Abstract:
A nonvolatile semiconductor memory device that realizes a multi-bit cell and a method for manufacturing the same includes manufacturing the nonvolatile semiconductor memory device to be capable of storing multi-bit data, for example, 4-bit data, in a single memory cell and, as a result, the integration degree of a NOR type nonvolatile semiconductor memory device can be improved.

Description:
[0001]    This application claims the benefit under 35 U.S.C. §119 of the Korean Patent Application No. 10-2006-0098760, filed on Oct. 11, 2006, which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    Among various high-integration nonvolatile memory devices, a flash electrically erasable programmable read-only memory (EEPROM) device has particular advantages of, for example, high programming speed and low electricity consumption. As a result they are used as a large-capacity storage medium for portable terminals such as a digital camera, portable personal computer, etc., or used in place of a conventional hard disc. 
         [0003]    Flash EEPROM devices may be generally classified, on the basis of a memory cell structure, into NAND-structure devices and NOR-structure devices. The NAND-structure devices have superior characteristics in the view of an integration degree, whereas the NOR-structure devices have superior random access time characteristics. In the NOR-structure devices, each of memory cells is independently connected to a bit line and a word line, and therefore, there is an advantage in that each cell interferes with other cells less during a writing operation or reading operation thereof. 
         [0004]    However, the NOR-structure devices require a contact for the inter-connection of each cell and a corresponding bit line. For this reason, the NOR-structure devices are disadvantageous in the view of an integration degree (i.e., decreasing size), as compared to the NAND-structure devices, which require only one contact per a single string, i.e. a single unit consisting of a plurality of cells connected to one another in series. 
       SUMMARY 
       [0005]    Embodiments relate to a NOR-type non-volatile semiconductor memory device that includes a plurality of memory cells, wherein each cell is configured to store multi-bit data. 
         [0006]    Embodiments relate to a nonvolatile semiconductor memory device that includes (a) a semiconductor substrate having a plurality of source/drain regions; (b) a spacer structure provided on either side end of each of the source/drain regions; (c) contacts and source lines alternately arranged on the source/drain regions; (d) control gates in contact with the spacer structure between the contacts and the source lines;(e) a poly metal dielectric (PMD) layer formed on the source lines surrounding the respective contacts; and (f) a metal wiring layer provided on the contacts and the PMD layer. 
         [0007]    Embodiments relate to a method for manufacturing a nonvolatile semiconductor memory device. In accordance with this method, the following steps are performed: (a) sequentially forming a first oxide layer, a first poly-silicon layer, and a first insulation layer on a semiconductor substrate; (b) implanting a dopant into the semiconductor substrate, which is exposed by an etching process performed using a photoresist pattern provided on the first insulation layer, to form source/drain regions; (c) performing a re-oxidation process to form a second oxide layer on the source/drain regions; (d) forming first spacers on the second oxide layer at opposite sides of the second oxide layer; (e) filling a second insulation layer between the neighboring first spacers, and removing the second insulation layer on the source regions; (f) forming source lines on the respective source regions from which the second insulation layer was removed; (g) forming second spacers to come into contact with the respective first spacers after removing the first insulation layer; (h) forming an upper silicon oxide layer on the source lines and forming a lower silicon oxide layer on an underside between the neighboring second spacers; (i) forming control gates between the neighboring second spacers; (j) performing a salicide process to reduce a resistance of the control gates; (k) forming a poly metal dielectric (PMD) layer covering the control gates, and planarizing the PMD layer by a chemical mechanical polishing (CMP) process; and (l) filling an electrically conductive material in a plurality of contact holes perforated through the PMD layer and the second insulation layer, to form contacts. 
     
     
       DRAWINGS 
         [0008]    Example  FIGS. 1 to 12  are sectional views illustrating the sequential processes of a method for manufacturing a nonvolatile semiconductor memory device to realize a multi-bit cell according to embodiments described herein. 
       
    
    
     DESCRIPTION 
       [0009]    Embodiments relate to a technology for storing multi-bit data in a single memory cell to improve the integration degree of the flash EEPROM devices. 
         [0010]    First, as shown in example  FIG. 1 , a first oxide layer  110 , a first poly-silicon layer  120 , and a first insulation layer  130  are sequentially formed on a semiconductor substrate  100 . The first oxide layer  110  may be made of any one selected from among a SiO 2 , SiON, La 2 O 3 , ZrO 2 , and Al 2 O 3  layer, or may be formed by laminating at least two layers selected from among them. The first oxide layer  110  may be formed, by growth or deposition, to have a thickness of approximately 30 Å to approximately 300 Å, and the first poly-silicon layer  120  is formed to have a thickness of approximately 100 Å to approximately 1,500 Å by depositing poly-silicon for the formation of floating gates. Also, the first insulation layer  130  may be made of an oxide layer of SiO 2  or a nitride layer of SiN. 
         [0011]    Next, as shown in example  FIG. 2 , a photoresist pattern  140  is provided on the first insulation layer  130  to define source/drain regions. After an etching process is performed using the photoresist pattern  140  to expose the semiconductor substrate  100  by removing predetermined regions of the first insulation layer  130 , the first poly-silicon layer  120 , and even the first oxide layer  110  on the semiconductor substrate  100 , a dopant can be implanted into the resulting exposed regions of the semiconductor substrate  100  to form source/drain regions  150 . Here, the etching process using the photoresist pattern  140  may be performed to remove only the first insulation layer  130  and the first poly-silicon layer  120  without removing the first oxide layer  110 , to expose the first oxide layer  110 . 
         [0012]    After implanting the dopant to form the source/drain regions  150  and performing a cleaning process, an annealing process is performed at a temperature of approximately 1,000° C. to approximately 1,100° C., to prevent unwanted diffusion of the dopant implanted when forming the source/drain regions  150 . 
         [0013]    After completing the annealing process, as shown in example  FIG. 3 , a re-oxidation process is performed to form a second oxide layer  160  on the source/drain regions  150 . Thereby, the second oxide layer  160  can be formed to have a thickness of approximately 90 Å to approximately 110 Å. 
         [0014]    After forming the second oxide layer  160 , an oxide layer of SiO 2  or a nitride layer of Si 3 N 4  is deposited on the semiconductor substrate  100 . As the deposited SiO 2  or Si 3 N 4  layer is subjected to an etch-back process, first spacers  170  as shown in example  FIG. 4  can be formed. Then, a second insulation layer  180  is deposited on the overall surface of the semiconductor substrate  100  to perform a gap-fill process. The gap-filled second insulation layer  180  is planarized by an etch-back process, and subsequently, is etched using a source-open mask (not shown) to open the source regions. Thereby, the second insulation layer  180  on the source regions is removed. Alternatively, the second insulation layer  180  may be planarized by a chemical mechanical polishing (CMP) process rather than the etch-back process. 
         [0015]    After removing the second insulation layer  180  on the source regions, as shown in example  FIG. 5 , an electrode material, for example, doped poly-silicon to form source lines  190  is deposited on the source regions to perform a gap-fill process. The gap-filled doped poly-silicon is planarized by an etch-back process, to form the source lines  190 . 
         [0016]    After forming the source lines  190 , as shown in example  FIG. 6 , a predetermined etching process is performed to remove the first insulation layer  130 , and a n-type dopant such as arsenic (As) or phosphorus (P) is implanted to give the first poly-silicon layer  120  the characteristics of floating gates. 
         [0017]    After implanting the n-type dopant, an oxide layer of SiO 2  or a nitride layer of Si 3 N 4  layer is deposited on the first poly-silicon layer  120 . The deposited SiO 2  or Si 3 N 4  layer is subjected to an etch-back process, to form second spacers  200  as shown in example  FIG. 7 . Subsequently, a dry etching process, such as a reactive ion etching (RIE), is performed on the first poly-silicon layer  120  having the second spacers  200  formed thereon. With the dry etching process, as shown in example  FIG. 8 , the first oxide layer  110  as well as the first poly-silicon layer  120  can be etched, and then, a cleaning process is performed. 
         [0018]    After forming a pattern by etching even the first oxide layer  110 , as shown in example  FIG. 9 , a predetermined oxidation process is performed, to form an upper silicon oxide layer  210  on the source lines  190 , and a lower silicon oxide layer  220  on the pattern obtained by etching the first oxide layer  110  as well as the first poly-silicon layer  120 . 
         [0019]    After forming the silicon oxide layers  210  and  220 , to form control gates  230  as shown in example  FIG. 10 , a control gate material, for example, at least one material selected from among poly-silicon, tungsten (W), silicon germanium (SiGe), silicon germanium carbide (SiGeC), molybdenum (Mo), molybdenum salicide (MoSi 2 ), titanium (Ti), titanium salicide (TiSi 2 ), and titanium nitride (TiN), is deposited on the lower silicon oxide layer  220  to perform a gap-fill process between the second spacers  200 . Preferably, poly-silicon is used as a gap-fill material. As the control gate material, gap-filled between the second spacers  200 , is planarized by an etch-back process, the control gates  230  can be formed. 
         [0020]    After forming the control gates  230 , as shown in example  FIG. 11 , a general salicide process, for example, using cobalt (Co) and TiN, is performed to reduce a resistance of the control gates  230 , and subsequently, an annealing process is performed at a temperature of approximately 400° C. to approximately 500° C. Then, a poly-metal dielectric (PMD) layer  240  is formed using a boron phosphorus silicate glass (BPSG), phosphorus silicate glass (PSG), or the like, and a surface of the PMD layer  240  is planarized by a CMP process. 
         [0021]    After flattening the PMD layer  240 , a predetermined photoresist pattern (not shown) is provided on the PMD layer  240 . The PMD layer and the second insulation layer  180  are etched using the predetermined photoresist pattern, to form contact holes. 
         [0022]    In relation to the contact holes formed as stated above, as shown in example  FIG. 12 , a barrier layer (not shown) made of, for example, titanium tantalum nitride (TiTaN), is formed at the sidewall of the respective contact holes, and a material such as tungsten is filled in the contact holes, to form contacts  250 . Of course, after forming the contacts  250 , a CMP process may be performed to planarize the PMD layer  240  having the contacts  250  formed therein. 
         [0023]    Thereafter, a metal wiring layer  260 , which is made of electrically conductive metal, for example, aluminum (Al), is formed on the PMD layer  240  having the contacts  250  by a general chemical vapor deposition (CVD) or physical vapor deposition (PVD) method. 
         [0024]    As shown in example  FIG. 12 , each of the contacts  250  are located between the neighboring source lines  190 , and consequently, the contacts  250  and the source lines  190  are periodically formed and alternately arranged with each other. 
         [0025]    Using the above-described embodiments, a nonvolatile semiconductor memory device, in which a single memory cell stores multi-bit data, for example, 4-bit data, can be manufactured, thereby improving the integration degree of a NOR type nonvolatile semiconductor memory device. In particular, since the nonvolatile semiconductor memory device operates using the gap-filled source lines  190 , the embodiments have the effect of eliminating a conventional self-aligned source (SAS) process, and reducing diffusion resistance. The reduced diffusion resistance results in a reduced resistance of the source lines  190  which improves the margin of cell current.