Abstract:
A method for forming a single-crystal silicon film of high quality is provided. The method includes the operations of: growing single-crystal silicon to a predetermined thickness of a crystal growth plate; depositing a buffer layer on the single-crystal silicon layer; forming a partition layer at a predetermined depth in the single-crystal silicon layer by implanting hydrogen ions in the single-crystal silicon layer from an upper portion of an insulating layer; attaching a substrate onto the buffer layer; and cutting the partition layer of the single-crystal silicon layer by heating the partition layer from the crystal growth plate to obtain a single-crystal silicon layer of a predetermined thickness on the substrate.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
   This application claims the benefits of Korean Patent Application No. 10-2004-0091851, filed on Nov. 11, 2004, in the Korean Intellectual Property Office, and U.S. patent application Ser. No. 60/657,736, filed on Mar. 3, 2005, the disclosure of which is incorporated herein in its entirety by reference. 

   BACKGROUND OF THE DISCLOSURE 
   1. Field of the Disclosure 
   The present disclosure relates to a method of fabricating a single-crystal silicon film and a method of fabricating a thin film transistor (TFT) adopting the same. 
   2. Description of the Related Art 
   Poly crystalline silicon (poly-Si) has higher carrier mobility than that of amorphous Si (a-Si), and thus, is utilized in a flat panel display device and in various electronic devices such as solar batteries. However, the carrier mobility and homogeneity of poly-Si are inferior to those of single-crystal Si. 
   Single-crystal Si is useful for a system on panel (SOP) structure, in which a system is formed on a display panel. The mobility of single-crystal Si is 300 cm 2 /Vs or higher. A high quality switching device used in a display device can be obtained from single-crystal Si having high mobility. 
   There are certain limitations in fabricating single-crystal Si, such as a limitation of processing temperature. When the single-crystal Si is fabricated, the processing temperature cannot rise over a certain temperature that can be endured by a material forming a substrate of the Si. 
   A method of fabricating a silicon-on-insulator (SOI) wafer using a so-called proprietary Smart-Cut technique includes an annealing process, the processing temperature of which rises up to 1000° C. The above method includes the operations of heat treating of a bare wafer having a predetermined thickness to form an oxide layer thereon, forming a boundary layer using hydrogen impurities by injecting hydrogen (H + ) ions under the surface of the wafer, bonding the wafer to a separate substrate and separating the boundary layer to retain silicon of a predetermined thickness on the substrate, and annealing the silicon left on the substrate at the high temperature. 
   The temperature may rise over 900° C. in the thermal oxidation process, and over 1,100° C. in the annealing process. The high-temperature processes may degrade the characteristics of the substrate. Therefore, the material that can be selected to form the substrate is limited by the high temperature process, and the selected material undergoes thermal shock. Thus, the performance of the device formed using the silicon may be degraded. 
   SUMMARY OF THE DISCLOSURE 
   The present invention may provide a method of fabricating single-crystal silicon in which a substrate does not experience thermal shock, and a method of fabricating a thin film transistor (TFT) using this method. 
   The present invention also may provide a method of fabricating single-crystal silicon on a substrate that is susceptible to heat degradation, and a method of fabricating a TFT using this method. 
   According to an aspect of the present invention, there is provided a method of fabricating single-crystal silicon including the operations of: growing single-crystal silicon to a predetermined thickness on a crystal growth plate; depositing a buffer layer on the single-crystal silicon layer; forming a partition layer at a predetermined depth in the single-crystal silicon layer by implanting hydrogen ions in the single-crystal silicon layer from an upper portion of an insulating layer; attaching a substrate to the buffer layer; and cutting the partition layer of the single-crystal silicon layer by heating the partition layer from the crystal growth plate to obtain a single-crystal silicon layer of a predetermined thickness on the substrate. 
   According to another aspect of the present invention, there is provided a method of fabricating a single-crystal silicon thin film transistor (TFT) including the operations of: growing a single-crystal silicon to a predetermined thickness on a crystal growth plate; depositing a buffer layer on the single-crystal silicon layer; forming a partition layer at a predetermined depth in the single-crystal silicon layer by implanting hydrogen ions in the single-crystal silicon layer from an upper portion of an insulating layer; attaching a substrate onto the buffer layer; cutting the partition layer of the single-crystal silicon layer by heating the partition layer from the crystal growth plate to obtain a single-crystal silicon layer of a predetermined thickness on the substrate; and fabricating a single-crystal silicon TFT on the substrate using the single-crystal silicon layer formed on the substrate. 
   The crystal growth plate may be an alumina (Al 2 O 3 ) substrate, and the substrate may be a glass substrate or a plastic substrate. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present invention will be further described in detailed exemplary embodiments thereof with reference to the attached drawings in which: 
       FIGS. 1A through 1G  are processing views of a method of fabricating a single-crystal silicon film according to the present invention; 
       FIG. 1H  is a view of an example of a thin film transistor (TFT) using the single-crystal silicon film according to the present invention; and 
       FIGS. 2A through 2H  are processing views of a method of fabricating the single-crystal silicon TFT according to the present invention. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   Hereinafter, preferred embodiments of a method of fabricating a single-crystal silicon (Si) film according to the present invention will be described with reference to the accompanying drawings. 
   Referring to  FIG. 1A , a Si epitaxial layer, that is, a single-crystal silicon film  12  and an oxide layer, for example, a buffer layer  11  are sequentially formed on an Al 2 O 3  substrate  1  for crystal growth, using a crystal growth method. It is desirable that a thickness of the single-crystal Si film  12  is approximately 0.5 μm or less. 
   Referring to  FIG. 1B , hydrogen ions (H+) are injected to form an implanted layer at an intermediate portion of the single-crystal Si film  12  as a partition layer  12   a.    
   Referring to  FIG. 1C , a glass or plastic substrate  10  attached to a supporter  20  by a bond layer  21  is bonded to the Si film  12 . To do this, the buffer layer  11  and the Si film  12  under the buffer layer  11  are activated by oxygen plasma, and the substrate  10  is attached to the Si film  12  in an air atmosphere at room temperature. 
   Referring to  FIG. 1D , thermal energy, for example, excimer laser of 308 nm, is applied evenly onto the crystal growth plate  1 . The implanted layer, that is, the partition layer  12   a , which experiences strain due to the impurities, is separated by the thermal energy, and then, the Si film  12  is separated into a Si film  12 ′ at the Al 2 O 3  substrate  1  side and a Si film  12  at the glass or plastic substrate  10  side, as shown in  FIG. 1F . In another method to separate the partition layer  12   a , the partition layer  12   a  is heated at a temperature of approximately 500° C. 
   Referring to  FIG. 1E , the supporter  20  is separated from the bottom surface of the substrate  10 , and after that, the TFT of  FIG. 1H  is fabricated using a general TFT fabrication method. The single-crystal Si on the substrate  10  is polished to have a predetermined thickness and an even surface by a polishing device before performing the TFT fabrication processes. 
   In the fabricated TFT, an active layer  12  including a source  12   a  and a drain  12   b  at both sides thereof is formed on the plastic or the glass substrate  10  from the single-crystal Si film in the above crystal growth and separation processes, and insulating layers  13  and  15  are formed on the active layer  12 . The insulating layer formed on the center upper portion of the active layer  12  is a gate insulating layer  13  that electrically insulates a gate  14  formed on the gate insulating layer  13  from the active layer  12 . Portions covering both sides of the active layer  12  and the gate  14  are also insulating layers. 
   In addition, the separated Al 2 O 3  substrate  1  in the above process is reintroduced into the processes for growing a new single-crystal Si film. Before being input into the processes, the remaining single-crystal silicon film layer on the Al 2 O 3  substrate  1  is polished. 
   Hereinafter, a method of forming the TFT using the Si film formed on the substrate will be described in greater detail. 
   Referring to  FIG. 2A , in order to fabricate the TFT using the single-crystal Si film obtained through the above-described processes as the active layer, the gate insulating layer  13  is formed on the Si film  12  to a thickness of approximately 1000 Å using an inductively coupled plasma chemical vapor deposition (ICP-CVD) method, a plasma enhanced chemical vapor deposition (PE-CVD) method, or a sputtering method. 
   If the substrate of the TFT is formed of plastic, the temperature of the heat treatment of a SiO 2  thin film should be controlled so as to prevent the substrate from being damaged. 
   Referring to  FIG. 2B , the gate  14  is formed on the gate insulating layer  13 . The gate insulating layer  13  and the gate  14  are patterned into a desired shape through following processes that are described hereafter. 
   Referring to  FIG. 2C , the gate  14  and the gate insulating layer  13  are etched in a dry etching method using a first mask (M 1 ). The mask has a pattern corresponding to the gate  14 . The gate  14  is patterned by the pattern of the mask and the gate insulating layer  13  is also patterned to be the same shape. Therefore, the Si film  12  is exposed through the portion that is not covered by the gate  14 . 
   Referring to  FIG. 2D , the portion of the Si film  12  that is not covered by the gate  21  is doped using an ion shower, and then, is activated by an XeCl excimer laser of 308 nm. 
   Referring to  FIG. 2E , the single-crystal Si film  12  that is not covered by the gate  14  is patterned using a second mask (M 2 ) in a dry etching method and then is doped to form a source  12   a  and a drain  12   b . The single-crystal Si that is not doped remains under the gate  21 , and performs as a channel. 
   Referring to  FIG. 2F , a third SiO 2  layer  15  is formed on the above stacked layers to a thickness of approximately 3000 Å as an interlayer dielectric (ILD) using ICP-CVD, PE-CVD, or a sputtering method. 
   Referring to  FIG. 2G , a source contact hole  15   a  and a gate contact hole  15   b  are formed on the third SiO 2  layer  15  using a third mask (M 3 ). 
   Referring to  FIG. 2H , a source electrode  16  and a drain electrode  17  are formed in the source contact hole  15   a  and the gate contact hole  15   b  to complete the TFT. 
   The above described method of fabricating a TFT is an example of a method of fabricating a TFT using a single-crystal Si film fabricated according to the present invention. However, this method can be modified in various ways. 
   According to the present invention, the single-crystal Si film can be readily obtained. Instead of the plastic or glass substrate that is susceptible to heat damage in the heat treatment process, the crystal growth plate is used to obtain a high quality single-crystal Si film. In addition, the partition layer can be formed in the single-crystal Si film formed on the crystal growth plate in the ion implantation process, and thus, a desired very thin Si film, the thickness of which is approximately 100 nm or thinner, can be obtained. 
   Therefore, according to the present invention, since the Si layer is formed on the plastic substrate or the glass substrate, a system on glass (SOG) or a system on plastic (SOP) structure using the single-crystal Si can be formed. Thus, according to the present invention, a high performance TFT having high reproducibility and less performance variation between the elements can be fabricated. In addition, the single-crystal Si is grown using the Al 2 O 3  substrate having a high thermal endurance, and then, moved onto the plastic or glass substrate, and thus, the Al 2 O 3  substrate can be repeatedly used to grow new single-crystal Si. 
   The method of fabricating the single-crystal Si can be applied to a solar battery using silicon, as well as to TFTs. 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.