Abstract:
Methods of forming phase-changeable memory devices include techniques to inhibit void formation in phase-changeable materials in order to increase device reliability. These techniques to inhibit void formation use an electrically insulating growth-inhibiting layer to guide the formation of a phase-changeable material region within a memory cell (e.g., PRAM cell). In particular, methods of forming an integrated circuit memory device include forming an interlayer insulating layer having an opening therein, on a substrate, and then lining sidewalls of the opening with a seed layer (i.e., growth-enhancing layer) that supports growth of a phase-changeable material thereon. An electrically insulating growth-inhibiting layer is then selectively formed on a portion of the interlayer insulating layer surrounding the opening. The formation of the growth-inhibiting layer is followed by a step to selectively grow a phase-changeable material region in the opening, but not on the growth-inhibiting layer.

Description:
REFERENCE TO PRIORITY APPLICATION 
       [0001]    This application claims priority to Korean Patent Application No. 10-2007-0117924, filed Nov. 19, 2007, the disclosure of which is hereby incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to methods of forming integrated circuit memory devices and, more particularly, to methods of forming nonvolatile memory devices. 
       BACKGROUND OF THE INVENTION 
       [0003]    One class of nonvolatile memory devices includes phase-changeable random access memory (PRAM) devices, which offer many advantageous electrical characteristics relative to FLASH, SRAM and DRAM memory devices. PRAM devices support non-volatile data storage, random access addressing and relatively high speed read and write operations. PRAM devices may also be configured to have relatively low power consumption requirements. 
         [0004]    The nonvolatile characteristics of the PRAM devices may be provided by configuring each memory cell with a chalcogenide alloy (e.g., GST: Ge 2 Sb 2 Te 5 ) having programmable resistivity characteristics. For example, during a write/programming operation, the chalcogenide alloy within a memory cell may undergo resistive heating to thereby alter the resistivity of the chalcogenide alloy and cause the memory cell to be “set” into one logic state or “reset” into another logic state. 
         [0005]      FIG. 1  illustrates a conventional diode-type PRAM cell  10 , which is electrically coupled to respective bit and word lines (BL and WL). In this PRAM cell  10 , the chalcogenide alloy (e.g., GST alloy) may be programmed to have a relatively high resistance state (high-R state) or a relatively low resistance state (low-R state). This state may be detected during a reading operation by biasing the bit line BL at a higher voltage relative to the word line to thereby establish a forward current path through the PRAM cell  10 . The magnitude of the established current (e.g., bit line current) in the forward current path is measured to determine the state (high-R or low-R) of the cell  10 . 
       SUMMARY OF THE INVENTION 
       [0006]    Methods of forming integrated circuit memory devices according to embodiments of the present invention include techniques to inhibit void formation in phase-changeable materials in order to increase device reliability. These techniques to inhibit void formation use an electrically insulating growth-inhibiting layer to guide the formation of a phase-changeable material region within a memory cell (e.g., PRAM cell). In particular, methods of forming an integrated circuit memory device include forming an interlayer insulating layer having an opening therein, on a substrate, and then lining sidewalls of the opening with a seed layer that operates as a growth-enhancing layer by supporting selective growth of a phase-changeable material thereon. An electrically insulating growth-inhibiting layer is then selectively formed on a portion of the interlayer insulating layer surrounding the opening. The formation of the growth-inhibiting layer is followed by a step to selectively grow a phase-changeable material region in the opening, but not on the growth-inhibiting layer. The growth-inhibiting layer may be a silicon oxide layer, a silicon nitride layer, a silicon oxynitride layer, a magnesium oxide layer and/or an aluminum oxide layer. 
         [0007]    According to some of these embodiments, the seed layer may include a transition metal oxide, such as titanium oxide, zirconium oxide, hafnium oxide and/or tantalum oxide. In addition, the step of forming a phase-changeable material region may include selectively growing the phase-changeable material region on the seed layer within the opening. The phase-changeable material region may be a chalcogenide material region. 
         [0008]    According to further embodiments of the invention, selectively depositing an electrically insulating growth-inhibiting layer includes sputter depositing the electrically insulating layer onto the interlayer insulating layer at a tilt angle in a range between 20° and 65° relative to a normal to the substrate. Furthermore, the step of lining sidewalls of the opening with a seed layer may include lining the sidewalls and an upper surface of the interlayer insulating layer with a seed layer having a thickness in a range between 10 Å and 30 Å. This step may be followed by selectively depositing an electrically insulating growth-inhibiting layer by sputter depositing the growth-inhibiting layer onto the seed layer at the tilt angle. 
         [0009]    According to still further embodiments of the present invention, a method of forming an integrated circuit memory device includes forming an interlayer insulating layer having an array of openings therein, on a substrate, and then lining sidewalls of the openings and an upper surface of the interlayer insulating layer with a metal oxide seed layer using a blanket deposition technique. An electrically insulating growth-inhibiting layer is then sputter-deposited onto the metal oxide seed layer at a tilt angle in a range between 20° and 65° relative to a normal to the substrate. This deposition at a substantial tilt angle inhibits deposition into the openings within the interlayer insulating layer. The openings are then filled with respective phase-changeable material regions by growing the phase-changeable material regions from portions of the metal oxide seed layer that are not covered by the growth-inhibiting layer. Each of these regions may be capped within a corresponding upper electrode and multiple upper electrodes may be electrically connected together by a bit line. 
         [0010]    According to additional embodiments of the invention, the step of forming the interlayer insulating layer includes forming an interlayer insulating layer having an array of openings therein that respectively include a lower electrode at a bottom of each opening. In these embodiments, the step of lining the openings includes covering the lower electrodes at the bottoms of the openings with the metal oxide seed layer. 
         [0011]    According to still further embodiments of the invention, a method of forming an integrated circuit memory device includes forming an electrically conductive word line in a semiconductor substrate and then forming a first interlayer insulating layer having a first opening therein that extends opposite the word line, on the semiconductor substrate. The first opening is filled with a P-N junction diode having a diode electrode thereon. A second interlayer insulating layer having a second opening therein, which exposes the diode electrode, is formed on the first interlayer insulating layer. A transition metal oxide seed layer, which may have a thickness in a range between 10 Å and 30 Å, is then deposited onto the second interlayer insulating layer and onto sidewalls of the second opening. Portions of the transition metal oxide seed layer, which extend outside the second opening, are then covered by sputter depositing an electrically insulating growth-inhibiting layer onto the metal oxide seed layer at a non-zero tilt angle relative to a normal to the substrate. The second opening is then filled with a phase-changeable material region by growing the phase-changeable material region from portions of the metal oxide seed layer within the second opening. An upper electrode is then formed on the phase-changeable material region. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is an electrical schematic of a conventional diode-type PRAM cell. 
           [0013]      FIGS. 2A-2D  are cross-sectional views of intermediate structures that illustrate methods of forming integrated circuit memory devices according to some embodiments of the present invention. 
           [0014]      FIGS. 3A-3B  are cross-sectional views of intermediate structures that illustrate methods of forming integrated circuit memory devices according to additional embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0015]    The present invention now will be described more fully herein with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout. 
         [0016]    Methods of forming integrated circuit memory devices according to embodiments of the present invention include forming a trench isolation region  112  in a substrate  110 , as illustrated by  FIG. 2A . This substrate  110  may be a semiconductor substrate containing a well region of first conductivity type therein and the trench isolation region  112  may be formed as a shallow trench isolation (STI) region, a selective polycrystalline silicon oxidation (SEPOX) region or a local oxidation of silicon (LOCOS) region, for example. The trench isolation region  112  may define an active region therebetween and this region may include a word line  114  (WL) of a memory device. This word line  114  may be formed as a semiconductor region of second conductivity type in the substrate  110 . Alternative word lines (e.g., polysilicon, metal, etc.) may also be used. This semiconductor word line region may form a P-N rectifying junction with an underlying portion of the substrate  110  that functions as a semiconductor well region of first conductivity type. 
         [0017]    A lower interlayer dielectric layer  120  is formed on the substrate  110  and an opening is formed therein that exposes the word line  114 . This opening may be formed by selectively etching the lower interlayer dielectric layer  120  using an etching mask (not shown). The lower interlayer dielectric layer  120  may be formed of a dielectric material, such as silicon oxide, silicon nitride and/or silicon oxynitride, for example. In particular, the dielectric material may be formed as an undoped silicate glass (USG) layer, a spin-on glass (SOG) layer, a borophosphosilicate glass (BPSG) layer, a phosphosilicate glass (PSG) layer, a tetraethyl orthosilicate (TEOS) glass layer, a plasma-enhanced TEOS layer or a high density plasma (HDP) oxide layer formed by chemical vapor deposition (CVD), for example. 
         [0018]    A diode (D), such as a P-N junction diode, is formed in the opening. This diode is illustrated as including a first semiconductor pattern  122 , which electrically contacts an underlying word line  114 , and a second semiconductor pattern  124 , which forms a P-N rectifying junction with the first semiconductor pattern  122 . The first semiconductor pattern  122  may be formed as a semiconductor region having the second conductivity type (e.g., N-type or P-type) and the second semiconductor pattern  124  may be formed as a semiconductor region having the first conductivity type (e.g., P-type or N-type), which is opposite the second conductivity type. In particular, the second semiconductor pattern  124  may be a P-type polycrystalline region and the first semiconductor pattern  122  may be an N-type polycrystalline region. Moreover, the word line  114  may be an N-type semiconductor line that is formed in a surrounding P-type well region. The first and second semiconductor patterns  122  and  124  may be formed as in-situ doped patterns during respective selective epitaxial growth (SEG) steps. In particular, the first and second semiconductor patterns  122  and  124  may be formed in sequence by epitaxially growing in-situ doped polycrystalline silicon in the opening in the lower interlayer dielectric layer  120 , using the underlying semiconductor word line  114  (e.g., single crystal silicon word line) as a “seed” for the epitaxial growth. 
         [0019]    Referring still to  FIG. 2A , a diode electrode  129  is formed on the diode D, as illustrated. This diode electrode  129  is illustrated as including a metal silicide pattern  126  and an electrically conductive pattern  128  on the metal silicide pattern  126 . The electrically conductive pattern  128  may include a metal pattern, a metal nitride pattern or a doped polysilicon pattern, for example. In particular, the electrically conductive pattern  128  may including an electrically conductive material selected from a group consisting of: tungsten (W), aluminum (Al), titanium (Ti), copper (Cu), tungsten nitride (WNx), titanium nitride (TiNx), aluminum nitride (AlNx), titanium aluminum nitride (TiAlNx) and/or tantalum nitride (TaNx). 
         [0020]    According to alternative embodiments of the present invention, the first and second semiconductor patterns  122  and  124 , the metal silicide pattern  126  and the electrically conductive pattern  128  may be formed by sequentially depositing these layers on the substrate  110  to form a composite of layers and then patterning the composite of layers by selectively etching the layers using a mask (not shown). A lower interlayer dielectric layer  120  may then be deposited on the patterned composite of layers. This dielectric layer may then be planarized for a sufficient duration to expose the electrically conductive pattern  128 . 
         [0021]    An upper interlayer dielectric layer  130  is formed on the lower interlayer dielectric layer  120  and then patterned (e.g., selectively etched) to define a contact hole  132  therein that exposes an upper surface of the electrically conductive pattern  128 . As illustrated by  FIG. 2B , a lower electrode  134  of a memory storage device is formed in the contact hole  132 . This lower electrode  134  may be formed as a highly conductive layer, such as a metal nitride layer. Thereafter, a “seed” layer  136  is deposited conformally on the upper interlayer dielectric layer  130  and into the contact hole  132 , as illustrated. This seed layer, which is electrically connected to the lower electrode  134 , may be deposited as a transition metal oxide layer having a thickness in a range between 10 Å and 30 Å, using an atomic layer deposition (ALD) or a chemical vapor deposition (CVD) technique. This transition metal oxide seed layer  136  may include a material selected from a group consisting of titanium oxide, zirconium oxide, hafnium oxide and tantalum oxide. 
         [0022]    Referring still to  FIG. 2B , the seed layer  136  is then covered by an electrically insulating layer. In particular, portions of the seed layer  136  extending outside the contact hole  132  are selectively covered by sputter depositing  30  an electrically insulating growth-inhibiting layer  138  onto the seed layer  136  at a non-zero tilt angle (A) relative to a normal  110   a  to the substrate  110 . This tilt angle (A) is sufficiently large to inhibit the formation of the growth-inhibiting layer  138  on the inner sidewalls of the seed layer  136  within the contact hole  132 . In particular, the tilt angle (A) is in a range between 20° and 65° relative to a normal  110   a  to the substrate  110  in order to inhibit deposition within the contact hole  132 . The growth-inhibiting layer  138  includes a material selected from a group consisting of silicon oxide, silicon nitride, silicon oxynitride, magnesium oxide and aluminum oxide, for example. The sputter depositing of the growth-inhibiting layer  138  may be performed in a conventional sputter deposition chamber that may be powered by a direct current (DC) or radio-frequency (RF) power source, for example. The sputter deposition chamber may include a sputter deposition target (e.g., containing the growth-inhibiting material) having a primary target surface that is rotated relative to a surface of a substrate holder containing a semiconductor wafer being processed. The chamber may also include an ionization source (e.g., Argon gas source injected into chamber) that is directed at the surface of the sputter deposition target. 
         [0023]    Referring now to  FIG. 2C , the contact hole  132  is filled with a phase-changeable material region  140  (having a phase-changeable resistance Rp), by selectively growing the phase-changeable material region  140  from exposed portions of the seed layer  136  within the contact hole  132 . This selective growth step may be performed using a chemical vapor deposition (CVD) technique. Other growth techniques may also be used. This phase-changeable material region may be a variable resistivity material, such as a chalcogenide composition (e.g., GST, AST, SST, GBT, . . . ), for example. An upper electrode  144  may be formed on and in electrical contact with the phase-changeable material region  140 , as illustrated by  FIG. 2D , in order to complete the structure of a phase-changeable memory cell within a multi-celled memory device. In particular, an electrically insulating dielectric layer  142  may be deposited on the phase-changeable material region  140  and then patterned to define an opening therein that is then filled with the upper electrode  144  using conventional processing techniques. This upper electrode  144  may be formed of an electrically conductive material such as polysilicon, metal (e.g., W, Al, Cu, Ta, Ti, Mo, etc.) and/or metal nitride (e.g., WNx, AlNx, TiNx, TaNx, MoNx, NbNx, TiSiNx, TiAlNx, TiBNx, ZrSiNz, WSiNx, WBNx, ZrAlNx, MoSiNx, MoAlNx, MoAlNx, TaSiNx, TaAlNx, etc.). A bit line  146  (BL) may then be formed on the upper electrode  144 , as illustrated. As will be understood by those skilled in the art, the series resistance and phase (e.g., crystalline or amorphous) of the phase-changeable material region may be determined during a memory read operation by passing a forward read current through the phase-changeable material region. This read current may be provided by enabling a selected bit line  146  as a current source and enabling a corresponding selected word line  144  as a current sink. 
         [0024]    According to alternative embodiments of the present invention, the phase-changeable material region  140  illustrated by  FIG. 2C  may be modified by planarizing  60  the phase-changeable material region  140  to have an upper surface that is planar with the growth-inhibiting layer  138 , as illustrated by  FIG. 3A . Alternatively, the planarization step  60  may be performed for a greater duration to expose the seed layer  136  or the upper interlayer dielectric layer  130 . Referring now to  FIG. 3B , an electrically insulating dielectric layer  142  may be deposited on the planarized phase-changeable material region  140  and then patterned to define an opening therein that is then filled with the upper electrode  144 . A bit line  146  may then be formed on the upper electrode  144 , as illustrated. Although not shown in  FIG. 3B , this bit line  146  may extend in a column direction across a two-dimensional array of phase-changeable memory cells having the structure illustrated by  FIG. 2D  or  3 B. 
         [0025]    In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.