# Patent

## Title
FinFET conformal junction and high EPI surface dopant concentration method and device

## Abstract

A method of forming a source/drain region with an abrupt, vertical and conformal junction and the resulting device are disclosed. Embodiments include forming a gate electrode over and perpendicular to a semiconductor fin; forming first spacers on opposite sides of the gate electrode; forming second spacers on opposite sides of the fin; forming a cavity in the fin adjacent the first spacers, between the second spacers; partially epitaxially growing source/drain regions in each cavity; implanting a first dopant into the partially grown source/drain regions with an optional RTA thereafter; epitaxially growing a remainder of the source/drain regions in the cavities, in situ doped with a second dopant; and implanting a third dopant in the source/drain regions.

## Background
TECHNICAL FIELD
The present disclosure relates to fabrication of fin-type field effect transistors (FinFETs) with epitaxially grown source/drain regions. The present disclosure is particularly applicable to devices for the 14 nanometer (nm) technology node and beyond.
BACKGROUND
In current processes of forming cavities for epitaxial growth of source/drain regions, non-vertical cavity sidewalls are formed, and conventional source/drain implantations result in non-uniform doping profiles. Consequently, a non-conformal junction is formed which in turn leads to threshold voltage non-uniformity along the fin height. During the device operation, the non-conformal junction will prevent the fin active region from full utilization, and it also degrades channel resistance and spreading resistance. Besides, the junction invasion at the fin tip worsens short channel effects.
FIG. 1A illustrates a desired cavity sidewall. FIG. 1B illustrates an implant profile after source/drain implantation, which includes a sloped sidewall (at 101). Adverting to FIG. 1C, after all thermal processes, the resulting dopant profile forms a gradient with a decreasing concentration from 103 to 113. As illustrated in FIG. 2A, conventional low energy and heavy dose source/drain implantation after epitaxial growth aimed for ohmic contact will introduce excessive dopant at the fin tip region 201. If a moderate energy source/drain implantation is employed, the middle to bottom effective gate length Leff is slightly reduced, but the junction over all is degraded at regions 203 in FIG. 2B and the junction profile is not straightened. A high energy implantation will cause serious tailing, as illustrated at 205 in FIG. 2C.
The conventional extension implantation techniques cannot straighten the junction. As illustrated in FIG. 3A, for FinFETs with fins 301 having a pitch 303 between 20 and 40 nm, extension implantation 305 is tilted with respect to the fins 301 to cover the entire fin sidewall. However, as illustrated in FIG. 3B, the resultant implantation 307 is non-conformal and non-uniform, and it will also cause both causes fin damage and junction uniformity issues. Thus, conventional implantation before or right after source/drain epitaxial growth will cause a graded junction, undesired junction tailing, a non-conformal junction, and fin damage.
A need therefore exists for methodology enabling formation of both a conformal junction and a high epi surface dopant concentration in a FinFET and the resulting device.
SUMMARY
An aspect of the present disclosure is a method of forming a source/drain region including partially epitaxially growing the source/drain region, doping the partially grown source/drain region, and epitaxially growing the remainder of the source/drain region with in situ doping, and doping the remainder of the region.
Another aspect of the present disclosure is a FinFET device having abrupt, vertical and conformal junction.
Additional aspects and other features of the present disclosure will be set forth in the description which follows and in part will be apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present disclosure. The advantages of the present disclosure may be realized and obtained as particularly pointed out in the appended claims.
According to the present disclosure, some technical effects may be achieved in part by a method including: forming a gate electrode over and perpendicular to a semiconductor fin; forming first spacers on opposite sides of the gate electrode; forming second spacers on opposite sides of the fin; forming a cavity in the fin adjacent the first spacers, between the second spacers; partially epitaxially growing source/drain regions in each cavity; implanting a first dopant into the partially grown source/drain regions; epitaxially growing a remainder of the source/drain regions in the cavities, in situ doped with a second dopant; and implanting a third dopant in the source/drain regions.
Aspects of the present disclosure include implementing a rapid thermal anneal (RTA) between implanting the first dopant and implanting the third dopant. Other aspects include partially epitaxially growing the source/drain regions includes growing the source/drain regions to a height of 0 to 80% of the depth of the cavity. Further aspects include implanting the first dopant with a dose of 1e14 cm−3 to 1e16 cm−3 and at an energy of 1 kiloelectron Volt (keV) to 10 keV. Another aspect includes implementing the RTA at a high temperature greater than 800° C. to repair fin damage, activate implanted dopants, and drive the dopants diffusing into the fin bottom region. Other aspects include in situ doping the second dopant with a concentration of 1e19 cm−3 to 1e21 cm−3. Additional aspects include implanting the third dopant with a concentration of 1e14 cm−3 to 1e16 cm−3 and at an energy of 0.5 keV to 2 keV. Another aspect includes implanting the first dopant in a direction perpendicular to a top surface of the partially epitaxially grown source/drain regions. Additional aspects include implanting the third dopant with zero degrees of rotation and with a maximum tilt with respect to the fin.
Another aspect of the present disclosure is a device including: a gate electrode over and perpendicular to a semiconductor fin; first spacers on opposite sides of the gate electrode; second spacers on opposite sides of the fin; an epitaxially grown source/drain region in the fin adjacent the first spacers, between the second spacers, the epitaxially grown source/drain region having a bottom portion and a top portion; a first dopant implanted in the bottom portion; a second dopant in situ doped in the top portion; and a third dopant implanted in the top portion, wherein the source/drain region has an abrupt, vertical and conformal junction boundary.
Aspects include the bottom portion having a height of 0 to 80% of the height of the eptiaxially grown source/drain region. Other aspects include the first dopant having a dose of 1e14 cm−3 to 1e16 cm−3 and being implanted at an energy of 1 kiloelectron Volt (keV) to 10 keV. Further aspects include the second dopant having a concentration of 1e19 cm−3 to 1e21 cm−3. Additional aspects include the third dopant having a concentration of 1e14 cm−3 to 1e16 cm−3 and being implanted at an energy of 0.5 keV to 2 keV. Another aspect includes the epitaxially grown source/drain region including eSiGe and the first, second, and third dopants including BF2. Further aspects include the epitaxially grown source/drain regions including SiP and the first, second, and third dopants including arsenic.
Another aspect of the present disclosure is a method including forming first and second parallel semiconductor fins on a substrate; forming a gate electrode over and perpendicular to the first and second semiconductor fins; forming first spacers on opposite sides of the gate electrode; forming a first mask over the first fin; forming second spacers on opposite sides of the second fin; forming a first cavity in the second fin adjacent each first spacer, between the second spacers; partially epitaxially growing eSiGe source/drain regions to a height of 0 to 80% of the depth of the first cavity in each first cavity; implanting a first BF2 into the partially grown eSiGe; epitaxially growing eSiGe for a remainder of the source/drain regions in the first cavities, in situ doped with a second BF2; removing the mask; forming a second mask over the second fin; forming third spacers on opposite sides of the first fin; forming a second cavity in the first fin adjacent each first spacer, between the third spacers; partially epitaxially growing SiP source/drain regions to a height of 0 to 80% of the depth of the second cavity in each second cavity; implanting a first arsenic into the partially grown SiP; epitaxially growing SiP for a remainder of the source/drain regions in the second cavities, in situ doped with a second arsenic; removing the second mask; implanting a third BF2 in the eSiGe source/drain regions; and implanting a third arsenic in the SiP source/drain regions.
Aspects include implementing a rapid thermal anneal (RTA) subsequent to implanting the first BF2 and/or subsequent to implanting the first arsenic, the RTA having a peak temperature higher than 800° C. and for a duration longer than 1 second. Other aspects include implanting the first arsenic and the first BF2 with a dose of 1e14 cm−3 to 1e16 cm−3, at an energy of 1 keV to 10 keV, and in a direction perpendicular to a top surface of the partially epitaxially grown source/drain regions. Further aspects include in situ doping the second arsenic and the second BF2 with a concentration of 1e19 cm−3 to 1e21 cm−3. Other aspects include implanting the third arsenic and the third BF2 with a concentration of 1e14 cm−3 to 1e16 cm−3, at an energy of 0.5 keV to 2 keV and at maximum tilt angle with respect to a plane perpendicular to the first and second fins and with zero rotation.
Additional aspects and technical effects of the present disclosure will become readily apparent to those skilled in the art from the following detailed description wherein embodiments of the present disclosure are described simply by way of illustration of the best mode contemplated to carry out the present disclosure. As will be realized, the present disclosure is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.



BRIEF DESCRIPTION OF THE DRAWINGS
The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawing and in which like reference numerals refer to similar elements and in which:
FIG. 1A schematically illustrates a desired cavity sidewall;
FIG. 1B schematically illustrates an implant profile after source/drain implantation;
FIG. 1C schematically illustrates an implant profile after all thermal processes;
FIGS. 2A through 2C schematically illustrate implant profiles after conventional low energy, moderate energy, and high energy implantations, respectively;
FIG. 3A schematically illustrates a tilted extension implantation for a FinFET with multiple fins;
FIG. 3B schematically illustrates the implant profile resulting from the implantation shown in FIG. 3A; and
FIGS. 4A through 7A and FIGS. 4B through 7B and 8 schematically illustrate a three-dimensional view and a cross-sectional view, along the length of a fin and across the fin, of a process flow, in accordance with an exemplary embodiment.



DETAILED DESCRIPTION
In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of exemplary embodiments. It should be apparent, however, that exemplary embodiments may be practiced without these specific details or with an equivalent arrangement. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring exemplary embodiments. In addition, unless otherwise indicated, all numbers expressing quantities, ratios, and numerical properties of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.”
The present disclosure addresses and solves the current problems of graded junctions, undesired junction tailing, non-conformal junctions, and fin damage attendant upon performing source/drain implantation right after source/drain epitaxial growth. In accordance with embodiments of the present disclosure, source/drain regions are partially epitaxially grown followed by a high dose, low energy implantation to straighten the junction at the middle-to-bottom region. An optional RTA can be implemented to repair the damage and further drive the dopant into the fin middle-to-bottom region. Next, the remainder of the source/drain region is epitaxially grown with a low concentration of in situ dopant to prevent aggressive dopant diffusion at the fin tip. Last, a high dose, low energy source/drain implantation is performed for ohmic contact.
Methodology in accordance with embodiments of the present disclosure includes forming a gate electrode over and perpendicular to a semiconductor fin and forming first spacers on opposite sides of the gate electrode. Then second spacers are formed on opposite sides of the fin, and a cavity is formed in the fin adjacent the first spacers, between the second spacers. Source/drain regions are partially epitaxially grown in each cavity, and a first dopant is implanted into the partially grown source/drain regions with an optional RTA thereafter. A remainder of the source/drain regions is epitaxially grown in the cavities and is in situ doped with a second dopant. Last, a third dopant is implanted in the source/drain regions.
Still other aspects, features, and technical effects will be readily apparent to those skilled in this art from the following detailed description, wherein preferred embodiments are shown and described, simply by way of illustration of the best mode contemplated. The disclosure is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.
FIGS. 4A through 7A and FIGS. 4B through 7B and 8 schematically illustrate a three-dimensional view and a cross-sectional view, along the length of a fin and across the fin, respectively, of a process flow, in accordance with an exemplary embodiment. Adverting to FIGS. 4A and 4B, silicon fins 401 and 403 are shown on a substrate 405. A gate electrode 407 is formed over and perpendicular to fin 401, with gate sidewall spacers 409 on opposite sides of the gate electrode. The gate electrode and gate sidewall spacers are also formed over and perpendicular to fin 403, but is not shown for illustrative convenience. FIN 403, for example for a PFET, is covered with a mask 411 during processing of fin 401, which is, for example, for an NFET. Once fin 403 is masked off, spacers 413 are formed on opposite sides of fin 401.
As illustrated in FIGS. 5A and 5B, a cavity 501 is etched in fin 401, between spacers 413 for a source/drain region. A corresponding cavity is formed on the opposite side of the gate electrode, but is not shown for illustrative convenience. The cavity is formed to a depth of 80% to 125% of the fin height.
Next, silicon phosphide (SiP) 601 is partially grown in the cavities to a height of 0 to 80% of the depth of the cavities 501, for example 50%. Arsenic 603 is implanted in SiP 601 with a low energy and a high dose, with zero tilt, to straighten the junction at the middle-to-bottom region. For example, arsenic may be implanted at an energy of 1 kiloelectron volt (keV) to 10 keV and a dose of 1e14 cm−3 to 1e16 cm−3, though “low energy” depends on the thickness of the SiP. An optional RTA can be implemented to further drive the implanted dopant into the fin lower part region. The RTA may have a peak temperature higher than 800° C. and last for a duration longer than 1 second. Then the upper surface of SiP is surface cleaned.
Adverting to FIGS. 7A and 7B, SiP 701 is grown in the remainder of the cavity, with in situ doping having a lighter concentration than arsenic 603. For example, arsenic is implanted in situ in SiP 701 with a dosage of 1e19 to 1e21 cm−3. The light concentration of dopant prevents aggressive dopant diffusion at the fin tip region.
Next, mask 411 is removed and a new mask (not shown for illustrative convenience) is formed over fin 401 to protect fin 401 during processing of fin 403. The steps described above for processing of fin 401 are then substantially repeated for fin 403, substituting embedded silicon germanium (eSiGe) for the SiP and born difluoride (BF2) for the dopant. In other words, spacers 803 are formed, and a cavity is etched in fin 403 on each side of the gate electrode to a depth of 80% to 125% of the fin height. eSiGe 803 is then partially grown in the cavity to a height of 0 to 80% of the depth of the cavities, for example 50%. BF2 is implanted in eSiGe 803 with a low energy and a high dose, with zero tilt, e.g. an energy of 1 keV to 10 keV and a dose of 1e14 cm−3 to 1e16 cm−3. An optional RTA may be implemented to further drive the implanted dopant into the fin lower part region. The RTA may have a peak temperature higher than 800° C. and last for a duration longer than 1 second. The epitaxial surface is surface cleaned and eSiGe 805 is grown in the remainder of the cavity, in situ doped with BF2 with a lighter concentration, for example with a dosage of 1e19 to 1e21 cm−3, resulting in the structure shown in FIG. 8.
After both the NFET and PFET source/drain regions are both epitaxially grown, each is implanted with a dopant with a high dose, for example 1e14 cm−3 to 1e16 cm−3, and low energy, for example 0.5 keV to 2 keV, e.g. 1 keV, for ohmic contact. The dopant for the NFET is arsenic and for the PFET is BF2. The last high dose source/drain implantation is performed across the fin, at an angle of 0 to 25° with respect to a surface perpendicular to the fin. An RTA and a laser spike anneal (LSA) then drive the dopants into the source/drain regions.
The embodiments of the present disclosure can achieve several technical effects, such as an improved junction without an extra mask, reduced effective gate length in the mid-to-bottom region of the source/drain region without implantation tailing, reduced dopant diffusion at the fin tip region, reduced dopant in the channel, and a conformal junction. Devices formed in accordance with embodiments of the present disclosure enjoy utility in various industrial applications, e.g., microprocessors, smart phones, mobile phones, cellular handsets, set-top boxes, DVD recorders and players, automotive navigation, printers and peripherals, networking and telecom equipment, gaming systems, and digital cameras. The present disclosure therefore enjoys industrial applicability in any of various types of highly integrated FinFET semiconductor devices, particularly for the 14 nm technology node and beyond.
In the preceding description, the present disclosure is described with reference to specifically exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the present disclosure, as set forth in the claims. The specification and drawings are, accordingly, to be regarded as illustrative and not as restrictive. It is understood that the present disclosure is capable of using various other combinations and embodiments and is capable of any changes or modifications within the scope of the inventive concept as expressed herein.

## Claims

1. A method comprising:
forming a gate electrode over and perpendicular to a semiconductor fin;
forming first spacers on opposite sides of the gate electrode;
forming second spacers on opposite sides of the fin;
forming a cavity in the fin adjacent the first spacers, between the second spacers;
partially epitaxially growing source/drain regions in each cavity;
implanting a first dopant into the partially grown source/drain regions;
epitaxially growing a remainder of the source/drain regions in the cavities, in situ doped with a second dopant; and
implanting a third dopant in the source/drain regions.

2. The method according to claim 1, further comprising implementing a rapid thermal anneal (RTA) between implanting the first dopant and implanting the third dopant.

3. The method according to claim 1, wherein partially epitaxially growing the source/drain regions comprises growing the source/drain regions to a height of 0 to 80% of the depth of the cavity.

4. The method according to claim 1, comprising implanting the first dopant with a dose of 1e14 cm−3 to 1e16 cm−3 and at an energy of 1 kiloelectron Volt (keV) to 10 keV.

5. The method according to claim 1, comprising in situ doping the second dopant with a concentration of 1e19 cm−3 to 1e21 cm−3.

6. The method according to claim 1, comprising implanting the third dopant with a concentration of 1e14 cm−3 to 1e16 cm−3 and at an energy of 0.5 keV to 2 keV.

7. The method according to claim 1, comprising implanting the first dopant in a direction perpendicular to a top surface of the partially epitaxially grown source/drain regions.

8. The method according to claim 1, comprising implanting the third dopant with zero degrees of rotation and with a maximum tilt with respect to the fin.

9. A method comprising:
forming first and second parallel semiconductor fins on a substrate;
forming a gate electrode over and perpendicular to the first and second semiconductor fins;
forming first spacers on opposite sides of the gate electrode;
forming a first mask over the first fin;
forming second spacers on opposite sides of the second fin;
forming a first cavity in the second fin adjacent each first spacer, between the second spacers;
partially epitaxially growing embedded silicon germanium (eSiGe) source/drain regions to a height of 0 to 80% of the depth of the first cavity in each first cavity;
implanting a first boron difluoride (BF2) into the partially grown eSiGe;
epitaxially growing eSiGe for a remainder of the source/drain regions in the first cavities, in situ doped with a second BF2;
removing the mask;
forming a second mask over the second fin;
forming third spacers on opposite sides of the first fin;
forming a second cavity in the first fin adjacent each first spacer, between the third spacers;
partially epitaxially growing silicon phosphide (SiP) source/drain regions to a height of 0 to 80% of the depth of the second cavity in each second cavity;
implanting a first arsenic into the partially grown SiP;
epitaxially growing SiP for a remainder of the source/drain regions in the second cavities, in situ doped with a second arsenic;
removing the second mask;
implanting a third BF2 in the eSiGe source/drain regions; and
implanting a third arsenic in the SiP source/drain regions.

10. The method according to claim 9, further comprising implementing a rapid thermal anneal (RTA) subsequent to implanting the first BF2 and/or subsequent to implanting the first arsenic, the RTA having a peak temperature higher than 800° C. and for a duration longer than 1 second.

11. The method according to claim 9, comprising implanting the first arsenic and the first BF2 with a dose of 1e14 cm−3 to 1e16 cm−3, at an energy of 1 kiloelectron Volt (keV) to 10 keV, and in a direction perpendicular to a top surface of the partially epitaxially grown source/drain regions.

12. The method according to claim 9, comprising in situ doping the second arsenic and the second BF2 with a concentration of 1e20 cm−3 to 1e21 cm−3.

13. The method according to claim 9, comprising implanting the third arsenic and the third BF2 with a concentration of 1e14 cm−3 to 1e16 cm−3, at an energy of 0.5 keV to 2 keV and at maximum tilt angle with respect to a plane perpendicular to the first and second fins and with zero rotation.