Patent Publication Number: US-10332842-B2

Title: Semiconductor devices with alignment keys

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. nonprovisional patent application is a divisional of U.S. patent application Ser. No. 15/608,747, filed on May 30, 2017 in the U.S. Patent and Trademark Office, which in turn claims priority under 35 U.S.C. § 119 from, and the benefit of, Korean Patent Application 10-2016-0127011, filed on Sep. 30, 2016 in the Korean Intellectual Property Office, the contents of which are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Technical Field 
     Embodiments of the present inventive concept are directed to a semiconductor device, and more particularly, to a semiconductor memory device that includes an alignment key. 
     Discussion of Related Art 
     Semiconductor devices have become increasingly integrated with the development of the electronics industry. It is challenging to fabricate a semiconductor device because of reduced process margins in an exposure process that defines fine patterns. High speed semiconductor devices are increasingly in demand with the development of the electronics industry, and the development of high speed and more highly integrated semiconductor device has been the subject of much research. 
     In general, to fabricate a semiconductor device, a predetermined material layer is formed on a semiconductor substrate, i.e., a wafer, and then a photolithography process is performed to form a desired pattern. The photolithography process is carried out to form a pattern by forming a photoresist layer on the semiconductor substrate on which the predetermined layer is formed, forming a photoresist pattern by exposing and developing the photoresist layer using a mask, and then etching the predetermined layer using the photoresist pattern. The exposure process has an important role in determining the fabrication accuracy of a method for the semiconductor device. When the exposure process is utilized to form a predetermined pattern on the semiconductor substrate, a photo alignment key is used to exactly align an exposure mask. 
     SUMMARY 
     Embodiments of the present inventive concept can provide a semiconductor device having enhanced process yield and reliability. 
     According to exemplary embodiments of the present inventive concept, a semiconductor device includes an alignment key on a substrate. The alignment key comprises a first sub-alignment key pattern that includes a first conductive pattern, a second conductive pattern, and a capping dielectric pattern that are sequentially stacked on the substrate; an alignment key trench that penetrates at least a portion of the first sub-alignment key pattern; and a lower conductive pattern in the alignment key trench. The alignment key trench comprises an upper trench provided in the capping dielectric pattern that has a first width; and a lower trench that extends downward from the upper trench that has a second width less than the first width. The lower conductive pattern includes sidewall conductive patterns that are separately disposed on opposite sidewalls of the lower trench. 
     According to exemplary embodiments of the present inventive concept, a semiconductor device comprises a substrate that includes a chip zone and a scribe lane zone; a gate line on the chip zone; and an alignment key on the scribe lane zone. The gate line includes a gate dielectric pattern, a lower gate pattern, an upper gate pattern, and a gate capping pattern that are sequentially stacked on the substrate. The alignment key comprises a first sub-alignment key pattern that includes a buffer dielectric pattern, a first conductive pattern, a second conductive pattern, and a capping dielectric pattern that are sequentially stacked on the substrate; an alignment key trench that penetrates at least a portion of the first sub-alignment key pattern, the alignment key trench including an upper trench that vertically penetrates a portion of the capping dielectric pattern and has a first width and a lower trench that extends downward from the upper trench and has a second width less than the first width; and sidewall conductive patterns that are separately disposed on opposite sidewalk of the lower trench. The buffer dielectric pattern, the first conductive pattern, the second conductive pattern, and the capping dielectric pattern include the same materials, respectively, as the gate dielectric pattern, the lower gate pattern, the upper gate pattern, and the gate capping pattern. 
     According to exemplary embodiments of the present inventive concept, a method of fabricating a semiconductor device includes providing a substrate that includes a first region and a second region; sequentially forming a first dielectric layer, a lower conductive layer, an upper conductive layer, and a second dielectric layer on the substrate; forming a first mask pattern on the substrate that covers a portion of the second dielectric layer in the first region and completely covers the second dielectric layer in the second region, and etching the substrate using the first mask pattern as an etching mask wherein a gate line is formed in the first region of the substrate. The gate line includes a gate dielectric pattern, a lower gate pattern, an upper gate pattern, and a gate capping pattern that are respectively formed by patterning the first dielectric layer, the lower conductive layer, the upper conductive layer, and the second dielectric layer in the first region. The method further includes removing the first mask pattern; forming source/drain regions in the substrate on opposite sides of the gate line; forming a lower interlayer dielectric layer on the first region of the substrate; forming a second mask pattern on the substrate that has first openings on the first region that overlap the source/drain regions and a trench-shaped second opening on the second region; etching portions of the lower interlayer dielectric layer exposed through the first openings using the second mask pattern to form lower contact holes that penetrate the lower interlayer dielectric layer and expose the source/drain regions, wherein the second dielectric layer and the upper conductive layer of the second region are sequentially etched to form a preliminary alignment key trench that exposes the lower conductive layer; and removing the second mask pattern. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified plan view that illustrates a semiconductor device according to exemplary embodiments of the present inventive concept. 
         FIG. 2  is a plan view that illustrates shapes of photo alignment keys. 
         FIG. 3  is a plan view that partly illustrates a semiconductor device of  FIG. 1 . 
         FIG. 4  is a cross-sectional view taken along lines I-I′ and II-II′ of  FIG. 3 . 
         FIGS. 5A to 5C  are cross-sectional views, corresponding to line II-II′ of  FIG. 3 , that illustrate other examples of alignment keys shown in  FIGS. 3 and 4 . 
         FIGS. 6 to 14  are cross-sectional views, corresponding to lines I-I′ and II-II′ of  FIG. 3 , that illustrate a method of fabricating a semiconductor device according to exemplary embodiments of the present inventive concept. 
         FIGS. 15 and 16  are cross-sectional views, corresponding to lines I-I′ and II-II′ of  FIG. 3 , that illustrate comparative examples that are compared with exemplary embodiments of the present inventive concept. 
         FIG. 17  is a cross-sectional view, corresponding to lines I-I′ and II-II′ of  FIG. 3 , that illustrates a semiconductor device according to exemplary embodiments of the present inventive concept. 
         FIGS. 18A to 18C  are cross-sectional views, corresponding to line II-II′ of  FIG. 3 , that illustrate other examples of alignment keys shown in  FIGS. 3 and 17 . 
         FIGS. 19 to 22  are cross-sectional views, corresponding to lines I-I′ and II-II′ of  FIG. 3 , that illustrate a method of fabricating a semiconductor device according to exemplary embodiments of the present inventive concept. 
         FIG. 23  is a cross-sectional view, corresponding to lines I-I′ and II-II′ of  FIG. 3 , that illustrates a semiconductor device according to exemplary embodiments of the present inventive concept. 
         FIGS. 24A to 24C  are cross-sectional views, corresponding to lines I-I′ and II-II′ of  FIG. 3 , that illustrates a semiconductor device according to exemplary embodiments of the present inventive concept. 
         FIG. 25  is a plan view that illustrates a semiconductor device according to exemplary embodiments of the present inventive concept. 
         FIG. 26  is a cross-sectional view taken along lines A-A′, B-B′, and C-C′ of  FIG. 25 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present inventive concept will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a simplified plan view that illustrates a semiconductor device according to exemplary embodiments of the present inventive concept.  FIG. 2  is a plan view that illustrates shapes of photo alignment keys. 
     Referring to  FIG. 1 , a semiconductor device  10  according to an embodiment includes a chip zone  12  and a scribe lane zone  14 . The chip zone  12  corresponds to one of a plurality of semiconductor chips formed on a semiconductor wafer, and the scribe lane zone  14  corresponds to a portion of scribe lane used to cut the semiconductor wafer into separate semiconductor chips after process steps that form the semiconductor chips on the semiconductor wafer have terminated. The chip zone  12  includes a cell region on which memory cells are formed and a peripheral circuit region on which peripheral circuits that control the memory cells are formed. For example, the chip zone  12  may include metal-oxide-semiconductor (MOS) transistors, a diode, or a resistor. The scribe lane zone  14  includes a test device group and photo alignment keys  16   a  and  16   b , referred to hereinafter as alignment keys. 
     According to embodiments, the alignment keys  16   a  and  16   b  have a shape similar to that of cell, contact, or trench. As shown in  FIG. 2 , the alignment keys  16   a  and  16   b  have various patterns AK 1 , AK 2 , and AK 3 . In accordance with their purpose, the alignment keys  16   a  and  16   b  can be classified as a local alignment key, a global alignment key, a registration alignment key, an overlay alignment key, and a measurement key. A trench-type alignment key and a semiconductor device including the same will hereinafter be described in detail. 
       FIG. 3  is a plan view that partly illustrates the semiconductor device of  FIG. 1 .  FIG. 4  is a cross-sectional view taken along lines I-I′ and II-II′ and of  FIG. 3 . 
     Referring to  FIGS. 3 and 4 , according to embodiments, a substrate  100  includes a first region R 1  and a second region R 2 . The substrate  100  is a semiconductor substrate such as a silicon substrate, a germanium substrate, or a silicon-germanium substrate. The first region R 1  is a portion of the chip zone  12  of  FIG. 1 , and the second region R 2  is a portion of the scribe lane zone  14  of  FIG. 1 . 
     According to embodiments, a gate line GL is disposed on the substrate  100  of the first region R 1 . For example, the gate line GL has a line or bar shape that extends in a first direction D 1  and crosses an active region PA defined in the substrate  100  of the first region R 1 . In the first region R 1 , the substrate  100  includes the active region PA at an upper portion defined by a device isolation pattern  102   p . The device isolation pattern  102   p  may include, for example, silicon oxide or silicon oxynitride. Although  FIGS. 3 and 4  show one gate line GL, exemplary embodiments of the present inventive concept are not limited thereto. 
     According to embodiments, the gate line GL includes a gate dielectric pattern  110   p , a lower gate pattern  115   p , an upper gate pattern  120   p , and a gate capping pattern  125   p  that are sequentially stacked. The gate dielectric pattern  110   p  includes an insulating material, for example, at least one of silicon oxide, silicon oxynitride, or a high-k dielectric such as a dielectric metal oxide such as hafnium oxide or aluminum oxide that have a dielectric constant greater than that of silicon oxide. The lower and upper gate patterns  115   p  and  120   p  include a conductive material. For example, the lower gate pattern  115   p  can include doped polysilicon and the upper gate pattern  120   p  includes at least one of a metal such as tungsten, aluminum, titanium, or tantalum, or a conductive metal nitride such as titanium nitride, tantalum nitride, or tungsten nitride. The gate capping pattern  125   p  includes an insulating material, such as silicon oxide, silicon nitride, or silicon oxynitride. 
     According to embodiments, the gate line GL is provided with gate spacers  135   p  on its sidewalls that extend in the first direction D 1  along the gate line GL. The gate spacers  135   p  include at least one of silicon oxide, silicon nitride, or silicon oxynitride. Source/drain regions PSD are disposed in the active region PA on opposite sides of the gate line GL. The source/drain regions PSD are doped with p- or n-type impurities. 
     According to embodiments, a lower interlayer dielectric layer  140  is disposed on the substrate  100  of the first region R 1 . The lower interlayer dielectric layer  140  covers the sidewalls of the gate line GL. The lower interlayer dielectric layer  140  includes at least one of silicon oxide, silicon nitride, or silicon oxynitride. The lower interlayer dielectric layer  140  exposes a top surface of the gate line GL, but exemplary embodiments of the present inventive concept are not limited thereto. 
     According to embodiments, a lower contact plug  152  is disposed on at least one of opposite sides of the gate line GL, and penetrates the lower interlayer dielectric layer  140  to connect to one of the source/drain regions PSD. A lower interconnect line  154  connected to the lower contact plug  152  is disposed on the lower interlayer dielectric layer  140 . The lower contact plug  152  and the lower interconnect line  154  include the same conductive material. For example, the lower contact plug  152  and the lower interconnect fine  154  can include at least one of a metal such as tungsten, titanium, or tantalum, or a conductive metal nitride such as titanium nitride, tantalum nitride, or tungsten nitride. In some embodiments, the lower contact plug  152  and the lower interconnect line  154  are simultaneously formed to constitute a single unitary structure. 
     According to embodiments, an alignment key AK is disposed on the substrate  100  of the second region R 2 . The alignment key AK includes an alignment key pattern KP and an alignment key trench Tk. The alignment key trench Tk vertically penetrates at least a portion of the alignment key pattern KP. In other words, the alignment key AK is a trench-type alignment key. Although the alignment key AK is illustrated as having one alignment key trench Tk, exemplary embodiments of the present inventive concept are not limited thereto. In some embodiments, the alignment key AK includes an alignment key pattern KP and a plurality of alignment key trenches Tk that penetrate the alignment key pattern KP. 
     According to embodiments, the alignment key pattern KP includes a first sub-alignment key pattern KP 1  and a second sub-alignment key pattern KP 2 . The first sub-alignment key pattern KP 1  includes a buffer dielectric pattern  110   k , a first conductive pattern  115   k , a second conductive pattern  120   k , and a capping dielectric pattern  125   k . In some embodiments, the alignment key trench Tk vertically penetrates a portion of the first sub-alignment key pattern KP 1 . For example, the alignment key trench Tk penetrates the capping dielectric pattern  125   k  and the second conductive pattern  120   k  to expose the first conductive pattern  115   k  through the alignment key trench Tk. 
     According to a present inventive concept, the alignment key trench Tk includes portions having different widths from each other. For example, the alignment key trench Tk includes an upper trench T 1  having a first width W 1  and a lower trench T 2  having a second width W 2  less than the first width W 1 . The lower trench T 2  extends downward from the upper trench T 1 . The first and second widths W 1  and W 2  of the alignment key trench Tk are measured in a second direction D 2 . The second direction D 2  is, for example, perpendicular to the first direction D 1 . The upper trench T 1  vertically penetrates a portion of the capping dielectric pattern  125   k . In this configuration, the upper trench T 1  is formed in the capping dielectric pattern  125   k . The upper trench T 1  has a depth d 1  less than a thickness of the capping dielectric pattern  125   k . The lower trench T 2  extends from the upper trench Tk to penetrate the capping dielectric pattern  125   k  and the second conductive pattern  120   k , to expose the first conductive pattern  115   k  through the lower trench T 2 . The alignment key trench Tk has a depth d of greater than or equal to about 30 nm, which is a sum of the depth d 1  of the upper trench T 1  and a depth d 2  of the lower trench T 2 . For example, the depth d of the alignment key trench Tk is in the range from about 30 nm to about 500 nm. The width W 2  of the lower trench T 2  is greater than or equal to about 100 nm. For example, the width W 2  of the lower trench T 2  is in the range from about 100 nm to about 5,000 nm. 
     According to embodiments, the second sub-alignment key pattern KP 2  includes a lower conductive pattern  156  and an upper conductive pattern  158 . The lower conductive pattern  156  is disposed in the lower trench T 2  and partially fills the lower trench T 2 . For example, the lower conductive pattern  156  includes sidewall conductive patterns  156   s  disposed on sidewalls of the lower trench T 2  and an interconnect conductive pattern  156   c  that connects bottom ends of the sidewall conductive patterns  156   s . The interconnect conductive pattern  156   c  is in contact with the first conductive pattern  115   k  exposed through the lower trench T 2 . The sidewall conductive patterns  156   s  and the interconnect conductive pattern  156   c  constitute a single unitary structure. The upper conductive pattern  158  is disposed on a top surface of the capping dielectric pattern  125   k . The upper conductive pattern  158  has inner sidewalls aligned with sidewalls of the capping dielectric pattern  125   k  that are exposed through the upper trench T 1 . 
     According to embodiments, the buffer dielectric pattern  110   k , the first conductive pattern  115   k , the second conductive pattern  120   k , and the capping dielectric pattern  125   k  of the first sub-alignment key pattern KP 1  have the same materials, respectively, as the gate dielectric pattern  110   p , the lower gate pattern  115   p , the upper gate pattern  120   p , and the gate capping pattern  125   p  of the gate line GL. The buffer dielectric pattern  110   k  includes at least one of, for example, silicon oxide, silicon oxynitride, or a high-k dielectric such as a dielectric metal oxide such as hafnium oxide or aluminum oxide that have a dielectric constant greater than that of silicon oxide. For example, the first conductive pattern  115   k  includes doped polysilicon, and the second conductive pattern  120   k  includes at least one of a metal such as tungsten, aluminum, titanium, or tantalum, or a conductive metal nitride such as titanium nitride, tantalum nitride, or tungsten nitride. The capping dielectric pattern  125   k  may include, for example, silicon oxide, silicon nitride, or silicon oxynitride. 
     According to embodiments, the lower conductive pattern  156  and the upper conductive pattern  158  of the second sub-alignment key pattern KP 2  include the same material as the lower contact plug  152  and the lower interconnect line  154 . For example, the lower contact pattern  156  and the upper interconnect line  158  include at least one of a metal such as tungsten, titanium, or tantalum, or a conductive metal nitride such as titanium nitride, tantalum nitride, or tungsten nitride. 
     According to embodiments, during a method of fabricating a semiconductor device, the alignment key trench Tk is provided with mask layers with different etch selectivities which are removed after a patterning process that uses the mask layers. After removing the mask layers from the alignment key trench Tk, the mask layers may partially remain to act as lifting failure sources. In some embodiments, the alignment key AK are configured to suppress lifting failure. This will be described in detail in the following description of a method of fabricating a semiconductor device. 
     According to embodiments, an upper interlayer dielectric layer is disposed on an entire surface of the substrate  100 . On the first region R 1  the upper interlayer dielectric layer covers the lower interconnect line  154 . On the second region R 2 , the upper interlayer dielectric layer fills the alignment key trench Tk. The upper interlayer dielectric layer includes silicon oxide, silicon nitride, or silicon oxynitride. 
       FIGS. 5A to 5C  are cross-sectional views, corresponding to line II-II′ of  FIG. 3 , that illustrate other examples of the alignment key shown in  FIGS. 3 and 4 . For brevity of the description, different configurations will be described. 
     Referring to  FIG. 5A , according to embodiments, the lower conductive pattern  156  of the second sub-alignment key pattern KP 2  includes only the sidewall conductive patterns  156   s . That is, the interconnect conductive pattern  156   c  of  FIGS. 3 and 4  is omitted. The sidewall conductive patterns  156   s  are separately disposed on the sidewalls of the lower trench T 2 . The first conductive pattern  115   k  have a top surface that defines a floor surface of the lower trench T 2  which is exposed through the lower conductive pattern  156 . 
     Referring to  FIG. 5B , according to embodiments, the second sub-alignment key pattern KP 2  includes only the lower conductive patterns  156 . That is, the upper conductive pattern  158  of  FIGS. 3 and 4  is omitted. 
     Referring to  FIG. 5C , according to embodiments, the second sub-alignment key pattern KP 2  includes only the sidewall conductive patterns  156   s . That is, the interconnect conductive pattern  156   c  and the upper conductive pattern  158  of  FIGS. 3 and 4  are omitted. 
       FIGS. 6 to 14  are cross-sectional views, corresponding to lines I-I′ and II-II′ of  FIG. 3 , that illustrate a method of fabricating a semiconductor device according to exemplary embodiments of the present inventive concept.  FIGS. 15 and 16  are cross-sectional views, corresponding to lines I-I′ and II-II′ of  FIG. 3 , that illustrate comparative examples that are compared with exemplary embodiments of the present inventive concept. For brevity of the description, a repetitive explanation will be omitted. 
     Referring to  FIGS. 3 and 6 , according to embodiments, a substrate  100  is provided that includes a first region R 1  and a second region R 2 . An active region PA is defined by forming a device isolation pattern  102   p  in the first region R 1  of the substrate  100 . For example, a shallow trench isolation (STI) process can be performed to form the device isolation pattern  102   p.    
     According to embodiments, a first dielectric layer  110 , a lower conductive layer  115 , an upper conductive layer  120 , and a second dielectric layer  125  are sequentially formed on the substrate  100 . The first dielectric layer  110 , the lower conductive layer  115 , the upper conductive layer  120 , and the second dielectric layer  125  cover all of the first and second regions R 1  and R 2 . The first dielectric layer  110  includes at least one of, for example, silicon oxide, silicon oxynitride, or a high-k dielectric such as a dielectric metal oxide such as hafnium oxide or aluminum oxide that have a dielectric constant greater than that of silicon oxide. For example, the lower conductive layer  115  includes doped polysilicon, and the upper conductive layer  120  includes at least one of a metal such as tungsten, aluminum, titanium, or tantalum, or a conductive metal nitride such as titanium nitride, tantalum nitride, or tungsten nitride. The second dielectric layer  125  includes, for example, silicon oxide, silicon nitride, or silicon oxynitride. The first dielectric layer  110 , the lower conductive layer  115 , the upper conductive layer  120 , and the second dielectric layer  125  can be formed through a deposition process such as CVD or PVD. 
     Referring to  FIGS. 3 and 7 , according to embodiments, a first mask pattern M 1  is formed on the substrate  100 . The second dielectric layer  125  of the first region R 1  includes a portion, where a gate line GL is formed, that is covered by the first mask pattern M 1  and a remaining portion that is exposed through the first mask pattern M 1 . The second dielectric layer  125  of the second region R 2  is completely covered by the first mask pattern M 1 . The first mask pattern M 1  includes a hardmask pattern or a photoresist pattern. 
     Referring to  FIGS. 3 and 8 , according to embodiments, the substrate  100  undergoes an etching process using the first mask pattern M 1  as an etching mask. A gate line GL is then formed on the substrate  100  of the first region R 1 . The gate line GL includes a gate dielectric pattern  110   p , a lower gate pattern  115   p , an upper gate pattern  120   p , and a gate capping pattern  125   p  that are respectively formed by patterning the first dielectric layer  110 , the lower conductive layer  115 , the upper conductive layer  120 , and the second dielectric layer  125  of the first region R 1 . During the formation of the gate line GL, the first mask pattern M 1  protects the layers  110 ,  115 ,  120 , and  125  of the second region R 2 . After the formation of the gate line GL, the first mask pattern M 1  is removed. 
     According to embodiments, gate spacers  135   p  are formed on sidewalk of the gate line GL. For example, the gate spacers  135   p  can be formed by forming a gate spacer layer on an entire surface of the substrate  100  and then performing a blanket anisotropic etching process. The gate spacer layer includes at least one of silicon oxide, silicon nitride, or silicon oxynitride. 
     According to embodiments, source/drain regions PSD are formed in the substrate  100  on opposite sides of the gate line GL. For example, the source/drain regions PSD can be formed by an ion implantation process using the gate line GL as an ion implantation mask. 
     Referring to  FIGS. 3 and 9 , according to embodiments, a lower interlayer dielectric layer  140  is formed on the substrate  100  of the first region R 1 . For example, the lower interlayer dielectric layer  140  can be formed by covering the entire surface of the substrate  100  with an insulating layer and then performing a planarization process on the insulating layer to expose a top surface of the gate line GL. As a result, the lower interlayer dielectric layer  140  has a top surface whose height is substantially the same as that of the top surface of the gate line GL. During the planarization process, the lower interlayer dielectric layer  140  is completely removed from the second region R 2 . 
     According to embodiments, a second mask pattern M 2  is formed on the substrate  100 . The second mask pattern M 2  has first openings OP 1  on the first region R 1  and a second opening OP 2  on the second region R 2 . The first openings OP 1  are shaped as a hole and overlap the source/drain regions PSD on opposite sides of the gate line GL. The second opening OP 2  is a trench that extends in the first direction D 1 . The second opening OP 2  has a width Wa that corresponds to the second width W 2  of the lower trench T 2  shown in  FIGS. 3 and 4 . The second mask pattern M 2  includes a hardmask pattern or a photoresist pattern. 
     Referring to  FIGS. 3 and 10 , according to embodiments, an etching process is performed using the second mask pattern M 2  as an etching mask to etch the lower interlayer dielectric layer  140  on portions exposed through the first openings OP 1 . The etching process uses an etchant on the substrate  100  that has a low etch rate and is performed until a top surface of the substrate  100  is exposed. Accordingly, lower contact holes  145  are formed that penetrate the lower interlayer dielectric layer  140  and expose the source/drain regions PSD. The etching process also sequentially etches the second dielectric layer  125  and the upper conductive layer  120  to form a preliminary alignment key trench Tp that exposes the lower conductive layer  115 . The lower conductive layer  115  is not removed from the second region R 2  during the etching process that forms the lower contact holes  145  since the lower conductive layer  115  is formed of doped polysilicon. In other words, when the preliminary alignment key trench Tp is simultaneously formed with the lower contact holes  145 , the lower conductive layer  115  of the second region R 2  acts as an etch stop layer. The preliminary alignment key trench Tp has a width that corresponds to the width Wa of the second opening OP 2 . After forming the lower contact holes  145  and the preliminary alignment key trench Tp, the second mask pattern M 2  is removed. 
     Referring to  FIGS. 3 and 11 , according to embodiments, a lower interconnect line layer  150  is formed on the substrate  100 . The lower interconnect line layer  150  of the first region R 1  completely fills the lower contact holes  145  and covers the top surface of the lower interlayer dielectric layer  140 . The lower interconnect line layer  150  of the second region R 2  partially fills the preliminary alignment key trench Tp and covers a top surface of the second dielectric layer  125 . The lower interconnect line layer  150  includes at least one of a metal such as tungsten, titanium, or tantalum, or a conductive metal nitride such as titanium nitride, tantalum nitride, or tungsten nitride. 
     Referring to  FIGS. 3 and 12 , according to embodiments, an organic mask layer  162  and a hardmask layer  164  are sequentially formed on the substrate  100 . The organic mask layer  162  is formed of a material having an etch selectivity with respect to the hardmask layer  164 . For example, the organic mask layer  162  can be formed of an SOH (spin on hardmask) layer. The SOH layer may include a carbon-based SOH layer or a silicon-based SOH layer. The hardmask layer  164  includes a silicon oxide layer, a silicon oxynitride layer, or a silicon nitride layer. 
     According to embodiments, on the first region R 1 , the organic mask layer  162  and the hardmask layer  164  cover the lower interconnect line layer  150  and have a flat top surface. On the second region R 2 , the organic mask layer  162  covers the lower interconnect line layer  150  and completely fills the preliminary alignment key trench Tp. The organic mask layer  162  has a stepped top surface on the second region R 2 . For example, on the second region R 2 , the organic mask layer  162  has a concave top surface that protrudes toward the substrate  100  at a portion that overlaps the preliminary alignment key trench Tp. On the second region R 2 , the hardmask layer  164  has a top surface whose profile is substantially the same as that of the top surface of the organic mask layer  162 . 
     According to embodiments, a third mask pattern M 3  is formed on the hardmask layer  164 . The third mask pattern M 3  has a third opening OP 3  on the first region R 1  and a fourth opening OP 4  on the second region R 2 . On the first region R 1 , the third opening OP 3  overlaps the lower interconnect line layer  150  except at portions to be formed into a lower interconnect line (see  154  of  FIG. 14 ). On the second region R 2 , the fourth opening OP 4  overlaps the stepped surfaces of the organic mask layer  162  and the hardmask layer  164 . The fourth opening OP 4  extends in the first direction D 1  along the preliminary alignment key trench Tp. The fourth opening OP 4  has a width Wb greater than the width Wa of the preliminary alignment key trench Tp. The third mask pattern M 3  includes, for example, a photoresist pattern. 
     In some embodiments, the organic mask layer  162  includes an organic material formed by a deposition process. For example, the organic mask layer  162  can be formed of an amorphous carbon layer (ACL). In this case, as shown in  FIG. 13 , the organic mask layer  162  partially fills the preliminary alignment key trench Tp. Likewise as shown in  FIG. 12 , on the second region R 2 , the organic mask layer  162  also has a concave top surface at a portion that overlaps the preliminary alignment key trench Tp. The formation of the organic mask layer  162  as shown in  FIG. 12  will hereinafter be described in detail. 
     Referring to  FIGS. 3 and 14  according to embodiments, the hardmask layer  164 , the organic mask layer  162 , and the lower interconnect line layer  150  are sequentially etched by an etching process that is performed on the substrate  100  on which the third mask pattern M 3  is formed. Consequently, on the first region R 1 , the lower interconnect line layer  150  on the lower interlayer dielectric layer  140  is patterned to form a lower interconnect line  154 . The lower interconnect line layer  150  that remains in the lower contact holes  145  forms the lower contact plugs  152 . The lower interconnect line layer  150  of the second region R 2  is also patterned to form an upper conductive pattern  158  and a lower conductive pattern  156 . When the upper and lower conductive patterns  158  and  156  are formed, the second dielectric layer  125  of the second region R 2  is partially etched to form an upper trench T 1  in the second dielectric layer  125  of the second region R 2 . The preliminary alignment key trench Tp has a lower portion below the upper trench T 1 . The remaining lower portion of the preliminary alignment key trench Tp forms the lower trench T 2 . On the second region R 2 , the layers  110 ,  115 ,  120 , and  125  remain after the lower and upper conductive patterns  156  and  158  are formed. The remaining first dielectric layer  110 , lower conductive layer  115 , upper conductive layer  120 , and second dielectric layer  125  form the buffer dielectric pattern  110   k , a first conductive pattern  115   k , a second conductive pattern  120   k , and a capping dielectric pattern  125   k . According to exemplary embodiments of the present inventive concept, during the patterning, of the lower interconnect line layer  150 , the third mask pattern M 3  and the hardmask layer  164  are completely removed, but the organic mask layer  162  may remain. An ashing process is used to remove the remaining organic mask layer  162 . Through the aforementioned processes, a semiconductor device of  FIGS. 3 and 4  can be fabricated. 
     According to embodiments, to form the lower interconnect line  154 , the third mask pattern M 3  is formed to completely cover the hardmask layer  164  of the second region R 2 . In this case, as shown in  FIG. 15 , a hardmask layer portion  164   r  may remain on the preliminary alignment key trench Tp even after the lower interconnect line  154  is formed. The presence of the hardmask layer portion  164   r  may be due to non-uniform etching caused by the stepped profile of the hardmask layer  164 . Even though an ashing process is subsequently performed to remove the organic mask layer  162 , as shown in  FIG. 16 , the hardmask layer portion  164   r  may still remain because of its etch selectivity with respect to the organic mask layer  162 . The remaining hardmask layer portion  164   r  can act as a lifting failure source in subsequent processes. However, according to exemplary embodiments of the present inventive concept, as the third mask pattern M 3  has the fourth opening OP 4  through which the stepped portion of the hardmask layer  164  is exposed, the hardmask layer  164  is completely removed when the lower interconnect line layer  150  is patterned. Lifting failure due to residue of the hardmask  164  can be prevented from occurring, and thus it is possible to provide a semiconductor device having enhanced process yield and reliability. 
     According to embodiments, during the steps shown in  FIGS. 12 and 14 , the lower interconnect line layer  150  can be differently patterned to form the alignment key patterns KP described with reference to  FIGS. 5A to 5C . 
       FIG. 17  is a cross-sectional view, corresponding to lines I-I′ and II-II′ of  FIG. 3 , that illustrates a semiconductor device according to exemplary embodiments of the present inventive concept. In the embodiment that follows, the first region R 1  is configured substantially the same as that described with reference to  FIGS. 3 and 4 . The second region R 2  is also configured substantially the same as that described with reference to  FIGS. 3 and 4 , except for differences in the configuration of the first sub-alignment key pattern KP 1  and the depth d 2  of the lower trench T 2 . For brevity of the description, different configurations will be principally described. 
     Referring to  FIGS. 3 and 17 , according to embodiments, the lower trench T 2  that extends downward from the upper trench T 1  penetrates the capping dielectric pattern  125   k , the second conductive pattern  120   k , the first conductive pattern  115   k , and the buffer dielectric pattern  110   k  to expose the substrate  100  through the lower trench T 2 . In other words, the alignment key trench Tk fully penetrates the first sub-alignment key pattern KP 1 . The sidewall conductive patterns  156   s  and the interconnect conductive pattern  156   c  in the lower trench T 2  are therefore be in contact with a top surface of the substrate  100  exposed through the lower trench T 2 . Although  FIG. 17  illustrates the upper trench T 1  as having depth d 1  that is less than the depth d 2  of the lower trench T 2 , embodiments are not limited thereto. In other embodiments, the depth d 1  of the upper trench T 1  may be greater than the depth d 2  of the lower trench T 2 . 
     According to embodiments, the first sub-alignment key pattern KP 1  further includes dielectric spacers  135   k  interposed between one of the sidewall conductive patterns  156   s  and one of sidewalls of the lower trench T 2 . That is, the first sub-alignment key pattern KP 1  includes the buffer dielectric pattern  110   k , the first conductive pattern  115   k , the second conductive pattern  120   k , the capping dielectric pattern  125   k , and further includes the dielectric spacers  135   k  disposed on sidewalk thereof. The dielectric spacers  135   k  extend in the first direction D 1  along the sidewalls of the lower trench T 2 . The dielectric spacers  135   k  include the same material as the gate spacers  135   p . For example, the dielectric spacers  135   k  includes at least one of silicon oxide, silicon nitride, or silicon oxynitride. Other components are substantially the same as those described with reference to  FIGS. 3 and 4 , and detailed descriptions thereof are omitted. 
       FIGS. 18A to 18C  are cross-sectional views, corresponding to line II-II′ of  FIG. 3 , that illustrate other examples of the alignment keys shown in  FIGS. 3 and 17 . In the embodiments that follow, configurations different from the alignment key of  FIGS. 3 and 17  will be principally described for brevity of the description. 
     Referring to  FIG. 18A , according to other embodiments, the lower conductive pattern  156  of the second sub-alignment key pattern KP 2  includes only the sidewall conductive patterns  156   s . That is, the interconnect conductive pattern  156   c  of  FIGS. 3 and 17  is omitted. The sidewall conductive patterns  156   s  are separately disposed on the sidewalk of the lower trench T 2 , and the substrate  100  has an exposed top surface that defines a floor of the lower trench T 2 . 
     Referring to  FIG. 18B , according to other embodiments, the second sub-alignment key pattern KP 2  includes only the lower conductive patterns  156 . That is, the upper conductive pattern  158  of  FIGS. 3 and 17  is omitted. Referring to  FIG. 18C , according to other embodiments, the second sub-alignment key pattern KP 2  includes only the sidewall conductive patterns  156   s . That is, the interconnect conductive pattern  156   c  and the upper conductive pattern  158  of  FIGS. 3 and 17  are omitted. 
       FIGS. 19 to 22  are cross-sectional views, corresponding to lines I-I′ and II-II′ of  FIG. 3 , that illustrate a method of fabricating a semiconductor device according to exemplary embodiments of the present inventive concept. For brevity of the description, a repetitive explanation will be omitted. 
     Referring to  FIGS. 3 and 19 , according to embodiments, a first mask pattern M 1   a  is formed on a resultant structure of  FIG. 6 . On the first region R 1 , the second dielectric layer  125  is partially covered with the first mask pattern M 1   a  at a portion where the gate line GL is to be formed. On the second region R 2 , the first mask pattern M 1   a  includes a fifth opening OP 5  through which the second dielectric layer  125  is exposed. The fifth opening OP 5  is a trench that extends in the first direction D 1 . The fifth opening OP 5  has a width Wa that corresponds to the second width W 2  of the lower trench T 2  shown in  FIG. 17 . 
     Referring to  FIGS. 3 and 20 , according to embodiments, the second dielectric layer  125 , the upper conductive layer  120 , the lower conductive layer  115 , and the second dielectric layer  125  are sequentially etched by an etching process using the first mask pattern M 1   a  as an etching mask. The gate line GL is then formed on the substrate  100  of the first region R 1 . On the second region R 2 , the preliminary alignment key trench Tp is also formed on the substrate  100  that penetrates the second dielectric layer  125 , the upper conductive layer  120 , the lower conductive layer  115 , and the second dielectric layer  125 , to expose a top surface of the substrate  100 . According to an embodiment, when the preliminary alignment key trench Tp is formed simultaneously with the gate line GL, the preliminary alignment key trench Tp can be formed deeper than the preliminary alignment key trench Tp of  FIG. 10 . After forming the gate line GL and the preliminary alignment key trench Tp, the first mask pattern M 1   a  is removed. 
     Referring to  FIGS. 3 and 21 , according to embodiments, the gate spacers  135   p  are formed on sidewalls of the gate line GL, and the dielectric spacers  135   k  are formed on sidewalls of the preliminary alignment key trench Tp. For example, the gate spacers  135   p  and the dielectric spacers  135   k  can be formed by forming a gate spacer layer on an entire surface of the substrate  100  and then performing a blanket anisotropic etching process. The gate spacer layer may include at least one of silicon oxide, silicon nitride, or silicon oxynitride. 
     According to embodiments, the source/drain regions PSD are formed in the substrate  100  on opposite sides of the gate line GL. For example, the source/drain regions PSD can be formed by an ion implantation process using the gate line GL as an ion implantation mask. 
     Referring to  FIGS. 3 and 22 , according to embodiments, the lower interlayer dielectric layer  140  is formed on the substrate  100  of the first region R 1 . The lower interlayer dielectric layer  140  includes the lower contact holes  145  that expose the source/drain regions PSD. The lower interlayer dielectric layer  140  and the lower contact holes  145  are formed by the same processes as those discussed with reference to  FIGS. 9 and 10 . The preliminary alignment key trench Tp is filled with the lower interlayer dielectric layer  140 , which is removed from the second region R 2  during or after the formation of the lower contact holes  145 . 
     Thereafter, according to embodiments, processes identical or similar to those described with reference to  FIGS. 11 to 14  may be executed to fabricate the semiconductor device of  FIGS. 3 and 17 . 
       FIG. 23  is a cross-sectional view, corresponding to lines I-I′ and II-II′ of  FIG. 3 , that illustrates a semiconductor device according to exemplary embodiments of the present inventive concept. In the embodiment that follows, the first region R 1  is configured substantially the same as that described with reference to  FIGS. 3 and 4 . The second region R 2  is configured substantially the same as that described with reference to  FIGS. 3 and 17 , except that the alignment key AK is formed in a field region. For brevity of the description, different configurations will be principally explained. 
     Referring to  FIGS. 3 and 23 , according to embodiments, the alignment key AK is disposed in a field region, i.e., a buried dielectric pattern  102   k . The buried dielectric pattern  102   k  is formed simultaneously with or after the formation of the device isolation pattern  102   p  of the first region R 1 . For example, the buried dielectric pattern  102   k  can be formed by recessing an upper portion of the substrate  100  of the second region R 2  and depositing an insulating layer in the recessed substrate  100  of the second region R 2 . The buried dielectric pattern  102   k  and the device isolation pattern  102   p  include the same material, such as silicon oxide or silicon oxynitride. 
     According to embodiments, as the alignment key AK is formed on the buried dielectric pattern  102   k , the buried dielectric pattern  102   k  can experience over-etching at its upper portion. As a result, the lower trench T 2  may have a floor surface that is recessed into the buried dielectric pattern  102   k , and the lower conductive pattern  156  is also formed inside the recessed portion of the buried dielectric pattern  102   k . In this configuration, a top surface of the substrate  100  is positioned higher than the floor surface of the lower trench T 2  and a bottom surface of the lower conductive pattern  156 . Other components are substantially the same as those described with reference to  FIGS. 3 and 17 , and detailed descriptions thereof are omitted. 
       FIGS. 24A to 24C  are cross-sectional views, corresponding to line II-II′ of  FIG. 3 , that illustrate other examples of the alignment key shown in  FIGS. 3 and 23 . Referring to  FIGS. 24A to 24C , the examples of  FIGS. 18A to 18C  can be incorporated into the embodiment of  FIG. 23 . For example, as shown in  FIG. 24A , the lower conductive pattern  156  of the second sub-alignment key pattern KP 2  may include only the sidewall conductive patterns  156   s . The sidewall conductive patterns  156   s  may be separately disposed on the sidewalls of the lower trench T 2 , and the buried dielectric pattern  102   k  may thus have an exposed top surface that defines the floor of the lower trench T 2 . Alternatively, as shown in  FIG. 24B , the second sub-alignment key pattern KP 2  may include only the lower conductive patterns  156 .  FIG. 24C  illustrates another alternative embodiment, in which the second sub-alignment key pattern KP 2  includes only the sidewall conductive patterns  156   s.    
       FIG. 25  is a plan view that illustrates a semiconductor device according to exemplary embodiments of the present inventive concept.  FIG. 26  is a cross-sectional view taken along lines A-A′, B-B′, and C-C′ of  FIG. 25 . For the sake of brevity, a repetitive description will be omitted. 
     Referring to  FIGS. 25 and 26 , according to embodiments, a substrate  100  includes a first region R 1  and a second region R 2 . The first region R 1  is a portion of the chip zone  12  of  FIG. 1 , and the second region R 2  is a portion of the scribe lane zone  14  of  FIG. 1 . The first region R 1  includes a cell region CR on which memory cells are formed and a peripheral circuit region PR on which peripheral circuits that control the memory cells are formed. The gate line GL, the source/drain regions PSD, the lower contact plugs  152 , and the lower interconnect lines  154  are provided on the peripheral circuit region PR, and the alignment key AK is provided on the second region R 2 . In an embodiment that follows, the peripheral circuit region PR and the second region R 2  are configured substantially the same as those of  FIGS. 3 and 4 , and detailed descriptions thereof are omitted. In addition, the embodiments of the alignment key AK shown in  FIGS. 5A to 5C, 17, 18A to 18C, 23, and 24A to 24C  can be incorporated into this embodiment. 
     According to embodiments, the substrate  100  of the cell region CR includes device isolation pattern  102   c , which defines cell active regions CA. The cell active regions CA have a bar shape whose longitudinal axis extends in a third direction that crosses the first and second directions D 1  and D 2 , and are arranged parallel to each other. 
     According to embodiments, word lines WL are provided buried in the substrate  100  of the cell region CR. For example, each of the cell active regions CA crosses a pair of the word lines WL. The word lines WL extend in the first direction D 1 , and are spaced apart from each other along the second direction D 2  perpendicular to the first direction D 1 . A cell gate dielectric pattern  106  is disposed between the substrate  100  and the word lines WL. The cell gate dielectric pattern  106  includes a dielectric material, such as at least one of a silicon oxide layer, a silicon oxynitride layer, or a high-k dielectric layer. The word lines WL include a conductive material, such as at least one of doped polysilicon, a metal, or a conductive metal nitride. Word line capping, patterns  108  are disposed on the word lines WL. The word line capping pattern  108 , the word line WL, and the cell gate dielectric pattern  106  are buried in grooves  104  formed in the substrate  100  of the cell region CR. The word line capping patterns  108  can include, for example, silicon oxide, silicon nitride, or silicon oxynitride. 
     According to embodiments, each of the cell active regions CA includes a first source/drain region SD 1  at a portion between a pair of the grooves  104  and a pair of second source/drain regions SD 2  at opposite edges. 
     According to embodiments, cell conductive lines CL are disposed on the substrate  100  of the cell region CR. The cell conductive lines CL extend side by side in the second direction D 2  and cross the word lines WL. Each of the cell conductive lines CL is connected to each of a plurality of first source/drain regions SD 1  arranged in the second direction D 2 . For example, the cell conductive lines CL can be bit lines. Each of the cell conductive lines CL includes a first cell conductive line  115   c , a second cell conductive line  120   c , and a cell capping line  125   c  that are sequentially stacked. The first cell conductive line  115   c  includes the same material as the lower gate pattern  115   p  or the first conductive pattern  115   k . For example, the first cell conductive line  115   c  can include a doped semiconductor material, such as doped polysilicon. The second cell conductive line  120   c  includes the same material as the upper gate pattern  120   p  or the second conductive pattern  120   k . For example, the second cell conductive line  120   c  can include at least one of a metal, such as tungsten, titanium, or tantalum, or a conductive metal nitride, such as titanium nitride, tantalum nitride, and/or tungsten nitride. The cell capping line  125   c  includes the same material as the gate capping pattern  125   p  or the capping dielectric pattern  125   k . For example, the cell capping line  125   c  may include silicon oxide, silicon nitride, or silicon oxynitride. 
     According to embodiments, each of the cell conductive lines CL further includes interconnect contacts  215  at portions that overlap the first source/drain regions SD 1 , and which penetrate the first cell conductive line  115   c . The interconnect contacts  215  include a doped semiconductor material, such as doped silicon. A cell buffer dielectric pattern  110   c  is interposed between the substrate  100  and the first cell conductive line  115   c . The interconnect contacts  215  penetrate the cell buffer dielectric pattern  110   c  into an upper portion of the substrate  100 . The cell buffer dielectric pattern  110   c  includes silicon oxide. 
     According to embodiments, cell dielectric liners  135   c  are disposed on sidewalls the cell conductive lines CL. The cell dielectric liners  135   c  extend in the second direction D 2  along the cell conductive lines CL. The cell dielectric liners  135   c  include at least one of, for example, silicon oxide, silicon nitride, or silicon oxynitride. 
     According to embodiments, the substrate  100  of the cell region CR also includes cell contact plugs  149  disposed thereon that are connected to the second source/drain regions SD 2 . Each of the cell contact plugs  149  includes a cell lower contact LC in contact with the second source/drain region SD 2  and a cell upper contact LP on the cell lower contact LC. The cell lower contact LC includes, for example, doped polysilicon. The cell upper contact LP includes the same material as the lower contact plug  152 , the lower interconnect line  154 , the lower conductive pattern  156 , or the upper conductive pattern  158 . For example, the cell upper contact LP can include at least one of a metal, such as tungsten, titanium, or, tantalum, or a conductive metal nitride such as titanium nitride, tantalum nitride, or tungsten nitride. Dielectric fences  147  are disposed between the cell contact plugs  149  and the cell conductive lines CL. The dielectric fences  147  include, for example, a silicon nitride layer or a silicon oxynitride layer. A portion of the cell upper contact LP extends onto a top surface of the dielectric fence  147 . 
     According to embodiments, an upper interlayer dielectric layer  170  is disposed on the substrate  100 . On the first region R 1 , the upper interlayer dielectric layer  170  covers the cell upper contacts LP and the lower interconnect lines  154 . On the second region R 2 , the upper interlayer dielectric layer  170  fills the alignment key trench Tk while covering the upper conductive pattern  158 . The upper interlayer dielectric layer  170  includes, for example, silicon oxide, silicon nitride, or silicon oxynitride. 
     According to embodiments, data storage elements DSP are disposed on the upper interlayer dielectric layer  170  of the cell region CR. Each of the data storage elements DSP is a capacitor. For example, the data storage elements DSP can include bottom electrodes each of which is connected to one of the cell upper contacts LP, a top electrode that covers the bottom electrodes, and a dielectric layer interposed between the bottom electrodes and the top electrode. The top electrode is a common electrode that covers the bottom electrodes. In some embodiments, each of the bottom electrodes has a hollow cylindrical shape. The bottom electrodes and the top electrode include a impurity-doped silicon, a metal, or a metal compound. The dielectric layer may be a single layer, or a combination thereof, and includes at least one of a metal oxide such as HfO 2 , ZrO 2 , Al 2 O 3 , La 2 O 3 , Ta 2 O 3 , and TiO 2 , and a perovskite dielectric material such as SrTiO 3 (STO), (Ba,Sr)TiO 3 (BST), BaTiO 3 , PZT, and PLZT. Although  FIGS. 25 and 26  show that the data storage elements DSP are connected to the cell upper contact LP through interconnect plugs  172  in the upper interlayer dielectric layer  170 , embodiments are not limited thereto. 
     In some embodiments, each of the data storage elements DSP includes a variable resistance structure. The variable resistance structure can be changed by a programming operation into one of a plurality of states that have different resistance values. In some embodiments, the variable resistance structure is a magnetic tunnel junction pattern that uses its magnetization directions. The magnetic tunnel junction pattern includes a reference magnetic pattern having a unidirectionally fixed magnetization direction, a free magnetic pattern having a magnetization direction that can be changed to be parallel or antiparallel to the magnetization direction of the reference magnetic pattern, and a tunnel barrier between the reference and free magnetic patterns. In other embodiments, the variable resistance structure includes a phase change material. The phase change material can change into an amorphous state or a crystalline state based on the temperature or the time heat is applied by a programming operation. The phase change material has a greater resistivity in the amorphous state than in the crystalline state. For example, the phase change material can include at least one chalcogenide element, such as Te or Se. In some embodiments, the variable resistance structure includes a transition metal oxide. An electrical path can appear or disappear in the transition metal oxide due to a programming operation. The transition metal oxide has a low resistance value when an electrical path is generated and a high resistance value when the electrical path is destroyed. 
     According to exemplary embodiments of the present inventive concept, the alignment key can be configured to include a trench and completely remove the mask layers from the trench. It is thus possible to suppress lifting failure of the mask layers that are not removed from but remain in the trench. Consequently, a semiconductor device can have enhanced process yield and reliability. 
     Although embodiments of the present disclosure have been described in connection with the exemplary embodiments as illustrated in the accompanying drawings, it will be understood to those skilled in the art that various changes and modifications may be made without departing from the technical spirit and features of exemplary embodiments of the present disclosure. It thus should be understood that the above-described exemplary embodiments are not limiting but illustrative in all aspects.