Abstract:
Cleaning and inspecting a surface of the substrate comprises subjecting the surface to the output of a laser source for applying a cleaning energy to the surface and thereby remove contaminants on the surface. The laser source is used for inspecting the surface being cleaned and to measure the effect of the cleaning.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention relates to Provisional Application Serial No. 60/078,625, filed Mar. 19, 1998, by Istvan M Boszormenyi, and entitled “INTEGRATED LASER CLEANING AND INSPECTION SYSTEM”. The contents of this application is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to laser cleaning and inspecting of surfaces. In particular the system is for use on disc surfaces which are used for recording data. 
     In most high technology industries, for instance, semiconductor device, hard disc or flat panel display manufacturing, improved performance is linked to the ability to reduced the feature size. Thus there is the narrower line width, smaller bit cell or pixel size. As a consequence, the size of detrimental contamination, for example, particles, steadily decreases. Hence, there is an increased demand for effective cleaning technologies, tools and processes. To reduce cost these cleaning processes need to be monitored closely. 
     Laser cleaning has emerged as a potential new dry cleaning technology to remove particles and other contaminants from surfaces. For example the Radiance (U.S. Pat. No. 5,024,968) process utilizes a pulsed intense light source (such as an excimer laser) in the presence of an inert gas flow over the surface to remove contamination. 
     With the reducing feature size the time to necessary to inspect a surface for cleanliness increases and it becomes impractical to inspect every surface or even the entire surface going through a cleaning process. Usually, samples are taken and a significant portion of these surfaces are analyzed for cleanliness. 
     Most commonly these inspection tools are based on light scattering. A small beam of light is directed at the surface and photomultiplier tubes detect the scattered light. The smaller the wavelength the smaller particles can be detected. 
     There is need top provide for an enhanced technique, system and apparatus for cleaning and inspecting surfaces 
     SUMMARY OF THE INVENTION 
     According to the invention cleaning and inspecting a surface of the substrate comprises subjecting the surface to the output of a laser source for applying a cleaning energy to the surface and thereby remove contaminants on the surface. The laser source is used for inspecting the surface being cleaned and to measure the effect of the cleaning. 
     The integrated laser cleaning and inspection system uses the light from laser cleaning light source as the inspection light source. The system allows: 
     a) in situ 100% surface inspection of every workpiece during laser cleaning 
     b) controlling the laser cleaning process 
     c) sorting the substrates based on cleanliness and damage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a representation of an integrated laser cleaning and inspection tool. 
     FIG. 2 is a flow diagram illustrating the laser cleaning process. 
     FIG. 3 is an example of modifying the laser beam cross-section to achieve uniform energy distribution. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following description, reference is made to the accompanying drawings which form a part hereof, and which show, by way of illustration, several embodiments of the present invention. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
     The invention combines laser cleaning and inspection in one tool. The laser beam used for cleaning is also used as the light source for the inspection. As the surface is being cleaned the level of cleanliness can be monitored at the same time. Since the entire surface of every workpiece needs to be cleaned and not just samples the tool allows 100% inspection which would be cost prohibitive if the inspection was to be carried out off-line. 
     A drawing of such an integrated system for cleaning and monitoring cleanliness for discs is shown in FIG. 1 with excimer laser  10  as a source for a beam  11  and a hard disc  12  as a substrate for cleaning. An ultraviolet (UV) laser beam  11  is favored in both cleaning and detection processes because it allows the removal and detection of smaller particles. The beam from the source  10  is directed through a beam homogenizer  13  and focusing lenses  14  to the disc  12 . 
     The intensity of the scattered light from contaminants on the substrate  12  is directed to focusing lenses  15  and collected with one or more photomultiplier tubes (PMT)  16 . The signal from the PMT  16  is used to control the cleaning process and to make decision on the quality of the substrate. A process control protocol is outlined in the flow diagram of FIG.  2 . In this diagram, 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 I 
                 intensity of scattered light from PMT 
               
               
                   
                 n 
                 number of laser pulses 
               
               
                   
                 φ 
                 angle 
               
               
                   
                 I cleam   
                 background intensity, scattering from a clean surface 
               
               
                   
                 n max   
                 maximum n allowed (e.g., n ave  + 2σ) 
               
               
                   
                 P 
                 laser power 
               
               
                   
                 P max   
                 maximum safe laser power. 
               
               
                   
                   
               
             
          
         
       
     
     At the start of the process the excimer laser  10  is activated to start cleaning as indicated by box  17 . The intensity of the scattered light and the angle of the scattered light is determined by the photomultiplier  16  as indicated in box  18 . Depending upon that determination, the cleaning continues as indicated in  19 . In this situation there are further pulses of light which are applied by the excimer laser  10 . The excimer laser  10  can increase in power, as indicated by  20 , if necessary. Where that power is increased greater than the maximum safe laser power as indicated in  21 , the process is stopped as indicated in  22 , since the substrate  12  would have flaws. The increase in power can be caused by either the number of laser pulses exceeding the maximum amount or the time of the pulses being applied increases beyond a maximum amount as indicated in  25 . As indicated in  23 , when the intensity of the scattered light as measured by the photomultiplier  16  increases in a number of pulses and angle beyond the amount necessary, then a substrate cleaning process is stopped as indicated in  24 . In the situation where the intensity of the scattered light relative to the number of laser pulses is greater than a predetermined number as indicated in  27 , then the process stops because of possible damage to the substrate as indicated in  26 . 
     The location of the laser spot on the disc surface is identified by the radial (r) and angular (α) position on the disc surface. The area to be scanned on the disc surface can be selected by choosing the appropriate radial and angular position limits. Angle θ 1  is the angle at which the detector(s) are placed to collect the scattered light from the disc surface. A number of detectors will be placed at different angles (0-90°) around the disc to ascertain the size of the particle. Angle θ 2  is the angle of incidence of the laser beam on the disc surface. This angle will be chosen, between 0-45°, to obtain maximum cleaning and minimum damage to the substrate. The maximum number of pulse n max  will vary from 30-200 Hz for different substrates. This quantity is used to control the amount of laser energy incident on the substrate. 
     For efficient cleaning of the discs the laser beam shape incident on the disc surface is modified with properly designed shutters and optics. This is done so that uniform energy is made incident throughout the disc surface. FIG. 3 shows a scheme of designing the beam cross-section  30  such that the desired overlap over two subsequent measurements can be obtained. 
     In this scheme for disc cleaning the scattered light intensity is measured as a function of number of laser pulses used and angular location ∝ on the disc. If the intensity reduces to a level characteristic of a clean surface there is no need for further exposure and the cleaning process is aborted. 
     There may be a need for a minimum exposure, however, to assure uniform surface properties on the post clean substrate. If the intensity is higher even after a n max  number of pulses applied, the laser power can be increased up to a the maximum safe laser power (P max ). If the scatter intensity increases with the number of pulses, surface roughening or other damage to the surface is likely. The discs are taken out of the process flow if there is indication of surface damage, or the maximum safe laser power is reached without reduction of the scatter intensity. The values of I clean , n max , and P max  are determined experimentally with calibration discs. 
     The geometry of the source  10  and detection PMT(s)  16  are optimized to allow discrimination of particles and other non-removable surface features such as pits, bumps and micro scratches. 
     In one preferred embodiment, laser cleaning and inspection procedures are carried out, for example, on a surface of a recording medium or disc substrate, prior to applying a thin layer of film of magnetic material to the surface. In further embodiments, such laser and inspection procedures may also, or alternatively, be carried out on the layer or film of magnetic material, after the material has been applied (such as sputtered on) to the substrate surface. 
     Combining laser cleaning with inspection results in savings in tool cost. The yield of downstream processes will increase because discs that cannot be cleaned are not be processed any further. 
     CONCLUSION 
     This concludes the description of the preferred embodiment of the invention. The following describes some alternative embodiments for accomplishing the present invention. 
     For example, any number of different types of surfaces could be used with the present invention. Those skilled in the art will recognize that the present invention could be applied to both magnetic and optical disk drives. 
     In another example, surfaces having different structures and components from those described herein could benefit from the present invention. Those skilled in the art will recognize that the system, method and apparatus could have a different steps and structures from that disclosed herein without departing from the scope of the present invention. Those skilled in the art will recognize that the present invention could be used with heads that only read, but do not record. Those skilled in the art will also recognize that the present invention could be used to position optical heads rather than magnetic heads. 
     The foregoing description of the preferred embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. `It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.