PRIORITY APPLICATION This application is a continuation of U.S. application Ser. No. 11/498,586, filed Aug. 3, 2006, which is incorporated herein by reference in its entirety.
TECHNICAL FIELD This disclosure relates generally to semiconductor structures, and more particularly, to strained semiconductor, devices and systems, and methods of forming the strained semiconductor, devices and systems.
BACKGROUND The semiconductor industry continues to strive for improvements in the speed and performance of semiconductor devices. Strained silicon technology has been shown to enhance carrier mobility in both n-channel and p-channel devices, and thus has been of interest to the semiconductor industry as a means to improve device speed and performance. Currently, strained silicon layers are used to increase electron mobility in n-channel CMOS transistors. There has been research and development activity to increase the hole mobility of p-channel CMOS transistors using strained silicon germanium layers on silicon.
FIG. 1A illustrates a known device for improved hole mobility with an n-type silicon substrate 101, a silicon germanium layer 102, a silicon capping layer 103, a gate oxide 104, a gate 105, and N+ source/drain regions 106 and 107. FIG. 1B illustrates a band structure for the device of FIG. 1A, and indicates that some carriers or holes are at the silicon-oxide interface and some are confined in the silicon germanium layer. Both the silicon germanium and the silicon capping layers will be strained if they are thin. Alternatively, the silicon germanium layer may be graded to a relaxed or unstrained layer resulting in more stress in the silicon cap layer. The crystalline silicon layer is strained by a lattice mismatch between the silicon germanium layer and the crystalline silicon layer.
More recently, strained silicon layers have been fabricated on thicker relaxed silicon germanium layers to improve the mobility of electrons in NMOS transistors. Structures with strained silicon on silicon germanium on insulators have been described as well as structures with strained silicon over a localized oxide insulator region. These structures yield high mobility and high performance transistors on a low capacitance insulating substrate.
Wafer bending has been used to investigate the effect of strain on mobility and distinguish between the effects of biaxial stress and uniaxial stress. Bonding a semiconductor onto bowed or bent substrates has been disclosed to introduce strain in the semiconductor. Stress can also be introduced by wafer bonding. Packaging can introduce mechanical stress by bending. Compressively-strained semiconductor layers have been bonded to a substrate.
FIGS. 2-4 illustrate some known techniques to strain channels and improve carrier mobilities in CMOS devices. FIG. 2 illustrates a known device design to improve electron mobility in NMOS transistors using a tensile strained silicon layer on silicon germanium. As illustrated, a graded silicon germanium layer 208 is formed on a p-type silicon substrate 209 to provide a relaxed silicon germanium region 210, upon which a strained silicon layer 211 is grown. The transistor channel is formed in the strained silicon layer 211. There is a large mismatch in the cell structure between the silicon and silicon germanium layers, which biaxially strains the silicon layer. As illustrated in FIG. 3, uniaxial compressive stress can be introduced in a channel 312 of a PMOS transistor to improve hole mobility using silicon germanium source/drain regions 313 in trenches adjacent to the PMOS transistor. Large improvements in hole mobility, up to 50%, have been made in PMOS devices in silicon technology using strained silicon germanium source/drain regions to compressively strain the transistor channel. Silicon-carbide source/drain regions in trenches adjacent to an NMOS transistor can introduce tensile stress and improve electron mobility. FIG. 4 illustrates a known device design to improve mobility for both NMOS and PMOS transistors using silicon nitride capping layers 414. These silicon nitride capping layers can be formed to introduce tensile stress for NMOS transistors and can be formed to introduce compressive stress for PMOS transistors.
Another proposal to improve device speed and performance involves higher mobility surfaces. For example, it has been proposed to bond unstrained (110) layers of silicon onto (100) surface substrates to improve hole mobility in unstrained channel regions of p-channel MOSFETs, and to amorphize the regions in which to fabricate n-channel transistors and recrystallize the (100) silicon seeded by the underlying (100) substrate to provide the unstrained channel region of n-channel MOSFETs with the high channel mobility characteristic of the (100) surface.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A illustrates a known device for improved hole mobility, and FIG. 1B illustrates a band structure for the device of FIG. 1A.
FIG. 2 illustrates a known device design to improve electron mobility in NMOS transistors using a tensile strained silicon layer on silicon germanium.
FIG. 3 illustrates a known device design to provide uniaxial compressive stress in a channel of a PMOS transistor using silicon germanium source/drain regions in trenches adjacent to the PMOS transistor.
FIG. 4 illustrates a known device design to improve mobility for both NMOS and PMOS transistors using silicon nitride capping layers.
FIGS. 5A-5I illustrate an embodiment where a semiconductor layer is bonded to tensile strain the semiconductor layer.
FIGS. 6A-6K illustrate an embodiment where a semiconductor layer is bonded to compressive strain the semiconductor layer.
FIG. 7 illustrates a top view of a structure in which a plurality of transistors are being formed, according to various embodiments.
FIGS. 8-14 illustrate various methods for straining semiconductor layers.
FIG. 15 is a simplified block diagram of a high-level organization of a memory device according to various embodiments.
FIG. 16 illustrates a diagram for an electronic system having one or more transistors with strained channels for improved mobility, according to various embodiments.
FIG. 17 illustrates an embodiment of a system having a controller and a memory, according to various embodiments.
DETAILED DESCRIPTION The following detailed description refers to the accompanying drawings which show, by way of illustration, specific aspects and embodiments in which the present subject matter may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present subject matter. The various embodiments of the present subject matter are not necessarily mutually exclusive as aspects of one embodiment can be combined with aspects of another embodiment. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the present subject matter. In the following description, the terms “wafer” and “substrate” are interchangeably used to refer generally to any structure on which integrated circuits are formed, and also to such structures during various stages of integrated circuit fabrication. Both terms include doped and undoped semiconductors, epitaxial layers of a semiconductor on a supporting semiconductor or insulating material, combinations of such layers, as well as other such structures that are known in the art. The term “horizontal” as used in this application is defined as a plane parallel to the conventional plane or surface of a wafer or substrate, regardless of the orientation of the wafer or substrate. The term “vertical” refers to a direction perpendicular to the horizontal as defined above. Prepositions, such as “on”, “side”, “higher”, “lower”, “over” and “under” are defined with respect to the conventional plane or surface being on the top surface of the wafer or substrate, regardless of the orientation of the wafer or substrate. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.
According to various method embodiments, a semiconductor layer is oriented to a substrate. The semiconductor layer has a surface orientation and is oriented to the substrate to provide a desired direction of conductance for the surface orientation. The oriented semiconductor layer is bonded to the substrate to strain the semiconductor layer.
According to various embodiments for forming a transistor, a strained semiconductor layer is formed on a substrate, which includes orienting a semiconductor layer to a substrate and bonding the oriented semiconductor layer to the substrate to strain the semiconductor layer. The semiconductor layer has a surface orientation and is oriented to provide a desired direction of conductance for the surface orientation. A gate insulator is formed on the strained semiconductor layer, a gate is formed on the gate insulator, and first and second diffusion regions define a channel beneath the gate insulator between the first and second diffusion regions.
According to various embodiments for forming a CMOS device, a strained semiconductor layer is formed on a substrate. A first semiconductor layer and a second semiconductor layer are oriented to a substrate. The first semiconductor layer has a first surface orientation and is oriented to provide a first desired direction of conductance for the first surface orientation to promote electron mobility. The second semiconductor layer has a second surface orientation and is oriented to provide a second desired direction of conductance for the second surface orientation to promote hole mobility. The first and second oriented semiconductor layers are bonded to the substrate to strain the semiconductor layer. An n-channel transistor is formed using the first semiconductor layer and a p-channel transistor is formed using the second semiconductor layer.
Various structure embodiments include a substrate and a crystalline semiconductor layer bonded to the substrate. The semiconductor layer has a surface orientation and a desired channel conductance direction for the surface orientation. The crystalline semiconductor layer has a local strained region. The structure further includes a gate oxide over the local strained region, a gate over the gate oxide, and first and second source/drain regions to provide a channel region with the desired channel conductance direction within in the local strained region.
For example, strips of silicon of different surface orientations and strip directions can be bonded onto silicon substrates of various surface orientations. The strip direction corresponds to a desired direction of conduction. In transistor embodiments, the desired direction of conduction for the strained silicon is the channel direction. The strips of silicon can be locally strained, and can either be tensile strained during the bonding process to improve the electron mobility and/or can be compressive strained during the bonding process to improve the hole mobility. The improved carrier mobility improves CMOS transistor performance. The carrier wafer or substrate can be a silicon wafer of any surface orientation, such as the common (100), (110) or (111) silicon substrates.
Tensile Strain Embodiments
FIGS. 5A-5I illustrate an embodiment where a semiconductor layer is bonded to tensile strain the semiconductor layer, such as is provided in U.S. Published Patent Application 20040224480, filed May 7, 2003 and entitled “Micromechanical Strained Semiconductor By Wafer Bonding.” U.S. 20040224480 is incorporated by reference herein in its entirety.
FIGS. 5A-5C illustrate a process for forming recesses in a substrate using a LOCal Oxidation of Silicon (LOCOS) process according to various embodiments. The LOCOS process is useful to form recesses in silicon substrates, and one of ordinary skill in the art will understand, upon reading and comprehending this disclosure, that other methods to form recesses in substrates can be used for silicon and other substrates.
FIG. 5A illustrates a semiconductor structure 515 toward the beginning of a LOCOS process. The semiconductor structure 515 includes a silicon substrate 516. A layer of silicon nitride 517 is deposited, such as by Chemical Vapor Deposition (CVD) and the like, on the silicon substrate and is etched to expose portions of the silicon substrate for subsequent selective oxidation. One of ordinary skill in the art will understand, upon reading and comprehending this disclosure, that the pattern of the silicon nitride affects the pattern and characteristics of the recesses and thus of the strained semiconductor film.
FIG. 5B illustrates the semiconductor structure 515 after the silicon substrate 516 has been oxidized. In various embodiments, the oxide 518 is thermally grown by means of wet oxidation. The oxide grows where there is no masking nitride. At the edges of the nitride, some oxidant diffuses laterally to grow under the nitride edges. This lateral growth has the shape of a slowly tapering oxide wedge and is commonly referred to as a “bird's beak.”
FIG. 5C illustrates the semiconductor structure 516 after the oxide has been removed. Recesses 519 remain where the oxidation occurred. Because of the formation of the recesses 519, the substrate 516, also referred to as a first wafer, can be referred to as a dimpled substrate as, in various embodiments, the substrate has a dimpled appearance. As provided below, a second wafer, or membrane, is bonded to the substrate such that portions of the second wafer are strained in the recesses of the substrate.
One benefit of the LOCOS process is that it is a common economical semiconductor fabrication process. Another benefit of the LOCOS process is the tapered bird's beak, which allows for controlled strain in the film. One of ordinary skill in the art will understand, upon reading and comprehending this disclosure, that the slowly tapering shape of the bird's beak is useful to controllably induce strain in ultra-thin semiconductor films. However, the tapered bird's beak shape is not required to practice the present subject matter. One of ordinary skill in the art will understand, upon reading and comprehending this disclosure, that other means for creating a recess or void in the substrate can be used. For example, a grinding process can be used to create a recess or a trench can be otherwise formed in the substrate.
FIGS. 5D-5H illustrate a method to form a strained semiconductor membrane using a bond cut process to bond a membrane to a substrate with recesses, according to various embodiments. The bond cut process involves bonding together two substrates, or wafers, and breaking off a section of at least one of the two substrate after the substrates have been bonded together. The substrate is also referred to herein in various embodiments as a first wafer or dimpled substrate, and the membrane is also referred to herein in various embodiments as a second wafer.
FIG. 5D illustrates a sacrificial semiconductor wafer 520, and FIG. 5E illustrates a semiconductor substrate 516. The substrate 516 includes a semiconductor material, and includes a number of recesses 519, such as illustrated in FIG. 5C. In various embodiments, the semiconductor material includes one of the following materials: silicon; germanium; silicon-germanium; gallium arsenide; indium phosphide; and other semiconductor materials. This list of potential semiconductor materials is not intended to be an all-inclusive list. The substrate is cut into wafer size patterns, and integrated circuits are formed thereon. In various embodiments, the sacrificial wafer includes various semiconductor material including but not limited to silicon, germanium, silicon-germanium, gallium arsenide, indium phosphide, and other semiconductor materials.
The sacrificial wafer 520 is a single crystal wafer, and is conditioned by implanting ions 521 into a surface. The ions are implanted along a plane, represented in FIG. 5D as a line 522, to define a surface layer 523 with a predetermined thickness. The plane is approximately parallel to the surface in which the ions are implanted. In various embodiments, hydrogen ions are used as implantation ions. The hydrogen ions can include H+, H2+, D+, and/or D2+ ions. The implanted ions act to form cavities along the plane 522. The cavities are joined through thermal processing, allowing the surface layer 523 to be removed from the remaining portion of the sacrificial wafer 524 at the cleavage plane 522. In various embodiments, this thermal processing occurs while the surface layer 523 is being bonded to the substrate 516, as shown in FIG. 5F. Once these cavities join and the surface layer is bonded to the substrate, the surface layer breaks off of the sacrificial wafer at the cleavage plane and remains bonded to the substrate. The remaining portion of the sacrificial wafer 524 can be used to form membranes for other substrates, thus reducing the overall cost for the manufacturing process of a wide variety of electronic devices.
FIG. 5F illustrates the surface layer 523 of the sacrificial wafer 520 bonded to the substrate 516. Before the surface layer is bonded to the substrate, the sacrificial wafer and the substrate can be cleaned using conventional cleaning procedures. In various embodiments, the bonding force includes the strong Van der Waal's force that naturally bonds surfaces together as the bonding force. In various embodiments, the Van der Waal's force provides an initial bonding force that is strengthened during subsequent thermal processing. As illustrated in FIG. 5F, the surface layer 523 of the sacrificial wafer 520 is bonded to the substrate 516 in an environment 525A at a first pressure. In various embodiments, the first pressure is a vacuum or a low pressure near a vacuum.
In various embodiments, the bonded wafers are heated to further bond the surface layer to the substrate and to cut the surface layer 523 from the sacrificial wafer. In various embodiments, the environment 525A has a bonding temperature within a range of approximately 300° C. to 400° C. Heating the sacrificial wafer joins the cavities in the cleavage plane 522, allowing the remaining portion 524 of the sacrificial wafer to be removed from the surface layer, which remains bonded to the substrate. The remaining portion 524 of the sacrificial wafer can be prepared and conditioned for another bond cut process.
The thickness of the surface layer 523 bonded to the substrate 516 is defined by the depth of ion implantation 521 during the bond cut process. In various embodiments, the thickness of the surface layer 523 is such that it does not yield or otherwise plastically deform under the desired mechanical strain induced by the bond. In various embodiments, the thickness of the surface layer 523 is less than 200 nm, such that it can be termed an ultra thin wafer. In various embodiments, the silicon layer has a thickness of about 0.1 microns (100 nm or 1000 Å). In various embodiments, the silicon layer has a thickness less than 0.1 microns. In various embodiments, the silicon layer has a thickness in a range of approximately 300 Å to 1000 Å.
In various embodiments, the silicon film is prepared for transistor fabrication. In various embodiments, the preparation of the film includes grinding, polishing, chemical etch, chemical etch with etch stops, and/or plasma assisted chemical etch, and the like, which can be used to further thin the film. Thus, the membrane bonded to the substrate illustrated in FIG. 5G can be thinner than the surface layer defined in the sacrificial layer in FIG. 5D. Device processing can be accomplished using conventional processes and procedures.
FIG. 5H illustrates the membrane 523 further bonded to the substrate 516 in the recesses 519 formed therein. The process is performed in an environment 525B having a second temperature. The second pressure is greater than the first pressure to force the membrane into the recesses. The volume between the membrane and the recessed substrate is a sealed volume, such that the pressure inside these volumes is approximately the first pressure. In various embodiments, the second pressure is atmospheric pressure. In various embodiments, the environment 525B has a bonding temperature within a range of approximately 800° C. to 1000° C. The portion of the membrane bonded to the substrate in the recesses is strained. One of ordinary skill in the art will understand, upon reading and comprehending this disclosure, that the recesses can be made with appropriate dimension to provide a desired tensile strain.
FIG. 5I illustrates a transistor fabricated with a strained semiconductor membrane, according to various embodiments. The illustrated transistor 530 includes a crystalline semiconductor substrate 516 with a recess 519, and a crystalline semiconductor membrane 523 bonded to the substrate 516 to provide the membrane 523 with a desired tensile strain in the recesses. A gate dielectric 531 is formed on the strained membrane, and a gate 532 is formed on the gate dielectric 531. First and second diffusion regions 533 and 534 are formed in the structure 530. The tensile strained semiconductor membrane 523 between the first and second diffusion regions 533 and 534 forms a tensile strained channel region 535.
Various embodiments tensile strain a thin semiconductor layer, such as a silicon layer, with a strain greater than 0.5% to achieve significant mobility enhancement. For further mobility enhancement, various embodiments tensile strain a thin semiconductor wafer, such as an ultra-thin silicon wafer with a thickness within a range of approximately 300 Å to 1000 Å, with a strain within a range of approximately 0.75% to approximately 1.5%. Various embodiments tensile strain a thin semiconductor layer, such as a thin silicon layer, with a strain in the range of approximately 1% to approximately 1.2% to reduce unnecessary strain and provide a margin of error without unduly affecting mobility enhancement. In various embodiments, the film is approximately 1000 Δ or less. In various embodiments, the channel length of the transistor is less than or equal to about 1000 Δ, and the thickness of the film is less than or equal to about 300 Δ. The strain enhances mobility in the channel, thus overcoming problems associated with heavy channel doping.
Compressive Strain Embodiment
FIGS. 6A-6K illustrate an embodiment where a semiconductor layer is bonded to compressive strain the semiconductor layer, such as is provided in U.S. patent application Ser. No. 11/356,335, filed Feb. 16, 2006 and entitled “Localized Compressive Strained Semiconductor.” U.S. patent application Ser. No. 11/356,335 is incorporated by reference herein in its entirety. The description that follows refers to embodiments with silicon and silicon dioxide or oxide. However, those of ordinary skill in the art will understand how to implement the teachings herein with other semiconductors and insulators.
FIG. 6A illustrates a crystalline silicon substrate 636 with a mask layer 637. The mask layer is patterned to define the areas where there will be localized compressive strain. Thus, the defined areas are used to provide a channel with compressive strain to improve hole mobility for p-channel transistors. In various embodiments, the mask is a silicon nitride. A thin native oxide is between the silicon nitride and the crystalline silicon substrate.
As illustrated in FIG. 6B, the exposed crystalline silicon 636 is etched at 638 to a desired depth on each side of the mask 637. A thick oxide layer 639 is deposited. The resulting structure is planarized, such as may be performed by a chemical mechanical planarization (CMP) process. The planarizing process stops on the raised silicon areas 640 to leave islands or strips of silicon 640 embedded in an oxide 639, such as is illustrated in the side view of FIG. 6C and the top view of FIG. 6D.
FIG. 6E illustrates the structure after an oxidation process. The dotted line 641 corresponds to the top surface 641 of the structure illustrated in FIG. 6C, and the dotted lines 642 correspond to the edges 642 of the oxide islands in FIG. 6C. The exposed silicon island 640 oxides rapidly, while the regions covered by the deposited oxide 639 oxidize much more slowly. The thickness of the deposited oxide and the subsequent oxidation is timed to leave the resulting silicon surface planar under the oxides of different thickness, and to provide the desired strain, as will be evident upon reading and comprehending this specification.
FIG. 6F illustrates the structure after the oxide is etched back to expose the crystalline substrate 643 and reduce the oxide in the island portion 640 of the oxide. A “bird's beak” is left at the edges of the oxide islands. The bird's beak has a similar shape to that formed by a LOCal Oxidation of Silicon (LOCOS) process. A native oxide 644 forms on the exposed silicon areas by exposure to air, water or peroxide.
FIGS. 6G-6H illustrate methods for providing an amorphous silicon layer in contact with the crystalline silicon on one side of the oxide island, according to various embodiments. As illustrated in FIG. 6G, an amorphous silicon layer 645 is deposited, and a silicon implant 646 breaks up the oxide such that the crystalline silicon substrate at 647 is able to seed the crystalline growth of the amorphous silicon layer. As illustrated in FIG. 6H, the native oxide is removed at 647 from one side of the oxide island and amorphous silicon 645 is deposited and patterned over the oxide islands. According to various embodiments, the thickness of the silicon film is within a range from approximately 100 nm to approximately 200 nm. Such thicknesses are capable of being mechanically compressed without affecting yield.
FIG. 6I illustrates a recrystallization process for the amorphous silicon layer, and further illustrates the bonding of the crystallized layer after the oxide island is removed. The recrystallization process is also referred to as a solid phase epitaxial (SPE) process, which includes depositing a thin amorphous silicon layer and annealing the structure to recrystallize the amorphous silicon, where one end of the amorphous layer is seeded to promote a desired crystalline growth. The recrystallization, as illustrated by the arrows 648, is seeded at 647 where the silicon layer 645 is in direct contact with the crystalline silicon substrate 636, and thus only grows from one side since the other side still has the unperturbed native oxide 643. According to various embodiments, the silicon film is recrystallized at temperatures from approximately 550° C. to approximately 700° C. The transistor channel is formed in this recrystallized silicon strip. The oxide island is etched from underneath the silicon strip to leave an empty space beneath the silicon strip. As illustrated by the arrow 649, a silicon strip or silicon bridge layer is influenced toward and bonded to the surface beneath the silicon layer. In various embodiments, the naturally occurring Van der Waal's force is sufficient to influence the bridge layer or film 645 into contact with the surface 650 beneath the silicon layer. In various embodiments, a nano-imprint mask is used to assist with influencing the film into contact with the surface beneath the silicon layer.
FIG. 6J illustrates the silicon layer bonded to the surface beneath the silicon layer. Since the length of the bowed silicon film strip is longer than the planar surface region of the silicon substrate, the film 645, now in crystalline form, will be under compressive stress, as illustrated by the arrows 651, after bonding to the substrate surface.
FIG. 6K illustrates a PMOS transistor 652 fabricated in the structure formed with crystalline silicon under compression. The remaining steps in the PMOS transistor fabrication can be achieved by conventional techniques, in which the compressively-strained ultra-thin silicon strip 645 forms the transistor channel region. For example, a gate insulator 653, such as silicon oxide or other gate insulator, is formed on the structure, a gate 654 is formed on the gate insulator, and source/drain regions 655 are formed to define a channel 645 beneath the gate and between the source/drain regions. The source/drain regions can be formed by an ion implantation process.
Locally Strained Semiconductor Embodiment
FIG. 7 illustrates a top view of a structure in which a plurality of transistors are being formed, according to various embodiments. The oxide 756 is illustrated by the dotted line and the pattern of silicon strips 757 is also illustrated. In another embodiment, a number of oxide regions are combined in the column direction to form one oxide area. For example, the column of oxide regions 756A-756E can be formed as one oxide area. As discussed above, these oxide areas can be used to provide a local tensile strain to the silicon strips or a local compressive strain to the silicon strips. According to various embodiments, the same substrate includes silicon strips with both locally tensile strained regions to promote electron mobility and locally compressive strained regions to promote hole mobility.
Surface Orientation/Conductance Direction
FIGS. 8-13 illustrate various methods for straining semiconductor layers. With reference to the embodiment illustrated in FIG. 8, as illustrated at 858 a semiconductor layer is oriented to a substrate to provide a desired direction of conductance of a surface orientation of the semiconductor layer. In embodiments in which strips of semiconductor are bonded to the substrate, the strips are formed in the direction of conductance. Other embodiments use larger membranes or films. The surface crystal orientation is conventionally provided using Miller indices in parentheses. The direction of conduction is provided using X Y Z coordinates in angle brackets, and is based on the same coordinate system used to identify the surface orientation of the semiconductor layer. For a given surface crystal orientation, some directions are more conductive than others. At 859, the oriented semiconductor layer is bonded to the substrate to strain the semiconductor layer. Various embodiments induce a compressive strain and various embodiments induce a tensile strain when the layer is bonded to the substrate. The thickness of the layer is sufficiently thin to permit the strain without yield. Various embodiments create the layer using a bond cut process, such as illustrated in FIGS. 5D-5G. Various embodiments remove the back of a sacrificial wafer, which has been bonded to the substrate, by a mechanical and chemical etch procedure. Various embodiments create the layer by depositing an amorphous layer and recrystallizing the layer using a solid phase epitaxial process, such as illustrated in FIGS. 6G-I.
FIG. 9 illustrates an embodiment of a method of bonding a (100) silicon layer to provide desired conductance in the <110> direction. In embodiments in which strips of silicon are bonded to the substrate, the strips are formed in the <110> direction. At 958, a (100) silicon layer is oriented to a substrate to provide a <110> direction of conductance for the (100) silicon layer. At 959, the oriented (100) silicon layer is bonded to the substrate to strain the silicon layer. Various embodiments bond the layer onto raised oxide areas on any carrier wafer to improve hole mobility by removing the oxide from under the strips and completing the bonding to leave the strip in compressive stress. Various embodiments bond the silicon layer over recessed oxide areas on any carrier wafer to improve electron mobility by removing the oxide from under the strips and completing the bonding to leave the strip in tensile stress.
FIG. 10 illustrates an embodiment of a method of bonding a (110) silicon layer to provide desired conductance in the <100> direction. Other directions of conductance can be used with respect to the (110) silicon layer. In embodiments in which strips of silicon are bonded to the substrate, the strips are formed in the <100> direction. At 1058, a (110) silicon layer is oriented to a substrate to provide a <100> direction of conductance for the (110) silicon layer. At 1059, the oriented (110) silicon layer is bonded to the substrate to strain the silicon layer. Various embodiments bond the layer onto raised oxide areas on any carrier wafer to improve hole mobility by removing the oxide from under the strips and completing the bonding to leave the strip in compressive stress. Various embodiments bond the silicon layer over recessed oxide areas on any carrier wafer to improve electron mobility by removing the oxide from under the strips and completing the bonding to leave the strip in tensile stress.
FIG. 11 illustrates an embodiment of a method of bonding a (111) silicon layer to provide desired conductance in the <110> direction. In embodiments in which strips of silicon are bonded to the substrate, the strips are formed in the <110> direction. At 1158, a (111) silicon layer is oriented to a substrate to provide a <110> direction of conductance for the (111) silicon layer. At 1159, the oriented (111) silicon layer is bonded to the substrate to strain the silicon layer. Various embodiments bond the layer onto raised oxide areas on any carrier wafer to improve hole mobility by removing the oxide from under the strips and completing the bonding to leave the strip in compressive stress. Various embodiments bond the silicon layer over recessed oxide areas on any carrier wafer to improve electron mobility by removing the oxide from under the strips and completing the bonding to leave the strip in tensile stress.
FIG. 12 illustrates an embodiment of a method of bonding (100) silicon layers to provide desired conductance in the <110> direction. As illustrated at 1258A and 1259A, a first (100) silicon layer is oriented to a substrate to provide a <110> direction of conductance of the first (100) silicon layer, and the first (100) silicon layer is bonded to the substrate to tensile strain the first silicon layer. As illustrated in 1258B and 1259B, a second (100) silicon layer is oriented to a substrate to provide a <110> direction of conductance of the first (100) silicon layer, and the second (100) silicon layer is bonded to the substrate to compressive strain the second silicon layer. Thus, on a same substrate, the strips with local tensile stress improve the mobility of n-channel MOSFETs and the strips with local compressive stress improve hole mobility of p-channel MOSFETs. Thus, the present subject matter can be implemented in CMOS design.
FIG. 13 illustrates an embodiment of a method of bonding a (100) silicon layer to provide a desired conductance in the <110> direction and bonding a (110) silicon layer to provide a desired conductance in the <100> direction. At 1358, a (100) silicon layer is oriented to a substrate to provide a <110> direction of conductance and a (110) silicon layer is oriented to the substrate to provide a <100> direction of conductance. At 1359, the oriented (100) silicon layer and the oriented (110) silicon layer are bonded to the substrate to strain the semiconductor layers. Local strain for either the (100) layer or the (110) layer can be either tensile strain or compressive strain. Since in this case the strips will all have the same height above the smooth surface of the carrier wafer the backs of the strips can also be mechanically polished as well as chemically polished. Removing the oxide from under the strips and completing the bonding will leave the strips in tensile stress improving the mobility of both electrons and holes in MOSFETs. The MOSFETs can be fabricated using conventional techniques.
The direction of a uniaxial strain can affect the carrier mobility. For example, as reported by Irie et al., “In-Plane Mobility Anisotropy and Universality Under Uni-Axial Strains In N- and P-MOS Inversion Layers On (100), (110), and (111) Si,” IEDM Technical Digest, 13-15 Dec. 2004, pp. 224-228, a <110> channel direction and a tensile strain direction in the <110> direction is desirable for improved electron mobility in a (100) silicon layer and a <100> channel direction and a tensile strain in the <100> direction is desirable for improved hole mobility in a (110) silicon layer. Thus, various embodiments uniaxially strain the semiconductor layer in a desired direction with respect to the desired direction for conduction to improve carrier mobility. With reference to FIG. 14, at 1458 a semiconductor layer is oriented to a substrate to provide a desired direction of conductance for a surface orientation of the semiconductor layer. At 1459 the oriented semiconductor layer is bonded to the substrate to strain the semiconductor layer. As illustrated by 1460, the bonding process includes uniaxially straining the semiconductor layer in a desired direction with respect to the desired direction of conduction to improve conductance.
Device/System Embodiments
FIG. 15 is a simplified block diagram of a high-level organization of various embodiments of a memory device according to various embodiments of the present subject matter. The illustrated memory device 1561 includes a memory array 1562 and read/write control circuitry 1563 to perform operations on the memory array via communication line(s) or channel(s) 1564. The illustrated memory device 1561 may be a memory card or a memory module such as a single inline memory module (SIMM) and dual inline memory module (DIMM). One of ordinary skill in the art will understand, upon reading and comprehending this disclosure, that semiconductor components in the memory array and/or the control circuitry are able to be fabricated using the strained semiconductor, as described above. For example, in various embodiments, the memory array and/or the control circuitry include p-channel transistors with improved hole mobility and/or n-channel transistors with improved electron mobility, as disclosed herein. The structure and fabrication methods for these devices have been described above.
The illustrated memory array 1562 includes a number of memory cells 1565 arranged in rows and columns, where word lines 1566 connect the memory cells in the rows and bit lines 1567 connect the memory cells in the columns. The read/write control circuitry 1563 includes word line select circuitry 1568, which functions to select a desired row. The read/write control circuitry 1563 further includes bit line select circuitry 1569, which functions to select a desired column. The read/write control circuitry 1563 further includes read circuitry 1570, which functions to detect a memory state for a selected memory cell in the memory array 1562.
FIG. 16 illustrates a diagram for an electronic system having one or more transistors with strained channels for improved mobility, according to various embodiments of the present subject matter. Electronic system 1671 includes a controller 1672, a bus 1673, and an electronic device 1674, where the bus 1673 provides communication channels between the controller 1672 and the electronic device 1674. In various embodiments, the controller and/or electronic device include p-channel transistors with improved hole mobility and/or n-channel transistors with improved electron mobility, as disclosed herein. The illustrated electronic system 1671 may include, but is not limited to, information handling devices, wireless systems, telecommunication systems, fiber optic systems, electro-optic systems, and computers.
FIG. 17 illustrates an embodiment of a system 1775 having a controller 1776 and a memory 1777, according to various embodiments of the present subject matter. The controller 1776 and/or memory 1777 may include p-channel transistors with improved hole mobility and/or n-channel transistors with improved electron mobility, as disclosed herein. The illustrated system 1775 also includes an electronic apparatus 1778 and a bus 1779 to provide communication channel(s) between the controller and the electronic apparatus, and between the controller and the memory. The bus may include an address, a data bus, and a control bus, each independently configured; or may use common communication channels to provide address, data, and/or control, the use of which is regulated by the controller. In an embodiment, the electronic apparatus 1778 may be additional memory configured similar to memory 1777. An embodiment may include a peripheral device or devices 1780 coupled to the bus 1779. Peripheral devices may include displays, additional storage memory, or other control devices that may operate in conjunction with the controller and/or the memory. In an embodiment, the controller is a processor. Any of the controller 1776, the memory 1777, the electronic apparatus 1778, and the peripheral devices 1780 may include p-channel transistors with improved hole mobility and/or n-channel transistors with improved electron mobility, as disclosed herein. The system 1775 may include, but is not limited to, information handling devices, telecommunication systems, and computers. Applications containing strained semiconductor films as described in this disclosure include electronic systems for use in memory modules, device drivers, power modules, communication modems, processor modules, and application-specific modules, and may include multilayer, multichip modules. Such circuitry can further be a subcomponent of a variety of electronic systems, such as cameras, video recorders and players, televisions, displays, games, phones, clocks, personal computers, wireless devices, automobiles, aircrafts, industrial control systems, and others.
The memory may be realized as a memory device containing p-channel transistors with improved hole mobility and/or n-channel transistors with improved electron mobility, as disclosed herein. It will be understood that embodiments are equally applicable to any size and type of memory circuit and are not intended to be limited to a particular type of memory device. Memory types include a DRAM, SRAM (Static Random Access Memory) or Flash memories.
Additionally, the DRAM could be a synchronous DRAM commonly referred to as SGRAM (Synchronous Graphics Random Access Memory), SDRAM (Synchronous Dynamic Random Access Memory), SDRAM II, and DDR SDRAM (Double Data Rate SDRAM).
This disclosure includes several processes, circuit diagrams, and semiconductor structures. The present subject matter is not limited to a particular process order or logical arrangement. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiments shown. This application is intended to cover adaptations or variations of the present subject matter. It is to be understood that the above description is intended to be illustrative, and not restrictive. Combinations of the above embodiments, and other embodiments, will be apparent to those of skill in the art upon reviewing the above description. The scope of the present subject matter should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.
