GB2270325A - Application of a thin metal layer to a polymeric substrate using screens - Google Patents

Description

2270325 Application of a thin metal layer to a polymeric substra:te This

invention relates to a process for applying a thin metallic layer, having a thickness of less than 1,000 nm, to a polymeric, web-like substrate which is moved along a cylindrical support in a vacuum chamber containing an evaporator crucible releasing metal vapour towards the support and two coating screens arranged between the evaporator crucible and the support and defining the limiting angles of the vapour jet striking the substrate.

The application of thin metal layers to polymeric substrates is of particular interest in the production of magnetic recording media. In comparison with conventional particulate magnetic media, coherent magnetic thin films permit recording at higher storage densities. This is due on the one hand to the small layer thickness of only from 20 to 1,000 nm and the associated low demagnetization effect and on the other hand to the larger number of molecular or elementary magnets per unit volume and the higher magnetization. While in the case of particulate recording media, longitudinal recording of the magnetic particles oriented along the tape running direction is usual, in highdensity magnetic thin films an oblique orientation of the molecular magnets in the coherent metal layer in accordance with the field lines in front of the head, is desirable. Substantially improved recording properties can be achieved by oblique deposition of the f erromagnetic material onto the substrate, as described inter alia for Co-Ni-0 layers of USA-3 242 632 and US-A-4 323 629 or for Co-Cr layers by R.

Sugita et al., Digest Intermag 1990, Paper FA-08. The angular range which is desired in each case and which decisively influences the properties of the applied magnetic layer is obtained by suitably arranging screens in the vapour deposition or sputtering of material. Compared with coating at right angles, however, the sometimes dramatically reduced efficiency of evaporation is a disadvantage in oblique incidence coating (A. Feuerstein et al., IME Trans.

Mag. 10 (1) (1984) 51). It has therefore been proposed, in the case of electron beam evaporation, to collect on a condensate plate some of the vapour incident outside the intended substrate range and to recycle the vapour to the crucible. In another method for increasing the efficiency of evaporation, the vapour jet is ionized and is directed at the substrate film by means of electric fields (DE-C 26 22 597). In a further process, the vapour cloud is guided to the substrate through a chimney having heated walls (see DE-

A-3204337).

It is an object of the present invention to modify the process of applying thin metal layers to a polymeric substrate by means of a PVD method by oblique deposition of the material so that the efficiency of evaporation can be optimized for a predetermined range of angles of incidence.

We have f ound that good results are achieved in a process f or the application of a thin metal layer with a thickness of less than 1, 000 nm to a polymeric, web-like substrate which is moved along a cylindrical support in a vacuum chamber having an evaporator crucible releasing the metal vapour toward the support and two coating screens arranged between the evaporator crucible and the support and defining the limiting angles of the vapour jet striking the substrate, if, in the case of predetermined limiting angles of incidence al and a2 which are given by the angles between the normals to the support at the edges of the screens and the connecting lines from the centre of the crucible to the corresponding edges of the screens, the centre of the evaporator crucible is arranged at the point P (xT/YT) in the coordinate system f or a f ixed YT position, and the positions of the coating screens which leave a region of the substrate limited by the angles 91 and 92 free for coating, the angles 91 and 92 each being calculated for the counterclockwise direction starting from the positive x axis of a coordinate system whose origin is on the axis of rotation of the support, are defined by the angles a, and U2 and the position of the crucible, so that, according to the formula 3 - f 02 ((P2'Xt,YT) cosn (p) dp A ((p,, (P2 dr xtr -V,) (91,Xt,YT) X 2 cosn (p) dp 11 2 A has a maximum value at the point xt = xT, where A is the amount of the metal vapour striking the substrate relative to the total evaporated amount, P, and P2 are the angles between the normal to the centre of the crucible and the connecting lines from the centre of the crucible to the edge of the particular screen and n is a number from 2 to 5.

Embodiments of the invention will now be described, by way of example, with particular reference to the following Examples and accompanying drawings, in which:

Figure 1 is a schematic view illustrating the geometric relationships for oblique incidence coating of a substrate with a metallised layer, Figures 2 and 3 show efficiencies of evaporation according to the Examples as a function of the position of the evaporator crucible and the positions of the screens for predetermined limiting angles of incidence, and Figure 4 is a program listing for calculating positions for the evaporator crucible and coating screens.

A vapour deposition station shown schematically in Figure 1 is used to illustrate the novel process of the present invention. Here, a web-like substrate 2 is passed over a cylindrical support 1 having a radius R and whose axis of rotation passes through the origin of an x/y coordinate system. By means of coating screens 3 and 3' positioned close to the surface of the support 1, a range 5 is selected, from a (metal) vapour jet emanating from an evaporator crucible 4, for condensation on the substrate.

The angular range 5 which is left free on the substrate 2 for vapour deposition is defined by the angles T1 and T2, the range of angles of incidence is defined by the angles a, and a2 and the position of the evaporator crucible is defined by the coordinates xt and yt. In the positioning of the crucible, the yt position is generally fixed (yt -- 1 YT). Assuming a linear crucible, the f ollowing relationships are obtained f rom the geometric arrangement for the coating angles P, and P2 (based on the normal 6 to the centre of the crucible):

( xt -COS(P1) P2.((PIIXCIYT) = arctan R ( YT-sin(P2) R -COS(P2) M(P2fXCPYT) = arctan R -sin(P2) R With the predetermining limiting angles of incidence a, and a2 and with the particular chosen position xt for a fixed position YT Of the crucible, the angles p, and 92 are obtained as solutions of the implicit equations X -COS(P1 (a,.' Xt) (p2.(al,xt) = 2700 arctan YT a, -(iii) sin(p,(al,x,))_ and X 'R -COST2 (a21 Xt) (P2 (CC2 1 Xt) = 27 0' ar ctan yc a2 -(IV) R -sin(p. (a2, xt) From these formulae I, II, III and IV, the following mathematical expression is obtained for the relative efficiency of evaporation A which remains in the substrate region defined by the angles D, and P2:

P2 (921XClyT) cosn (P) dp A ((p, r (P21 Xt 1 -VT) - 41(91,XC'YT) (V) 7C 2 CoSI2 (p) dp 2 where n is from 2 to 5.

For predetermined values of R, al, a2, YT and n, and depending on xt, T1 and T2 can be calculated from formulae (III) and (IV), P, and P2 can be calculated from this and from formulae (I) and (II) and finally A can be calculated from this and from formula (V) using a numerical integration. A corresponding program is shown in Figure 4. The position XT Of the centre of the evaporator crucible and the screen positions T1(xT) and (P2(xT) at which the efficiency of evaporation is a maximum can be determined from the curves A(xt), 91(xt) and 92(xt).

The two Examples below are intended to illustrate the novel process and, by way of example, for predetermined parameters R, yt, al, a2 and n, to demonstrate the optimum positions of the evaporator crucible and of the coating screens.

EXAMPLE 1

In a coating apparatus corresponding to Figure 1 and having a support radius R, the YT position of the crucible is defined by -1.5 R, the limiting angles of incidence a, and a2 are def ined by the angles 900 and 400 and the exponent n is 3. Using the program listed in Figure 4, A(xt) [Figure 2a] and qpl(xt) and (P2(xt) [Figure 2b] were calculated. From the Figures, the crucible position xT with optimum efficiency of evaporation and the associated screen positions can be determined: xT = -0.64 R, (P1(xT)=1940, T2(xT)=2300.

EXAMPLE 2

The parameters differ from those of Example 1 in that the angle (xl is 700 and the angle a2 is -200. The corresponding calculations are shown in Figures 3a and 3b. The Figures have the following values for the configuration 10 with the optimum efficiency of evaporation: xT = -0.27 R, (P1(xT)=227c', (P2(xT)=2670.

F1 G. 4 program bvtpat2 c S include: 'bvt.incl call calc-constbeta-effi lf(accepted(10nce more the stuffl,1Y1)) goto 10 stop end real4 function phi(x,y,r,alpha,phimin,phimx,phiestimte,list) c C evaluates the transzendental expression C phi + arctg((rcos(phi) - x)/(rsin(phi) -y)) alpha + 1.5pi C The result for phi can only lie in the intervall (phimin, phimax]. C if alpha - +90 degrees. then phi - phimin, C if alpha - -90 degrees, then phi - phimax. c implicit none logical list real4 x,y,r,alpha,phimin.phimx,phiestinate, ph:Lminr,phimaxr,rad:Lan,p!32,alpharpi32, rhvold, rhvnew, rhv, deltaphi, phii data p132 14.71238891!1.5 3.14159 radian/57.295779/ if(list) then write(,) 'here function PHI: x,y,r,alpha,phimin, phimax' write(,) x,y,r,alpha,phimin, phimax end if alpharpi32 - alpha/radian - pi32 phiminr - phimin/radian phimxr - phimax/radian deltaphi - (phimaxr -phiminr)1100.0 phli - phleatimate/radian rhvnew - phi! + atan2((rco3(phil)-x),(rsin(phli)-y)) + alpharp132 if(list) write(,) 'value of phi:',philradian, 1 rhvnew: 1, rhvnew rhvold - rhvnew phi! - phii + deltaphi if(phii.lt.phiminr) then if (list) write(,) 'Abort: phii.lt.phiminrl phi - phiminr radian return end if:1f(phil.gt. phimaxr) then if (list) write(,) 'Abort: phil.qt.phimxrl phi - phimxr radian return end if rhvnew - phii + atan2((rcos(phii)-x),(rsin(phii)-y)) + alpharp132 if(list)write(,) 'value of phi:l,ph:Liradian,' rhvnew:',rhvnew i0(abs(rhvnew).1-.1.0e-5) then!abort iteration if(list) write(,) Abort: abs(rhvnew).1t.1.0e-5' phi - phii radian return end if if(rhvnew rhvold At. 0.0) then!a root of the equation was deltaphi deltaphi/(-2.0) just passed, reverse direction goto 10 and decrease step size end if i.l;(abs(rhvnew).gt.abs(rhvold)) then!change direction of search deltaphi - -1.0 deltaphi goto 10 end if goto 10!continue adding deltaphi to phi end subroutine calc constbeta effi c C calculates the efficiency of evaporation for given angles of incidence alphalc C and alpha2c as function of x-position. The Y-position of the crucible is kept C constant. C The final plot will be the efficiency over the x-coordinate. $ include: Ibvt.inc' real xarr(200),yarr(200), phiap11(200), phiap22(200) double precision rdef logical list character100 title integer narr data narr/2001 alphalc/85.0/ alpha2c/40.01 write(5,10) f ormat (/ 1, ' Now enter parameters for Efficiency over X-position I(Alphalc,alpha2c-const)ll 1x,78(-')) rr - rdef('Radius of central roll ImmI',dble(r). 1.OdO,1000.OdO) xleft-rdef('Left limit of X-interval [m]',dble(x002.0), -1.dLO, 1.d10) xright-rdef('Right limit of X-interval [=m]I,O.OdO, dble(xleft),1.d10) y000- rdef(IY-position of crucible fmmll,dble(y00), -1.d37,0.OdO) exponn-rdef('Exponent of cosn-evap. characteristics', dble(expon),1.OdOS.OdO) C now specify the desired angles of incidence (measured as usual with respect C to the surface normal) alphalc rdef('Angle of incidence alphal [degree]', dble(alphalc),-90.OdO,+90.ODO) alpha2c - rdef('Angle of incidence alpha2 [degree]', dble(alpha2c),-90.OdO,dble(alphalc)) list - false. if (accepted('Extensive listingl,INI)) list - true. write(,) if(.not. accepted('Parameter O.K.','Y1)) goto 5 Cl C create the title line for the plot write(title,90) rr,yOOO,myint(exponn),alphalc,alpha2c format(IR [mm]-1,f6.1,'; YOO [mm]-',F6.1,1; Exp-1,12, 1; Alphal, 2 [degree]:',F6.1,'->',f6.1) C now calculate the arrays for cos2 characteristics write(5,300) 300 format(P No. X-pos phiapl phiap2 betal beta2 'efficiency'/lx,68('=')) deltax (xright-xleft)/narr do 500 1 - 1,narr xarr(i) - xleft + ideltax C now calculate the phi-range that can only be reached by particles leaving C the crucible. This range is specified by phiminn and phimxx. phicenter 1.5pi - atan(xarr(i)/y000) distance sqrt(xarr(i)xarr(i) + y000y000) gamma - asin (rr/distance) delta - 0.5pi - gamma phiminn - (phicenter - delta) radian phimaxx - (phicenter + delta) radian C now calculate the phiapl and phiap2 which yield the desired angles of C incidence alphal and alpha2. These values must lie in the interval C [phiminn, phimaxx] if(i.eq.1) then!start with reasonable estimate phiestimate - (phimaxx + phim:Lnn)/2.0 else phiestimate - phiapll(i-1) end if phiapll(i) - phi (xarr(i) y000,rr, alphalc,phiminn, phimaxx, phiestimate,list) if(i.eq.1) then!start with reasonable estimate phiestimate - (phimaxx + phiminn)/2.0 else phiestimate - phiap22(i-1) end if phiap22(1) - phi(xarr(i),y000,rr, alpha2c,phiminn, phimxx, phiestimate,list) C now calculate the beta angles for the coating window and the efficiency C for the evaporation process betalcc atan2(rrcoi(phiapll(i)lradian) - xarr(i), rrsin(phiapll(i)lradian) - y000) beta2cc - atan2(rrcos(phlap22(i)lradian) - xarr(i), rrsin(phiap22(i)/radian) - y000) betalec - betalcc radian beta2cc beta2cc radian yarr(l) - effic(betalcc, beta2cc, exponn)/ effic(-90.,90.,exponn) write(5,400):L,xarr(i),phiapll(!),phlap22(i), betalcc,beta2cc,yarr(i) 400 format(lx,i3,1)1,5f8.2,f8.5) 500 continue call hpsgra(xarr,xarr,yarr,yarr,narr,title) C create the title line for the plot of upper apperture position ko write(title,520) 520 format('Position of Apperture no. 1 (upper apperture)l) write (5, 525) 525 formatU 1 Now plotting angles of upper apperture! (RET to cont.) call hpsgra(xarr, xarr,phlapll,phiapll,narr,title) C create the title line for the plot of lower apperture position write (title, 530) 530 format('Position of Apperture no. 2 (lower apperture)l) write (5, 535) 535 format(/ ' Now plotting angles of lower apperture! (RET to cont.) call hpsgra(xarr, xarr,phiap22,phiap22,narr,title) return end subroutine tinfo C return end block data emil C some constants required for the calculation are initialized here $ include: Ibvt.inct Data titlel/ISimulation of CoNi-Flux (one-dimensional crucible paralle 1 to cylinder assumed)'/ title211Shape of columns obtained by oblique incidence evaporatio n in roll coaterl/ r/295.0/ x00/-295.0/ YOV-501A/ radian/57.295779/ pi/3.14159261 nofdp1149/ phiapl/180.01 phlap2/219.0/ 13X/0/ expon/2.01 iangopt/1/ rangopt/1.01 end Real4 Function effic(xmin,xmax,nexp) C C calculates the integral over cos(x)nexp within the limits xmin and xmax C (values passed to this routine in degrees!!).

C Nexp is the exponent (may be any real value) implicit none real xmin,xmax,nexiD real xmi,xma,x,valuel,value2,h integer i,n xmi = xmin 57.295779 xma = xmax 57.295779 n - 100!integration interval splitted up in n regions h - (xma-xmi)l(n+n) valuel = 0.0 value2 = 0.0 Do I = 1,n-1 x = xmi + h (i+i) value2 = value2 + cos(x)nexp x - x - h valuel - valuel + cos(x)nexp end do valuel valuel + cos(xmah)nexp!for valuel loop up to n required effic h13.0 (4.valuel + 2.value2 + cos(xmi)nexp + cos(xma)nexp return end -------------------------- C this file is the include file for BVT.FOR character80 titlel,title2 real xang(800),yflux(800),sx(SOO),sy(800) logical accepted common lparam/ r,xOO,y00,nofdp,efficiency,cefficiency,radian,pi, phimin, phimax, betal,beta2,betalc,beta2c, phiapl,phiap2,alphalc,alpha2c, expon,, iangopt,rangopt /data/ xang,yflux,sx,sy,isx,titlel,title2 - a-

Claims (3)

1. A process for applying a thin metallic layer of a thickness of less than 1,000 = to a polymeric, web-like substrate which is moved along a cylindrical support in a vacuum chamber containing an evaporator crucible releasing metal vapour toward the support and two coating screens arranged between the evaporator crucible and the support and defining the limiting angles of the vapour jet striking the substrate, wherein, in the case of predetermined limiting angles of incidence a, and a2 which are given by the angles between the normals to the support at the edges of the screens and the connecting lines from the centre of the crucible to the corresponding edges of the screens, the centre of the evaporator crucible is arranged at the point P(xT/YT) in the coordinate system for a fixed YT Position, and the positions of the coating screens which leave a region of the substrate limited by the angles T1 and T2 free for coating, the angles T1 and T2 each being calculated in the counterclockwise direction starting from the positive x axis of a coordinate system whose origin is on the axis of rotation of the support, are defined by the angles a, and a2 and the position of the crucible, so that, according to the formula f 1P2 OP2,XC'_VT) cosn (p) dp p A ((p, g P2 1 Xt 1 YT) 2 cosn (p) dp 2 A has a maximum value at the point xt = xT, where A is the 25 relative amount of the metal vapour striking the substrate, P, and P2 are the angles between the normal to the centre of the crucible and the connecting lines from the centre of the crucible to the edge of the particular screen and n is a number from 2 to 5.

2. A process for applying a thin metallised layer having a thickness less than 1,000 nm to a polymeric web, the process being substantially as herein described with reference to Figures 1 to 4 of the accompanying drawings and 5 to the foregoing Examples.

3. Magnetic recording media having a thin metal layer applied to a polymeric web-like substrate by a process as claimed in claim 1 or 2.