With the increasingly more demanding requirement for more functionality and higher speed in integrated circuits, integrated circuit devices are increasingly down-scaled. This introduces the need of having new devices and more flexibility in the design and the manufacturing of integrated circuits.
Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Further, spatially relative terms, such as “underlying,” “below,” “lower,” “overlying,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.
A thin-film omega transistor and complementary transistors including a thin-film omega transistor and a Fin Field-Effect (FinFET) are provided. The methods of forming the same are provided. In accordance with some embodiments of the present disclosure, the thin-film omega transistor includes a fin-shaped gate, a gate dielectric on the top surface and the sidewalls of the fin-shaped gate, an oxide semiconductor layer over the gate dielectric to act as a channel, and a source region and a drain region over and contacting the oxide semiconductor layer. With the fin structures being adopted, the thin-film omega transistor has a high current. In addition, the thin-film omega transistor may form complementary devices with FinFETs. Embodiments discussed herein are to provide examples to enable making or using the subject matter of this disclosure, and a person having ordinary skill in the art will readily understand modifications that can be made while remaining within contemplated scopes of different embodiments. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements. Although method embodiments may be discussed as being performed in a particular order, other method embodiments may be performed in any logical order.
Gate fins 24 are formed on dielectric layer 22. In accordance with some embodiments, gate fins 24 are formed of a conductive material, which may be discussed in detail in subsequent paragraphs.
Gate dielectric 26 is formed on the sidewalls and the top surfaces of gate fins 24. Gate dielectric 26 is formed of a dielectric material, so that gate fins 24 are electrically insulated from the subsequently formed oxide semiconductor layer 28. In accordance with some embodiments, gate dielectric 26 comprises silicon oxide, silicon nitride, silicon oxynitride, a high-k dielectric material such as hafnium oxide, aluminum oxide, hafnium zirconium oxide (HfZrO2), combinations thereof, multi-layers thereof, or the like. In accordance with some embodiments, gate dielectric 26 is formed through deposition, and hence includes horizontal portions extending on the top surface of dielectric layer 22. In accordance with alternative embodiments, gate dielectric 26 is formed through an oxidation process, in which a surface layer of each of gate fins 24 are oxidized to form the gate dielectric 26. The corresponding gate dielectric 26 does not include horizontal portions extending on the top surface of dielectric layer 22.
Oxide semiconductor layer 28 is formed on gate dielectric 26. Oxide semiconductor layer 28 comprises an oxide, and includes two sidewall portions on the sidewall portions of gate dielectric 26, and top portions over the top surface portions of gate dielectric 26. Accordingly, oxide semiconductor layer 28 has an omega shape, and the resulting transistor is referred to as a thin-film omega transistor. Gate fins 24, gate dielectric 26, and oxide semiconductor layers 28 collectively form fin structures protruding higher than dielectric layer 22.
In accordance with some embodiments, the oxide semiconductor layer 28 is for forming an n-type transistor, which is turned on when a positive bias voltage is applied on gate fins 24 (relative to the voltage on the respective source region). The respective oxide semiconductor layer 28 may include indium (In). Since indium has 5s electron orbit, the resulting oxide is conductive. By mixing indium with other elements such as gallium, (Ga), zinc (Zn), tungsten (W), and/or the like, the conductivity of the resulting oxide may be adjusted to have semiconductor characteristic. In accordance with some embodiments when the resulting transistor is an n-type transistor, oxide semiconductor layer 28 may be formed of or comprise Indium Tin Oxide (ITO), Indium Oxide (InO), Indium Gallium Zinc Oxide (IGZO), Indium Zinc Oxide (IZO), Indium Tungsten Oxide (IWO), or the like, or combinations thereof,
In accordance with alternative embodiments, the oxide semiconductor layer 28 is for forming a p-type transistor, which is turned on when a negative bias voltage is applied on the gate (relative to the voltage on the respective source region). The respective oxide semiconductor layer 28 may also include an oxide such as NiO, CuO, Cr2O3, Co3O4, Mn3O4, or the like. The example n-type transistor and p-type transistor are shown as transistor 20N and 20P (
Thin-film omega transistor 20 further includes source/drain regions 60. Throughout the description, source/drain region(s) may refer to a source or a drain, individually or collectively dependent upon the context. Source/drain regions 60 may be in physical contact with oxide semiconductor layer 28, with no silicide layer in between. In accordance with some embodiments, source/drain regions 60 are formed of or comprise Ti, TiN, W, Al, Mo, Ni, or the like, or alloys thereof.
In accordance with some embodiments, FinFET 120 is formed based on semiconductor substrate 34. Shallow Trench Isolation (STI) regions 36 may be formed over a bulk portion of semiconductor substrate 34, with a semiconductor strip 38 being between STI regions 36. The top portion of semiconductor strip 38 may protrude higher than the top surfaces of STI regions 36 to form protruding semiconductor fin 40. Gate stack 46, which includes gate dielectric 42 and gate electrode 44, is formed on protruding semiconductor fin 40. The portions of protruding semiconductor fin 40 on the opposite sides of gate stack 46 may be replaced with an n-type semiconductor material to form the source/drain regions of an n-type transistor, or replaced with a p-type semiconductor material to form the source/drain regions of a p-type transistor. In accordance with some embodiments, FinFET 120 is formed using a front-end-of-line process. The formation of FinFET 120 may involve high temperatures, which may be higher than about 700° C.
Thin-film omega transistor 20 is formed over FinFET 120. In accordance with some embodiments, thin-film omega transistor 20 overlaps at least a part, or an entirety of, FinFET 120. This may reduce the routing distance between thin-film omega transistor 20 and FinFET 120 when they are electrically interconnected.
In accordance with some embodiments, the operation of thin-film omega transistor 20 is similar to the operation of FinFET 120. For example, when a positive voltage VGS is applied between gate fin 24 and the source region 60 of an n-type thin-film omega transistor 20, a conductive channel in oxide semiconductor layer 28 is turned on to electrically connect source region 60 to the corresponding drain region 60. Accordingly, current I1 flows between drain region 60 and source region 60. Conversely, when a voltage VGS lower than the threshold voltage of the n-type thin-film omega transistor 20 is applied between gate fin 24 and the source region 60, the channel in oxide semiconductor layer 28 is turned off to electrically disconnect source region 60 from the corresponding drain region 60. Conversely, for a p-type thin-film omega transistor 20, a negative voltage VGS turns on the channel, while a small negative voltage, zero voltage, or a positive voltage VGS turns off the channel.
It is appreciated that the processes shown in
After the formation of FinFET 120, some overlying features such as gate contact plugs, source/drain contact plugs, ILD(s), etch stop layer(s) may then be formed over FinFET 120. In accordance with some embodiments, the vertical space between thin-film omega transistor 20 and FinFET 120 may be filled with ILD(s), etch stop layer(s), and may or may not include IMDs, which may be low-k dielectric layers.
The process then turns to the process shown in
Referring to
In above-illustrated embodiments, gate fins 24 may be patterned by any suitable method. For example, the gate fins 24 may be patterned using one or more photolithography processes, including double-patterning or multi-patterning processes. Generally, double-patterning or multi-patterning processes combine photolithography and self-aligned processes, allowing patterns to be created that have, for example, pitches smaller than what is otherwise obtainable using a single, direct photolithography process. For example, in one embodiment, a sacrificial layer is formed over a substrate and patterned using a photolithography process. Spacers are formed alongside the patterned sacrificial layer using a self-aligned process. The sacrificial layer is then removed, and the remaining spacers, or mandrels, may then be used to pattern the fins.
The width W1 of gate fins 24 are selected to be not too big and not too small. If gate fins 24 are too wide, the usage of chip area is low, and the gate control of the fin will be poor. Conversely, if gate fins 24 are too narrow, gate fins 24 may collapse due to the significant height of gate fins 24. In accordance with some embodiments, the width W1 of gate fins 24 is in the range between about 5 nm and about 30 nm. The total count of gate fins 24 in a thin-film omega transistor may be in the range between 2 and 10 (while a single fin is also possible). It is realized that if a single gate fin 24 is adopted, there may be poor mobility. If too many gate fins 24 are adopted for one transistor, the chip area occupied by the corresponding device is too large. The height H1 of gate fins 24 may be in the range between about 20 nm and about 100 nm. The spacing S1 of gate fins 24 may be in the range between about 20 nm and about 120 nm.
Oxide semiconductor layer 28 may be formed through ALD, PVD, CVD, or the like. For example, when ALD is used to form IGZO, the precursor may include (3-dimethylaminopropyl)-dimethyl indium (DADI) as the indium precursor, diethylzinc (DEZ) as the zinc precursor, and trimethylgallium (TMGa) as the gallium precursor. O2 plasma may be used for introducing oxygen. The wafer temperature during the deposition of oxide semiconductor layer 28 may be in the range between about 180° C. and about 250° C.
The thickness T2 of oxide semiconductor layer 28 is selected to be in certain range, and oxide semiconductor layer 28 is not to be too thick or too thin. When oxide semiconductor layer 28 is too thick, the carrier concentration in oxide semiconductor layer 28 is too high, and may cause the threshold voltage of the respective transistor to be too low (such as having zero threshold voltage or even negative threshold voltage), which means the transistor may be always turned on. When oxide semiconductor layer 28 is too thin, the carrier concentration is too high, and the threshold voltage is too high. In accordance with some embodiments, the thickness T2 of oxide semiconductor layer 28 is in the range between about 2 nm and about 15 nm.
In accordance with some embodiments, oxide semiconductor layer 28 comprises a homogeneous oxide semiconductor material, which may be selected from an aforementioned material. In accordance with alternative embodiments, oxide semiconductor layer 28 may be a composite layer include two or more sub-layers, which are formed of materials different from each other. For example, oxide semiconductor layer 28 may include a lower sub-layer 28A and an upper sub-layer 28B over lower sub-layer 28A. Upper sub-layer 28B may have a higher conductivity value than the lower sub-layer 28A. The interface between sub-layers 28A and 28B are illustrated as being dashed to indicate that oxide semiconductor layer 28 may be formed of a homogeneous material or may include sub-layers. Lower sub-layer 28A and upper sub-layer 28B may both be oxide semiconductor layers forming using materials selected from the above-recited candidate groups of materials. For example, lower sub-layer 28A and upper sub-layer 28B may both be the indium-containing semiconductor layers, with the upper sub-layer 28B having a higher indium atomic percentage than the lower sub-layer 28A.
In accordance with some embodiments, upper sub-layer 28B comprises a high-concentration oxide semiconductor material, which have a higher carrier concentration than lower sub-layer 28A. Accordingly, upper sub-layer 28B may have a higher conductivity value than lower sub-layer 28A. With upper sub-layer 28B having a higher carrier concentration, the contact resistance between source/drain regions 60 and oxide semiconductor layer 28 may be reduced. The type (p-type or n-type) of lower sub-layer 28A is the same as that of upper sub-layer 28B. For example, when upper sub-layer 28B is for forming an n-type transistor, and may comprise ITO, InO, IGZO, IZO, IWO, or the like, or combinations thereof, lower sub-layer 28A may also be selected from any of ITO, InO, IGZO, IZO, IWO, or the like. When upper sub-layer 28B is for forming a p-type transistor, and may comprise ITO, InO, IGZO, IZO, IWO, or the like, or combinations thereof, lower sub-layer 28A may also be selected from any of NiO, CuO, Cr2O3, Co3O4, Mn3O4, or the like.
Lower sub-layer 28A and upper sub-layer 28B may include same elements with different percentages of the elements. For example, lower sub-layer 28A and upper sub-layer 28B may both be one of ITO, InO, IGZO, IZO, IWO, with the indium atomic percentage IC28B in upper layer 28B being higher than the atomic percentage IC28A in lower layer 28A. For example, the ratio of IC28A/IC28B may be higher than about 1.2, and may be in the range between about 1.2 and 2.0. The formation process may include deposit lower sub-layer 28A, and increase the flow rate of the indium-containing gas to deposit upper sub-layer 28B. Alternatively, one of lower sub-layer 28A and the upper sub-layer 28B may comprise an element (such as tin, gallium, zirconium, nickel, Cu, Cr, Co, and/or Mn) that is not in the other one of lower sub-layer 28A and the upper sub-layer 28B.
Next, source/drain openings 58 are formed by etching-through dielectric layer 56 and etch stop layer 54, with the etch stop layer 54 being used for stop etching of dielectric layer 56. The respective process is illustrated as process 212 in the process flow 200 as shown in
In accordance with some embodiments, source/drain regions 60 are formed of a homogeneous material, which may be the metallic material. In accordance with alternative embodiments, source/drain regions 60 are multi-layer regions including a plurality of sub-layers. For example,
In the operation of thin-film omega transistor 20, when a proper bias voltage VGS (higher than the threshold voltage) is applied, a channel 28C (
10A, 10B, 11A, 11B, 12A, 12B, 13A, 13B, 14A, 14B, 15A, and 15B illustrate the cross-sectional views of intermediate stages in the formation of a thin-film omega transistor 20 including a work-function layer in accordance with some embodiments. Unless specified otherwise, the materials and the formation processes of the components in these embodiments are essentially the same as the like components denoted by like reference numerals in the preceding embodiments. The details regarding the formation process and the materials of the components in these embodiments may thus be found in the discussion of the preceding embodiments. The processes are also shown in the process flow shown in
Referring to
Referring to
As shown in
The embodiments of the present disclosure have some advantageous features. By forming thin-film omega transistors having omega-shaped channel regions, the chip areas occupied by the corresponding transistors is increased, while the saturation currents of the transistors can still be increased. Thin-film omega transistors may be formed directly over front-end-of-line transistors such as FinFETs, so that the chip areas are further saved.
In accordance with some embodiments of the present disclosure, a method comprises forming a first thin-film omega transistor comprising forming a gate fin over a first dielectric layer; forming a first gate dielectric on sidewalls and a top surface of the gate fin; depositing a first oxide semiconductor layer over the first gate dielectric, wherein the gate fin, the first gate dielectric, and the first oxide semiconductor layer collectively form a fin structure; forming a source region contacting first sidewalls and a first top surface of a first portion of the first oxide semiconductor layer; and forming a drain region contacting second sidewalls and a second top surface of a second portion of the first oxide semiconductor layer.
In an embodiment, the method further comprises forming a FinFET on a semiconductor substrate, wherein the first dielectric layer is overlying the semiconductor substrate and the FinFET. In an embodiment, the first thin-film omega transistor overlaps the FinFET. In an embodiment, the first thin-film omega transistor and the FinFET are of opposite conductivity types, and the method further comprises electrically interconnecting the first thin-film omega transistor and the FinFET to form a complementary device. In an embodiment, each of the source region and the drain region comprises an additional oxide semiconductor layer; and a metallic layer on the additional oxide semiconductor layer. In an embodiment, the forming the source region and the drain region comprises forming a second dielectric layer on the fin structure; forming a source opening and a drain opening exposing the first portion and the second portion, respectively, of the first oxide semiconductor layer; depositing the additional oxide semiconductor layer extending into the source opening and the drain opening; and depositing the metallic layer on the additional oxide semiconductor layer.
In an embodiment, the additional oxide semiconductor layer has a higher conductivity value than the first oxide semiconductor layer. In an embodiment, both of the first oxide semiconductor layer and the additional oxide semiconductor layer comprise indium oxide, and wherein the additional oxide semiconductor layer has a higher indium atomic percentage than the first oxide semiconductor layer. In an embodiment, the method further comprises forming a second thin-film omega transistor immediately neighboring the first thin-film omega transistor, wherein the second thin-film omega transistor comprises a second gate dielectric and a second oxide semiconductor layer on the second gate dielectric, wherein the first thin-film omega transistor and the second thin-film omega transistor are discrete transistors electrically and signally disconnected from each other, and wherein the first oxide semiconductor layer and the second oxide semiconductor layer are portions of a continuous oxide semiconductor layer.
In an embodiment, the method further comprises forming a second thin-film omega transistor immediately neighboring the first thin-film omega transistor, wherein the second thin-film omega transistor comprises a second gate dielectric and a second oxide semiconductor layer, wherein the first thin-film omega transistor and the second thin-film omega transistor are discrete transistors electrically and signally disconnected from each other, and wherein the first oxide semiconductor layer and the second oxide semiconductor layer are separated from each other by an etch stop layer and an additional dielectric layer. In an embodiment, the first gate dielectric and the second gate dielectric are portions of a continuous dielectric layer.
In accordance with some embodiments of the present disclosure, a structure comprises a first dielectric layer; and a thin-film omega transistor comprising a gate fin over the first dielectric layer; a gate dielectric on sidewalls and a top surface of the gate fin; an oxide semiconductor layer over the gate dielectric; a source region contacting first sidewalls and a first top surface of a first portion of the oxide semiconductor layer; and a drain region contacting second sidewalls and a second top surface of a second portion of the oxide semiconductor layer; an etch stop layer over and contacting the oxide semiconductor layer; and a second dielectric layer over the etch stop layer, wherein the source region and the drain region are in the etch stop layer and the second dielectric layer. In an embodiment, the structure further comprises a FinFET on a semiconductor substrate, wherein the first dielectric layer is over the semiconductor substrate and FinFET, and wherein the thin-film omega transistor overlaps the FinFET.
In an embodiment, the thin-film omega transistor and the FinFET are of opposite conductivity types, and the structure further comprises metal lines and contact plugs electrically interconnecting the thin-film omega transistor and the FinFET to form a complementary device. In an embodiment, each of the source region and the drain region comprises an additional oxide semiconductor layer having a U-shaped cross-sectional-view shape; and a metallic layer between opposite sidewall portions of the additional oxide semiconductor layer. In an embodiment, the additional oxide semiconductor layer has a higher conductivity value than the oxide semiconductor layer. In an embodiment, both of the oxide semiconductor layer and the additional oxide semiconductor layer comprise indium oxide, and wherein the additional oxide semiconductor layer has a higher indium atomic percentage than the oxide semiconductor layer.
In accordance with some embodiments of the present disclosure, a structure comprises a first dielectric layer; a thin-film omega transistor comprising a conductive fin protruding higher than a top surface of the first dielectric layer; a gate dielectric on the conductive fin; an oxide semiconductor layer on the gate dielectric, wherein the oxide semiconductor layer has a substantially omega-shaped cross-sectional-view shape; a source region contacting a first portion of the oxide semiconductor layer; and a drain region contacting a second portion of the oxide semiconductor layer; and a dielectric layer over and contacting a third portion of the oxide semiconductor layer, wherein the third portion is between, and interconnects, the first portion and the second portion.
In an embodiment, the source region comprises an additional oxide semiconductor layer comprising a bottom portion over and contacting the oxide semiconductor layer; and sidewall portions over, and connecting to opposite ends of, the bottom portion; and a metallic region over the bottom portion and between the sidewall portions. In an embodiment, the oxide semiconductor layer comprises a first sub-layer having a first conductivity value; and a second sub-layer over the first sub-layer, wherein the second sub-layer has a second conductivity value higher than the first conductivity value.
The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.
This application claims the benefit of the following provisionally filed U.S. patent application: Application No. 63/364,831, filed on May 17, 2022, and entitled “Metal Oxide Thin Film Omega Transistor (TFOT) for CFET CMOS Application Integrated in BEOL,” which application is hereby incorporated herein by reference.
Number | Date | Country | |
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63364831 | May 2022 | US |