Memory cell having resistance variable film and method of making the same

[0001] In integrated circuit (IC) devices, resistive random access memory (RRAM) is an emerging technology for next generation non-volatile memory devices. RRAM refers to a memory structure including an array of RRAM cells each storing a bit of data using resistance, rather than electronic charge. In some applications, a RRAM cell includes a resistance variable layer, which is an insulating material capable of being configured to provide a conductive path through a filament formed after application of a predetermined threshold voltage. Once the filament is formed, the filament is operable to be set (i.e., re-formed, resulting in a lower resistance across the RRAM cell) or reset (i.e., broken, resulting in a high resistance across the RRAM) by appropriately applied voltages. The low and high resistance states thus are utilized to indicate a digital signal of “1” or “0,” and thereby provide a non-volatile memory cell that can store a bit.

[0007] It is understood that the following disclosure provides one or more different embodiments, or examples, for implementing different features of the disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, examples and are not intended to be limiting. In accordance with the standard practice in the industry, various features in the drawings are not drawn to scale and are used for illustration purposes only.

[0008] Moreover, spatially relative terms, for example, “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top,” “bottom,” “left,” “right,” etc. as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for ease of the present disclosure of one features relationship to another feature. The spatially relative terms are intended to cover different orientations of the device including the features.

[0009] FIG. 1A is a cross-sectional view of a portion of an electrical device 100 including an RRAM cell 110 in accordance with one or more embodiments. FIG. 1B is an enlarged view of regions A1 and A2 in FIG. 1 in accordance with one or more embodiments. Device 100 includes a substrate 120, one or more interconnection layers 130 over substrate 120, and RRAM cell 110 over interconnection layers 130. RRAM cell 110 is formed within another interconnection layer 140 above interconnection layers 130.

[0010] RRAM cell 110 includes a first electrode 112, a second electrode 114 covering first electrode 112, a resistance variable film 116 between first electrode 112 and second electrode 114, and a conductive member 118 on second electrode 114. Resistance variable film 116 has an upper portion 116a over first electrode 112 and extending along an upper surface 112a of first electrode 112. Resistance variable film 116 also has a side portion 116b extending along a side surface 112b of first electrode 112. Second electrode 114 is over resistance variable film 116. Second electrode 114 has a side surface 114a, and a portion of side surface 112a of first electrode 112 and a portion of side surface 114a of second electrode 114 sandwiches a portion of the side portion 116b of resistance variable film 116. RRAM cell 110 further includes a dielectric layer 142 over an upper surface 112a of first electrode 112, an etch stop layer 144 covering second electrode 114 and surrounding a lower portion of conductive member 118, and another dielectric layer 146 over second electrode 114 and etch stop layer 144 and surrounding conductive member 118. Etch stop layer 144 and dielectric layer 146 extend beyond the portion occupied by RRAM cell 110 in the interconnection layer 140. In some embodiments, dielectric layer 142 is a hard mask layer. In some embodiments, dielectric layer 142 is omitted.

[0011] In some embodiments, conductive member 118 is formed by first performing an etching process to define an opening (374 in FIG. 3J) in dielectric layer 146. The portion of resistance variable film 116 sandwiched by side surface 112b of first electrode 112 and side surface 114a of second electrode 114 are arranged away from being directly under the opening 374. Compared with a configuration that a sandwiched portion of resistance variable film is directly under where a via opening and/or a trench opening is formed, the portion of resistance variable film 116 sandwiched between side surface 112b and side surface 114a according to the embodiments described herein is less likely to be affected or damaged by an etching process for forming the opening 374.

[0012] In some embodiments, first electrode 112 and/or second electrode 114 are electrically coupled to one or more electrical components on substrate 120 though the one or more layers of interconnection layers 130. In some embodiments, first electrode 112 has a circular shape or a polygon shape when it is viewed from the top of the RRAM cell 110. In some embodiments, first electrode 112 has one or more layers of conductive materials. In some embodiments, first electrode 112 has a material comprising platinum (Pt), aluminum, copper, titanium nitride (TiN), gold (Au), titanium (Ti), tantalum (Ta), tantalum nitride (TaN), tungsten (W), tungsten nitride (WN), or combinations thereof. In some embodiments, first electrode 112 has a width W1 ranging from 70 nm to 300 nm. In some embodiments, second electrode 114 has one or more layers of conductive materials. In some embodiments, second electrode 114 has a circular shape or a polygon shape when it is viewed from the top of the RRAM cell 110. In some embodiments, second electrode 114 has a material comprising Pt, Al, Cu, TiN, Au, Ti, Ta, TaN, W, WN, or combinations thereof. In some embodiments, second electrode 114 has a width W2 greater than W1.

[0013] In some embodiments, second electrode 114 includes a main portion 114b and a capping layer 114c extending between main portion 114b and resistance variable film 116. In some embodiments, main portion 114b has a material comprising Ti, Ta, TiN, or TaN. In some embodiments, capping layer 114c has a material comprising Ti, Pt, or ruthenium (Ru).

[0014] Substrate 120 herein generally refers to a bulk substrate on which various layers and device structures are formed. In some embodiments, the bulk substrate includes silicon or a compound semiconductor, such as GaAs, InP, Si/Ge, or SiC. Examples of the layers include dielectric layers, doped layers, polysilicon layers, or conductive layers. Examples of the device structures include transistors, resistors, and/or capacitors, which may be interconnected through one or more interconnect layers 130, interconnection layer 140, and/or one or more interconnect layers above interconnection layer 140 to additional integrated circuits.

[0015] Interconnection layers 130 include various conductive lines and via plugs arranged to electrically coupling the active and passive electrical devices on substrate 120 and to electrically coupling RRAM cell 110 with one or more of the active and passive electrical devices on substrate 120. As depicted in FIG. 1A, interconnection layers 130 include a conductive line 132 and a dielectric layer 134 surrounding the conductive line 132. Interconnection layer 140 is on dielectric layer 134. First electrode 112 of RRAM cell 110 is electrically coupled to the conductive line 132, which is in turn electrically coupled with one or more of active and passive electrical devices on substrate 120. In some embodiments, the one or more interconnection layers 130 are omitted, and interconnection layer 140 is on substrate 120. In some embodiments, one or more other interconnection layers, passivation layers, and bump structures are formed over interconnection layer 140.

[0016] In some embodiments, dielectric layers 134 and 146 have a material including silicon oxide, fluorinated silica glass (FSG), carbon doped silicon oxide, tetra-ethyl-ortho-silicate (TEOS) oxide, phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), BLACK DIAMOND® (APPLIED MATERIALS of Santa Clara, Calif.), amorphous fluorinated carbon, low dielectric constant (low-k) dielectric material, or combinations thereof. In some embodiments, conductive line 132 has a material including Al, Cu, Ti, Ta, W, molybdenum (Mo), TaN, TiN, WN, metal silicide, silicon, or combinations thereof. In some embodiments, etching stop layer 144 includes a dielectric material such as silicon carbide (SiC) or silicon oxy-nitride (SiON).

[0017] In some embodiments, resistance variable film 116 has a material comprising a high dielectric constant (high-k) dielectric material, a binary metal oxide, or a transition metal oxide. In some embodiments, resistance variable film 116 has a thickness ranging from 1 nm to 10 nm. As depicted in FIG. 1B, the portion of resistance variable film 116 sandwiched between upper surface 112a of first electrode 112 and lower surface 114a of second electrode 114 has a height H ranging from 20 nm to 100 nm.

[0018] Resistance variable film 116 is capable of being processed to form one or more “filaments” 160 to provide a conductive path such that resistance variable film 116 has a low resistance characteristic between upper surface 112a of first electrode 112 and lower surface 114a of second electrode 114. In some embodiments, the filaments 160 is formed by lining-up defect (e.g. oxygen) vacancies in a bottom portion of resistance variable film 116 between side surface 112b of first electrode 112 and side surface 114a of second electrode 114. In some embodiments, filaments 160 are formed by applying a voltage level greater than a predetermined threshold “forming voltage.” Once filaments 160 are formed, filaments 160 remain present in the resistance variable film 116. Other operations (reset operation and set operation) disconnect or reconnect the resistance variable film 116 using a set voltage and/or a reset voltage having voltage levels less than the forming voltage.

[0019] FIG. 2 is a flow chart of a method 200 of making an RRAM cell 110 in accordance with one or more embodiments. FIGS. 3A-3K are cross-sectional views of a portion of an electrical device 100 including an RRAM cell 110 at various stages of manufacture in accordance with one or more embodiments. Components similar to those depicted in FIGS. 1A and 1B are given the same reference numbers. It is understood that additional operations may be performed before, during, and/or after the method 200 depicted in FIG. 2, and that some other processes may only be briefly described herein.

[0020] FIG. 3A is a cross-sectional view of electrical device 100 after performing operations 205, 210, and 215. As depicted in FIG. 2 and FIG. 3A, electrical device 100 includes a memory region 310 and a periphery region 320. Electrical device 100 includes a dielectric layer 134 formed over a substrate 120 (FIG. 1). Dielectric layer 134 has a conductive line 132 formed in memory region 310 and a conductive line 332 formed in periphery region 320.

[0021] In some embodiments, dielectric layer 134 has a material including silicon oxide, fluorinated silica glass (FSG), carbon doped silicon oxide, tetra-ethyl-ortho-silicate (TEOS) oxide, phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), BLACK DIAMOND® (APPLIED MATERIALS of Santa Clara, Calif.), amorphous fluorinated carbon, low-k dielectric material, or combinations thereof. In some embodiments, dielectric layer 134 is formed by performing a chemical vapor deposition (CVD) process, an atomic layer deposition (ALD) process, a high density plasma CVD (HDPCVD) process, or a spin-on glass process.

[0022] In some embodiments, conductive lines 132 and 332 include Al, Cu, Ti, Ta, W, Mo, TaN, TiN, WN, metal silicide, silicon, or combinations thereof. In the embodiment depicted in FIG. 3A, conductive lines 132 and 332 are formed by lithography patterning and etching in the dielectric layer 134 and depositing one or more layers of conductive materials over the patterned dielectric layer 134, and subsequently performing a planarization process to form the conductive lines 132 and 332. Upper surfaces 132a and 332a of conductive lines 132 and 332 are substantially coplanar with an upper surface 134a of dielectric layer 134.

[0023] In operation 205, a layer of conductive material (“conductive layer 342”) is formed over dielectric layer 134 and the substrate 120 in both memory region 310 and periphery region 320. In some embodiments, conductive layer 342 is only formed in memory region 310. In some embodiments, conductive layer 342 is formed using a process including electroless plating, sputtering, electro plating, PVD, or ALD. In some embodiments, conductive layer 342 has a material including Pt, Al, Cu, TiN, Au, Ti, Ta, TaN, W, WN, or combinations thereof. In some embodiments, conductive layer 342 has a thickness ranging from 10 nm to 100 nm.

[0024] In operation 210, a layer of dielectric material, such as a hard mask material, (“dielectric layer 344”) is formed over the conductive layer 342 in both memory region 310 and periphery region 320. In operation 215, a patterned photo resist layer 346 is formed over the dielectric layer 344 for defining first electrode 112. In some embodiments, operation 210 is omitted, and patterned photo resist layer 346 is formed on conductive layer 342.

[0025] FIG. 3B is a cross-sectional view of electrical device 100 after performing operation 220. As depicted in FIG. 2 and FIG. 3B, in operation 220, conductive layer 342 and dielectric layer 344 are etched using patterned photo resist layer 346 as a mask. In some embodiments, operation 220 comprises performing a dry etching process or a wet etching process. After operation 220, first electrode 112 and dielectric layer 142 over first electrode 112 are formed over the dielectric layer 134. In some embodiments, dielectric layer 142 is omitted. In some embodiments, first electrode 112 has a width W1 ranging from 70 nm to 300 nm.

[0026] FIG. 3C is a cross-sectional view of electrical device 100 after performing operations 225, 230, and 235. As depicted in FIG. 2 and FIG. 3C, in operation 225, a layer of resistance variable material (“resistance variable layer”) 352 is deposited over dielectric layer 146 and first electrode 112. In some embodiments, resistance variable layer 352 extends over dielectric layer 146 in memory region 310 and periphery region 320. In some embodiments, resistance variable layer 352 is conformally deposited over an upper surface 142a of dielectric layer 142 and side surfaces 142b and 112b of dielectric layer 142 and first electrode 112. Resistance variable layer 352 has a resistivity capable of switching between a high resistance state and a low resistance state, by application of an electrical voltage. In some embodiments, the resistance variable layer 352 has a material including a high-k dielectric material, a binary metal oxide, or a transition metal oxide. In some embodiments, resistance variable layer 352 includes nickel oxide, titanium oxide, hafnium oxide, zirconium oxide, zinc oxide, tungsten oxide, aluminum oxide, tantalum oxide, molybdenum oxide, or copper oxide. In some embodiments, resistance variable layer 352 is formed by performing a pulse laser deposition (PLD) process or an ALD process, such as an ALD process with a precursor containing zirconium and oxygen. In some embodiments, resistance variable layer 352 has a thickness ranging from 1 nm to 10 nm.

[0027] As depicted in FIG. 2 and FIG. 3C, in operation 230, one or more layers of conductive materials (“conductive layer”) 354 is deposited over resistance variable layer 352 in memory region 310 and periphery region 320. In some embodiments, conductive layer 354 is formed using a process including electroless plating, sputtering, electro plating, PVD, or ALD. In some embodiments, conductive layer 354 has a material including Pt, Al, Cu, TiN, Au, Ti, Ta, TaN, W, WN, or combinations thereof. In some embodiments, conductive layer 354 has a thickness ranging from 10 nm to 100 nm. In some embodiments, conductive layer 354 includes a layer of capping material for forming capping layer 114c (FIG. 1B) and a layer of conductive material for forming main portion 114b (FIG. 1B). In some embodiments, conductive material for forming core portion 114b includes Ti, Ta, TiN, or TaN. In some embodiments, material for forming capping layer 114c includes Ti, Pt, or Ru.

[0028] Moreover, in operation 235, a patterned photo resist layer 356 is formed over conductive layer 354 in memory region 310 for defining second electrode 114.

[0029] FIG. 3D is a cross-sectional view of electrical device 100 after performing operation 240. As depicted in FIG. 2 and FIG. 3D, in operation 240, resistance variable layer 352 and conductive layer 354 are etched using patterned photo resist layer 356 as a mask. In some embodiments, operation 240 comprises performing a dry etching process or a wet etching process. In some embodiments, operation 240 further includes removing patterned photo resist layer 356 after the etching. After operation 240, second electrode 114 and dielectric layer 142 over first electrode 112 are formed over the dielectric layer 134. In some embodiments, dielectric layer 142 is omitted.

[0030] FIG. 3E is a cross-sectional view of electrical device 100 after performing operation 245. As depicted in FIG. 2 and FIG. 3E, in operation 245, an etch stop layer 144 is formed over the first electrode 112 and second electrode 114 and blanket formed over dielectric layer 134 in memory region 310 and periphery region 320. The etching stop layer 144 formed over second electrode 114 is usable to prevent second electrode 114 from being oxidized. In some embodiments, the etching stop layer 144 includes a dielectric material such as SiC or SiON. In some embodiments, etch stop layer 144 is formed by performing a CVD process, an ALD process, or a plasma enhanced CVD (PECVD) process.

[0031] FIG. 3F is a cross-sectional view of electrical device 100 after performing operation 250. In operation 250, dielectric 146 is formed over the etch stop layer 144 in memory region 310 and periphery region 320. In some embodiments, dielectric layer 146 has a material including silicon oxide, fluorinated silica glass (FSG), carbon doped silicon oxide, tetra-ethyl-ortho-silicate (TEOS) oxide, phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), BLACK DIAMOND® (APPLIED MATERIALS of Santa Clara, Calif.), amorphous fluorinated carbon, low-k dielectric material, or combinations thereof. In some embodiments, dielectric layer 146 is formed by performing a CVD process, an ALD process, a HDPCVD process, or a spin-on glass process.

[0032] FIGS. 3G-3I are cross-sectional view of electrical device 100 at various stage during operation 255. FIG. 3J is a cross-sectional view of electrical device 100 after performing operation 255.

[0033] As depicted in FIG. 3G and FIG. 2, operation 255 includes forming a patterned photo resist layer 362 over dielectric layer 146 for defining one or more via openings over second electrode 114 and conductive line 332.

[0034] As depicted in FIG. 2 and FIG. 3H, operation 255 further includes etching a portion dielectric layer 146 and a portion of etch stop layer 144 using patterned photo resist layer 362 as a mask. As a result, a via opening 364 above second electrode 114 is defined in memory region 310 and a via opening 366 above conductive line 332 is defined in periphery region 320. In some embodiments, via opening 364 extends downwardly to expose an upper surface of second electrode 114. In some embodiments, via opening 366 extends downwardly to expose an upper surface of conductive line 332. In some embodiments, the formation of openings 364 and 366 includes performing a dry etching process or a wet etching process. After performing the etching for forming via openings 364 and 366, patterned photo resist layer 362 is from the upper surface of dielectric layer 146.

[0035] As depicted in FIG. 3I and FIG. 2, operation 255 further includes filling a dielectric material in via openings 364 and 366 to form sacrificial via plugs 368. Upper surface 368a of sacrificial via plugs 368 are substantially coplanar with the upper surface 146a of dielectric layer 146. In some embodiments, sacrificial via plugs 368 include a bottom anti-reflection coating (BARC) material. Then, a patterned photo resist layer 372 is formed over dielectric layer 146 for defining one or more trench openings over conductive line 332 in periphery region 320 and second electrode 114 in memory region 310.

[0036] As depicted in FIG. 2 and FIG. 3J, operation 250 further includes etching a portion dielectric layer 146, sacrificial via plugs 368, and/or a portion of etch stop layer 144 using patterned photo resist layer 372 as a mask. As a result, an opening 374 above second electrode 114 is defined in memory region 310 and an opening 376 above conductive line 332 is defined in periphery region 320. In some embodiments, opening 374 is also referred to as a combination of a via opening 374a and a trench opening 374b. In some embodiments, opening 376 is also referred to as a combination of a via opening 376a and a trench opening 376b. Opening 374 exposes an upper surface 114a of second electrode 114, and opening 376 exposes an upper surface 332a of conductive line 332. In some embodiments, the formation of openings 374 and 376 includes performing a dry etching process or a wet etching process. After performing the etching for forming via openings 374 and 376, patterned photo resist layer 372 is from the upper surface of dielectric layer 146.

[0037] FIG. 3K is a cross-sectional view of electrical device 100 after performing operation 260. As depicted in FIG. 2 and FIG. 3K, in operation 260, a conductive material is deposited to fill opening 374 to form conductive member 118 electrically coupled with second electrode 114 and to fill opening 376 to form conductive member 382 electrically coupled with conductive line 332. Conductive member 118 is also referred to as a combination of via plug 118a and conductive line 118b directly on via plug 118a. Conductive member 382 is also referred to as a combination of via plug 382a and conductive line 382b directly on via plug 382a. In some embodiments, the conductive material for filling openings 374 and 376 includes Al, Cu, Ti, Ta, W, molybdenum (Mo), TaN, TiN, WN, metal silicide, silicon, or combinations thereof. In some embodiments, conductive line 118b of conductive member 118 being substantially level with conductive line 382b of conductive member 382.

[0038] After operation 260, the resulting structure in memory region 310 has a similar structure to electrical device 100 depicted in FIG. 1A.

[0039] In accordance with one embodiment, a manufacture includes a first electrode having an upper surface and a side surface, a resistance variable film over the first electrode, and a second electrode over the resistance variable film. The resistance variable film extends along the upper surface and the side surface of the first electrode. The second electrode has a side surface. A portion of the side surface of the first electrode and a portion of the side surface of the second electrode sandwich a portion of the resistance variable film.

[0040] In accordance with another embodiment, a manufacture includes a first electrode having an upper surface and a side surface, a first dielectric layer over the upper surface of the first electrode, a resistance variable film having an upper portion and a side portion, and a second electrode over the resistance variable film. The upper portion of the resistance variable film is over the first dielectric layer. The side portion of the resistance variable film extends along the side surface of the first electrode. The second electrode covers the upper portion and the side portion of the resistance variable film. The second electrode has a side surface. A portion of the side surface of the first electrode and a portion of the side surface of the second electrode sandwich a portion of the side portion of the resistance variable film.

[0041] In accordance with another embodiment, a method includes forming a first electrode over a substrate. A resistance variable film is formed to cover an upper surface of the first electrode and a side surface of the first electrode. A second electrode is formed to cover an upper portion of the resistance variable film and a side portion of the resistance variable film. A portion of the first electrode and a portion of the second electrode sandwich a portion of the side portion of the resistance variable film.

[0042] The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.