltage transistors. In several applications it is desired to have a low source to drain leakage as the higher gate voltage allows more overdrive. This is achieved by increasing the doping from 3E18 to 5E18 thus reducing the Source to Drain leakage to 2 pA in the hybrid FinFET transistor device of the present invention. The low leakage value (2 pA) of Ioff for the high-voltage transistors makes these devices particularly suitable for use in SRAM memory cells. The hybrid FinFET transistor device of the present invention is suitable for an FPGA switch with an overdriven gate, where the source-drain voltage is limited to VDD.

[0040] There are other applications of the hybrid device, such as protect or addressing devices. In this case, the source-drain voltage must be higher. In such applications, two hybrid FinFET devices of the present invention can be connected in series to overcome and issues resulting from their shorter channel length.

[0041] While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art that many more modifications than mentioned above are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.