TECHNICAL FIELDThis invention relates to silicon-on-insulator comprising integrated circuitry and to methods of forming silicon-on-insulator comprising integrated circuitry, including wafer bonding methods.[0001]
BACKGROUND OF THE INVENTIONA problem which motivated the invention related to overcoming undesired floating body effects inherent in silicon-on-insulator field effect transistors. Such is characterized by channel region voltage inherently floating during operation, thereby affecting the threshold voltage and operation consistency of the transistor. Floating body effect typically is not an issue in bulk semiconductor circuitry, as the bulk substrate is tied or held to a specific voltage such that the substrate voltage and threshold voltage are not allowed to float. However in silicon-on-insulator field effect transistors, such does not presently occur and is particularly problematic in what are known as partially depleted silicon-on-insulator transistors. A partially depleted silicon-on-insulator transistor has its channel region only partially extending through the thickness of the silicon layer beneath the transistor gate. Factors which determine whether a field effect transistor is partially or fully depleted include the thickness of the silicon layer and the thickness of the source/drain region within the silicon layer.[0002]
Floating body effect or voltage is determined by forward current leakage to the source and reverse leakage to the drain. One known prior art method of reducing the floating body effect is to increase the source/drain junction forward bias current, thus resulting in any charge build-up in the body promptly being discharged to the source.[0003]
The following invention was motivated in addressing the above identified problems, although such is in no way so limited. The invention is limited only by the accompanying claims as literally worded without limiting reference to the specification, and in accordance with the doctrine of equivalents.[0004]
SUMMARYThe invention includes silicon-on-insulator comprising integrated circuitry and methods of forming silicon-on-insulator circuitry, including wafer bonding methods. In one implementation, a wafer bonding method of forming silicon-on-insulator comprising integrated circuitry includes nitridizing at least a portion of an outer surface of silicon of a device wafer. After the nitridizing, the device wafer is joined with a handle wafer.[0005]
In one implementation, a method of forming silicon-on-insulator comprising integrated circuitry includes nitridizing an interface of the silicon comprising layer of silicon-on-insulator circuitry with the insulator layer of the silicon-on-insulator circuitry. After the nitridizing, a field effect transistor gate is formed operably proximate the silicon comprising layer.[0006]
In one implementation, a method of forming silicon-on-insulator comprising integrated circuitry includes forming the silicon comprising layer of the silicon-on-insulator circuitry. A pair of source/drain regions are formed in the silicon comprising layer and a channel region is formed in the silicon comprising layer which is received intermediate the source/drain regions. A transistor gate is formed operably proximate the channel region. The insulator layer of the silicon-on-insulator circuitry is formed. The insulator layer is formed to comprise a first silicon dioxide comprising region in contact with the silicon comprising layer and running along at least a portion of the channel region between the source/drain regions. A silicon nitride comprising region is formed in contact with the first silicon dioxide comprising region and runs along at least a portion of the channel region. A second silicon dioxide comprising region is formed in contact with the silicon nitride comprising region. The silicon nitride comprising region is received intermediate the first and second silicon dioxide comprising regions.[0007]
Integrated circuitry is also contemplated regardless of the method of fabrication.[0008]
BRIEF DESCRIPTION OF THE DRAWINGSPreferred embodiments of the invention are described below with reference to the following accompanying drawings.[0009]
FIG. 1 is a diagrammatic view of a wafer in process in accordance with an aspect of the invention.[0010]
FIG. 2 is a view of the FIG. 1 wafer at a processing step subsequent to that shown by FIG. 1.[0011]
FIG. 3 is a view of the FIG. 2 wafer at a processing step subsequent to that shown by FIG. 2.[0012]
FIG. 4 is a view of the FIG. 3 wafer at a processing step subsequent to that shown by FIG. 3, and positioned relative to another wafer.[0013]
FIG. 5 is a view of the FIG. 4 wafers at a processing step subsequent to that shown by FIG. 4.[0014]
FIG. 6 is an enlarged diagrammatic sectional view of a portion of the joined wafers of FIG. 5 after subsequent processing.[0015]
FIG. 7 is a view of an alternate embodiment to that depicted by FIG. 6.[0016]
FIG. 8 is a view of another alternate embodiment to that depicted by FIG. 6.[0017]
FIG. 9 is a view of still another alternate embodiment to that depicted by FIG. 6.[0018]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTSThis 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).[0019]
A first embodiment of a method of forming silicon-on-insulator comprising integrated circuitry is described with reference to FIGS. 1-6, and comprises a wafer bonding method. FIG. 1 depicts a device wafer or[0020]first substrate10. Preferably, such comprises a bulkmonocrystalline silicon substrate12. 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. Also in the context of this document, the term “layer” encompasses both the singular and the plural unless otherwise indicated.Substrate12 includes anouter surface14. Someportion15 thereof is intended to be joined with another substrate, as will be apparent from the continuing discussion in a preferred wafer bonding method of forming silicon-on-insulator comprising integrated circuitry. In the depicted and preferred embodiment,outer surface14 comprises crystalline silicon.
Referring to FIG. 2, at least a portion of outer silicon surface of[0021]device wafer10 is nitridized, with the depictedportion including portion15 and all ofouter surface14, to form a siliconnitride comprising region16. By way of example only, such nitridizing might include any one or combination of ion implanting, direct plasma nitridation, remote plasma nitridation, and chemical vapor deposition. The nitridation might also be conducted to be void of either direct or remote nitrogen containing plasma exposure, for example by furnace annealing in a nitrogen containing atmosphere. Example nitrogen containing species for any of the above include N2, NOx, NH3and N2O. A preferred thickness forregion16 is from about 5 Angstroms to about 50 Angstroms.
Referring to FIG. 3, at least a portion of[0022]nitride comprising layer16 is oxidized, preferably to form a silicon dioxide orsilicon oxynitride layer18. In one preferred embodiment,nitride comprising layer16 has a thickness of from about 5 Angstroms to about 50 Angstroms at the conclusion of the oxidizing. An exemplary thickness foroxide layer18 is from about 50 Angstroms to about 500 Angstroms.
Referring to FIG. 4, device wafer or[0023]first substrate10 is depicted diagrammatically proximate a handle wafer orsecond substrate20.Second substrate20 also preferably comprises a bulkmonocrystalline silicon substrate22 which has been oxidized to form a silicondioxide comprising layer24. An example process for forminglayer24 includes thermal growth or deposition, for example by CVD. For purposes of the continuing discussion,handle wafer20 can be considered as comprising a silicondioxide comprising surface25.
Referring to FIG. 5,[0024]device wafer10 is joined withhandle wafer20, with the preferred embodiment depicting joiningdevice wafer10 with silicondioxide comprising surface25 ofhandle wafer20. Such forms a joinedsubstrate30. Such comprises but one preferred embodiment of an aspect of the invention. Such aspect includes a wafer bonding method of forming silicon-on-insulator comprising integrated circuitry whereby the method comprises nitridizing at least a portion of an outer surface of silicon of a device wafer. Thereafter, the device wafer is joined with the handle wafer and regardless of what subsequent processing occurs to finally form integrated circuitry. One exemplary method to bondsubstrate10 withsubstrate20 includes applying a suitable high voltage with opposite polarity on the device wafer and on the handle wafer. Pressing the substrates together at elevated temperature and pressure can also result in a suitable bonding. Further, by way of example only and if the oxide layer is very thin, a thermal oxidation can be conducted while pressing them together a high pressure.
The most preferred embodiment ultimately includes forming the integrated circuitry to comprise a silicon-on-insulator field effect transistor, for example and by way of example only, that depicted by FIG. 6. FIG. 6 depicts joined[0025]substrate30 having been polished or otherwise etched back to form the depictedsilicon comprising material12 from what was theindependent device wafer10. Further thinning of joinedsubstrate30 can be accomplished by polishing or chemical/etching means, if desired. An exemplarythickness form material12 in FIG. 6 is from about 1000 Angstroms to about 2000 Angstroms. A pair of source/drain regions32 and34 have been formed withinsilicon comprising layer12. Agate construction36 overliessilicon comprising layer12 intermediate source/drain regions32 and34. Such is diagrammatically shown to include agate dielectric layer38,insulative sidewall spacers40, and a conductivetransistor gate region41. Exemplary materials forlayers38 and40 include silicon dioxide and silicon nitride, with exemplary materials forgate region41 including conductively doped polysilicon and silicides.
In the depicted and preferred embodiment, layers/[0026]regions16/18/24 comprise aninsulator layer42 of the silicon-on-insulator circuitry which contactssilicon comprising layer12. Such results in the formation of aninterface43 ofsilicon comprising layer12 of the silicon-on-insulator circuitry withinsulator layer42 of the silicon-on-insulator circuitry. Source/drain regions32 and34, as shown, extend to be in contact withinsulator layer42. Also in the depicted and preferred embodiment, source/drain regions32 and34 andtransistor gate construction36 form achannel region44 which is received intermediate the source/drain regions, and in the preferred embodiment, is partially depleted (not extending completely through the thickness of silicon comprising layer12) in operation, as shown. Regardless,nitridized portion16 is received intermediate source/drain regions32,34 andsilicon dioxide18/24. Siliconnitride comprising region16 ideally has greater leakage current characteristics whereby increased leakage current can occur across that portion ofsilicon comprising layer12 received between source/drain regions32 and34 than would otherwise occur in the absence of siliconnitride comprising region16. Alternately considered, and in no way by means of limitation, source/drain forward bias current and leakage are increased, which preferably increases trap density and reduces carrier lifetime, which results in higher junction current.
The above describes but one exemplary preferred embodiment of nitridizing an interface of a silicon comprising layer of silicon-on-insulator circuitry with an insulator of the silicon-on-insulator circuitry. After such nitridizing, a field effect transistor gate is formed operably proximate the silicon nitride comprising layer. The above-described preferred embodiment comprises forming the circuitry by joining a first substrate comprising the silicon comprising layer with a second substrate comprising the insulator layer to form a joined substrate. In the above-described depicted preferred embodiment, the nitridizing includes nitridizing at least one of the first and second substrates prior to the joining. Accordingly, either or both of the substrates could be nitridized prior to the joining. By way of example only, the invention also contemplates nitridizing at least a portion of an outer surface of silicon[0027]dioxide comprising layer24 ofhandle wafer20 with or without any nitridation or oxidation of any portion of the outer surface ofdevice wafer10. Accordingly, in such embodiment, the outer surface of the device wafer to which the handle wafer is joined might comprise crystalline silicon, silicon nitride and/or silicon dioxide.
The invention also contemplates a lesser preferred embodiment wherein the nitridizing of the interface occurs after forming the joined substrate. For example, the FIG. 6 construction might be formed by conducting an ion implant after joining to form silicon[0028]nitride comprising region16.
Regardless of the method of fabrication, the invention also contemplates silicon-on-insulator comprising integrated circuitry, by way of example only, such as the integrated circuitry depicted by FIG. 6. The invention contemplates a substrate comprising an insulator layer of silicon-on-insulator circuitry where such insulator layer comprises silicon dioxide. The silicon-on-insulator circuitry comprises a semiconductive silicon comprising layer received proximate the insulator layer, with the silicon comprising layer comprising a pair of source/drain regions formed therein and a channel region formed therein which is received intermediate the source/drain regions. A transistor gate is received operably proximate the channel region. A silicon nitride comprising region is received intermediate the silicon dioxide comprising layer and the source/drain regions, and runs along at least a portion of the channel region between the source/drain regions.[0029]
FIG. 6 depicts a construction whereby a silicon[0030]nitride comprising region16 runs entirely along and against the channel region between the source/drain regions. FIGS. 7 and 8 depictalternate embodiments30aand30bcomprising alternate siliconnitride comprising regions16aand16b, respectively. Like numerals from the first described embodiment are utilized where appropriate, with differences being indicated by the respective suffixes “a” and “b”. By way of example only, each of FIGS. 7 and 8 show alternate embodiments wherein the respective silicon nitride comprising regions run only along a portion ofchannel region44 between source/drain regions32 and34.
Further by way of example only, FIG. 9 depicts an alternate construction contemplated in both a method and in circuitry independent of the method in accordance with aspects of the invention. FIG. 9 depicts a[0031]wafer fragment30ccomprising an alternate embodiment siliconnitride comprising region16c. Such could, by way of example only, be formed by any of the nitridation and joining methods described above. Like numerals from the first described embodiment are utilized where appropriate, with differences being indicated with the suffix “c”.Insulator layer42cis formed to comprise a first silicondioxide comprising region50 in contact withsilicon comprising layer12 and running along at least a portion ofchannel region44 between source/drain regions32 and34. An exemplary thickness forregion50 is from about 10 Angstroms to 30 Angstroms. Siliconnitride comprising region16cis formed in contact with first silicondioxide comprising region50 and runs along at least a portion ofchannel region44. A second silicondioxide comprising region52 is formed in contact with siliconnitride comprising region16c, with siliconnitride comprising region16cbeing received intermediate first silicondioxide comprising region50 and second silicondioxide comprising region52.
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.[0032]