Particle counting method and particle counter

Abstract

The object of the present invention is to provide a particle counter that can count particles in aerosol having a particle size of from 2 nm to 50 nm in an operating pressure range from an atmospheric pressure through a reduced pressure to a low vacuum and calculate a particle size distribution. The present invention provides a particle counter that charges particles existing in the aerosol and then applies an electrostatic field to the particles, and a particle counter that charges the particles existing in the aerosol and then mixes the aerosol with a non-charged sheath gas flow shaped like a laminar flow and applies an electrostatic field to the particles. This can get the respective particles into traces depending on their particle size. Thus, it is possible to count the number of particles having specific traces. Further, by using an electron multiplier for exciting cluster ions to detect the charged particles and operating it as a high-pass filter, even if the number density of the particles is small, it is possible to effectively count the particles.

What is claimed is:  
     
         1 . A particle counting method, comprising the steps of: 
 taking in as aerosol a process gas in a process apparatus for conducting a physical or chemical reaction in a reduced vapor phase including a vacuum;    charging particles existing in the aerosol;    then applying an electrostatic field to the particles to get the respective particles into traces depending on their particle sizes; and    measuring the number of particles having specific traces to thereby calculate the particle size distribution of the particles floating in the process apparatus.    
     
     
         2 . A particle counting method according to  claim 1 , wherein an electron amplifier tube for exciting cluster ions is used for detecting the charged particles.  
     
     
         3 . A particle counting method according to  claim 1 , wherein the step of measuring the number of particles having specific traces to thereby calculate the particle size distribution of the particles floating in the process apparatus is replaced with the step of measuring the number of particles having particle sizes larger than a specific particle size to thereby perform a high-pass filtering.  
     
     
         4 . A particle counting method according to  claim 1 , wherein the step of measuring the number of particles having specific traces to thereby calculate the particle size distribution of the floating particles in the process apparatus is replaced with the step of measuring a spatial number density of particles having particle sizes larger than a specific particle size on the basis of three or more specific particle sizes by the use of a high-pass filtering operation to thereby predict a particle size distribution in a range covering all particle sizes.  
     
     
         5 . A particle counting method, comprising the steps of: 
 taking in as aerosol a process gas in a process apparatus for conducting a physical or chemical reaction in a vapor phase;    charging particles existing in the aerosol;    then mixing the aerosol with a non-charged sheath gas flow shaped like a laminar flow and applying an electrostatic field to the particles existing in the aerosol to thereby get the respective particles into traces depending or their particle sizes; and    detecting particles having specific traces and measuring the number of particles to thereby calculate the particle size distribution of the particles floating in the process apparatus.    
     
     
         6 . A particle counting method according to clam  5 , further comprising the step of taking in atmosphere in a clean zone, in which the process apparatus to be measured is disposed, as a non-charged sheath gas.  
     
     
         7 . A particle counting method according to clam  5 , in the step of detecting the charged particles, further comprising the step of modulating an electrostatic field intensity applied to a classifying region at low frequency and amplifying the electric signal of detecting the charged particles tuned to the low frequency in a narrow band.  
     
     
         8 . A particle counting method according to clam  5 , further comprising the step of applying voltage to a conductive plate, which is disposed after the taken-in aerosol is subjected to a charging process and can apply voltage to the aerosol flow, to thereby electrostatically attract and remove floating ions included in the aerosol.  
     
     
         9 . A particle counting method according to  claim 5 , 
 wherein the step of mixing the aerosol with a non-charged sheath gas flow shaped like a laminar flow and applying an electrostatic field to the particles existing in the aerosol to thereby get the respective particles into traces depending on their particle sizes is replaced with the step of applying the electrostatic field to the particles in the aerosol to thereby get the respective particles-into traces, and    wherein the step of detecting particles having specific traces and measuring the number of particles to thereby calculate the particle size distribution of the particles floating in the process apparatus is replaced with the step of calculating the number of particles having particle sizes close to a specific particle size to thereby perform a band-pass filtering.    
     
     
         10 . A particle counting method according to clam  5 , wherein the step of detecting particles having specific traces and measuring the number of particles to thereby calculate the particle size distribution of the particles floating in the process apparatus is replaced with the step of measuring a spatial number density of particles having particle sizes larger than a specific particle size on the basis of three or more specific particle sizes by the use of a band-pass filtering operation to thereby predict a particle size distribution in a range covering all particle sizes.  
     
     
         11 . A particle counter comprising: 
 aerosol introducing means connected to an aerosol supply source provided on an object to be measured;    charging means for charging the aerosol introduced by the aerosol introducing means arid a group of particles existing in the aerosol;    floating ion attracting and removing means for attracting and removing floating ions that interfere with the measurement of the charged particles charged by the charging means;    particle classifying means for classifying the group of charged particles from which the floating ions are attracted and removed; and    sheath gas carrying line for making a sheath gas into a laminar flow and supplying the sheath gas to the particle classifying means,    wherein the particle classifying means mixes the aerosol with the non-charged sheath gas flow shaped like a laminar flow and then applies an electrostatic field to the non-charged sheath gas to get the respective particles existing in the aerosol into traces depending on their particle sizes to thereby classify the particles.    
     
     
         12 . A particle counter according to  claim 11 , further comprising measuring means for detecting the particles having specific traces and counting the number of particles.  
     
     
         13 . A particle counter according to  claim 11 , further comprising sheath gas taking-in means for taking in atmosphere in a clean zone where the object to be measured is disposed.  
     
     
         14 . A particle counter according to  claim 11 , wherein the particle classifying means has amplifying means that modulates an electrostatic field intensity applied to a classifying region at a low frequency and amplifies the electric signal of detecting the charged particles tuned to the low frequency in a narrow band to detect the charged particles.  
     
     
         15 . A particle counter according to  claim 11 , wherein the particle classifying means has a conductive member capable of applying voltage to the aerosol flow and applies voltage to conductive member to thereby electrostatically attract and remove floating ions in the aerosol.