RU2536317C1 - Method to manufacture magnetoresistive sensor - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: invention relates to the field of automatics and magnetometry. The method to manufacture a magnetoresistive sensor consists in formation of a Winston bridge on an insulating substrate by means of vacuum sputtering of a magnetoresistive structure with subsequent formation of magnetoresistive strips by the method of photolithographic etching and sputtering of the first conducting layer with subsequent formation of links, conductors and contact sites by the method of photolithographic etching, application of the first insulating layer from polyimide with its subsequent imidisation in vacuum, sputtering of the second conducting layer and formation of a flat inductance coil on it "set/reset" by the method of photolithographic etching, application of the second insulating layer from polyimide with its subsequent imidisation in vacuum, sputtering of the third conducting layer and formation of a flat inductance "offset" coil on it by the method of photolithographic etching, application of a structural protection with subsequent opening of contact sites of the first conducting layer, at the same time conducting layers are produced by means of vacuum sputtering of a Cr-Cu-Cr structure, which is etched in layers and selectively, and on contact sites that are on the first conducting layer, they additionally create a film of Al by means of its sputtering on the sensor after application of the structural protection with subsequent photolithographic etching.

EFFECT: invention of the method provides for improved technical characteristics: increased specific sensitivity, reduced unbalance and lower cost of a sensor.

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Description

The invention relates to the field of automation and magnetometry and can be used in the manufacture of displacement sensors, devices for measuring electric current and magnetic fields, namely, in the manufacture of angle sensors, devices with galvanic isolation, magnetometers, electronic compasses, etc.

Known magnetoresistive sensor described in US patent 5247278, CL. H01L, 43/00 dated July 11, 1989. It is formed by vacuum deposition of magnetoresistive and conductive layers on a silicon wafer, followed by photolithographic etching of the pattern. To obtain magnetoresistive strips, a cobalt-containing alloy of NiFeCo is sprayed, and Al + 4% Cu is sprayed for conductive paths, jumpers between magnetoresistive strips and contact pads. To isolate the silicon wafer and the upper conductive layer, SiO ₂ + Si ₃ N ₄ is applied, respectively.

The disadvantage of this method is the inability to create reliable insulation, because silicon oxide and nitride films have a high level of internal stress and crack during the manufacture of the sensor. This is especially noticeable when a more complex sensor structure with two flat “set / reset” and “offset” inductors is manufactured, where three layers of thicker insulation are required than the thickness indicated in this patent (~ 1 μm).

This disadvantage is taken into account in the "Method of manufacturing a magnetoresistive sensor", RF patent 2463688 C1, cl. H01L 43/12 of 06/23/2011, taken as a prototype.

In this method, a polyimide varnish is used as insulation, which is imidized when heated in vacuum by applying a magnetic field in the plane of the substrate in the direction of the OLD, and the structure of V-Cu-Ni is used as the electrically conductive material instead of Al, because the latter is etched in the etchant for polyimide when forming vias and opening contact pads.

This method significantly increased the reliability of the sensor and the yield, however, it is not without drawbacks.

First of all, this refers to the fidelity of the pattern pattern on the conductive layer. So the etching of the structure of V-Cu-Ni does not provide the necessary accuracy due to the fact that the etching can reach 10 microns or more. This leads to an increase in the gaps in the manufacture of the Barber poles, which leads to a decrease in the displacement field, and thereby to a decrease in the sensitivity of the sensor, as well as to an increase in the unbalance of the Winston bridge.

In addition, the deposition of the upper layer of nickel involves welding the gold wire to the contact pads, which is, firstly, expensive, and secondly, low-tech, because high silicon conductivity requires the application of high power, which often leads to burnout of the electrode and does not provide the necessary strength of the welded joint. This reduces the yield, and thereby increases the cost of the sensor.

The technical result of the proposed method is to increase technical characteristics (increase specific sensitivity, reduce imbalance), as well as reduce its cost.

The specified technical result is achieved in that in a method for manufacturing a magnetoresistive sensor, which consists in forming a Winston bridge on an insulating substrate by vacuum deposition of a magnetoresistive structure, followed by the formation of magnetoresistive strips by photolithographic etching and spraying of the first conductive layer with subsequent formation of jumpers, conductors and contact pads using the photolith method etching, applying the first insulating layer of polyimide with the last imidizing it in a vacuum, sputtering a second conductive layer and forming a “set / reset” flat inductor on it using photolithographic etching, applying a second polyimide insulating layer, then imidizing it in a vacuum, spraying a third conductive layer and forming a flat inductor on it "Offset" by photolithographic etching, applying structural protection, followed by opening the contact pads of the first conductive layer, the conductive layers are obtained by vacuum th sputtering structure Cr-Cu-Cr, which is etched in layers and selectively, while the exposed contact pads located on the first conductive layer is formed Al film by sputtering it onto the sensor, followed by photolithographic etching.

On figa, 1b and 1c shows the topology of the sensor:

1a - Winston bridge, pads formed on the first conductive layer and conductive tracks of three functional elements (Winston bridge, set / reset inductors and offset bias):

1 - contact pad with a conductive path of the inductor "set / reset";

2 - contact pad with a conductive track of Winston Bridge;

3 - contact pad with a conductive track of Winston Bridge;

4 - contact pad with a conductive track of Winston Bridge;

5 - contact pad with a conductive path of the inductance coil "offset";

6 - contact pad with a conductive path of the inductor "set / reset";

7 - contact area with a conductive track of Winston Bridge;

8 - contact pad with a conductive path of the inductance coil "offset".

1b - Winston bridge and a set / reset inductor formed on a second conductive layer.

1c - Winston bridge, “set / reset” inductor and “offset” inductor formed on a third conductive layer.

Figure 2 shows the topology of one of the shoulders of the Winston bridge:

9 - magnetoresistive strips with pointed ends;

10-jumpers

11 - Barber poles.

Figure 3 shows the structure of the sensor in the context:

12 - substrate;

13 - insulation from SiO ₂ ;

14 - insulation of Si ₃ N ₄ ;

15 - magnetoresistive structure;

16 - the first conductive layer;

17 - Barber poles (Cr-Cu-Cr) formed on the first conductive layer;

18 - the first insulation of polyimide;

19 is a set / reset inductor (Cr-Cu-Cr) formed on a second conductive layer;

20 - second insulation from polyimide;

21 is an offset coil (Cr-Cu-Cr) formed on the third conductive layer;

22 - constructive protection;

23 - contact pads (Al);

24 - interlayer connections.

An example implementation of the method.

The proposed method was implemented in the manufacture of a magnetoresistive sensor having an odd HEC.

The sensor consists of a Winston bridge (contact pads 2, 3, 4, 7 of figa), a set / reset inductor (contact pads 1, 6 of figa) and an offset coil (contact pads 5, 8 of fig. .1a).

The Winston bridge contains four shoulders (Fig. 2), each of which consists of magnetoresistive strips with pointed ends 9, jumpers 10 and Barber poles 11, which allow shifting the SEC of the sensor to a linear region.

The content and sequence of technological operations for the manufacture of the sensor can be understood from a consideration of figure 3.

On a silicon wafer 12 containing insulation of SiO ₂ 13 with a thickness of 0.3 μm and Si ₃ N ₄ 14 with a thickness of 0.15 μm, the magnetoresistive structure of Fe (15%) Ni (65%) Co (20%) - Ta-Fe was sprayed (15%) Ni (65%) Co (20%) 15 with a thickness of ~ 50-60 nm and formed magnetoresistive strips 9 (figure 2) by photolithography and etching in the composition:

Nitric acid 100 ml Sodium Fluoride 10 g Potassium nitrate 30 g Distilled water 20 ml

Etching temperature (18-23) ° C, etching time 40-60 s.

Next, the first conductive layer of Cr-Cu-Cr was applied with a total thickness of ~ 0.5 μm, a mask was created by photolithography and contact pads and conductive paths of three functional elements were formed - Winston Bridge 2, 3, 4, 7 (Fig. 1a), inductor “Set / reset” 1, 6 (Fig. 1a), an “offset” inductor 5, 8 (Fig. 1a), as well as the Barber pole 17 (Fig. 3) and jumper 10 (Fig. 2).

Chromium etching was carried out in an etchant HCl: H ₂ O = 1: 1 at a temperature of (40 ± 5) ° C. This etchant is selective with respect to copper and acts as a metal resist when etched in the composition:

Phosphoric Acid 60 ml Acetic acid 10 ml Nitric acid 10 ml Distilled water 20 ml

Etching temperature (40 ± 5) ° C.

After etching, the copper was again etched with chromium in hydrochloric acid, which etched the upper thin layer of cobalt-containing alloy to tantalum, leaving it only under the Barber poles and jumpers. Such separate etching made it possible to reduce the etching of the Cr – Cu – Cr structure and to obtain the Barber poles and the gaps between them of the required size (17 × 17 μm, respectively).

Next, the application of varnish HELL 910318, 20 and its imidization in vacuum was carried out according to the prototype (patent RU 2463688 C1).

The first insulating varnish layer AD-9103 18 2-4 μm thick was applied to the surface of the substrate with the Winston bridge formed by centrifugation.

Next, the insulation layer was dried stepwise: at a temperature of 60 ° C for 10 min, at a temperature of 80 ° C for 10 min, at a temperature of 100 ° C for 10 min, at a temperature of 120 ° C for 30 min.

The insulation layer was imidized in a vacuum installation at a temperature of 350–380 ° C in a magnetic field of 120–140 Oe applied in the plane of the substrate in the same direction as in the deposition of the magnetoresistive structure “FeNi (FeNiCo) -Ta-FeNi (FeNiCo)” .

To manufacture the set / reset inductance coil 19, a second conductive layer of Cr-Cu-Cr with a thickness of ~ 2 μm was sprayed and photolithographic etching of the pattern was performed in accordance with Fig. 16.

Next, the operation was repeated for applying varnish HELL 9103 18 and its imidization in vacuum according to the regime indicated earlier.

To manufacture the “offset” inductor 21, a third conductive layer of Cr-Cu-Cr ~ 2 μm thick was sprayed and photolithographic etching of the pattern was performed in accordance with FIG.

AD-9103 23 varnish was applied as structural protection, and then it was heat-treated in air at a temperature of 200 ° C for 30 min. Next, varnish was opened on the pads 1-8 of the first conductive layer.

The last operations were spraying an aluminum film of ~ 1 μm on the finished sensor (with exposed contact pads 1-8 of the first conductive layer) and its photolithographic etching according to the figure, which allows aluminum 23 to be left only on contact pads 1-8 of the first conductive layer.

Inter-level connections 24 from the inductors 19, 21 to the conductive tracks of the corresponding contact pads of the sensor were obtained by the so-called "cascade method", which consists in the fact that inter-level connections 24 are formed by sputtering the transition windows simultaneously with the sputtering of the conductive layer of the corresponding level and making the circuit diagram by photolithography, moreover, inter-level compounds form a larger size than the size of the transition windows in plan, and in each subsequent insulation layer etch odnye larger windows than in the previous (see. Patent №2474004 for the invention RU 2474004 C1 on August 16, 2011).

Thus, in the proposed method, the use of known materials and manufacturing methods of the sensor, but when changing the sequence of operations and using the selective properties of the etchants Cr and Cu in the manufacture of drawing elements from the first, second and third conductive layers, gave a new positive effect, which consists in improving the technical characteristics of the sensor and reducing its cost.

Thus, the ability to more accurately reproduce the pattern of the template on the Cr-Cu-Cr structure made it possible to increase the sensitivity of the sensor with Barber poles from 0.5 mV / (V × E) to 0.8-0.9 mV / (V × E), reduce the imbalance of the Winston bridge on average from 8-12 mV to 4-6 mV, which made it possible to abandon the fitting resistance and thereby reduce the size of the sensor and exclude the fitting operation of the Winston bridge from the technology.

The use of Al on top of the pads allowed us to apply ultrasonic welding of aluminum foil, while the strength of the welded joint increased from 20-22 g for gold wire to 50 g for aluminum foil (it was determined by the dynamometric method by tearing aluminum foil from an aluminum gearbox). In addition, in this case, it is obvious that this operation, and in general the sensor, is cheaper than the welding of gold wire.

In a similar way, a sensor was made, the Winston bridge of which contains inclined strips. The output of suitable sensors with an imbalance of 4 mV increased by 30% compared with the prototype.

Claims (1)

A method of manufacturing a magnetoresistive sensor, which consists in forming a Winston bridge on an insulating substrate by vacuum deposition of a magnetoresistive structure, followed by the formation of magnetoresistive strips by photolithographic etching and spraying of the first conductive layer, followed by the formation of jumpers, conductors and contact pads by photolithographic etching, applying the first polyolithographic etching layer followed by its imidization in a vacuum, spraying a second the sheathing layer and forming a “set / reset” flat inductor on it by photolithographic etching, applying a second polyimide insulating layer followed by imidization in vacuum, spraying the third conductive layer and forming a “offset” flat inductor on it using photolithographic etching, applying structural protection followed by opening the contact pads of the first conductive layer, characterized in that the conductive layers are obtained by vacuum deposition of a Cr-Cu-Cr structure, which The etch is etched in layers and selectively, and on the exposed contact pads located on the first conductive layer, an Al film is additionally formed by spraying it onto the sensor followed by photolithographic etching.

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