Patent Publication Number: US-2011061684-A1

Title: Cleaning method for semiconductor wafer

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2009-208231, filed on Sep. 9, 2009, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a cleaning method for a semiconductor wafer. 
     BACKGROUND 
     According as device pattern is being thinned by development of the semiconductor manufacturing technology, there is desired a cleaning technology capable of removing particles as finer pollutant material from a semiconductor wafer. 
     Hitherto, a two-fluid jet cleaning apparatus as a single wafer cleaning apparatus is constituted as described below. Namely, droplet (droplet mist) in which gas such as dry air or nitrogen, etc. and liquid such as deionized water, etc. are mixed so that they are misted is jetted onto the surface of a rotating semiconductor wafer. 
     Along with this jet operation, scanning is performed from the central part of the semiconductor wafer in a direction of the outer peripheral part. Thus, particles on the semiconductor wafer are removed and cleaned. 
     Moreover, there is also known a technology in which such two-fluid jet cleaning apparatus is applied to remove particles by the lift-off action by using APM (mixed liquid of ammonia, hydrogen peroxide water and water, etc.) (see Japanese Patent Laid-Open No. 2004-335671). 
     However, in the case where particles attached on the semiconductor wafer surface is fine even with the above-described two-fluid jet cleaning apparatus, it was difficult to remove such fine particles (e.g., particle having height not more than 70 nm). 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
       A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. 
         FIG. 1  is a measurement diagram of film thickness of water on a semiconductor wafer; 
         FIG. 2A  is a model diagram indicating the state immediately before a droplet collides; 
         FIG. 2B  is a model diagram indicating the state immediately after a droplet has collided; 
         FIG. 3  is a diagram showing particle removal efficiency by two-fluid jet cleaning using deionized water; 
         FIG. 4  is a conceptual diagram of a two-fluid jet cleaning apparatus according to a first embodiment of the present invention; 
         FIG. 5  is a model diagram showing the surface state of a semiconductor wafer according to the first embodiment of the present invention; 
         FIG. 6  is a diagram showing particle removal efficiency by two-fluid jet cleaning using dilute IPA aqueous solution according to the first embodiment of the present invention; 
         FIG. 7  is a model diagram showing the surface state of a semiconductor wafer according to a second embodiment of the present invention; 
         FIG. 8  is a model diagram showing the surface state of a semiconductor wafer according to a third embodiment of the present invention; 
         FIG. 9  is a model diagram showing the surface state of a semiconductor wafer according to a fourth embodiment of the present invention; 
         FIG. 10  is a conceptual diagram schematically representing the main part of a cleaning apparatus for a semiconductor wafer according to a fifth embodiment of the present invention; 
         FIG. 11  is a cross sectional diagram of a two-fluid jet nozzle according to the fifth embodiment of the present invention; 
         FIG. 12  is a model diagram showing the surface state of a semiconductor wafer according to the fifth embodiment of the present invention; 
         FIG. 13  is a conceptual diagram schematically representing the main part of a cleaning apparatus for a semiconductor wafer according to a first modified example of the fifth embodiment of the present invention; 
         FIG. 14  is a conceptual diagram schematically representing the main part of a cleaning apparatus for a semiconductor wafer according to a seventh embodiment of the present invention; 
         FIG. 15  is a conceptual diagram schematically representing the main part of a cleaning apparatus for a semiconductor wafer according to an eighth embodiment of the present invention; 
         FIG. 16  is a schematic diagram indicating stagnant layer of water and particle on a semiconductor wafer; 
         FIG. 17  is a schematic diagram indicating stagnant layer of dilute IPA aqueous solution and particle on a semiconductor wafer; 
         FIG. 18  is a conceptual diagram indicating the state of stagnant layer of chemical liquid in which additive agent for controlling zeta potential is added to dilute IPA aqueous solution and particle according to a ninth embodiment of the present invention; 
         FIG. 19A  is a conceptual diagram indicating repulsive force exerted on particle in the case where zeta potential is controlled according to the ninth embodiment of the present invention; 
         FIG. 19B  is a conceptual diagram indicating the behavior of particle in the case where zeta potential is controlled according to the ninth embodiment of the present invention; 
         FIG. 20  is a diagram indicating particle removal efficiency in the case where two-fluid jet cleaning is carried out by using cleaning liquid in which alkaline chemical liquid is added to control zeta potential according to the ninth embodiment of the present invention; 
         FIG. 21  is a schematic diagram indicating the locus of nozzle for discharging chemical liquid onto a semiconductor wafer according to the embodiment of the present invention; 
         FIG. 22  is a conceptual diagram schematically representing the main part of a cleaning apparatus for a semiconductor wafer according to a tenth embodiment of the present invention; 
         FIG. 23  is a chart showing PRE of the particle of SiN according to a tenth embodiment of the present invention; 
         FIG. 24  is a conceptual diagram schematically representing the main part of a cleaning apparatus for a semiconductor wafer according to a eleventh embodiment of the present invention; and 
         FIG. 25  is a chart showing the relation between the temperature of cleaning liquid, and the viscosity of cleaning liquid according to a eleventh embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various connections between elements are hereinafter described. It is noted that these connections are illustrated in general and, unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect. 
     Embodiments of the present invention will be explained with reference to the drawings as next described, wherein like reference numerals designate identical or corresponding parts throughout the several views. 
     The cleaning method for a semiconductor wafer with cleaning liquid according to one aspect of the invention includes: cleaning the semiconductor wafer while the temperature of the surface of the semiconductor wafer is from 30 degrees to 50 degrees, the cleaning liquid has lower surface tension and viscosity than water. 
     Prior to description of the embodiment of the present invention, the inventors will describe how to realize this invention. 
     The inventors conducted various experiments in order to analyze the phenomenon such that fine particles cannot be removed even with the two-fluid jet cleaning apparatus described in the Related Art to analyze the experiment result thereof. 
     The inventors have paid attention to the fact that the surface of semiconductor is wet also after such a semiconductor wafer is wetted by water to rotate such a semiconductor wafer to spray droplets on the surface thereof by centrifugal force. The result of the experiment relating thereto will now be described. 
     A semiconductor wafer wetted by water is rotated to measure the film thickness of water on the semiconductor wafer.  FIG. 1  shows the relationship of elapsed time, film thickness of water on the semiconductor wafer and distance from the center of the semiconductor wafer in the case where the semiconductor wafer is rotated at rotational speed of 500 rpm. 
     The abscissa of  FIG. 1  indicates distance (mm) from the center of the semiconductor wafer, and the ordinate indicates film thickness (nm) of water. The film thickness of water was determined by utilizing interference of light. In  FIG. 1 , the time since supply of water is stopped is described. Namely, water on a wafer is drained from the wafer by rotation after supply of water is stopped. In  FIG. 1 , changes of film thicknesses of water after 5 sec., 10 sec., 20 sec., 30 sec., 40 sec., and 50 sec. are passed are illustrated as graphical representation. 
     In  FIG. 1 , explanation will be given by taking an example of film thickness at the position of about 50 mm from the center of a semiconductor wafer. In the case where difference of measurement result at the above-mentioned position (film thickness of water which is removed or separated every 10 sec.) is described, when the remaining film at the time of 20 sec. is subtracted from the remaining film at the time of 10 sec., water of about 1500 nm/10 sec. is drained. 
     Further, when the remaining film at the time of 30 sec. is subtracted from the remaining film thickness at the time of 20 sec., water of about 1100 nm/10 sec. is drained. When the remaining film at the time of 40 sec. is subtracted from the remaining film at the time of 30 sec., water of about 700 nm/10 sec. is drained. When the remaining film at the time of 50 sec. is subtracted from the remaining film at the time of 40 sec. as final difference, water of about 640 nm/10 sec. is drained. 
     From this result, it is said that water on a wafer is drained until the first 30 sec. at a high speed larger than about 1 μm/10 sec., and speed of water removed from the wafer for 20 sec. subsequent thereto is dried at dry speed of 600 to 700 nm/10 sec. From this fact, it is said that there results dry condition where a large amount of water are drained from the wafer for several ten sec. from immediately after shift to dry step after supply of water is stopped, and discharge speed becomes slow at the latter half of dry process. 
     From this phenomenon, it is said that the first step is rotational discharge dry step of liquid in which dynamic flow of liquid (water flow layer: layer of water freely flowing by centrifugal force, etc.) is main. At the latter half step, it is said that since discharge speed is lowered, there results evaporation dry step in which evaporation dry step from the surface in which dynamic discharge is not expected is main. 
     From the result obtained from  FIG. 1 , it is considered that since droplet sprayed toward the outside of a semiconductor wafer is not observed at the time when thickness becomes equal to about 70 nm or less which is obtained from the last interference fringe, water flow does not already exist so that most of film layer is so-called wet layer (stagnant layer) of the semiconductor wafer surface. Such wet layer can practically only be removed by vaporization. 
     Namely, it was found out that layer of water having thickness of about 70 nm or less (wet layer: stagnant layer) in which the dynamic movement by, e.g., centrifugal force or droplet shape change at the time of two-fluid cleaning, etc. cannot be taken in is left on the semiconductor wafer. In this specification, such water layer will be referred to as stagnant layer. 
     It is to be noted that the above-mentioned result also depends upon dry process condition (the rate of rotations, acceleration), kind of underlying film and three-dimensional shape. 
     Namely, it has been found out that stagnant layer having thickness of 70 nm or less always exists on a wet semiconductor wafer. 
     That is, the inventors have confirmed that there exists water layer serving as stagnant layer which does not flow even by centrifugal force. The inventors peculiarly have attained the finding that cleaning of the semiconductor wafer by water flow flowing on the upper surface of the stagnant layer is carried out in a manner as described below. 
     It is assumed that large, medium and small three particles  110  to  112  shown in  FIGS. 2A and 2B  exist on a semiconductor wafer  100 . The cleaning process by two-fluid jet of the semiconductor wafer  100  in this case will be described. 
     Namely,  FIGS. 2A and 2B  represent, in a model form, the state where force is applied to particles  110  to  112  by droplet  103  included in droplet mist jetted toward the surface of the semiconductor wafer  100  by using the two-fluid jet cleaning apparatus.  FIG. 2A  represents the state immediately before a droplet  103  collides, and  FIG. 2B  represents the state immediately after the droplet  103  has collided. 
     As shown in  FIG. 2A , particles  110  to  112  having different sizes and stagnant layer  101  are attached on the surface of the semiconductor wafer  100 . Moreover, a water flow layer  102  flowing in a surface direction exists above the stagnant layer  101 . These particles  110  to  112  are placed in the state where the lower portion thereof is partially embedded within the stagnant layer  101 . 
     Here, it is assumed that, as an example, the height (diameter) of the particle  110  is about 90 nm, the height of the particle  111  is about 140 nm, the height of the particle  112  is about 180 nm, the thickness of the stagnant layer  101  is about 70 nm, the thickness of the water flow layer  102  is about 5 μm and the radius of droplet  103  is about 20 μm. 
     It should be noted that the size of droplet  103  is represented in a contracted form as compared to the stagnant layer  101 , etc. for clarifying explanation. 
     Next, as shown in  FIG. 2B , when droplet  103  included in droplet mist collides with water flow layer  102  on the surface of the semiconductor wafer  100 , the droplet  103  and the water flow layer  102  thereof are mixed and deformed so that there results a droplet collision fluid layer  120 . In this specification, the water flow layer  102  deformed by collision of the droplet  103  will be referred to as droplet collision fluid layer  120 . 
     By collision, plural waves concentrically spreading toward outer circumferential direction of the semiconductor wafer  100  take place at the droplet collision fluid layer  120 . Force of these waves is applied to particles  111 ,  112 . Thus, particles  111 ,  112  having medium diameter and large diameter are separated from the surface of the semiconductor wafer  100 . As a result, these particles  111  and  112  are removed. 
     However, the particle  110  having small diameter of which greater part is embedded within the stagnant layer  101  cannot effectively undergo force of the droplet collision fluid layer  120 . Accordingly, this particle cannot be removed. 
     Namely, the inventors peculiarly have attained the following matter. It has been found that it is impossible to remove fine particles embedded within the stagnant layer  101  and having height not more than film thickness (e.g., not more than about 70 nm) of the stagnant layer  101  by existence of the stagnant layer  101 . In concrete terms, it has become clear as shown in  FIG. 3  that there is fine particle diameter dependency in Particle Removal Efficiency (PRE) in the case of two-fluid jet cleaning using ordinary deionized water (DIW), and removal of fine particle having a height of 60 nm or less is difficult. 
     In addition, in the case of PSL (Polystyrene Latex) particle, it has been found out that according as the particle diameter becomes smaller, the particle removal efficiency is deteriorated to more degree. 
     The inventors have made this invention on the basis of the above-described peculiar findings. 
     The embodiments of the present invention will now be described with reference to the attached drawings. These embodiments do not limit the present invention. 
     In the embodiments described below, a fundamental principle is that the previously described stagnant layer  101  is thinned, or completely removed to physically apply force to particles exposed therefrom to remove them. 
     First, in the first to fourth embodiments, attention is drawn to the property of the cleaning liquid and wettability of the surface of the semiconductor wafer  100  to thin the stagnant layer  101 , or to completely remove such layer. 
     It is to be noted that pattern having uneven portions is formed on the surface of that semiconductor wafer subject to cleaning process. 
     First Embodiment 
     The first embodiment of the present invention will be described with reference to  FIGS. 4 to 6 . 
     In this embodiment, chemical liquid having surface tension lower than that of water and viscosity lower than that of water such as alcohol based liquid or fluoric based liquid is used as cleaning liquid in the cleaning processing using single wafer cleaning apparatus in place of water. 
     For example, cleaning is carried out by using isopropyl alcohol (IPA) as alcohol based chemical liquid, or hydrofluoroether (HFE) as fluoric based chemical liquid. In this case, it is preferable that concentration of the chemical liquid is high. 
     Explanation will be given with respect to the example where two-fluid jet cleaning apparatus shown in  FIG. 4  is used as the single wafer cleaning apparatus. In this case, droplet mist  307  in which two-fluid of the cleaning liquid and gas are mixed is jetted toward the surface of the semiconductor wafer  100 . WRD indicates wafer rotation direction. Since surface tension and viscosity of cleaning liquid are lower than those of water, the film thicknesses of the stagnant layer  101  and water flow layer  102  of cleaning liquid which are necessarily formed on the semiconductor wafer  100  as shown in  FIG. 5  become thinner than the film thickness in the case where water is used. 
     Thus, the droplet  103  included in droplet mist  307  can become close to the surface of the semiconductor wafer  100 . Accordingly, fine particle (height not more than 70 nm) embedded within the stagnant layer  101  in the case where water is used is exposed from the thinned stagnant layer  101 . Under such state, droplet collision fluid layer takes place by droplet  103  which has arrived at the surface of the semiconductor wafer  100 . Thus, particles are efficiently removed by force of wave that droplet collision fluid layer has as has been described with reference to  FIGS. 2A and 2B . 
     As an example of this embodiment,  FIG. 6  shows particle removal efficiency by two-fluid jet cleaning using dilute IPA aqueous solution (IPA dilute DIW). As shown in  FIG. 6 , it becomes clear that particle removal efficiency of particle not more than 60 nm is improved as compared to the two-fluid jet cleaning using deionized water shown in  FIG. 3 . 
     In accordance with this embodiment, even in the case where wettability of the surface of the semiconductor wafer  100  is high, since surface tension of cleaning liquid is low, it is possible to make an improvement such that the thickness of the stagnant layer  101  of the cleaning liquid becomes thin. 
     Moreover, in accordance with this embodiment, since cleaning liquid having low surface tension is used as described above, the cleaning liquid is apt to be entered into corner portions of pattern having uneven portions. As a result, it is possible to carry out cleaning of particles existing thereat. 
     In addition, in the case where cleaning is carried out by using, e.g., water as a modified example of the first embodiment, cleaning liquid in which surface active agent which permits the surface of the semiconductor wafer  100  to be hydrophobic is mixed into water is used. Thus, surface tension of cleaning liquid can be lowered. Accordingly, the stagnant layer  101  becomes thin. As a result, it is possible to effectively remove fine particles. 
     Second Embodiment 
     The second embodiment of the present invention will now be described with reference to  FIG. 7 . This embodiment relates to a cleaning method in which cleaning liquid having high surface tension (e.g., water, etc.) and a semiconductor wafer having low wettability (water repellency property) surface are combined. In this specification, the property for repelling cleaning liquid is referred to as water repellency. 
     In accordance with this embodiment, stagnant layer  101  of cleaning liquid is not formed on the surface of a semiconductor wafer  100  having low wettability (water repellency) as shown in  FIG. 7 . Thus, there is no possibility that fine particles on the semiconductor wafer  100  are embedded within the stagnant layer  101 . Accordingly, it is possible to effectively remove fine particles by force produced as the result of the fact that cleaning liquid having high surface tension flows within the surface of the semiconductor wafer  100 . 
     Third Embodiment 
     The third embodiment of the present invention will now be described with reference to  FIG. 8 . This embodiment differs from the first embodiment in that semiconductor wafer having low wettability (water repellency) is used. 
     Namely, this embodiment relates to a cleaning method in which cleaning liquid having surface tension lower than that of water, and a semiconductor wafer having surface of low wettability (water repellency) are combined. 
     In accordance with this embodiment, stagnant layer  101  of cleaning liquid is not formed on the surface of a semiconductor wafer  100  having low wettability (water repellency) as shown in  FIG. 8 . Accordingly, it is possible to effectively remove fine particles on a semiconductor wafer  100  in a manner similar to the second embodiment. 
     Fourth Embodiment 
     The fourth embodiment of the present invention will now be described with reference to  FIG. 9 . This embodiment differs from the first embodiment in that, in performing cleaning processing by using single wafer cleaning apparatus, water repellency processing liquid which permits the semiconductor wafer  100  to be water-repellent is used. 
     Namely, e.g., silicon resin coating agent is used as water repellency processing liquid, thereby allowing, in advance, the semiconductor wafer  100  to be placed in high water-repellent state. In concrete terms, the surface of the semiconductor wafer is converted into the surface having high water repellency by using silane coupling agent such as hexamethyl disilazan (HMDS) or tetramethylsilyl diethylamine (TMSDMA), etc. 
     As shown in  FIG. 9 , since the surface of the semiconductor wafer  100  caused to be in water-repellent state is not wetted by water, stagnant layer  101  is not formed. Accordingly, it is also possible to supply water onto the surface of rotating a semiconductor wafer  100  to remove particles  110  to  112  only by centrifugal force. 
     Moreover, in the case where two-fluid jet cleaning apparatus is used as single wafer cleaning apparatus, the semiconductor wafer itself is first caused to have high water repellency so that water having high pressure used for cleaning is not entered into gaps of fine pattern. Accordingly, it is possible to reduce damage applied to fine pattern from lateral direction. 
     In this case, particles hardly exist gaps of fine pattern. Most of them exist at broad pattern portion. 
     Moreover, in accordance with this embodiment, the surface including particles is caused to be water-repellent as monolayer (single molecular layer). In this case, particle has the structure and is large as compared to fine pattern. For this reason, those particles physically undergo force by droplet so that such particles are removed. 
     In addition, it is preferable that after particles are removed, ashing processing is carried out to remove water repellency coating film. 
     Then, a method of thinning the previously described stagnant layer  101  on the basis of point of view different from the above-described embodiments to carry out cleaning processing will be described. In the following embodiments, a fundamental principle is that stagnant layer  101  is thinned by pressure of gas to physically apply force to particles exposed therefrom to remove them. 
     In the following embodiments, the surface of the semiconductor wafer  100  is assumed to be hydrophilic. 
     Fifth Embodiment 
     The fifth embodiment of the present invention will be described with reference to  FIGS. 10 to 12 . 
       FIG. 10  is a conceptual diagram schematically indicating the main part of a cleaning apparatus for a semiconductor wafer according to this embodiment. As shown in  FIG. 10 , the cleaning apparatus for a semiconductor wafer includes a three-fluid jet nozzle  300  including a two-fluid jet nozzle  301 , and a gas jet nozzle  302 . 
     The two-fluid jet nozzle  301  serves to jet droplet mist  307  from a jet hole  301   b  of the front end, which is produced as the result of the fact that two-fluid of liquid (e.g., deionized water, etc.) and gas (second gas; e.g., dry air or nitrogen, etc.) are mixed, in a manner substantially perpendicular to the surface of the semiconductor wafer  100 . Moreover, the gas jet nozzle  302  serves to jet gas  308  (first gas; e.g. dry air or inactive gas such as nitrogen, etc.) with a certain angle relative to vertical direction with respect to the surface of the semiconductor wafer  100 . 
     Since this cleaning apparatus uses, in addition to two-fluid, a fluid different therefrom, such cleaning apparatus is referred to as three-fluid jet cleaning apparatus in this specification. 
     A gas inlet  303  to which gas  308  is supplied is provided at the upper part of the three-fluid jet nozzle  300 . The gas inlet  303  is configured to communicate with jet hole  302   a  of the gas jet nozzle  302  through gas passage penetrated through the internal part of a conduit  301   a . Moreover, an inlet  304  for respectively separately supplying gas and liquid into the two-fluid jet nozzle  301  is also provided at the upper part of the three-fluid jet nozzle  300 . This inlet  304  is also configured to communicate with jet hole  301   b  of the two-fluid jet nozzle  301  through the gas passage and the liquid passage which are penetrated through the internal part of the conduit  301   a  which is separated from the gas passage through which gas  308  is passed. 
     The cross sectional structure of the front end part of the two-fluid jet nozzle  301  will now be described with reference to  FIG. 11 . 
     As shown in  FIG. 11 , the two-fluid jet nozzle  301  includes a liquid passage  400  at the central part thereof, and includes a gas passage  401  in such a manner to concentrically surround the liquid passage  400 . Liquid supplied from the inlet  304  is passed through the liquid passage  400  of the inside, and gas is passed through the gas passage  401 . Thus, the liquid and the gas are jetted as mixed droplet mist  307  from the jet hole  301   b  of the front end of the two-fluid jet nozzle  301 . 
     As a result, the liquid and the gas result in droplet mist  307  more effectively mixed on the downstream side relative to the mixed point of liquid and gas. It is to be noted that there may be employed a configuration in which liquid is delivered to the outside, and gas is delivered to the inside. 
     The operation of the cleaning apparatus for semiconductor wafer according to this embodiment will now be described in detail. 
     First, stage (not shown) horizontally holds a semiconductor wafer  100 , and rotates the semiconductor wafer  100  around the vertical axis passing through the center of the semiconductor wafer  100 . The rate of rotations is, e.g., 300 to 500 rpm. 
     Subsequently, gas  308  is jetted from the jet hole  302   a  of the front end of the gas jet nozzle  302 , and droplet mist  307  is jetted from the jet hole  301   b  of the front end of the two-fluid jet nozzle  301 . It is preferable that jet speed of gas  308  is higher than jet speed of droplet mist  307 . The jet speed of the droplet mist  307  is, e.g., 20 to 50 m/sec. Moreover, jet speed of gas  308  is, e.g., 150 to 300 m/sec. Further, the region of the surface of the semiconductor wafer  100  at which gas  308  arrives is the region at which droplet mist  307  arrives. 
     In this example, region  310  wetted by droplet mist  307  is formed on the surface of the semiconductor wafer  100 . 
     Here, the surface state in the case where jet of the above-described gas  308  is carried out in advance with respect to the semiconductor wafer  100  where stagnant layer  101  exists on the surface thereof, and droplet mist  307  is jetted thereafter will be described with reference to  FIG. 12 . 
     In  FIG. 12 , since respective components are the same as those of  FIGS. 2A ,  2 B, the same reference numerals are respectively attached to the same components, and the description thereof will be omitted. 
     When gas  308  is jetted onto the stagnant layer  101 , its thickness is thinned by pressure of gas  308 . Namely, as shown in  FIG. 12 , the stagnant layer  101  becomes thinner than that of  FIGS. 2A ,  2 B, and fine particles  110  to  112  are exposed toward the outside of the stagnant layer  101  further as compared to those of  FIGS. 2A ,  2 B. 
     In this case, the thickness of the stagnant layer  101  remaining on the surface of the semiconductor wafer  100  depends upon jet speed (pressure) of gas  308 . For example, when jet speed of gas  308  is further increased, the thickness of the stagnant layer  101  becomes thinner. 
     Subsequently, droplet collision fluid layer takes place (not shown) by droplet  103  which has arrived at the surface of the semiconductor wafer  100  under the state where particles  110  to  112  are exposed from the stagnant layer  101  in this way. As described by making reference to  FIGS. 2A and 2B , particles  110  to  112  are efficiently removed by force of wave that the droplet collision fluid layer has. 
     On the other hand, when the droplet collision fluid layer loses kinetic energy, moisture which has formed the droplet collision fluid layer becomes integral with the stagnant layer  101 . Accordingly, the stagnant layer  101  becomes thick again. However, the stagnant layer  101  is thinned again by continuously jetted gas  308  for a time period until next droplet  103  arrives. 
     Namely, for a time period during which gas  308  is jetted, the stagnant layer  101  is always maintained thin. Accordingly, the droplet  103  can become close to the semiconductor wafer surface. As a result, particles are apt to be removed. 
     Moreover, the three-fluid jet nozzle  300  is scanned by a scanning unit (not shown) along the surface in the direction of the outer peripheral part from the central part of the semiconductor wafer  100  together with jet of the gas  308  and the droplet mist  307  which have been described above (SD: Scanning Direction). Scanning speed is, e.g., 0.01 to 0.05 m/sec. In accordance with the jet, scanning operation of three-fluid jet nozzle  300  and rotation of the semiconductor wafer  100 , particles of the entirety of the surface of the semiconductor wafer  100  are removed. 
     As described above, in accordance with this embodiment, gas  308  can be first directly jetted onto the semiconductor wafer to thereby thin the stagnant layer  101 . Accordingly, fine particles embedded within the stagnant layer  101  are exposed to increase the probability where droplet  103  and fine particle are caused to be in contact with each other. Accordingly, it is possible to efficiently remove fine particles. 
     In addition, since jet of gas  308  can be manipulated separately from jet of droplet mist  307 , it is possible to jet droplet mist  307  and gas  308  without mixing them. Namely, since the droplet mist  307  and the gas  308  have different velocity vectors, it is difficult to accelerate droplet  103  included within droplet mist  307  by high speed gas  308 . Accordingly, it is possible to thin the thickness of the stagnant layer  101  without applying excessive damage to fine pattern of the semiconductor wafer surface. 
     First Modified Example of the Fifth Embodiment 
     The first modified example of the fifth embodiment will now be described with reference to  FIG. 13 . This modified example differs from the fifth embodiment in that angle of the gas jet nozzle  602  can be freely adjusted. 
     As shown in  FIG. 13 , the gas jet nozzle  602  includes an adjustment screw  605  between hoses  603 ,  604 , and includes an adjustment screw  606  between the hose  604  and the two-fluid jet nozzle  301 . By such a configuration, the gas jet nozzle  602  can freely adjust direction of jet hole  602  of the front end by using adjustment screws  605 ,  606 . Accordingly, it is possible to adjust jet direction of the gas  308 . 
     In accordance with this embodiment, since jet angle of gas  308  can be freely adjusted, it is possible to freely control the thickness of stagnant layer  101  which has taken place within the area where droplet mist  307  is jetted. Accordingly, high speed gas  308  is jetted at a suitable angle, thus making it possible to maintain the thickness of the stagnant layer  101  to be thin. 
     Second Modified Example of the Fifth Embodiment 
     The second modified example of the fifth embodiment will now be described. In this modified example, angle of gas jet nozzle  302  is caused to be different from that of the fifth embodiment. 
     Namely, referring to  FIG. 10 , setting is made such that high speed gas  308  is jetted in correspondence with the scanning direction of the three-fluid jet nozzle  300  before droplet mist  307  is jetted. For example, if the scanning direction of the three-fluid jet nozzle  300  is a direction from right direction to left direction in  FIG. 10 , gas  308  is jetted in advance into the region of the left side of the region where droplet mist  307  is jetted. Since the three-fluid jet nozzle  300  is scanned, droplet  103  included within subsequently arriving droplet mist  307  collides with the region where gas  308  is jetted in advance so that the stagnant layer  101  has been thinned. 
     Accordingly, also in this modified example, since gas  308  jetted at a high speed during scanning operation thins the stagnant layer  101 , the probability where the droplet  103  and the fine particle are in contact with each other can be increased. Accordingly, it is possible to efficiently remove particles. 
     Sixth Embodiment 
     The sixth embodiment of the present invention will now be described. This embodiment differs from the fifth embodiment in that cleaning processing is carried out while changing jet speed of the gas  308 . 
     Namely, in this embodiment, in jetting gas  308  from oblique direction with an angle being changed by using the cleaning apparatus for a semiconductor wafer according to the fifth embodiment, the jet speed is changed into high speed or low speed in accordance with the size of pattern of surface of the semiconductor wafer  100 . 
     In concrete terms, at the portion where the size of the pattern is small (e.g., fine pattern having pattern width of about 40 nm or less), the jet speed of gas  308  is caused to be lower than that of the fifth embodiment. At the part where the size of the pattern is large, or the part where pattern does not exist so that the semiconductor wafer surface is planar, the jet speed is caused to be higher than that of the fifth embodiment. 
     Accordingly, in accordance with this embodiment, it is possible to suitably disperse stagnant layer  101  in accordance with pattern shape without damaging the fine pattern of the surface of the semiconductor wafer  100  thus to thin its thickness. Thus, droplet  103  included within the droplet mist  307  can be closer to the surface of the semiconductor wafer  100  thus to have ability to remove fine particles embedded within the stagnant layer  101 . 
     Seventh Embodiment 
     The seventh embodiment of the present invention will now be described with reference to  FIG. 14 . This embodiment differs from the fifth embodiment in that there are provided two sets of gas jet nozzles  700 ,  701 . 
     Namely, as shown in  FIG. 14 , three-fluid jet nozzle  710  includes inlets  704 ,  705  for gas  308  and an inlet  706  for gas and liquid. Moreover, there is employed a structure such that penetrated two sets of gas passages  707 ,  708  are provided thus to communicate with respective jet holes  700   a ,  701   a  of two sets of gas jet nozzles  700 ,  701 . By the configuration having two sets of gas jet nozzles  700 ,  701 , it is possible to individually manipulate gas  308  and droplet mist  307  with degree of freedom higher than that of the fifth embodiment to jet them without performing mixing operation. Accordingly, it is possible to freely control the gas  308  and the droplet mist  307  in accordance with requirement of cleaning. 
     Eighth Embodiment 
     The eighth embodiment of the present invention will now be described with reference to  FIG. 15 . 
     This embodiment differs from the fifth embodiment in that the two-fluid jet nozzle and the gas jet nozzle are constituted as integral type nozzle (three-fluid jet nozzle). 
       FIG. 15  represents a cross sectional diagram of the three-fluid jet nozzle according to this embodiment. As shown in  FIG. 15 , this three-fluid jet nozzle  800  includes a two-fluid jet nozzle composed of a liquid passage  400  of the central part, and a gas passage  401  concentrically disposed in such a manner to surround the liquid passage  400 ; and a concentrical gas passage  801  disposed in a manner to surround the gas passage  401 . 
     Liquid (e.g., deionized water, etc.) is supplied from the liquid passage  400 , and gas (second gas: e.g., dry air or nitrogen, etc.) is supplied from the gas passage  401 . Thus, droplet mist  307  is formed and is jetted onto the semiconductor wafer  100  from the jet hole  803 . Moreover, high speed gas  308  (first gas; for example, dry air or inactive gas, such as, nitrogen, etc.) is delivered, and is jetted around the portion of the droplet mist  307  from the jet hole  802 . Namely, the three-fluid jet nozzle  800  is configured to flow and jet the liquid, the first gas and the second gas. 
     Moreover, the three-fluid jet nozzle  800  is scanned in such a manner that droplet  103  included within droplet mist  307  collides with the region where the stagnant layer  101  is removed by pressure of gas  308  on the surface of the semiconductor wafer  100 . 
     In accordance with this embodiment, since droplet mist  307  is jetted in the state where the stagnant layer  101  is maintained thin by high speed gas  308  similarly to the fifth embodiment, it is possible to effectively remove fine particles. Moreover, since jet speeds of the droplet mist  307  and the gas  308  can be individually manipulated, even if the jet speed of droplet mist  307  is maintained low and only the jet speed of gas  308  is caused to be high, the droplet mist  307  and gas  308  are not mixed. Accordingly, since the droplet  103  included in droplet mist  307  is not accelerated by gas  308 , there is low possibility that damage is applied to fine pattern by droplet  103 . 
     Moreover, in accordance with this embodiment, since the space occupied by the gas jet nozzle  302  of the fifth embodiment is unnecessary, process space can be reduced. 
     It should be noted that, in accordance with the fifth to eighth embodiments which have been described above, if the stagnant layer  101  is thinned, the above-described effects can be obtained irrespective of the rate of rotations of the semiconductor wafer  100 , and scanning speeds of three-fluid jet nozzles  300 ,  710  and  800 . 
     Moreover, in the fifth to eighth embodiments, cleaning liquid of the first embodiment may be used to form droplet mist  307 . In this case, it is possible to efficiently remove particles as compared to the fifth to eighth embodiments. 
     Further, cleaning may be carried out by water-repellent semiconductor wafers which have been described in the second to forth embodiments. Also in this case, it is possible to efficiently remove particles as compared to the fifth to eighth embodiments. 
     It is to be noted that since there is the case where large droplets cannot be entered into corner portions of fine pattern in the above-described embodiments, it is preferable that droplet jetted by the two-fluid jet cleaning apparatus or the three-fluid jet cleaning apparatus has diameter of 5 μm or less. 
     Ninth Embodiment 
     The ninth embodiment of the present invention will now be described with reference to  FIGS. 16 to 20 . This embodiment differs from the first embodiment in that cleaning liquid in which chemical liquid for controlling zeta potential is mixed into dilute IPA aqueous solution is used as a cleaning liquid in the cleaning processing using single wafer cleaning apparatus. 
     In this specification, the zeta potential refers to a potential of the surface of particle in contact with cleaning liquid and potential of the surface of underlying film in contact with cleaning liquid. 
       FIG. 16  is a schematic diagram indicating stagnant layer of water and particle on the semiconductor wafer. As previously described, particles  110  to  112  are embedded within the stagnant layer  101  of water. 
       FIG. 17  is a schematic diagram indicating stagnant layer of dilute IPA aqueous solution and particles on the semiconductor wafer. As previously described, since the thickness of the stagnant layer  101  of the dilute IPA aqueous solution is thinner than that of water, the particles  110  to  112  are exposed to more degree as compared to the state of  FIG. 16 . 
     For this reason, particles  110  to  112  are apt to be removed by force of wave that the droplet collision fluid layer  120  has. A particle  150  indicates a particle which has been separated and removed from the surface of the semiconductor wafer  100 . 
       FIG. 18  is a schematic diagram indicating the state of the stagnant layer of chemical liquid in which additive agent for controlling zeta potential is added to dilute IPA aqueous solution and particles. As additive agent thereof, there is used alkaline chemical liquid or surface active agent for controlling zeta potential. 
     For example, as alkaline chemical liquid, ammonium hydroxide (NH4OH) or choline, etc. may be used. Thus, control is made such that zeta potential is negative. Since the particle  150  desorbed from the semiconductor wafer  100  has negative zeta potential, such particle  150  is not attached again to the fluid layer  120  having negative zeta potential. 
       FIGS. 19A and 19B  are schematic diagrams indicating the behavior of particle in the case where zeta potential is controlled. When zeta potential of particle  150  and zeta potential of underlying film  170  on the semiconductor wafer  100  are controlled as shown in  FIG. 19A  so that there is provided negative potential, repulsive force is exerted therebetween. As a result, as shown in  FIG. 19B , particle  150  is dispersed into water flow layer  102 , and is drained toward the outside of the bath. This phenomenon is based on zeta potential effect. This zeta potential does not depend upon the diameter of the particle  150 . In addition, this zeta potential can be measured by the electrophoresis method. 
     Particle removal efficiency in the case where two-fluid jet cleaning is carried out by using cleaning liquid in which alkaline chemical liquid is added to control zeta potential is shown in  FIG. 20 . It is found out that removal efficiency of particle having a height of 40 nm is improved as compared to the case of the two-fluid jet cleaning using deionized water in which alkaline chemical liquid is not added. Moreover, also as compared to the two-fluid jet cleaning using dilute IPA aqueous solution described in the first embodiment, it becomes possible to efficiently remove fine particles in shorter time. 
     As described above, in accordance with this embodiment, after micro particle  150  having a height of about 40 nm is desorbed from the semiconductor wafer  100 , particle  150  can be removed without being attached to the semiconductor wafer  100  again. 
     It is to be noted that there may be employed an approach to use, as cleaning liquid, HFE, which is described in the first embodiment, solution in which a very small amount of IPA is added into HFE, water in which surface active agent is mixed, etc. to mix alkaline chemical liquid for controlling the previously described zeta potential into the cleaning liquid. 
     Moreover, there may be employed an approach to mix surface active agent for controlling zeta potential into HFE or solution in which a very small amount of IPA is added into HFE. As a surface active agent to be mixed, there may be employed one kind of surface active agent having both the effect to allow the substrate surface to be hydrophobic and the effect to control zeta potential. In addition, plural kinds of surface active agents having the above-described respective effects may be mixed. Namely, implementation may be carried out in the state changed as occasion demands depending upon circumstances. 
     Moreover, there may be used acid cleaning liquid in which acid chemical liquid is mixed into IPA, HFE or solution in which a very small amount of IPA is added into HFE. In that case, as chemical liquid for controlling zeta potential, surface active agent, etc. may be mixed. 
     Further, cleaning may be carried out by using a water repellent semiconductor wafer which has been described in the third and fourth embodiments. In this case, it is possible to more efficiently remove particles. 
     In addition, droplet mist  307  may be formed by using cleaning liquid of this embodiment also in the fifth to eighth embodiments. In this case, it is possible to more efficiently remove particles. 
     It should be noted that there may be employed, in the above-described first to ninth embodiments, an approach to scan the nozzle  180  along the surface in a diameter direction of the semiconductor wafer  100  to carry out discharge operation of chemical liquid onto the semiconductor wafer  100  by single scanning operation (see  FIG. 21 ). 
     Thus, since cleaning liquid after cleaning is immediately drained similarly to the case where scanning operation is carried out from the central part toward the direction of the outer peripheral part, it is possible to prevent removed particle from being attached to the semiconductor wafer  100  again. 
     Tenth Embodiment 
     The tenth embodiment of the present invention will now be described with reference to  FIGS. 22 and 23 . This embodiment differs from the first embodiment in that raising the temperature of a semiconductor wafer  100  during washing described above in the cleaning processing. 
       FIG. 22  represents an operation of a wafer cleaning apparatus in this embodiment. First, while the stage which is not illustrated holds a semiconductor wafer  100  horizontally, it is made to rotate around the perpendicular axis passing through the center of the semiconductor wafer  100 . For example, the number of rotation is 300-500 rpm. It can spurt out at the back of the semiconductor wafer  100 , such as hot carrier gas including nitrogen, and warm water. Thereby, the surface temperature of the semiconductor wafer  100  can be adjusted. 
       FIG. 23  represents the result of having performed two-fluid jet cleaning to the wafer of normal temperature using IPA (dIPA) diluted to 10% with pure water, the result of having performed two-fluid jet cleaning to the wafer heated to 45 degrees by warm water using IPA diluted with pure water to 10% and the result of having performed two-fluid jet cleaning to the wafer heated to 45 degrees by warm water using the solution which mixed IPA diluted with pure water to 10% and a choline solution diluted with pure water to 4% at a rate of 35:1, respectively. In this embodiment, it estimates Particle Removal Efficiency (PRE) of the particle of SiN. In addition, the diameters of a particle which evaluated ware 40 nm, 80 nm, and 100 nm, and the processing time by two-fluid jet cleaning was 192 seconds. 
     As shown in  FIG. 23 , it was confirmed that PRE of the wafer heated to 45 degrees by warm water higher than that of the wafer of normal temperature in all the diameters of a particle. It is considered to be for a particle to become easy to jump out of stagnant layer because of the quantity of motion of the particle increases by making the wafer surface into high temperature. 
     In addition, when performing two-fluid jet cleaning using IPA, it is desirable to control the temperature on the surface of a wafer at 50 degrees or less, more preferably in the range of 30 degrees to 50 degrees. 
     When the surface temperature of a wafer exceeds 50 degrees, even if it is under washing, IPA of domains which is separated from a nozzle will evaporate (for example, wafer central part in case a nozzle is in the perimeter etc.), and dryness will start partially. 
     Since it becomes impossible to remove simply even if it will use two-fluid, if the wafer surface once dries and a particle sticks to an under layer and the particle is firmly connected with the under layer, it is not desirable. 
     As shown above, the fine particles on the surface of a semiconductor wafer is effectively removable by using the cleaning method of the semiconductor wafer concerning the tenth embodiment. In addition, adjustment of the surface temperature of the wafer indicated in this embodiment can also be carried out combining other embodiments mentioned above. 
     Eleventh Embodiment 
     The tenth embodiment of the present invention will now be described with reference to  FIGS. 24 and 25 . 
     This embodiment differs from the tenth embodiment in that the temperature of a semiconductor wafer  100  is raised at 80 degrees or more during cleaning. 
     As shown in  FIG. 24 , the composition of the cleaning apparatus of the semiconductor wafer  100  concerning this embodiment is the same as that of the first embodiment. 
     It can spurt out at the back of the semiconductor wafer  100 , such as hot carrier gas including nitrogen, and warm water. 
     An example of operation of two-fluid jet cleaning apparatus shown in  FIG. 24  is explained. In this case, droplet mist  307  in which two-fluid of the cleaning liquid and gas are mixed is jetted toward the surface of the semiconductor wafer  100 . 
     A boiling temperature of the cleaning liquid is higher than that of water and a surface tension of the cleaning liquid is lower than that of water. The cleaning liquid, for example, is ethylene glycol, propylene glycol, diethylene glycol, and acetic acid. Moreover, it is desirable that the cleaning liquid is rinsed easily by water. Ethylene glycol, propylene glycol, diethylene glycol, and acetic acid are rinsed easily by water. 
     Ethylene glycol, propylene glycol, diethylene glycol, and acetic acid have viscosity greatly higher than water, and it is difficult to use for the cleaning liquid for cleaning the wafer with fine pattern formed on the surface. 
     However, as shown in  FIG. 25 , the viscosity of cleaning liquid falls as the temperature of cleaning liquid rises, and the viscosity of the cleaning liquid becomes near equally with the viscosity of water above 80 degrees. 
     In this embodiment, the cleaning liquid, for example, is ethylene glycol, propylene glycol, diethylene glycol, and acetic acid, a boiling temperature of them is higher than that of water and a surface tension of them is lower than that of water. And by making temperature on the surface of a wafer into 80 degrees or more, the quantity of motion of a particle can be raised and the fine particle which adheres on the surface of a semiconductor wafer can be removed effectively 
     In this embodiment, a temperature of the cleaning liquid is not limited. However, as for the temperature of cleaning liquid, it is desirable that it is high temperature more from a viewpoint in which the viscosity of cleaning liquid is reduced by maintaining the temperature on the surface of a semiconductor wafer at 80 degrees or more. 
     While the embodiments of the present invention have been described above in detail, practical configurations are not limited to the above-described embodiments, but the present invention may be implemented in variously modified forms within the scope which does not depart from the gist of the present invention. 
     For example, the single wafer cleaning apparatus is not limited to the two-fluid jet cleaning apparatus or the three-fluid jet cleaning apparatus. 
     Moreover, while explanation has been given on the assumption that a semiconductor wafer subject to cleaning is such that pattern of elements is formed on the surface thereof, any surface state may be employed. For example, flat surface may be also employed. 
     Further, cleaning apparatus for a semiconductor wafer and cleaning method for a semiconductor wafer according to the embodiments of the present invention may be also used for cleaning of substrate other than a semiconductor wafer such as glass substrate of liquid crystal display device, etc. 
     Furthermore, there may be employed an approach to thin the stagnant layer thereafter to apply force to fine particles by methods other than the two-fluid jet cleaning to remove those fine particles. 
     In addition, droplet mist produced at the outside of the two-fluid jet nozzle may be supplied to the two-fluid jet nozzle.