Patent Publication Number: US-2005115672-A1

Title: Chemical etching process and system

Description:
FIELD OF THE INVENTION  
      The present invention relates to a method and apparatus for etching devices and cleaning thin disks, for example semiconductor wafers, glass substrates, photomasks and compact disks. More particularly, the present invention applies Bernoulli theorem to generate an instantaneous local vacuum effect on a surface of a working object by injecting an air stream, so as to easily remove residues residing in the trenches or on the surface of the working object. By suitably controlling an etchant spray and an air injection, an etching rate not only can be continuously kept steady, but also a maximum etching depth can be dramatically increased. Also, the present invention can be used for cleaning semiconductor devices with an extremely small gate width.  
     BACKGROUND OF THE INVENTION  
      In semiconductor fabrication processes, wet etching mainly uses chemical reactions between a thin film material and a specific solution to remove the thin film not covered by photo-resist. Traditional wet etching process is to first submerse a thin film material into a specific etchant for etching and then control the concentration of the etchant, the etching time, the reaction temperature, the uniformity of the etchant by stirring, and other parameters. However, in the etching process, the etchant is continuously consumed and thus lowers the concentration thereof and even forms a non-uniform concentration distribution of the etchant. Although the non-uniform etchant will increasingly become uniform through diffusion mechanism or mass transfer by stirring, it is relatively slow to get a uniform etchant or hard to control the uniformity thereof. Moreover, after the thin film material is etched, it needs to be transferred to another place for cleaning residues and the etchant residing in the trenches or on the surface thereof. In the meantime, the etchant residing in the trenches thereof still continues to etch. This will result in an inaccurate control of the etching time.  
      In addition, there is a conventional high-speed-spin etching table used for the etching process, which generates a relative movement between a surface of a working object to be etched and airflow there above. According to the Bernoulli effect, when the high-speed airflow flows over the surface of the working object, a negative pressure even vacuum occurs on the surface thereof, which can suck out residues residing in the trenches or on the surface of the working object. However, the magnitude of the negative pressure generated by this method will be decreasing with approaching to the rotational axis of the working object due to a smaller tangential velocity, which is equal to the angular velocity multiplied by the radius of rotation thereof. Therefore, the negative pressure might be not enough to suck out the residues residing in the trenches or on the surface close to the center of rotation of the working object. This method not only needs a driving power to rotate the etching table, but also the etching table is hard to be quickly accelerated and decelerated to a desired state due to the inertia effect. And it is impossible to spray etchant onto the working object and suck out the residues simultaneously at a high-speed rotation. Furthermore, more power needs to be input for getting a desired negative pressure or vacuum. Therefore, the method cannot effectively generate an enough negative pressure. And the high-energy consumption will also increase the production cost. The vacuum effect due to a high-speed rotation is proportional to the square of the radius of rotation. Therefore, the etching ability becomes a function of the radius of rotation, and thus the uniformity of products is highly influenced.  
      In view of the above problems, the present invention provides with a better chemical etching process and apparatus.  
     SUMMARY OF THE INVENTION  
      An object of the present invention is to provide with a chemical etching process and apparatus, which applies Bernoulli theorem to generate an instantaneous local vacuum effect on a surface of a working object through injecting an air stream. Furthermore, the present invention provides with an etchant spray system and an etching table, which allows the working object to be moved in translation or rotation. Also, by suitably controlling the etching time, the concentration of etchant and the uniformity of etchant and quickly cleaning residues or etchant on the surface of the working object can achieve an optimum etching and cleaning result.  
      To achieve the above objects, a chemical etching process and apparatus according to the present invention comprises at least a control unit, an etching unit, an etchant supply unit and an air supply unit. Various process parameters can be input through a programmable electronic device of the control unit to control the operations of the etching unit, the etchant supply unit and the air supply unit. The etching unit has an etching table incorporated with the etchant supply unit and the air supply unit for providing a proper etching environment for the working object. Respective flow control valves and electromagnetic valves of the etchant unit and the air supply unit, which are controlled by the control unit, can be used to adjust the etchant flow rate and the airflow rate.  
      The objects, features and effectiveness of the present invention will be readily understood to those skilled in the art after reading the detailed description of the preferred embodiment thereof in reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention will be apparent to those skilled in the art by reading the following description of a preferred embodiment thereof, with reference to the attached drawings, in which:  
       FIG. 1  illustrates a framework of a chemical etching process and apparatus according to the present invention;  
       FIG. 2  is a drawing of schematically illustrating a part of the chemical etching apparatus of the present invention; and  
       FIG. 3  is a flow diagram of the chemical etching process of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Referring to  FIG. 1 , a chemical etching process and apparatus according to the present invention comprises a control unit  10 , an etching unit  20 , an etchant supply unit  30  and an air supply unit  40 . The control unit  10  has a programmable electronic device through which various process parameters are input to control the operations of the etching unit  20 , the etchant supply unit  30  and the air supply unit  40 . The etching unit  20  has an etching table incorporated with the etchant supply unit  30  and the air supply unit  40  for providing a proper etching environment for a working object to be etched. The etchant supply unit  30  is an apparatus for supplying etchant, which is equipped with flow control valves and electromagnetic valves respectively for controlling the flow rate and the on/off operation of etchant supply through the control unit  10 . Also, the air supply unit  40  is an apparatus for injecting air, which is equipped with flow control valves and electromagnetic valves respectively for controlling the flow rate and the on/off operation of air stream through the control unit  10 .  
      The etching unit  20  comprises an etching table having a driving gear (not shown in Figures) for moving the working object in translation or rotation. The driving gear has a position control element and a speed control element (not shown in Figures). The control unit  10  respectively outputs a control signal to the position control element and the speed control element for controlling the position and the speed of the working object.  
      The control unit  10  outputs a control signal to the flow control valves and the electromagnetic valves of the etchant supply unit  30  for controlling the etchant flow rate and the on/off operation of etchant supply.  
      Also, the control unit  10  outputs a control signal to the flow control valves and the electromagnetic valves of the air supply unit  40  for controlling the airflow rate and the on/off operation of air supply.  
      Referring to  FIG. 2 , which illustrates a schematic view of a part of the chemical etching apparatus of the present invention, the etching unit  20  comprises an etching table for the etching work of the working object  21 . The etchant supply unit  30  and the air supply unit  40  respectively comprise a spray element  31  and an air nozzle  41  for spraying etchant and injecting air. The spray element  31  and the air nozzle  41  are positioned in accordance with the etched direction of the working object  21 .  
      The etching table of the etching unit  20  has a driving gear (not shown) for tightly fixing the working object  21  so as to drive it rotate.  
      The spray element  31  has a proper opening of etchant spray, at which the outlet pressure of the etchant varies with the flow rate thereof supplied from the etchant supply unit  30 .  
      The spray element  31  can be multiple arranged in proper positions for matching with the etching process of the working object.  
      Therefore, the multiple spray elements  31  can respectively supply various etchants, buffer solutions or de-ionized water in accordance with the needs of the etching process.  
      The air nozzle  41  can be multiple arranged in proper positions above the surface of the working object  21  for matching with the needs of the etching process. Each of included angles  25  between each of the air nozzles  41  and the corresponding horizontal line  23  thereof can be respectively adjusted depending on actual needs of the etching process. The included angles  25  are between 0-30 degrees.  
      The air nozzle  41  has a proper opening of air injection, at which the outlet pressure of air varies with the injected airflow rate from the air supply unit  40 .  
      The direction of the air injection from the air nozzle  41  and the horizontal line  23  being parallel to the surface of the working object  21  form the included angle  25 , which can be horizontal.  
      The opening of the air nozzle  41  can be flat.  
      The air supplied from the air supply unit  40  can be instead of nitrogen gas (N2).  
      Referring to  FIG. 3 , which illustrates a flow diagram of a complete chemical etching process according to the present invention, step  501  is to install a working object  21  to be etched onto the etching table of the etching unit  20 . Step  502  is to apply the driving gear of the etching unit  20  to tightly fix and then move the working object  21  through the control of the control unit  10 . Step  503  is to spray an adequate quantity of etchant and stop the etchant spray after a preset time through the control unit  10  controlling flow control valves and electromagnetic valves of the etchant supply unit  30 . The working object  21  will be etched in the period of the etchant contacting with the surface thereof. Step  504  is to start to inject an adequate quantity of air in the time t after step  503  through the control unit  10  controlling flow control valves and electromagnetic valves of the air supply unit  40 . The injected air is used for removing residues residing in the trenches or on the surface of the working object  21 . Step  505  is to stop the injecting air supply through the control unit  10  controlling the flow control valves and the electromagnetic valves of the air supply unit  40 . Step  506  is to judge through the control unit  10  if the repeated etching time in total attains the required preset etching times. If not, then return to step  503  and continue to perform step  503  through step  506 . If yes, then proceed to step  507  for further process. Step  507  is to determine through the control unit  10  if the etchant needs to be replenished. If yes, then replenish the etchant and return to step  503 . If not, proceed to step  508 . Step  508  is to stop the rotation of the etching table of the etching unit  20  and then take out the finished working object  21  through the control of the control unit  10 .  
      In Step  3 , one of the multiple spray elements of the etchant supply unit  30  can be selected as spraying buffer solution for meeting with the needs of the etching process.  
      In addition, in Step  507 , the alternative to replenishing etchant for the etchant supply unit  30  is to replace with de-ionized water, so that the step  503  becomes a cleaning step for cleaning the surface of the working object  21 . The leaning frequency is determined by step  506 .  
      In addition, step  503  through step  507  can be RCA cleaning method.  
      The features of the present invention are summarized as followings:  
      (1) A chemical etching apparatus according to the present invention applies Bernoulli theorem to generate an instantaneous local vacuum effect on the surface of a working object through injecting an air stream with a special included angle with the surface of the working object, which can easily remove residues residing in the trenches or on the surface of the working object. In the meantime, the etchant is continuously replenished from the etchant supply unit so as to keep the etching rate steady.  
      (2) Additionally, if the above etching process is changed to be a cleaning process, in which etchants shall be instead of cleaning solutions, residues residing in the trenches or on the surface of the etched object will be cleaned/sucked out and a drying result will be further attained. The cleaning method can also be used for removing impurities in the trenches of a wafer for a semiconductor fabrication process.  
      (3) The chemical etching apparatus of the present invention can control the etching time and the concentration of etchant through the control unit so as to attain an intermittent etching reaction. Therefore, an over-etching problem of a conventional wet etching process due to improper control of the etching time can be avoided.  
      (4) The method for generating an instantaneous vacuum effect on the surface of the working object not only can shorten the time to reach a vacuum effect but also is favorable to the intermittent etching control. Moreover, the required energy for injecting air is very small relative to that for driving a high-speed spin etching table.  
      The chemical etching process and apparatus of the present invention can sufficiently clean the residues residing in the trenches of the surface of the working object and thereby avoid the hindrance of etchant approaching to and contacting with the surface thereof and obtain an optimum etching depth and an optimum cleaning result with high efficiency, energy saving and the convenience in controlling the intermittent air injection.  
      The above statement is only for illustrating the preferred embodiment of the present invention, and not for giving any limitation to the scope of the present invention. It will be apparent to those skilled in this art that all equivalent modifications and changes shall fall within the scope of the appended claims and are intended to form part of this invention.