# Patent

## Title
Methods of forming field effect transistors on substrates

## Abstract

The invention includes methods of forming field effect transistors. In one implementation, the invention encompasses a method of forming a field effect transistor on a substrate, where the field effect transistor comprises a pair of conductively doped source/drain regions, a channel region received intermediate the pair of source/drain regions, and a transistor gate received operably proximate the channel region. Such implementation includes conducting a dopant activation anneal of the pair of source/drain regions prior to depositing material from which a conductive portion of the transistor gate is made. Other aspects and implementations are contemplated.

## Background
RELATED PATENT DATA
This pated resulted from a continuation application of U.S. patent application Ser. No. 12/969,418 which was filed Dec. 15, 2010, which issued as U.S. Pat. No. 8,426,273 on Apr. 23, 2013, which is a divisional of U.S. patent application Ser. No. 11/215,477 which was filed Aug. 30, 2005, which issued as U.S. Pat. No. 7,867,851 on Jan. 11, 2011.


TECHNICAL FIELD
This invention relates to methods of forming field effect transistors.
BACKGROUND OF THE INVENTION
A continuing goal in integrated circuitry design is to make ever denser, and therefore smaller, circuit devices. This results in thinner layers and smaller geometries. Further, new deposition techniques and materials are constantly being developed to enable circuit devices to be made smaller than the previous generations. Additionally, circuit design sometimes fabricates the devices to be substantially horizontally oriented relative to an underlying substrate, and sometimes substantially vertically oriented.
One common integrated circuit device is a field effect transistor. Such includes a pair of source/drain regions having a semiconductive channel region received operably therebetween. A conductive gate is received operably proximate the channel region, and is separated therefrom by a gate dielectric. Application of a suitable voltage potential to the gate enables current to flow between the source/drain regions through the channel region, with the transistor being capable of essentially functioning as a switch.
The source/drain regions of a field effect transistor typically include semiconductive material which has been doped with a conductivity enhancing impurity of a first and/or second conductivity type. Such dopant impurity might be intrinsically provided during the fabrication of the material from which the source/drain region is fabricated, or subsequently for example by suitable gas phase diffusion or ion implanting. The conductivity type (n or p) of the transistor is determined/designated by the conductivity type of highest dopant concentration portion of the source/drain regions. Specifically, p-channel or PMOS devices have their source/drain highest dopant concentration of p type, and n-channel or NMOS devices have their source/drain highest dopant concentration of n type.
Regardless, the dopants as initially provided are eventually subjected to a high temperature dopant activation anneal to impart desired and necessary operating characteristics to the source/drain regions. However, some present and future generation conductive gate materials are/will be comprised of elemental-form metals, alloys of elemental metals, and conductive metal compounds. Such materials can be adversely affected by the typical temperatures and times required to achieve dopant activation by anneal. For example, certain metal materials (i.e., titanium, titanium nitride, molybdenum silicide, nickel silicide, titanium silicide, and cobalt silicide) are thermally unstable and result in stress/strain induced stacking faults or react with the dielectric when subjected to the high temperature anneals typically required to achieve dopant activation.
While the invention was motivated in addressing the above identified issues, it is in no way so limited. The invention is only limited by the accompanying claims as literally worded, without interpretative or other limiting reference to the specification, and in accordance with the doctrine of equivalents.
SUMMARY
The invention includes methods of forming field effect transistors. In one implementation, the invention encompasses a method of forming a field effect transistor on a substrate, where the field effect transistor comprises a pair of conductively doped source/drain regions, a channel region received intermediate the pair of source/drain regions, and a transistor gate received operably proximate the channel region. Such implementation includes conducting a dopant activation anneal of the pair of source/drain regions prior to depositing material from which a conductive portion of the transistor gate is made.
In one implementation, a method of forming a field effect transistor includes ion implanting conductivity enhancing impurity dopant into semiconductive material of a substrate to form highest dopant concentration portions of a pair of source/drain regions. A dopant activation anneal is conducted of the highest dopant concentration portions of the pair of source/drain regions. After the dopant activation anneal, material is deposited from which a conductive portion of the transistor gate of the transistor is made.
In one implementation, a method of forming a field effect transistor includes ion implanting conductivity enhancing impurity dopant into an implant region of semiconductive material of a substrate to a highest dopant concentration for a pair of source/drain regions. After the ion implanting, a dopant activation anneal of the implant region is conducted. After the dopant activation anneal, an opening is etched through the implant region into semiconductive material of the substrate. Gate dielectric and conductive material of the transistor gate of the transistor are formed within the opening.
In one implementation, a method of forming an n-channel field effect transistor and a p-channel field effect transistor on a substrate includes ion implanting p-type conductivity enhancing impurity dopant into semiconductive material of a substrate to form highest dopant concentration portions of a pair of source/drain regions of the p-channel field effect transistor. Before or thereafter, n-type conductivity enhancing impurity dopant is ion implanted into semiconductive material of the substrate to form highest dopant concentration portions of the pair of source/drain regions of the n-channel field effect transistor. A dopant activation anneal is simultaneously conducted of the highest dopant concentration portions of the pair of source/drain regions of each of the n-channel field effect transistor and of the p-channel field effect transistor. After the dopant activation anneal, material is deposited from which conductive portions of the transistor gates of the transistors are made.
Other aspects and implementations are contemplated.



BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are described below with reference to the following accompanying drawings.
FIG. 1 is a diagrammatic top plan view of a semiconductor substrate in process in accordance with an aspect of the invention.
FIG. 2 is a view of the FIG. 1 substrate taken through line 2-2 in FIG. 1.
FIG. 3 is a view of the FIG. 1 substrate at a processing subsequent to that depicted by FIG. 1.
FIG. 4 is a view of the FIG. 3 substrate taken through line 4-4 in FIG. 3.
FIG. 5 is a view of the FIG. 3 substrate at a processing subsequent to that depicted by FIG. 3.
FIG. 6 is a view of the FIG. 5 substrate taken through line 6-6 in FIG. 5.
FIG. 7 is a view of the FIG. 5 substrate at a processing subsequent to that depicted by FIG. 5.
FIG. 8 is a view of the FIG. 7 substrate taken through line 8-8 in FIG. 7.
FIG. 9 is a view of the FIG. 7 substrate at a processing subsequent to that depicted by FIG. 7.
FIG. 10 is a view of the FIG. 9 substrate taken through line 10-10 in FIG. 9.
FIG. 11 is a view of the FIG. 9 substrate at a processing subsequent to that depicted by FIG. 9.
FIG. 12 is a view of the FIG. 11 substrate taken through line 12-12 in FIG. 11.
FIG. 13 is a view of the FIG. 11 substrate at a processing subsequent to that depicted by FIG. 11.
FIG. 14 is a view of the FIG. 13 substrate taken through line 14-14 in FIG. 13.
FIG. 15 is a view of the FIG. 13 substrate at a processing subsequent to that depicted by FIG. 13.
FIG. 16 is a view of the FIG. 15 substrate taken through line 16-16 in FIG. 15.
FIG. 17 is a view of the FIG. 15 substrate at a processing subsequent to that depicted by FIG. 15.
FIG. 18 is a view of the FIG. 17 substrate taken through line 18-18 in FIG. 17.
FIG. 19 is a view of the FIG. 17 substrate at a processing subsequent to that depicted by FIG. 17.
FIG. 20 is a view of the FIG. 19 substrate taken through line 20-20 in FIG. 19.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8).
Exemplary preferred methods of forming a field effect transistor on a substrate are described with reference to FIGS. 1-20. By way of example only, the field effect transistor might be p-type or n-type. Regardless, the field effect transistor will comprise a pair of conductively doped source/drain regions, a channel region received intermediate the pair of source/drain regions, and a transistor gate received operably proximate the channel region. An exemplary preferred embodiment method is described in forming both an n-channel field effect transistor and a p-channel field effect transistor on a substrate, although methods in accordance with the invention might be utilized to fabricate only a single conductivity type field effect transistor.
Referring to FIGS. 1 and 2, an exemplary substrate fragment in process is indicated generally with reference numeral 10. Such preferably comprises a semiconductive substrate, with the depicted preferred example comprising bulk monocrystalline semiconductive material 12 (for example, silicon), although other substrates (for example, semiconductor-on-insulator substrates) are also contemplated. In the context of this document, the term “semiconductor substrate” or “semiconductive substrate” is defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
Trench isolation material 14 has been formed relative to substrate 12, for example comprising one or a combination of silicon dioxide and silicon nitride. In the depicted example, semiconductive material 12 has been suitably background doped with p-type material (i.e., boron) to define a p-well 20 having a suitable dopant concentration to function as an NMOS channel. Trench isolation regions 14 have been fabricated to define an exemplary substrate area 16 in which an n-channel field effect transistor will be fabricated, and an area 18 in which a p-channel field effect transistor will be fabricated.
Referring to FIGS. 3 and 4, n-channel region/area 16 has been suitably masked, for example with a photoresist layer 22. Suitable background n-type doping has occurred to form an n-well region 24 within p-channel region/area 18.
Referring to FIGS. 5 and 6, p-type conductivity enhancing impurity dopant has been ion implanted into a first region 26 of semiconductive material 24 of the substrate to a highest dopant concentration for the pair of source/drain regions of the p-channel field effect transistor being fabricated. An exemplary implant material is boron, for example deposited to an exemplary dopant concentration of from 1×1013 ions/cm3 to 1×1016 ions/cm3. An exemplary thickness of implanted first region 26 is from 300 Angstroms to 500 Angstroms, with an exemplary depth for peak implant concentration being from 200 Angstroms to 400 Angstroms. A conductivity enhancing impurity might be provided within first region 26 by any existing or yet-to-be developed manner, including those other than ion implanting, for example by gas phase diffusion. Regardless, in this exemplary embodiment, first region 26 will be fabricated to comprise a pair of source/drain regions 28 of the p-channel field effect transistor being fabricated, with region 26 constituting the highest dopant concentration portions thereof and as will become apparent from the continuing discussion. Accordingly, separate portions of first region 26 will constitute the highest dopant concentration portions of source/drain regions 28.
Further in one exemplary preferred embodiment, and as shown, aspects of the invention contemplate ion implanting a conductivity modifying impurity dopant into semiconductive material 24 of the substrate to form at least one lower dopant concentration portion 30 received proximate each highest dopant concentration portion of region 26 of each source/drain region 28. By way of example only, lower dopant concentration portion 30 is depicted as being received below first region 26. Further by way of example only, such region might comprise one or a combination of a threshold voltage (Vt) adjust implant and a lightly doped drain (LDD) implant. Such is depicted as comprising a Vt adjust implant of opposite conductivity type to that of p+ region 26. An example dopant material comprises arsenic, for example implanted to concentration of from 1×1012 ions/cm3 to 1×1013 ions/cm3. Regardless, the lower dopant concentration portions formed proximate each highest dopant concentration portion of the field effect transistor might be of the same conductivity type as the highest dopant concentration portion, or of different conductivity types. Further if of the same conductivity type, the dopant of the lower dopant concentration portions and the dopant of the highest dopant concentration portions might be of the same or different compositions.
Referring to FIGS. 7 and 8, p-channel region/area 18 has been masked, for example with photoresist 32, and an n-type conductivity enhancing impurity dopant has been ion implanted into a second region 34 of semiconductive material 20 of the substrate to a highest dopant concentration for the pair of source/drain regions of the n-channel field effect transistor being fabricated. An exemplary dopant concentration is the same as that described above for first region 26. An exemplary suitable n-type implant material is arsenic, and exemplary preferred thickness and peak implant depth for second region 34 are the same as those for first region 26. A conductivity enhancing impurity might be provided within first region 26 by any existing or yet-to-be developed manner, including those other than ion implanting, for example by gas phase diffusion. Regardless, in this exemplary embodiment, second region 34 will be fabricated to comprise a pair of source/drain regions 36 of the n-channel field effect transistor being fabricated, with region 34 constituting the highest dopant concentration portions thereof and as will become apparent from the continuing discussion. Accordingly, separate portions of second region 34 will constitute the highest dopant concentration portions of source/drain regions 36.
FIGS. 7 and 8 also depict exemplary preferred ion implanting of a conductivity modifying impurity dopant into the semiconductive material of the substrate to form at least one lower dopant concentration portion 38 proximate each highest dopant concentration portion of region 34 of source/drain regions 36 being fabricated. As above, a preferred orientation for implant region 38 is lower in the semiconductive material than are the highest dopant concentration portions of region 34. Further as described above with connection to the relationship between first region 26 and lower dopant concentration region 30, lower dopant concentration portions of region 38 might be of the same conductivity type as those of the portions of region 34, or of different conductivity types. If of the same conductivity type, the dopants might be of the same composition or of different compositions. In the depicted example, region 38 is depicted as comprising a Vt adjust implant of opposite conductivity type to that of n+ region 34. An example dopant material comprises boron, for example implanted to concentration of from 1×1012 ions/cm3 to 1×1013 ions/cm3.
The above exemplary orderings of masking and forming the respective p-type and n-type regions could of course be reversed.
Referring to FIGS. 9 and 10, photoresist mask 32 (not shown) has been removed, and the substrate subjected to a dopant activation anneal to simultaneously activate the dopants in regions 16 and 18. Any existing or yet-to-be developed anneal technique effective for dopant activation where required is contemplated. By way of example only, one exemplary preferred technique includes exposing the substrate to rapid thermal processing (RTP) at a temperature of at least 920° C. for from 10 seconds to 90 seconds, or furnace anneal at a temperature of at least 600° C. for from 20 minutes to 60 minutes.
Referring to FIGS. 11 and 12, and after the dopant activation anneal, a first opening 44 has been etched through first region 26 (and also through lower dopant concentration portion 30 received therebeneath) into semiconductive material 24 of the substrate. Further, a second opening 46 has been etched through second region 34 (and also preferably through lower dopant concentration portion 38 received therebeneath) into semiconductive material 20 of the substrate. Such is preferably conducted simultaneously, for example utilizing one or more common masking and etching steps. Such is also depicted, by way of example only, as forming openings 44 and 46 to extend over and within trench isolation 14. In this exemplary embodiment, and by way of example only, desired field effect transistor gates will be formed within openings 44 and 46. Further, opening 44 is laterally centered relative to implant region 26 in at least one respective straight line cross-section of the substrate, for example the cross-section line 12-12 as shown in FIG. 11. Also, opening 46 is laterally centered relative to implant region 34 in at least one respective straight line cross-section of the substrate, for example the cross-section line 12-12 as shown in FIG. 11.
For example, FIGS. 13 and 14 depict forming a suitable gate dielectric 50 within first opening 44 and second opening 46. Such might comprise the same or different one or more materials for the respective transistors being fabricated, with examples including one or a combination of silicon dioxide, silicon nitride, aluminum oxide, hafnium oxide and zirconium oxide, and other preferred high-k dielectric materials. Also, different gate dielectric thickness can be provided if desired for the different p-channel and n-channel devices.
Referring to FIGS. 15 and 16, conductive material 54 of the transistor gate of the p-channel field effect transistor has been formed over gate dielectric 50 within first opening 44 and conductive material 54 of the transistor gate of the n-channel field effect transistor has been formed over gate dielectric 50 within second opening 46. The conductive material of the transistor gate of the p-channel field effect transistor and the conductive material of the transistor gate of the n-channel field effect transistor might be of the same or different compositions. Ideally, such are typically of at least slightly modified compositions for obtaining different and desired work functions for the respective p-channel and n-channel devices. Accordingly in such processing, separate depositions might occur relative to the material deposited to within openings 44 and 46, or a commonly deposited material 54 subjected to separate masked processings of such material within the respective openings 44 and 46.
Exemplary preferred conductive material from which conductive portions of the transistor gates are made include elemental-form metal (including alloys thereof), conductive metal compounds, and less preferably conductively doped semiconductive material (i.e., conductively doped polysilicon). Exemplary preferred materials include TaSiN for n-channel devices and TiN for p-channel devices. However of course, other elemental metals and metal compounds are contemplated.
FIGS. 15 and 16 depict the formation of conductive material 54 as comprising a deposition which overfills openings 44 and 46. FIGS. 17 and 18 depict a preferred-embodiment subsequent removing of some of such deposited conductive material effective to recess material 54 to within openings 44 and 46. Such thereby forms an n-channel gate 60 and a p-channel gate 62. Each source/drain region 28 for the p-channel field effect transistor is comprised of an exemplary highest dopant concentration portion 26 and at least one lower dopant concentration portion 30, in the exemplary preferred embodiment. Likewise, each source/drain region 36 of the n-channel field effect transistor is comprised of a highest dopant concentration portion 34 and at least one lower dopant concentration portion 38. Arrows 65 depict the exemplary channels formed for current flow upon application of suitable voltage to the respective gates 60 and 62.
Referring to FIGS. 19 and 20, exemplary subsequent processing is depicted. Specifically, an insulative layer 70 (for example silicon nitride) has been deposited over the substrate. An exemplary thickness range for layer 70 is from 50 Angstroms to 200 Angstroms. A thicker, different composition, insulative material layer 71 (i.e., silicon dioxide deposited by the decomposition of tetraethylorthosilicate) has been formed over layer 70. An exemplary thickness range for layer 71 is from 1,000 Angstroms to 10,000 Angstroms. Contact openings 72 have been fabricated into and through layers 71 and 70 to provide the desired exposure to the respective source/drain regions and conductive material extending from the transistor gates. Suitable conductive contacts (not shown) would be formed thereto for the effective connection of such components with other conductive interconnects or devices (i.e., capacitors and/or conductive interconnect lines).
The above processing, by way of example only, depicts the semiconductive material of first region 26, the semiconductive material of second region 34, and the semiconductive material beneath such regions into which first opening 44 and into which second opening 46 are etched to each comprise bulk monocrystalline semiconductive material, for example bulk monocrystalline silicon. However, aspects of the invention also contemplate such semiconductive material as comprising other than bulk monocrystalline material, for example semiconductor-on-insulator substrates and material, and other substrates whether existing or yet-to-be developed.
Such exemplary preferred embodiments also depict the fabrication of the field effect transistor gate within an opening or trench formed within a semiconductor substrate such as bulk monocrystalline semiconductor material. However, the invention is in no way so limited. Aspects of the invention contemplate conducting a dopant activation anneal of a pair of source/drain regions prior to depositing material from which a conductive portion of the transistor gate is made regardless of the substrate or transistor orientation/structure. For example, and by way of example only, the field effect transistor gate could be formed outwardly of a bulk monocrystalline semiconductive material substrate, for example with respect to a conventional or yet-to-be developed horizontal/planar transistor, and wherein the pair of source/drain regions where subjected to a dopant activation anneal prior to the fabrication of a conductive portion of a transistor gate received operably between the source/drain regions over a channel region formed therebetween. Likewise, the invention contemplates conducting a dopant activation anneal of a pair of elevated source/drain regions of a horizontally-oriented field effect transistor, and for example regardless of whether such elevated source/drain regions are formed on or over bulk monocrystalline semiconductive material.
In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.

## Claims

1. A method of forming a field effect transistor on a substrate, the field effect transistor comprising a pair of source/drain regions, a channel region received intermediate and elevationally below the pair of source/drain regions, and a transistor gate received operably proximate the channel region, the method comprising:
providing a pair of trench isolation regions extending into a background doped semiconductive material over a substrate;
ion implanting conductivity enhancing impurity dopant into the background doped semiconductive material between the pair of trench isolation regions to form highest dopant concentration portions of the pair of source/drain regions, the highest dopant concentration portions comprising 1×1013 to 1×1016 ions/cm3;
conducting a dopant activation anneal, the semiconductive material having an exposed uppermost surface during the implanting and the anneal;
prior to conducting the dopant activation anneal, ion implanting conductivity modifying impurity dopant into semiconductive material of the substrate to form at least one lower dopant concentration portion proximate each highest dopant concentration portion, the conductivity modifying impurity dopant being of an opposite conductivity type than dopant in the highest conductivity concentration portions;
after the dopant activation anneal, etching an opening through the highest dopant concentration portion and lower dopant portion and into the background doped semiconductive material, the opening extending to a first depth that is less than a second depth to which the isolation regions extend; and
depositing material from which a conductive portion of the transistor gate is made into the opening.

2. The method of claim 1 wherein the deposited material from which a conductive portion of the transistor gate is made comprises elemental-form metal.

3. The method of claim 1 wherein the deposited material from which a conductive portion of the transistor gate is made comprises a conductive metal compound.

4. The method of claim 1 wherein the deposited material from which a conductive portion of the transistor gate is made comprises conductively doped semiconductive material.

5. The method of claim 1 wherein the pair of source/drain regions is formed within bulk monocrystalline background doped semiconductive material of the substrate.

6. The method of claim 5 wherein the field effect transistor gate is formed outwardly of the bulk monocrystalline semiconductive material.

7. The method of claim 1 wherein the pair of source/drain regions comprises elevated source/drain regions of a horizontally oriented field effect transistor.

8. The method of claim 6 wherein the substrate comprises bulk monocrystalline semiconductive material, the elevated source/drain regions being formed on the bulk monocrystalline semiconductive material.

9. A method of forming a field effect transistor on a substrate, the field effect transistor comprising a pair of laterally spaced conductively doped source/drain regions, a channel region received intermediate and elevationally below the pair of source/drain regions, and a transistor gate received operably proximate the channel region, the method comprising:
providing a pair of trench isolation regions within a semiconductive material of a substrate;
ion implanting into an implant region of the semiconductive material of the substrate between the pair of trench isolation regions to a highest dopant concentration for the pair of source/drain;
after the ion implanting, conducting a dopant activation anneal of the implant region, an uppermost surface of the semiconductive material being exposed during the implanting and the anneal;
prior to conducting the dopant activation anneal, ion implanting conductivity modifying impurity dopant into semiconductive material of the substrate to form at least one lower dopant concentration portion below the implant region, the opening being etched through the portion, the conductivity modifying impurity dopant being of an opposite conductivity type relative to the source/drain region dopant;
after the dopant activation anneal, etching an opening through the implant region and through the lower dopant concentration portion into material of the substrate, the opening extending less than a depth of the trench isolation regions into the semiconductive material; and
forming conductive material of the transistor gate within the opening.

10. The method of claim 9 wherein the opening is laterally centered relative to the implant region in at least one straight line cross section of the substrate.