Abstract:
The present invention relates to a semiconductor device and a method of manufacture thereof, being capable of improving the high integration by increasing a cell region while securing the reliability of device and the process margin through forming a cell region and a core region with the stacking structure.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   The priority of Korean patent application number 10-2007-0128346, filed on Dec. 11, 2007, which is incorporated by reference in its entirety, is claimed. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a semiconductor device, and more specifically to a method of increasing the level of integration while maintaining the reliability of a device by using a stacked structure. 
   A semiconductor device comprises of a plurality of circuits. Generally, a memory semiconductor device like DRAM is comprised of a cell region, a core region, and a peripheral region. The cell region stores data. The core region has a circuit for accessing data stored in the cell region. The peripheral region has a circuit for driving the memory semiconductor device and the data input/output. 
   In the cell region, memory cells including a cell transistor and a cell capacitor are arranged in an array type. Such a cell region includes a plurality of unit cell arrays. 
   In the core region, the circuit including a sub-word line driver and a sense amplifier is formed. At this time, the sub-word line driver drives the sub-word line according to the voltage level of the main word line. The sense amplifier senses and amplifies the data of a cell. 
   A bank includes a plurality of unit cell arrays and a plurality of core regions. For example, in the case of the DDR2 512 Mbit device, it has four banks. The peripheral region in which the circuit including a free decoder, an input buffer, and an output buffer is formed is provided between these banks. 
   Recently, more circuits, particularly, more memory cells have to be formed in a limited chip area, since high integration is required as the size of the semiconductor device has been reduced. 
   However, a trade-off relation exists between the net die increment and the reliability assurance of a device. Thus, the reliability of a device is decreased if the net die is increased. That is, in the current DRAM structure, there is a structural limit in increasing the net die while not reducing the reliability of a device. 
   BRIEF SUMMARY OF THE INVENTION 
   Embodiments of the present invention relate to maintaining the reliability of a semiconductor device and improve the integration through increasing a cell region by forming the cell region and a core region with a stacked structure. 
   According to an embodiment of the present invention, a semiconductor device includes a cell array region formed on a first semiconductor substrate; and a core circuit unit formed on a second semiconductor substrate over the cell array. 
   The core circuit unit comprises at least one of a sense amplifier and a sub-word line driver. The sense amplifier is electrically connected to a bit line of the cell array. The sub-word line driver is electrically connected to a word line of the cell array. The second semiconductor substrate is an epitaxial growth layer with the first semiconductor substrate as a seed layer. The semiconductor device according to an embodiment of the present invention further comprises a contact region for forming the second semiconductor substrate by growing the first semiconductor substrate. The semiconductor device according to an embodiment of the present invention further comprises an insulating layer formed between the cell array region and the second semiconductor substrate. The insulating layer has a thickness range from 500 Å to 5,000 Å. The insulating layer is formed with one of an oxide film, a nitride film and the combinations thereof. 
   According to an embodiment of the present invention, a method of fabricating a semiconductor device includes forming a cell array on a first semiconductor substrate; forming a second semiconductor substrate over the cell array; and forming a core circuit on the second semiconductor substrate. 
   The forming a second semiconductor substrate comprises forming a contact hole which exposes the first semiconductor substrate by selectively etching a interlayer dielectric layer included in the cell array; and growing the first semiconductor substrate through the contact hole. The method of fabricating a semiconductor device according to an embodiment of the present invention further comprises planarly etching the grown up semiconductor substrate. The growing the first semiconductor substrate performs an epitaxial growth method with the first semiconductor substrate exposed through the contact hole as a seed layer. The method of fabricating a semiconductor device according to an embodiment of the present invention further comprises forming an insulating layer between the cell array and the second semiconductor substrate. The insulating layer has a thickness range from 500 Å to 5,000 Å. The insulating layer is formed with one of an oxide film, a nitride film and the combinations thereof. The forming a core circuit comprises forming a device isolation structure defining an active region in the second semiconductor substrate; and forming a transistor on the active region. The method of fabricating a semiconductor device according to an embodiment of the present invention further comprises electrically connecting a sense amplifier of the core circuit and a bit line of the cell array. The method of fabricating a semiconductor device according to an embodiment of the present invention further comprises electrically connecting a sub-word line driver of the core circuit and a word line of the cell array. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a layout of a semiconductor device according to an embodiment of the present invention. 
       FIG. 2  is a cross-sectional view taken along I-I′ of the semiconductor device of  FIG. 1 . 
       FIGS. 3   a  to  3   d  are cross-sectional views showing the manufacturing method of the semiconductor device of  FIG. 2 . 
   

   DESCRIPTION OF EMBODIMENTS 
     FIG. 1  is a layout of a semiconductor device according to an embodiment of the present invention, showing banks of the semiconductor device. 
   The semiconductor device includes a first semiconductor substrate region  102 , a second semiconductor substrate region  104  and a cell/core region  108 . 
   The unit cell array including word lines (not shown), bit lines (not shown), and memory cells are formed on the first semiconductor substrate region  102 . Each memory cell includes a cell transistor and a cell capacitor. 
   The second semiconductor substrate region  104  is used as a core circuit region where circuits such as sense amplifier and a sub-word line driver are formed. The second semiconductor substrate region  104  includes a contact region  106 , and formed over the first semiconductor substrate region  102 . That is, in the present embodiment, the first semiconductor substrate region  102  and the second semiconductor substrate region  104  are formed in a stacked structure. 
   Since the first semiconductor substrate region  102  and the second semiconductor substrate region  104  are formed on different layers, the size of the first semiconductor substrate region  102  can be increased. Therefore, the cell efficiency and the process margin can be improved as the cell array region is increased. In one embodiment, the contact region  106  is formed at outer side of the first semiconductor substrate region  102 , but may be formed at other locations. 
   The cell/core region  108  is a region including the first semiconductor substrate region  102  and the second semiconductor substrate region  104 . 
     FIG. 2  is a cross-sectional view taken along I-I′ of the semiconductor device of  FIG. 1 . 
   The semiconductor device includes a cell array unit  260  and a core circuit unit  290 . At this time, the cell array unit  260  and the core circuit unit  290  are formed in a stacked structure. For example, the core circuit unit  290  is formed over the cell array unit  260 . 
   The cell array unit  260  includes memory cells having a gate  230  and a capacitor  250 . The memory cells are arranged in an array. In the present embodiment, for the sake of convenience, only two memory cells are shown. 
   The cell array unit  260  includes the gate  230 , a bit line  240  and the capacitor  250 . The gate  230  is formed in a first active region  210   a  of a first semiconductor substrate (or first semiconductor material)  210  defined by a first device isolation structure  220 . And the bit line  240  is formed in a second interlayer dielectric layer  243  while being electrically connected to a landing plug  233   b  formed between the gates  230 . The capacitor  250  is formed on a storage electrode contact plug  247  and a third interlayer dielectric layer  245 . The storage electrode contact plug  247  is electrically connected to a landing plug  233   s , and is formed within the second interlayer dielectric layer  243  and the third interlayer dielectric layer  245 . In addition, the third interlayer dielectric layer  245  is formed on the bit line  240  and the second interlayer dielectric layer  243 . 
   The core circuit unit  290  includes a second semiconductor substrate (or second semiconductor material)  270 , a second device isolation structure  273 , and a transistor  280 . The second semiconductor substrate  270  is formed over the cell array unit  260 . At this time, the second semiconductor substrate  270  may be formed with an epitaxial growth layer which uses the first semiconductor substrate  210  as a seed layer. For example, a first to a fourth interlayer dielectric layer  235 ,  243 ,  245 ,  249  are selectively etched until the first semiconductor substrate  210  is exposed so that the contact hole  253  is formed. Then, the epitaxial growth is carried out with the first semiconductor substrate  210  exposed in the lower portion of the contact hole  253  as a seed layer so that the second semiconductor substrate  270  can be formed. In other embodiments, the second semiconductor substrate (or layer) may be formed using different methods according to application. 
   The transistor  280  is formed on a second active region  270   a  defined with the second device isolation structure  273 . The transistor  280  may be an element used to form the core circuit such as a sense amplifier or a sub-word line driver. The transistor  280  may be electrically connected to the word line (not shown) or the bit line  240  of the cell array unit  260 . An insulating layer  263  is formed between the second semiconductor substrate  270  and the capacitor  250  in order to isolate the cell array unit  260  and the core circuit unit  290 . The insulating layer  263  may be formed with one of the oxide film, the nitride film and combinations thereof. 
     FIGS. 3   a  to  3   d  are cross-sectional views showing the manufacturing method of the semiconductor device of  FIG. 2 . 
   A first device isolation structure  320  is formed on a first semiconductor substrate  310  including a cell array region  3000   c  and a contact region  3000   p  to define a first active region  310   a . A gate  330  is formed on the first active region  310   a . In the present embodiment, the gate  330  has the recess structure, but it is not limitative. 
   A first interlayer dielectric layer  335  is formed on the first device isolation structure  320 , the first active region  310   a , and the gate  330 . Then, a landing plug contact hole (not shown) exposing the first active region  310   a  is formed between the gates  330  by eliminating a part of a first interlayer dielectric layer  335 . And a first conductive layer (not shown) is formed so that the landing plug contact hole can be filled. Landing plugs  333   s ,  333   b  are isolated by using a planarizing etch for the first conductive layer until the upper portion of the gate  330  is exposed. 
   A second interlayer dielectric layer  343  is formed on the landing plugs  333   s ,  333   b , the gate  330 , and the first interlayer dielectric layer  335 . Then, a part of a second interlayer dielectric layer  343  is selectively etched in order to expose the landing plug  333   b  so that a bit line contact hole (not shown) is formed. After a second conductive layer (not shown) is formed on the second interlayer dielectric layer  343  including the bit line contact hole, a bit line  340  is formed by patterning the second conductive layer with a bit line mask (not shown). 
   A third interlayer dielectric layer  345  is formed on the bit line  340  and the second interlayer dielectric layer  343 . A storage electrode plug contact hole (not shown) which exposes the landing plug  333   s  is formed by selectively etching a part of the third interlayer dielectric layer  345  and the second interlayer dielectric layer  343 . After a third conductive layer (not shown) is formed on the third interlayer dielectric layer  345  including the storage electrode plug contact hole, a storage electrode contact plug  347  is formed by planarly etching the third conductive layer. 
   Then, after a fourth interlayer dielectric layer  349  is formed on the storage electrode contact plug  347 , the fourth interlayer dielectric layer  349  is selectively etched to form a storage electrode contact hole (not shown) exposing the storage electrode contact plug  347 . After a fourth conductive layer (not shown) is formed on the fourth interlayer dielectric layer  349  including the storage electrode contact hole, a bottom plate  355  is formed by planarly etching the fourth conductive layer. 
   Then, after the dip-out process is performed to eliminate the fourth interlayer dielectric layer  349  of the cell array region  3000   c , a dielectric layer (not shown) and an top plate  357  are formed on the first semiconductor substrate  310  including the bottom plate  355 . At this time, the capacitor  350  includes the bottom plate  355 , the dielectric layer, and the top plate  357 . As a result, a cell array  360  is formed in the cell array region  3000   c . As to the method for forming the cell array on the semiconductor substrate  310 , other methods apart from the above-described method can be applied. 
   Thereafter, an insulating layer  363  is formed over the first semiconductor substrate  310  including the unit cell array region  3000   c  and the contact region  3000   p . The insulating layer  363  electrically isolates the core circuit to be formed from the cell array  360 . In addition, the insulating layer  363  may be formed to a thickness of 500 Å to 5,000 Å. The insulating layer  363  may be formed with one of an oxide film, a nitride film and combinations thereof. Other dielectric materials may be used in other implementations. 
   Referring to  FIG. 3   b , after a photosensitive layer (not shown) is formed on the insulating layer  363 , the photosensitive pattern  365  is formed through an exposure and development process for the photosensitive layer by using the mask (not shown), exposing a part of the contact region  3000   p . Then, a contact hole  353  which exposes the first semiconductor substrate  310  is formed by selectively etching the insulating layer  363  and an interlayer dielectric layer  367  using the photosensitive pattern  365  as a mask. 
   Referring to  FIG. 3   c , the photosensitive pattern  365  is removed. A second semiconductor substrate  370  is epitaxially grown on the insulating layer  363  using a portion of the first semiconductor substrate  310  exposed by the contact hole  353  as a seed layer. The second semiconductor substrate  370  fills the contact hole  353  due to the epitaxial growth method. In one embodiment, the epitaxial growth method is performed in a temperature range of 350° C. to 850° C. The epitaxial growth method fills the contact hole  353 . And the growth time can be controlled so that the second semiconductor substrate  370  is formed over unit cell array region  3000   c  and the contact region  3000   p.    
   Then, the second semiconductor substrate  370  is planarized. The planarization process can be performed using the chemical mechanical polishing (CMP), the etch-back method, or both. Although the second semiconductor substrate  370  is formed over both the cell array region  3000   c  and the contact region  3000   p , the invention is not limited to such an embodiment. For example, the second semiconductor substrate  370  can be formed on a part of the cell array region  3000   c  or the contact region  3000   p.    
   Referring to  FIG. 3   d , a second device isolation structure  373  defining a second active region  370   a  is formed in the second semiconductor substrate  370 . A transistor  380  is formed on the second active region  370   a . The second semiconductor substrate  370  and the transistor  380  form a core circuit  390  such as a sense amplifier and a sub-word line driver. In addition to the sense amplifier and the sub-word line driver, the core circuit  390  may have other types of circuits. 
   Thereafter, in the subsequent interconnection forming process, an interconnection (not shown) which electrically connect the word line (not shown) of the cell array  360 , or the bit line  340  to the core circuit  390  is formed. For example, the interconnection is formed in order that the sense amplifier of the core circuit  390  is connected to the bit line  340 , while the interconnection is formed in order for the sub-word line driver of the core circuit  390  to be connected to the word line. After that, the subsequent processes such as a fuse formation process is performed and the semiconductor device can be completed. 
   As described above, by forming the first semiconductor substrate in which the cell array is formed and the second semiconductor substrate in which the core circuit is formed with the stacked structure, the present invention can increase the cell array region while securing the reliability and the process margin of a device. 
   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.