Abstract:
An apparatus and a method for operating the same. The method includes providing an apparatus which includes a chamber, wherein the chamber includes first and second inlets, an anode and a cathode structures in the chamber, and a wafer on the cathode structure. A cleaning gas is injected into the chamber via the first inlet. A collecting gas is injected into the chamber via the second inlet. The cleaning gas when ionized has a property of etching a top surface of the wafer resulting in a by-product mixture in the chamber. The collecting gas has a property of preventing the by-product mixture from depositing back to the surface of the wafer.

Description:
FIELD OF THE INVENTION 
     The present invention relates to by-products of cleaning processes, and more specifically relates to processes for collecting the by-products resulting from cleaning processes. 
     BACKGROUND OF THE INVENTION 
     In a typical fabrication process for forming a transistor, before forming the two contacting regions to provide electrical paths to the two source/drain regions of the transistor, a cleaning process is performed to remove native oxide layers at bottom walls of the two contact holes. This cleaning process usually creates by-products that may contaminate the surface of the wafer. Therefore, there is a need for a collecting process to prevent these by-products from contaminating the wafer. 
     SUMMARY OF THE INVENTION 
     The present invention provides a device fabrication process. First, an apparatus is provided which includes (a) a chamber, wherein the chamber includes a first inlet and a second inlet, (b) an anode structure in the chamber, (c) a cathode structure in the chamber, wherein the cathode structure is more negatively charged than the anode structure, and (d) a wafer on the cathode structure. Then, a cleaning gas is injected into the chamber via the first inlet. Then, a collecting gas is injected into the chamber via the second inlet. The cleaning gas when ionized has a property of etching a top surface of the wafer resulting in a by-product mixture in the chamber. The collecting gas has a property of preventing the by-product mixture from depositing back to the surface of the wafer. 
     The present invention also provides a fabrication apparatus. The apparatus includes (a) a chamber; (b) an anode structure in the chamber; and (c) a cathode structure in the chamber. The cathode structure is more negatively charged than the anode structure. The apparatus further includes a wafer on the cathode structure; (e) a plasma region formed between the anode structure and the cathode structure; and (f) a cleaning gas in the chamber. The plasma region includes a plasma resulting from an ionization of the cleaning gas in the plasma region. The plasma region includes (g) a collecting gas in the chamber but not in the plasma region. 
     The present invention provides a collecting process that prevents the by-product contamination problem of the prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a cross section view of a semiconductor structure, in accordance with embodiments of the present invention. 
         FIG. 2  illustrates a schematic view of a chamber structure used for processing the semiconductor structure of  FIG. 1 , in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a cross section view of a semiconductor structure  100 , in accordance with embodiments of the present invention. More specifically, in one embodiment, the semiconductor structure  100  comprises a semiconductor (e.g., silicon, . . . ) substrate  110 , a first silicide region  120   a , a second silicide region  120   b , a dielectric layer  130 , a first contact hole  140   a , and a second contact hole  140   b.    
     In one embodiment, the dielectric layer  130  comprises silicon dioxide (SiO 2 ), silicon nitride (Si x N y ), or a low-K carbon containing material. In one embodiment, the first contact hole  140   a  and the second contact hole  140   b  are formed by etching the dielectric layer  130  with RIE (reactive ion etching) until the first and second silicide regions  120   a  and  120   b  are exposed to the surrounding ambient. 
     Assume that two electrical contacting regions (not shown) are to be formed in the first and second contact holes  140   a  and  140   b  so as to provide electrical paths down to the first and second silicide regions  120   a  and  120   b , respectively. As a result, it should be noted that, the surrounding ambient usually has oxygen, therefore, the first and second silicide regions  120   a  and  120   b  chemically react with the oxygen of the surrounding ambient to form native silicon oxide layers (not shown) on the bottom walls of the first and second contact holes  140   a  and  140   b . It should be noted that, the resultant native silicon oxide layers prevent the subsequently formed electrical contacting regions (not shown) from making good electrical contacts with the silicide regions  120   a  and  120   b , respectively. As a result, in one embodiment, a cleaning process is performed to remove the native silicon oxide layers before the electrical contacting regions are formed in the first and second contact holes  140   a  and  140   b . In one embodiment, the cleaning process is performed in the chamber structure  200  ( FIG. 2 ). 
       FIG. 2  illustrates a schematic view of a chamber structure  200  used for processing the semiconductor structure  100  of  FIG. 1 , in accordance with embodiment of the present invention. More specifically, in one embodiment, the chamber structure  200  comprises a grounding shield  210 , a pedestal  230 , a collecting gas exhaust  250 , a collecting gas supply  260   a , a collecting gas inlet  260   a ′, a cleaning gas supply  260   b , a cleaning gas inlet  260   b ′, a chamber wall  270 , a radio frequency source  280 , and a ground connector  290 . 
     In one embodiment, the cleaning process of the semiconductor structure  100  in the chamber structure  200  is as follows. Illustratively, the cleaning process starts with the placing of the semiconductor structure  100  on top of the pedestal  230  in the chamber structure  200  as shown. 
     Next, in one embodiment, the grounding shield  210  is electrically grounded, and the pedestal  230  is electrically connected to the radio frequency source  280 . As a result, the pedestal  230  is negatively charged resulting in the grounding shield  210  being more electrically positive than the pedestal  230 . Therefore, the pedestal  230  becomes a cathode  230  whereas the grounding shield  210  becomes an anode  210 . As a result, an electric field is formed between the cathode  230  and the anode  210 . 
     Next, in one embodiment, a cleaning gas is injected from the cleaning gas supply  260   b  into the chamber structure  200  via the cleaning gas inlet  260   b ′. In one embodiment, the cleaning gas inlet  260   b ′ is disposed in proximity to the wafer  110 . In one embodiment, the cleaning gas comprises argon and HF. Under an electric field energy of the electric field formed between the cathode  230  (the pedestal  230 ) and the anode  210  (the grounding shield  210 ), argon molecules are ionized resulting in a plasma region  220 . It should be noted that, the plasma region  220  includes places in the chamber structure  200  where the electric field energy is stronger than an argon-ionizing threshold. 
     It should be noted that the ionizing potential of Argon is about 15.8 eV. Also, the energy in the plasma region  220  can be higher than this value of 15.8 eV. This is because of the following two reasons. First, electron energy follows a Maxwell-Boltzmann distribution, resulting in some points in the plasma region  220  necessarily having energy higher than 15.8 eV. Second, Thermal exicitation can drive energies higher than 15.8 eV. 
     The ionization of the argon molecules provides electrons and argon ions for the plasma region  220 . Under the electric field energy, the electrons travel toward the grounding shield  210  (the anode  210 ). Also under the electric field energy, the argon ions travel toward the pedestal  230  (the cathode  230 ) and bombard the native silicon oxide layers of the semiconductor structure  100 . 
     It should be noted that, while the argon ions bombard and the HF chemically reacts with the native silicon oxide layers resulting in the native silicon oxide layers being removed, the argon ions also bombard and the HF also chemically reacts with the dielectric layer  130  of the semiconductor structure  100  resulting in by-product particles of the cleaning process. 
     It should be noted that, the by-product particles of the cleaning process are dispersed into inner space of the chamber structure  200 . Some of the by-product particles adhere to the chamber wall  270  while some others of the by-product particles deposit back onto the semiconductor structure  100 . The deposition back of the by-product particles to the semiconductor structure  100  is not good for the formation of the electrical contacting regions in the first and second contact holes  140   a  and  140   b  (with reference to  FIG. 1 ). As a result, in one embodiment, a by-product collecting process is performed simultaneously with the cleaning process so as to prevent the deposition back of the by-products to the semiconductor structure  100  or to a next semiconductor structure (not shown) being subsequently processed in the chamber structure  200 . 
     In a first embodiment, assume that the dielectric layer  130  comprises silicon dioxide (SiO 2 ). As a result, the by-product of the cleaning process comprises silicon dioxide. It should be noted that, silicon dioxide adheres well to the chamber wall  270 . As a result, the by-product collecting process may be omitted in this case. 
     In a second embodiment, assume alternatively that the dielectric layer  130  comprises silicon nitride (Si x N y ). As a result, a first by-product mixture comprising N 2 , Si, and silicon nitride (Si x N y ) is created by the cleaning process. In this case, in one embodiment, during the by-product collecting process, a first collecting gas is injected from the collecting gas supply  260   a  into the chamber structure  200  via the collecting gas inlet  260   a ′. In one embodiment, the collecting gas inlet  260   a ′ is disposed in proximity to the chamber wall  270 . 
     Illustratively, the first collecting gas comprises N 2  and NF 3 . As a result, the first collecting gas serves as a catalyst to enhance the formation of Si 3 N 4  from the first by-product mixture. It should be noted that Si 3 N 4  adheres adequately to the chamber wall  270 . As a result, this essentially prevents the first by-product mixture of the cleaning process from depositing back to the semiconductor structure  100  or to the next semiconductor structure being subsequently processed in the chamber structure  200 . 
     In a third embodiment, assume alternatively that the dielectric layer  130  comprises a low-K carbon containing material or more generally a carbon containing dielectric material (such as polyimide). As a result, a second by-product mixture comprising carbon (C) and carbon containing materials is created by the cleaning process. In one embodiment, during the by-product collecting process, a second collecting gas from the collecting gas supply  260   a  is injected into the chamber structure  200  via the collecting gas inlet  260   a′.    
     In one embodiment, the second collecting gas comprises ionized hydrogen. As a result, the ionized hydrogen chemically reacts with the carbon (C) and carbon containing materials to form hydrocarbon gases. One of the resulting hydrocarbon gases can be methane (CH 4 ). 
     In one embodiment, the resulting hydrocarbon gases formed by the by-product collecting process are pumped out of the chamber structure  200  via the collecting gas exhaust  250 . As a result, this essentially prevents the second by-product mixture of the cleaning process from depositing back to the semiconductor structure  100  or to the next semiconductor structure being subsequently processed in the chamber structure  200 . 
     It should be noted that the ionized hydrogen of the second collecting gas is positively charged. It should also be noted that the plasma region  220  comprises argon ions, which are positively charged. As a result, the ionized hydrogen tends to stay away from the plasma region  220 . 
     In one embodiment, the first and second collecting gases are ionized before being injected into the chamber structure  200  via the collecting gas inlet  260   a ′. In one embodiment, the first and second collecting gases are injected into the chamber structure  200  but outside the plasma region  220 . 
     In one embodiment, the semiconductor structure  100  can be a transistor and the cleaning process and the by-product collecting process can be performed before filling the first and second contact holes  140   a  and  140   b  with the two electrical contacting regions. 
     In summary, the cleaning process to remove the native silicon oxide layers may create the unwanted by-product particles that may deposit back to the semiconductor structure  100  or to the next semiconductor structure being subsequently processed in the chamber structure  200 . 
     If the dielectric layer  130  comprises silicon nitride (Si x N y ), then the cleaning process creates the first by-product mixture of N 2 , Si, and silicon nitride (Si x N y ). As a result, the first collecting gas comprising N 2  and NF 3  serves as the catalyst to enhance the formation of Si 3 N 4 , which adheres adequately to the chamber wall  270 . 
     If the dielectric layer  130  comprises a low-K carbon containing material, then the cleaning process creates the second by-product mixture of carbon (C) and carbon containing materials. As a result, the second collecting gas comprising ionized hydrogen chemically reacts with the second by-product mixture to form hydrocarbon gases which can be simultaneously pumped out of the chamber structure  200 . 
     In short, the by-product collecting process essentially prevents the by-product particles of the cleaning process from depositing back to the semiconductor structure  100  or to the next semiconductor structure being subsequently processed in the chamber structure  200 . 
     In the embodiments described above, the cleaning gas and the collecting gas are introduced simultaneously into the chamber structure  200  via the cleaning gas supply  260   b  and the collecting gas supply  260   a , respectively. Alternatively, the cleaning gas and the collecting gas can be introduced into the chamber structure  200  via a single gas inlet (not shown) alternatingly. That is a first amount of the cleaning gas is first introduced into the chamber structure  200  via the single gas inlet. Then, a second amount of the collecting gas is introduced into the chamber structure  200  via the single gas inlet. Then, a third amount of the cleaning gas is introduced into the chamber structure  200  via the single gas inlet, and so on. 
     In the embodiments described above, with reference to  FIG. 1 , the regions  120   a  and  120   b  comprise a silicide material (e.g., nickel silicide). Alternatively, the regions  120   a  and  120   b  can comprise copper, aluminum, or tungsten, etc. 
     While particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.