Etching method for forming grooves in Si-substrate and fin field-effect transistor

An etching method adapted to forming grooves in Si-substrate and FinFET transistor manufactured thereof are provided. The etching method includes providing a silicon substrate, at least two gate structures formed on the silicon substrate and at least two gate spacer structures disposed on the silicon substrate; performing a first etching process on the silicon substrate to form a first groove, which has a base and two inclined sidewalls, ascending to respective bottoms of the gate structures, and are interconnected with the base, respectively; and performing a second etching process on the silicon substrate at the base of the first groove, so as to form a second groove in an inverted -symbol shape, wherein the two inclined sidewalls of the first groove are interconnected with the second groove respectively, and the first etching process is substantially different from the second etching process.

FIELD OF THE INVENTION

The invention relates to an etching method and semiconductor device structure, and more particularly to an etching method adapted for forming grooves in Si-substrate and a fin field-effect transistor (FinFET) manufactured thereby.

BACKGROUND OF THE INVENTION

When employing semiconductor processes for manufacturing a fin field-effect transistor (FinFET), it is always essential to grow a superior silicon germanium epitaxial material layer in a silicon substrate. Besides, prior to the growth of the silicon germanium epitaxial layer, it is necessary to form grooves in the silicon substrate, and then grow the silicon germanium epitaxial layer in the grooves in the Si-substrate.

However, since there are distinct electrical requirements for various types of transistor devices, it thus becomes necessary to grow silicon germanium epitaxial material layers in various shapes and depths. Under the circumstances, it will become insufficient to form grooves in the Si-substrate by simply utilizing a single etching process. However, once several etching processes have been carried out, it will become impossible to retain the specific contours of grooves, since the pre-formed grooves will suffer from the problem of over-etching, resulted from the corrosion by subsequent etching processes.

In view of the aforementioned reasons, there is a need to provide an improved etching method and a fin field-effect transistor (FinFET) device structure with a polygonal silicon germanium epitaxial material layer for solving the above-mentioned problems.

SUMMARY OF THE INVENTION

Hence, according to the invention, an etching method for forming grooves in Si-substrate and a fin field-effect transistor (FinFET) as manufactured thereby are provided, so as to meet the distinct electrical requirements for various types of fin field-effect transistor (FinFET) devices, and improve the electrical performance of devices.

In order to achieve the above advantages and the others, according to the invention, an etching method adapted for forming grooves in Si-substrate is provided, that includes providing a silicon substrate, at least two gate structures being formed on the silicon substrate and at least two gate spacer structures being disposed on the silicon substrate; performing a first etching process on the silicon substrate so as to form a first groove, wherein the first groove has a base and two inclined sidewalls, which are ascending to respective bottoms of the gate structures, are interconnected with the base, respectively; and performing a second etching process on the silicon substrate at the base of the first groove so as to form a second groove in an inverted-symbol shape, wherein the two inclined sidewalls of the first groove are interconnected with the second groove, respectively, and the first etching process is substantially different from the second etching process.

Further, according to the invention, a fin field-effect transistor (FinFET) is provided, that comprises a silicon substrate; at least two gate structures disposed on the silicon substrate; at least two gate spacer structures; and a semiconductor structure. Here, the at least two gate spacer structures are disposed on the silicon substrate. Further, the semiconductor structure is embedded in the silicon substrate, and has an ascending portion and a portion in an inverted-symbol shape that is interconnected with the ascending portion, wherein the ascending portion ascends to respective bottoms of the gate structures. Preferably, the semiconductor structure further includes an arc-shaped portion that is interconnected with the portion in the inverted-symbol shape.

Furthermore, according to the invention, a fin field-effect transistor (FinFET) is provided, that comprises a silicon substrate; at least two gate structures disposed on the silicon substrate; at least two gate spacer structures; and a semiconductor structure. Here, the at least two gate spacer structures are disposed on the silicon substrate. Further, the semiconductor structure is embedded in the silicon substrate, and has an ascending portion and an arc-shaped portion that is interconnected with the ascending portion, wherein the ascending portion ascends to respective bottoms of the gate structures. Preferably, the semiconductor structure further includes a portion in an inverted-symbol shape that is interconnected with the arc-shaped portion.

In summary, according to the invention, several etching methods adapted for forming grooves in Si-substrate are provided, which involves utilizing dry etching and wet etching processes for forming first grooves with two ascending sidewalls to respective bottoms of the gate structures in advance, and further performing a surface oxidation process on the sidewalls of the grooves for forming a silicon oxide film adapted for preventing over-etching phenomenon, and sequentially carrying out a vertical-depression-formed dry etching process or a lateral-depression-formed dry etching process for forming subsequent second grooves or even third grooves, eventually the preparation of various of grooves in Si-substrate is accomplished. Moreover, silicon germanium epitaxial layers are so formed in the grooves in Si-substrate as to serve as an epitaxial drain structure or an epitaxial source structure in the fin field-effect transistor (FinFET). Accordingly, it is possible to meet distinct electrical requirements for various devices.

For making the above and other purposes, features and benefits become more readily apparent to those ordinarily skilled in the art, the preferred embodiments and the detailed descriptions with accompanying drawings are set forth in the following descriptions.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1A-1Fare cross-sectional views illustrating an etching method adapted for forming grooves in Si-substrate according to one embodiment of the invention. Firstly, by referring toFIGS. 1A-1Bas a whole, according to the one embodiment of the invention, the etching method adapted for forming grooves in Si-substrate includes providing a silicon substrate110, wherein the silicon substrate110has at least two gate structures120, and respective sidewalls of the gate structures120are encircled by a gate spacer structure122; performing a first etching process on the silicon substrate110for forming a first groove R1, wherein the first groove R1has a base Br1and two inclined sidewalls Sw interconnected with the base Br1, respectively, and the two inclined sidewalls Sw ascend to respective bottoms of the gate structures120. InFIG. 1A, the silicon substrate110is exemplified by three gate structures120disposed thereon, but it is not intended to limit the invention to such an example. Further, the first groove R1is formed in the silicon substrate110between the adjacent gate structures120.

It is notable that, the first etching process involves carrying out a dry etching process in advance, for removing a corresponding portion of the silicon substrate110so as to form the (partially-formed) first groove R1roughly. Then, a wet etching process is utilized for eliminating or removing the residues, and the wet etching is further carried out and the ascending inclined sidewalls Sw are thus created along crystallographic planes of the silicon substrate110to respective bottoms of the gate structure120, so as to form a (well-formed) first groove R1.

Again, by referring toFIGS. 1C-1Das a whole, after forming the first grooves R1, according to the one embodiment of the invention, the etching method adapted for forming grooves in Si-substrate further includes forming patterned protection layers in the first grooves R1, wherein the silicon substrate110at the base Br1of the first groove R1is exposed by the patterned protection layers, and the patterned protection layers are, for example, patterned silicon oxide films. Steps of forming the patterned silicon oxide films involve of carrying out a surface oxidation process on the exposed silicon substrate110in the first groove R1, so as to form a silicon oxide film130on surfaces of the exposed silicon substrate110in the first groove R1(as shown inFIG. 1C), and then, a breakthrough etching process is carried out for removing the silicon oxide film130at the base Br1, so that the silicon substrate110at the base Br1is exposed (as shown inFIG. 1D), eventually the preparation of patterned silicon oxide films is accomplished. Therefore, the patterned silicon oxide films merely consist of the silicon oxide films130formed on the ascending sidewalls Sw of the first grooves R1. The breakthrough etching process can utilize, for example, fluorine-containing plasma gas for removing the silicon oxide film130at the base Br1, wherein the fluorine-containing plasma gas is selected from the group consisting of carbon tetrafluoride (CF4), hexafluoroethane (C2F6), octafluorocyclobutane (C4F8) and a mixture thereof.

By referring toFIGS. 1E-1F, after removing the silicon oxide film130on the silicon substrate110at the base Br1, according to the one embodiment of the invention, the etching method adapted for forming grooves in Si-substrate further involves a second etching process performed on the base Br1of the first groove R1, so as to form a second groove R2in an inverted-symbol shape or in an U shape, wherein the inclined sidewalls Sw of the first groove R1interconnect with the second groove R2, respectively (as shown inFIG. 1E), and then, the wet etching process, for example, using the diluted hydrofluoric acid (DHF), is still employed for removing the silicon oxide films130disposed on the inclined sidewalls Sw, so as to accomplish the preparation of grooves in the Si-substrate. In the subsequent processes adapted for manufacturing fin field-effect transistor (FinFET) device, silicon germanium epitaxial layers are sequentially formed in the first and second grooves R1, R2including the grooves in the Si-substrate, so as to form an epitaxial drain structure or an epitaxial source structure. Moreover, it is notable that, the second etching process is substantially different from the first etching process. The second etching process adapted for forming the second grooves R2in the inverted-symbol shape or in the U shape is an anisotropic etching method, for example, a vertical-depression-formed dry etching process. In addition, a first plasma gas as employed therein is, for example, hydrogen bromide (HBr).

It is worthy to mention that, prior to performing the second etching process, a purpose of overlaying the sidewalls Sw of the first grooves R1with the silicon oxide films130, via performing the surface oxidation process on the silicon substrate110in the first groove R1, resides or results in that the silicon oxide film130is used to protect the sidewalls Sw of the first groove R1from being etched by the first plasma gas as employed in the vertical-depression-formed dry etching process, during the second etching process, so as to retain the contours of the sidewalls Sw of the first groove R1. Moreover, according to another embodiment, the patterned protection layer is, for example, a patterned polymer film. Therefore, a polymer film can be alternatively formed on the surface of the first groove R1, in replacement of (or in lieu of) forming the silicon oxide film via the surface oxidation process. Besides, once the polymer film on the base is removed, the preparation of the patterned polymer film will be accomplished. Then, the second etching process is subsequently carried out on the base of the silicon substrate, so as to form the second groove R2. The method for forming the polymer film involves, for example, in the use of difluoromethane (CH2F2) gas or trifluoromethane (CHF3) gas for depositing the polymer film.

FIGS. 2A-2Eare cross-sectional views illustrating an etching method adapted for forming grooves in Si-substrate according to another embodiment of the invention. After accomplishing the second groove R2in the inverted-symbol shape or in the U shape as shown inFIG. 1E, for example, it is still possible to sequentially perform etching processes on the silicon substrate at the base of the second groove R2, so that grooves configured in other shapes can be formed, via manufacturing processes set forth below. Firstly, preparing a device structure as shown inFIG. 1E, which is depicted inFIG. 2Aas well. Prior to accomplishing the device structure ofFIG. 2A, the previous processes are all the same as those ofFIGS. 1A-1D, and duplicated descriptions are thus omitted. As illustrated inFIG. 2A, the two inclined sidewalls Sw of the first groove R1are still overlaid with the silicon oxide films130. InFIG. 2A, the sidewalls Sw can be overlaid by the polymer film alternatively, in replacement of the silicon oxide film, and thus, it is not intended to limit the invention to such an example. Next, by referring toFIG. 2B, a patterned protection layer is formed in the second groove R2, wherein the base Br2of the second groove R2is exposed by the patterned protection layer. The patterned protection layer is, for example, a patterned silicon oxide film, and steps of forming the patterned silicon oxide film in the second groove R2involve performing a surface oxidation process on the exposed silicon substrate110in the second groove R2, so as to form a silicon oxide film132on the surface of the exposed silicon substrate110in the second groove R2(as shown inFIG. 2B). Next, a breakthrough etching process is carried out for removing the silicon oxide film132at the base Br2of the second groove R2, and the base Br2of the silicon substrate110is further exposed (as shown inFIG. 2C), eventually the preparation of the patterned silicon oxide film is accomplished. Next, a third etching process, for example, a lateral-depression-formed dry etching process, is carried out on the silicon substrate110at the base Br2, so as to form a third groove R3in a circular shape (as shown inFIG. 2D), wherein the third groove R3interconnects with the second groove R2, and the second groove R2interconnects with the first groove R1. Next, the wet etching process, for example, using the diluted hydrofluoric acid (DHF), is employed for removing the silicon oxide film130in the first groove R1and the silicon oxide film132in the second groove R2(as shown inFIG. 2E), so that eventually the preparation of grooves in Si-substrate is accomplished. The lateral-depression-formed dry etching process involves employing a second plasma gas for etching the silicon substrate110, wherein the second plasma gas, for example, is selected from the group consisting of hydrogen fluoride (HF), nitrogen trifluoride (NF3) and and chlorine gas (Cl2) and a mixture thereof. Moreover, after forming the third grooves, for example, depending on the process requirement, it is possible to sequentially etch the other grooves in a circular shape or in an inverted-symbol shape downwards; therefore, it is not intended to limit the invention to such an example. In the subsequent processes adapted for manufacturing fin field-effect transistor (FinFET) device, silicon germanium epitaxial layers are sequentially formed in the first, second and third grooves R1, R2, R3consisting of the grooves in Si-substrate, so as to form an epitaxial drain structure or an epitaxial source structure.

It is worthy to mention that, the patterned protection layer is, for example, a patterned polymer film. Therefore, it is also possible to form the polymer film on the surface of the exposed silicon substrate110in the second groove R2, in replacement of forming the silicon oxide film on the silicon substrate110in the second groove R2via carrying out the surface oxidation process thereon. Once the polymer film on the base Br2is removed, the preparation of the patterned polymer film is accomplished. Then, a third etching process is subsequently carried out on the silicon substrate110at the base Br2, so as to form a plurality of third grooves R3. Finally, the wet etching process is carried out for removing the silicon oxide film and the polymer film remaining on respective sidewalls of the grooves, and thus, the preparation of grooves in Si-substrate is accomplished. The method of forming the polymer film involves, for example, employing CH2F2gas or CHF3gas for depositing the polymer film.

FIGS. 3A-3Care cross-sectional views illustrating an etching method adapted for forming grooves in Si-substrate according to yet another embodiment of the invention. In theFIGS. 1A-1F, an etching method of forming grooves in Si-substrate is provided; those are composed of the first grooves R1with two ascending sidewalls Sw and the second grooves R2in an inverted-symbol shape or in a U shape. However, in this embodiment, an etching method of forming grooves in Si-substrate is provided, which are composed of the first grooves R1with two ascending sidewalls Sw and the second grooves R2in a circular shape, including preparing a device structure as illustrated inFIG. 1Dfirstly, which is depicted inFIG. 3Ain detail. Prior to accomplishing the structure ofFIG. 3A, the previous processes are all the same as those ofFIGS. 1A-1C, and duplicated descriptions are thus omitted. As illustrated inFIG. 3A, the two inclined sidewalls Sw of the first groove R1are still overlaid with the silicon oxide films130, and the silicon oxide films130at the base Br1has been removed. InFIG. 3A, the sidewalls Sw can be overlaid by the polymer film alternatively, in replacement of the silicon oxide film, and thus, it is not intended to limit the invention to such an example. Next, the second etching process, for example, a lateral-depression-formed dry etching process, is carried out on the silicon substrate110at the base Br1of the first groove R1, so as to form a second groove R2in a circular shape (as shown inFIG. 3B), and then, the wet etching process, for example, using the diluted hydrofluoric acid (DHF), is still employed for removing the silicon oxide films130disposed on the sidewalls Sw (as shown inFIG. 3C), so as to accomplish the preparation of grooves in Si-substrate. Here, the inclined sidewalls Sw of the first groove R1interconnect with the second groove R2respectively. The lateral-depression-formed dry etching process involves employing a second plasma gas for etching the silicon substrate110, wherein the second plasma gas, for example, is selected from the group consisting of hydrogen fluoride (HF), nitrogen trifluoride (NF3) and chlorine gas (Cl2) and a mixture thereof.

FIGS. 4A-4Eare cross-sectional views illustrating an etching method adapted for forming grooves in Si-substrate according to still yet another embodiment of the invention. After forming the second groove R2in the circular shape as illustrated inFIG. 3B, for example, it is possible to sequentially etch the grooves configured in other shapes downwards, and the manufacturing processes are set forth below. Firstly, preparing a device structure as illustrated inFIG. 3B, which is depicted inFIG. 4Ain detail. As illustrated inFIG. 4A, the two inclined sidewalls Sw of the first groove R1are still overlaid with the silicon oxide films130, and the second groove R2is in a circular shape. InFIG. 4A, the sidewalls Sw can be overlaid by a polymer film alternatively, in replacement of the silicon oxide film, and thus, it is not intended to limit the invention to such an example. Next, a patterned protection layer is formed in the second groove R2, wherein the base Br2of the second groove R2is exposed by the patterned protection layer. Here, the patterned protection layer is, for example, a patterned silicon oxide film, and steps of forming the patterned silicon oxide film in the second groove R2involve performing a surface oxidation process on the exposed silicon substrate110in the second groove R2, so as to form a silicon oxide film432on the surface of the exposed silicon substrate110in the second groove R2(as shown inFIG. 4B), and then, carrying out a breakthrough etching process for removing the silicon oxide film432at the base Br2of the second groove R2, so that the silicon substrate110at the base Br2is exposed (as shown inFIG. 4C), thus eventually the preparation of the patterned silicon oxide film is accomplished. Next, a third etching process, for example, a vertical-depression-formed dry etching process, is carried out on the silicon substrate110at the base Br2, so as to form a third groove R3in an inverted-symbol shape or in an U shape (as shown inFIG. 4D); and then, the wet etching process, for example, using the diluted hydrofluoric acid (DHF), is still employed for removing the silicon oxide film130disposed on the first groove R1and the silicon oxide film432in the second groove R2, so as to accomplish the preparation of grooves in Si-substrate (as shown inFIG. 4E). The first plasma gas as employed in the vertical-depression-formed dry etching process is, for example, hydrogen bromide (HBr). Moreover, after forming the third grooves R3, for example, depending on the process requirement, it is possible to sequentially etch the other grooves in a circular shape or in an inverted-symbol shape downwards, therefore, it is not intended to limit the invention to such an example. In the subsequent processes adapted for manufacturing fin field-effect transistor (FinFET) device, silicon germanium epitaxial layers are sequentially formed in the first, second and third grooves R1, R2, R3consisting of the grooves in Si-substrate, so as to form an epitaxial drain structure or an epitaxial source structure.

It is worthy to mention that, the patterned protection layer is, for example, a patterned polymer film. Therefore, in replacement of the step of performing the surface oxidation process on the silicon substrate110in the second groove R2for forming silicon oxide film, an alternative embodiment is to form a polymer film on the surface of exposed silicon substrate110in the second groove R2. The same descriptions of subsequent processes are thus omitted.

FIGS. 5A-5Care cross-sectional views illustrating an etching method adapted for forming grooves in Si-substrate according to still yet another embodiment of the invention. In theFIGS. 4A-4E, an etching method of forming grooves in Si-substrate is provided; which are composed of the first grooves R1with two ascending sidewalls Sw, the second grooves R2in a circular shape, and the third grooves in an inverted-symbol shape or in a U shape. However, in this embodiment, an etching method is provided, that is, after forming the second grooves in a circular shape, it is sequential to etch the third grooves in a circular shape downwards, that involves preparing a device structure as shown inFIG. 4Cfirstly, as depicted inFIG. 5Aas well. As illustrated inFIG. 5A, the two inclined sidewalls Sw of the first groove R1are still overlaid with the silicon oxide film130, and the sidewall of the second groove R2in the circular shape is still overlaid with the silicon oxide film432, and the silicon oxide film432at the base Br2of the second groove R2has been removed. Next, a third etching process, for example, a lateral-depression-formed dry etching process, is carried out on the silicon substrate110at the base Br2of the second groove R2, so as to form a third groove R3in a circular shape (as shown inFIG. 5B), and then, the wet etching process, for example, using the diluted hydrofluoric acid (DHF), is still employed for removing the silicon oxide films130disposed on the sidewalls Sw of the first groove R1and the silicon oxide film432on the sidewall of the second groove (as shown inFIG. 5C), so as to accomplish the preparation of grooves in Si-substrate. Moreover, after forming the third grooves, for example, it is possible to sequentially etch the other grooves in a circular shape or in an inverted-symbol shape downwards, therefore, it is not intended to limit the invention to such an example.

FIG. 6is a schematic diagram depicting fin field-effect transistor (FinFET) according to another embodiment of the invention. By referring toFIG. 6, a fin field-effect transistor (FinFET)600comprises a silicon substrate610, at least two gate structures620disposed on the silicon substrate610, at least two gate spacer structures622, and a semiconductor structure630. As illustrated inFIG. 6, it is exemplified by three gate structures620and three gate spacer structures622; however, it is not intended to limit the invention to such an example. Each of the gate spacer structures622is disposed on the silicon substrate610, and encircles respective sidewalls of the gate structures620. The semiconductor structure630is embedded in the silicon substrate610, and the semiconductor structure630has a plurality of ascending portions632and a first U-shaped portion634interconnected with the ascending portions632, wherein the ascending portions632ascend to the bottoms of the neighboring gate structures620. A material made up of the semiconductor structure630is, for example, a silicon germanium epitaxial material, and the semiconductor structure630, for example, function as an epitaxial drain structure or an epitaxial source structure in the fin field-effect transistor (FinFET).

Moreover, It is worthy to mention that, depending on the process requirement or electrical requirement for device, according to the invention, the semiconductor structure in the fin field-effect transistor (FinFET), which is provided with the structure composed of the ascending portions632and the first U-shaped portion634as shown inFIG. 6, can be substituted with, for example, a semiconductor structure730as shown inFIG. 7, which has the ascending portions632and a first circular portion734, in place of the semiconductor structure630. Alternatively, the semiconductor structure630can be substituted by a semiconductor structure830as shown inFIG. 8, which has the ascending portions632, a first U-shaped portion634and a second circular portion836. Alternatively, the semiconductor structure630can be substituted with a semiconductor structure930as shown inFIG. 9, which has the ascending portions632, the first circular portion734, and a second circular portion936. Alternatively, the semiconductor structure630can be substituted by a semiconductor structure932as shown inFIG. 10, which has the ascending portions632, the first circular portion734, and a second U-shaped portion636.

According to the another embodiment of the invention, the device structure as illustrated inFIG. 6is prepared by forming grooves in Si-substrate via the etching method as shown inFIGS. 1A-1Fin advance, and then growing the silicon germanium epitaxial layer in the grooves in Si-substrate. The device structure as illustrated inFIG. 7is prepared by forming grooves in Si-substrate via the etching method as shown inFIGS. 3A-3Cin advance, and then growing the silicon germanium epitaxial layer in the grooves in Si-substrate. The device structure as illustrated inFIG. 8is prepared by forming grooves in Si-substrate via the etching method as shown inFIGS. 2A-2Ein advance, and then growing the silicon germanium epitaxial layer in the grooves in Si-substrate. The device structure as illustrated inFIG. 9is prepared by forming grooves in Si-substrate via the etching method as shown inFIGS. 4A-4Ein advance, and then growing the silicon germanium epitaxial layer in the grooves in Si-substrate. The device structure as illustrated inFIG. 10is prepared by forming grooves in Si-substrate via the etching method as shown inFIGS. 5A-5Cin advance, and then growing the silicon germanium epitaxial layer in the grooves in Si-substrate.

In summary, according to various embodiments of the invention, several etching methods for grooves in Si-substrate are provided, which involve forming the first grooves those have two ascending sidewalls to the bottom of gate structures by employing dry etching and wet etching processes in advance, next, performing surface oxidation processes on the sidewalls of the grooves for forming a silicon oxide film, in order to avoid an over-etching phenomenon, and then, performing a vertical-depression-formed dry etching process or a lateral-depression-formed dry etching process for forming a second groove and even a third groove subsequently, eventually the preparation of a various types of grooves in Si-substrate can be accomplished. Besides, the silicon germanium epitaxial layer is so grown in the grooves in Si-substrate as to serve as an epitaxial drain structure or an epitaxial source structure in the fin field-effect transistor (FinFET). Accordingly, it is possible to meet distinct electrical requirements for various devices.