International Business Machines Corporation, a New York corporation; Macronix International Corporation, Ltd., a Taiwan corporation, and Infineon Technologies A.G., a German corporation, are parties to a Joint Research Agreement.
1. Field of the Invention
The present invention relates to high density memory devices based on phase change based memory materials, including chalcogenide based materials and other materials, and to methods for manufacturing such devices.
2. Description of Related Art
Phase change based memory materials are widely used in read-write optical disks. These materials have at least two solid phases, including for example a generally amorphous solid phase and a generally crystalline solid phase. Laser pulses are used in read-write optical disks to switch between phases and to read the optical properties of the material after the phase change.
Phase change based memory materials, like chalcogenide based materials and similar materials, also can be caused to change phase by application of electrical current at levels suitable for implementation in integrated circuits. The generally amorphous state is characterized by higher resistivity than the generally crystalline state, which can be readily sensed to indicate data. These properties have generated interest in using programmable resistive material to form nonvolatile memory circuits, which can be read and written with random access.
The change from the amorphous to the crystalline state is generally a lower current operation. The change from crystalline to amorphous, referred to as reset herein, is generally a higher current operation, which includes a short high current density pulse to melt or break down the crystalline structure, after which the phase change material cools quickly, quenching the phase change process, allowing at least a portion of the phase change structure to stabilize in the amorphous state. It is desirable to minimize the magnitude of the reset current used to cause transition of phase change material from crystalline state to amorphous state. The magnitude of the reset current needed for reset can be reduced by reducing the size of the phase change material element in the cell and of the contact area between electrodes and the phase change material, so that higher current densities are achieved with small absolute current values through the phase change material element.
One direction of development has been toward forming small pores in an integrated circuit structure, and using small quantities of programmable resistive material to fill the small pores. Patents illustrating development toward small pores include: Ovshinsky, “Multibit Single Cell Memory Element Having Tapered Contact,” U.S. Pat. No. 5,687,112, issued Nov. 11, 1997; Zahorik et al., “Method of Making Chalogenide [sic] Memory Device,” U.S. Pat. No. 5,789,277, issued Aug. 4, 1998; Doan et al., “Controllable Ovonic Phase-Change Semiconductor Memory Device and Methods of Fabricating the Same,” U.S. Pat. No. 6,150,253, issued Nov. 21, 2000.
Problems have arisen in manufacturing such devices with very small dimensions, and with variations in process that meet tight specifications needed for large-scale memory devices. It is desirable therefore to provide a memory cell structure having small dimensions and low reset currents, and a method for manufacturing such structure.
A first aspect of the invention is directed to a phase change memory device comprising a memory cell access layer and a memory cell layer, operably coupled to the memory cell access layer, comprising a photolithographically formed phase change memory cell. The memory cell comprises first and second electrodes, having first and second opposed, spaced apart sides, and a phase change bridge positioned between the first and second sides and electrically coupling the first and second sides to one another. The phase change bridge has a length, a width and a thickness, the width measured between the first and second sides and the length measured perpendicular to the width. The width, the thickness and the length are less than a minimum photolithographic feature size of the process used to form the phase change memory cell. In some embodiments the minimum photolithographic feature size is about 200 mm, the width is about 10 to 100 nm, the length is about 10 to 50 nm, and the thickness is about 10 to 50 nm.
A second aspect of the invention is directed to a method for making a phase change memory device. A memory cell access layer is formed on a substrate, the memory cell access layer comprising an access device and a top surface. A memory cell layer is formed and is operably coupled to the memory cell access layer, the memory cell layer comprising a photolithographically formed phase change memory cell. The memory cell comprises first and second electrodes, having first and second opposed, spaced apart sides, and a phase change bridge positioned between the first and second sides and electrically coupling the first and second sides to one another. The phase change bridge has a length, a width and a thickness. The memory layer forming step comprises reducing the size of photoresist masks used in the memory layer forming step so that the width and the length of the phase change bridge are each less than a minimum photolithographic feature size of the process used to form the phase change memory cell.
The method described herein for formation of the phase change bridge, for use in a memory cell in a phase change read only memory (PCRAM) device, can be used to make small phase change gates, bridges or similar structures for other devices.
Various features and advantages of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawings.
The following description of the invention will typically be with reference to specific structural embodiments and methods. It is to be understood that there is no intention to limit the invention to the specifically disclosed embodiments but that the invention may be practiced using other features, elements, methods and embodiments. Like elements in various embodiments are commonly referred to with like reference numerals.
Memory cell layer 16 comprises a first electrode 42 contacting top surface 38 and first plug 35, a second electrode 44 contacting top surface 38, and a third electrode 46 contacting top surface 38 and second plug 36. First and second electrodes 42, 44 are separated by a gap 48 while second and third electrodes 44, 46 are separated by a gap 50. First and second phase change bridges 52, 54 are formed within first and second gaps 48, 50 between and in contact with top surface 38 and in contact with the side walls 55 defining electrodes 42, 44, 46. As shown in
Memory cell layer 16 also includes a conductive bit line 62 separated from electrode 42, 44 and 46 by a separation layer 64, typically made of a dielectric material such as silicon dioxide. An electrically conductive plug 67 extends through a via formed through second separation layer 64 to electrically connect bit line 62 and second electrode 44.
A method for making phase change memory devices will now be discussed with reference to
Electrodes 42, 44, 46 in the illustrated embodiments are preferably TiN or TaN. Alternatively, these components may be TiAlN or TaAlN, or may comprise, for further examples, one or more elements selected from the group consisting essentially of Ti, W, Mo, Al, Ta, Cu, Pt, Ir, La, Ni, and Ru and alloys thereof. Plugs 35, 36, 67 are typically made of tungsten while common source line 34 and bit line 62 are typically created by copper metallization; other types of metallization, including aluminum, titanium nitride, and tungsten based materials, can be used as well.
Embodiments of the memory cell include phase change based memory materials, including chalcogenide based materials and other materials, for phase change bridges 52, 54. Chalcogens include any of the four elements oxygen (O), sulfur (S), selenium (Se), and tellurium (Te), forming part of group VI of the periodic table. Chalcogenides comprise compounds of a chalcogen with a more electropositive element or radical. Chalcogenide alloys comprise combinations of chalcogenides with other materials such as transition metals. A chalcogenide alloy usually contains one or more elements from column six of the periodic table of elements, such as germanium (Ge) and tin (Sn). Often, chalcogenide alloys include combinations including one or more of antimony (Sb), gallium (Ga), indium (In), and silver (Ag). Many phase change based memory materials have been described in technical literature, including alloys of: Ga/Sb, In/Sb, In/Se, Sb/Te, Ge/Te, Ge/Sb/Te, In/Sb/Te, Ga/Se/Te, Sn/Sb/Te, In/Sb/Ge, Ag/In/Sb/Te, Ge/Sn/Sb/Te, Ge/Sb/Se/Te and Te/Ge/Sb/S. In the family of Ge/Sb/Te alloys, a wide range of alloy compositions may be workable. The compositions can be characterized as TeaGebSb100-(a+b).
One researcher has described the most useful alloys as having an average concentration of Te in the deposited materials well below 70%, typically below about 60% and ranged in general from as low as about 23% up to about 58% Te and most preferably about 48% to 58% Te. Concentrations of Ge were above about 5% and ranged from a low of about 8% to about 30% average in the material, remaining generally below 50%. Most preferably, concentrations of Ge ranged from about 8% to about 40%. The remainder of the principal constituent elements in this composition was Sb. These percentages are atomic percentages that total 100% of the atoms of the constituent elements. (Ovshinsky '112 patent, cols 10-11.) Particular alloys evaluated by another researcher include Ge2Sb2Te5, GeSb2Te4 and GeSb4Te7 (oboru Yamada, “Potential of Ge—Sb—Te Phase-Change Optical Disks for High-Data-Rate Recording”, SPIE v.3109, pp. 28-37 (1997).) More generally, a transition metal such as chromium (Cr), iron (Fe), nickel (Ni), niobium (Nb), palladium (Pd), platinum (Pt) and mixtures or alloys thereof may be combined with Ge/Sb/Te to form a phase change alloy that has programmable resistive properties. Specific examples of memory materials that may be useful are given in Ovshinsky '112 at columns 11-13, which examples are hereby incorporated by reference.
Phase change alloys are capable of being switched between a first structural state in which the material is in a generally amorphous solid phase, and a second structural state in which the material is in a generally crystalline solid phase in its local order in the active channel region of the cell. These alloys are at least bistable. The term amorphous is used to refer to a relatively less ordered structure, more disordered than a single crystal, which has the detectable characteristics such as higher electrical resistivity than the crystalline phase. The term crystalline is used to refer to a relatively more ordered structure, more ordered than in an amorphous structure, which has detectable characteristics such as lower electrical resistivity than the amorphous phase. Typically, phase change materials may be electrically switched between different detectable states of local order across the spectrum between completely amorphous and completely crystalline states. Other material characteristics affected by the change between amorphous and crystalline phases include atomic order, free electron density and activation energy. The material may be switched either into different solid phases or into mixtures of two or more solid phases, providing a gray scale between completely amorphous and completely crystalline states. The electrical properties in the material may vary accordingly.
Phase change alloys can be changed from one phase state to another by application of electrical pulses. It has been observed that a shorter, higher amplitude pulse tends to change the phase change material to a generally amorphous state. A longer, lower amplitude pulse tends to change the phase change material to a generally crystalline state. The energy in a shorter, higher amplitude pulse is high enough to allow for bonds of the crystalline structure to be broken and short enough to prevent the atoms from realigning into a crystalline state. Appropriate profiles for pulses can be determined, without undue experimentation, specifically adapted to a particular phase change alloy. A material useful for implementation of a PCRAM described herein is Ge2Sb2Te5. Other types of phase change materials can also be used.
For additional information on the manufacture, component materials, use and operation of phase change random access memory devices, see U.S. patent application Ser. No. 11/155,067, filed 17 Jun. 2005, entitled Thin Film Fuse Phase Change Ram And Manufacturing Method.
Advantages of an embodiment described herein include that the current used in reset and programming is confined in a small volume allowing high current density and resultant local heating at lower reset current levels and lower reset power levels.
While the present invention is disclosed by reference to the preferred embodiments and examples detailed above, it is to be understood that these examples are intended in an illustrative rather than in a limiting sense. It is contemplated that modifications and combinations will occur to those skilled in the art, which modifications and combinations will be within the spirit of the invention and the scope of the following claims.
Any and all patents, patent applications and printed publications referred to above are hereby incorporated by reference.
This application claims the benefit of provisional patent application No. 60/736,722 filed 15 Nov. 2005.
Number | Name | Date | Kind |
---|---|---|---|
3271591 | Ovshinsky | Sep 1966 | A |
3530441 | Ovshinsky | Sep 1970 | A |
4599705 | Holmberg et al. | Jul 1986 | A |
4719594 | Young et al. | Jan 1988 | A |
4876220 | Mohsen et al. | Oct 1989 | A |
4959812 | Momodomi et al. | Sep 1990 | A |
5166096 | Cote et al. | Nov 1992 | A |
5166758 | Ovshinsky et al. | Nov 1992 | A |
5177567 | Klersy et al. | Jan 1993 | A |
5332923 | Takeuchi et al. | Jul 1994 | A |
5391901 | Tanabe et al. | Feb 1995 | A |
5515488 | Hoppe et al. | May 1996 | A |
5534712 | Ovshinsky et al. | Jul 1996 | A |
5687112 | Ovshinsky | Nov 1997 | A |
5789277 | Zahorik et al. | Aug 1998 | A |
5789758 | Reinberg | Aug 1998 | A |
5814527 | Wolstenholme et al. | Sep 1998 | A |
5831276 | Gonzalez et al. | Nov 1998 | A |
5837564 | Sandhu et al. | Nov 1998 | A |
5869843 | Harshfield | Feb 1999 | A |
5879955 | Gonzalez et al. | Mar 1999 | A |
5902704 | Schoenborn et al. | May 1999 | A |
5920788 | Reinberg | Jul 1999 | A |
5952671 | Reinberg et al. | Sep 1999 | A |
5958358 | Tenne et al. | Sep 1999 | A |
5970336 | Wolstenholme et al. | Oct 1999 | A |
5985698 | Gonzalez et al. | Nov 1999 | A |
5998244 | Wolstenholme et al. | Dec 1999 | A |
6011725 | Eitan | Jan 2000 | A |
6025220 | Sandhu | Feb 2000 | A |
6031287 | Harshfield | Feb 2000 | A |
6034882 | Johnson et al. | Mar 2000 | A |
6066870 | Siek | May 2000 | A |
6077674 | Schleifer et al. | Jun 2000 | A |
6077729 | Harshfield | Jun 2000 | A |
6087269 | Williams | Jul 2000 | A |
6087674 | Ovshinsky et al. | Jul 2000 | A |
6104038 | Gonzalez et al. | Aug 2000 | A |
6111264 | Wolstenholme et al. | Aug 2000 | A |
6114713 | Zahorik | Sep 2000 | A |
6117720 | Harshfield | Sep 2000 | A |
6147395 | Gilgen | Nov 2000 | A |
6150253 | Doan et al. | Nov 2000 | A |
6153890 | Wolstenholme et al. | Nov 2000 | A |
6177317 | Huang et al. | Jan 2001 | B1 |
6185122 | Johnson et al. | Feb 2001 | B1 |
6189582 | Reinberg et al. | Feb 2001 | B1 |
6236059 | Wolstenholme et al. | May 2001 | B1 |
RE37259 | Ovshinsky | Jul 2001 | E |
6271090 | Huang et al. | Aug 2001 | B1 |
6280684 | Yamada et al. | Aug 2001 | B1 |
6287887 | Gilgen | Sep 2001 | B1 |
6314014 | Lowrey et al. | Nov 2001 | B1 |
6320786 | Chang et al. | Nov 2001 | B1 |
6339544 | Chiang et al. | Jan 2002 | B1 |
6351406 | Johnson et al. | Feb 2002 | B1 |
6372651 | Yang et al. | Apr 2002 | B1 |
6420215 | Knall et al. | Jul 2002 | B1 |
6420216 | Clevenger et al. | Jul 2002 | B1 |
6420725 | Harshfield | Jul 2002 | B1 |
6423621 | Doan et al. | Jul 2002 | B2 |
6429064 | Wicker | Aug 2002 | B1 |
6456525 | Perner et al. | Sep 2002 | B1 |
6462353 | Gilgen | Oct 2002 | B1 |
6483736 | Johnson et al. | Nov 2002 | B2 |
6487114 | Jong et al. | Nov 2002 | B2 |
6501111 | Lowrey | Dec 2002 | B1 |
6511867 | Lowrey et al. | Jan 2003 | B2 |
6512241 | Lai | Jan 2003 | B1 |
6514788 | Quinn | Feb 2003 | B2 |
6534781 | Dennison | Mar 2003 | B2 |
6545903 | Wu | Apr 2003 | B1 |
6555860 | Lowrey et al. | Apr 2003 | B2 |
6563156 | Harshfield | May 2003 | B2 |
6566700 | Xu | May 2003 | B2 |
6567293 | Lowrey et al. | May 2003 | B1 |
6579760 | Lung | Jun 2003 | B1 |
6586761 | Lowrey | Jul 2003 | B2 |
6589714 | Maimon et al. | Jul 2003 | B2 |
6593176 | Dennison | Jul 2003 | B2 |
6597009 | Wicker | Jul 2003 | B2 |
6605527 | Dennison et al. | Aug 2003 | B2 |
6605821 | Lee et al. | Aug 2003 | B1 |
6607974 | Harshfield | Aug 2003 | B2 |
6613604 | Maimon et al. | Sep 2003 | B2 |
6617192 | Lowrey et al. | Sep 2003 | B1 |
6620715 | Blosse et al. | Sep 2003 | B1 |
6621095 | Chiang et al. | Sep 2003 | B2 |
6627530 | Li et al. | Sep 2003 | B2 |
6639849 | Takahashi et al. | Oct 2003 | B2 |
6673700 | Dennison et al. | Jan 2004 | B2 |
6744088 | Dennison | Jun 2004 | B1 |
6791102 | Johnson et al. | Sep 2004 | B2 |
6797979 | Chiang et al. | Sep 2004 | B2 |
6800504 | Li et al. | Oct 2004 | B2 |
6800563 | Xu | Oct 2004 | B2 |
6805563 | Ohashi | Oct 2004 | B2 |
6808991 | Tung et al. | Oct 2004 | B1 |
6815704 | Chen | Nov 2004 | B1 |
6830952 | Lung et al. | Dec 2004 | B2 |
6850432 | Lu et al. | Feb 2005 | B2 |
6859389 | Idehara et al. | Feb 2005 | B2 |
6861267 | Xu et al. | Mar 2005 | B2 |
6864500 | Gilton | Mar 2005 | B2 |
6864503 | Lung | Mar 2005 | B2 |
6867638 | Saiki et al. | Mar 2005 | B2 |
6888750 | Walker et al. | May 2005 | B2 |
6894305 | Yi et al. | May 2005 | B2 |
6903362 | Wyeth et al. | Jun 2005 | B2 |
6909107 | Rodgers et al. | Jun 2005 | B2 |
6927410 | Chen | Aug 2005 | B2 |
6933516 | Xu | Aug 2005 | B2 |
6936840 | Sun et al. | Aug 2005 | B2 |
6937507 | Chen | Aug 2005 | B2 |
6937637 | Thornton et al. | Aug 2005 | B1 |
6972430 | Casagrande et al. | Dec 2005 | B2 |
6992932 | Cohen | Jan 2006 | B2 |
7023009 | Kostylev et al. | Apr 2006 | B2 |
7033856 | Lung et al. | Apr 2006 | B2 |
7042001 | Kim et al. | May 2006 | B2 |
7067864 | Nishida et al. | Jun 2006 | B2 |
7067865 | Lung et al. | Jun 2006 | B2 |
7122281 | Pierrat | Oct 2006 | B2 |
7126149 | Iwasaki et al. | Oct 2006 | B2 |
7132675 | Gilton | Nov 2006 | B2 |
7166533 | Happ | Jan 2007 | B2 |
7214958 | Happ | May 2007 | B2 |
7220983 | Lung | May 2007 | B2 |
7238994 | Chen et al. | Jul 2007 | B2 |
7251152 | Roehr | Jul 2007 | B2 |
7277317 | Le Phan et al. | Oct 2007 | B2 |
7321130 | Lung et al. | Jan 2008 | B2 |
20010055838 | Walker et al. | Dec 2001 | A1 |
20020081833 | Li et al. | Jun 2002 | A1 |
20040051094 | Ooishi | Mar 2004 | A1 |
20040248339 | Lung | Dec 2004 | A1 |
20050029502 | Hudgens | Feb 2005 | A1 |
20050093022 | Lung | May 2005 | A1 |
20050201182 | Osada et al. | Sep 2005 | A1 |
20050212024 | Happ | Sep 2005 | A1 |
20050215009 | Cho | Sep 2005 | A1 |
20060043617 | Abbott | Mar 2006 | A1 |
20060108667 | Lung | May 2006 | A1 |
20060110878 | Lung et al. | May 2006 | A1 |
20060118913 | Yi et al. | Jun 2006 | A1 |
20060154185 | Ho et al. | Jul 2006 | A1 |
20060175599 | Happ | Aug 2006 | A1 |
20060234138 | Fehlhaber et al. | Oct 2006 | A1 |
20060284157 | Chen et al. | Dec 2006 | A1 |
20060284158 | Lung et al. | Dec 2006 | A1 |
20060284214 | Chen | Dec 2006 | A1 |
20060284279 | Lung et al. | Dec 2006 | A1 |
20060286709 | Lung et al. | Dec 2006 | A1 |
20060286743 | Lung et al. | Dec 2006 | A1 |
20070030721 | Segal et al. | Feb 2007 | A1 |
20070108077 | Lung et al. | May 2007 | A1 |
20070108429 | Lung | May 2007 | A1 |
20070108430 | Lung | May 2007 | A1 |
20070108431 | Chen et al. | May 2007 | A1 |
20070109836 | Lung | May 2007 | A1 |
20070109843 | Lung et al. | May 2007 | A1 |
20070111429 | Lung | May 2007 | A1 |
20070115794 | Lung | May 2007 | A1 |
20070117315 | Lai et al. | May 2007 | A1 |
20070121363 | Lung | May 2007 | A1 |
20070121374 | Lung et al. | May 2007 | A1 |
20070126040 | Lung | Jun 2007 | A1 |
20070131922 | Lung | Jun 2007 | A1 |
20070131980 | Lung | Jun 2007 | A1 |
20070138458 | Lung | Jun 2007 | A1 |
20070147105 | Lung et al. | Jun 2007 | A1 |
20070154847 | Chen et al. | Jul 2007 | A1 |
20070155172 | Lai et al. | Jul 2007 | A1 |
20070158632 | Ho | Jul 2007 | A1 |
20070158633 | Lai et al. | Jul 2007 | A1 |
20070158645 | Lung | Jul 2007 | A1 |
20070158690 | Ho et al. | Jul 2007 | A1 |
20070158862 | Lung | Jul 2007 | A1 |
20070161186 | Ho | Jul 2007 | A1 |
20070173019 | Ho et al. | Jul 2007 | A1 |
20070173063 | Lung | Jul 2007 | A1 |
20070176261 | Lung | Aug 2007 | A1 |
20070224726 | Chen et al. | Sep 2007 | A1 |
20070246699 | Lung | Oct 2007 | A1 |
Number | Date | Country |
---|---|---|
WO 0045108 | Aug 2000 | WO |
WO 0079539 | Dec 2000 | WO |
WO 0145108 | Jun 2001 | WO |
Number | Date | Country | |
---|---|---|---|
20070121374 A1 | May 2007 | US |
Number | Date | Country | |
---|---|---|---|
60736722 | Nov 2005 | US |