SEMICONDUCTOR DEVICE AND MANUFACTURING METHOD THEREOF

A semiconductor device and its manufacturing method are provided. The semiconductor device includes a substrate, an oxygen-containing protrusive structure disposed above the substrate, a metal oxide layer, a gate dielectric layer disposed on the metal oxide layer, and a gate disposed on the gate dielectric layer. The oxygen-containing protrusive structure has a first surface, a second surface opposite to the first surface, and sidewalls connected to the first and second surfaces. The metal oxide layer includes first, second, and third portions. The first portion covers the first surface. The second portion is connected to the first portion and covers the sidewalls of the oxygen-containing protrusive structure. A resistivity of the second portion gradually decreases away from the first portion. The third portion is connected to the second portion and extends from the sidewalls of the oxygen-containing protrusive structure in a direction away from the oxygen-containing protrusive structure.

BACKGROUND

Technical Field

The disclosure relates to a semiconductor device and a manufacturing method thereof; more particularly, the disclosure relates to a semiconductor device including an oxygen-containing protrusive structure and a manufacturing method thereof.

Description of Related Art

Generally, a semiconductor layer of a thin film transistor (TFT) may be divided into a channel region and a doped region. If a carrier concentration of the doped region is high, and if a carrier concentration between the doped region and the channel region is suddenly dropped, a large lateral electric field may be accordingly generated near a drain of the TFT during an operation under a large current, and degradation of the semiconductor device may be induced. However, if the carrier concentration of the doped region is reduced to prevent said degradation of the semiconductor device, an operating current of the semiconductor device may be insufficient. Therefore, how to reduce the lateral electric field near the drain of the semiconductor device while maintaining sufficient operating current is an issue to be solved at present.

SUMMARY

The disclosure provides a semiconductor device and a manufacturing method thereof which may reduce a lateral electric field near a drain, so as to improve reliability of the semiconductor device.

In an embodiment of the disclosure, a semiconductor device that includes a substrate, an oxygen-containing protrusive structure, a metal oxide layer, a gate dielectric layer, and a first gate is provided. The oxygen-containing protrusive structure is disposed above the substrate. The oxygen-containing protrusive structure has a first surface, a second surface opposite to the first surface, and a plurality of sidewalls connected to the first surface and the second surface. The metal oxide layer includes a first portion, a second portion, and a third portion. The first portion covers the first surface of the oxygen-containing protrusive structure. The second portion is connected to the first portion and covers the sidewalls of the oxygen-containing protrusive structure. A resistivity of the second portion gradually decreases away from the first portion. The third portion is connected to the second portion and extends from the sidewalls of the oxygen-containing protrusive structure in a direction away from the oxygen-containing protrusive structure. The gate dielectric layer is disposed on the metal oxide layer. The first gate is disposed on the gate dielectric layer.

In an embodiment of the disclosure, a manufacturing method of a semiconductor device includes following steps. A substrate is provided. An oxygen-containing protrusive structure is formed above the substrate, where the oxygen-containing protrusive structure has a first surface, a second surface opposite to the first surface, and a plurality of sidewalls connected to the first surface and the second surface. A metal oxide layer is formed on the oxygen-containing protrusive structure, where the metal oxide layer includes a first portion, a second portion, and a third portion. The first portion covers the first surface of the oxygen-containing protrusive structure. The second portion is connected to the first portion and covers the sidewalls of the oxygen-containing protrusive structure. The third portion is connected to the second portion and extends from the sidewalls of the oxygen-containing protrusive structure in a direction away from the oxygen-containing protrusive structure. A gate dielectric layer is formed on the metal oxide layer. A first gate is formed on the gate dielectric layer, where the first gate is overlapped with the metal oxide layer in a normal direction of a top surface of the substrate. A doping process is performed on the metal oxide layer to reduce a resistivity of the third portion of the metal oxide layer and gradually decrease a resistivity of the second portion of the metal oxide layer away from the first portion.

DESCRIPTION OF THE EMBODIMENTS

Reference is now made in detail to exemplary embodiments of the disclosure, and examples of the exemplary embodiments are described in the accompanying drawings. Whenever possible, the same reference numbers are used in the drawings and descriptions to indicate the same or similar parts.

FIG.1is a schematic cross-sectional view of a semiconductor device according to an embodiment of the disclosure.

With reference toFIG.1, a semiconductor device1includes a substrate100, an oxygen-containing protrusive structure122, a metal oxide layer130, a gate dielectric layer140, and a first gate150. In this embodiment, the semiconductor device1further includes a buffer layer110, an interlayer dielectric layer160, a source172, and a drain174.

A material of the substrate100may include glass, quartz, organic polymer, or an opaque/reflective material (e.g., a conductive material, metal, wafer, ceramics, or other applicable materials), or other applicable materials. If the conductive material or the metal is used, the substrate100is covered by an insulation layer (not shown) to prevent short circuits. In some embodiments, the substrate100is a flexible substrate, and the material of the substrate100is, for instance, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyester (PES), polymethylmethacrylate (PMMA), polycarbonate (PC), polyimide (PI), metal foil, or other flexible materials. The buffer layer110is located on the substrate100, and a material of the buffer layer110may include aluminum oxide, silicon nitride oxide (SiNO), silicon nitride, or other insulation materials, which should however not be construed as a limitation in the disclosure.

The oxygen-containing protrusive structure122is disposed above the substrate100and the buffer layer110; that is, the buffer layer110is disposed between the substrate100and the oxygen-containing protrusive structure122. The oxygen-containing protrusive structure122has a first surface122a, a second surface122bopposite to the first surface122a, and a plurality of sidewalls122cconnected to the first surface122aand the second surface122b. For instance, in this embodiment, the oxygen-containing protrusive structure122is a trapezoidal structure, the second surface122bfaces a surface of the buffer layer110, an area occupied by the first surface122ais smaller than an area occupied by the second surface122b, and the sidewalls122care connected to the first surface122aand the second surface122bto form an inclined surface. Therefore, at the sidewalls122cof the oxygen-containing protrusive structure122, a thickness of the oxygen-containing protrusive structure122gradually decreases from the center to the edge. A material of the oxygen-containing protrusive structure122may include silicon oxide, SiNO, or other appropriate oxygen-containing insulation materials. In some embodiments, an oxygen concentration of the oxygen-containing protrusive structure122is higher than an oxygen concentration of the buffer layer110. For instance, when the material of the oxygen-containing protrusive structure122includes silicon oxide, and the material of the buffer layer110includes silicon nitride or SiNO, the oxygen concentration of the buffer layer110is lower than the oxygen concentration of the oxygen-containing protrusive structure122. Alternatively, when the materials of the buffer layer110and the oxygen-containing protrusive structure122are both SiNO, the oxygen concentration of the buffer layer110is lower than the oxygen concentration of the oxygen-containing protrusive structure122. In some embodiments, when the material of the buffer layer110includes silicon nitride or SiNO, the oxygen-containing protrusive structure122and the buffer layer110contain hydrogen atoms, and a hydrogen concentration of the buffer layer110is higher than a hydrogen concentration of the oxygen-containing protrusive structure122.

The metal oxide layer130is located on the oxygen-containing protrusive structure122and the buffer layer110. For instance, the metal oxide layer130includes a first portion132, a second portion134, and a third portion136. The first portion132covers the first surface122aof the oxygen-containing protrusive structure122. The second portion134is connected to the first portion132and covers the sidewalls122cof the oxygen-containing protrusive structure122. The third portion136is connected to the second portion134and extends from the sidewalls122cof the oxygen-containing protrusive structure122in a direction away from the oxygen-containing protrusive structure122. In some embodiments, a material of the metal oxide layer130includes quaternary metal compounds, such as indium gallium zinc oxide (IGZO), indium tin zinc oxide (ITZO), aluminum zinc tin oxide (AZTO), indium tungsten zinc oxide (IWZO), and so forth, or includes oxides composed of any three of the following ternary metals: gallium (Ga), zinc (Zn), indium (In), tin (Sn), aluminum (Al), and tungsten (W).

The gate dielectric layer140is disposed on the metal oxide layer130and the buffer layer110, and the first gate150is disposed on the gate dielectric layer140. The first gate150is overlapped with the first portion132in a normal direction ND of a top surface of the substrate100but is not overlapped with the second portion134nor the third portion136. In other words, the first portion132of the metal oxide layer130may constitute a channel region ch, and the second portion134and the third portion136may constitute a doped region dp. In some embodiments, the second portion134may constitute a lightly doped region ldp, and the third portion136may constitute a heavily doped region hdp.

The oxygen-containing protrusive structure122may provide an oxygen element to the metal oxide layer130in the manufacturing process. The larger the thickness of the oxygen-containing protrusive structure122is, the more oxygen the oxygen-containing protrusive structure may provide to the metal oxide layer130; the smaller the thickness of the oxygen-containing protrusive structure122is, the less oxygen the oxygen-containing protrusive structure may provide. The higher the oxygen concentration of the metal oxide layer130, the higher the resistivity of the metal oxide layer130. On the contrary, the lower the oxygen concentration of the metal oxide layer130, the lower the resistivity of the metal oxide layer130. In other words, the thickness of the oxygen-containing protrusive structure122affects the oxygen concentration of the metal oxide layer130and further poses an impact on its resistivity. For instance, the first portion132of the metal oxide layer130covers a central portion of the oxygen-containing protrusive structure122of a relatively large thickness, and most of the second portion134of the metal oxide layer130covers an edge portion of the oxygen-containing protrusive structure122of a gradually reduced thickness. Therefore, the oxygen concentration of the first portion132is higher than the oxygen concentration of the second portion134, and the resistivity of the first portion132is higher than the resistivity of the second portion134. Since the thickness of the edge portion of the oxygen-containing protrusive structure122covered by the second portion134gradually decreases in a direction away from the first portion132, the oxygen concentration of the second portion134also gradually decreases in the direction away from the first portion132, so that the resistivity of the second portion134gradually decreases away from the first portion132. As such, the issue of a lateral electric field generated due to a sudden change to the resistivity of the metal oxide layer130may be solved to a great extent by arranging the second portion134, thereby improving the reliability of the semiconductor device1.

In this embodiment, since a width L1 of the first gate150is slightly smaller than a width of the first surface122aof the oxygen-containing protrusive structure122, the second portion134in the doped region dp partially covers a part of the first surface122aof the oxygen-containing protrusive structure122, which should however not be construed as a limitation in the disclosure. In other embodiments, since the width L1 of the first gate150is slightly larger than or equal to the width of the first surface122aof the oxygen-containing protrusive structure122, the second portion134in the doped region dp does not cover the first surface122aof the oxygen-containing protrusive structure122.

The third portion136of the metal oxide layer130is not in contact with the oxygen-containing protrusive structure122, and therefore the third portion136has a lower oxygen concentration than that of the first portion132and that of the second portion134. That is, the resistivity of the first portion132and the resistivity of the second portion134are both higher than the resistivity of the third portion136.

The interlayer dielectric layer160is disposed on the gate dielectric layer140and covers the first gate150. A material of the interlayer dielectric layer160and the gate dielectric layer140includes, for instance, silicon oxide, silicon nitride, SiNO, or other appropriate materials. The source172and the drain174are located on the interlayer dielectric layer160and penetrate the interlayer dielectric layer160and the gate dielectric layer140, so as to be electrically connected to the third portion136of the metal oxide layer130. Since the resistivity of the third portion136is smaller than the resistivity of the second portion134, an interface resistance between the source172and the third portion136and an interface resistance between the drain174and the third portion136may be reduced, thereby increasing an operating current of the semiconductor device1.

For the purpose of clarity, inFIG.1, a clear boundary line is illustrated between the first portion132and the second portion134and between the second portion134and the third portion136of the metal oxide layer130, but it should be understood that these boundary lines are only provided for explanation. In the actual structure, there may be no such clear boundary lines because of the gradual changes between the first portion132and the second portion134and between the second portion134and the third portion136.

FIG.2AtoFIG.2Eare schematic cross-sectional flowcharts of a manufacturing process of the semiconductor device depicted inFIG.1.

With reference toFIG.2A, a substrate100is provided, a buffer layer110is formed on the substrate100, and an oxygen-containing material layer120is deposited on the substrate100and the buffer layer110.

With reference toFIG.2B, the oxygen-containing material layer120is patterned by performing a dry etching process or a wet etching process to expose a partial surface of the buffer layer110, whereby an oxygen-containing protrusive structure122is formed. The oxygen-containing protrusive structure122is, for instance, a trapezoidal structure and has a first surface122a, a second surface122bopposite to the first surface122a, and a plurality of sidewalls122cconnected to the first surface122aand the second surface122b.

With reference toFIG.2C, a metal oxide layer130′ is conformally formed on the oxygen-containing protrusive structure122and the buffer layer110. The metal oxide layer130′ may include a first portion132, a second portion134, and a third portion136. The first portion132covers the first surface122aof the oxygen-containing protrusive structure122. The second portion134is connected to the first portion132and covers the sidewalls122cof the oxygen-containing protrusive structure122. The third portion136is connected to the second portion134and extends from the sidewalls122cof the oxygen-containing protrusive structure122in a direction away from the oxygen-containing protrusive structure122.

With reference toFIG.2D, a gate dielectric layer140is formed on the metal oxide layer130′, and a first gate150is formed on the gate dielectric layer140, where the first gate150is overlapped with the metal oxide layer130′ in a normal direction ND of a top surface of the substrate100. For instance, the first gate150may be overlapped with the first portion132in the normal direction ND of the top surface of the substrate100.

In some embodiments, before the gate dielectric layer140and the first gate150are formed, an annealing process may be performed on the metal oxide layer130′ or the gate dielectric layer140to adjust an oxygen distribution in the metal oxide layer130′ by the oxygen-containing protrusive structure122. For instance, the first portion132and the second portion134of the metal oxide layer130′ are located on the oxygen-containing protrusive structure122, and thus the oxygen-containing protrusive structure122may provide oxygen to the first portion132and the second portion134in the annealing process; the third portion136is not formed on the oxygen-containing protrusive structure122, and thus the oxygen in the third portion136may be easily dissipated, so that the oxygen concentration of the third portion136is lower than the oxygen concentration of the first portion132and the oxygen concentration of the second portion134. In other embodiments, the annealing process is performed on the metal oxide layer130′ or the gate dielectric layer140after the gate dielectric layer140is formed and before the first gate150is formed to adjust the oxygen distribution in the metal oxide layer130′ by the oxygen-containing protrusive structure122. For instance, the oxygen-containing protrusive structure122may provide oxygen to the first portion132and the second portion134in the annealing process, so as to increase the oxygen concentration of the first portion132and the oxygen concentration of the second portion134, which allows the oxygen concentration of the first portion132and the oxygen concentration of the second portion134to be higher than the oxygen concentration of the third portion136.

With reference toFIG.2D, a doping process P is performed on the metal oxide layer130to reduce the resistivity of the third portion136of the metal oxide layer130and gradually decrease the resistivity of the second portion134of the metal oxide layer130away from the first portion132. For instance, a hydrogen plasma process is performed on the metal oxide layer130by applying the first gate150as a mask, so that the second portion134and the third portion136that are not overlapped with the first gate150in the normal direction ND of the top surface of the substrate100constitute a doped region dp, and the first portion132overlapped with the first gate150in the normal direction ND of the top surface of the substrate100constitutes a channel region ch. In some embodiments, the second portion134may constitute a lightly doped region ldp, and the third portion136may constitute a heavily doped region hdp. In some embodiments, a width L2 of the oxygen-containing protrusive structure122may be larger than a width L1 of the first gate150, which is conducive to an increase in the distance between the first portion132and the third portion136.

During the hydrogen plasma process, the oxygen in the metal oxide layer130may react with hydrogen to create oxygen vacancies in the metal oxide layer130, thereby reducing the resistivity of the metal oxide layer130. Besides, the thickness of the oxygen-containing protrusive structure122covered by the second portion134gradually decreases, and the third portion136is not in contact with the oxygen-containing protrusive structure122; therefore, the oxygen concentration of the second portion134gradually decreases in the direction away from the first portion132, and the oxygen concentration of the second portion134is higher than the oxygen concentration of the third portion136. As a result, after the hydrogen plasma process, the resistivity of the second portion134may gradually decrease from the first portion132, and the resistivity of the second portion134is higher than the resistivity of the third portion136.

With reference toFIG.2E, an interlayer dielectric layer160is formed on the gate dielectric layer140and covers the first gate150. After that, openings O1 and O2 penetrating the interlayer dielectric layer160and the gate dielectric layer140are formed, and the openings O1 and O2 are respectively overlapped with the third portion136in the normal direction ND of the top surface of the substrate100.

After that, with reference toFIG.1, a source172and a drain174are formed on the interlayer dielectric layer150and fill the openings O1 and O2, so as to be electrically connected to the metal oxide layer130.

After the above process, the fabrication of the semiconductor device1is substantially completed.

FIG.3is a schematic cross-sectional view of a semiconductor device according to another embodiment of the disclosure. Note that the reference numbers and some contents provided in the embodiment depicted inFIG.1are used in the embodiment depicted inFIG.3, where the same or similar numbers are applied to denote the same or similar elements, and the description of the same technical content is omitted. The description of the omitted content may be found in the previous embodiment and will not be provided hereinafter.

With reference toFIG.3, the main difference between a semiconductor device2shown inFIG.3and the semiconductor device1shown inFIG.1lies in that the semiconductor device2further includes an extension structure124. The extension structure124is located between the third portion136of the metal oxide layer130and the substrate100and is connected to the oxygen-containing protrusive structure122integrally, and a thickness T1 of the oxygen-containing protrusive structure122between the first surface122aand the second surface122bis larger than a thickness T2 of the extension structure124. A material of the extension structure124is the same as the material of the oxygen-containing protrusive structure122. The thickness of the oxygen-containing protrusive structure122gradually decreases with proximity to the edge, and the thickness T1 of the oxygen-containing protrusive structure122between the first surface122aand the second surface122bis larger than the thickness T2 of the extension structure124; hence, the oxygen concentration of the first portion132is higher than the oxygen concentration of the second portion134, and the oxygen concentration of the second portion134is higher than the oxygen concentration of the third portion136. Thereby, the resistivity of the first portion132is higher than the resistivity of the second portion134, and the resistivity of the second portion134is higher than the resistivity of the third portion136. In addition, since the thickness of a part of the oxygen-containing protrusive structure122covered by the second portion134gradually decreases with proximity to the edge, the oxygen concentration of the second portion134gradually decreases in the direction away from the first portion132, so that the resistivity of the second portion134gradually decreases in the direction away from the first portion134. As such, the issue of a lateral electric field generated due to a sudden change to the resistivity of the metal oxide layer130may be solved to a great extent by arranging the second portion134, thereby improving the reliability of the semiconductor device2. Besides, since the resistivity of the third portion136is smaller than the resistivity of the second portion134, the interface resistance between the source172and the third portion136and the interface resistance between the drain174and the third portion136may be reduced, thereby increasing an operating current of the semiconductor device2.

FIG.4AtoFIG.4Dare schematic cross-sectional flowcharts of a manufacturing process of the semiconductor device depicted inFIG.3. Here,FIG.4AtoFIG.4Dmay be considered as schematic cross-sectional views of the manufacturing method of the semiconductor device following the steps depicted inFIG.2A. The description of the steps inFIG.2Amay be found in the previous embodiment and will not be provided hereinafter.

With reference toFIG.4A, an oxygen-containing material layer120is patterned by performing a dry etching process or a wet etching process, so as to remove a part of the oxygen-containing material layer120without exposing the surface of a buffer layer110covered by the oxygen-containing material layer120, so as to form an oxygen-containing structure122and an extension structure124. The oxygen-containing protrusive structure122is, for instance, a trapezoidal structure and has a first surface122a, a second surface122bopposite to the first surface122a, and a plurality of sidewalls122cconnected to the first surface122aand the second surface122b. The extension structure124is integrally connected to the oxygen-containing protrusive structure122, and a thickness T1 of the oxygen-containing protrusive structure122between the first surface122aand the second surface122bis larger than a thickness T2 of the extension structure124.

With reference toFIG.4B, a metal oxide layer130′ is conformally formed on the oxygen-containing protrusive structure122and an extension structure124. The metal oxide layer130′ may include a first portion132, a second portion134, and a third portion136. The first portion132covers the first surface122aof the oxygen-containing protrusive structure122. The second portion134is connected to the first portion132and covers the sidewalls122cof the oxygen-containing protrusive structure122. The third portion136is connected to the second portion134and extends from the sidewalls122cof the oxygen-containing protrusive structure122in a direction away from the oxygen-containing protrusive structure122. The extension structure124is located between the third portion136and the buffer layer110.

With reference toFIG.4C, a gate dielectric layer140is formed on the metal oxide layer130′, and a first gate150is formed on the gate dielectric layer140, where the first gate150is overlapped with the metal oxide layer130′ in a normal direction ND of a top surface of the substrate100. For instance, the first gate150may be overlapped with the first portion132in the normal direction ND of the top surface of the substrate100.

In some embodiments, before the gate dielectric layer140and the first gate150are formed, an annealing process may be performed on the metal oxide layer130′ or the gate dielectric layer140to adjust an oxygen distribution in the metal oxide layer130′ by the oxygen-containing protrusive structure122. In other embodiments, the annealing process is performed on the metal oxide layer130′ or the gate dielectric layer140after the gate dielectric layer140is formed and before the first gate150is formed to adjust the oxygen distribution in the metal oxide layer130′ by the oxygen-containing protrusive structure122.

With reference toFIG.4C, a doping process P is performed on the metal oxide layer130to reduce the resistivity of the third portion136of the metal oxide layer130and gradually decrease the resistivity of the second portion134of the metal oxide layer130away from the first portion132. For instance, a hydrogen plasma process is performed on the metal oxide layer130by applying the first gate150as a mask, so that the second portion134and the third portion136that are not overlapped with the first gate150in the normal direction ND of the top surface of the substrate100constitute a doped region dp, and the first portion132overlapped with the first gate150in the normal direction ND of the top surface of the substrate100constitutes a channel region ch. In some embodiments, the second portion134may constitute a lightly doped region ldp, and the third portion136may constitute a heavily doped region hdp. In some embodiments, a width L2 of the oxygen-containing protrusive structure122may be larger than a width L1 of the first gate150, which is conducive to an increase in the distance between the first portion132and the third portion136.

After the hydrogen plasma process, the resistivity of the second portion134may gradually decrease away from the first portion132, and the resistivity of the second portion134is higher than the resistivity of the third portion136.

With reference toFIG.4D, an interlayer dielectric layer160is formed on the gate dielectric layer140and covers the first gate150. After that, openings O1 and O2 penetrating the interlayer dielectric layer160and the gate dielectric layer140are formed, and the openings O1 and O2 are respectively overlapped with the third portion136in the normal direction ND of the top surface of the substrate100.

After that, with reference toFIG.3, a source172and a drain174are formed on the interlayer dielectric layer150and fill the openings O1 and O2, so as to be electrically connected to the metal oxide layer130.

After the above process, the fabrication of the semiconductor device2is substantially completed.

FIG.5is a schematic cross-sectional view of a semiconductor device according to still another embodiment of the disclosure. Note that the reference numbers and some contents provided in the embodiment depicted inFIG.1are used in the embodiment depicted inFIG.5, where the same or similar numbers are applied to denote the same or similar elements, and the description of the same technical content is omitted. The description of the omitted content may be found in the previous embodiment and will not be provided hereinafter.

With reference toFIG.5, the main difference between a semiconductor device3shown inFIG.5and the semiconductor device1shown inFIG.1lies in that the semiconductor device3further includes a second gate180which may be disposed between the substrate100and the oxygen-containing protrusive structure122. For instance, the second gate180is disposed between the substrate100and the buffer layer110. That is, the semiconductor device3is a dual-gate transistor, and thus the performance and the stability of the semiconductor device3may be improved. A width L3 of the second gate180may be larger than the width L2 of the oxygen-containing protrusive structure122, so as to separate the electric field between the gate and the drain in the semiconductor device3, thereby improving the reliability of the semiconductor device3.

FIG.6AtoFIG.6Dare schematic cross-sectional flowcharts of a manufacturing process of the semiconductor device depicted inFIG.5.

With reference toFIG.6A, a substrate100is provided, a second gate180is formed on the substrate100, and a buffer layer110is formed on the second gate180and the substrate100and covers the second gate180.

With reference toFIG.6B, an oxygen-containing protrusive structure122is formed on the buffer layer110. The oxygen-containing protrusive structure122is, for instance, a trapezoidal structure and has a first surface122a, a second surface122bopposite to the first surface122a, and a plurality of sidewalls122cconnected to the first surface122aand the second surface122b. After that, a metal oxide layer130′ is conformally formed on the oxygen-containing protrusive structure122and the buffer layer110. The metal oxide layer130′ may include a first portion132, a second portion134, and a third portion136. The first portion132covers the first surface122aof the oxygen-containing protrusive structure122. The second portion134is connected to the first portion132and covers the sidewalls122cof the oxygen-containing protrusive structure122. The third portion136is connected to the second portion134and extends from the sidewalls122cof the oxygen-containing protrusive structure122in a direction away from the oxygen-containing protrusive structure122. In an embodiment, the width L3 of the second gate180may be larger than the width L2 of the oxygen-containing protrusive structure122.

With reference toFIG.6C, a gate dielectric layer140is formed on the metal oxide layer130′, and a first gate150is formed on the gate dielectric layer140, where the first gate150is overlapped with the metal oxide layer130′ in a normal direction ND of a top surface of the substrate100. For instance, the first gate150may be overlapped with the first portion132in the normal direction ND of the top surface of the substrate100.

In some embodiments, before the gate dielectric layer140and the first gate150are formed, an annealing process may be performed on the metal oxide layer130′ or the gate dielectric layer140to adjust an oxygen distribution in the metal oxide layer130′ by the oxygen-containing protrusive structure122. In other embodiments, the annealing process is performed on the metal oxide layer130′ or the gate dielectric layer140after the gate dielectric layer140is formed and before the first gate150is formed to adjust the oxygen distribution in the metal oxide layer130′ by the oxygen-containing protrusive structure122.

With reference toFIG.6C, a doping process P is performed on the metal oxide layer130to reduce the resistivity of the third portion136of the metal oxide layer130and gradually decrease the resistivity of the second portion134of the metal oxide layer130away from the first portion132. For instance, a hydrogen plasma process is performed on the metal oxide layer130by applying the first gate150as a mask, so that the second portion134and the third portion136that are not overlapped with the first gate150in the normal direction ND of the top surface of the substrate100constitute a doped region dp, and the first portion132overlapped with the first gate150in the normal direction ND of the top surface of the substrate100constitutes a channel region ch. In some embodiments, the second portion134may constitute a lightly doped region ldp, and the third portion136may constitute a heavily doped region hdp. In some embodiments, the width L2 of the oxygen-containing protrusive structure122may be larger than the width L1 of the first gate150, which is conducive to an increase in the distance between the first portion132and the third portion136.

After the hydrogen plasma process, the resistivity of the second portion134may gradually decrease away from the first portion132, and the resistivity of the second portion134is higher than the resistivity of the third portion136.

With reference toFIG.6D, an interlayer dielectric layer160is formed on the gate dielectric layer140and covers the first gate150. After that, openings O1 and O2 penetrating the interlayer dielectric layer160and the gate dielectric layer140are formed, and the openings O1 and O2 are respectively overlapped with the third portion136in the normal direction ND of the top surface of the substrate100.

After that, with reference toFIG.5, a source172and a drain174are formed on the interlayer dielectric layer150and fill the openings O1 and O2, so as to be electrically connected to the metal oxide layer130.

After the above process, the fabrication of the semiconductor device3is substantially completed.