Patent Publication Number: US-2005133156-A1

Title: Apparatus and method for wafer planarization

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an apparatus and a method for wafer planarization and, more particularly, to an apparatus and a method used to planarize the entire surface of a wafer by spraying high-pressure etchant vapor into the wafer surface, which can substitute an existing CMP (Chemical Mechanical Polish) process.  
      2. Background of the Related Art  
       FIG. 1   a  through  FIG. 1   c  illustrate a conventional spin type wafer processing equipment.  
      Referring to  FIG. 1   a , a spin type of wafer processing equipment to substitute the existing CMP equipments comprises a wafer chuck  10  on which a wafer is loaded and a chemical supply line  14  to supply etching chemical solution to an upper part of the wafer chuck. Once a wafer  12  is loaded on the wafer chuck, this wafer chuck rotates and the chemical solution is dropped and supplied to this rotating wafer through the chemical supply line. The chemical supply line moves back and forth across the wafer.  14   a  and  14   b  represent chemical supply lines placed between the wafer center and wafer edge.  
      Referring to  FIG. 1   b , the virtual line  18  shows moving path of the chemical supply line  14 . A centrifugal force by wafer rotation affects the chemical supplied to wafer, so the chemical moves from first supplied points to wafer edges. Therefore, the result of a wafer processing such as etching, strip and cleaning is different by the regions on a wafer.  
      Referring to  FIG. 1   c , during the wafer rotation, wafer processing chemical on the center of wafer has high relative velocities to the wafer and experiences a centrifugal force directed outward this wafer. Accordingly, the chemical moves fast to the first region (R 1 ) at a distance of radius r from the first supplied point. Outside this R 1  region, the relative velocity between the chemical and the wafer  12  is near 0 and the movement toward wafer edge becomes very slow even though the chemicals still get affected by the centrifugal force. That is, the chemical arriving at the second region (R 2 ) between the first region (R 1 ) and the edge moves together with the wafer without fast movement directed to the wafer edge. This difference in moving speed of chemicals by the regions on a wafer, results in different reaction time by the regions. The reaction time is longer on the first region (R 1 ) than on the second region (R 2 ). Owing to the reaction time difference, on a wafer, processing time is short for the first region (R 1 ) and long for the second region (R 2 ). Therefore, the first region (R 1 ) is processed thickly and the second region (R 2 ) thinly.  
      This spin type wafer processing equipment has advantage that wafer surface can be planarized without using existing CMP equipment. By avoiding mechanical polishing by the friction with the polishing pad of the CMP equipment, the defects like scratch can be prevented. Furthermore, slurry needs not be used, so production cost and the expense for processing byproducts can be saved.  
      However, for the above-described spin type wafer processing equipment, etching chemical have a enough reaction time only for limited wafer region, so it is difficult to evenly planarize the entire surface of the wafer. To solve this problem, it is necessary to repeat the wafer processing with changing processing conditions. For example, during an at the above oxide etching process, after the first process is performed the second etching process should be performed under the condition that the first region (R 1 ) with thicker oxide is given a longer reaction time and the second region (R 2 ) with thinner oxide is given a shorter reaction time. This two-step process becomes a main reason for increasing the wafer processing time and lowering semiconductor equipment productivity.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention is directed to an apparatus and a method for wafer planarization that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
      An object of the present invention is to provide an apparatus and a method used to planarize the entire surface of a wafer by spraying high pressure etchant vapor into the wafer surface which can substitute an existing CMP (Chemical Mechanical Polish) process to substantially obviate one or more problems due to limitations and disadvantages of the related art.  
      To achieve this object, in accordance with the purpose of the invention, as embodied and broadly described herein, an apparatus for wafer planarization comprises: a liquid nitrogen supply tank; a nitrogen gas transfer tube linked with the liquid nitrogen supply tank by a valve; an etchant supply tube linked with the nitrogen gas transfer tube; an etchant supply tank for containing etchant linked with the etchant supply tube; and a chamber with a spray nozzle part linked with the nitrogen gas transfer tube attached to the upper part thereof and a wafer rotating equipment placed in the lower part thereof.  
      Additionally, to achieve the object of the present invention, a method for wafer planarization comprises: emitting nitrogen gas into a transfer tube; mixing the emitted nitrogen gas with etchant; planarizing a wafer by spraying the mixed etchant on the entire surface of wafer through a spraying nozzle part of chamber; and cleaning the wafer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings;  
       FIG. 1   a  through  FIG. 1   c  illustrate a conventional spin type wafer processing equipment.  
       FIG. 2   a  and  FIG. 2   b  illustrate a wafer planarization equipment using high pressure etchant vapor in accordance with the teachings of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
       FIG. 2   a  and  FIG. 2   b  illustrate a wafer planarization equipment using high pressure etchant vapor.  
       FIG. 2   a  is a sketch illustrating a wafer planarization apparatus of the present invention. This wafer planarization apparatus comprises a supply part to provide high pressure etchant and a chamber part  50  for wafer planarization. The supply part comprises a liquid nitrogen (LN 2 ) supply tank  20 , an etchant supply tank  30  and a spraying nozzle part  40  and the chamber part comprises a wafer rotating equipment  45  and a cleaning unit not shown.  
      Referring to  FIG. 2   a , liquid nitrogen at ultra low temperature is stored in the storing tank  20  at high pressure. When a tank valve opens, the pressure decreases so fast that the triple point at which all three phases of solid, liquid and gas can coexist is formed and high pressure is generated. This high pressure makes nitrogen gas vaporized from the liquid nitrogen emit into a nitrogen gas transfer tube  21 . This transfer tube  21  is linked to an etchant supply tube  33 , which is in turn linked to the etchant supply tank  30  containing etchant. At the confluence of the nitrogen gas transfer tube  21  and the etchant supply tube  33 , low pressure is generated due to the nitrogen gas moving through the transfer tube at high speed. Thus, there is significant pressure difference between the confluence at low atmospheric pressure and the etchant supply tube  33  at atmospheric pressure. This significant pressure difference makes the etchant  31  in the etchant supply tank  30  rise through the etchant supply tube  33  and mix with the nitrogen gas. The etchant  31  is stored, dilated with de-ionized water and a sensor  32  attached to the etchant supply tank  30  can detect the remaining volume of the etchant in the store tank. In addition, the exit of the etchant supply tube  33  at the confluence is made of a nozzle so that the etchant rising through this supply tube  33  transforms into fine particles and these particles are mixed with the nitrogen gas. This nitrogen gas plays a role as carrier. The fine particles of the etchant are carried by this nitrogen gas, pass through the transfer tube  21  linked to the chamber part  50 , and then arrive at the spray nozzle part  40  attached to the upper part of the interior of chamber part  50 . There may be plural nozzles in the spray nozzle part  40  so that the etchant can be sprayed uniformly on the entire surface of a wafer through these nozzles. The etchant is sprayed onto the rotating wafer at a high speed as fume of fire particles at a high pressure, due to the fine holes of the nozzles and the high pressure of the nitrogen gas.  
      Further processes for etching are as follows. For example, silicon oxide (SiO 2 ) is positioned on a wafer surface and an etchant is hydrofluoric acid (HF). The silicon oxide reacts with the hydrofluoric acid (HF) as vapor as below. 
 
SiO 2 +HF→SiO 4 ↑+H 2 O↑
 
      The above reaction causes only an isotropic etching which is inappropriate to planarization. Therefore, to induce an anisotropic etching, the wafer is rotated at high speed. By rotating the wafer at high speed and spraying uniformly the etchant of fire particles in vapor, the wafer is etched anisotropically in the same direction as that of the wafer rotation and planarized.  
       FIG. 2   b  represents the wafer rotating equipment  45 . A wafer  51  is put between the top of a clamp  52  and a wafer stage  53  for a fixation by a lift  54  for a loading and an unloading. The clamp  52  is positioned at the upper edge of the stage  53  to fix the wafer. The stage  53  is positioned at the upper part of the lift on which the wafer is positioned. The lift  54  is positioned at the upper part of the rotation actuation. The wafer  51  then rotates by a high speed rotation actuator  55  with a motor. After the wafer  51  is planarized by the etchant in vapor, it is cleaned with de-ionized water sprayed from a cleaning nozzle (not shown).  
      The foregoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.