Magnetoresistance effect type head having a damage immune film structure

A magnetoresistance effect type head including a ceramic substrate, a first magnetic film provided on the ceramic substrate, a second magnetic film provided above the first magnetic film, first and second insulating films provided between the first and second magnetic films, a magnetoresistance effect type film provided between the first and second insulating films, a bias film provided between the first and second insulating films in contact with the magnetoresistive film for applying magnetic field to the magnetoresistive film, a first conductive film provided between the first and second insulating films and above the bias film to be nearly as thick as the mean free path of free electrons, and a second conductive film of an electrode structure mutually separated between the first and second insulating films in contact with the first conductive film. The first conductive film is a nickel-chromium film or a chromium film which is resistive to a fluorocarbon-series gas to be used for etching. The second conductive film is made of a metal which is etched with a fluorocarbon-series gas and which has a thickness of 200 nm or more. The bias film and the magnetoresistance effect type film are protected from over-etching. The second conductive layer is made up of two metallic layers having contact tightness with the second insulating film and a third metallic layer which is sandwiched between the two metallic layers and which has a conductivity larger than the two metallic layers and also a thickness larger than the two metallic layers.

BACKGROUND OF THE INVENTION 
The present invention generally relates to a magnetoresistance effect type 
head and a manufacturing method therefor and, more particularly, to a 
technique which can be effectively used for a magnetic head of a magnetic 
disc device or the like. 
A magnetoresistive head is a reproduction exclusive head utilizing such a 
phenomenon that the electric resistance of a magnetoresistance effect type 
film, which will be sometimes referred to merely as the MR film, 
hereinafter, varies depending on its magnetizing direction. 
The magnetoresistive head comprises lower and upper magnetic shield films 
made of magnetic material and an MR element disposed between the upper and 
lower magnetic shield films. The MR element has an MR film, bias films for 
applying a horizontal bias to the MR film, and a pair of conductive 
electrodes for passing a signal detection signal to the MR film. A 
magnetic domain control layer may be provided in the MR element to provide 
a single magnetic domain to the MR film. A current is continuously passed 
to the MR film through the conductive electrodes, and a voltage between 
the electrodes is continuously detected. When a leak magnetic field 
ranging from a magnetic recording medium to the MR film varies, this 
causes the magnetizing direction of the MR film to be varied so that the 
resistance of the MR film is changed and a signal is generated between the 
electrodes. In this manner, information is reproduced from the medium. 
The processes for forming the electrodes and MR film of the prior art MR 
element include (a) formation of the MR film on the electrodes and (b) 
formation of the electrodes on the MR film. 
The process (a) has a problem that the formation of the MR film on the 
electrodes involves the formation of steps in the MR film and the 
formation of magnetic walls in the steps, which results in generation of 
Barkhausen noise at the time of reproduction. 
The process (b) can avoid such a problem as the formation of the steps in 
the MR film unlike the process (a), but process (b) is defective in that 
the formation of the electrodes on the MR film causes damage of the MR 
film. More specifically, when an electrode film is formed on the MR film 
and then subjected to an ion milling for formation of the electrodes for 
example, the MR film is damaged because of its subjection to ions. 
For the purpose of minimizing the damage of the MR film, there has been 
suggested an electrode processing method which is based on a reactive ion 
etching. In this method, as shown in JP-A-Hei 4-3306, a film Nb, Ta, Ti or 
the like capable of being subjected to a dry etching with use of such a 
fluorocarbon gas as a CF.sub.4 gas for formation of electrodes, or a film 
of Au, Pt, Cr or the like capable of being subjected to an etching with 
use of a chlorine-series gas, is formed on an MR or bias film subjected to 
a patterning of a predetermined shape, and subsequently the etched film is 
subjected to an etching to form electrodes having a desired shape. During 
the over-etching for the formation of the electrodes with use of the 
fluorocarbon gas or chlorine-series gas, the MR or bias film is subjected 
to the etching and therefore damaged. 
Disclosed in JP-A-63-117309 (U.S. Pat. No. 4,713,708) is a 
magnetoresistance effect type head reader/converter in which a spacer film 
and a soft magnetic thin film are provided on an MR film. This invention 
also discloses vertical/horizontal biasing effects based on the use of a 
vertical bias film and a soft bias film. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a magnetoresistive head 
and a manufacturing method therefor which can prevent the damage of MR and 
bias films when subjected to an electrode processing process with use of a 
gas and thus which can improve its performances. 
Another object of the present invention is to provide a magnetoresistive 
head which can prevent the damage of MR and bias films when a first 
conductive film formed on a second conductive film is subjected to a 
reactive ion etching for formation of electrodes and thereby which can 
improve its performances. 
Typical ones alone of inventions disclosed in the present application will 
be summarized below. 
In accordance with an aspect of the present invention, there is provided a 
magnetoresistive head in which an MR film and different bias films are 
formed, a first conductive film resistive to a reactive ion etching with 
use of a fluorocarbon-series gas is formed on the MR and bias films, and 
then a second conductive film to be formed as conductive electrodes is 
formed on the first conductive film. 
In this case, the first conductive film should be nonmagnetic and resistive 
to the reactive ion etching. It may be made of Cr or NiCr alloy film as 
mentioned later. Further, it may be made of Cr, V, Ag, Au, Cu, Pt and Pd. 
It may be a non magnetic metal alloy including at least two of Fe, Co, Ni, 
Cr, V, Ag, Au, Cu, Pt and Pd. Further, the first conductive film is 
required to be non-magnetic and not to contain two or more of Fe, Co and 
Ni. While the second conductive film is subjected to the reactive ion 
etching with use of the fluorocarbon-series gas for formation of 
conductive electrodes, the first conductive film can exhibit a high 
resistance to the over-etching of the MR film and thus can act as a 
protective film for avoiding the damage of the MR film. 
In accordance with another aspect of the present invention, there is 
provided a method for manufacturing a magnetoresistive head in which a 
first conductive film resistive to a reactive ion etching with use of a 
fluorocarbon-series gas is formed on an MR and different bias films, a 
second conductive film is formed directly on the first conductive film as 
tightly contacted therewith at least partly and then subjected to the 
reactive ion etching. 
The first conductive film is made of Cr, Ni-Cr, or at least one of Cr, V, 
Fe, Co, Ni, Ag, Au, Cu, Pt and Pd or an alloy thereof. Note that the first 
conductive film is required not to contain two or more of Fe, Co and Ni. 
The second conductive film is made of, for example, Nb, Ta, W or Mo. 
The first conductive film resistive to the reactive ion etching with use of 
a fluorocarbon-series gas and formed on the MR film acts as a protective 
film for preventing the etching damage of the MR film and bias films (for 
applying a bias magnetic field) when the second conductive film for 
formation of conductive electrodes is subjected to the over-etching. 
With such a structure, since the MR and bias films can be reliably 
protected from the reactive ion etching, such a situation can be avoided 
that when the thicknesses of the MR and bias films vary from their 
predetermined values, this undesirably involves variations in the 
characteristics of the MR element, which means in that the performances of 
the magnetoresistance effect type head can be reliably improved. 
The requirement that the first film be electrically conductive is because a 
current must be passed from the conductive electrodes through the first 
conductive film to the MR film. 
The above and other objects and novel features of the present invention 
will be obvious from the description in conjunction with the attached 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Magnetoresistance effect type heads and their manufacturing methods in 
accordance with different embodiments of the present invention will be 
detailed with reference to the accompanying drawings. 
FIGS. 1A to 1C schematically show cross-sectional views showing exemplary 
steps of a method for manufacturing a magnetoresistance effect type head 
in accordance with an embodiment of the present invention; and FIGS. 2A to 
2C schematically show cross-sectional views showing exemplary steps of a 
method for manufacturing a prior art magnetoresistance effect type head 
for comparison with the head of FIGS. 1A to 1C. 
The inventors has confirmed a problem in the prior art magnetoresistance 
effect type head by comparing the manufacturing steps of the prior art 
head of FIGS. 2A to 2C with those of the head of the embodiment of FIGS. 
1A to 1C. 
More specifically, a lower magnetic shield film 7 of 1 .mu.m thick is 
formed on a substrate 11 made of ceramic or the like material. Formed on 
the substrate 11 is a lower magnetic gap layer 8 made of Al.sub.2 O.sub.3 
having a thickness of 180-300 nm (200 nm in the present example). Formed 
on the gap layer 8 is a vertical bias film 12 (not shown but which will 
described later). Sequentially formed as stacked on the vertical bias film 
12 are a permalloy MR film 6 of 20 nm thick, a shunt bias Nb film 5 of 15 
nm thick and a soft bias film 4 of 20 nm thick and made of NiFeNb 
respectively in predetermined shapes. In the head of the first embodiment 
shown in FIG. 1A, such a Cr protective film 3 as to be described later is 
formed on the soft bias film 4. Further in the structures of FIGS. 1A and 
2A, an electrode film 2a of 220 nm thick and made of Nb for formation of 
electrodes 2, and then a photoresist pattern 1 for formation of a mask are 
sequentially formed on the protective film 3. 
The electrodes 2 of the electrode film 2a are subjected to a reactive ion 
etching (RIE) with use of a mixture gas of CF.sub.6 and 5% of O.sub.2 and 
with use of the photoresist pattern 1 as the mask to fabricate an MR 
element (refer to FIGS. 1B and 2B). 
Formed on the MR element is an upper magnetic gap layer 9 made of Al.sub.2 
O.sub.3 and having a thickness of 140-240 nm (160 nm in the present 
embodiment), on which an upper magnetic shield film 10 is formed to 
thereby form a magnetoresistance effect type head (refer to FIGS. 1C and 
2C). In this connection, the upper and lower magnetic shield films 10 and 
7 may comprise an NiFe film, a CoTaZr film or an FeAlSi film. 
Shown in FIGS. 2A to 2C are cross-sectional views of the magnetoresistance 
effect type head when viewed from a magnetic disk (not shown) toward the 
sliding surface of the head. The drawings to be given in the following are 
also the similar cross-sectional views. In this connection, the electrodes 
2 may be made of Ta, W or Mo. 
Also formed on the same substrate 11 is an MR element (not shown) having no 
such upper and lower magnetic shield films. As a result of measuring the 
MR element with respect to its voltage-magnetic field curve, it has been 
found that a bias magnetic field of the soft bias film is not 
substantially applied to the MR film. Further, the plus and minus sides of 
the waveform of a signal reproduced by the head are poor in their symmetry 
even when a sense current to the MR element is varied. This is because a 
proper horizontal bias is not applied from the soft bias film or shunt 
bias film to the MR film 6. In this way, no bias magnetic field is applied 
to the MR film 6. This is considered to be due to the fact that, during 
over-etching of the etching operation of the electrode film 2a, the soft 
bias film 4 and shunt bias film 5 on the MR film 6 are also exposed to the 
over-etching to be thereby damaged. 
For the purpose of avoiding such a defect, as mentioned earlier, in the 
magnetoresistance effect type head and its manufacturing method of the 
present embodiment 1, the Cr protective film 3 (first conductive film) of 
5 nm thick is formed on the soft bias film 4, the known photoresist is 
subjected to light exposure to form a mask, and then subjected to an ion 
milling with use of an argon gas to form such an island as shown (refer to 
the layers 3 to 6 in FIG. 1 or the layers 4 to 6 in FIG. 2). Formed on the 
island is the electrode film 2a (second conductive film) of 220 nm thick 
and made of Nb material. With the both structures of FIGS. 1A and 2A, the 
electrode film 2a is subjected to the reactive ion etching with use of the 
mixture gas of CF.sub.4 and 5% of O.sub.2 to form the electrodes 2. The 
formation of the Cr protective film by sputtering is required to be 
carried out at a temperature of below 200.degree. C., because the film 
formation at temperatures above 200.degree. C. causes Cr in the protective 
film to be diffused into the soft bias film, thus deteriorating its 
characteristics. 
The material of the protective film 3 is not limited to the aforementioned 
Cr but may be any material, so long as the material is electrically 
conductive and highly resistive to the etching with use of the mixture gas 
of CF.sub.4 and 5% of O.sub.2. For example, the protective film 3 may be a 
non-magnetic, conductive film of Ni-Cr, V, Fe, Co, Ni, Cu, Pd, Ag, Pt, Au 
or the like of specific resistance above 40 .mu..OMEGA. cm, because 
current flowing through this film should be suppressed at a low level. In 
the reactive ion etching (RIE), CF.sub.4 in the mixture gas may be 
replaced by an SF.sub.6 gas. 
When the magnetoresistance effect type head of the present embodiment thus 
manufactured is subjected to measurements for its voltage-magnetic field 
curve, it has been confirmed that bias magnetic field is increased with 
the increasing sense current so that a proper bias magnetic field can be 
applied. Further, when the head fabricated in such a manner as mentioned 
above is optimized in its sense current, a reproduced signal can be made 
highly symmetrical with respect to the plus and the minus components of an 
input signal. 
Other heads having the Cr protective films 3 of 3 nm and 20 nm thick were 
fabricated. Our experiments have shown that, in the case of the head with 
the 3 nm-thick protective film 3, the protective film 3 disappears during 
the over-dry etching and the head exhibits a poor bias characteristic; in 
the case of the head with the 20 nm-thick protective film 3, a portion of 
the sense current flowing through the protective film 3 becomes large. 
Since the magnetic field applied to the soft film under the influence of 
the current flowing through the protective film is opposite in direction 
to the magnetic field applied to the soft bias film 4 under the influence 
of the current flowing through the shunt bias current 5 and MR films, 
these heads exhibited poor bias characteristics. Thus, it is considered 
that the thickness of the protective film is preferably between about 5 
and 16 nm. The thickness of the soft bias film is in a range of between 20 
and 30 nm. The shunt bias film has a thickness of preferably 15-20 nm. It 
is preferable that the MR film has a thickness of 15-30 nm. Saturation 
magnetic flux densities Bs of the soft bias film 4 and MR film 6 were 
0.6-1.0 T and 0.9-1.1 T respectively. 
More specifically, even in the case where the film is made of conductive 
material, the thickness of the film is made as thin as nearly the mean 
free path of free electrons, the electric resistive value of the film 
becomes large. Thus, the aforementioned problem is avoided by making the 
protective film 3 as thin as about 5-16 nm to reduce the current flowing 
through the film 3. The conductivity of the protective film 3 is large 
with respect to the current flowing through the film in its thickness 
direction and thus no troubles take place in the current flow from the 
electrode 2 through the protective film 3 to the MR film 6. 
FIG. 3 shows a further detailed structure of the MR element shown in FIG. 
1C. It is already known that the provision of the vertical bias film 12 
and the soft bias film 4 improves the characteristics of the 
magnetoresistance effect type element. The vertical bias film may comprise 
an anti-ferromagnetic film made of NiO or FeMn, a two-layer permanent 
magnet film of a CoCrTa layer and a Cr layer, or a permanent magnet film 
made of CoPt or CoPtCr. 
A magnetoresistance effect type head and its fabricating method in 
accordance with a second embodiment are shown by its fabricating steps in 
FIGS. 4As to 4C. In the present embodiment, an electrode film 20 is made 
up of three layers, that is, Nb layers (of 20 nm and 60 nm thick) and an 
Au layer of a small resistivity sandwiched by the Nb layers. 
More specifically, an electrode film 20a comprising the aforementioned 20 
nm-thick Nb, 140 nm-thick Au and 60 nm-thick Nb layers for formation of 
the electrode 20 is formed on a protective film 3, and a photoresist 
pattern 1 is formed on the electrode film 20a (refer to FIG. 4A). 
The upper Nb and Au layers (of 20 nm and 140 nm thick, respectively) is 
then subjected to an ion milling with use of the photoresist pattern 1 as 
a mask. In this process, the lowermost Nb layer (of 60 nm thick) of the 
electrode film 20a functions as an ion milling stopper. The upper Nb layer 
acts to improve the contact tightness with an Al.sub.2 O.sub.3 film (to be 
explained later). The material Nb may be replaced by other suitable 
material, such as Cr, Ti, Ta, Mo, V, as necessary. Next, the resultant 
structure is subjected to a reactive ion etching (RIE) with use of a 
mixture gas of CF.sub.4 and 5% of O.sub.2 to remove the remaining lower Nb 
layer (refer to FIG. 4B). For the purpose of reducing the number of steps, 
an element not having the upper Nb layer formed therein may be formed. 
Subsequently, as in the first embodiment, an upper magnetic gap layer 9 
made of Al.sub.2 O.sub.3 material and of 160 nm thick is formed on the 
resultant structure, and an upper magnetic shield film 10 is formed on the 
upper magnetic gap layer 9 (refer to FIG. 4C) to thereby form a 
magnetoresistance effect type head. As a result of measuring the MR 
element without the upper and lower magnetic shield films fabricated on 
the same substrate 11 with respect to its voltage-magnetic field curve, it 
has been confirmed that its sense current and bias magnetic field can both 
be increased and a suitable bias magnetic field can be applied. The head 
fabricated in such a manner as mentioned above, when the sense current is 
optimized, exhibited a reproduced signal having a good symmetrical 
waveform to an input signal. In addition, the noise of the head could be 
more reduced than that of the first embodiment. 
Shown in FIG. 5 is a third embodiment of the present invention, in which 
the soft bias film 5 and the MR film 6 are exchanged in the structure of 
the first or second embodiment. Even with the structure of the third 
embodiment, a head having a good bias characteristic was obtained. Even in 
this case, when the electrode 20 is made of the electrode film 20a 
comprising 3 Nb (20 nm), Au (140 nm) and Nb (60 nm) layers, the head noise 
can be more suppressed. 
A fourth embodiment corresponds to the magneto-resistance effect type head 
of the first or second embodiment but the soft bias film 4 is removed 
therefrom. Even in the fourth embodiment, a head having a good bias 
characteristic could be obtained. The fabricating steps of the 
magnetoresistance effect type head of the fourth embodiment are shown in 
FIGS. 6A to 6C. The shunt bias film 5 is made of, for example, Nb having a 
thickness of preferably 27-50 nm, while the MR film 6 is made to have a 
thickness of preferably 15-30 nm. 
Even in the fourth embodiment, if an electrode 20 is used, made of the 
electrode film 20a comprising 3 Nb (20 nm), Au (140 nm) and Nb 60 nm) 
layers, the head noise can be more suppressed. 
A fifth embodiment, though not specifically shown, corresponds to the 
structure of the fourth embodiment but the shunt bias film 5 and the MR 
film 6 are exchanged. Even with the present structure, a head having a 
good bias characteristic could be obtained. 
In a sixth embodiment, the MR film 6 of 20 nm thick and made of permalloy; 
any of an Ni-Fe-Nb ternary alloy film, a Co-Ni-Fe ternary alloy film, an 
Fe-Ni-Cr alloy film, a Co-Zr-Mo amorphous film and Co-Zr-Cr amorphous 
film, usable as the soft bias film 4; and Nb, Ta, Mo and W films were 
exposed to a reactive ion etching environment with use of a mixture gas of 
CF.sub.4 and 5% of O.sub.2 corresponding to the over-etching at the time 
of processing the electrode 2 or 20, and damages of the films were 
examined. The examined results are shown in FIG. 7. 
As shown, when the Ni-Fe-Nb ternary alloy film, permalloy film (Ni-Fe), 
Co-Ni-Fe ternary alloy film, Fe-Ni-Cr alloy film, Co-Zr-Mo amorphous film 
and Co-Zr-Cr amorphous film are subjected to 4 minutes of reactive ion 
etching (RIE), corresponding to the over-etching of the processing of the 
electrode 2 (20), the thicknesses of these films are reduced by 4-6 nm. 
That is, these films are damaged by the RIE process. As a result of the 
similar experiments conducted on Co-Zr-Ta, Co-Zr-Nb and Co-Hf-Ta-Nb films 
as other Co-series amorphous films, it has been found that these materials 
are also damaged by the RIE process. 
The Ta, Mo and W film are completely removed through 4 minutes of the RIE 
process. 
When it is desired to use these films as the aforementioned MR film or 
various bias films, the damage to these films during the RIE process must 
be prevented. 
For the purpose of preventing the damage, a protective film made of Cr and 
Ni-Cr non-magnetic alloy was formed on these films to have a thickness of 
3 nm, 5 nm, 8 nm or 10 nm, and then subjected to a reactive ion etching 
with use of a mixture gas of CF.sub.4 and 5% of O.sub.2. As a result, 
since the 3 nm-thick protective film of Cr and Ni-Cr alloy is removed 
through the RIE process within 4 minutes, the MR film or bias film located 
below the protective film are damaged. However, when the thickness of the 
protective film of Cr and Ni-Cr alloy is made to be more than 5 nm, since 
the protective film is not removed through 4 minutes of the RIE process, 
the damage of the MR or bias film located below the protective film can be 
avoided. 
As a protective film other than the Cr and Ni-Cr protective films, a V, Fe, 
Ni, Cu, Pd, Ag, Pt or Au film or an alloy film thereof is preferable 
because of their high resistance to the reactive ion etching (RIE) with 
SF.sub.6 or CF.sub.4 gas. 
Although the invention has been explained in the foregoing in conjunction 
with the embodiments, it goes without saying that the present invention is 
not limited to these embodiments but may be modified in various ways 
without departing from its subject matter.