Abstract:
A method for forming a semiconductor device includes: etching a hard mask layer and a conductive layer formed on a semiconductor substrate, a lower structure being formed on the semiconductor substrate; forming a sacrificial insulating layer at upper parts of the etched hard mask layer and the etched conductive layer of a peripheral circuit region; forming an isolation insulating layer at an upper part of an isolation insulating layer of a cell region; forming spacers at sidewalls of the etched hard mask layer, the etched conductive layer, and the isolation insulating layer of the cell region, respectively; forming storage electrode contact plugs at both sides of each of the spacers, respectively; and removing the sacrificial insulating layer to expose the semiconductor substrate of the peripheral circuit region, and etching the lower structure to expose the semiconductor substrate of the peripheral circuit region.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to Korean patent application number 10-2009-0127901, filed on Dec. 21, 2009, which is incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a method for forming a semiconductor device, more particularly, to a method for forming a semiconductor device including a buried gate structure. 
         [0003]    Among semiconductor memory devices, a dynamic random access memory (DRAM) is constructed of a plurality of unit cells, each including a capacitor and a transistor. The capacitor is used to temporarily store data. The transistor is used to move data between a bit line and the capacitor according to a control signal using the characteristics of a semiconductor to change an electric conductivity according to an environment. The transistor is composed of three regions including a gate, a source, and a drain. Charge transfer occurs between the source and the drain according to a control signal input to the gate. The charge transfer between the source and the drain is achieved through a channel region using the characteristics of the semiconductor. 
         [0004]    A typical transistor is manufactured on a semiconductor substrate. After a gate is formed on the semiconductor substrate, impurities are doped on both sides of the gate to form a source and a drain. In this case, a channel region of a transistor is formed between the source and the drain under the gate. The transistor having such a horizontal channel region occupies a predetermined area of a semiconductor substrate. In the case of a complicated semiconductor memory device, it becomes difficult to reduce a total area due to a plurality of transistors included therein. 
         [0005]    When the total area of a semiconductor memory device is reduced, the number of semiconductor memory devices per wafer may be increased to enhance productivity. Various methods have been proposed to reduce the total area of the semiconductor memory device. Among them, one method uses a recess gate in which a recess is formed in a substrate and a gate is formed in the recess to form a channel region along a curve of the recess, instead of a conventional planar gate with a horizontal channel region. In addition to the recess gate, research into a buried gate has been made. In this case, an entire part of the gate is buried in the recess to form the buried gate. 
         [0006]    Meanwhile, in order to form a semiconductor device with a buried gate according to the related art, a bit line of a cell region and a gate of a peripheral circuit region are simultaneously patterned. 
         [0007]    In summary, after a bit line of a cell region and a gate of a peripheral circuit region are simultaneously patterned, an interlayer dielectric layer is deposited on the entire upper parts of the cell region and the peripheral circuit region to define a storage electrode contact. At this time, Boron Phosphorous Silicate Glass (BPSG) is used as an interlayer dielectric layer material to fill the space between the bit lines of the cell region. Here, a spacer is thickly formed over an upper part of the gate of the peripheral circuit region to prevent boron of the BPSG from permeating into a semiconductor substrate of the peripheral circuit region. 
         [0008]    However, in this procedure, the spacer at an upper part and a sidewall of a bit line in the cell region is also thickly formed as well. This reduces a contact area between an active region and a storage electrode contact, and thus increases resistance. Furthermore, when the BPSG is applied as the interlay dielectric layer, a thermal process should be essentially performed. This causes a problem where a gate operation current of the peripheral circuit region is decreased and a leakage current is increased. Moreover, when a storage electrode is formed in the cell region, a hard mask layer (over the bit line in the cell region) is thickly formed as an etch stopping layer. In the same manner, a gate formed in the peripheral circuit region also turns out to have a thick hard mask. A gate pattern and a storage electrode pattern with a high aspect ratio makes it hard to properly adjust a tiling angle during an implant process. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    Embodiments of the present invention are directed to a method for forming a semiconductor device with a buried gate that may prevent degradation of the semiconductor device occurring when subsequent processes are simultaneously applied to a cell region and a peripheral circuit region by simultaneously patterning a bit line of the cell region and a gate of the peripheral circuit region. 
         [0010]    According to an embodiment of the present invention, a method for forming a semiconductor device includes: etching a hard mask layer and a conductive layer formed on a semiconductor substrate, a lower structure being formed on the semiconductor substrate; forming a sacrificial insulating layer over the etched hard mask layer and the etched conductive layer of a peripheral circuit region; forming an isolation insulating layer on a device isolation region of a cell region; forming spacers at sidewalls of the etched hard mask layer, the etched conductive layer, and the isolation insulating layer of the cell region, respectively; forming storage electrode contact plugs at both sides of each of the spacers, respectively; and etching the lower structure to expose the semiconductor substrate of the peripheral circuit region to form a gate. 
         [0011]    In accordance with an embodiment of the present invention, before etching a hard mask layer and a conductive layer, a method for forming a semiconductor device further includes forming a buried gate in the semiconductor substrate of the cell region. 
         [0012]    The lower structure includes a bit line contact plug formed at a lower part of the conductive layer of the cell region; and a poly-silicon layer formed at the peripheral circuit region. 
         [0013]    In accordance with an embodiment of the present invention, after etching a hard mask layer and a conductive layer, a method for forming a semiconductor device further includes coating a capping insulating layer on the etched hard mask layer and the etched conductive layer. 
         [0014]    Etching the lower structure of the peripheral circuit region includes etching the lower structure by using the capping insulating layer formed on the etched hard mask layer and the etched conductive layer of the peripheral circuit region. 
         [0015]    Forming a sacrificial insulating layer at the peripheral circuit region includes forming the sacrificial insulating layer at an upper entire part; and removing the sacrificial insulating layer of the cell region using a cell open mask. A sacrificial insulating layer includes a plasma enhanced tetra ethyl ortho silicate (PETEOS) layer or a high density plasma (HDP) layer. Forming a sacrificial insulating layer is formed at 300° C. to 500° C. Forming an isolation insulating layer on the device isolation region of a cell region includes forming an interlayer dielectric layer over the cell region; removing the interlayer dielectric layer to expose the upper part of the device isolation region; forming an isolation insulating layer on the interlayer dielectric layer and a region in which the interlayer dielectric layer is removed; removing the isolation insulating layer formed on the interlayer dielectric layer; and removing the interlayer dielectric layer remaining at a sidewall sides of the isolation insulating layer. 
         [0016]    The isolation insulating layer comprises a nitride layer. Removing the isolation insulating layer is performed by a dry etch process. Removing the interlayer dielectric layer is performed by a wet etch process. 
         [0017]    In accordance with an embodiment of the present invention, after forming the spacers, a method for forming a semiconductor device further includes etching the lower structure of the cell region to form a bit line by using the spacers as an etch mask. 
         [0018]    Forming storage electrode contact plugs at both sides of each of the spacers, respectively, includes forming a conductive layer for a storage electrode contact plug over the cell region and the peripheral circuit region; and performing a planarization etch process to expose the upper part of the etched hard mask layer of the cell region and the isolating insulating layer of the peripheral region and removing the sacrificial insulating layer of the peripheral circuit region. Removing the sacrificial insulating layer of the peripheral region is performed by using a different etching selectivity of the storage node contact plug and the hard mask or by wet etch process. 
         [0019]    In accordance with an embodiment of the present invention, after etching the lower structure of the peripheral circuit region, a method for forming a semiconductor device further includes performing an oxididation process with respect to the peripheral circuit region. 
         [0020]    In accordance with an embodiment of the present invention, after etching the lower structure of the peripheral circuit region, a method for forming a semiconductor device further includes forming a spacer nitride layer at an upper entire part; forming a spacer oxide layer on the spacer nitride layer; and performing a blanket etch to expose the semiconductor substrate of the peripheral circuit region. 
         [0021]    In accordance with an embodiment of the present invention, after performing the blanket etch, a method for forming a semiconductor device further includes implanting ions into the semiconductor substrate of the peripheral circuit region. 
         [0022]    In accordance with an embodiment of the present invention, after implanting the ions, a method for forming a semiconductor device further includes forming an etch stopping layer over the cell region and the peripheral circuit region. 
         [0023]    In a method for forming a semiconductor device with a buried gate according to the present invention, a gate current of a peripheral circuit region may be increased and a leakage current be decreased because BPSG is not used at the peripheral circuit region as an interlayer dielectric layer. After the formation of a storage electrode contact, a gate is patterned to make a thickness of a hard mask layer of a gate of the peripheral circuit region thin, thereby providing a profitable effect in a formation of lightly doped drain (LDD) junction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIGS. 1   a  to  FIG. 1   q  are cross-sectional views illustrating a method for forming a semiconductor device according to a first embodiment of the present invention wherein (i) indicates a cell region and (ii) indicates a peripheral circuit region. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0025]    Embodiments of the present invention are described with reference to the accompanying drawings in detail. 
         [0026]      FIGS. 1A  to  FIG. 1Q  are cross-sectional views illustrating a method for forming a semiconductor device according to a first embodiment of the present invention. In  FIGS. 1A  to  FIG. 1Q , an (i) shows a cell region and an (ii) shows a peripheral circuit region. 
         [0027]    Referring to  FIG. 1A  and  FIG. 1B , a gate poly-silicon  106  is formed on a semiconductor substrate  100  including an active region  104  and a device isolation region  102  ( FIG. 1A ). Before the formation of the poly-silicon  106 , a gate oxide layer (not shown) may be further formed. In this case, the poly-silicon  106  and a poly silicon  122  ( FIG. 1G ) formed on the gate poly silicon  106  at a subsequent step form a part of a gate electrode formed in a peripheral circuit region (ii). 
         [0028]    After a photo resist pattern (not shown) is formed at an upper part of the peripheral circuit region using a cell open mask, the gate poly-silicon  106  of the cell region (i) is removed by using the photo resist pattern as an etch mask ( FIG. 1B ). 
         [0029]    Referring to  FIG. 1C , after a hard mask layer  108  defining a buried gate is formed at an entire surface, a photo resist pattern (not shown) defining a buried gate is formed on the hard mask layer  108 . A hard mask layer  108  and the semiconductor substrate  100  are etched by using the photo resist pattern (not shown) as an etch mask to form a trench  110  for the buried gate. The trench  110  for the buried gate is preferably formed in the cell region (i) only. 
         [0030]    Referring to  FIG. 1D , a gate electrode layer  112  and a insulating layer  114  are formed to bury the trench  110  for the buried gate. Here, although not shown, an oxide layer and barrier metal may be further formed on the trench  110 . Meanwhile, the gate electrode layer  112  is preferably formed of W, TiN, Ti or Ta. 
         [0031]    Referring to  FIG. 1E , an interlayer insulating layer  116  is formed over the cell region(i) and the peripheral circuit region (ii) on an entire upper surface. The interlayer insulating layer  116  is etched using a mask for a bit line contact plug exposing the active region  104  to form a bit line contact hole  118 . An insulating layer is coated on the bit line contact hole  118 . An etch-back is performed to form a spacer  120  at a sidewall of the bit line contact hole  118 . 
         [0032]    Referring to  FIG. 1F , a conductive layer is formed to fill the bit line contact hole  118  ( FIG. 1E ), and then a planarizing process is performed until the interlayer insulating layer  116  is exposed to form a bit line contact plug  122 . A photo resist pattern (not shown) is formed at the cell region (i), the interlayer insulating layer  116  of the peripheral circuit region (ii) is removed by using the photo resist pattern as an etch mask. In this case, the interlayer insulating layer  116  of the peripheral circuit region (ii) is preferably removed by a dry etch process. The hard mask layer  108  is preferably removed. 
         [0033]    Referring to  FIG. 1G , a poly-silicon  123  is formed at an entire surface, a photo resist pattern (not shown) is formed on the poly-silicon  123  of the peripheral circuit region (ii). Next, the poly-silicon  123  formed at the cell region (i) is removed using the photo resist pattern as an etch mask. A planarization etch process is performed to expose the interlayer insulating layer  116  of the cell region (i) and thus remove a step difference between the cell region (i) and the peripheral circuit region (ii). 
         [0034]    Referring to  FIG. 1H  and  FIG. 1I , a barrier metal  124 , a conductive layer  126 , hard mask layers  128  and  130 , and an anti-reflecting layer  132  are sequentially formed at an entire surface ( FIG. 1H ). Then, a photo resist pattern (not shown) is formed on the anti-reflecting layer  132 , and then the underlying layers in the cell region (i) are etched until the interlayer insulating layer  116  of the cell region (i) is exposed by using the photo resist pattern as an etch mask. A capping insulating layer  134  is formed at an entire surface ( FIG. 1I ). The capping insulating layer  134  preferably is a nitride layer. Then, the hard mask layer  130 , the anti-reflecting layer  132  and the photo resist pattern (not shown) are removed. 
         [0035]    At this step, the cell region (i) and the peripheral circuit region (ii) are simultaneously patterned by using the photo resist pattern formed on the anti-reflecting layer  132  as an etch mask. The bit line of the cell region and a gate of the peripheral circuit region are sequentially formed in each separate process, can prevent defects generated by the influence equally applied to the bit line and the gate. 
         [0036]    Referring to  FIG. 1J  and  FIG. 1K , a sacrificial insulating layer  136  is formed on an entire upper part ( FIG. 1J ). Here, the sacrificial insulating layer  136  preferably is an oxide layer formed at a low temperature, for example, a high density plasma (HDP) layer or a plasma enhanced tetra ethyl ortho silicate (PETEOS) layer. In this case, the sacrificial insulating layer  136  is preferably formed at 300° C. to 500° C. Next, a photo resist pattern is formed on the peripheral circuit region (ii) using a cell open mask, and then a sacrificial insulating layer  136  of the cell region (i) is removed by using the photo resist pattern as an etch mask. 
         [0037]    An interlayer dielectric layer  138  is formed on the cell region (i) ( FIG. 1K ). In this case, the interlayer dielectric layer  138  is preferably formed of BPSG. Here, because the sacrificial insulating layer  136  is formed on the peripheral circuit region (ii), the interlayer dielectric layer  138  formed on the cell region (i) the interlayer dielectric layer  138  does not form the peripheral circuit region (ii). Accordingly, conventional problems due to implanting boron ions into the peripheral circuit region (ii) can be prevented. And sacrificial insulating layer  136  is formed at a low temperature, negative effects by the sacrificial insulating layer  136  can be minimized, and thus operational characteristics of the gate in the peripheral circuit region (ii), including the leakage current characteristics can be significantly improved. 
         [0038]    Referring to  FIG. 1L , a photo resist pattern (not shown) is formed on the interlayer dielectric layer  138  of the cell region (i) using an exposure mask defining a device isolation region. The interlayer dielectric layer  138  is etched exposing the capping insulating layer  134  formed in the peripheral region (ii) by using the photo resist pattern as an etch mask. Next, an isolation insulating layer is formed at the cell region and the peripheral circuit region. The isolation insulating layer preferably is a nitride layer. 
         [0039]    Referring to  FIG. 1M , a photo resist pattern is formed at the peripheral circuit region (ii), and the isolation insulating layer  140  and the interlayer dielectric layer  138  is removed by using the photo resist pattern as an etch mask. At this time, the isolation insulating layer is preferable removed by a dry etch process. Meanwhile, the interlayer dielectric layer  138  thereof is preferably removed by a wet etch process. 
         [0040]    Then, an insulting layer is formed at the cell region (i) and an etch-back is performed to form a spacer  144  at a sidewall of an isolation insulating layer  140  in the isolation region  102  of the cell region (i) and the spacer  144  in the cell region is formed at a sidewall of the hard mask pattern  128   a,  the conductive layer pattern  126   a,  the barrier metal pattern  124   a,  and the insulating layer  116 . Next, the insulating layer  116  and the hard mask layer  108  are etched to expose the semiconductor substrate  100  by using the spacer  144  as an etch mask, thereby forming a complete bit line  142 . Subsequently, a conductive layer  146  is formed at an entire surface. At this time, the conductive layer  146  for the storage electrode contact plug is formed to be electrically connected with the active region  104  of the cell region (i). 
         [0041]    Referring to  FIG. 1N , a planarization etch process on the conductive layer  146  is performed to expose the hard mask layer pattern  128   a  to form a storage electrode contact plug  148 . In this procedure, it is preferred that the isolation insulating layer  140  remaining on the sacrificial insulating layer  136  in the peripheral circuit region (ii) is also removed by the planarization etch process. Then, the sacrificial insulating layer  136  is removed to expose the capping insulating layer  134  disposed on the peripheral circuit region (ii). In this case, since the sacrificial insulating layer  136  has a different etch selectivity with respect to the storage electrode contact plug  148  and the hard mask layer pattern  128   a  remaining on the upper most part of the cell region (i), it may be removed without an additional mask process. For example, the sacrificial insulating layer  136  in the peripheral circuit region (ii) is preferably removed by a wet etch. 
         [0042]    Referring to  FIG. 1O , the poly-silicon  106  is patterned to expose the semiconductor substrate  10  by using the capping insulating layer  134  of the peripheral circuit region (i), thereby forming the gate  150  in the peripheral circuit region (ii). At this time, a gate poly-silicon  106  at a lower part of the gate  150  is exposed, a selective oxidizing process with respect to the lower part of the gate  150  is preferably performed to oxio the gate poly-silicon  106  and the semiconductor substrate  100 . As illustrated previously, the selective oxidie process performed at the lower part of the gate  150  may improve the Gate Induced Drain Leakage (GIDL) characteristics of the gate  150 . 
         [0043]    Referring to  FIG. 1P , a nitride layer spacer material and an oxide layer spacer material are deposited on an entire upper surface, a blank etch is executed to form gate spacers  152  and  154  at sidewalls of the gate  150 , respectively. Subsequently, ions are preferably implanted into the semiconductor substrate  100  to form source/drain regions (not shown) by using the gate spacer  154  as a mask. According to the present invention, the gate  150  in the peripheral circuit region (ii) the bit line  142  in the cell region (i) are formed at a separate process step, negative effects onto each other can be prevented. For example, in order to enhance the operation characteristics of the gate  150 , ions can be implanted by easily adjusting an ion implantation angle during a lightly doped drain (LDD) implantation process. 
         [0044]    Referring to  FIG. 1Q , an etch stopping layer  156  is formed at an entire upper part. In this case, the etch stopping layer  156  preferably is a nitride layer. Here, it is preferred that the etch stopping layer  156  serves as an etch stopping layer for a subsequent procedure in the peripheral circuit region (ii). At this time, because the etch stopping layer  156  is formed after the storage electrode contact plug is formed in the cell region (i), it may be formed with a sufficient thickness. In a conventional art, an etch stopping layer is formed before a storage electrode contact plug is formed. Accordingly, a formation region of the storage electrode contact plug is partially buried to form the etch stopping layer with an insufficient thickness. However, in the present invention, because the etch stopping layer is formed after forming the storage electrode contact plug, it can be formed with a sufficient thickness. 
         [0045]    As is clear from the forgoing description, in the method for forming a semiconductor device according to the present invention, after a first etch is performed to partially define a bit line and a gate of a peripheral circuit region at a cell region, and a storage electrode contact plug of the cell region is formed, the gate of the peripheral circuit region is manufactured through a second etch. Accordingly, the bit line and the gate of the cell region and the peripheral circuit region are simultaneously formed to solve a problem occurring due to execution of the same process. 
         [0046]    It will be apparent to those skilled in the art that various modifications and variation can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.