Semiconductor device with liner structure and method for fabricating the same

Abstract

This disclosure provides a semiconductor device including a substrate, a contact, a landing pad, a bit line, and an air gap. The contact is disposed above the substrate. The landing pad is disposed above the contact. The landing pad includes a plug, a first spacer, and a second spacer. The plug is disposed above and contacts the contact. The first spacer is disposed above the plug. The second spacer clamps a protrusion of the plug. The bit line is disposed above the substrate. The air gap is disposed between the contact and the bit line.

Description

Semiconductor element with linear structure and manufacturing method thereof This application is a division of application No. 113111710, filed on March 28, 2024, which claims priority to and the benefit of U.S. regular application No. 18 / 425,115, filed on January 29, 2024, the contents of which are incorporated herein by reference in their entirety. The present disclosure relates to a semiconductor device and a method for manufacturing the semiconductor device, and more particularly to a semiconductor device having multiple linear structures and a method for manufacturing the semiconductor device. Semiconductor components are essential to many modern applications. With advances in electronics technology, semiconductor components are becoming increasingly smaller, while providing greater functionality and incorporating more integrated circuits. This miniaturization has led to the consolidation and packaging of various types and sizes of semiconductor components, providing different functions, into a single module. Furthermore, numerous manufacturing processes are required to integrate these various types of semiconductor components. However, the manufacturing and integration of semiconductor devices involves many complex steps and operations. The integration of semiconductor devices is becoming increasingly complex. This increased complexity in the manufacturing and integration of semiconductor devices can lead to defects. Therefore, there is a growing need to improve the semiconductor device manufacturing process to address these issues. The above description of “prior art” only provides background technology, does not admit that the above description of “prior art” discloses the subject matter of the present disclosure, does not constitute the prior art of the present disclosure, and any description of the above “prior art” should not be regarded as any part of this case. One embodiment of the present disclosure provides a semiconductor device comprising a substrate, a contact, a landing pad, a bit line, and an air gap. The contact is disposed above the substrate. The landing pad is disposed above the contact. The landing pad comprises a plug, a first spacer, and a second spacer. The plug is disposed above and in contact with the contact. The first spacer is disposed above the plug. The second spacer clamps a protruding portion of the plug. The bit line is disposed above the substrate. The air gap is disposed between the contact and the bit line. Another embodiment of the present disclosure provides a semiconductor device comprising a substrate, an etch stop layer, a first lower plug, a second lower plug, a first upper plug, a second upper plug, and an air gap. The etch stop layer is disposed above the substrate. The first lower plug and the second lower plug are disposed above the substrate and protrude from an upper surface of the etch stop layer. The first upper plug and the second upper plug are disposed above the first lower plug and the second lower plug, respectively. The air gap is disposed between the first upper plug and the second upper plug. An upper surface of the first lower plug is rounded. The first upper plug contacts a first sidewall of the first lower plug. Another embodiment of the present disclosure provides a method for fabricating a semiconductor device, comprising providing a substrate; forming a contact over the substrate; forming a bit line over the substrate; forming a liner structure to enclose an air gap, wherein the liner structure is formed between the contact and the bit line; and forming a landing pad over the contact, the method comprising: forming a barrier layer; forming a plug to contact the contact; and forming a first spacer and a second spacer over the plug. The first spacer is disposed over the plug, and the second spacer sandwiches a protruding portion of the plug. The present disclosure provides embodiments of a semiconductor device structure and a method for fabricating the same. In some embodiments, the semiconductor device structure includes a first dielectric liner portion disposed adjacent to a first interconnect structure and a second dielectric liner portion disposed adjacent to a second interconnect structure. The semiconductor device structure also includes a filler portion surrounded by the second dielectric liner portion and an air gap enclosed within the first dielectric liner portion, which helps reduce capacitive coupling between adjacent interconnect structures and can reduce resistance-capacitance (RC) delay. As a result, the performance (e.g., operating speed) and reliability of the semiconductor device structure can be improved. The above has provided a relatively broad overview of the technical features and advantages of the present disclosure to facilitate a better understanding of the detailed description of the present disclosure that follows. Other technical features and advantages that constitute the subject matter of the claims of the present disclosure are described below. Those skilled in the art will appreciate that the concepts and specific embodiments disclosed below can be readily utilized to modify or design other structures or processes to achieve the same objectives as those of the present disclosure. Those skilled in the art will also appreciate that such equivalent constructions do not depart from the spirit and scope of the present disclosure as defined by the appended claims. Specific examples of components and configurations are described below to simplify the embodiments of the present disclosure. Of course, these embodiments are for illustration only and are not intended to limit the scope of the present disclosure. For example, the description of a first component formed on a second component may include embodiments in which the first and second components are in direct contact, and may also include embodiments in which additional components are formed between the first and second components so that the first and second components are not in direct contact. In addition, the embodiments of the present disclosure may repeat reference numbers and / or letters in many examples. The purpose of these repetitions is for simplicity and clarity, and unless otherwise specified in the text, they do not in themselves represent a specific relationship between the various embodiments and / or configurations discussed. Furthermore, for ease of description, spatially relative terms such as "beneath," "below," "lower," "above," and "upper" may be used herein to describe the relationship of one element or feature to another element or feature as illustrated in the figures. These spatially relative terms are intended to encompass different orientations of the element in use or operation in addition to the orientation depicted in the figures. The device may be in other orientations (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein should be interpreted accordingly. FIG1 is a schematic cross-sectional view illustrating a semiconductor device structure 100a according to some embodiments of the present disclosure. As shown in FIG1 , according to some embodiments, the semiconductor device structure 100a includes a semiconductor substrate 101, a first dielectric layer 103 disposed above the semiconductor substrate 101, and a second dielectric layer 105 disposed above the first dielectric layer 103. In some embodiments, the semiconductor device structure 100a also includes a plurality of interconnect structures 119a, 119b, 119c, and 119d disposed above the second dielectric layer 105. In some embodiments, interconnect structures 119a, 119b, 119c, and 119d are separated from each other. Each of interconnect structures 119a, 119b, 119c, and 119d includes a first conductive portion and a second conductive portion disposed above the first conductive portion. For example, interconnect structure 119a includes a first conductive portion 107a and a second conductive portion 109a, interconnect structure 119b includes a first conductive portion 107b and a second conductive portion 109b, interconnect structure 119c includes a first conductive portion 107c and a second conductive portion 109c, and interconnect structure 119d includes a first conductive portion 107d and a second conductive portion 109d. In some embodiments, semiconductor device structure 100a includes dielectric liner portions 131a, 131b, 131c, and 131d disposed above second dielectric layer 105. Each dielectric liner portion 131a, 131b, 131c, and 131d is disposed between two adjacent interconnect structures. In some embodiments, each of dielectric liner portions 131a, 131b, 131c, and 131d is in direct contact with the first conductive portion and the second conductive portion of the two adjacent interconnect structures. In some embodiments, an air gap 134 is enclosed in dielectric liner portion 131a, and a filler portion 137' is surrounded by dielectric liner portion 131d. In some embodiments, the filling portion 137' is separated from the second dielectric layer 105 by the dielectric liner portion 131d. In some embodiments, the filling portion 137' is separated from two adjacent interconnect structures 119c and 119d by the dielectric liner portion 131d. In addition, the semiconductor device structure 100a includes a capping layer 141 disposed over the interconnect structures 119a, 119b, 119c, 119d, the dielectric liner portions 131a, 131b, 131c, 131d, and the filling portion 137'. In some embodiments, the capping layer 141 is in direct contact with the upper surfaces of the interconnect structures 119a, 119b, 119c, 119d (i.e., the upper surfaces of the second conductive portions 109a, 109b, 109c, 109d), the upper surfaces of the dielectric liner portions 131a, 131b, 131c, 131d, and the upper surface of the filling portion 137'. Furthermore, the semiconductor device structure 100a has a first region A and a second region B. In some embodiments, the interconnect structures 119a and 119b, the dielectric liner portions 131a and 131b, and the air gap 134 are located in the first region A. In some embodiments, the interconnect structures 119c and 119d, the dielectric liner portions 131c and 131d, and the filling portion 137' are located in the second region B. As shown in FIG1 , in accordance with some embodiments, the space between interconnect structures 119 a and 119 b is occupied by dielectric liner portion 131 a and air gap 134, and the space between interconnect structures 119 c and 119 d is occupied by dielectric liner portion 131 d and filling portion 137 ′. Because the space occupied by dielectric liner portion 131 a and air gap 134 is smaller than the space occupied by dielectric liner portion 131 d and filling portion 137 ′, first region A is also referred to as a small gap-filling region, and second region B is also referred to as a large gap-filling region. In some embodiments, in the cross-sectional view of FIG. 1 , the space occupied by dielectric liner portion 131 a and air gap 134 has a width W1, and the space occupied by dielectric liner portion 131 d and filling portion 137 ′ has a width W2, and width W2 is greater than width W1. Width W1 is also referred to as the bottom width of dielectric liner portion 131 a, and width W2 is also referred to as the bottom width of dielectric liner portion 131 d. In some embodiments, bottom width W2 of dielectric liner portion 131 d in large gap-filling region B is greater than bottom width W1 of dielectric liner portion 131 a in small gap-filling region A. In FIG1 , four interconnect structures 119 a, 119 b, 119 c, 119 d and four dielectric liner portions 131 a, 131 b, 131 c, 131 d are shown. However, the number is not limited to this. In some other embodiments, the number of interconnect structures and dielectric liner portions can be adjusted based on design requirements. Similarly, in FIG1 , an air gap 134 is shown in the small gap filling region A, and a filling portion 137 ′ is shown in the large gap filling region B. It should be understood that the number is not limited to this. For example, in some other embodiments, the number of air gaps in the small gap filling region A and the number of filling portions in the large gap filling region B can be adjusted based on design requirements. FIG2 is a schematic cross-sectional view illustrating a semiconductor device structure 100 b according to some embodiments of the present disclosure. The semiconductor device structure 100 b is similar to the semiconductor device structure 100 a. However, according to some embodiments, in the semiconductor device structure 100 b , the filler portion 137 ′ is replaced by another filler portion 139 ′, and the filler portions 137 ′ and 139 ′ are made of different materials. In some embodiments, the filler portion 137' of the semiconductor device structure 100a comprises a low-k dielectric material, and the filler portion 139' of the semiconductor device structure 100b comprises an energy-removable material. In some embodiments, the filler portion 139' comprising the energy-removable material is surrounded by the dielectric liner portion 131d. The details of this embodiment are similar to those of the previously described embodiments and will not be repeated here. FIG3 is a schematic cross-sectional view illustrating a semiconductor device structure 200a according to some embodiments of the present disclosure. Semiconductor device structure 200a is similar to semiconductor device structure 100a. However, in semiconductor device structure 200a, dielectric liner portions 231a and 231b are formed in a first region A (i.e., a small gap-filling region), dielectric liner portions 231c and 231d are formed in a second region B (i.e., a large gap-filling region), a filling portion 237a is surrounded by dielectric liner portion 231a, and a filling portion 237b is surrounded by dielectric liner portion 231d. In semiconductor device structure 200a, no air gap exists in dielectric liner portion 231a in first region A. According to some embodiments, similar to semiconductor device structure 100a, the bottom width W2 of dielectric liner portion 231d is greater than the bottom width W1 of dielectric liner portion 231a. Furthermore, in some embodiments, filling portions 237a and 237b are made of the same material. For example, filling portions 237a and 237b include a low-k dielectric material. In some embodiments, the filling portion 237a in the first region A has a width W3, and the filling portion 237b in the second region B has a width W4, where the width W4 is greater than the width W3. In some embodiments, the cover layer 141 directly contacts the upper surfaces of the filling portions 237a and 237b. The details of this embodiment are similar to those of the previously described embodiments and will not be repeated here. FIG4 is a schematic cross-sectional view illustrating a semiconductor device structure 200b according to some embodiments of the present disclosure. Semiconductor device structure 200b is similar to semiconductor device structure 200a. However, in semiconductor device structure 200b, filling portions 237a and 237b are replaced by filling portions 239a and 239b, respectively. According to some embodiments, filling portions 239a and 239b are made of the same material, but different from the material of filling portions 237a and 237b in semiconductor device structure 200a. In some embodiments, the filling portions 237a and 237b of the semiconductor device structure 200a include a low-k dielectric material, and the filling portions 239a and 239b of the semiconductor device structure 200b include an energy-removable material. Details of this embodiment are similar to those of the previously described embodiments and will not be repeated here. FIG5 is a flow chart illustrating a method for fabricating a semiconductor device structure (e.g., semiconductor device structure 100a or 100b) according to some embodiments of the present disclosure. The fabrication method 10 includes steps S11, S13, S15, S17, S19, S21, S23, S25, and S27. Steps S11 through S27 of FIG5 will be described in detail in conjunction with the following figures (e.g., FIG7 through FIG15). FIG6 is a flow chart illustrating a method for fabricating a semiconductor device structure (e.g., semiconductor device structure 200a or 200b) according to some embodiments of the present disclosure. The fabrication method 30 includes steps S31, S33, S35, S37, S39, S41, S43, S45, and S47. Steps S31 through S47 of FIG6 will be described in detail in conjunction with the following figures (e.g., FIG16 through FIG20). 7-13 are cross-sectional views illustrating intermediate stages of forming a semiconductor device structure 100a according to some embodiments. As shown in FIG7 , a semiconductor substrate 101 is provided. The semiconductor substrate 101 may be a semiconductor wafer, such as a silicon wafer. Alternatively or additionally, the semiconductor substrate 101 may include an elemental semiconductor material, a compound semiconductor material, and / or an alloy semiconductor material. Examples of elemental semiconductor materials may include, but are not limited to, crystalline silicon, polycrystalline silicon, amorphous silicon, germanium, and / or diamond. Examples of compound semiconductor materials may include, but are not limited to, silicon carbide, gallium arsenide, gallium phosphide, indium phosphide, indium arsenide, and / or indium antimonide. Examples of alloy semiconductor materials may include, but are not limited to, SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and / or GaInAsP. In some embodiments, semiconductor substrate 101 includes an epitaxial layer. For example, semiconductor substrate 101 includes an epitaxial layer covering a bulk semiconductor. In some embodiments, semiconductor substrate 101 is a semiconductor-on-insulator (SIO) substrate, which may include a substrate, a buried oxide layer overlying the substrate, and a semiconductor layer overlying the buried oxide layer, such as a silicon-on-insulator (SOI) substrate, a silicon-germanium-on-insulator (SGOI) substrate, or a germanium-on-insulator (GOI) substrate. The SIO substrate may be fabricated using separation by implantation of oxygen (SIMOX), wafer bonding, and / or other suitable methods. According to some embodiments, as shown in FIG7 , a first dielectric layer 103 and a second dielectric layer 105 are sequentially formed on the semiconductor substrate 101. The respective steps are shown as steps S11 and S13 in the preparation method 10 shown in FIG5 . In some embodiments, the first dielectric layer 103 and the second dielectric layer 105 are made of or include silicon oxide, silicon nitride, or silicon oxynitride. In some embodiments, the first dielectric layer 103 is made of borosilicate glass (BSG), silicon dioxide (SiO 2) or a combination thereof, or including borosilicate glass (BSG), silicon dioxide (SiO In some embodiments, the second dielectric layer 105 is made of or includes borophosphosilicate glass (BPSG), tetraethoxysilane (TEOS), or a combination thereof. The fabrication technique for the first dielectric layer 103 may include a deposition process, such as a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, an atomic layer deposition (ALD) process, a spin-on process, or other suitable methods. Some processes for forming the second dielectric layer 105 are similar or identical to those for forming the first dielectric layer 103 and are not further described here. Furthermore, the second dielectric layer 105 may also be referred to as an interlayer dielectric (ILD) layer. Next, according to some embodiments, as shown in FIG8 , a first conductive layer 107 and a second conductive layer 109 are sequentially formed over the second dielectric layer 105 . The respective steps are shown as steps S15 and S17 in the preparation method 10 shown in FIG5 . In some embodiments, the first conductive layer 107 and the second conductive layer 109 are made of or include tungsten (W), aluminum (Al), copper (Cu), titanium (Ti), tantalum (Ta), titanium nitride (TiN), tantalum nitride (TiN), other suitable materials, or combinations thereof. In some embodiments, the first conductive layer 107 is made of or includes titanium nitride (TiN), and the second conductive layer 109 is made of or includes tungsten (W). The fabrication techniques for the first conductive layer 107 may include a deposition process, such as a CVD process, a PVD process, an ALD process, a metal-organic chemical vapor deposition (MOCVD) process, a sputtering process, an electroplating process, or other suitable methods. Some processes for forming the second conductive layer 109 are similar or identical to those for forming the first conductive layer 107 and are not further described here. Furthermore, the first conductive layer 107 may also be referred to as a barrier layer. Still referring to FIG. 8 , according to some embodiments, a patterned mask 111 having a plurality of openings (e.g., openings 114 and 116) is formed over the second conductive layer 109. In some embodiments, opening 114 is located in the first region A, and opening 116 is located in the second region B, with the second conductive layer 109 partially exposed by openings 114 and 116. In some embodiments, the width of opening 116 (i.e., width W2) is greater than the width of opening 114 (i.e., width W1). In some embodiments, the second conductive layer 109 and the patterned mask 111 comprise different materials, thereby enabling different etch selectivities in a subsequent etching process. Subsequently, according to some embodiments, an etching process is performed using patterned mask 111 as an etching mask to form openings 124 and 126 that penetrate first conductive layer 107 and second conductive layer 109, as shown in FIG9 . In some embodiments, a width of opening 126 in second region B (i.e., width W2) is greater than a width of opening 124 in first region A (i.e., width W1). These steps are shown as step S19 in preparation method 10 shown in FIG5 . Furthermore, according to some embodiments, a top surface area TSA2 of the second dielectric layer 105 exposed by the opening 126 is larger than a top surface area TSA1 of the second dielectric layer 105 exposed by the opening 124. In some embodiments, the etching process for forming the openings 124 and 126 includes a wet etching process, a dry etching process, or a combination thereof. After forming openings 124 and 126, a plurality of interconnect structures 119a, 119b, 119c, and 119d are obtained. In some embodiments, the remaining portions of first conductive layer 107 and second conductive layer 109 are hereinafter referred to as first conductive portions 107a, 107b, 107c, 107d and second conductive portions 109a, 109b, 109c, and 109d. As described above, according to some embodiments, as shown in FIG9 , each of interconnect structures 119a, 119b, 119c, and 119d includes a first conductive portion and a second conductive portion disposed above the first conductive portion. Then, according to some embodiments, as shown in FIG10 , the patterned mask 111 is removed. In some embodiments, the patterned mask 111 is removed by a stripping process, an ashing process, an etching process, or other suitable processes. After the patterned mask 111 is removed, the upper surfaces of the second conductive portions 109 a, 109 b, 109 c, and 109 d are exposed. Next, according to some embodiments, as shown in FIG11 , a dielectric liner layer 131 is conformally formed over the structure of FIG10 . In some embodiments, dielectric liner layer 131 is formed within openings 124 and 126 and over the upper surfaces of second conductive portions 109 a, 109 b, 109 c, and 109 d. These steps are shown as step S21 in method 10 shown in FIG5 . In some embodiments, the thickness of dielectric liner layer 131 is adjusted such that an air gap 134 is enclosed in the portion of dielectric liner layer 131 filling opening 124, while opening 126 remains unfilled by dielectric liner layer 131. In some embodiments, dielectric liner layer 131 has a thickness T1, a width W1 of opening 124 is less than twice the thickness T1, and a width W2 of opening 126 is greater than twice the thickness T1. Furthermore, in some embodiments, dielectric liner layer 131 is made of or includes boron carbon nitride (BCN). However, any other suitable dielectric material may be utilized. The fabrication technique for dielectric liner layer 131 may include a deposition process, such as a CVD process, a PVD process, an ALD process, a spin-on process, or other suitable methods. In some embodiments, air gap 134 is enclosed (or sealed) within the portion of dielectric liner layer 131 that fills opening 124. In other words, air gap 134 is not exposed. Subsequently, according to some embodiments, as shown in FIG12 , a filling layer 137 is formed over the dielectric liner layer 131. In some embodiments, the remaining portion of the opening 126 (also referred to as 126′) in the structure of FIG11 is filled with the filling layer 137. These steps are shown as step S23 in the preparation method 10 shown in FIG5 . In some embodiments, since the air gap 134 in the first region A is surrounded by the dielectric liner layer 131, the air gap 134 is separated from the filling layer 137 by the dielectric liner layer 131. In some embodiments, the filling layer 137 is made of or includes a low-k dielectric material. For example, the dielectric constant (k value) of the low-k dielectric material can be less than approximately 3.0. In some embodiments, the filling layer 137 is formed using a sputtering process. However, any other suitable deposition method may be used. Then, according to some embodiments, as shown in FIG16 , the filling layer 137 and the dielectric liner layer 131 are partially removed to expose the interconnect structures 119 a, 119 b, 119 c, and 119 d (i.e., the second conductive portions 109 a, 109 b, 109 c, and 109 d). These steps are shown as step S25 in the preparation method 10 shown in FIG5 . After the filling layer 137 and the dielectric liner layer 131 are partially removed, dielectric liner portions 131 a, 131 b, 131 c, and 131 d and a filling portion 137 ′ are obtained. In some embodiments, dielectric liner portions 131a, 131b and air gap 134 are located in first region A, and dielectric liner portions 131c, 131d and filling portion 137' are located in second region B. In some embodiments, filling layer 137 and dielectric liner layer 131 are partially removed by a planarization process, an etch-back process, or a combination thereof. The planarization process may include a chemical mechanical polishing (CMP) process. Next, according to some embodiments, a capping layer 141 is formed over the interconnect structures 119a, 119b, 119c, and 119d, as shown in FIG1. ​​In some embodiments, the capping layer 141 is formed over and in direct contact with the upper surfaces of the interconnect structures 119a, 119b, 119c, and 119d (i.e., the upper surfaces of the second conductive portions 109a, 109b, 109c, and 109d), the upper surfaces of the dielectric liner portions 131a, 131b, 131c, and 131d, and the upper surface of the filling portion 137′. Each step is shown as step S27 in the preparation method 10 shown in FIG. 5 . In some embodiments, the cover layer 141 is made of or includes a silicon-based material, such as silicon nitride (Si 3N 4) Silicon oxynitride (SiON) or silicon dioxide (SiO 2) In some embodiments, capping layer 141 is made of or includes carbonitride, with or without an additional dopant such as boron (B). Capping layer 141 can be fabricated using a deposition process such as CVD, PVD, ALD, spin-on coating, or other suitable methods. After forming capping layer 141, semiconductor device structure 100a is obtained. 14 and 15 are cross-sectional views illustrating intermediate stages of forming a semiconductor device structure 100b according to some embodiments. It should be noted that the steps for forming the semiconductor device structure 100b prior to the structure shown in FIG14 are substantially identical to the steps for forming the semiconductor device structure 100a shown in FIG7-11 , and the relevant detailed descriptions can be found in the foregoing text and will not be repeated here. According to some embodiments, as shown in FIG14 , after forming the dielectric liner layer 131, a filling layer 139 is formed over the dielectric liner layer 131. In some embodiments, the remaining portion of the opening 126 (i.e., 126′ in FIG11 ) is filled with the filling layer 139. These steps are shown as step S23 in the preparation method 10 shown in FIG5 . In some embodiments, since the air gap 134 in the first region A is surrounded by the dielectric liner layer 131, the air gap 134 is separated from the filling layer 139 by the dielectric liner layer 131. In some embodiments, the filling layer 139 is made of or includes an energy-removable material. In some embodiments, the energy-removable material includes a thermally decomposable material. In some other embodiments, the energy-removable material includes a photon-decomposable material, an electron beam-decomposable material, or other suitable energy-decomposable material. In some embodiments, the energy-removable material includes a base material and a decomposable porogen material that is substantially removed upon exposure to energy (e.g., heat). In this case, the base material may include hydrogen silsesquioxane (HSQ), methyl silsesquioxane (MSQ), porous polyarylether (PAE), porous SiLK, or porous silicon dioxide (SiO 2), and the decomposable porogen material may include a porogen organic compound that can provide porosity in the space originally occupied by the energy-removable material (i.e., filler layer 139) during subsequent processing. In some embodiments, the formation technique of filler layer 139 includes a sputtering process. However, any other suitable deposition method may be used. Subsequently, according to some embodiments, as shown in FIG15 , the filling layer 139 and the dielectric liner layer 131 are partially removed to expose the interconnect structures 119 a, 119 b, 119 c, and 119 d (i.e., the second conductive portions 109 a, 109 b, 109 c, and 109 d). These steps are shown as step S25 in the preparation method 10 shown in FIG5 . After the filling layer 139 and the dielectric liner layer 131 are partially removed, dielectric liner portions 131 a, 131 b, 131 c, and 131 d and a filling portion 139 ′ are obtained. In some embodiments, dielectric liner portions 131a, 131b and air gap 134 are located in first region A, and dielectric liner portions 131c, 131d and filling portion 139' are located in second region B. In some embodiments, filling layer 139 and dielectric liner layer 131 are partially removed by a planarization process, an etch-back process, or a combination thereof. The planarization process may include a CMP process. Then, according to some embodiments, a capping layer 141 is formed over the interconnect structures 119a, 119b, 119c, and 119d, as shown in Figure 2. In some embodiments, the capping layer 141 is formed over and in direct contact with the upper surfaces of the interconnect structures 119a, 119b, 119c, and 119d (i.e., the upper surfaces of the second conductive portions 109a, 109b, 109c, and 109d), the upper surfaces of the dielectric liner portions 131a, 131b, 131c, and 131d, and the upper surface of the filling portion 139'. Each step is shown as step S27 in the preparation method 10 shown in FIG. 5 . The details of the cover layer 141 can be substantially the same as shown and discussed in FIG1 , and therefore will not be repeated here. After forming the cover layer 141, the semiconductor device structure 100b can be obtained. In some embodiments, a heat treatment process can be performed to convert the filling portion 139' into an air gap (not shown). In some embodiments, the heat treatment process is optional. In some embodiments, the temperature used in the heat treatment process can be high enough to effectively burn off the filling portion 139', leaving an air gap surrounded by the dielectric liner portion 131d and the cover layer 141. In some other embodiments, the temperature used in the heat treatment process is selected so that the filling portion 139' is converted into an air gap surrounded or enclosed by the remaining portion of the filling portion 139'. Figures 16 to 18 are cross-sectional views illustrating intermediate stages of forming a semiconductor device structure 200a according to some embodiments. It should be noted that the steps for forming the semiconductor device structure 200a prior to the structure shown in Figure 16 are substantially the same as the steps for forming the semiconductor device structure 100a shown in Figures 7-10 (steps S31 to S39 in the preparation method 30 shown in Figure 6 are the same as steps S11 to S19 in the preparation method 10 shown in Figure 5), and the relevant detailed description can be found in the previous text and will not be repeated here. According to some embodiments, as shown in FIG16 , after forming openings 124 and 126, a dielectric liner layer 231 is conformally formed over the structure of FIG10 . In some embodiments, dielectric liner layer 231 is formed within openings 124 and 126 and over the upper surfaces of second conductive portions 109 a, 109 b, 109 c, and 109 d. These steps are shown as step S41 in the fabrication method 30 shown in FIG6 . In some embodiments, the thickness of the dielectric liner layer 231 is adjusted so that the width of a gap 234 (i.e., the remaining portion of the opening 124) formed in the first region A is smaller than the width of the opening 126' (i.e., the remaining portion of the opening 126) formed in the second region B. For example, the width W4 of the opening 126' is greater than the width W3 of the gap 234. In some embodiments, the width W3 represents a width measured at the widest portion of the gap 234. 10 and 16 , the dielectric liner layer 231 has a thickness T2, the width W1 of the opening 124 is less than twice the thickness T2, and the width W2 of the opening 126 is greater than twice the thickness T2. In some embodiments, the opening 124 in the first region A is partially filled with the dielectric liner layer 231, and no enclosed air gap exists in the dielectric liner layer 231. Some materials and processes used to form the dielectric liner layer 231 are similar or identical to those used to form the dielectric liner layer 131 and are not further described herein. Next, according to some embodiments, as shown in FIG17 , a filling layer 237 is formed over the dielectric liner layer 231. In some embodiments, the gap 234 in the first region A (i.e., the remaining portion of the opening 124 after the dielectric liner layer 231 is formed) and the opening 126′ in the second region B (i.e., the remaining portion of the opening 126 after the dielectric liner layer 231 is formed) are filled with the filling layer 237. These steps are shown as step S43 in the preparation method 30 shown in FIG6 . In some embodiments, filler layer 237 is made of or includes a low-k dielectric material. For example, the dielectric constant (k value) of the low-k dielectric material can be less than approximately 3.0. In some embodiments, filler layer 237 is formed using a sputtering process. However, any other suitable deposition method may be used. Subsequently, according to some embodiments, as shown in FIG18 , the filling layer 237 and the dielectric liner layer 231 are partially removed to expose the interconnect structures 119 a, 119 b, 119 c, and 119 d (i.e., the second conductive portions 109 a, 109 b, 109 c, and 109 d). These steps are shown as step S45 in the preparation method 30 shown in FIG6 . After the filling layer 237 and the dielectric liner layer 231 are partially removed, dielectric liner portions 231 a, 231 b, 231 c, and 231 d and filling portions 237 a and 237 b are obtained. In some embodiments, dielectric liner portions 231a, 231b and filling portion 237a are located in first region A, and dielectric liner portions 231c, 231d and filling portion 237b are located in second region B. In some embodiments, filling layer 237 and dielectric liner layer 231 are partially removed by a planarization process, an etch-back process, or a combination thereof. The planarization process may include a CMP process. Then, according to some embodiments, a capping layer 141 is formed over the interconnect structures 119a, 119b, 119c, and 119d, as shown in Figure 3. In some embodiments, the capping layer 141 is formed over and in direct contact with the upper surfaces of the interconnect structures 119a, 119b, 119c, and 119d (i.e., the upper surfaces of the second conductive portions 109a, 109b, 109c, and 109d), the upper surfaces of the dielectric liner portions 231a, 231b, 231c, and 231d, and the upper surfaces of the filling portions 237a and 237b. Each step is shown as step S47 in the preparation method 30 shown in FIG. 6 . The details of the capping layer 141 may be substantially the same as those shown and discussed in FIG1 , and thus will not be repeated here. After the capping layer 141 is formed, the semiconductor device structure 200 a is obtained. Figures 19 and 20 are cross-sectional views illustrating intermediate stages of forming a semiconductor device structure 200b according to some embodiments. It should be noted that the steps for forming the semiconductor device structure 200b prior to the structure shown in Figure 19 are substantially the same as the steps for forming the semiconductor device structure 200a shown in Figure 16, and the relevant detailed description can be found in the previous text and will not be repeated here. According to some embodiments, as shown in FIG19 , after forming dielectric liner layer 231, a filling layer 239 is formed over dielectric liner layer 231. In some embodiments, gap 234 and opening 126′ are filled with filling layer 239. These steps are shown as step S43 in preparation method 30 shown in FIG6 . In some embodiments, filler layer 239 is made of or includes an energy removable material. The details of the energy removable material can be substantially the same as those shown and discussed in FIG14 , and therefore will not be repeated here. In some embodiments, the fabrication technique of filler layer 239 includes a sputtering process. However, any other suitable deposition method may be utilized. Next, according to some embodiments, as shown in FIG20 , the filling layer 239 and the dielectric liner layer 231 are partially removed to expose the interconnect structures 119 a, 119 b, 119 c, and 119 d (i.e., the second conductive portions 109 a, 109 b, 109 c, and 109 d). These steps are shown as step S45 in the preparation method 30 shown in FIG6 . After the filling layer 239 and the dielectric liner layer 231 are partially removed, dielectric liner portions 231 a, 231 b, 231 c, and 231 d and the filling portions 239 a and 239 b are obtained. In some embodiments, dielectric liner portions 231a, 231b and filling portion 239a are located in first region A, and dielectric liner portions 231c, 231d and filling portion 239b are located in second region B. In some embodiments, filling layer 239 and dielectric liner layer 231 are partially removed by a planarization process, an etch-back process, or a combination thereof. The planarization process may include a CMP process. Subsequently, according to some embodiments, a capping layer 141 is formed over the interconnect structures 119a, 119b, 119c, and 119d, as shown in Figure 4. In some embodiments, the capping layer 141 is formed over and in direct contact with the upper surfaces of the interconnect structures 119a, 119b, 119c, and 119d (i.e., the upper surfaces of the second conductive portions 109a, 109b, 109c, and 109d), the upper surfaces of the dielectric liner portions 231a, 231b, 231c, and 231d, and the upper surfaces of the filling portions 239a and 239b. Each step is shown as step S45 in the preparation method 30 shown in FIG. 6 . The details of the capping layer 141 can be substantially the same as those shown and discussed in FIG1 , and therefore will not be repeated here. After forming the capping layer 141, the semiconductor device structure 200b can be obtained. In some embodiments, a heat treatment process can be performed to convert the filling portions 239a and 239b into air gaps (not shown). In some embodiments, the heat treatment process is optional. In some embodiments, the temperature used in the heat treatment process can be high enough to effectively burn away the filling portions 239a and 239b to form the air gaps. In some other embodiments, the temperature used in the heat treatment process is selected so that an air gap surrounded or enclosed by the remaining portion of the filling portion is obtained in the first region A and / or the second region B of the semiconductor device structure 200b. The present disclosure provides embodiments of semiconductor device structures and methods for fabricating the same. In some embodiments, the semiconductor device structure (e.g., semiconductor device structure 100a or 100b) includes a first interconnect structure, a second interconnect structure, a first dielectric liner portion disposed adjacent to the first interconnect structure, and a second dielectric liner portion disposed adjacent to the second interconnect structure. The semiconductor device structure also includes a filler portion surrounded by the second dielectric liner portion, and an air gap is enclosed in the first dielectric liner portion, which helps reduce capacitive coupling between adjacent interconnect structures and can reduce RC delay. As a result, the performance (e.g., operating speed) and reliability of the semiconductor device structure can be improved. In some embodiments, the semiconductor device structure (e.g., semiconductor device structure 200a or 200b) includes a first interconnect structure, a second interconnect structure, a first dielectric liner portion disposed adjacent to the first interconnect structure, and a second dielectric liner portion disposed adjacent to the second interconnect structure. The semiconductor device structure also includes a first filler portion surrounded by the first dielectric liner portion and a second filler portion surrounded by the second dielectric liner portion. The materials of the first filler portion and the second filler portion can be selected to reduce capacitive coupling between adjacent interconnect structures and reduce RC delay. As a result, the performance (e.g., operating speed) and reliability of the semiconductor device structure can be improved. In addition, the first filler portion and the second filler portion having different widths can be formed from the same material through the same process steps. Therefore, manufacturing costs and processing time can be reduced. In some embodiments, the semiconductor device structures 100 a , 100 b , 200 a and / or 200 b may be integrated into another structure, such as a semiconductor structure 300 with metal plugs shown in FIG. 21 and a semiconductor device 500 with contacts shown in FIG. 42 . Please refer to Figure 21. Figure 21 is a schematic diagram of a semiconductor structure 300 according to some embodiments of the present disclosure. In some embodiments, the semiconductor structure 300 includes a memory structure. The semiconductor structure 300 includes a substrate 301, a plurality of isolation structures 303, a plurality of word lines 305, an active region 307, a first insulating film 309, a second insulating film 311, a third insulating film 313, a fourth insulating film 315, a contact 317, a bit line contact 319, a first capping layer 321, a bit line 323, a plurality of capacitor contacts 325, a plurality of plugs 327, and a plurality of landing pads 329. As shown in FIG. 21 , the semiconductor structure 300 further includes a plurality of pad structures 331 and a plurality of air gaps 333 disposed in the plurality of pad structures 331. A plurality of isolation structures 303 may be disposed in the substrate 301 and separated from one another. The plurality of isolation structures 303 define an active region 307. A plurality of word lines 305 may be disposed in the substrate 301 and separated from one another. Each of the plurality of word lines 305 includes a bottom layer 305a, a middle layer 305b, and a top layer 305c. The bottom layers 305a may be disposed inwardly in the substrate 301. The middle layers 305b may be disposed on the bottom layers 305a, respectively. An upper surface of the middle layers 305b may be lower than an upper surface of the substrate 301. The top layers 305c may be disposed on the middle layers 305b, respectively. An upper surface of the top layer 305c may be co-located with the upper surface of the substrate 301. The active region 307 may include a first doped region 307a and a plurality of second doped regions 307b. The first doped region 307a is disposed between adjacent pairs of word lines 305. The second doped regions 307b are respectively disposed between the isolation structures 303 and the word lines 305. A first insulating film 309 may be disposed on the substrate 301. Contacts 317 are disposed in the first insulating film 309 and electrically connected to the first doped region 307a. The capacitor contacts 325 are disposed on and electrically connected to the second doped region 307b, respectively. In some embodiments, the contacts 317 include tungsten. A second insulating film 311 may be disposed on the first insulating film 309. A bit line contact 319 may be disposed in the second insulating film 311. A first capping layer 321 may be disposed in the second insulating film 311 and on an upper surface of the contact 317. The first capping layer 321 is disposed between the bit line contact 319 and the contact 317. Furthermore, the first capping layer 321 may be disposed on and adhered to each sidewall of the bit line contact 319. In some embodiments, the first capping layer 321 includes tungsten nitride. A third insulating film 313 may be provided on the second insulating film 311. A bit line 323 may be provided in the third insulating film 313 and on the bit line contact 319 and the first capping layer 321. A fourth insulating film 315 may be provided on the third insulating film 313. A plurality of plugs 327 may be provided to pass through the fourth insulating film 315. The plurality of plugs 327 may be electrically connected to the capacitor contacts 325, respectively. Each capacitor contact 325 includes a neck 325a and a head 325b above the neck 325a. A width 325bW measured at the widest portion of the head 325b is greater than a width 325aW of the neck 325a. In some embodiments, the head 325b has a curved sidewall 325c. In some embodiments, the head 325b has a tapered profile. Each landing pad 329 includes a first spacer 329a and a second spacer 329b. The first spacer 329a is disposed on a protruding portion 327a of the capacitor plug 327, and the second spacer 329b is disposed on a sidewall of the protruding portion 327a. In some embodiments, the width 329bW of the second spacer 329b is greater than the width 327W of the capacitor plug 327. A topmost surface of the second spacer 329b is higher than an upper surface of the first spacer 329a. In some embodiments, the first spacer 329a comprises polysilicon, and the second spacer 329b comprises a metal silicide of the polysilicon of the first spacer 329a. In some embodiments, the landing pad 329 is formed above the capacitor plug 327, the first spacer 329a, and the second spacer 329b above the capacitor contact 325. In some embodiments, the first spacer 329a, the second spacer 329b, and the capacitor plug 327 are collectively referred to as the landing pad 329. Each pad structure 331 is provided in the second insulating film 311 and the third insulating film 313. In addition, each pad structure 331 is provided between the capacitor contact 325 and the bit line 323. An air gap 333 is provided in the pad structure 331 and is surrounded by the pad structure 331. In some embodiments, the liner structure 331 and the air gap 333 have a relatively lower dielectric layer than the second insulating film 311 and / or the third insulating film 313. Therefore, the effective capacitance between the capacitor contact 325 and the bit line 323 can be reduced. In other words, the capacitive coupling between the capacitor contact 325 and the adjacent bit line 323 can be reduced, and the RC constant can be reduced. It should be noted that the number of pad structures 331 and air gaps 333 is provided for illustrative purposes, however, the present disclosure is not limited thereto. Various numbers of pad structures 331 and air gaps 333 are within the intended scope of the present disclosure. In other embodiments, the air gap 333 may not be surrounded by the liner structure 331 . In such embodiments, the air gap 333 is exposed to the fourth insulating film 315 . Please refer to Figures 22 to 41. Figures 22 to 41 are cross-sectional views illustrating intermediate stages of forming a semiconductor structure 300 according to some embodiments of the present disclosure. 22 , a substrate 301 may be provided. For example, the substrate 301 may include silicon, doped silicon, silicon germanium, silicon on insulator, silicon on sapphire, silicon germanium on insulator, silicon carbide, germanium, gallium arsenide, gallium phosphide, ferrous arsenide phosphide, gallium phosphide, or indium gallium phosphide. In FIG. 23 , a plurality of isolation structures 303 may be formed in a substrate 301. The plurality of isolation structures 303 are separated from each other in a cross-sectional view and define an active region 307. For example, the plurality of isolation structures 303 may comprise an insulating material such as silicon oxide, silicon nitride, silicon oxynitride, silicon nitride oxide, fluoride-doped silicate, or the like. In some embodiments, silicon oxynitride refers to a material containing silicon, nitrogen, and oxygen, wherein the proportion of oxygen is greater than the proportion of nitrogen. Silicon nitride oxide refers to a material containing silicon, oxygen, and nitrogen, wherein the proportion of nitrogen is greater than the proportion of oxygen. In FIG24 , a plurality of trench openings 305′ can be formed in a substrate 301. A lithography process can be used to pattern the substrate 301 to define the locations of the plurality of trench openings 305′. An etching process, such as an anisotropic dry etching process, can be performed to form the plurality of trench openings 305′ in the substrate 301. 25 , after the etching process, multiple bottom layers 305 a may be formed and attached to the sidewalls and bottoms of the multiple trench openings 305 ′. For example, the multiple bottom layers 305 a may include silicon oxide, silicon oxynitride, silicon oxynitride, silicon nitride, or the like. In FIG26 , a plurality of intermediate layers 305 b may be formed on the plurality of bottom layers 305 a. Each upper surface of the plurality of intermediate layers 305 b may be lower than an upper surface of the substrate 301. For example, the plurality of intermediate layers 305 b may include doped polysilicon, a metal material, or a metal silicide. For example, the metal silicide may be nickel silicide, platinum silicide, titanium silicide, molybdenum silicide, cobalt silicide, tantalum silicide, tungsten silicide, or the like. A plurality of top layers 305 c may be formed on the plurality of intermediate layers 305 b. Each upper surface of the plurality of top layers 305 c may be in the same vertical plane as the upper surface of the substrate 301. For example, the plurality of top layers 305 c may include silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, or the like. In FIG27 , a first doping region 307 a and a second doping region 307 b may be formed in an active region 307 of a substrate 301. The first doping region 307 a is disposed between adjacent pairs of word lines 305. The second doping regions 307 b are disposed between a plurality of isolation structures 303 and the plurality of word lines 305. The first doping region 307 a and the second doping region 307 b are each doped with a dopant such as phosphorus, arsenic, or antimony. The first doping region 307 a and the second doping region 307 b each have a dopant density ranging from approximately 1E17 atoms / cm 3 to about 1E19 atoms / cm 3 doping concentration. 28 , a first insulating film 309 may be formed on a substrate 301. For example, the first insulating film 309 may include silicon nitride, silicon oxide, silicon oxynitride, undoped quartz glass, borosilicate glass, phosphosilicate glass, borophosphosilicate glass, or a combination thereof, but is not limited thereto. In FIG. 29 , a contact 317 can be formed in the first insulating film 309. A lithography process can be used to pattern the first insulating film 309 to define the location of the contact 317. An etching process, such as an anisotropic dry etching process, can be performed after the lithography process to form an opening in the first insulating film 309. After the etching process, a conductive material, such as aluminum, copper, tungsten, cobalt, or other suitable metal or metal alloy, can be deposited in the opening to form the contact 317 through a metallization process, such as chemical vapor deposition, physical vapor deposition, sputtering, or the like. A planarization process, such as chemical mechanical polishing, can be performed after the metallization process to remove excess deposited material and provide a substantially flat surface for subsequent processing steps. Contact 317 is disposed on and electrically connected to first doped region 307a. In one embodiment, contact 317 comprises tungsten. When an upper surface of contact 317 is exposed to oxygen or air, multiple defects may be easily formed on the upper surface of contact 317 comprising tungsten. These defects may affect the yield of semiconductor structure 300. A second insulating film 311 may be formed on the first insulating film 309. The second insulating film 311 may include the same material as the first insulating film 309, but is not limited thereto. A lithography process may be used to pattern the second insulating film 311 to define the position of the bit line contact 319. An etching process, such as an anisotropic dry etching process, may be performed after the lithography process to form a bit line contact opening in the second insulating film 311. An upper surface of the contact 317 may be exposed through the bit line contact opening. A cleaning process using a reducing agent may be optionally performed to remove defects on the upper surface of the contact 317. The reducing agent may be titanium tetrachloride, tantalum tetrachloride, or a combination thereof. After the cleaning process, a first capping layer 321 can be formed to cover the bottom and sidewalls of the bit line contact opening. In some embodiments, the first capping layer 321 includes tungsten nitride. The first capping layer 321 can prevent the upper surface of the contact 317 from being exposed to oxygen or air; therefore, the first capping layer 321 can reduce the formation of defects on the upper surface of the contact 317. A conductive material such as aluminum, copper, tungsten, cobalt, or other suitable metal or metal alloy is deposited in the bit line contact through a metallization process such as chemical vapor deposition, physical vapor deposition, sputtering, or the like to form the bit line contact 319. A planarization process such as chemical mechanical polishing can be performed after the metallization process to remove excess deposited material and provide a substantially flat surface for subsequent processing steps. In FIG30 , a third insulating film 313 may be formed on the second insulating film 311. The third insulating film 313 may include the same material as the first insulating film 309, but is not limited thereto. A lithography process may be used to pattern the third insulating film 313 to define the positions of the bit lines 323. An etching process, such as an anisotropic dry etching process, may be performed after the lithography process to form bit line trench openings 323′ in the third insulating film 313. In some embodiments, the lithography process may further pattern the third insulating film 313 to define the positions of a plurality of contact holes 325′, and an etching process may be performed to form the plurality of contact holes 325′ penetrating the third insulating film 313, the second insulating film 311, and the first insulating film 309. In other words, the contact holes 325′ are considered to be deep holes, while the bit line trench openings 323′ are considered to be relatively shallow holes. In FIG31 , bitline trench opening 323′ and contact hole 325′ can be filled with a material by a process such as chemical vapor deposition, physical vapor deposition, sputtering, or the like. In some embodiments, contact hole 325′ is deeper than bitline trench opening 323′, and bitline trench opening 323′ can be completely filled with filling material 323-1, while contact hole 325′ can be partially filled with filling material 325-1, which can be the same as filling material 323-1. In some embodiments, the upper portion of contact hole 325′ in third insulating film 313 is not filled with filling material 325-1. In Figure 32, an etching process, such as an isotropic etching process, can be performed to remove a portion of the third insulating film 313 around the contact hole 325' to form a plurality of transition holes 325", which have a narrow portion 325"-1 occupied by the filling material 325-1 in the second insulating film 311 and a wide portion 325"-2 in the third insulating film 313. In FIG33 , fill material 325-1 and fill material 323-1 are stripped from transition hole 325″ and bit line trench opening 323′, respectively. After stripping the fill material, a conductive material such as aluminum, copper, tungsten, cobalt, or other suitable metal or metal alloy is deposited in the plurality of bit line trench openings 323′ to form bit lines 323 and in the transition hole 325″ to form a plurality of capacitor contacts 325 by a metallization process such as chemical vapor deposition, physical vapor deposition, sputtering, or the like. A planarization process, such as chemical mechanical polishing, may be performed after the metallization process to remove excess deposited material and provide a substantially planar surface for subsequent processing steps. The capacitor contact 325 includes a neck 325a and a head 325b above the neck 325a. In some embodiments, the head 325b has a curved sidewall 325c. In some embodiments, the head 325b has a tapered profile. 34 , a patterned mask 401 having a plurality of openings 403 is formed on the third insulating film 313. The third insulating film 313 is partially exposed through the openings 403. In some embodiments, the third insulating film 313 and the patterned mask 401 include different materials so that the etching selectivity can be different in a subsequent etching process. 35 , an etching process is performed using patterned mask 401 as an etching mask to form a plurality of openings 405 penetrating second insulating film 311 and third insulating film 313. First insulating film 309 is partially exposed through openings 405. In some embodiments, the etching process for forming openings 405 includes a wet etching process, a dry etching process, or a combination thereof. In FIG36 , patterned mask 401 is removed. In some embodiments, patterned mask 401 is removed by a stripping process, an ashing process, an etching process, or other suitable processes. After patterned mask 401 is removed, the upper surface of third insulating film 313, head portion 325 b of capacitor contact 325, and bit line 323 are exposed. In FIG. 37 , a dielectric liner layer 407 is conformally formed in the openings 405 and over the upper surface of the third insulating film 313 , the head 325 b of the capacitor contact 325 , and the bit line 323 . In some embodiments, a thickness 407T of the dielectric liner layer 407 is adjusted such that the air gap 333 is enclosed in the portion of the dielectric liner layer 407 filling the opening 405. In some embodiments, a width 405W of the opening 405 is less than twice the thickness 407T of the dielectric liner layer 407. Furthermore, in some embodiments, dielectric liner layer 407 is made of or includes boron carbon nitride (BCN). However, any other suitable dielectric material may be utilized. Fabrication techniques for dielectric liner layer 407 may include a deposition process, such as a CVD process, a PVD process, an ALD process, a spin-on process, or other suitable methods. In some embodiments, air gap 333 is enclosed (or sealed) within the portion of dielectric liner layer 407 that fills opening 405. In FIG. 38 , the dielectric liner layer 407 is partially removed to form a liner structure 331. In some embodiments, the dielectric liner layer 407 is removed by a planarization process, an etch-back process, or a combination thereof. The planarization process may include a chemical mechanical polishing (CMP) process. It should be understood that the air gap 333 does not protrude from the upper surface of the third insulating film 313. Therefore, after the planarization process and / or the etch-back process, the air gap 333 is still closed (or sealed) by the liner structure 331. In FIG39 , a fourth insulating film 315 may be formed on the third insulating film 313. The fourth insulating film 315 may include, but is not limited to, the same material as the first insulating film 309. A photolithography process may be used to pattern the fourth insulating film 315 to define the locations of the plurality of capacitor plugs 327. After the lithography process, an etching process, such as an anisotropic dry etching process, may be performed to form a plurality of plug openings through the fourth insulating film 315 to expose the head portion 325 b. Following the etching process, a conductive material, such as aluminum, copper, tungsten, cobalt, or another suitable metal or metal alloy, is deposited in the plurality of plug openings via a metallization process, such as chemical vapor deposition, physical vapor deposition, sputtering, or the like, to form a plurality of capacitor plugs 327 above the head portion 325 b. In some embodiments, a plurality of barrier layers 341 may be disposed between the capacitor plugs 327 and the fourth insulating film 315, respectively. A planarization process, such as chemical mechanical polishing, may be performed after the metallization process to remove excess deposited material and provide a substantially flat surface for subsequent processing steps. 40 , an etch-back process is performed to remove a top portion of the fourth insulating film 315, exposing a protruding portion 327 a of the capacitor plug 327 and a top portion 341 a of the barrier layer 341. In some embodiments, after the etch-back process, the top surface of the capacitor plug 327 is higher than the top surface of the fourth insulating film 315, and the sidewalls of the top portion 341 a are exposed. 41 , a deposition process is performed to form a liner layer 329 ′ that covers the upper surface of the fourth insulating film 315 , the upper surface of the protruding portion 327 a , the upper surface of the top portion 341 a , and the sidewalls of the top portion 341 a . In some embodiments, the liner layer 329 ′ is a silicon-containing layer, such as a polysilicon layer. After depositing the liner layer 329', a thermal treatment is performed to form a plurality of landing pads 329 above the fourth insulating film 315. Each landing pad 329 includes a capacitor plug 327, a barrier layer 341, a first spacer (metal silicide) 329a above the protrusion 327a, and a second spacer (metal silicide) 329b on the sidewalls of the top portion 341a. In some embodiments, the thermal treatment is a silicidation process. The thermal treatment transforms the protruding portion 327a and a portion of the liner layer 329' into first spacers 329a, and transforms the top portion 341a of the barrier layer 341 and the liner layer 329' into second spacers 329b. Based on the thermal treatment, the landing pad 329 is formed without using lithography, that is, the landing pad 329 is self-aligned with the capacitor plug 327. In some embodiments, the thickness and shape of the protruding portion 327a and the top portion 341a may be changed after the thermal treatment (not shown in FIG. 21 ). After the thermal treatment, the semiconductor structure 300 is formed. Please refer to Figures 42a and 42b. Figure 42a is a schematic diagram of a semiconductor device 500 according to some embodiments of the present disclosure. Figure 42b is a partially enlarged view of a semiconductor device 500 according to some embodiments of the present disclosure. In some embodiments, the semiconductor device 500 includes a memory structure, such as a dynamic random access memory (DRAM). The semiconductor device 500 includes a first dielectric layer 503 disposed above a semiconductor substrate 501, a metal plug 519a, a metal plug 519b, and a metal plug 519c. The semiconductor device 500 includes a first dielectric layer 503, a metal plug 519a, a metal plug 519b, and a metal plug 519c disposed over a semiconductor substrate 501. Furthermore, in some embodiments, an etch stop layer 505 is disposed over the first dielectric layer 503, and the metal plugs 519a, 519b, and 519c protrude from the etch stop layer 505. It should be understood that although FIG42a only illustrates three first metal plugs, the present disclosure is not limited thereto. Depending on product requirements, the number of first metal plugs in semiconductor device 500 may be fewer than or greater than three. Referring to FIG42b , first metal plug 519a includes an upper portion 519a1 protruding from upper surface 505T of etch stop layer 505 and a lower portion 519a2 below upper portion 519a1. In some embodiments, the first metal plug 519a, the first metal plug 519b, and the first metal plug 519c are the same. It should be understood that the following disclosure related to the first metal plug 519a can also be applied to the first metal plug 519b and the first metal plug 519c. In some embodiments, the etch stop layer 505 and the first dielectric layer 503 surround the lower portion 519a2 of the first metal plug 519a, and the upper portion 519a1 of the first metal plug 519a has a rounded (or curved) top surface TS. In some embodiments, the etch stop layer 505 and the first dielectric layer 503 abut each sidewall of the lower portion 519a2. In some embodiments, the top surface TS of the upper portion 519a1 is convex and connects a first sidewall SW1 of the upper portion 519a1 to a second sidewall SW2 of the upper portion 519a1. Furthermore, semiconductor device 500 includes a second metal plug 537a, a second metal plug 537b, and a second metal plug 537c, respectively disposed over first metal plug 519a, first metal plug 519b, and first metal plug 519c. Semiconductor device 500 also includes a second dielectric layer 507 and a third dielectric layer 523. Second dielectric layer 507 is disposed over etch stop layer 505, and third dielectric layer 523 is disposed over second dielectric layer 507. Semiconductor device 500 also includes a silicide layer 521a, a silicide layer 521b, and a silicide layer 521c. The silicide layer 521a is disposed between the first metal plug 519a and the second metal plug 537a; the silicide layer 521b is disposed between the first metal plug 519b and the second metal plug 537b; and the silicide layer 521c is disposed between the first metal plug 519c and the second metal plug 537c. By forming the silicide layers 521a, 521b, and 521c, the contact resistance between the first metal plugs (e.g., 519a, 519b, 519c) and the second metal plugs (e.g., 537a, 537b, 537c) can be reduced, thereby improving the performance of the semiconductor device 500. However, in some other embodiments, the silicide layers 521a, 521b, and 521c can be omitted. The second metal plug 537a extends to contact the upper surface 505T of the etch stop layer 505. In some embodiments, the first sidewall SW1 of the upper portion 519a1 is in direct contact with the second metal plug 537a, and the second sidewall SW2 of the upper portion 519a1 is in direct contact with the second dielectric layer 507. The second dielectric layer 507 is separated from the first sidewall SW1. A height H1 of the first sidewall SW1 is substantially the same as a height H2 of the second dielectric layer 507. In the context of the present disclosure, the word "substantially" means preferably at least 90%, more preferably 95%, even more preferably 98%, and most preferably 99%. More specifically, the upper surface TS of the upper portion 519 a 1 has a highest point TP, and the highest point TP is higher than the upper surface 507T of the second dielectric layer 507 . That is, the upper portion 519 a 1 protrudes from the upper surface 507T of the second dielectric layer 507 . In addition, the top surface TS of the upper portion 519a1 is separated from the second metal plug 537a by the silicide layer 521a, and the silicide layer 521a extends between the top surface TS and the third dielectric layer 523. A portion of the silicide layer 521a is exposed at and in direct contact with the third dielectric layer 523. In other words, a portion of the third dielectric layer 523 is disposed above the upper portion 519a1. The second metal plug 537a is separated from the second dielectric layer 507 by an air gap 536a1 and an air gap 536a2; the second metal plug 537b is separated from the second dielectric layer 507 by an air gap 536b1 and an air gap 536b2; and the second metal plug 537c is separated from the second dielectric layer 507 by an air gap 536c1 and an air gap 536c2. By forming the air gaps 536a1, 536a2, 536b1, 536b2, 536c1, and 536c2, parasitic capacitance between adjacent second metal plugs can be reduced, thereby improving the operating speed of the semiconductor device 500. However, in some embodiments, the air gaps 536a1, 536a2, 536b1, 536b2, 536c1, and 536c2 can be omitted. Semiconductor device 500 further includes bit lines 550a, 550b, and 550c, and a fourth dielectric layer 539. Bit lines 550a, 550b, and 550c are disposed above and electrically connected to second metal plugs 537a, 537b, and 537c. Bit lines 550a, 550b, and 550c are also electrically connected to first metal plugs 519a, 519b, and 519c via second metal plugs 537a, 537b, and 537c. Fourth dielectric layer 539 surrounds bit lines 550a, 550b, and 550c. In semiconductor device 500, because first metal plugs 519a, 519b, and 519c have rounded upper surfaces, the contact area between first metal plugs 519a, 519b, and 519c and second metal plugs 537a, 537b, and 537c is increased compared to a configuration in which the first metal plugs have flat upper surfaces and the second metal plugs are perfectly aligned with the first metal plugs. The rounded upper surfaces of first metal plugs 519a, 519b, and 519c can result in a corresponding reduction in the resistance between first metal plugs 519a, 519b, and 519c and second metal plugs 537a, 537b, and 537c, thereby improving overall device performance. Furthermore, since first metal plugs 519a, 519b, and 519c do not have sharp portions, the electric field intensity on the circular upper surfaces of first metal plugs 519a, 519b, and 519c is uniformly distributed. Consequently, the lifespan of semiconductor device 500 can be significantly extended, and the performance and reliability of the device can be improved. Furthermore, since etch stop layer 505 abuts the sidewalls of first metal plugs 519a, 519b, and 519c, exposure of underlying electronic components can be prevented during the process of forming second metal plugs 537a, 537b, and 537c, and problems caused by misalignment between first metal plugs 519a, 519b, and 519c and second metal plugs 537a, 537b, and 537c can be prevented or reduced. In addition, the semiconductor device 500 further includes a liner structure 560a and a liner structure 560b. The liner structure 560a is disposed between the second metal plug 537a and the second metal plug 537b, and the liner structure 560b is disposed between the second metal plug 537b and the second metal plug 537c. As shown in Figures 42a and 42b, semiconductor device 500 includes an air gap 565a and an air gap 565b, respectively, surrounded by a liner structure 560a and a liner structure 560b. The liner structures 560a and 560b extend from the upper surface 505T to the lower surface of the fourth dielectric layer 539. The liner structures 560a and 560b do not contact the bit lines 550a, 550b, and 550c. In other words, the liner structures 560a and 560b penetrate the entire second dielectric layer 507 and the entire third dielectric layer 523. In various embodiments, the pad structure 560b and the air gap 565b may be omitted. By forming the liner structure 560 a , the liner structure 560 b , the air gap 565 a , and the air gap 565 b , parasitic capacitance between adjacent second metal plugs can be reduced, thereby improving the operating speed of the semiconductor device 500 . Please refer to Figures 43 to 61. Figures 43 to 61 are cross-sectional views illustrating intermediate stages of forming a semiconductor device 500 according to some embodiments of the present disclosure. 43 , a semiconductor substrate 501 is provided. The semiconductor substrate 501 may be part of an integrated circuit (IC) die that includes various passive and active microelectronic elements, such as resistors, capacitors, inductors, diodes, p-type field effect transistors (pFETs), n-type field effect transistors (nFETs), metal oxide semiconductor field effect transistors (MOSFETs), complementary metal oxide semiconductor (CMOS) transistors, bipolar junction transistors (BJTs), laterally diffused MOS (LDMOS) transistors, high voltage transistors, high frequency transistors, fin field effect transistors (FinFETs), other suitable IC components, or combinations thereof. Depending on the stage of IC fabrication, semiconductor substrate 501 may include features configured to form IC features (e.g., doped regions, isolation features, gate features, source / drain features, interconnect features, other features, or combinations thereof). For clarity, semiconductor substrate 501 has been simplified. It should be understood that additional features may be added to semiconductor substrate 501, and that some of the features described below may be replaced, modified, or eliminated in other embodiments. A first dielectric layer 503 , an etch stop layer 505 , and a second dielectric layer 507 are sequentially disposed over the semiconductor substrate 501 . The material of the first dielectric layer 503 includes silicon oxide, silicon carbide, silicon nitride, silicon oxynitride, other suitable materials or combinations thereof, and the manufacturing technology of the first dielectric layer 503 includes a deposition process, such as a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, an atomic layer deposition (ALD) process, a spin coating process or other suitable processes. Some materials and processes used to form the etch stop layer 505 and the second dielectric layer 507 are similar or identical to the materials and processes used to form the first dielectric layer 503 and are not described again herein. It should be understood that, according to some embodiments, the material of the etch stop layer 505 is different from the material of the second dielectric layer 507. After forming the second dielectric layer 507, a photoresist pattern 509 having a plurality of openings 512 is disposed over the second dielectric layer 507, and the openings 512 expose the second dielectric layer 507. In some embodiments, the photoresist pattern 509 may be fabricated by a deposition process and a patterning process. The deposition process for forming the photoresist pattern 509 may include a CVD process, a high-density plasma chemical vapor deposition (HDPCVD) process, a spin coating process, or other suitable processes. The patterning process for forming the photoresist pattern 509 may include a lithography process. The lithography process may include photoresist coating (e.g., spin coating), soft baking, mask alignment, exposure, post-exposure baking, photoresist development, rinsing, and drying (e.g., hard baking). 44 , an etching process is performed on the semiconductor substrate 501 using the photoresist pattern 509 as a mask. The etching process is performed until the upper surface 501T of the semiconductor substrate 501 is exposed, and a plurality of openings 514 are formed below the openings 512 . The openings 514 are surrounded by the remaining second dielectric layer 507, the remaining etch stop layer 505, and the remaining first dielectric layer 503. The etching process may be a dry etching process, a wet etching process, or a combination thereof. 45 , a metal layer 517 is deposited to fill the openings 514 and the openings 512 . The metal layer 517 also extends onto the photoresist pattern 509 . In some embodiments, the metal layer 517 includes copper (Cu). In some other embodiments, the metal layer 517 includes tungsten (W), cobalt (Co), titanium (Ti), aluminum (Al), tantalum (Ta), or other suitable materials. In addition, in some embodiments, the metal layer 517 is formed using a CVD process, a PVD process, an ALD process, a plating process (e.g., electroplating), a sputtering process, or other suitable processes. 46 , a portion of the metal layer 517 on the photoresist pattern 509 is removed to form a metal portion 517 a, a metal portion 517 b, and a metal portion 517 c. More specifically, according to some embodiments, the portions of the metal layer 517 covering the photoresist pattern 509 are removed, while the portions of the metal layer 517 deposited in the openings 512 and 514 remain. In some embodiments, excess portions of the metal layer 517 are removed by a planarization process or an etching process. The planarization process may be a chemical mechanical polishing (CMP) process. 47 , the photoresist pattern 509 is removed. In some embodiments, during the removal process of the photoresist pattern 509, portions of the metal portions 517 a, 517 b, 517 c protruding from an upper surface 507T of the second dielectric layer 507 are slightly etched, resulting in first metal plugs 519 a, 519 b, 519 c (i.e., remaining metal portions 517 a, 517 b, 517 c). Specifically, according to some embodiments, each first metal plug 519 a , 519 b , 519 c penetrates the second dielectric layer 507 , the etch stop layer 505 , and the first dielectric layer 503 to be electrically connected to the electronic components in the semiconductor substrate 501 . 48 , an anisotropic etching process is performed to partially remove first metal plugs 519 a , 519 b , and 519 c , so that each of the etched first metal plugs 519 a , 519 b , and 519 c has a rounded (or curved) top surface TS. In some embodiments, top surface TS is a convex surface. As described above, the highest point TP of the top surface TS is higher than the top surface 507T of the second dielectric layer 507. More specifically, an edge E of the top surface TS is in direct contact with the top surface 507T of the second dielectric layer 507. In some embodiments, the anisotropic etching process is a dry etching process. In FIG49 , silicide layers 521a, 521b, and 521c are deposited over first metal plugs 519a, 519b, and 519c through a silicide process. In some embodiments, the silicide process includes a metal material deposition process and an annealing process performed sequentially. In some embodiments, the deposition process of the silicide process includes a PVD process, an ALD process, or other suitable process. After the annealing process, unreacted metal material is removed. In some embodiments, the silicide layers 521a, 521b, and 521c include one or more of copper silicide, tungsten silicide, cobalt silicide, titanium silicide, nickel silicide, and molybdenum silicide. As described above, by forming the silicide layers 521a, 521b, and 521c, the contact resistance between the first metal plugs (e.g., 519a, 519b, and 519c) and the upper conductive features (e.g., second metal plugs 537a, 537b, and 537c shown in FIG. 42 ) can be reduced, thereby improving device performance. In some other embodiments, the silicide process is not performed and the silicide layers 521a, 521b, and 521c can be omitted. In FIG50 , a third dielectric layer 523 is formed to cover the second dielectric layer 507 and the silicide layers 521 a, 521 b, and 521 c. The top surface TS is separated from the third dielectric layer 523 by the silicide layers 521 a, 521 b, and 521 c. Some materials and processes for forming the third dielectric layer 523 are similar or identical to those used to form the first dielectric layer 503 and are not described again herein. In some embodiments, the material of the third dielectric layer 523 is different from the material of the etch stop layer 505. 51 , a photoresist pattern 525 having a plurality of openings 528 is disposed over the third dielectric layer 523, and the third dielectric layer 523 is exposed through the openings 528. Some materials and processes used to form the photoresist pattern 525 are similar or identical to those used to form the photoresist pattern 509 and are not described again herein. In FIG52 , an etching process is performed on the structure using the photoresist pattern 525 as a mask. The etching process is performed until the silicide layers 521 a, 521 b, and 521 c or the first metal plugs 519 a, 519 b, and 519 c are exposed. A plurality of openings 530 are formed in the remaining third dielectric layer 523, and a plurality of gaps 532 are formed in the remaining second dielectric layer 507. The etching process may be a dry etching process, a wet etching process, or a combination thereof. In some embodiments, the positions of the openings 518 above the second dielectric layer 507 result in the openings 530 exposing portions of the second dielectric layer 507 during the etching process, and removing the exposed portions of the second dielectric layer 507 to form the gaps 532. According to some embodiments, the upper surface 505T of the etch stop layer 505 is exposed through the gaps 532. As described above, the etch stop layer 505 can protect the underlying electronic components from being exposed during the etching process. Furthermore, each of the first metal plugs 519a, 519b, and 519c has a first sidewall SW1 and a second sidewall SW2 opposite the first sidewall SW1. In some embodiments, the first sidewall SW1 is exposed through the gap 532, while the second sidewall SW2 remains covered by the second dielectric layer 507. In some embodiments, after forming the openings 530 and the gaps 532, portions of the silicide layers 521a, 521b, and 521c are sandwiched between the third dielectric layer 523 and the corresponding first metal plug. 53 , an energy-removable material 535 is disposed on the sidewalls of the openings 518, the sidewalls of the openings 530, and the sidewalls of the gaps 532. Since the energy-removable material 535 occupies a portion of the openings 528 and the openings 530, the space of the openings 528 and the openings 530 is reduced. In some embodiments, the energy-removable material 535 comprises a thermally decomposable material. In other embodiments, the energy-removable material 535 comprises a photon-decomposable material, an electron-beam-decomposable material, or other suitable energy-decomposable material. Specifically, in some embodiments, the energy-removable material 535 comprises a base material and a decomposable porogen material that is substantially removed upon exposure to energy (e.g., heat). In some embodiments, the base material may include hydrogen silsesquioxane (HSQ), methyl silsesquioxane (MSQ), porous polyarylether (PAE), porous SiLK, or porous silicon dioxide (SiO 2), and the decomposable porogen material may include a porogen organic compound that can provide porosity to the space originally occupied by the energy-removable material 535 during subsequent processing. In some embodiments, the energy-removable material 535 is formed by a deposition process and an etching process. In some embodiments, the deposition process includes CVD, PVD, ALD, spin coating, or other suitable processes, and the etching process includes a reactive ion etching (RIE) process to remove excess portions above the photoresist pattern 525. 54 , the openings 518, the openings 530, and the gaps 532 are filled with a metal layer 537, and the metal layer 537 extends onto the photoresist pattern 525. The metal layer 537 is in direct contact with the first metal plugs 519a, 519b, 519c and the etch stop layer 505. In some embodiments, the metal layer 537 includes copper (Cu). In some other embodiments, the metal layer 537 includes tungsten (W), cobalt (Co), titanium (Ti), aluminum (Al), tantalum (Ta), or other suitable materials. In addition, in some embodiments, the metal layer 537 is formed using a CVD process, a PVD process, an ALD process, a plating process (e.g., electroplating), a sputtering process, or other suitable processes. 55 , a planarization process is performed to remove the photoresist pattern 525, excess portions of the metal layer 537, and the energy-removable material 535 above the third dielectric layer 523. The planarization process may be a CMP process. 56 , a patterned mask 601 having a plurality of openings 603 is formed over the third dielectric layer 523, the metal layer 537, and the energy-removable material 535. The third dielectric layer 523 is partially exposed through the openings 603. In some embodiments, the third dielectric layer 523 and the patterned mask 601 comprise different materials, so that the etching selectivity can be different in a subsequent etching process. 57 , an etching process is performed using patterned mask 601 as an etching mask to form a plurality of openings 605 penetrating third dielectric layer 523 and second dielectric layer 507. Etch stop layer 505 is partially exposed through openings 605. In some embodiments, the etching process used to form openings 605 includes a wet etching process, a dry etching process, or a combination thereof. In FIG58 , the patterned mask 601 is removed. In some embodiments, the patterned mask 601 is removed by a stripping process, an ashing process, an etching process, or other suitable processes. After the patterned mask 601 is removed, the upper surfaces of the third dielectric layer 523, the metal layer 537, and the energy-removable material 535 are exposed. In FIG. 59 , a dielectric liner layer 607 is conformally formed in the openings 605 and over the respective upper surfaces of the etch stop layer 505 , the third dielectric layer 523 , the metal layer 537 , and the energy removable material 535 . In some embodiments, a thickness 607T of the dielectric liner layer 607 is adjusted so that an air gap 565a and an air gap 565b are enclosed in each portion of the dielectric liner layer 607 filling the openings 605. In some embodiments, a width 605W of the openings 605 is less than twice the thickness 607T of the dielectric liner layer 607. Furthermore, in some embodiments, dielectric liner layer 607 is made of or includes boron carbon nitride (BCN). However, any other suitable dielectric material may be utilized. The fabrication technique for dielectric liner layer 607 may include a deposition process, such as a CVD process, a PVD process, an ALD process, a spin-on process, or other suitable methods. In some embodiments, air gaps 565a and 565b are enclosed (or sealed) within the portions of dielectric liner layer 607 that fill the openings 605. In other words, air gaps 565a and 565b are not exposed. In FIG60 , dielectric liner layer 607 is partially removed to form a liner structure 560 a and a liner structure 560 b. In some embodiments, dielectric liner layer 607 is removed by a planarization process, an etch-back process, or a combination thereof. The planarization process may include a chemical mechanical polishing (CMP) process. It should be understood that air gaps 565 a and 565 b do not protrude from the upper surface of third dielectric layer 523. Therefore, after the planarization process and / or the etch-back process, air gaps 565 a and 565 b are still enclosed (or sealed) by liner structures 560 a and 560 b, respectively. In FIG61 , a fourth dielectric layer 539 is formed to cover the third dielectric layer 523, the energy-removable material 535, the second metal plug 537 a, the second metal plug 537 b, the second metal plug 537 c, the liner structure 560 a, and the liner structure 560 b. Some of the materials and processes used to form the fourth dielectric layer 539 are similar or identical to those used to form the first dielectric layer 103 and are not described again here. After forming the fourth dielectric layer 539, bit lines 550a, 550b, and 550c are formed in the fourth dielectric layer 539. In some embodiments, the bit lines 550a, 550b, and 550c are formed by a lithography process for defining a plurality of bit line locations, a deposition location for forming a plurality of bit line locations at the locations defined by the lithography process, and a CMP process for planarizing the upper surfaces of the bit lines 550a, 550b, and 550c. After forming the bit lines 550a, 550b, and 550c, a thermal treatment is used to remove the decomposable porogen material of the energy-removable material 535 to produce a plurality of pores, and the pores are filled with air, so that air gaps 536a1, 536a2, 536b1, 536b2, 536c1, 536c2 are obtained between the second metal plugs 537a, 537b, 537c and the third dielectric layer 523, as shown in FIG. 42a. In some other embodiments, the heat treatment process may be replaced by a phototreatment process, an electron beam treatment process, a combination thereof, or other suitable energy treatment process. For example, ultraviolet (UV) light or laser light may be used to remove the decomposable porogen material of the energy-removable material 535 to obtain the air gaps 536a1, 536a2, 536b1, 536b2, 536c1, and 536c2. As previously described, because air has a relatively low dielectric constant, air gaps (e.g., air gaps 536a1, 536a2, 536b1, 536b2, 536c1, 536c2, 565a, and 565b) can be incorporated into semiconductor device 500 to reduce parasitic capacitance within second metal plugs 537a, 537b, and 537c, thereby improving the operating speed of semiconductor device 500. In some other embodiments, energy-removable material 535 and air gaps 536a1, 536a2, 536b1, 536b2, 536c1, and 536c2 are not formed. In these cases, second metal plugs 537a, 537b, and 537c can directly contact third dielectric layer 523. Because the first metal plugs 519a, 519b, and 519c have a rounded (or curved) top surface TS, the contact area between the first metal plugs 519a, 519b, and 519c and the second metal plugs 537a, 537b, and 537c (or the contact area between the silicide layers 521a, 521b, and 521c and the second metal plugs 537a, 537b, and 537c) is increased compared to a configuration in which the first metal plugs have a flat top surface and the second metal plugs are perfectly aligned with the first metal plugs. The increased contact area of ​​the rounded top surface TS can result in a corresponding reduction in the resistance between the first metal plugs 519a, 519b, and 519c and the second metal plugs 537a, 537b, and 537c, thereby improving the overall performance of the device. Furthermore, since the first metal plugs 519a, 519b, 519c do not have sharp portions, the electric field intensity on the circular upper surface TS of the first metal plugs 519a, 519b, 519c is evenly distributed, thereby significantly extending the life of the semiconductor device 500 and improving the performance and reliability of the device. In addition, since the etch stop layer 505 is adjacent to the sidewalls of the first metal plugs 519a, 519b, 519c, the underlying electronic components can be prevented from being exposed during the process of forming the second metal plugs 537a, 537b, 537c, and problems caused by misalignment between the first metal plugs 519a, 519b, 519c and the second metal plugs 537a, 537b, 537c can be prevented or reduced. One embodiment of the present disclosure provides a semiconductor device comprising a substrate, a contact, a landing pad, a bit line, and an air gap. The contact is disposed above the substrate. The landing pad is disposed above the contact. The landing pad comprises a plug, a first spacer, and a second spacer. The plug is disposed above and in contact with the contact. The first spacer is disposed above the plug. The second spacer clamps a protruding portion of the plug. The bit line is disposed above the substrate. The air gap is disposed between the contact and the bit line. Another embodiment of the present disclosure provides a semiconductor device comprising a substrate, an etch stop layer, a first lower plug, a second lower plug, a first upper plug, a second upper plug, and an air gap. The etch stop layer is disposed above the substrate. The first lower plug and the second lower plug are disposed above the substrate and protrude from an upper surface of the etch stop layer. The first upper plug and the second upper plug are disposed above the first lower plug and the second lower plug, respectively. The air gap is disposed between the first upper plug and the second upper plug. An upper surface of the first lower plug is rounded. The first upper plug contacts a first sidewall of the first lower plug. Another embodiment of the present disclosure provides a method for fabricating a semiconductor device, comprising providing a substrate; forming a contact over the substrate; forming a bit line over the substrate; forming a liner structure to enclose an air gap, wherein the liner structure is formed between the contact and the bit line; and forming a landing pad over the contact, the method comprising: forming a barrier layer; forming a plug to contact the contact; and forming a first spacer and a second spacer over the plug. The first spacer is disposed over the plug, and the second spacer sandwiches a protruding portion of the plug. Embodiments disclosed herein have several advantageous features. In some embodiments, a semiconductor device structure includes a first dielectric liner portion and a second dielectric liner portion disposed adjacent to a first interconnect structure and a second interconnect structure, respectively. The semiconductor device structure also includes a filler portion surrounded by the second dielectric liner portion and an air gap enclosed within the first dielectric liner portion, which helps reduce capacitive coupling between adjacent interconnect structures and can reduce resistance-capacitance (RC) delay. As a result, the performance and reliability of the semiconductor device structure can be improved. Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations may be made without departing from the spirit and scope of the present disclosure as defined by the claims. For example, many of the processes described above may be implemented in different ways, and other processes or combinations thereof may be substituted for many of the processes described above. Furthermore, the scope of this application is not limited to the specific embodiments of the processes, machines, manufacture, compositions of matter, means, methods, and steps described in the specification. Those skilled in the art will understand from the disclosure herein that existing or future developed processes, machines, manufacture, compositions of matter, means, methods, or steps that function the same as or achieve substantially the same results as the corresponding embodiments described herein may be used in accordance with this disclosure. Accordingly, such processes, machines, manufacture, compositions of matter, means, methods, or steps are intended to be within the scope of this application. 10: Preparation method 30: Preparation method 100a: Semiconductor device structure 100b: Semiconductor device structure 101: Semiconductor substrate 103: First dielectric layer 105: Second dielectric layer 107: First conductive layer 107a: First conductive portion 107b: First conductive portion 107c: First conductive portion 107d: First conductive portion 109: Second conductive layer 109a: Second conductive portion 109b: Second conductive portion 109c: Second conductive portion 109d: Second conductive portion 111: Patterned mask 114: Opening 116: Opening 119a: Interconnect structure 119b: Interconnect structure 119c: Interconnect structure 119d: Interconnect structure 124: opening 126: opening 126': opening 131: dielectric liner layer 131a: dielectric liner portion 131b: dielectric liner portion 131c: dielectric liner portion 131d: dielectric liner portion 134: air gap 137: filling layer 137': filling portion 139: filling layer 139': filling portion 141: cover layer 200a: semiconductor device structure 200b: semiconductor device structure 231: dielectric liner layer 231a: dielectric liner portion 231b: dielectric liner portion 231c: dielectric liner portion 231d: dielectric liner portion 234: gap 237: filling layer 237a: filling portion 237b: Filling portion 239: Filling layer 239a: Filling portion 239b: Filling portion 300: Semiconductor structure 301: Substrate 303: Isolation structure 305: Word line 305': Trench opening 305a: Bottom layer 305b: Intermediate layer 305c: Top layer 307: Active region 307a: First doped region 307b: Second doped region 309: First insulating film 311: Second insulating film 313: Third insulating film 315: Fourth insulating film 317: Contact 319: Bit line contact 321: First covering layer 323: Bit line 323-1: Filling material 323': Bit line trench opening 325: Capacitor contact 325-1: Filling material 325': Contact hole 325": Transition hole 325"-1: Narrow portion 325"-2: Wide portion 325a: Neck 325aW: Width 325b: Head 325bW: Width 325c: Curved sidewall 327: Plug 327a: Protrusion 327W: Width 329: Landing pad 329': Liner layer 329a: First spacer 329b: Second spacer 329bW: Width 331: Liner structure 333: Air gap 341: Barrier layer 341a: Top portion 401: Patterned mask 403: Opening 405: Opening 405W: Width 407: Dielectric liner layer 407T: Thickness 500: Semiconductor device501: semiconductor substrate 501T: upper surface 503: first dielectric layer 505: etch stop layer 505T: upper surface 507: second dielectric layer 507T: upper surface 509: photoresist pattern 512: opening 514: opening 517: metal layer 517a: metal portion 517b: metal portion 517c: metal portion 518: opening 519a: metal plug 519a1: upper portion 519a2: lower portion 519b: metal plug 519c: metal plug Plug 521a: Silicide layer 521b: Silicide layer 521c: Silicide layer 523: Third dielectric layer 525: Photoresist pattern 528: Opening 530: Opening 532: Gap 535: Energy-removable material 536a1: Air gap 536b1: Air gap 536c1: Air gap 536a2: Air gap 536b2: Air gap 536c2: Air gap 537: Metal layer 537a: Second metal plug 537b: Second metal plug 537c: Second metal plug 539: Fourth dielectric layer 550a: Bit line 550b: Bit line 550c: Bit line 560a: Pad structure 560b: Pad structure 565a: Air gap 565b: Air gap 601: Patterned mask 603: Opening 605: Opening 605W: Width 607: Dielectric liner layer 607T: Thickness A: First region B: Second region E: Edge H1: Height H2: Height S11: Step S13: Step S15: Step S17: Step S19 :Step S21:Step S23:Step S25:Step S27:Step S31:Step S33:Step S35:Step S37:Step S39:Step S41:Step S43:Step S45:Step S47:Step SW1:First side wall SW2:Second side wall T1:Thickness T2:Thickness TP:Highest point TS:Top surface TSA1:Top surface area TSA2:Top surface area W1:Width W2:Width W3:Width W4:Width Z:Direction Aspects of the present disclosure are best understood from the following detailed description when read in conjunction with the accompanying drawings. It should be understood that, in accordance with standard industry practice, various features are not drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or decreased for clarity of discussion. FIG1 is a schematic cross-sectional view illustrating a semiconductor device structure according to some embodiments of the present disclosure. FIG2 is a schematic cross-sectional view illustrating a semiconductor device structure according to some embodiments of the present disclosure. FIG3 is a schematic cross-sectional view illustrating a semiconductor device structure according to some embodiments of the present disclosure. FIG4 is a schematic cross-sectional view illustrating a semiconductor device structure according to some embodiments of the present disclosure. FIG5 is a flow diagram illustrating a method for preparing a semiconductor device structure according to some embodiments of the present disclosure. FIG6 is a flow diagram illustrating a method for preparing a semiconductor device structure according to some embodiments of the present disclosure. FIG7 is a schematic cross-sectional view illustrating an intermediate stage in which a first dielectric layer and a second dielectric layer are sequentially formed above a semiconductor substrate during the formation of a semiconductor device structure according to some embodiments of the present disclosure. FIG8 is a schematic cross-sectional view illustrating an intermediate stage in which a first conductive layer, a second conductive layer, and a patterned mask are sequentially formed above the second dielectric layer during the formation of a semiconductor device structure according to some embodiments of the present disclosure. Figure 9 is a schematic cross-sectional view illustrating an intermediate stage of using a patterned mask as an etching mask to form a first opening and a second opening to penetrate the first conductive layer and the second conductive layer during the formation of a semiconductor device structure according to some embodiments of the present disclosure. Figure 10 is a schematic cross-sectional view illustrating an intermediate stage of removing the patterned mask during the formation of the semiconductor device structure according to some embodiments of the present disclosure. Figure 11 is a schematic cross-sectional view illustrating an intermediate stage of forming a dielectric liner layer in the first opening and the second opening during the formation of the semiconductor device structure according to some embodiments of the present disclosure. Figure 12 is a schematic cross-sectional view illustrating an intermediate stage of forming a filling layer above the dielectric liner layer during the formation of the semiconductor device structure according to some embodiments of the present disclosure. Figure 13 is a schematic cross-sectional view illustrating an intermediate stage of partially removing the filling layer and the dielectric liner layer to expose the second conductive layer during the formation of the semiconductor device structure according to some embodiments of the present disclosure. Figure 14 is a schematic cross-sectional view illustrating an intermediate stage of forming a filling layer above the dielectric liner layer during the formation of the semiconductor device structure according to some embodiments of the present disclosure. FIG15 is a schematic cross-sectional view illustrating an intermediate stage of partially removing a filler layer and a dielectric liner layer to expose a second conductive layer during formation of a semiconductor device structure according to some embodiments of the present disclosure. FIG16 is a schematic cross-sectional view illustrating an intermediate stage of forming a dielectric liner layer within a first opening and a second opening during formation of a semiconductor device structure according to some embodiments of the present disclosure. FIG17 is a schematic cross-sectional view illustrating an intermediate stage of forming a filler layer above a dielectric liner layer during formation of a semiconductor device structure according to some embodiments of the present disclosure. FIG18 is a schematic cross-sectional view illustrating an intermediate stage of partially removing a filler layer and a dielectric liner layer to expose a second conductive layer during formation of a semiconductor device structure according to some embodiments of the present disclosure.FIG19 is a schematic cross-sectional view illustrating an intermediate stage of forming a filling layer above a dielectric liner layer during the formation of a semiconductor device structure according to some embodiments of the present disclosure. FIG20 is a schematic cross-sectional view illustrating an intermediate stage of partially removing the filling layer and the dielectric liner layer to expose a second conductive layer during the formation of a semiconductor device structure according to some embodiments of the present disclosure. FIG21 is a schematic cross-sectional view illustrating a semiconductor structure according to some embodiments of the present disclosure. FIG22 to FIG41 are schematic cross-sectional views illustrating an intermediate stage of forming the semiconductor structure shown in FIG21 according to some embodiments of the present disclosure. FIG42a is a schematic cross-sectional view illustrating a semiconductor structure according to some embodiments of the present disclosure. FIG42b is a partially enlarged schematic view illustrating the semiconductor device shown in FIG42a according to some embodiments of the present disclosure. FIG43 to FIG61 are schematic cross-sectional views illustrating an intermediate stage of forming the semiconductor structure shown in FIG42a and FIG42b according to some embodiments of the present disclosure. 100a: semiconductor device structure 101:Semiconductor substrate 103: first dielectric layer 105: second dielectric layer 107a: first conductive portion 107b: first conductive portion 107c: first conductive portion 107d: first conductive portion 109a: second conductive portion 109b: second conductive portion 109c: second conductive portion 109d: second conductive portion 119a: Interconnection structure 119b: Interconnection structure 119c: Interconnection Structure 119d: Interconnection structure 131a: Dielectric liner portion 131b: Dielectric liner portion 131c: Dielectric liner part 131d: Dielectric liner part 134: Air Gap 137': Filling part 141: Covering layer A: First area B: Second Area W1: width W2: width

Claims

1. A semiconductor element, comprising: One base; An etch stop layer is disposed above the substrate; A first lower plug and a second lower plug are disposed above the substrate and protrude from an upper surface of the etch stop layer; a first upper plug and a second upper plug are respectively disposed above the first lower plug and the second lower plug; an air gap is disposed between the first upper plug and the second upper plug; and a gasket structure is disposed between the first upper plug and the second upper plug, wherein the gasket structure closes the air gap, wherein an upper surface of the first lower plug is circular, wherein the first upper plug contacts a first sidewall of the first lower plug; wherein the first upper plug is a landing pad, the landing pad including a central plug, a first gap and a second gap, the first gap being disposed above an upper surface of the central plug, and the second gap being disposed on a sidewall of a protruding portion of the central plug and clamping the protruding portion; wherein a top surface of the second gap is higher than an upper surface of the first gap.

2. The semiconductor device as claimed in claim 1, wherein the first upper plug is also in contact with the etch stop layer.

3. The semiconductor device as described in claim 1 further includes: A first dielectric layer is disposed above the substrate, wherein the etch stop layer is disposed above the first dielectric layer; A second dielectric layer is disposed above the etch stop layer; And a third dielectric layer, disposed above the second dielectric layer.

4. The semiconductor element as claimed in claim 3, wherein a second sidewall of the first lower plug is in contact with the second dielectric layer.

5. The semiconductor element as claimed in claim 4, wherein a height of the first sidewall of the first lower plug is substantially the same as a height of the second sidewall of the first lower plug.

6. The semiconductor element as claimed in claim 3, wherein the first sidewall of the first lower plug is separated from the second dielectric layer.

7. The semiconductor device as claimed in claim 3, wherein the third dielectric layer partially covers the first underpinning plug.

8. The semiconductor device as described in claim 3 further comprises: A first metal silicate layer is disposed on the first lower plug; And a second metal silicate layer is disposed on the second lower plug.

9. The semiconductor device as claimed in claim 8, wherein the first upper plug contacts the first metal silicate layer, and the second upper plug contacts the second metal silicate layer.

10. The semiconductor device as claimed in claim 8, wherein the first metal silicate layer and the second metal silicate layer are in contact with the third dielectric layer.

11. The semiconductor device as described in claim 1, further comprising: A fourth dielectric layer is disposed on the first upper plug, the second upper plug, and the pad structure; A first bit line and a second bit line are disposed in the fourth dielectric layer, wherein the first bit line and the second bit line are respectively disposed on the first upper plug and the second upper plug.

12. The semiconductor device as claimed in claim 11, wherein the pad structure does not contact the first bit line and the pad structure does not contact the second bit line.

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