KR20200084373A - How to reduce the leakage current of storage capacitors for display applications - Google Patents

Abstract

Embodiments of the present disclosure generally relate to a method for forming a metal-insulator-metal (MIM) capacitor for display applications. The method comprises forming a metal electrode on a substrate; And exposing the metal electrode to a nitrogen-containing plasma in a processing chamber. The substrate is maintained at a temperature in the range of about 20 degrees Celsius to about 200 degrees Celsius when the metal electrode is exposed to a nitrogen-containing plasma, the exposure converting the surface of the metal electrode to nitride. The method further includes forming a high K dielectric layer on the nitride surface of the metal electrode in the same processing chamber. Due to the plasma treatment of the metal electrode, the leakage current of the MIM capacitor is reduced, and the breakdown field of the MIM capacitor is improved.

Description

How to reduce the leakage current of storage capacitors for display applications

[0001] Embodiments of the present disclosure generally relate to a method for forming a layer stack comprising a dielectric layer having a high dielectric constant (high K) value for display devices. More specifically, embodiments of the present disclosure relate to a method for forming a metal-insulator-metal (MIM) capacitor used in thin-film transistor (TFT) circuits.

[0002] Display devices have been widely used for a wide range of electronic applications, such as TVs, monitors, mobile phones, MP3 players, e-book readers, personal digital assistants (PDAs), and the like. In some devices, the pixel circuit in the backplane of the display panel utilizes TFTs and capacitors to control the color or brightness of each pixel of the display screen. The capacitors hold the charge to maintain the gate voltage of the driving TFT, so that color or luminance is maintained between the two resulting frame refreshes. A storage capacitor in a TFT circuit is generally a MIM structure that includes a layer of dielectric material disposed between two metal electrodes. Capacitance is determined by the dielectric constant of the dielectric material and the area of the capacitor.

[0003] Conventionally, silicon nitride having a dielectric constant of about 7 has been used as the dielectric material. As the resolution of the display increases, the area of each pixel continues to shrink. Therefore, the area for storage capacitors is very limited. To achieve the same capacitance, high K materials, such as zirconium dioxide (ZrO ₂ ), are utilized as the dielectric material. However, ZrO ₂ has a lower electron energy band gap when compared to silicon nitride. When ZrO ₂ is integrated with the bottom and top electrodes, the capacitor leakage current is high, the breakdown field is low, which makes the display device less stable and less reliable.

[0004] Accordingly, there is a need for a method for forming MIM capacitors for manufacturing stable and reliable display devices.

[0005] Embodiments of the present disclosure generally relate to a method for forming a metal-insulator-metal (MIM) capacitor for display applications. In one embodiment, the capacitor includes a first metal electrode and nitride disposed on the first metal electrode. Nitride is formed at a temperature ranging from about 20 degrees Celsius to about 200 degrees Celsius. The capacitor further includes a high K dielectric layer disposed on the nitride, and a second metal electrode disposed on the high K dielectric layer.

[0006] In another embodiment, a method includes forming a first metal electrode on a substrate; And exposing the first metal electrode to the nitrogen-containing plasma in the processing chamber. A portion of the first metal electrode is converted to nitride having a work function greater than 4.33 eV. Nitride is formed at a temperature ranging from about 20 degrees Celsius to about 200 degrees Celsius. The method comprises forming a high K dielectric layer on the nitride in the processing chamber; And forming a second metal electrode on the high K dielectric layer.

[0007] In another embodiment, a method includes forming a first metal electrode on a substrate; And exposing the first metal electrode to the nitrogen-containing plasma in the processing chamber. The substrate is maintained at a temperature ranging from about 50 degrees Celsius to about 180 degrees Celsius, and a portion of the first metal electrode is converted to nitride. The method comprises forming a high K dielectric layer on the nitride in the processing chamber; And forming a second metal electrode on the high K dielectric layer.

In a manner in which the above-listed features of the present disclosure can be understood in detail, a more detailed description of the present disclosure, briefly summarized above, may be made with reference to the embodiments, some of which are attached. It is illustrated in the drawings. It should be noted, however, that the appended drawings are merely illustrative of exemplary embodiments of the present disclosure and should not be regarded as limiting the scope of the present disclosure, which will allow other equally valid embodiments of the present disclosure. Because it can.
1 is a cross-sectional view of a processing chamber that can be used to process a metal layer, according to one embodiment of the present disclosure.
2 is a cross-sectional view of a processing chamber that can be used to process a metal layer, according to one embodiment of the present disclosure.
3 is a flow diagram of a method for forming a MIM capacitor, according to one embodiment of the present disclosure.
4A-4D illustrate schematic cross-sectional views of a MIM capacitor during different stages of the method of FIG. 3.
To facilitate understanding, identical reference numbers have been used where possible to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially included on other embodiments without further recitation.

[0014] Embodiments of the present disclosure generally relate to a method for forming a metal-insulator-metal (MIM) capacitor for display applications. The method comprises forming a metal electrode on a substrate; And exposing the metal electrode to a nitrogen-containing plasma in a processing chamber. The substrate is maintained at a temperature in the range of about 20 degrees Celsius to about 200 degrees Celsius when the metal electrode is exposed to a nitrogen-containing plasma, the exposure converting the surface of the metal electrode to nitride. The method further includes forming a high K dielectric layer on the nitride surface of the metal electrode in the same processing chamber. Due to the plasma treatment of the metal electrode, the leakage current of the MIM capacitor is reduced, and the breakdown field of the MIM capacitor is improved.

[0015] The terms “top,” “below,” “between,” and “top” as used herein refer to the relative position of one layer relative to other layers. Thus, for example, one layer disposed above or below another layer may directly contact another layer, or may have one or more intervening layers. Moreover, one layer disposed between the layers may be in direct contact with the two layers, or may have one or more intervening layers. In contrast, the first layer of the “top” of the second layer contacts the second layer. Additionally, the relative position of one layer relative to other layers is provided on the assumption that operations are performed on the substrate, without considering the absolute orientation of the substrate.

1 is a schematic cross-sectional view of one embodiment of a chemical vapor deposition (CVD) processing chamber 100 that can be used to perform the embodiments discussed herein. In the chamber 100, the metal electrode may be treated with nitrogen-containing plasma or oxygen-containing plasma. Additionally or alternatively, a high K dielectric layer, such as a ZrO ₂ layer, can be deposited on the treated metal electrode. One suitable CVD processing chamber, such as a plasma enhanced CVD (PECVD) processing chamber, is available from Applied Materials, Inc. located in Santa Clara, California. It is contemplated that other deposition chambers, including deposition chambers from other manufacturers, may be utilized to practice the present disclosure.

[0017] The chamber 100 generally includes one or more walls 142, a bottom 104, and a cover 112, which define the process volume 106. Gas distribution plate 110 and substrate support assembly 130 are disposed within process volume 106. The process volume 106 is accessed through a slit valve opening 108 formed through the wall 142 so that the substrate 102 can be transferred into and out of the chamber 100.

[0018] The substrate support assembly 130 includes a substrate receiving surface 132 for supporting the substrate 102. The stem 134 couples the substrate support assembly 130 to the lift system 136, and the lift system 136 raises and lowers the substrate support assembly 130 between the substrate transfer position and the processing position. A shadow frame 133 can be selectively disposed over the periphery of the substrate 102 during processing to prevent deposition on the edge of the substrate 102. The lift pins 138 are movably disposed through the substrate support assembly 130 and adapted to space the substrate 102 from the substrate receiving surface 132. Substrate support assembly 130 may also include heating and/or cooling elements 139, wherein heating and/or cooling elements 139 may have a predetermined temperature, such as about 200 degrees Celsius or less, such as , About 20 degrees Celsius to about 200 degrees Celsius, or about 50 degrees Celsius to about 180 degrees Celsius, utilized to hold the substrate support assembly 130. In one embodiment, the substrate support assembly 130 is maintained between about 100 degrees Celsius and about 150 degrees Celsius during processing.

[0019] The substrate support assembly 130 may also include ground straps 131 to provide an RF return path around the periphery of the substrate support assembly 130.

[0020] The gas distribution plate 110 is coupled to the wall 142 or cover 112 of the chamber 100 by a suspension 114 at its periphery. The gas distribution plate 110 is also attached to the cover 112 by one or more central supports 116 to control the straightness/curvature of the gas distribution plate 110 and/or to help prevent sagging. It is coupled. It is contemplated that one or more central supports 116 may be utilized. The gas distribution plate 110 can have different configurations with different dimensions. The gas distribution plate 110 has a downstream surface 150. A plurality of apertures 111 are formed through the gas distribution plate 110. The downstream surface 150 faces the upper surface 118 of the substrate 102 disposed on the substrate support assembly 130. The apertures 111 can have different shapes, number, densities, dimensions, and distributions across the gas distribution plate 110. In one embodiment, the diameter of the apertures 111 may be selected from about 0.01 inches to about 1 inch.

[0021] The gas source 120 is coupled to the cover 112 to provide one or more gases to the process volume 106 through the cover 112 and then through the aperture 111 formed in the gas distribution plate 110. . The gas source 120 may be a nitrogen-containing gas source. A vacuum pump 109 is coupled to the chamber 100 to maintain the gas in the process volume 106 at a predetermined pressure.

[0022] RF power source 122 is coupled to cover 112 and/or gas distribution plate 110 to provide RF power, the RF power being from one or more gases, such as a gas distribution plate from nitrogen-containing gas ( An electric field is generated between the gas distribution plate 110 and the substrate support assembly 130 so that plasma can be generated between the 110 and the substrate support assembly 130. RF power can be applied at various RF frequencies. For example, RF power may be applied at a frequency of about 0.3 MHz to about 200 MHz. In one embodiment, RF power is provided at a frequency of 13.56 MHz.

[0023] A remote plasma source 124, such as an inductive coupling remote plasma source, can also be coupled between the gas source 120 and the gas distribution plate 110. Between the processing of the substrates, a cleaning gas may be energized at a remote plasma source 124 to remotely provide plasma utilized to clean chamber components. The cleaning gas entering process volume 106 may be further excited by RF power provided to gas distribution plate 110 by power source 122. Suitable cleaning gases include (but are not limited to) NF ₃ , F ₂ , and SF ₆ .

In one embodiment, the substrate 102 that can be processed in the chamber 100 may have a surface area of 10,000 cm ² or more, such as 25,000 cm ² or more, such as about 55,000 cm ² or more. It is understood that after processing, the substrate can be cut to form other smaller devices.

2 is a schematic cross-sectional view of an atomic layer deposition (ALD) chamber 200 that can be used to practice the embodiments discussed herein. In the chamber 200, the metal electrode may be treated with nitrogen-containing plasma or oxygen-containing plasma. Additionally or alternatively, a high K dielectric layer, such as a ZrO ₂ layer, can be deposited on the treated metal electrode. In one embodiment, the ALD chamber 200 is a plasma enhanced ALD (PE-ALD) chamber. The chamber 200 generally includes a chamber body 202, a lid assembly 204, a substrate support assembly 206, and a process kit 250. The lid assembly 204 is disposed on the chamber body 202, and the substrate support assembly 206 is disposed at least partially within the chamber body 202. The chamber body 202 includes a slit valve opening 208 formed on the sidewall of the chamber body 202 to provide access to the processing chamber 200. In some embodiments, chamber body 202 includes one or more apertures in fluid communication with a vacuum system (eg, vacuum pump). Apertures provide an outlet for gases in chamber 200. The lid assembly 204 includes one or more differential pump and purge assemblies 220. Differential pump and purge assemblies 220 are mounted to lid assembly 204 with bellows 222. The bellows 222 allows the pump and purge assemblies 220 to move vertically relative to the lid assembly 204 while still maintaining a seal against gas leaks. When the process kit 250 is raised to the processing position, the first seal 286 and the second seal 288 on the process kit 250 come into contact with the differential pump and purge assemblies 220. The differential pump and purge assemblies 220 are connected to a vacuum system (not shown) and maintained at a low pressure.

[0026] As shown in FIG. 2, the lid assembly 204 includes an RF cathode 210 that can generate a plasma of reactive species in the chamber 200 and/or in the process kit 250. The RF cathode 210 can be heated by electrical heating elements (not shown), and can be cooled by circulation of cooling fluids. Any power source that can activate gases into the reactive species and maintain the plasma of the reactive species can be used. For example, RF or microwave (MV) based power discharge techniques can be used. Activation can also be generated by exposure to heat-based techniques, gas decomposition techniques, high intensity light sources (eg, UV energy), or x-ray sources.

[0027] The substrate support assembly 206 can be disposed at least partially within the chamber body 202. The substrate support assembly 206 includes a substrate support member or susceptor 230 for supporting the substrate 102 for processing within the chamber body. The susceptor 230 couples to the substrate lift mechanism (not shown) through a shaft 224 or shafts 224 extending through one or more openings 226 formed in the bottom surface of the chamber body 202. Ring. The substrate lift mechanism is flexibly sealed to the chamber body 202 by a bellows 228 that prevents vacuum leakage from around the shafts 224. The substrate lift mechanism allows the susceptor 230 to be moved vertically within the chamber 200 between the lower robot entry position and processing, process kit transfer and substrate transfer positions as shown. In some embodiments, the substrate lift mechanism moves between fewer positions than the positions described.

[0028] As shown in FIG. 2, susceptor 230 includes one or more bore 234 through susceptor 230 to accommodate one or more lift pins 236. Each lift pin 236 is mounted so that the lift pin 236 can slide freely within the bore 234. The support assembly 206 is movable such that when the support assembly 206 is in the lower position, the upper surface of the lift pins 236 can be positioned over the substrate support surface 238 of the susceptor 230. Conversely, when the support assembly 206 is in the raised position, the top surface of the lift pins 236 is positioned below the top substrate support surface 238 of the susceptor 230 or the top substrate support of the susceptor 230. It is located substantially planar with the surface 238. When in contact with the chamber body 202, the lift pins 236 push the lower surface of the substrate 102 to lift the substrate from the susceptor 230. Conversely, the susceptor 230 can lift the substrate 102 from the lift pins 236.

[0029] In some embodiments, the substrate 102 can be secured to the susceptor 230 using a vacuum chuck (not shown), an electrostatic chuck (not shown), or a mechanical clamp (not shown). The temperature of the susceptor 230 during processing in the ALD chamber 200 (eg, by a process controller) to affect the temperature of the process kit 250 and substrate 102 to improve the performance of the processing. Can be controlled. The susceptor 230 may be heated, for example, by electrical heating elements (not shown) in the susceptor 230. The temperature of the susceptor 230 may be determined by pyrometers (not shown) in the chamber 200.

[0030] In some embodiments, susceptor 230 includes process kit insulated buttons 237 that may include one or more seals 239. The process kit insulated buttons 237 can be used to support the process kit 250 on the susceptor 230. One or more seals 239 in the process kit insulation buttons 237 are compressed when the susceptor lifts the process kit 250 to the processing position.

3 is a flow diagram of a method 300 for forming a MIM capacitor, according to one embodiment of the present disclosure. 4A-4D illustrate schematic cross-sectional views of a MIM capacitor during different stages of the method 300 of FIG. 3. The method 300 begins at operation 302 by forming a first metal electrode 402 on the substrate 400, as shown in FIG. 4A. The substrate 400 may be the substrate 102 shown in FIGS. 1 and 2. Substrate 400 may have different combinations of films, structures, or layers previously formed on substrate 400 to enable formation of different device structures or different film stacks on substrate 400. Can. The substrate 400 can be any of a glass substrate, a plastic substrate, a polymer substrate, a roll-to-roll substrate, or any other suitable transparent substrate suitable for forming a thin film transistor thereon for display applications. The first metal electrode 402 can be made of any suitable metal, such as titanium (Ti) or molybdenum (Mo). In some embodiments, the first metal electrode 402 includes two or more metal layers, such as a first Ti layer, an aluminum (Al) layer disposed on the first Ti layer, and a first agent disposed on the Al layer. It is a multi-layer stack comprising 2 Ti layers. The first metal electrode 402 can be formed on the substrate 400 by any suitable method. In one embodiment, the first metal electrode 402 is deposited on the substrate 400 by a physical vapor deposition (PVD) process. As shown in FIG. 4A, the first metal electrode 402 has a thickness t ₁ ranging from about 500 Angstroms to about 5000 Angstroms.

[0032] In operation 304, as shown in FIG. 4B, the first metal electrode 402 is exposed to a nitrogen-containing plasma. Reactive species in the nitrogen-containing plasma, such as nitrogen radicals, modify the surface of the metal electrode 402 and convert the surface of the metal electrode 402 to nitride 404. In one embodiment, nitride 404 is titanium nitride or molybdenum nitride. In another embodiment, metal electrode 402 includes a native oxide (not shown) formed on metal electrode 402, and reactive species in the nitrogen-containing plasma convert the native oxide surface to oxynitride. For example, nitride 404 is titanium oxynitride.

The substrate 400 including the first metal electrode 402 formed on the substrate 400 is within a processing chamber, such as the chamber 100 shown in FIG. 1 or the chamber 200 shown in FIG. 2. Is placed. In one embodiment, the nitrogen-containing plasma is formed by introducing a gas into the processing chamber to excite the gas. The gas may be a nitrogen-containing gas, such as ammonia (NH ₃ ). There is no oxygen in the gas. The gas does not contain oxygen because any oxidation of the first metal electrode 402 can reduce the performance of the capacitor. The nitrogen containing plasma can be capacitively coupled, inductively coupled, or microwave induced. The substrate 400 is maintained at a temperature ranging from about 20 degrees Celsius to about 200 degrees Celsius during exposure to a nitrogen-containing plasma. Since the substrate 400 is made of glass or polymer, any temperature higher than 200 degrees Celsius can damage the substrate 400. In one embodiment, the temperature of the substrate is maintained at about 50 degrees Celsius to about 180 degrees Celsius, such as about 100 degrees Celsius to about 150 degrees Celsius. In other words, the nitride 404 is formed at a temperature of about 20 degrees Celsius to about 200 degrees Celsius, such as about 50 degrees Celsius to about 180 degrees Celsius, such as about 100 degrees Celsius to about 150 degrees Celsius. The first metal electrode 402 is exposed to a nitrogen-containing plasma for a duration ranging from about 30 seconds to about 10 minutes, such as from about 1 minute to about 5 minutes.

The nitride 404 has a thickness t _{2 in} the range of about 10 Angstroms to about 50 Angstroms. The remaining first metal electrode 402 has a thickness t ₃ ranging from about 450 Angstroms to about 4990 Angstroms. Since the nitride 404 is converted from a portion of the first metal electrode 402, as shown in FIG. 4B, the sum of the thicknesses t ₂ and t ₃ is equal to the thickness t ₁ . In some embodiments, the sum of the thicknesses t ₂ and t ₃ is different from the thickness t ₁ . By converting a portion of the first metal electrode 402 to nitride 404, the work function is increased because the work function of the nitride 404 is greater than the work function of the first metal electrode 402. For example, the first metal working electrode 402 is made of Ti having a work function of 4.33 eV, and the nitride 404 is titanium nitride having a work function greater than 4.33 eV, such as 4.75 eV.

Next, in operation 306, a high K dielectric layer 406 is formed on the nitride 404, as shown in FIG. 4C. The high K dielectric layer 406 is made of any suitable dielectric material having a K value of 20 or more, such as ZrO ₂ , aluminum oxide (Al ₂ O ₃ ), titanium dioxide (TiO ₂ ), or hafnium dioxide (HfO ₂ ) do. In some embodiments, high K dielectric layer 406 is a multi-layer stack that includes at least one layer of high K dielectric material. In one embodiment, the high K dielectric layer 406 includes a ZrO ₂ layer and a silicon nitride (SiN) layer. In another embodiment, the high K dielectric layer 406 includes a layer of high K dielectric material sandwiched between two dielectric layers. The high K dielectric layer 406 formed on the nitride 404 has a K value in the range of about 20 to about 50. The high K dielectric layer 406 has a thickness in the range of about 250 Angstroms to about 900 Angstroms. In one embodiment, the high K dielectric layer 406 is deposited in the same chamber where the first metal electrode 402 is exposed to a nitrogen-containing plasma or an oxygen-containing plasma. In one embodiment, the chamber is a PE-ALD chamber, such as the chamber 200 shown in FIG. 2. In one embodiment, precursors utilized to deposit the high K dielectric layer 406 include a zirconium-containing precursor and an oxygen-containing precursor. Suitable zirconium-containing precursors are zirconium-organometallic precursors, such as tetrakis(ethylmethylamino)zirconium (TEMAZ), tris(dimethylamino)cyclopentadienyl zirconium((C ₅ H ₅ )Zr[N(CH ₃ ) ₂ ] ₃ ) and the like. Suitable oxygen-containing precursors include H ₂ O, O ₂ , O ₃ , H ₂ O ₂ , CO ₂ , NO ₂ , N ₂ O, and the like. In another embodiment, the chamber is a PECVD chamber, such as chamber 100 shown in FIG. 1.

[0036] In operation 308, a second metal electrode 408 is formed on the high K dielectric layer 406, as shown in FIG. 4D. The second metal electrode 408 may or may not be made of the same material as the first metal electrode 402. The second metal electrode 408 may be deposited by the same deposition process as the first metal electrode 402. After forming the second metal electrode 408, an annealing process may be performed after metallization.

[0037] By treating the first metal electrode of the MIM capacitor with a nitrogen-containing plasma, the leakage current of the MIM capacitor is reduced, and the breakdown field of the MIM capacitor is improved. Moreover, the K value of the high K dielectric layer is not affected by the plasma treatment of the first metal electrode.

[0038] Although the foregoing is related to embodiments of the present disclosure, other and additional embodiments can be devised without departing from the basic scope of the present disclosure, and the scope of the present disclosure is determined by the following claims. do.

Claims (15)

A first metal electrode;
A nitride disposed on the first metal electrode, wherein the nitride is formed at a temperature ranging from about 20 degrees Celsius to about 200 degrees Celsius;
A high K dielectric layer disposed on the nitride; And
A second metal electrode disposed on the high K dielectric layer
Containing,
Capacitor. According to claim 1,
The first metal electrode includes titanium, and the nitride includes titanium nitride,
Capacitor. According to claim 1,
The first metal electrode includes molybdenum, and the nitride includes molybdenum nitride,
Capacitor. According to claim 1,
The high K dielectric layer comprises zirconium dioxide, hafnium dioxide, titanium dioxide, or aluminum oxide,
Capacitor. According to claim 1,
The second metal electrode includes the same material as the first metal electrode,
Capacitor. According to claim 1,
The second metal electrode comprises a different material than the first metal electrode,
Capacitor. Forming a first metal electrode on the substrate;
Exposing the first metal electrode to a nitrogen-containing plasma in a processing chamber—a portion of the first metal electrode is converted to nitride having a work function greater than 4.33 eV, and the nitride is about 20 degrees Celsius to about 200 degrees Celsius Formed at a temperature in the range ―;
Forming a high K dielectric layer on the nitride in the processing chamber; And
Forming a second metal electrode on the high K dielectric layer
Containing,
Way. The method of claim 7,
The processing chamber is a plasma enhanced atomic layer deposition chamber,
Way. The method of claim 7,
The processing chamber is a plasma enhanced chemical vapor deposition chamber,
Way. The method of claim 7,
The nitrogen-containing plasma is formed by exciting a nitrogen-containing gas, and the nitrogen-containing gas contains ammonia,
Way. The method of claim 7,
The substrate is maintained at a temperature in a range of about 20 degrees Celsius to about 200 degrees Celsius during the step of exposing the first metal electrode to the nitrogen-containing plasma.
Way. Forming a first metal electrode on the substrate;
Exposing the first metal electrode to a nitrogen-containing plasma in a processing chamber, wherein the substrate is maintained at a temperature in the range of about 50 degrees Celsius to about 180 degrees Celsius, and a portion of the first metal electrode is converted to nitride;
Forming a high K dielectric layer on the nitride in the processing chamber; And
Forming a second metal electrode on the high K dielectric layer
Containing,
Way. The method of claim 12,
The processing chamber is a plasma enhanced atomic layer deposition chamber,
Way. The method of claim 12,
The high K dielectric layer comprises zirconium dioxide, hafnium dioxide, or aluminum oxide,
Way. The method of claim 12,
The temperature ranges from about 100 degrees Celsius to about 150 degrees Celsius,
Way.

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