EP1093132A2 - Planer trimming resistor, its application and manufacturing process - Google Patents

Abstract

The device has a substrate (1), a resistive layer (3) and a contact layer (6) on the resistive layer and with higher conductivity than and in contact with it at least at individual points (4). Material can be removed locally (7) above the resistive layer. The contact layer does not extend beyond the edges of the resistive layer. The resistive and contact layers can be strip-shaped with connection contacts at opposite ends of the contact layer. Independent claims are also included for the following: 1. a resistive bridge circuit; 2. a sensor with a deformable substrate and at least one resistance element; and 3. a method of manufacturing a balancing resistance.

Description

State of the art

The invention relates to a planar trimming resistor with a substrate and one deposited thereon Resistor layer, a resistor bridge circuit and a sensor that such Use trimming resistor and procedure to manufacture the trimming resistor respectively the resistance bridge circuit or the Sensors.

Trimming resistors are used in circuits, which were initially manufactured with a certain tolerance and their behavior afterwards by adjusting the resistance value of said Trimming resistors is set exactly. There are Trimmer resistors with a planar resistance layer known, the resistance value after installation of the trimming resistor in a circuit local removal of material from the resistance layer can be adjusted. This is the result Problem that a change in resistance value by removing material of the resistance layer also affects their capacity, especially if if the resistance layer is in the immediate Extends near another conductor, e.g. because they are only separated by a thin layer of insulation is deposited on a metallic substrate. Such a change in capacity can change the value of the Nullify the comparison if the behavior of the overall circuit to be calibrated not only from Resistance value, but also from the capacity of the Adjustment resistance is affected. This Problem always occurs when the trimming resistor Is part of a resonance circuit.

Advantages of the invention

The present invention makes a planar Trimming resistor of the type described in the introduction created its capacity through the matching process is not affected.

This advantage is achieved in that a contact layer, which have better conductivity than that Has resistance layer on the resistance layer is arranged so that it is at least individual positions in contact with the latter stands, and the at least locally ablating Treatment is accessible. If at one such a resistance, the contact layer locally is eliminated, this has the consequence that a Current that would otherwise flow through the contact layer would have, at least partially, in the resistance layer is pushed so that by the removal the contact layer controls the resistance value is increased. But at the same time the resistance layer exist under the worn contact layer remains, the one opposite the substrate changes electrically conductive surface of the Trimming resistor not, and its capacity is not changed by the removal process.

In principle, the contact layer may extend over the Limits of the resistance layer beyond on the substrate extend. However, those areas are allowed the contact layer that is not above the Resistance layer, cannot be removed, otherwise the surface of the balancing resistor would be reduced and thus the capacity would be affected undesirably. To such To rule out problems, it is appropriate to Contact layer in the manufacture of the balancing resistor dimensioned so that they do not have the Edges of the resistance layer protrude.

The contact layer and the resistance layer are preferably formed in strips. Connection contacts are on opposite ends of the contact layer strip intended. The Stripes can be zigzag or meandering in a space-saving manner be arranged on the substrate. The trimming resistor preferably has a passivation layer on the the resistance layer essentially covered and only locally individual Window that has the conductive contact enable the contact layer with the resistance layer.

The passivation layer is between two windows preferably one bottleneck of the contact layer intended. At such a narrow point to cut through the contact layer particularly easily, their severance means that a electrical current that would otherwise pass through the contact layer would have flowed between the two windows must take the path across the resistance layer.

The passivation layer is not just for protection the resistance layer from environmental influences, their Window structure also has the advantage that it is enough to keep the contact layer on a small Cut length between two windows to the current path in the resistance layer around the im Compared to this length greater distance between extend two windows.

A preferred application of the trimming resistor is a resistance bridge circuit. At a such a bridge circuit are conveniently the Resistance elements and the at least one trimming resistor formed on the same substrate. So the resistance elements and the Trimming resistor partly with the same process steps getting produced.

Another preferred application of the trimming resistor is a sensor that is a deformable Comprises substrate and at least one resistance element, its resistance due to deformation of the substrate is changeable and the one according to the invention Trimming resistor is assigned. This resistance element can in turn be part of a Resistor bridge circuit.

The sensor can advantageously be act a pressure sensor; the substrate can be part a pressure capsule of such a sensor.

The invention further relates to a method for Manufacture a trimming resistor in which a Resistance layer on an insulating substrate is separated and structured, and in which over the resistance layer in at least local Contact with this formed a contact layer which has better conductivity than the resistance layer Has.

Before the formation of the Contact layer preferably a passivation layer applied the windows to manufacture of local contact. For structuring the different layers are photolithographic Process or - especially with sensors advantageous - laser structuring process. The Contact layer can in particular also by sputtering of the layer material are generated. It is also conceivable to apply the material of the Contact layer directly through a mask, see above that the contact layer on the resistance layer (separated by passivation) immediately in the desired shape is created.

The resistance is preferably adjusted by cutting the contact layer between two Windows, preferably by laser ablation. This Laser ablation is with the same equipment feasible, which may also previously be used for laser structuring of the different layers used have been.

Further features and advantages of the invention result itself from the following description of exemplary embodiments with reference to the figures.

characters

Figure 1 shows a plan view of a section a trimming resistor according to the invention.

Figure 2 shows the section in section along the Line II-II from Figure 1.

Figure 3 shows a second section along the line III-III from Figure 1.

Figure 4 shows a resistance bridge with balancing resistors according to the invention on a Membrane of a pressure sensor;

Figure 5 shows part of this pressure sensor in Cut; and

Figure 6 shows the individual steps of the manufacturing process 4 and 5.

Description of the embodiments

Figures 1, 2 and 3 show a section of a trimming resistor according to the invention in a Top view or in two cuts. The Trimming resistor is on a substrate 1, here a stainless steel sheet with an insulation layer 2 built on it from silicon oxide. It includes one Resistance layer 3 made of a material with moderate good conductivity on the insulation layer 2 forms a meandering or zigzag pattern, of which two full periods are shown in Figure 1 are.

On the resistance layer 3 is on its entire Surface with the exception of individual windows 4, a passivation layer 5, which consists of Silicon nitride or like the insulation layer 2 Silicon oxide exists. A contact layer 6 from one Metal with good electrical conductivity, here gold, follows the meandering course of the resistance layer 3, but has a lower one Width than this and is placed so that its edges nowhere over the edges of the resistance layer 3 survive. The contact layer 6 is over the Window 4 with the resistance layer 3 in conductive Contact.

There are contact connections (not shown) at the opposite ends of the strip-like Contact layer 6.

Since the conductivity of the contact layer 6 is clear is better than that of the resistance layer 3, flows in the unbalanced state of the balancing resistor a current in the essentially through the contact layer 6. To the resistance it is intended to adjust the contact layer 6 at a narrow point, e.g. to area 7 cut through. To do this cutting, the method of laser ablation is suitable, especially with an excimer laser. So that's it easily possible, one on area 7 dosed laser energy so that the Contact layer 6 at the point in question is removed without the underlying one Resistor layer 3 with damaged becomes. For this purpose e.g. the materials the contact layer 6 and the resistance layer 3 and the wavelength of the laser are chosen so that the ablation energy of the contact layer 6 is smaller than that of the resistance layer 3, so that the energy of the excimer, even after it Destruction of the contact layer 6 the resistance layer 3 reached, not enough to do this too to destroy. But there are also other - known - Cutting processes, such as spark erosion, applicable.

As an aid to protecting the resistance layer 3 the composition of the Passivation layer 5 serve. For example, by suitable choice of the silicon content of the passivation layer 5 possible, the penetration depth of the laser radiation so that this over the Total thickness of the passivation layer 5 from this is absorbed and so their energy in their distributed over the entire volume. Compared to that the penetration depth of the radiation in the metals or semiconductor materials of the contact layer respectively the resistance layer essential smaller, so that the heating induced by the laser of these layers are on a thin surface layer of these concentrated and sufficient to evaporate this surface layer.

If the contact layer 6 cuts at the narrow point 7 is, the current is forced between the the bottleneck 7 adjacent windows 4 through the Resistive layer 3 to flow. By destroying the contact layer 6 between a selectable number of windows 4 it is possible in this way, the Path length that the current in the resistance layer 3 must travel, and thus the resistance value of the Gradually adjust the trimming resistor very precisely.

Figures 4 and 5 show a preferred application example of the balancing resistance described above.

Figure 4 is a plan view of the membrane 12 of a Pressure sensor, which is the role of the substrate 1 plays. There are four resistance elements on this membrane R1, R2, R3, R4 with connections A1, A2, A3, A4 interconnected to a Wheatstone bridge. Trimmer resistors A1, A2 with reference to figures 1 to 3 are described with the resistance elements R3, R4 connected in series. The resistance elements and the trimming resistors are in a common process, to which later is discussed in more detail on the membrane 12 generated; have the resistance elements R1, R2, R3, R4 a resistance layer, that of the resistance layer 3 corresponds to the trimming resistors, however, they do not have a continuous one Contact layer, and the passivation layer 5 is over the resistance elements R1, R2, R3, R4 with Except for their connection pads throughout.

Figure 5 shows the membrane 12 of Figure 4 in cross section. It is part of a high pressure sensor 11 and is in one piece with a rigid metal frame 13 connected. Is between the two sides the membrane 12 a pressure drop, this leads to a deformation of the membrane 12, and it comes to Example if the pressure below the membrane is higher is as above, in the area of the resistance elements R1 and R2 for compression and in the area of the resistance elements R3 and R4 to stretch at the Surface of the membrane. Affect these deformations the conductivity of the resistance layers of the resistance elements and thus cause a detuning the Wheatstone Bridge leading to one two of the connections K1 to K4, from Zero different measuring voltage leads.

For this application, the resistance layer expediently selected a material that a significant dependence of the specific resistance from deformation. As suitable Materials here are e.g. polycrystalline silicon, Chromium-nickel alloy or platinum to mention. NiCr layers show practically none Temperature dependence of the resistance, but one relatively small effect when bending while polycrystalline silicon a non-linear temperature dependency, but a much larger one Has an effect when bending. Platinum shows also a clear effect with a linear Temperature dependence of the resistance. Suitable Layer thicknesses range from 500 to 600 nm for polycrystalline silicon and from 50 to 100 nm for CrNi or platinum.

In general, the layer thicknesses should be chosen so that the layer conductivity of the resistance layer is smaller than that of the contact layer, regardless the specific conductivities for this Layers of materials used.

In Figure 6, the successive stages are A to H of the method for producing a trimming resistor according to Figures 1 to 3 respectively the equipped with trimming resistors A1, A2 Sensor shown in Figures 4 and 5.

Stage A shows the still empty substrate 1 or the pressure cell of Figure 5, consisting of the Frame 13 and the membrane 12. This substrate will first subjected to an incoming inspection for roughness and then wet first and then finally cleaned by argon sputtering. The substrate treated in this way is then opened preheated to about 300 ° C for a PECVD oxide deposition prepare. Then the Insulation layer 2 in a thickness of 7-10 microns Silicon oxide deposited. This insulation layer on the substrate is randomly checked for thickness and tension controlled.

Starting from the coated substrate 1 (stage B) the resistance layer 3 is sputtered applied. The surface resistance is checked by the 4-tip method, and the layer thickness is determined by X-ray fluorescence (Level C).

A structuring step follows in which the first, a large-area resistance layer the meandering structure shown in Figure 1 will be produced. For this structuring can a photolithographic technique or a laser structuring technique be used. The photolithographic Technique involves applying one Lacquer layer, the exposure of the lacquer layer with the desired pattern and its development post-chemical etching of those areas by development have lost their paint layer, and finally the removal of the rest Paint layer. The laser structuring stops particularly advantageous structuring process Here, laser light becomes a suitable energy density through a mask on the surface of the membrane irradiated. With the help of the deepening on the It is the back of the membrane 12 (see FIG. 5) possible, the sensor suitable for structuring to center. Also, the coated layer automatically brought to the focus level. The Laser exposure through the mask causes that layer material exposed to the laser radiation is removed (ablated) so that the multitude the steps of the photolithographic process can be omitted.

The strength of the absorption of the excimer laser radiation used in the insulation layer 2 can by setting a desired silicon content the insulation layer can be varied. this makes possible it that radiation that towards the end of erosion the resistance layer 3 the insulation layer 2 reached, absorbed over their entire thickness and so the interface between Substrate and insulation layer not or not in of such strength that it becomes a Damage to this boundary layer could result. A such a silicon-rich oxide layer can also be used advantageous due to a sputtered silicon oxide layer to reach. Such a sputtered layer also has the advantage that the subsequent resistance layer to be applied a higher Long-term stability achieved because of the resistance layer protected from hydrogen is, which is usually in PECVD oxide or Nitride layers built into the deposition becomes. Consequently, should also before the Passivation of the resistance layer a sputtered Oxide layer can be provided.

Stage (D) shows the substrate with the finished structured one Resistance layer 3.

At this stage there is an optical control instead, then a passivation layer 5 separated (level E). Thickness and tension of this Layer are made in a similar way to the resistance layer 3 checked in step (C). Subsequently annealing takes place at 350 ° C. For a subsequent structuring of the passivation layer 5 can in turn be a photolithographic Technology or laser structuring applied as already for the structuring of the resistance layer 3 described. In this structuring step window 4 will be above of the remaining pieces of the resistance layer 3 generated. Those pieces that are one of the Resistance elements R1 to R4 are to be obtained two windows for the connection contacts, those pieces that have the trimming resistors A1, A2 should form a variety of distributed over their surface Windows.

The finished structured passivation layer 5 (Level F) is checked optically.

In a subsequent step, the contact layer 6 applied by sputtering. The material for the contact layer 6 is preferred Gold - also because of its stability against Environmental influences - with a layer thickness of 0.3 used up to 0.5 nm. If necessary, however including a metallic adhesive layer and a more metal as a diffusion barrier in the same Step applied. Aluminum or nickel come as materials also in question. The thickness of the Contact layer 6 is then made using X-ray fluorescence controlled.

For the subsequent structuring of the contact layer 6 come the photolithographic Process or the process of laser structuring in question. The nominal dimensions of the contact layer areas, the the contact layer of the trimming resistors are intended to be chosen that taking into account mask tolerances and other manufacturing inaccuracies guaranteed is that the one that remains after structuring Nowhere in the contact layer over the edge protrudes from the underlying resistance layer. This measure ensures that the capacitance of the resistance elements and the trimming resistors exclusively through the area its resistance layers 3 is fixed and of possible inaccuracies in positioning the contact layers cannot be influenced. So it is possible to connect the bridge with one high degree of symmetry of the capacity of their individual To make branches. Consequently, the bridge circuit in a wide frequency range of input voltages be operated without unequal distributions the capacity to the individual Branches their output voltage depending on frequency influence.

An alternative in the production of the contact layer 6 is the use of a "shadow mask", the contact during the application of the material only those areas on the surface of the Leaves substrates on the finished sensor a contact layer is actually needed. On this way there is the possibility of structuring to save the contact layer completely, that is called the stage (G) of the production is skipped.

Stage (H) shows the sensor with the structured contact layer 6.
At this stage of the production, after all the coating and structuring steps have been completed, the bridge circuit can be calibrated.

When subsequently measuring the resistance bridge becomes an input voltage to diagonally opposite Connections, e.g. K1, K3, the bridge circuit applied, and an output voltage to the measured on the other two outputs. If this from Zero is different, is an adjustment of the sensor required, which takes place in that at a of the two trimming resistors A1, A2 ranges of Contact layer as the area 7 of Figure 1 in the Number to be destroyed as is necessary to the Bring output voltage to zero. This local Destruction is carried out with an excimer laser. If the previous structuring steps already done by laser ablation have been expediently the same Lasers are also used for the adjustment. It are also other - known - methods for Cutting, such as spark erosion, applicable.

The proposed method is excellent for the production of high pressure sensors in Large series, because the manufacturing steps up to Level (H) can be advantageous in a holder for a large number of sensors performed simultaneously without any steps in between are an individual treatment of the Require sensors; after adjustment is the Sensor completely finished, without further coating steps would be required.

Only then can the sensor be adjusted when the membrane 12 with the metal frame 13th - Figure 5 - been welded to a pressure nozzle is what may be a minor Detuning the resistance bridge can result.

Claims (24)

Planar matching resistor with a substrate (1) and a resistive layer deposited thereon (3), characterized in that a contact layer (6) that have better conductivity than has the resistance layer on the resistance layer (3) is arranged, at least individual points (4) with the resistance layer (3) in conductive contact and at least locally (7) above the resistance layer (3) of an ablative Treatment is accessible. Trimmer resistor according to claim 1, characterized characterized in that the contact layer (6) is not protrudes over the edges of the resistance layer (3). Trimmer resistor according to claim 1 or 2, characterized characterized in that the contact layer (6) and the resistance layer (3) is strip-shaped, and that connection contacts at opposite ends the contact layer (6) are provided. Trimmer resistor according to claim 3, characterized characterized in that the stripes zigzag or are arranged in a meandering shape on the substrate (1). Trimming resistor according to one of the previous ones Claims, characterized in that a Insulation layer (2) between the resistance layer (3) and the substrate (1) is arranged. Trimming resistor according to one of the preceding claims, characterized in that the resistance layer (3) is enclosed between the substrate (1) and a passivation layer (5) which has windows (4) through which the contact layer (6) touches the resistance layer. Trimmer resistor according to claim 6, characterized characterized in that the contact layer (6) each has a narrow point (7) between two windows (4). Trimmer resistor according to claim 6 or 7, characterized characterized in that the contact layer (6) at least one point (7) between two windows (4) is severed. Trimmer resistor according to one of the preceding claims, characterized in that the resistance layer (3) consists of a nickel-chromium alloy, of platinum or of poly-silicon. Trimmer resistor according to one of the preceding claims, characterized in that the contact layer (6) comprises a layer of gold. Trimming resistor according to one of the preceding claims, characterized in that the contact layer (6) has an adhesive layer and / or a diffusion barrier on its underside. Resistor bridge circuit, characterized in that they have at least one trimming resistor (A1, A2) according to one of the preceding claims having. Resistor bridge circuit according to claim 12, characterized in that the resistance elements (R1, R2, R3, R4) of the resistance bridge circuit and the trimming resistor (A1, A2) on the same Substrate (11) are formed. Sensor with a deformable substrate (1.12) and at least one resistance element (R3, R4), characterized in that the resistance element (R3, R4) a trimming resistor (A1, A2) after a of claims 1 to 11 is assigned. Sensor according to claim 14, characterized in that the resistance element (R3, R4) part of a Resistor bridge circuit is. Sensor according to claim 14 or 15, characterized in that the substrate (1,12) part of a Pressure capsule is. Method for producing a trimming resistor, in which a resistance layer (3) deposited an isolated substrate (1) and is structured, characterized in that about the resistance layer (3) in at least local Contact with this formed a contact layer (6) which has better conductivity than that Has resistance layer. A method according to claim 17, characterized in that on the resistance layer (3) before the formation of the contact layer (6) a passivation layer (5) is applied to the window (4) for establishing the local contact. Method according to Claim 17 or 18, characterized in that the resistance layer (3) and / or optionally the passivation layer (5) are structured photolithographically and / or by laser radiation. A method according to claim 17, 18 or 19, characterized characterized in that the contact layer (6) is generated by sputtering or vapor deposition. Method according to one of Claims 17 to 20, characterized in that an insulation layer (12) is produced on the substrate (11) before the resistance layer (3) is produced by sputtering on a silicon layer. Method according to one of claims 17 to 21, characterized in that the material of the contact layer (6) applied through a mask becomes. Method according to one of claims 17 to 22, characterized in that for the adjustment of the Trimming resistor (A1, A2) the contact layer (6) between two windows (4) is cut to a current flow through the resistance layer (3) force. A method according to claim 23, characterized in that cutting through laser ablation or spark erosion occurs.

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