Abstract:
A method of cleaning a turbo pump is described. The turbo pump is coupled with a CVD chamber of depositing a material and thus accumulates the material therein. The method includes switching off the turbo pump and using another pump to pump a reactive gas, which can react with the material to form gaseous products, through the turbo pump. Thereby, the turbo pump is cleaned up and is prevented from being a particle source in subsequent CVD operations.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This is a continuation application of an application Ser. No. 11/754,806, filed May 29, 2007. The entirety of the above-mentioned patent are hereby incorporated by reference herein and made a part of this specification. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to maintenance of equipment used in integrated circuit (IC) manufacture, and more particularly to a method of cleaning a turbo pump installed to a chemical vapor deposition (CVD) chamber and a chamber/turbo pump clean process based on the same method. 
       BACKGROUND OF THE INVENTION 
       [0003]    The CVD technology is widely utilized in IC fabricating processes. For a CVD process needing low pressure like a LPCVD or high-density plasma CVD (HDP-CVD) process, a vacuum pump is installed to the deposition chamber. For a traditional pump like a rotary pump can merely make a low pressure in the order of mTorr, it is usually used in combination with a turbo pump as the required pressure is in the order of Torr. 
         [0004]    An exemplary structure of a HDP-CVD system for depositing silicon oxide with a rough pump for rough pumping and a turbo pump is shown in  FIG. 1 . The chamber  100  has therein a wafer chuck  110  and gas inlets  120 . The rough pump  140  is coupled with the chamber  100  via a rough line  130 , the turbo pump  150  is coupled with the same by a gate valve, and the rough pump  140  is contiguous with the turbo pump  150  via a foreline  160 . In the CVD process, the throttle valve of the rough line  130  is closed but the gate valve is opened, and the rough pump  140  and the turbo pump  150  are both switched on. The unreacted gases and the by-products are conducted from the chamber  100  and through the gate valve, the turbo pump  150 , the foreline  160  and the rough pump  140  and then exhausted to a pipeline (not shown). 
         [0005]    Because silicon oxide film also accumulates in the chamber  100  to be particle source, the chamber  100  has to be cleaned after being used to process a plurality of wafers. In such a clean process, a halogen-containing gas and its reactive radical capable of reacting with silicon oxide to form gaseous products, such as NF 3  and fluorine radical, is delivered through the gas inlets  120  into the chamber  100  with the throttle valve of the rough line  130  opened, the gate valve closed and the rough pump  140  switched on, as shown in  FIG. 1 . However, even with such a chamber clean step, the reduction in particle number and the mean wafer between clean (MWBC) success ratio are still limited due to the unstable non-lot and inline particle performance. 
         [0006]    The particles are suspected to come from the turbo pump  150  because the particles accumulated in the turbo pump  150  may be streamed back to the chamber  100  during a pressure transition of the film formation process. The silicon oxide particles inside the turbo pump  150  cannot be effectively removed by NF 3  and fluorine radical because the gate valve is closed in the chamber clean step and the chamber  100  is non-contiguous with the turbo pump  150 . 
       SUMMARY OF THE INVENTION 
       [0007]    In view of the foregoing, this invention provides a method of cleaning a turbo pump coupled with a CVD chamber, which can effectively remove the particles of the deposited material accumulated in the turbo pump. 
         [0008]    This invention also provides a chamber/turbo pump clean process based on the above method of cleaning a turbo pump. 
         [0009]    The method of cleaning a turbo pump of this invention is applied to a turbo pump coupled with a CVD chamber for depositing a material and having accumulated the material therein. The method includes using another pump to pump a reactive gas, which can react with the material to form gaseous products, through the turbo pump. 
         [0010]    In many cases of Si-based IC industry, the material deposited in a CVD chamber is a Si-containing material like silicon oxide, silicon nitride or poly-Si, and the reactive gas is a halogen-containing gas that may include at least one of NF 3  and F-radical. 
         [0011]    The chamber/turbo pump clean process of this invention is based on the method of cleaning a turbo pump of this invention, including at least a chamber clean step and a turbo-pump clean step performed in sequence. In the chamber clean step, the reactive gas is injected into the CVD chamber to remove at least a portion of the material therein. In the turbo pump clean step, another pump is used to pump, from the CVD chamber, the reactive gas through the turbo pump. 
         [0012]    It is particularly noted that in the whole specification and claims of this invention, a pump being contiguous with the CVD chamber means that gas can be drawn from the chamber to it without passing another pump, and a pump is still deemed non-contiguous with the chamber even if it can draw gas from the chamber through another pump. 
         [0013]    By using the method of cleaning a turbo pump of this invention, the material accumulated in a turbo pump coupled with a CVD chamber can be removed effectively, so that the turbo pump is no longer a particle source of the corresponding CVD process. 
         [0014]    In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
           [0016]      FIG. 1  shows an exemplary structure of a HDP-CVD system with a rough pump and a turbo pump as well as a chamber clean step in the prior art. 
           [0017]      FIG. 2  depicts a method of cleaning a turbo pump coupled with a CVD chamber according to a first embodiment of this invention. 
           [0018]      FIG. 3  shows a flow chart of a chamber/turbo pump clean process according to the first embodiment of this invention. 
           [0019]      FIG. 4  shows a flow chart of a chamber/turbo pump clean process according to a second embodiment of this invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0020]    The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed. 
         [0021]    It is particularly noted that though the deposited material is a silicon-containing one, the reactive gas is a halogen-containing gas and the CVD system discussed is the illustrated one in the following embodiments of this invention, the invention can also be applied to a CVD system having other configuration and/or depositing other genus of material, if only a suitable reactive gas can be found and the piping design of the CVD system allows another pump to pump the reactive gas through the turbo pump. 
         [0022]    In addition, though the (non-)contiguity state of the rough pump with the CVD chamber is controlled by a throttle valve of a rough line and the (non-) contiguity state of the turbo pump with the CVD chamber is controlled by a gate valve in the following embodiments, the states may alternatively be controlled by other means. 
       First Embodiment 
       [0023]      FIG. 2  depicts a method of cleaning a turbo pump coupled with a CVD chamber according to the first embodiment of this invention. The structure of the chamber  100  and the arrangement of the chamber  100 , the rough pump  140 , the turbo pump  150 , the rough line  130  and the foreline  160  are all the same as the above mentioned. However, in the method of this embodiment, the turbo pump  150  is switched off, the throttle valve of the rough line  130  between the chamber  100  and the rough pump  140  is closed to make the rough pump  140  non-contiguous with the chamber  100 , and the gate valve between the chamber  100  and the turbo pump  150  is opened to make the turbo pump  150  contiguous with the chamber  100  and make the cleaning gas flow through the turbo pump  150  to remove the particles. 
         [0024]    The chamber  100  may be a HDP-CVD chamber used in a process requiring a very low pressure. The wafer chuck  110  may be an electrostatic chuck of mono-polar type or bi-polar type or their combination. The deposited material may be silicon oxide, silicon nitride or poly-Si. 
         [0025]    Because the rough pump  140  is contiguous with the turbo pump  150  via the foreline  160 , closing the throttle valve of the rough line  130  and opening the gate valve makes the reactive gas (e.g., NF 3  and fluorine radical) injected into the chamber  100  to be pumped, from the chamber  100 , through the turbo pump  150  and foreline  160  by the rough pump  140 , as illustrated in  FIG. 2 . Therefore, the silicon-containing material accumulated in the turbo pump  150  can be removed effectively. 
         [0026]    In the above method, the duration of pumping the halogen-containing gas through the turbo pump  150  may range from 600 seconds to 3600 seconds. Moreover, it is preferred to heat up the turbo pump  150  after the turbo pump  150  is switched off but before the throttle valve of the rough line  130  is closed, so as to increase the rate of the reaction between the Si-containing material and the halogen-containing gas and improve the cleaning efficiency. 
         [0027]    The above method may be applied every a constant number of wafers, such as every 500 wafers, processed in the chamber  100  and/or be applied during a preventive maintenance (PM) of the chamber  100 , in which each part of the CVD system is cleaned thoroughly and the dome of the chamber  100  replaced by a new one. 
         [0028]    In addition, when the above method is to be applied every a constant number of wafers processed in the chamber  100 , the thickness of the silicon-containing material accumulated in the chamber  100  may be checked in advance. When the thickness is checked to be not larger than a tolerable value, the method is applied without a clean step of the chamber  100  using the halogen-containing gas as a reactive gas before it. When the thickness is checked to be larger than the tolerable value, the method is applied after a clean step of the chamber  100  using the halogen-containing gas. The purpose of the thickness checking is to save unnecessary chamber cleaning. 
         [0029]    In addition, when the above method is applied during a preventive maintenance (PM) of the chamber  100 , it is usually applied after a clean step of the chamber  100  that uses the halogen-containing gas as the reactive gas. 
         [0030]      FIG. 3  shows a flow chart of a chamber/turbo pump clean process according to the first embodiment of this invention, wherein the reactive gas is a F-containing gas or F-radical.  FIGS. 1-2  are also referred to in the following descriptions of the same. 
         [0031]    Firstly, a CVD chamber having been used on a number (e.g., ˜500) of wafers or having been subjected to preventive maintenance planning is provided (step  300 ). 
         [0032]    In the step  302 , the gate valve between the chamber  100  and the turbo pump  150  is closed to make the turbo pump  150  non-contiguous with the chamber  100 , the throttle valve of the rough line  130  between the chamber  100  and the rough pump  140  is opened to make the rough pump  140  contiguous with the chamber  100 , and the rough pump  140  and turbo pump  150  both are kept switched on, as shown in  FIG. 1 . 
         [0033]    In next step  304 , a high-flow clean step is performed to the chamber  100 , wherein the F-containing gas or F-radical is injected from the gas inlets  120  and the flow rate of the same is set such that the pressure in the chamber  100  is in the order of Ton, so as to remove at least a portion of the Si-containing material accumulated on the inner wall of the CVD chamber  100  above a level approximately corresponding to the position of the wafer chuck  110 , as indicated by the dash lines in  FIG. 1 . 
         [0034]    After the high-flow clean step, a low-flow clean step can be performed (step  306 ) in option, wherein the flow rate of the F-containing gas or F-radical injected from the gas inlets  120  is set such that the pressure in the CVD chamber is in the order of mTorr, so as to remove at least a portion of the silicon-containing material on the inner wall of the CVD chamber  100  below the level indicated by the dash lines in  FIG. 1 . 
         [0035]    The high-flow and low-flow clean steps together constitute a chamber clean step. Alternatively, the chamber clean step may include only an above high-flow clean step as a single clean step, because the material accumulated on the inner wall above the level affects the particle numbers on wafers much more that that on the inner wall below the level due to the gravity and the substantially downward gas flow caused by the pumps. 
         [0036]    In next step  308 , the turbo pump  150  switched off, the throttle valve of the rough line  130  between the chamber  100  and the rough pump  140  is closed to make the rough pump  140  non-contiguous with the chamber  100  and the gate valve between the chamber  100  and the turbo pump  150  is opened to make the turbo pump  150  contiguous with the chamber  100 , as shown in  FIG. 2 , so as to clean the turbo pump  150 . The cleaning mechanism has been described above, and the duration of the turbo pump clean step may range from 600 seconds to 3600 seconds. Moreover, it is preferred to heat up the turbo pump  150  after the turbo pump  150  switched off but before the throttle valve of the rough line  130  is closed to improve the cleaning efficiency, as mentioned above. 
         [0037]    In next step  310 , the throttle valve of the rough line  130  between the chamber  100  and the rough pump  140  is opened to make the rough pump  140  contiguous with the chamber  100 , and the gate valve between the chamber  100  and the turbo pump  150  is closed previously to make the turbo pump  150  non-contiguous with the CVD chamber  100 , as shown in  FIG. 1 . It is noted that the fluorine-containing gas or fluorine radical is not supplied from the gas inlets  120  at this moment. 
         [0038]    In next step  312 , an H 2 -passivation step is performed to the CVD chamber  100  to remove the fluorine remaining inside the chamber  100  after the step of cleaning the turbo pump  150 , by means of reactions between hydrogen and fluorine. The reaction gas used therein may include H 2 , Ar and O 2 , and plasma is generated from the reaction gas with suitable RF power allowing reactions between hydrogen and fluorine to occur. 
         [0039]    In addition, when the reaction gas used in the H2-passivation step contains H 2  and O 2 , moisture is also formed in the CVD chamber  100  by the reaction between hydrogen and oxygen caused by the plasma. In such a case, it is preferred to bake the chamber  100  (step  314 ) at a temperature higher than 100° C. after the H 2 -passivation step and remove the moisture in the chamber  100  for the processing of subsequent wafers. 
         [0040]    In addition, the above chamber/turbo pump clean process may be applied every a constant number of wafers, such as every 500 wafers, processed in the CVD chamber and/or be applied during a preventive maintenance of the chamber  100 . In a chamber/turbo pump clean process applied every a constant number of wafers processed in the chamber  100 , the period of the high-flow clean step is preferably shorter to prevent overheating of the dome of the chamber  100 . In a chamber/turbo pump clean process applied during the preventive maintenance, the period of the high-flow clean step is set longer before the dome replacement of the chamber  100  to confirm that there is enough clean time for the particles in the turbo pump  150  to be removed completely. 
         [0041]    Moreover, when the above chamber/turbo pump clean process is to be applied every a constant number of wafers processed in the chamber  100 , it may be conducted after the thickness of the silicon-containing material accumulated in the CVD chamber  100  is checked to be larger than a tolerable value. 
         [0042]    Furthermore, to make a CVD chamber  100  having been subjected to the above chamber/turbo pump clean process ready for the processing of subsequent wafers, a pre-coating step is usually conducted after the above chamber/turbo pump clean process to deposit a thin film, generally a thin oxide film, on the inner wall of the CVD chamber  100 , so as to condition the chamber environment in advance for the wafer-to-wafer repeatability between the wafers processed before the above clean process and those processed after the above clean process. 
       Second Embodiment 
       [0043]      FIG. 4  shows a flow chart of a chamber/turbo pump clean process according to the second embodiment of this invention, wherein the reactive gas is also a fluorine-containing gas or fluorine radical. This process features a shorter equipment up-time, such as one shorter by 4%, as compared with that of the first embodiment.  FIG. 1  is also referred to in the following descriptions. 
         [0044]    The chamber/turbo pump clean process is conducted after the thickness of the material accumulated in the chamber is checked to be larger than a tolerable value, and the check is conducted every a less number of wafers, such as 25 wafers, or a whole lot of wafers processed in the CVD chamber  100 . 
         [0045]    In the step  400 , a chamber in which the thickness of the accumulated material is larger than a tolerable value is provided. In the step  402 , the gate valve between the chamber  100  and the turbo pump  150  is closed to make the turbo pump  150  non-contiguous with the chamber  100 , the throttle valve of the rough line  130  between the CVD chamber  100  and the rough pump  140  is opened to make the rough pump  140  contiguous with the chamber  100 , and the rough pump  140  and the turbo pump  150  both are kept switched on, as shown in  FIG. 1 . 
         [0046]    In next step  404 , a high-flow clean step is performed to the chamber  100 , wherein the F-containing gas or F-radical is injected from the gas inlets  120 , and the flow rate of the same is set such that the pressure in the chamber  100  is in the order of Torr, so as to remove at least a portion of the Si-containing material accumulated on the inner wall of the CVD chamber  100  above a level approximately corresponding to the position of the wafer chuck  110  and as indicated by the dash lines in  FIG. 1 . 
         [0047]    After the high-flow clean step, a low-flow clean step can be performed (step  406 ) in option, wherein the flow rate of the fluorine-containing gas injected from the gas inlets  120  is set such that the pressure in the CVD chamber is in the order of mTorr, so as to remove at least a portion of the silicon-containing material on the inner wall of the CVD chamber  100  below the level indicated by the dash lines in  FIG. 1 . 
         [0048]    The high-flow and low-flow clean steps constitute a chamber clean step, but the chamber clean step may alternatively include only an above high-flow clean step. 
         [0049]    In next step  408 , the throttle valve of the rough line  130  between the chamber  100  and the rough pump  140  is closed to make the rough pump  140  non-contiguous with the chamber  100  and the gate valve between the chamber  100  and the turbo pump  150  is operationally opened and closed in turns to make the turbo pump  150  alternately contiguous and non-contiguous with the chamber  100  to clean the turbo pump  150 , wherein the turbo pump  150  is kept at the on-state. In such an embodiment, the duration of the turbo pump clean step may range from 1 second to 10 seconds. Moreover, it is preferred to heat up the turbo pump  150  before the clean step to improve the cleaning efficiency, as mentioned above. The turbo pump may be made contiguous and non-contiguous with the CVD chamber for at least three cycles. 
         [0050]    In next step  410 , the throttle valve of the rough line  130  between the chamber  100  and the rough pump  140  is opened to make the rough pump  140  contiguous with the chamber  100 , and the gate valve between the chamber  100  and the turbo pump  150  is closed to make the turbo pump  150  non-contiguous with the CVD chamber  100 , as shown in  FIG. 1 . It is noted that the fluorine-containing gas or fluorine radical is not supplied from the gas inlets  120  at this moment. 
         [0051]    In next step  412 , an H 2 -passivation step is performed to the CVD chamber  100  to remove the fluorine remaining inside the chamber  100  after the step of cleaning the turbo pump  150 . In next step  414 , the chamber  100  is baked at a temperature higher than 100° C. to remove the moisture in the chamber  100 . The details of the steps  412  and  414  are the same as those mentioned in the first embodiment. 
         [0052]    By using the method of cleaning a turbo pump of this invention, the material accumulated in a turbo pump coupled with a CVD chamber can be removed effectively and completely so that the turbo pump is no longer a particle source. 
         [0053]    While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.