GB2312865A - Apparatus for the diagnosis of a surface and subsequent selective removal of layers by laser - Google Patents

Description

2312865 APP.ARATUS FOR THE DIAGNOSIS OF A SURFACE AND T11-11E SUBSEQUENT

SEtECTIVE REMOVAL OF LAYERS PACKGROUND OF THE INVENTION The invention resides in an apparatus for the diagn,,-5'.5 of a sur-.5ace a-rid the z--Libsecr..lent selective re:noval of lavers fror. this surf- ace by irradiation with a pulsed laser wk-lich inCludes the optIcal element-s for the diagnosis and the treat- ment of the surface by a laser beam.

US Patents 4,15588,835 and 4,737,628 disclose inethods and an apparatus for diagnosing a surface before laver thereof are selectIvely rer;.cved by a pulsed laser beam. For thle diagnosis, the surface is Illuminated by light. cf known spectral comoosition. The light reflected from this surface ls subjected tc. spectral analysis by way of a diff-raction screen. From te spectral composlition of th-ie reflected light, the -reflection properties of the surface and consequently their cclor car, be deterTmined by ccr.n.parison wIth earlier determined 1S comparison spectral testing results. It is therefore possible to decide tc what degree a layer removal has proceeded that is whether a layer removal was sufficient by the irradiation to T in time or whether ,h.-.i.ch it was subjected at a certain poJ-rit the removal of surface layers must be ccntirued.

A reproducible illumination ofF the surface is very impor tant -i.n. this process since only t4hen can the light reflected f r on... the surface be compared with giver. standards in a suf f, ciently accurate manne-r. However, thils condition is not nec- essarily fulfil-led with prior art arrangernents as they are disclosed in US patent 4,588,885. In the procedure disclosed therein, it is particularly disadvantageous that the diagnosis is detrimentally affected by the surface renoval itself.

During the removal of surface layers by pulsed laser beams, there is generated with each pulse a strong light flash whose spectrai. composition and brightness depend to a great degree on the respective layer and which acts as an undesir able pulsed additional illurmination. F-i-,r'hermore, the sudden vaporization of the layers generates a relatively large amount of vapors which may change the spectral coirLiDos--'11--icr- and the intensity of the illuminating light as well as that of the reflected light in an unpredictable manner. This is particularly true if the laser _Js operated at a relatively high repe- tit-lon rate and the time between the pulses is _insuffic-Lent to completely suck away the vapors. In addition, the operating area Zs rapi- ll-v soiled - inspite of the suction-ing off of vapors - by dust clepcs4;. -t-io.n- whereby the illumination conditions may also be changed in an unpredictable manner. It the suct..4.oning proce,--'ure and the diagnosis are performed wit-hin the same space, an optincizing of the area for both procedures is practically impossible.

DE 44 26 490 discloses an apparatus for the analysis by laser light of mechlanical components which are moved by a mov- ing unit. In the apparatus", the part to be analyzed is first i.l1=...ina- .ed and recorded by a camera, for example a CCD cantera. With an evaluation unit, the lightest and, consequently, blank metallic portion of the component is determ-ined. a_nd the laser light is then directed onto this lightest port-Jon for a laser-ind-aced spark spectroscopy. Although, with this arrangement, the recording of the picture and the part to be analyzedl and subjected to the laser light or the plasma generated there-by and em-itted therefrom are spatially separated in the dl rection of movement of the moving unit, the pictures recorded by the cainera are still detrimentally affected by the laser light or rather, the plasma generated thereby.

It is;the object of- the present invention to provide an apparaxtus for tihe diagnosis of a surface and the selective removal of lavers therefron, by means of a laser beam wherein the diagnosis step can be accurately performed so that the subsequent layer re=oval step can be properly executed.

SIUMMAIRY OF THE INVENTION in an apparatus for the diagnosis of a surlEace and the subsequent selective removal of layers frorn the surface by a pulsed laser beam wherein repeatedly areas of the surface to be diagnosed are illuminated, t'-,-e light- reflected from the J.1- surfaces is diffracted into spectral ranges inte.nsities are measured and compared with standards and depending or- this comparison layers are removed by pulsed laser beans from the surface areas diagnosed, the spaces in which the diagnosis of the surface areas and the laser irradiation procedures are performc-d, are spatial-1v separrated and sealed fror. one an3ther against dust and light- conta-mination.

In order to prevent the diagnosis frc.,rt being detrimentally affected by the layer removal by the pulsed laser bear., a) the diagnosis area and the laver rer,.,..cval area are spatial-1v separated from one another in a light and dust-sealed manner so tll^za'.- flashes and vapors generated by the --c-T-rova-l of layers cannot detrimentally af-fect the diagnosis: and.

b) The diagnosis is performed in a -L.4:-rre-',y spaced manner ahead of the layer removal so that it is known before the beginning of the layer remcval where and to what degree layers still need to be removed.

The invention will be described below in greater detail on the basis of the acconpanying drawings.

BRIEF DESCRIPTION OF THE n6PYRINGS

Fig. 1 shows schematically, in a perspective view, an am paratus accord-i.n.g to the invention, Fig. 2 is a longitudinal cross-sectional view of the ap paratus shown in Fig. 1, Fig. 3 shcws a typical sample of surface areas to be di agnosed and subsecraently, irradiated, those surface areas be ing designated "foot prints", Fig. 4 shows a sample like that sho.wn, in Fig. 1 wIt-hin the diagnostic area.

is DESCRIPTION OF A. PREFERPED E1MBWIMENT

The apparat-us as shown in figures 1 and 2 consists of an operating head 3 a diagnosis housing 12 which are in..oved of a coate-1 sutstrate 1C such t_ogether across the surface 5 th.at Che laser irradiation zene 8 can first be d'Lagrio.-;Gd in a spatially and timely separated manner fro-m the subsequent laser treat- ment procedure. The laser beam '. of a pulsed TEA-CO.2 laser (not shown) is guided, by a mirror syste-m 2 into the operating head J35. In the operating head, there is a pivotable mirror 4 which directs the laser beam 1 ontc the surface 5 f-rox, which a layer is to be removed. The size of the surface area 7 which can be irradiated with each pulse, is determined by the beam. guide and geometry and must coincide with a diagnosed surface area (-footprint) wInich has been deter.m-i---ed earliler bv a computer. The location of the surf-ace area 7 de- pends on the position of the pivotable mirror 4 and the position of -he oFerating head 3. If the p--vctL-able mirror 4 _Js pivoted about the axis 6, an area 8 within 7-he pivot range of mirror 4 can be irradiated. if additionally the operating head 3 is moved across the surface 5 in the direction T normal to the plane o_lf th.e pivot movement S, a path 11 with a width of the pivot range of 'the irradiation area 8 can be -4--radiated on the surface 5.

The apparatus for the diagnosis is arranged in the hous ing 12 which is mounted on the operating head 3. F1g. 2 is a cross-sectional view of the operating head 3 and the diagnosis housing 12. In order to separate the diagnosis ch.amber 13 from the operating 14 and from the surrounding area in a lIght- and dust-tight- =anner, there are provided separating wa,!,.ls 15 which have sealing lips 1-6 disposed on the surface 5.

A color camera 18 is mounted on the diagnosis 12 whereby the diagnosis area 19 within the sealed chamber 1-3 can be observed. W4hthin the diagnosis housing 12, there is -illu- is mination equipment 20 by which the diagnosis area 19 can be illuminated in a homogenous rrhanner.

Fig. 3 shows, in an exemplary manner, a sample 21 of surface areas 7 which are subsequently irradiated by a laser beam 1, after the pivotable mirror 4 has comnleted a full nivot moveme-nt 5 and, at the same time, the opera--ing head 3 has been move:i transversely in the direction T. In this example, the mivot r.to,7ement 5 _is faster than -the translatory moveTment of the operating head 3 in the direction T.

rig. 9 shows -the sample 21 within the diagnosis housj-'.ng 12. If the color camera 18 takes a picture at any -.o.ment, it can record the sar..tple 21 consisting of a multitude of surface areas 7 as far as they are disposed in the diagnosis area 19. With a known pivot movement 5 of the p,.votaL-le mirror 4 and a known translatory movement of the operating head 3 in the di- rection T, the time period is k-.n-own-- which passes between the momentarv recording tine, and the point of time, at which the laser beam guide, controlled by the pivat move.ment of the pivotable mirror 4 and the translatory mover.ent of the operating head 3, directs t.L-e laser bean. to the respective surface areas of the s-2r..ple 21. If it is then possible to evaluate the ro:ri.eritary record-ing sufficiently fast for all the surface areas within the diagnosis area 19, the laser pulse can be selectively blocked or released fzr each of the surface areas 7 3 of the sample 21. To this end, it -is advantageous first to transfer the complete nomentaty record of the camera into the computer memory (not shown) and then to divide it in the memcry into the particular surface areas 7 according to the san--pie 21 and f_inally to compare the color information of each- surface area 7 with the standards. The laser pulses can th-en be blocked or released by the cornputer dependling on the respective coiitoarisc-ri as s.Don as the laser bea:n guide has reached the resmective surface area.

Claims (2)

1 of a s..y-face and the A.. An apparatus for the diagnosis subsequent sellective removal of layers fron, this surface by irradiation with a pulsed laser, said apparatus includ=g optical elerv.ent5 for the diagnosis and for the subsequent treatmen.t of the surface by a laser beam, wherein a) areas oil- th-le su--face to be diagnosed are il-l,,-i,.inatedt in zones, by light of a predetermined spectral cOmposition, the -light refIected from the surface a--=-as is d",.,-fra--ted into spectral ranges whose -i.-.tenz,:it-;_es are measured and --cmpared with s tandards, b) depending on this comparison at least one laser pulse is --eleased which causes the rer...cval of a layer from the starface area d-iagnosed, c) and then the procedures a) and bi are _repeated for additional sur- face areas untlil the whole surface area from which layers have to be removed is treated, said apparatus including a housIng enclosing said optical el-e-.ne.,,.ts for the diagnosis off the surface areas and, in spaced relationship from said housing, equipment for the -irrad'a.'-,on of the surface areas by laser beam exposure, said housing havIing sealing means such that a diagnosis of the surface areas performed in said housing is n.:.-- affected by dust and _light contamination from the adjacent area in which said laser irradiation takes place.

2. An arrangement according to claim 1, wherein said housing is mounted to a,-. operating head which includes said equipment for IL-he irradiation of the surface areas by laser bean, exposure and said housing includes walls separating the area containing said optical elem.ents and said irradilation equipment and having sealing lips engaging said'surface.