Abstract:
The present invention relates to a method for isolating semiconductor devices. The method includes the steps of: forming a patterned pad nitride layer pattern to open at least one isolation region on the substrate; forming a first trench and a second trench by etching the exposed substrate; depositing a first oxide layer to fill the first trench by performing an atomic layer deposition (ALD) method; etching a portion of the first oxide layer which is filled into the wide trench; and depositing a second oxide layer by performing a deposition method.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method for forming a semiconductor device; and, more particularly, to a method for isolating semiconductor devices on a semiconductor substrate with use of a shallow trench isolation method.  
       DESCRIPTION OF RELATED ARTS  
       [0002]     As known, a device isolation technology has been employed to electrically isolate individual devices such as transistors and capacitors during fabrication of a semiconductor integration circuit. Among various methods of the device isolation technology, a local oxidation of silicon (LOCOS) method and a shallow trench isolation (STI) method are commonly adopted.  
         [0003]     The LOCOS method forms a nitride layer-based mask pattern on an active region of a silicon substrate and thermally oxidating the silicon substrate with use of the mask pattern as a mask. Although the LOCOS method is a simple oxidation process as described above, the LOCOS method is disadvantageous that an oxide layer is formed in a wide area and a bird&#39;s beak phenomenon occurs at an interfacial surface between the oxide layer and the silicon substrate because of a lateral oxidation during the thermal oxidation process. Particularly, the bird&#39;s beak phenomenon is a cause for degrading a gate oxide layer and reducing an area of an active region.  
         [0004]     Because of these disadvantages, it is limited to apply the LOCOS method to highly integrated devices. As a result of this limitation, the STI method is more widely employed. Specifically, the STI method forms a device isolation region by forming a shallow trench in a substrate and then burying an oxide layer into the trench. These serial steps of the STI method make it possible to solve the above described problems related to the LOCOS method. Therefore, the STI method is applied to form a device isolation structure in highly integrated devices, e.g., a dynamic random access memory device with 256 megabytes.  
         [0005]      FIG. 1  is a cross-sectional view of a semiconductor device obtained after an oxide layer for filling a trench is deposited by performing a conventional STI method.  
         [0006]     As shown, a pad oxide layer  11  and a nitride layer  12  are formed on a substrate  10 , and trenches are formed by performing an etching process with use of a device isolation mask. Subsequently, an oxide layer  13  is deposited into the trench and is subjected to a chemical mechanical polishing (CMP) process. Afterwards, the nitride layer  12  and the pad oxide layer  11  are removed.  
         [0007]     In the above STI method, a chemical vapor deposition (CVD) method is commonly used to deposit the oxide layer  13 . However, in case of a micro-trench gap-filling, the oxide layer  13  is deposited by performing a high density plasma (HDP)—CVD method.  
         [0008]     Typically, device isolation regions, i.e., field oxidation regions, in a semiconductor device are defined in a wide area and a relatively shallow area. Especially, in a DRAM memory device with several gigabytes, a device isolation region in a cell array region is needed to be defined in a shallow area, while a device isolation region in a peripheral circuit region is needed to be defined in a wide area.  
         [0009]     However, in a gigabyte level DRAM memory device having a trench defined with a depth of about 0.25 μm and a width less than about 0.1 μm, voids are formed within this micro-trench even if an oxide layer is filled into the micro-trench with use of a HDP-CVD method.  FIG. 1  shows the above-explained void, which is denoted with the reference symbol A.  
         [0010]     In the Korean Laid-Open No. 2001-0058498 disclosed on Jul. 6, 2001, entitled “Method for Forming Trench Type Isolation Layer of Semiconductor Device,” the entire contents of which being incorporated hereby reference, an oxide layer for use in a trench burial is deposited into trenches by performing an atomic layer deposition (ALD) method which has an excellent step coverage property.  
         [0011]      FIG. 2  is a cross-sectional view for describing another conventional method for depositing an oxide layer for use in a trench burial into trenches.  
         [0012]     As shown, a pad oxide layer  21  and a nitride layer  22  are formed on a substrate  20 , and trenches are formed by performing an etching process with use of a device isolation mask. A first oxide layer  23  is then formed with such a thickness to fill a micro-trench. At this time, the first oxide layer  23  is formed by employing an ALD method. A second oxide layer  24  is consecutively deposited by performing a HDP-CVD method. At this time, the second oxide layer  24  is deposited until completely filling the wide trench.  
         [0013]     The reason for consecutively performing the HDP-CVD method after the ALD method is because the HDP-CVD method has an advantage in product yields compared to the ALD method which requires a long deposition time for the trench burial.  
         [0014]     However, even in this conventional method, a void denoted as B in  FIG. 2  might be generated in the wide trench during the HDP-CVD method because the wide trench becomes narrow in its width due to the ALD deposition of the first oxide layer  23 .  
       SUMMARY OF THE INVENTION  
       [0015]     It is, therefore, an object of the present invention to provide a method for isolating semiconductor devices with use of a shallow trench isolation method capable of preventing generation of voids within both of a micro-trench and a wide trench.  
         [0016]     In accordance with an aspect of the present invention, there is provided a method for isolating devices on a substrate by forming a trench, including the steps of: forming a patterned pad nitride layer pattern to open at least one isolation region on the substrate; forming a first trench and a second trench by etching the exposed substrate; depositing a first oxide layer to fill the first trench by performing an atomic layer deposition (ALD) method; etching a portion of the first oxide layer which is filled into the wide trench; and depositing a second oxide layer by performing a deposition method. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The above and other objects and features of the present invention will become better understood with respect to the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:  
         [0018]      FIG. 1  is a cross-sectional view of a semiconductor device obtained after an oxide layer for filling a trench is deposited by performing a conventional shallow trench isolation (STI) method;  
         [0019]      FIG. 2  is a cross-sectional view of a semiconductor device obtained after an oxide layer for filling a trench is deposited by performing another conventional STI method; and  
         [0020]      FIGS. 3A  to  3 G are cross-sectional views of a semiconductor device for describing a method for forming a STI structure in accordance with a preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.  
         [0022]      FIGS. 3A  to  3 G show cross-sectional views of a semiconductor device for describing a method for forming a STI structure in accordance with a preferred embodiment of the present invention.  
         [0023]     Referring to  FIG. 3A , a pad oxide layer  31  is formed on a substrate  30  with a thickness ranging from about 25 Å to about 200 Å. Then, a nitride layer  32  is deposited on the pad oxide layer  31  with a thickness ranging from about 1000 Å to about 2000 Å.  
         [0024]     Next, the nitride layer  32  and the pad oxide layer  31  are patterned by performing an etching process with use of a device isolation mask, thereby obtaining a patterned nitride layer  32 A and a patterned pad oxide layer  31 A. Then, exposed portions of the substrate  30  are subjected to a dry etching process to thereby form trenches. At this time, the exposed portions of the substrate  30  are etched with a thickness ranging from about 2000 Å to about 4000 Å. As shown in  FIG. 3B , there are a micro-trench  33 A formed in a cell region and a wide trench  33 B formed in a peripheral circuit region.  
         [0025]     Subsequently, a first oxide layer  34  is deposited by performing an atomic layer deposition (ALD) method such that the first oxide layer  34  fills the micro-trench  33 A. The first oxide layer  34  is formed with a thickness, which is greater than about one half of a thickness required by the design rule, so that the first oxide layer  34  completely fills the micro-trench  33 A in the cell region.  
         [0026]     Preferably, the thickness of the first oxide layer  34  ranges from about 300 Å to about 500 Å. Also, the first oxide layer  34  is formed by repeating a cycle of alternately providing a source gas of silicon selected from a group of Si x Cl y  such as silicon tetrachloride (SiCl 4 ) and disilicon hexachloride (Si 2 Cl 6 ) and an oxygen source gas such as water (H 2 O) and hydrogen peroxide (H 2 O 2 ) into a reaction chamber.  
         [0027]     Herein, the subscripts x representing an atomic ratio of silicon is in a range from about 1 to about 4, while the subscript y representing an atomic ratio of chloride is in a range from about 1 to about 8. Particularly, the fist oxide layer  34  is deposited at a temperature preferably ranging from about 20° C. to about 400° C. Moreover, it is possible to add one of pyridine (C 5 H 5 N) and ammonia (NH 3 ) as a catalyst to decrease a reaction activation energy level during the deposition of the first oxide layer  34 .  
         [0028]     It is also preferred that the first oxide layer  34  is treated with a thermal process for the purpose of densification. The thermal process is generally carried out at a temperature ranging from about 500° C. to about 1200° C. in an atmosphere selected from a gas group consisting of hydrogen (H 2 ), oxygen (O 2 ), nitrogen (N 2 ), ozone (O 3 ) and nitrous oxide (N 2 O) and mixed H 2  and O 2  for more than 5 minutes. However, the thermal process in this preferred embodiment adopts a rapid thermal process (RTP) carried out at a temperature greater than about 600° C. for about more than 5 seconds.  
         [0029]     Meanwhile, it is possible to perform a lateral oxidation process prior to depositing the first oxide layer  34  in order to eliminate damaged portions of the substrate  30  caused by the etching process for forming the micro-trench  33 A and the wide trench  33 B and to improve interfacial characteristics. Also, a liner oxide layer and/or a liner nitride layer can be formed. At this time, the liner nitride layer serves as an etch stop layer when the first oxide layer  34  is etched.  
         [0030]     Referring to  FIG. 3D , a region in which the micro-trench  33 A is formed in the cell array region is masked, while a region in which the wide trench  33 B is formed in the peripheral circuit region is opened. Then, the first oxide layer  34  formed in this opened region is etched by employing a wet and/or dry etching process, thereby obtaining a patterned first oxide layer  34 A.  
         [0031]     Referring to  FIG. 3E , a second oxide layer  35  is formed on an entire surface of the above resulting structure by performing a high density plasma-chemical vapor deposition (HDP-CVD) method with use of a reaction gas of silane (SiH 4 ). The second oxide layer  35  has a thickness greater than each depth of the micro-trench  33 A and the wide trench  33 B. That is, the thickness of the second oxide layer  35  is greater than about 5000 Å. Instead of using the HDP-CVD oxide layer, it is also possible to employ an undoped silicon glass (USG) layer deposited by performing one of atmospheric pressure (AP)—CVD method and a sub-atmospheric (SA)-CVD method with use of a reaction gas of tetraethylorthosilicate (TEOS).  
         [0032]     Referring to  FIG. 3F , a chemical mechanical polishing (CMP) process is performed to the second oxide layer  35  and the patterned first oxide layer  34 A shown in  FIG. 3E  by using the patterned nitride layer  32 A as a CMP stop layer. The CMP process planarizes the patterned first oxide layer  34 A and the second oxide layer  35  until the top surface of the patterned nitride layer  32 A is exposed, thereby respectively providing a planarized first oxide layer  34 B and a planarized second oxide layer  35 A.  
         [0033]     Referring to  FIG. 3G , the exposed patterned nitride layer  32 A and the patterned pad oxide layer  31 A are removed by a wet etching process, and other typical subsequent processes are performed to complete the device isolation process.  
         [0034]     On the basis of the above-described preferred embodiment, it is possible to improve device reliability by preventing generation of voids in the first and the second oxide layers for use in the trench burial. Also, an increase in depth and a decrease in width of the trench lead to an improvement on a scale of device integration. Furthermore, the use of the insulation layer formed in the cell array region through the ALD method which dose not use a plasma, i.e., the first oxide layer, makes it possible to minimize damages to the substrate, thereby improving a refresh characteristic.  
         [0035]     The present application contains subject matter related to the Korean patent application No. KR 2003-0098428, filed in the Korean Patent Office on Dec. 29, 2003, the entire contents of which being incorporated herein by reference.  
         [0036]     While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope and spirit of the invention as defined in the following claims.