CA1159792A - Permalloy thin film electroplating system - Google Patents

Abstract

MAGNETOSTRICTIVE ALLOY THIN FILM ELECTROPLATING
METHOD
Abstract of the Disclosure A thin film of low magnetostriction Permalloy* 80%
nickel - 20% iron + 1% is electroplated onto a substrate in a bath having a ratio of from 5.8:1 to 23:1 ratio of Ni to Fe ions with a plating current density from 10 ma/cm2 - 200 ma/cm2 when plating in sheet form or an Ni/Fe ratio of from 25:1 to 86:1 with a current density of from 2 ma/cm2 - 60 ma/cm2 when plating through a mask. The fluid in the system is constantly mixed, replenished with fresh iron, acid, and other reagents, is adjusted in temperature and subjected to a continuous laminar regime of mixing. The Fe++ ion concentration required is inverse to the circulation of bath fluid across the substrate.
Fresh solution is added to the bath from a reservoir where the above adjustments are made. The inlet for the fresh solution is at the lower end of the plating chamber and directed at a bath mixer which includes a slot through which the fresh solu-tion is directed to optimize mixing in the plating chamber.
Complexing agents are avoided. High speed plating is obtained with about 24.4 g/l of Ni++, 1.05 g/l of Fe , 25 g/l of H3BO3, 0.2 g/l of Na saccharin and a pH of 1.5 to 3.6.
* Trade Mark

Description

Background of the Invention Field of the Invention The invention relates to chemistry, involving electrical energy and more particularly, electrolytic cell apparatus with an agitator and a solution controlling system.
Description of the Prior Art United States patent No. 3,652,442 of Powers et al entitled "Electroplating Cell Including Means to Agitate the Electrolyte in Laminar Flow" shows a bath container including q~

~ 159792 a reciprocat ng arm with a stirring paddle compo~ed of a

2 base port~on trian~ular in cross-section with sharp edges

3 facing forward and back to ~inimize turbulence and an apex

4 in the center pointing upwardly which is relatlvely blunt. ~
transverse member is spaced abo~e the base ?ortion having an 6 inverted form of the same cross-section so the base membe 7 and the transverse member define a slot through which the 8 fluid near the base of the bath container can pass as the 9 paddle is reciprocated back and rorth across the base of the container to stir the electrolyte. However, this patent 11 does not provide any means fo~ circulating or replenishing 12 the bath. The patent describes a bath with 109 g/l of NiCl7 6H20, 13 3-88 g/l of FeC12 4H20, 12.5 g/l H3B03, 0.4 g/l Na Lauryl 14 Sulfate, and 0.5 g/l saccharin, in a magnetic field of 40 Oe at a bath te~perature of 20C by means of the continuous 16 plating technique with continuous agitation with the paddle, 17 for plating a flat sheet. With respect to the above formulaticn, 18 for plating a flat sheee, the nickel-to-iron ratio of ions 19 is believed to be excessive. On the other hand, the plating rate for deposition into photoresist mask defined ?atterns 21 is not defined at all.
22 United States patent No. 3,317,410 of Croll et al 23 for "Agitation System for Electrodeposition of ~lagnetic 24 Alloys" shows a plating system with continuous circulation of f luid and te~perature control, where the solution i3pinges 26 at right angles onto the cathode, which is uniform for ~ery 27 small areas only.
28 Unitet States patent No. 3,649,509 of ~ora-~etz e~
29 al.for "Electrodeposition Systems" includes means for ~ecyclJng fluid through a conduit into which heat, acid and speci~ic 31 gravity additives are applied. The system includes no ~; 32 paddle, the fluid is admitted far from the su~strate ,o be 33 plated, no ions to be plated are added, and no teachin2 Yo975-~65 2 l 159792 l relative to Permalloy alloy is included. Measurement is auto-matic and continuous, but adjustment is manual and intermittent.
Furthermore, manual adjustment is unreliable, requires labor and there may be a long response time in comparison to the p:Lating time, and there may be resulting large fluctuations in solution temperature, pH and specific gravity. Also, specific gravity is not a correct measure of the rate of consumption of reagents comprising the alloy being plated and, in particular, of iron which is the most sensitive reagent in terms of main-taining a constant quantity level.
U.S. Patent No. 3,505,547 of Ambrosia et al teaches a bath for depositing Permalloy alloys in which Fe++ ions are in a concentration in the range of lO 3 to 5 x lO 2 mole per liter and Ni ions are in a concentration of 10 to 5 x 10 mole per liter, such as 0.2 mole (52 grams) NiSo4, and 0.2 mole (55 grams) FeSO4 per liter. In another example, it teaches use of 0.4 mole (105 grams) NiSo4 and 0.1 mole (27.8 grams) FeSO4.
In still another case, 0.4 mole (105 grams) NiSO4 and 0.2 mole (55 grams) FeSO4 are provided. In each case, 10 grams of H3BO3 were used along with metallic ion additives with negative deposition potentials such that they do not codeposit in an amount of lO to 10 mole per liter. The pH is from 1.3 to 7.
U.S. Patent No. 3,716,464 of Kovac et al teaches a method of electrodepositing Ni-Fe (80-20) alloys. It also teaches use of a NiSo4 and FeSO4 solution with concentration levels such as 20/80 and 5/95 (1/19) of (Fe/Ni) sol. with about .3417 g/l of Fe and 6.72 g/l of Ni (based on NiSo4 6H2O = 30 g/l and FeSO4 7H2O = 1.7 g/l, with a peak current density of ma/cm and with a maximum plating rate of 125 A/min). 'The pH is 3.0 @ 25 C and 10 g/l of NaK-tartrate is used as a complexing agent.
* Trade Mark l 1~9792 In a publication by Bartelson et al entitled "Electrodeposition of Ni-Fe Films," a solution of 25-60 g/l of Ni as nickel sulfamate, 1-3 g/l of Fe as ferrous ammonium sulfate, 25 g/l of boric acid, 1 g/l of saccharin, 0.5 g/l of sodium lauryl sulfate, pH 3.7-3.0, temperature 25-30C, cathode current density 4.3~8.6 ma/cm2 is disclosed. However, the sulfamate ion is a complexing agent which complexes both nickel and iron.

Summary of the Invention In one aspect of the invention, there is provided a nickel-iron electroplating method, for electroplating a nickel-iron film onto a sheet substrate of a metallic material, including the steps of providing a plating fluid bath having an Fe++ ion concentration of about 1-14 g/l, an Ni ~ ion concentration of about 7-37 g/l; maintaining said bath at a pH of about 1-3.6; maintaining the bath at a tempexature of from 20-35C; employing a plating current density of about 10-200 ma/cm2; the Fe ion concentration required in the bath for a predetermined Ni percentage in the nickel-iron film being an inverse function of circulation of bath fluid across said substrate.
In another aspect of the invention, there is provided a nickel-iron electroplating method including the process of electroplating nickel-iron films containing about 20% iron 1% onto a sheet substrate of a metallic material, said method including employing a plating current density of about 10-200 ma/cm2, a plating bath fluid with an Fe ion concentration of about 1.1-1.7 g/ll an Ni ion ~, Yo9-75-065B 4 l 159792 concentration of about 7-37 g/l, and a pH of about 1-3.6, and maintaining said fluid at a temperature of 20-35C, wherein required Fe ion concentration required to produce said films with 20~ iron 1% is an inverse function of

5 circulation of bath fluid across said substrate.
In accordance with this invention a nickel-iron electroplating system is provided including cell means for containing a plating bath, an anode, a cathode to be plated with a nickel-iron alloy comprising on the order of 20 lO iron, about 1%. The cell includes first and second vertical end walls, means for holding a wafer to be plated in the cathode of the cell with the surface to be plated supported facing the anode. A reciprocable mixer is provided or agitation without substantial turbulence 15 supported by bearing means for providing longitudinal ; stirring action by reciprocation between the end walls cyclically over the surface of the cathode. The mixer includes a pair of parallel transverse blocks having a substantial slot there-between. Each block has a 20 symmetrical wedge shape with substantial opening defined between the blocks. The blocks have sharp edges facing the directions towards which the blade is adapted to reciprocate. An inlet , Yo9-75-065B 4a ~.
1 ~

1 o the cell exists in one of said end walls aligned with the 2 cathode surface whereby the inlet is adapted to pass fluid 3 through the slot directly onto the surface of one end of the 4 cathode. A reservoir for electrolyte is provided having an outlet connected by conduit means to the inlet, and there is

6 means for pumping fluid up from the reservoir into the inlet

7 via the conduit means. An outlet from the cell at an upper

8 portion thereof high above the base of the cell has a second

9 conduit means for carrying electrolyte into the reservoir.
Preferably, a thermostatic control, a temperature sensor an~
11 heating means are connected to the reservoir for maintaining 12 the reservoir substantially at 25C. A pH sensor and a 13 dispenser for dilute acid and an Fe++ ion are provided for 14 tispensing the acid and the ion through a valve into the reservoir. Stirring means is provided in the reservoir for 16 maintaining a unifor~ set of temperature, pH, iron ion and 17 related conditions. For high speed plating,the electrolyte ~' 18 comprises about 24.4 g/l of Ni , 1. 05 g/l of Fe , 2.5 gJl 19 of H3BO3, 0.2 g/l of Na Saccharin, and a p~ of 1.5 - 3.6 with a current density from about 2 - 200 ma/cm . Further in 21 accordance with this invention, a thin film o~ low magneto-~` 22 striction Permalloy alloy 80~ nickel - 20~ iron + 1% is , 23 electroplated in a bath having a ratio of about25:1 to ` 24 86:1 g/liter ratio o~ Ni to Fe ions with an overall plating ~ 25 current density of about 2 - 110 ma/cm when plating through -~ 26 - a mask. Complexing agents are avoided.
~,, 27 In prior practice in which a Permalloy alloy film , j , 28 is plated over a cathode which nas recesses and raised areas, 29 or when it is necessary .o plate a Permalloy all~y fi~m throug'n i~ 30 a resist maska the strong compo-qition dependence upon s~all Yo975-065 5 , ; ~ :
.

l 1~9~92 1 urrent density variation is extremely undesirable. For instance, U.S. patent No. 3,853,715 tries to minimize this problem by intro-ducing narrow nonplated frames around each pattern. While useful for large dimension patterns, the solution given in the above-mentioned patent is impractical in the case of very small patterns such as the T and I bars in a bubble memory. Heretofore in gen-eral, the nickel:iron ratio in baths has been 80:1, and the film composition has been strongly dependent on the current density.
In addition, the plating rate was so high that it became diffi-cult to control. Prior baths are very sensitive to small varia-tions in temperature, pH, iron concentration as well as small variations in the conditions used for agitation.

Brief Description of the Drawings FIG. 1 shows a schematic diagram of a plating system in accordance with this invention.
FIG. 2 shows a partially cut away perspective view of the plating cell of FIG. 1.
FIG. 3~shows a perspective view of the reservoir of FIG. 1, partially cut away.
FI5. 4A shows a graph of percentage of iron by wt. vs. pH.
FIG. 4B shows a graph of percentage of iron by wt. vs.
temperature.
FIG. 5 shows a graph of percentage of Fe in a film by weight vs. plating current per unit area relative to the limits of the tolerance band for producing Permalloy films of 19-21 Fe by weight.
FIG. 6 shows a graph of the coercive force Hc, of the anisotrophy field Hk and the anisotrophy field dispersion ~ ' vs. weight percent of Fe.

1 1597~2 FIG. 7 shows a graph of permeability vs. frequency 2 for the sheet films plated from this bath in two different 3 states of annealing.
4 FIG. 8 is a graph of isocomposition lines of FeC12'7H2O in grams per liter vs. the overall current density 6 in matcm for plating through a mask.
7 FIG. 9 is a graph of percentage of iron in the 8 film vs. overall current when plating T and I bar patterns 9 through a mask.

Description of a Pre~erred Embodiment 11 FIG. 1 shows apparatus adapted for practising this 12 invention. The plating of nickel-iron alloys is performed 13 in container 12. The walls are composed of a dielectric 14 material such as glass or a plastic such as polymethacrylate.
A cathode 14 is composed of a metal plate having platers 16 tape composed of an insoluble polymer adhesively secured to 17 the exterior thereof on the edges and lower surface to 18 protect it from the electroplating bath and thus giving a 19 very ill defined current density and current density distri-bution. Cathode 14 includes apertures 15 havin~ countersinks 21 not exceeding 0.025" and preferably only 0.010" thickness on ~22 the tops and counterbores on the bottom into which discs of 23 a substrate 17 to be plated are inserted and supported on i 24 elastomeric dlscs 19. Discs 19 hold discs 17 in firm contact with cathode 14 to permit electrical current to flow 26 through the contact between them. Substrate materials 17 which have been found appropriate include 1 lt4 inch diameter 28 sapphire, garnet, various ceramics or Si wafers covered with 29 thermal SiO2 and metallized with 50A to 200A of Ti and lOGA
O
to lOOOA of Cu, Permalloy, Au, etc.
31 Cathode 14 is secured by screws to a dielec.ric 32 material base 18 which holds discs 19 in place, recessed not ~;' ~YO975-065 7 l 159792 1 ~ore than 0.0025 in. from the top surface of the cathode.
2 Base 18 rests upon the botto~ of container 12. Electrica 3 contact to cathode 14 is provided by brass support post 20 4 which is fastened to c.athode 14. Post 20 is covered with platers tape to insulate it wherever it is immersed in the 6 electroplating bath, when container 12 is filled. Post 20 7 is connected at terminal 22 to a source of electrical current, 8 not shown.
9 Anode 24 is composed of wire mesh screening, and it is supported by an insulated frame including upright 11 polymethacrylate block 40, horizontal block 41, bolts 42, 12 and polyme~hacrylate block 43. Anode 24 is composed of 13 inert platinum, solid nickel or of a combination or an inert 14 Pt sheet and a Ni wire mesh. Terminal metal strip 28 is connected at one end to anode 24.
16 The bath level during plating is above anode 24, 17 so anode 24 is immersed in the bath during plating. The 18 bath is constantly replenished and its temperature is controlled 19 by recirculation from a reservoir 39 where it is refreshed by dispensing acid, iron and preferably also ~a Saccharin, 21 Na lauryl sulfate and/or [Ni ] if needed and constantly 22 stirred by a reciprocating mixer 35 otherwise referred to 23 herein as a paddle, which travels back and forth above the 24 surface of cathode 14 at an approximate distance of 1/32 to 1/8 inch for providing agitation of the bath with minimal 26 turbulence. The mixer 35 is carried by upright arms 34 27 which are secured at their top ends to transverse member 33 28 (FIG. 2) which is secured at the center to link arm 36 which 29 is secured by pin 37 to crank 38 which is secured to r'otate about the shaft of the electric motor 32. ~hen motor 32 ls 31 energized, the arm 36 drives mixer 35 back and fortn with 32 simple harmonic reciprocal motion at a substantially unifor~

1 1597g2 rate near the center of container 12 where the substrates 17 are located. In addition, fresh electroplating bath fluid is pumped into container 12 from reservoir 39 by means of tubes 67 and 68, self-priming, positive displacement pump 66, filter 84, and tube 44. Filter 84 filters out particles of 1 micron size and above, preferably. When fresh bath enters container 12, it is introduced into weir 45 contair.ing a baffle 46 for diverting the bath fluid down towards elongated transverse inlet 49 through wall 51 separating weir 45 and plating cell 47. The mixer 35 is composed of two horizontal transverse blades forming a slot 48 between them which is close to horizontal alignment with inlet 49. The inlet 49 is preferably aligned to direct fluid directly onto the upper surface of cathode 14 to supply the fresh solution directly to the substrates 17.
Each of the two transverse blades has a symmetrical wedge shape with sharp opposing edges facing towards end walls 51 and 52 of plating cell 47. There are also two confronting points of the blades which define the slot 48. As a result of reciprocation of the blades of mixer 35, the bath ~ solution near the cathode is mixed thoroughly with a : substantially laminar flow having little turbulence to avoid . nonuniform polarization, so as to minimize the formation of : a depletion zone which could lead to formation of an iron hydroxide precipitate with too high a pH and hydrogen evolution at the cathode and avoids [Fe ] depletion near the cathode since the solubility product of [Fe +]-[OH ]2 has much lower solubility than the solubility product [Ni ]-[OH ] . In addition, it is necessary to mix the solution to minimize pitting caused by the formation of H2 Yos-7s-06ss 9 ~, ''~

bubbles in identically the same spots on the surface of the cathode at all times during electrolysis. The sharp edges of the transverse blocks facing end walls 51 and 52 of cell chamber 47 reduce turbulence by providing minimal resistance to flow. The triangular cross-section of the ' ~ YO9-75-065B 9a `' ~ ''`

l 159792 l blades of mixer 35 provides the set of confronting blunted 2 apexes over which fluid flows with a flat base. In scirrin~, 3 the fluid is forced to flow through slot 48 between the two 4 blocks and over the upper block to mix with the bulk of the solution in cell 47. As the mixture passes through slot 48, 6 laminar flow at the cathode surface is restored. The fluid 7 entering via inlet 49 passes immediately through slot 48 8 when mixer 35 is near end wall 51, and then the fresh fluid g is carried along with mixer 35 as it moves towards end wall 52.
11 The current path through the plating bath has a 12 cross-sectional area substantially equal to the cross-13 sectional area of cathode 14 and anode 24, i.e., the current 14 across the electrodes 14 and 24 is confined to the boundaries thereof and is not allowed to diverge or spread in its path 16 between fiaid electrodes 14 and 24. As a result, the current 17 density is relatively constant throughout the whole cathode 18 area 14. The current density is found to be relatively 19 uniform and well defined; and the current density value can be predicted at any point on the cathode 14, since they are 21 the same at any given point thereon. Consequently, films 22 produced in the electroplating cell of this invention are 23 uniformly thick throughout, and where metal alloys are being 24 plated, the metal compositions which are normally a very strong function of the local current density will also be 26 uniform over the entire film.
27 When the bath leaves plating cell 47, it passes 28 into outlet weirbox 54 through slot 53 in wall 52 up above 29 anode 24. A fluid level sensor 70 in weirbox 54 is con-nected by wires 71 to the operational controller portion of 31 pump 66. Weirbox 54 is connected via outlet tube 55 to 32 return the fluid by gravity from weirbox 54 to reservoir 39 !
33 for treatment, (see FIG. 3).
, )9-75-065 10 :

l 159792 1 The temperature is controlled by an expanded scale mercury thermometer 56 read by a capacitive sensor 57 such as a Ther-mowatch unit made by I2R company which signals temperature control 58 via wires 11 to operate a quartz encapsulated heat-ing element 60 immersed in fluid in reservoir 39 and connected electrically to control 58 via wires 10. In addition, pH
meter 61 is connected by wires 26 to sensors 62 which sense the pH in the solution. The pH meter 61 is connected by wires 27 to comparator 70 which is connected to operate a valve 63 to permit a solution of Fe++ ions and dilute HCl contained in burette 65 to flow through tubes-64 into reservoir 39, as required. A stirring mechanism is included within the reser-voir 39 in the form of a magnetically driven propeller or stirrer 75 connected by magnetic drive comprising a set of permanent bar magnets 77 and 78 located respectively above and below the base 79 of reservoir 39. Magnet 78 is located within control unit 76 which provides variable speed control of turn-ing of magnet 78. Alternatively a non-contaminating mechanical stirrer can be used.
The temperature in reservoir 39 is maintained preferably at from 25 - 30C. Fluid jacket walls 80 and chamber inner ; walls 81 form a space filled with fluid which is further temp-erature controlled by pumping fluid through tubing 82 wrapped about walls 81 by means of a circulator pump, not shown, in order to maximize temperature uniformity. The cooling coils can also be inserted directly into the reservoir tank provid-ing they are noncontaminating and provided they do not interfere with regular agitation of the bath. The precise temperature used is less important than uniformity in temperature in order that the yield of the films produced will be quite uniform.
,: .

l l a~
1 A flowmeter 83 is connected in series with tube 44 2 to monitor the rate of flow from pump 66 into weir 45 because 3 the rate of recirculation is in part a measure of the rate 4 of agitation resulting from the solution being forced into the cell via the thin, wide, slot-shaped inlet 49.

6 Bath and Process 7 Batch-fabricated,magnetic bubble devices and 8 magnetic recording thin film heads utilize Permalloy films 9 which are in the range of 2000A to lO,OOOA thick for bubble O O
devices and 5000A to 50,000A (0.5 to 5 ~m ) thick for recording 11 heads. Most of these fabrication processes require for the 12 films to be plated in 2000A to lO,OOOA steps in bubble 13 devices and up to 2 to 8 ~m high steps in recording head 14 devices. Films must also be plated over cathodes in which some areas are blocked off with photoresist. The vertical 16 steps and blocked-off areas with resist introduce local 17 current density variations. Such local current density 18 variations result in local composition and thickness differences.
19 For the electroplating process to be commercially useful in fabrication of magnetlc bubble devices and magnetic 21 recording heads, the plating rate of the film should be 22 reasonably high, but not uncontrollably high (local current 23 density equivalent to 5 ma/cm2 to 120 ma/cm2). For practical ,, .
24 and economical reasons, it should be possible to plate a :,; :
500A to 5 ~m thick film in 2 to 30 minutes. The film com-26 position should vary much less as a function or current ;~ 27 density than it does for prior art baths used for plating of~:j O o 28 200 A to 2,000 A films, used for plated random access thin 29 film memories such as flat film or coupled magnetic ri~m memories.

: ~1 ", ,. ;
~ .
..... .. .. _ . _ 1. 1~97g2 -`
IHigh plating rate baths have been developed fo~
2 fabrication of plated magnetic wire memories. The Permalloy 3film thickness on the wires is typically 5,000 A to 10,000 4 A thick. The prior art form agitation used has been forced flow agitation with impingment which is usually very highly 6 turbulent. Due to the nature of the wire fabrication process, 7 these films have to be plated in l to 8 minutes of the wire 8 residence time in the plating cell. Although some of these 9 baths are known, the literature available lacks important details about the baths, cell design or the exact plating 11 conditions.
12The high plating rate Permalloy bath described 13 below is adapted for the purpose of fabrication of thin film 14 magnetic bubble devices and recording heads. Optimum plating conditions are described. The described plating bath satisfies 16 the current magnetic film property requirements for fabrication 17 of such products. Despite this, certain further improvements 18 in control of various plating parameters and in magnetic 19 properties are being sought.

~lagnetic Film Property Requirements for Fabrication of 21 Thin Film Bu~ble Devices and Recording Heads 22It is necessary that the films used in fabrication 23 of recording heads are magnetically anisotropic. ~agnetic 24 anisotropy permits use of rotational switching to improve the frequency response of the devices. Although it is de ired 26 to have a square easy axis loop with a lou re~anence, the ~' '~ 27 exact value of the coercive force H is not critically 28 important. It is preferred, however, that Hc be below 0.&
I
29 Oe. The exact value of the easy axis dispersion a, and skew B, are also not critically important for the proper operation 31 of the devlce. The important magnetic parameters affecting 32 the signal output of the device are: hard direction re~anence, . , .
33 saturatlon magnetization ~s~ initial permeability ~, and 34 electrical resistivity of the film p.

1 ~59792 1 High resistivity is particularl~J important for 2 heads to be operated at high frequencies. Since the read 3 signal depends on all four quantities enumerated above, it 4 is desired to minimize the hard direction remanence and ~o maximize each of the last three quaneieies. Furthermore, 6 since ~i is proportional to ~Is/Hk, in order to ~a,ximize 7 it is desired to minimize the anisotropy field Hk, while 8 retaining the magnetic orientation of the fil~. !

9 Experimental Apparatus and Procedures The basic composition of the plating bath and the 11 plating conditions are shown in Table I. The electroplating 12 cell used in developing and optimizing this bath consists of 13 the rectangular Lucite*(polymethacrylate)container enclosing 14 the cell of FIGS. 1 and 2 in which the botto~ of the cell ~epre~ents the cathode ant the top of the cell represents 1'6 the anode. The anode-cathote arrangement can be reversed o.
17 placet on its side so'long as the mixer or paddle agitator 18 35 and the inlet slot 49 facilitating the mixing and entry ,l9 of the fresh solution respectively are also suitably rotated (such that agitation and refreshing of the cathode surface 21 is continuously maintained). Both the anode 24 and the , 22~ cathodè 14 fill the cell 47 substan;ially fro~ ~all to all 23 in each direction. This arrangment results in a unifor~
,, , ~ 24 prlmary current distributlon over the whole cathode area.
~' 25 All fllms for recording heat devices are plated in a 40 Oe ,. . .
, ,~ 26 magnetic field provided by permanent ~anets 25 sho~n in 27 phantom,in FIG. 2. After plating, all films are anneal2d 28 for 2 hours at 200C in a 40 Oe easy axis field. SubsequentlY, 29 tkey can be additionally annealed for 2 hours at 200C in ~; 30 * Trade Mark , ': ~ ' ' ' '' .

the absence of a magnetic~field or for 2 hours at 200C in a 2 cross-field or both. The static magnetic properties 3 of the films are measured before annealing, after easy-axis 4 annealing and after the annealing in absence of the field and/or the cross-field when it is used.
6 The static magnetic properties of the films, 7 coercive force H , anisotropy field Hk, easy axis dispersion 8 plus skew, a ~ ~, and magnetostriction ~ are ~easured using 9 a 60-cycle inductive B-H loop tester. The magnetic moment, M , of several films was measured using a force magnetometer.
11 Currently, each sample is compared on a B-H loop tester with 12 a standard sample. The initial permeability ~i of each 13 sample is measured. The electrical resistivity p of the 14 films is measured using a four-point probe.
The film thickness is evaluated from the weight 1~ gain of the sample during plating and from a profilometer 17 measurement. The film thickness is subsequently verified 18 using an X-ray fluorescence and/or a wet chemical technique.
19 The film composition is also determined using the X-ray fluorescence technique or a wet chemical technique.

~;' .
; Discussion of Plating Parameters and Their Effect on Film 24 Composition and Magnetic Properties ~,25 The following plating parameters were investigated:
., ;~ 26 a. Current density.
; 27 b. pH and the rate of change of pH during plating.
28 c. Temperature and the rate of change of temperature ~,.ij .
~j 29 during plating.

YOg75-06515 : .
:

~ 159792 d. Agitation (height of the paddle over the 2 cathode at a fi~ed rate of travel of the paddle).
3 e. Operation of the apparatus with recirculation 4 agitation only and no paddle movement and operàtion of the cell with no recirculation and 6 with paddle agitation only. Operation witn 7 both paddle movement and recirculation.
8 f. Speed of movement of the paddle in presence and 9 in absence of recirculation.
g. Change of [Fe ] ion content of the bath and ll the rate of cons~mption of the ~FE ] ion 12 during plating.
13 h. Partial and/or complete substitution of chloride 14 ion by sulfate and by fluoride ions.
i. Change in sodium saccharin content.
16 j. Type of anode (inert Pt, soluble Ni, and mixed 17 Ni-Pt).
18 k. Additi~n of cobalt sulfate to the bath.
19 Because of the preferential electrodeposition of iron in presence of nickel, most of the commercial (30/20) Permalloy 21 electroplating baths are operated with a high nickel-to-iron 22 ratio in solution. (I. W. ~olf, Electrochem. Technology, pp.
~23 164-7, 1, No. 5-6, 1963; W. O. Freitag, J. S. ~athias, ; 24 Electroplating and Metal Finishing, pp. 42-47, February, 1964;
and T. R. Long, J. Appl. Physics, 31, Suppl. 5, 1960.) Z6 In the baths described in the first t~o references 27 immediately preceding, the films are plated at very low 28 ~ current densities (~5 matcm ) and therefore it takes 20 to 29 30 minutes to deposlt a 0.5 to 1 ~m film. In addition, the composition of the films deposited from Y0975-065 ~6 ',~ `; , ~ .

1 1597g2 --1 hese baths is e~tremely sensitive to ~inute current density 2 variations (see FIG. 5 curve labeled Wolf's~bath). These fil~s 3 exhibit a tensile stress, with a nonuniform stress gradient 4 thrGugh the thickness of the film (the films curl when removed from the substrate).
6 FIGS. 4A , 4B and 5 and Table II summarize the effect 7 of the more important plating parameters on the film composition 8 and on magnetic properties of sheet films. The reader is 9 referred to these FIGS. 4A, 4B, and 5 and in particular to Table II. FIG. 5 gives a comparison of the rate of change 11 of the iron content in the film with current density for the 12 present bath and for a Wolf's type bath. ~
13 The well known Wolf's bath gives an iron composition 14 vs. current density curve shown in dotted line form in FIG.
5. This curve shows a very sharp essentially vertical line 16 with the tolerance band lines marking a 19 - 21~ Fe tolerable 17 spread of the metal Composition required for Permalloy Ni-Fe 18 alloy corresponding to a current range of 7-8 ma/cm , which 19 means that a slight 1 ma/cm shift in current can throw the bath out of the Permalloy l9 -21% Fe alloy range. In the i 21 case of curve A, the corresponding current range is 55 - 65 22 ma/cm2, which is a far wider range in absolute terms and as 23 a percentage of the current than that for the Wolf's bath.
24 Cur~e A is based upon 2~ thick films with weak agitation.
25 The pH is allowed-to change from 2.5 to 2.9 while plating, 26 and the iron content of about 1.35 g/l is allowed to drop.
27 Curve B shows the result of intense agitation and adjustment ~; 28 of pH at 2.5 and iron at 1.41 g/l. Note that for Curve B, , above 80 ma/c~2 and for Curve A, between 5 and 20 ~a/c~2, , I YOg75-065 17 :, : ` .
, ~` .
.~ .

l 1~979~ --l `he result is practically independent of current density.
2 The films plated from the present bàth at current densities 3 anywhere between 5 and about lO0 ma/cm2 show very small 4 internal stress gradient. The stress gradient is uniform throughout the thickness of the film, and when the film is 6 lifted off the substrate, it does not curl.
7 Films plated at low current densities, i.e., ~ 30 8 ma/cm2 initiall~, when only ~ 0.5 ~m thick, have an extremely 9 pronounced texture orientation. The 110 plane is in the plane of the film. As the thickness increases, orientation 11 diminishes. The orientation diminishes more rapidly in films 12 plated at higher current densities. Films plated at ~ 60 13 ma/cm2 show very little grain orientation. All films are 14 under a tensile stress. The stress has a uniform gradient through the thickness of the film. Upon heating to 200C
16 for 2 to 4 hours, the tensile stress increases.
17 FIG. 6 is a plot of static magnetic properties Hc, 18 Hk, and a + B for the 2 ~m thick films as a function of the 19 weight % of Fe in the film. All solid lines in FIG. 6 represent films which were annealed in an easy axis field.
21 The dashed curve represents values of Hk for the 2 ~m 22 thick films after they have been annealed in a cross-field.
23 The hard axis (cross-field) annealing results in lowering of 24 the Hk value by about 50% to 80% based on the original Hk value in a plated form. Thé Hc, and a ~ ~ values are not 26 shown for the films after hard axis annealing because Hc in 27 the 2 ~m thick films changes only very slightly during the 28 hard axis annealing. The a + ~ increased during the hard 29 axis anneal by about 25%.
, .

1 ~97~
~ FIG. 7 summarizes the results of the measurement 2 ,f the initial permeability ~i as a function of frequency 3 for various thicknesses of films after the easy axis annealing 4 and also for the same films after a subsequent hard axis annealing. The ~i value of the easy axis annealed films at 6 low frequencies is about 2,000. This value is in good 7 agreement with the initial permeability reported for Permalloy 8 alloy in bulk form. After hard axis annealing, the initial 9 permeability ~i of these films is approximately 4,000. This is again in good agreement with the ~i Ms/Hk relation, 11 since the hard axis annealing result is a 50~ to 80 12 decrease of the Hk value.
13 From the shape of the curves in FIG. 7, it can be 14 concluded that in films thinner than 2 ~m, during switching, eddy current damping does not play a major role. This is 16 as predicted on the basis of 20 micro Q - cm resistivity and 17 of the resulting calculated skin depth.
18 For the puspose of fabrication of the high frequency 19 heads for di2c file applications, it is desired to maintain the high initial permeability of the films at 2,000 or 4,000 21 to much higher frequencies than is presently the case. The 22 high initial permeability, at high frequencies, can be 23 maintained by increasing the electrical resistivity of the 24 films. This bath is quite amenable to addition or a third element for deposition of ternary alloys of higher resistivity.
26 Based on the investigation of the effect of different 27 plating variables on the Permalloy composition re?orted in .. . .
28 FIGS. 4A and 4B and Table II, it is concluded that in order 29 to plate 80/20 nickel-iron films reproducibly on a commercial ' ; : ' l 159792 production basis, it is necessary to control pH within 2 approximately + 0.1, temperature within approximately +
3 0.5C, and iron content of the bath within approximately +
4 5~ of the initial value. It is also necessary to control the current density within about + 5% and the agitation rate 6 wlthin certain prescribed limits. The last two can be 7 easily controlled by using a well-regulated power supply, a 8 reproducibly fixed distance of the agitation paddle 35 above g the cathode, a fixed recirculation rate, and a substantially fixed rate of travel of paddle 35. The first three variables ll require constant adjustment during eacn plating run because 12 they tend to change continuously during deposition. Constant 13 recirculation of the solution during plating removes the 14 partially altered solution from the plating tank and continuously introduces from a large reservoir freshly adjusted solution.
16 The ~llter constantly re~oves any precipitate or sediment 1~ formed ~uring the electrolysis. Thus, recirculation serves 18 a tual function: a) removal of partially spent solution for 19 its adjustment in the reservoir and removal of the residues, and b) assistance in obtaining uniform agitation of the 21 plating solution in the tank.

' .
22 Example I
23 During deposition of 2 ~m of fil~ out of a ty?ical 24 800 ml bath, the pH of the bath increased by approximately 0.3 to 0.5 pH units (from 2.5 to approximately 2.9), the 26 temperature increased by approximately 0.5C and the iron 27 content decreased by approximately 2~o (while tne nickel 28 content remained nearly constant). When an inert, large 29 area Pt screen anode was used, the pH instead of increasing, decreased by approximately 0.2 to 0.4 pH units (from 2.5 to :~i 31 about 2.1).

Yo975-065 20 ;:

l 1~9792 1 The reproducibility can be improved and the useful 2 life of the bath can be extended by preparing a large volume 3 of bath and recirculating a portion of it through the plating 4 cell 47, while at the same time constantly monitoring the S pH, temperature and intermittently measuring the iron content 6 of the bath in the reservoir and suitably adjusting all 7 three quantities within the limits shown above.
8 Referring to the arrangement of FIG. 1, the reservoir 9 plating tank and a suitable recirculation system provided excellent results. The pH was controlled only within + 0.2 11 units, the temperature within + 0.4C, and automatic control was 12 provided for the lron content. This resulted in greatly 13 improved reproducibility of the plated films. Later a 14 system was employed whlch permittet the pH control to within + 0.05 pH unit, temperature to within + 0.3C and the iron 16 content of the bath to within approximately 4%.
17 The high plating rate bath of Table I permits 18 plating of films at a rate as high as 1 ~m/min. and also 19 plating of films at a rate as low as 500 A/min. The plated film composition is relatively insensitive to small current 21 density variations. Magnetic properties of the ?lated films 22 are quite acceptable for use in thin film magnetic recording 23 heads.

~;'. ' .
'' ' ; ', .
;' .

1 1597g2 l TABLE I
2 Preferred Plating_Bath Conditions 3 Opti~um Ranges 4 NiCl 6H 0*109 g/l 30 to 150 g/l FeC12 4H20* 5.25 g/l 4.5 to 5.77 g/l 6 ~3B03 25 g/l 12.5 to 25 g/l 7 Na Saccharin 0.8 g/l 0 to 2 g/l 8 Na Lauryl Sulfate (Maprofix)***0.2 g/l Fixed value 9 pH 2.5 + 0.1 1.5 to 3.6 Current Density 60 ma/cm2 10 to 120 ma/cm2 11 Na Citrate, tartrate, 10 to 80 g/l 10 to 80 g/l 12 oxalate, phosphate**

13 * In addition to chloride salts, sulfate and fluoride salts 14 may be used. The chloride ion can be co~pletely or partially 8ub5tituted by a sulfate ion. Alternatively, ammonium sulfate 16 ~alt can be added to the bath in amounts of 50 to 150 g/l.
17 ** Addition of complexing agents is optional.
18 Plating rate About 10,000 A/min (2~ oer 2 min) 19 at 60 ma/cm Agitation Continuous laminar flow 21 Rate of travel of the paddle about 22 8"/sec in a reciprocating fashion at 23 about 1/32" spacing above the cathoa--~ .
24 with a range of spacing of 0 - 1/4"
Anode Pt sheet wrapped with ~i wlre mesh ~26 Temperature 25 + 0.5C 20 to 35C
- ~ 27 Cathode Current Efficiency About 80X - 90~.
***Trade Mark -l Y0975-065 22 . I .

` 1 In Table I the ratios of Ni:Fe are as follows:
2 Conversion 3 LowFactor 2 6H2o 30 g/l x.247 Ni 7.4 g/1 C 2 4H20 4.5 g/l x.2815 Fe++ 1.27 g/l 6 Ni:Fe ion weight ratio 5.8:1 7 Optimum 8 NiC126H2o 109 g/l x.247 Ni 26.92 g/l C12 4H20 5.25 g/l x.2815 Fe 1.48 g/1 Ni:Fe ion weight ratio 18.2:1 11 High 12 2 6H2O 150 g/1 x.247 Ni 37.05 g/l 13 FeC1 '4H 0 5.72 g/1 x.2815 Fe 1.61 g/l 14 Ni:Fe ion weight ratio 23.0:1 ' `'~:

. ,-. , ':

,~"~ ' '. ' .

., ~ , l 1~97~2 lTABLE II
2Summary of the Effect of Various Plating 3Parameters on the Film Composition and on the 4Magnetic Properties 5 Current Density id As current density increases, the 6 iron content decreases. (FIG. 5) 7 The rate of change is 0.4% Fe/ma/cm 8 for most of Curve A and part of 9 Curve B in FIG. 5.
lO pH As pH increases in the 1.5 .o 3.5 pH
11 range, the iron content decreases.
12 (FIGS. 4A, 4B and 5) The rate oI chan~
13 is 5.55% Fe/pH unit.
14 Temperature As temperature increases in the 20 to 35C range, iron content in 16 the film decreases. (FIGS. 3A, 3B
17 and 4) The rate of change is ;l18 0.75% Fe/C.
19 Agitation As the mixer distance increases from near contact with the cathode to 21 about 1/4" above the cathode at a ~22 fixed id of about 60 ma/cm , the ; iron content lncreases. The deposit 24 acquires a "burned" appearance~
- eventually passivates completely ~ 26 when the limiting current is reached -~27 at which metal ions cannot be supplied ~ .
l 28 any faster.
¦ 29 Change of Iron Content A lOZ change in iron content in the ~; 30 bath results in about 3 to 4% change 31 in iron content in the film.

Y0~75-065 24 ~ ~ .

~ 159792 1 TABLE II (continued) 2 Rate of Depletion of Iron l~hen using 800 ml of solution in 3 connection with the Pt inert 4 electrode, approximately 1.85% of iron and 0.45% of nickel are used 6 per 1 ~m of deposited film. When 7 using a soluble nickel electrode or 8 a mixed Pt-Ni electrode, nickel in 9 the bath remains unchanged. After plating 5 ~m of film out of an 11 800 ml bath, about 9. 3h' of the 12 original iron in the bath is depleted.
13 Type of Anode (1) When using an inert Pt anode, pH of 14 the S00 ml bath decreases from 2.5 to about 2.1 during the course of 16 depo~itlon of a 2 ~m film.
17 (2) When using a soluble nickel anode, }8 the pH increases rapidly. When using lg a mixed Pt-Ni anode, the pH of the 800 ml bath increases from 2.5 to 21 about 2.9 much more slowly.
,, 22 Substitution of Cl by When Cl is substituted by S04 , 23 S04 and by F slightly lower Hc, a + ~ and Hk are 2~4 ~ obtained. When Cl is substituted 25 ~ by F , there are no major changes 26~ in film compositior. or magnetic 27~ ~ properties.
,...: , ; ~28 Change in Na Saccharin When Na Saccharin is completely ~l~; 29 absent, films are highly stressed and llft off the substrate after 31 aboùt 1 to 1.5 ~m of film is depositec , j l ; Y0975-065 25 :, :"'' ' ' l 159792 l TABLE II (continued) 2 At about 0.4 g/l of ~a Saccharin, 3 the internal stress is sufficiently 4 reduced that 5 to 8 ~ thick films can be readily plated. Beyond 0.4 g/l 6 and up to 2 g/l of Na Saccharin, only 7 very slight changes in magnetic 8 properties are observed.
g Addition of Cobalt Sulfate In amounts up to 2.3 g/l~ H decre&ses~

~ + B decreases, however, Hk nearly 11 doubles. The film contains about 12 10% Co.

14 ~ ution for Burette 65 15 FeCl ' 4H 0 20 g/l or equivalent a~ount of 16 FeSO4 17 HCl Enough to produce pH 0.5 solution 18 In cases in which a Permalloy film is plated over 19 a cathode which has recesses and raised areas or when it is , .
20 necessary to plate a Permalloy film through a resist mask ~21 (both of which situations occur in fabricating magnetic thin 22 film heads and bubble memory overlays), the strong composi~ion`
dependence upon small current density variation is extremely 2;4 undesirable and, inteed, makes it impossible to electroplate 2;5~ ~usable films. In connection with wire memory fabrication, ~ 2~6 ~ othe-r baths were developed which permit electroplating i 27 permalloy f ilms at very high rates. (T. R. Long, J. Appl.
,'1 ~ ' 28 ~hysics, 31, Suppl, (5) 1960; E. Toledo, R. ~lo, Plating, 57, 29 p.~ 43, 1970.) ~: ~ Y09i5-065 26 ~;, ,-, : . , .

l 159792 1 The present bath, plating technique and apparatus for electrodeposition of Permalloy films permit reproducible dep-osition of 80/20 films from low nickel:iron ratio baths at rates which are both practical and easy to control when plating films anywhere from 1,000 A to 5 microns thick. This bath has an excellent throwing power. At low, moderately high, and high current densities and in presence of strong agitation, it gives deposits whose composition is nearly independent of the current density (see FIG. 5 curves A and B, FIG. 9 curves AA and BB
and FIG. 8, curves A, B, C, D, and E). These features make the bath unique and particularly useful for plating various magnetic devices in which it is necessary to deposit the film through a resist mask.
Below are given the key features of the bath, plating apparatus and technique and properties of the resulting films:
1. The film composition is only slightly dependent on current density of 20 to 85 ma/cm and is even completely independent of the current density variation over a wide range ;; of currents below 20 ma/cm and above 80 ma/cm . tAt high agitation rates and moderately high current densities, the composition is substantially independent of the current density.) 2. The films are relatively stress free even when plated up to 25 ~ thick. The films do not curl when lifted off the substrate, which indicates that the stress gradient through the thickness of the film is linear. The features described in (1) and (2) permit electroplating very narrow (down to 2.5~) ; lines and patterns through a mask without lifting or peeling of the pattern.

:

l 159792 1 3. The films deposited from this bath possess a 2 high initial permeability. The permeability of these films 3 can be increased further by hard axis annealing. The high 4 initial permeahility, substantially closed hard axis loops, and easy magnetic switching, without hard axis 6 locking andtor without excessive remanance, make the 7 films particularly useful for fabricating magnetic thin 8 film recording devices.
9 4. The films plated from this bath, when using the disclosed pH, temperature control, and iron 11 addition and control, are uniform with respece to 12 composition throughout their thickness except for the 13 first 100 to 300A in which there is a composition 14 gradient.
5. The film deposition rate, while it can be 16 relatively high (up to about l~m/min), is slow enough 17 to allow accurate thickness control in films which are 18 only 500 A thick.
19 6. The bath is relatively insensitive to variations ln temperature.
21 7. The plating apparatus is designed so as 22 to permit controlling pH at 2.5 + 0.05, temperature at 23 25 + 0.5C, and iron in the bath at 1.41 + 0.02 g/l.
24 The pH is controlled using a pH stat composed of meter 61 and comparator 76 coupled with solenoid valve 63 and , . . .
26 the burette 65 containing HCl solution and Fe ions , 27 described above in Table III.
, .

:~ "
.,~ , -, ~ . .
:

l 1~97~2 8. Since the rate of loss of iron is directly 2 proportional to the rate of change of the pH, iron is 3 added simultaneously from burette 65 while adjusting 4 the pH. The rate of Fe consumption can be observed during plotting without any adjustment to produce a 6 calibration curve. It has been found that the rate of 7 [Fe ] consumption is proportional to the change of the 8 pH. Based on the calibration curve, a suitable make up 9 solution is prepared, as wiil be obvious to those skilled in the art. Up to 100 ~m of Permalioy is 11 plated onto a 4.5" x 4.5" substrate with iron [Fe ]
12 ions in the bath being maintained at 1.41 g/l and pH at 13 2.5 + 0.05. The bath composition is shown in Table I.
14 Composition of the HCl-Iron make-up solution is shown in Table III.
16 9. The bath is normally operated under 17 conditions (pH ant total iron in the bath) under which 18 ferric ion in excess of about 0.01 g/l precipitates out 19 and is filtered out prior to entering the plating cell.

10. The ferric ion formation can be further 21 reduced by addition of complexing ions such as citrate, 22 tartrate, oxalate, phosphate, isoascorbic acid, and the 23 like. All of the above, when added in small quantities, 24 do not substantially alter the plating conditions under Z5 which an 80/20 composition is obtained. Ir. addition, 26 the ferrous to ferric ion oxidation can also be diminished 27 by preparing the iron make-up solution using FeSO4-4H2O-HCl 28 solution (rather than FeC12-4H20) and by addin& ammonium 29 sulfate salt to the bath.

, _ 1 1597g2 2Bath Plating Conditions for Plating Through .'lasks 3 Optimum Ranges 2 2 109 g/l 70 - 180 g/l 2 2 1.5 g/l 1.1 to 3.8 g/l 6 H3B03 25 g/l 12.5 to 25 g/l 7 Na Saccharin 0.8 g/l 0.4 to 0.8 g/l 8 Na Lauryl Sulfate 0.2 gil 0.2 g/l to 0.4 g/l 9 H2O make up to 1 liter make up to 1 liter id ,~ 5 ma/cm 5 to 40 ma/cm2

11 Plating rate 500A/min 500 - 30,000A/min

12 pH 2.5 1.5 to 3.6

13 ~a Citrate, tartrate

14 oxalate, phosphate** 10 to 30 g/l 10 to 30 g/l ~Ni++] 26.9 g/l 17 to 44 g/l 16 ~e+ ~ .42 g/l .31 to 1.07 g/l 17 Ni:Fe ratio in g/l ' 64:1 86:1 to 25.1:1 g/l I
**Addition of complexing agents is optional.
~, 19 One of the unique features of this bath, when used in ~, 20~ connection with the plating apparatus discussed, is the ;' 21 extremely broad range of current densities under which it can -" ~ 22 be used to plate sound, usable NiFe deposits in sheet film ~ '23, form.
''' ~24 Even more unique,is the capability of the same bath ~, 2'5 with only minor ad~ustment of the lFe++~ concentration to be . , :
26 used for plating discrete patterns through masks with ~, 27 excellent thickness and compositional uniformity.

;~ 28 In particular, films were plated in 2.5Ym an~
, ~ .
~,, 29 25ym wide lines, ~slots] in resist with varying spaces and into 2.5ym T and I bar patterns. FIG. 9 shows the ~;' 31 relationship between the percentage of Fe in the film and .' ~ . , Yo975-065 30 ~ ~ .

1 15g792 1 the current density for both the 2.5~m pattern on varying spaces from 2 0.25~m through 500~m. While in this case no attempt was made to obtain 3 a 20/80:Fe/~i composition from FIG. 9, it is obvious that excellent 4 compositional uniformity was obtained when overall current density of 5ma/cm2 through 25 ma/cm2 was used. From curve M and the bars around 6 each point showing the spread of data in the 50 points examined, it is 7 clear that smallest deviation from the mean takes place at an overall ,., O
8 current density of 5 ma/cm' (equivalent to a 1545A/min plating rate 9 Table V). As the current density is increased to an overall value of lO
ma/cm2 (5,000A/min plating rate Table V) to 20 ma/cm2 (9,OOOA/min plating 11 rate), the deviation from the mean increases (long vertical bars in FIG.
12 9). At an overall current density of 40 ma/cm2 equivalent to a plating 13 rate of 30,000A/min, the mean value is shifted considerably downward to 14 a lower %Fe and the spread of %Fe over isolated 2.5~m patterns is very large. The deviation of the film thickness is very large compared to 16 the deviation for 5 and 10 ma/cm2 average current densities. Table V
17 shows examples of mean thickness and thickness spread for the 5, 10, 20, 18 40 and 60 ma/cm overall current density. A similar situation exists in 19 the case of plating of 25~m bars at varying spaces on curve 3-B, except the absolute value of the mean %Fe is slightly lower at 5 ma/cm2, 10 21 ma/cm2 and 25 ma/cm2. .
22 FIG. 8 represents the relationship between the iron [Fe ] ion 23 content of the bath and the overall current density for the platin~ of 24 2.5~m lines and T and I bar patterns for bubble memory devices through masks. The curves marked A through E are isocomposition lines, w th 26 curve E representing 20~ Fe, D about 22% Fe, C about 25% Fe, B about , ~ Y0975-065 -31-'' ' l 159792 .
1 40% Fe, and A abol~t 50~ Fe in the film. This figure points to the key 2 part of the invention showing the fact that while plating through masks, 3 the film composition does not vary over relatively broad range of c~rrent 4 densities (namely, 5 ma/cm2 through almost 20 ma/cm2 of the overall current density). Such behavior is most unique and unexpected in electro-6 plating baths which are known to have anomalous codeposition of Fe with 7 the host metal. It permits the dimensions of the patterns and the 8 spacing of the patterns ro vary over a rather large range without adversely 9 affecting the film composition or thickness from a spottospot on the cathode plated through a mask.
11 Plating Through a Mask 12 In plating from the bath of this invention onto a metallic 13 film coated with a mask of a photoresist or the like, results have been 14 obtained using the bath compositions outlined below in Examples II - V
for providing 80/20 compositions of nickel and iron.
16 Example II
17 The bath included the constituents as follows:
18 NiC12 6H2 lO9 g/l 26.9 g/l [Ni ]
19 F Cl 4H 0 1.85 g/l .521 g/l [Fe ]
H3B03 12.5 g/l 21 Na Saccharin 0.4 g/l 22 Na Lauryl Sulfate 0.4 gtl 23 H20 ma~e up to 1 liter 2 24 The overall plating current de~sity was 20 ma/cm , and a pH level of 2.5 was maintained. An excellent film was produced. The Ni:Fe ratio in the 26 bath was 51.6:1 in g/l.
~', , ' .

.,~ . . .

`~ ' -~ . , 1 Example III
2 The same bath as in Example II was used with the only exceptions as 3 fo]~lows:
4 Fe~,12 4}l20 1.1 g/l .31 g/l [Fe ]
Na Lauryl Sulfate 0.2 g/l 6 The overall plating current density was 10 ma/cm with a pH of 2.5.
7 Similar results were achieved.
8 In this case, the nickel-iron ion g/l ratio in the bath was 9 84.3:1 Example IV
11 The same bath as in Example III was used with the only exceptions as 12 follows:
13 FeC12 3.8 g/l 1.07 g/l [Fe ]
14 H3B03 25 g/l Na Saccharin 0.8 g/l 16 Na Lauryl Sulfate 0.4 g/l 17 The overall plat$ng current density was 40 ma/cm and pH was held a~
18 2.5. The nickel-iron g/l ratio in the bath was 25:1. ~o recirculation 19 was used other than paddle agitation and bath volu~e was 200cc. This bath was used for plating a single 2~m film.
21 Example V
22 The same bath as in Example IV was used with the only exception as 23 follows:
24 FeC12 1.5 g/l 0.472 g/l [Fe ]
The overall plating current density was 5 ma/cm2 for a plating rate of 26 1545A/min and 10 ma/cm for a plating rate of 5000A/min (Table V). The 27 pH was held at 2.5. The nickel-iron g/l ratio in the bath was 63.74:1.
28 Platin2 Non-80/20 Range Ni/Fe Composition: Sheet Form 29 In plating from the bath of this invention of a metallic film in sheet form, favorable results have been obtained using the bath ,, .

YO975-065 ~33~

~,'- ~ .

1 1S~7g2 l compositions outlined below in E~amples VI to X for providing nickel-2 iron films.
3 Example VI
4 The bath inc'uded the cons~ituents as follows:

2 2 109 g/l 26.9 g/l [Ni ]
FeCl2 4 2 5.0 g/l 1.4 g/l ~Fe ]
3 3 25 g/l 8 Na Saccharin 0.8 g/l 9 Na Lauryl Sulfate 0.5 gfl pH 2.5 11 The plating current density was 5 ma/cm2 at a plating rate of 1545A/min.
12 The film produced was 50% Fe. The Ni:Fe ratio in the bath was 19.2:1 in 13 g/l.
14 Example VII
The same bath as in Example VI was~ used with the only differences as 16 follows:
17 The plating current density was 10 ma/cm2, the plating rate 18 was about 5000A/min, and the percentage of Fe was about 52.
19 Example VIII
The same bath as in Example VI was used with the only differences as 21 follows:
22 The plating current density was 20 ma/cm , the plating rate O
23 was lO,OOOA/min and the percentage of Fe was about 50.
24 Example IX
The same bath as in Example VI was used with the only differences as 26 follows:
27 The plating current density was 40 ma/cm , the ?lating tate 28 was 30,000A/min, and the percentage of Fe was about 30.
~.~

' .

1 15g7~2 1 Example X
2 The same bath as in Example VI was used with the only differences 3 as follows:
4 The plating current density was 60 ma/cm2, the plating rate WélS 55,000A/min, and the percentage of Fe was about 20.
6 Plating 80/20 Ni/Fe Composition - Sheet Form 7 In plating from the bath of this invention to form a metallic 8 film in sheet form, favorable results have been obtained using the bath 9 compositions outlined below in the Examples XI and XII for providing 80/20 Ni/Fe films.
11 Example XI
12 Ni 2 2 109 g/l 26.9 g/l ~Ni 3 13 FeCl 4H 0 5.25 g/l 1.45 g/l [Fe ]
14 H3B03 25 g/l Na Saccharin 0.8 g/l 16 Na Lauryl Sulfate 0.2 g/l 17 pH 2.5 + 0.1 18 The plating current density was 60 ma/cm2, Na citrate, tartrate, oxalate, 19 or phosphate was included to 10 to 30 g/l. The percentage of iron in the films produced was 20 + 2. The plating rate was about lO,OOOA/min. The 21 Ni:Fe ratio was 18.55:1 in the bath in g/l.
22 Example XII
NiC12 6 2 40 g/l 10 g/l ~Ni ]
24 NiS04 6H2 20 g/l 4.5 g/l [Ni++~
FeCl2 2 4.5 g/l 1.25 g/l [Fe ]
26 Na Saccharin 0.8 g/l 27 Na Lauryl Sulfate 0.2 g/l ;l 28 pH 2.5 + 0.1 29 Temperature 25C + 0.5C

~', l 1597~2 1 The current density was 30 ma/cm2, and the plating rate was 2 about 5,OOOA/min. The percentage of Fe in the films produced was 20 +
3 2. There were 14.5 g/l of [Ni ] and 1.25 g/l of [Fe ] for an ~i:Fe 4 ratLo of 11.6:1 in the bath in g/l.
Plating With Prior Art Bath 6 Example XIII
7 A plating bath of the composition shown in U.S. patent 3,652,442 was 8 prepared to cons$st of:
9 NiC12 6 2 109 g/l 26.9 g/l Ni F Cl 4H O 3.9 g/l 1.10 g/l Fe 11 3 3 12.5 g/l 12 Na Lauryl Sulfate 0.2 g/l 13 Na Saccharin 0.4 g/l 14 Temperature 25C
Current density 20 ma/cm2 16 Films were plated from this bath as prepared without adjusting 17 the pH to 2.5 through a 2.5 ~m aperture mask.
18 The films had very highly modular surfaces with some "burning"
19 around the edges and showed very large thickness variations over the surfaces of the wafers, and showed signs of severe internal stresses and 21 flaking. The nickel:iron ratio in the bath was 24.4:1.
22 Even though the bath shown above is similar to the ~ath in 23 Example IV, it gives "burned" (black: rough and oxidized which are also 24 too high in iron) deposits which also are too high in iron content to be useful in magnetic bubble memory devices.
26 Example XIV
27 When plating bath #3 from U.S. patent 3,652,442 was used 28 without adjustment of pH in connection with the present apparatus a~d 29 plated at 25C with agltation as described in Table 1 and at the ":,, - 1 1597g2 1 preferred current density of 60 ma/cm , the films had high Hc values, partially open B-H loops, and showed distinctly less that 15% Fe. This range thus shows itself to be too low to produce 80:20 magnetic films.
We have found that automatic and continuous measurement with automatic adjustment avoids long response times and large fluctuations in solution temperature, pH, and specific gravity.
The large storage reservoir tank permits holding fluctuations low, and provides automatic quick response to any changes. It has been found also that specific gravity is not a satisfac-tory measure of the rate of consumption of reagents, particu-larly [Fe ~ which is the most sensitive quantity (reagent).
The change of ~Fe ~ is proportional to pH as taught herein, and hence it is necessary to measure pH only on a continuous basis and to predetermine the [Fe++] ion consumption in order to make an appropriate adjustment in the [Fe ~ content of the bath along with adding acid. ~Fe++] is lost through plating out and through oxidation to tFe ] . At a pH above 3.5, ; [Fe ~ will tend to precipitate to a small degree, which is then taken out by the filter in the line. Measurements have yielded a calibration curve not included herein which shows ; the close relationship of the change of pH due to Fe + consump-tion. This data has been used to precalculate the ratio of Hc to ~Fe ~ added while adjusting pH as shown in Table III
above.

~ ' . ' ~ .

; r :~1 , ; .

l 1~9792 1 Table V
2Plating Through the ~lask with Long Line Openings 3Varying from 2.5 ~m to 25 ~m with Varying Spaces 4Plating Rate Average Spread of Da.a for a Wafer 6 5 ma/cm 1545A/min 1540 1550 7 spread of compositlon 47 to 52%-Fe (FIG. 9) 8 10 ma/cm 5000A/min 4375 S333 9 spread of composition 48 to 53% Fe 20 ma/cm 9000A/min 8700 12,167 11 spread of composition 45 to 54% Fe 12 40 ma/cm 25,000A/min 18,000 30,000 13 deposits very nodular and "burned"
14 spread of composition 22 to 52~ Fe 60 ma/cm 50,000A/min 35,000 57,000 16 deposits very nodular and "burned"
17 spread of composition 11 to 23~/o Fe 18 Table VI
19 Process Limits for Ni-Fe Plating Without 20"Burning", with Sound. Bright Deposits and Good Adhesion 21 Sheet Form 2 Through a ~as'~
22 Plating Current Density 10-200 ma/cm 2-60 ma/cm :
23 [Fe ] l - 14 g/l 0.3 - 1.0 g/l 24 [Ni ] 7 - 37 g/l 17 - 44 g/l Agitation none to ultrasonic mechanicai agitacion ,~
: ~ 26 pH 1 - 3.6 1 - 3.6 ~ 27 Temperature 20 - 35C 20 - 35C

~:, ,:;' . ' .

'I .

~: .
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1 15'3792 2Limits for Plating ~ Fe, 20io Fe +1~

3Sheet Form 2 Ihrough a ~ask 4Plating Current Density 10-200 ma/cm 2-60 ma/cm [Fe ] 1.1 - 1.7 g/l 0.3 - 0.7 gl [Ni ] 7 - 37 g/l 17 - 44 g/l 7 Agitation, pH and tem?erature ranges were the same GS in 8 TABLE VI.

.

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, I .
~ !

~ - ,

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A nickel-iron electroplating method, for electroplating a nickel-iron film onto a sheet substrate of a metallic material, including the steps of:
(a) providing a plating fluid bath having an Fe++ ion concentration of about 1-14 g/l, an Ni++ ion concentration of about 7-37 g/l;
(b) maintaining said bath at a pH of about 1 - 3.6;
(c) maintaining the bath at a temperature of from 20°C -35°C;
(d) employing a plating current density of about 10 - 200 ma/cm2;
the Fe++ ion concentration required in the bath for a predetermined Ni percentage in the nickel-iron film being an inverse function of circulation of bath fluid across said substrate.

2. A nickel-iron electroplating method as defined in claim 1 and further including the steps of:
(i) monitoring the pH of the bath and producing an electrical signal as a function of a chemical concentration present in the bath and indicative of the pH of the bath, and (ii) in response to said electrical signal, automatically dispensing at least one reagent including Fe++
ions through a valve into said bath thereby restoring the desired pH within the range of 1 - 3.6.

3. A nickel-iron electroplating method as defined in claims 1 or 2 wherein said bath fluid has a nickel-iron ratio of about 5.8:1 to about 23:1.

4. A nickel-iron electroplating method including the process of electroplating nickel-iron films containing about 20% iron ? 1% onto a sheet substrate of a metallic material, said method including employing a plating current density of about 10 - 200 ma/cm2, a plating bath fluid with an Fe++ ion concentration of about 1.1 - 1.7 g/l, an Ni++ ion concentration of about 7 -37 g/l, and a pH of about 1 - 3.6, and maintaining said fluid at a temperature of 20° -35°C, wherein required Fe++ ion concentration required to produce said films with 20% iron +1% is an inverse function of circulation of bath fluid across said substrate.

5. An electroplating method in accordance with claim 4 including:
containing a plating bath fluid in a cell having an anode, and a cathode including said substrate to be plated with said nickel-iron film, holding said cathode with the surface to be plated facing the anode of said cell, passing said plating bath fluid directly onto the surface of said cathode by means of an inlet to said cell aligned with the surface of said cathode, pumping fluid up from a reservoir into said inlet via conduit means, returning plating bath fluid to said reservoir, sensing the chemical concentration present in said system, which is indicative of the pH of the bath and automatically dispensing a reagent including at least Fe++ ions by means of a reagent dispenser into said reservoir in response to the chemical concentration sensed in said system.

6. A method in accordance with claim 5 wherein said bath has a nickel-iron ratio of about 10:1 to about 20:1.

7. A method in accordance with claim 5 including providing agitation without substantial turbulence.

8. A method in accordance with claim 5 wherein said chemical concentration is sensed by a pH sensor, and said reagent dispenser dispenses acid and Fe++ ions.

9. A method in accordance with claim 5 wherein the temperature of said bath is automatically maintained by a temperature sensor, a thermostatic control, and heating means.

10. A nickel-iron electroplating method for electroplating a nickel-iron film onto a sheet substrate of a metallic material, said method including:
employing a plating current density selected from the group comprising:
(a) 10 - 200 ma/cm2 and (b) 2 - 60 ma/cm2 when said substrate has a mask deposited on it;
a plating bath fluid having an Fe++ ion concentration selected from the group comprising:
(a) 1-14 g/l and (b) 0.3 g/1 - 1.0 g/l when said substrate has a mask deposited on it;
said bath having an Ni++ ion concentration selected from the group comprising:
(a) 7-37 g/l and (b) 17-44 g/l when said substrate has a mask deposited on it;
said bath fluid having a pH of about 1-3.6, and maintaining said fluid at a temperature of about 20° - 35°C, wherein the Fe++ ion concentration required in the bath for plating is inverse to circulation of said plating bath fluid across said substrate.