WO2005012893A1 - Microstructured chemical sensor - Google Patents

Microstructured chemical sensor Download PDF

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Publication number
WO2005012893A1
WO2005012893A1 PCT/DE2004/001647 DE2004001647W WO2005012893A1 WO 2005012893 A1 WO2005012893 A1 WO 2005012893A1 DE 2004001647 W DE2004001647 W DE 2004001647W WO 2005012893 A1 WO2005012893 A1 WO 2005012893A1
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WO
WIPO (PCT)
Prior art keywords
layer
idt
metallization level
chemical sensor
sensor according
Prior art date
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PCT/DE2004/001647
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German (de)
French (fr)
Inventor
Heribert Weber
Doris Schielein
Christian Krummel
Christoph Schelling
Original Assignee
Paragon Ag
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Publication date
Priority claimed from DE10347415A external-priority patent/DE10347415A1/en
Application filed by Paragon Ag filed Critical Paragon Ag
Priority to JP2006520669A priority Critical patent/JP2006528767A/en
Priority to EP04762495A priority patent/EP1649271A1/en
Priority to US10/565,984 priority patent/US7453254B2/en
Publication of WO2005012893A1 publication Critical patent/WO2005012893A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
    • G01N27/125—Composition of the body, e.g. the composition of its sensitive layer
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
    • G01N27/121—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid for determining moisture content, e.g. humidity, of the fluid

Definitions

  • the invention relates to a chemical sensor with a first metallization level arranged on a substrate, in which an electrode structure is formed, a passivation layer applied on the first metallization level and structured by contact holes, and with one on the passivation layer and in the contact holes by means of dispensing. , Screen printing or inkjet process and subsequent sintering produced sensitive ceramic layer.
  • Electrodes in which the electrical resistance of a sensitive layer, usually comprising metal oxides, can be evaluated with the aid of an evaluation structure, the electrodes, are known in many designs, in particular as gas or moisture sensors.
  • Porous ceramic layers for example Sn0 2 or W0 3 , are generally used as sensitive layers for gas detection, the electrical surface conductivity of which changes when gases are adsorbed.
  • the porous ceramic layers can be made selectively sensitive to certain gases by means of dopants.
  • the resistivities of such ceramics are very high. This means that the measuring resistances also become large.
  • the evaluation structure therefore usually consists of an interdigital structure (IDT; "Interdigitated Transducers”), that is to say of two coplanar, interdigitated electrodes. This corresponds to a parallel connection of the resistances formed laterally between the individual fingers of different polarity and thus a reduced internal sensor resistance or an increased sensitivity of the sensor.
  • IDT Interdigitated Transducers
  • a temperature measuring resistor is often also provided on the sensor, it being possible for all elements of the metallization to be structured, for example from platinum, in one metallization level.
  • a passivation layer typically silicon oxide, is often provided on the metallization level.
  • the passivation layer is to be structured through contact holes in order to enable contact between the electrodes and the sensitive layer applied to the passivation layer.
  • a microstructured silicon membrane sensor with a sensitive layer applied to an Si0 2 , Si 3 N membrane is known, for example, from DE 197 10 358 AI.
  • the heating and temperature measurement structures are passivated by means of a silicon oxide layer, to which an interdigital, three-dimensional electrode structure is then applied, into which a sensitive layer is filled using screen printing technology.
  • the sensitive ceramic layer when it is produced by screen printing, it has to be sintered after it has been applied as a thick-layer paste. Any mechanical tensions that occur or remain, in particular interfacial tensions, can lead to the detachment of layer material and particle generation. The effects of eg Sn0 2 or W0 3 on other micromechanical processes are unclear, so that there is a general risk of contamination.
  • the porosity of the metal oxide ceramic produced during sintering is desirable on the one hand because the high sensitivity of the ceramic is due to the high surface-to-volume ratio. At the same time, however, the porosity has a negative effect on the mechanical stability of the layer. The most important requirement for stability is that the ceramic layers adhere to the substrate and the electrodes over the life of the sensor. In addition, the electrical contact between ceramic and electrodes must not degenerate.
  • the ceramic layers are currently produced directly on the passivation layers. It has been shown that the adhesion of the ceramics is often insufficient.
  • the object of the invention is to improve the situation with regard to liability.
  • the invention is based on the generic chemical sensor in that an adhesion promoter layer is provided which is designed as a second metallization level and which is arranged between the passivation layer and the ceramic layer.
  • the upper metallization applied in two layers makes it possible to better bind the porous, sensitive ceramic layers to the substrate provided by the passivation layer.
  • the metallic adhesion promoter layer arranged between two contact hole openings in the upper level leads to a strong spatial limitation of the electrical field lines, and thus also to the current paths between two interdigital electrode fingers, which ultimately strongly limits the active zone in the sensitive ceramics, which is associated with the advantage of improved protection against sensor poisoning, for example through silicone.
  • the second metallization level in particular, but not only, in connection with the sensor electrodes.
  • the adhesion promoter layer can also be used in the bond area of the sensor - if it is suitable as a bonding material.
  • the second metallization level is preferably applied in such a way that it comes to lie in the contact holes on the first metallization level.
  • a further passivation layer is arranged between the adhesion promoter layer and the ceramic layer and is structured such that the adhesion promoter layer is partially passivated.
  • two coplanar electrodes are structured in the electrode structure of the first metallization level, and that the second metallization level is not at a defined electrical potential.
  • the advantages mentioned result in the improvement of the adhesion and the narrowing of the functional ceramic zone by means of equipotential surfaces.
  • the electrode structure of the first metallization level forms a first electrode
  • the second metallization level is designed as a second electrode and is at a defined electrical potential, so that the sensitive ceramic layer is provided with a vertical electrode arrangement.
  • the lateral expansion of the ceramic layer can no longer be determined by technical requirements and can be reduced if necessary.
  • the electrodes are interdigital electrodes, but this is also possible in all other embodiments.
  • a heating structure and a temperature measurement structure are preferably formed in the first metallization level.
  • the structures of the metallization are preferably applied to the front of an Si substrate which has a membrane.
  • FIG. 1 shows a cross section of a sensor according to the invention
  • FIG. 2 in the same representation, a variant of the sensor
  • FIG. 3 in the same representation, shows a schematically simplified section of the cross section according to FIGS. 1 and 2.
  • FIG. 1 shows a silicon substrate 1 in which, for example by etching a cavity 2 from the back of the substrate 1, a dielectric membrane 3 is produced, which can consist of a layer sequence of, for example, silicon dioxide and silicon nitride.
  • a first metallization level for example made of platinum, is located above the membrane 3.
  • This metallization is structured in such a way that the heating structure 4 and the interdigital electrode fingers of different polarity IDT 1 and IDT 2, and optionally a temperature resistor 5, are formed for the chemical sensor.
  • IDT 1 and IDT 2 for example, it is advantageous to converting the burst membrane layer, here silicon nitride, into a silicon oxide layer 3 'on the surface.
  • the passivation layer 6 There are holes 7 in the passivation layer 6, which serve for contacting the ceramic layer 9 and the bondlands.
  • the adhesion promoter layer 8 which serves to promote adhesion for the ceramic layer 9, and which, as described further below in connection with FIG. 3, is optionally set to a defined potential and then as a second interdigital electrode IDT 2 can serve, in which case the first metallization level with respect to the evaluation structure has only interdigital electrode fingers IDT 1 of the same polarity.
  • the second metallization level can be applied in such a way that it comes to lie in the contact hole openings 7 on the first metallization level.
  • a further passivation layer 10 can optionally lie on the second metallization 8. It in turn contains holes for connection purposes.
  • the silicon raw wafer is first thermally oxidized.
  • An LPCVD nitride is then deposited or an oxide is produced.
  • the first metallization and its structuring into heater 4, temperature sensor 5 and interdigital electrode IDT are then deposited on the front of the wafer.
  • a passivation layer 6 is then applied, for example a CVD oxide.
  • the etching mask for the cavern etching for producing the membrane 3 is defined on the back of the wafer.
  • the sensor can be controlled more quickly due to the reduced heat dissipation.
  • the adhesion promoter layer 8 or the second metallization level for example made of the materials Au, is applied. Cr / Au, Pt, Pd, W or Sn.
  • the adhesion promoter layer 8 is subsequently structured in such a way that it only remains in the area between the interdigital electrode fingers on which the ceramic is intended to adhere afterwards and, if appropriate, still on the bondlands.
  • the contact holes 7 are then etched into the passivation layer 6 on the front of the wafer, and the adhesion promoter layer 8 can partially serve as an etching mask.
  • the application of the adhesive layer 8 and etching of the contact holes 7 can also be carried out in the reverse order.
  • a protective lacquer is applied to the front and the caverns 2 are produced from the rear by anisotropic etching.
  • the paste dot is applied and sintered in an oven to form the porous ceramic layer 9. Further details on the known process steps can be found in DE 197 10 358 AI mentioned above.
  • FIG. 3 shows to explain the function of the invention that goes beyond the improved mediation
  • a voltage is applied between the two interdigital electrodes IDT 1 and IDT 2.
  • the measurement signal is tapped as current.
  • the upper, second metallization level that is to say the structured adhesion promoter layer 8
  • both IDTs are implemented in the lower, first metallization level.
  • the current paths between the IDTs would run exclusively over the ceramic layer, as indicated in FIG. 3 by the arrow shown in broken lines.
  • the adhesion promoter layer 8 according to the invention however, they run, as shown, between the latter and the two IDTs.
  • the current path then leads outside the contact holes 7 via the adhesion promoter layer 8.
  • a change in the conductivity in the periphery of the ceramic dot or ceramic layer 9, for example due to poisoning, advantageously plays practically no role in this configuration, since the electrical field lines and thus the current paths are very limited in space.
  • the upper, second metallization level (bonding agent layer 8) is set to a defined potential (e.g. 0V), it can be used as IDT 2. In this case, the electrode spacing is effectively approximately half as large as in the case of a floating adhesive layer 8.

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Abstract

The invention relates to a sensor comprising a first metallization plane located on a substrate (1), a passivation layer (6) that is structured by contact holes (7) and is applied to said substrate and a sensitive ceramic layer (9) formed by thick-film technology on the passivation layer and in the contact holes (7). The aim of the invention is to improve the adhesion of the ceramic layer (9). To achieve this, the sensor is provided with an adhesion promoter layer (8) that is configured as a second metallization plane and is located between the passivation layer (6) and the ceramic layer (9).

Description

Mikrostrukturierter chemischer SensorMicrostructured chemical sensor
Die Erfindung betrifft einen chemischen Sensor, mit einer auf einem Substrat angeordneten ersten Metallisierungsebene, in der eine Elektrodenstruktur ausgebildet ist, einer auf der ersten Metallisierungsebene aufgebrachten, durch Kontaktlö- eher strukturierten Passivierungsschicht, und mit einer auf der Passivierungsschicht und in den Kontaktlöchern mittels Dispens-, Siebdruck- oder InkJet-Verfahrens und anschließendem Sintern erzeugten sensitiven Keramikschicht.The invention relates to a chemical sensor with a first metallization level arranged on a substrate, in which an electrode structure is formed, a passivation layer applied on the first metallization level and structured by contact holes, and with one on the passivation layer and in the contact holes by means of dispensing. , Screen printing or inkjet process and subsequent sintering produced sensitive ceramic layer.
Chemische Sensoren, bei denen der elektrische Widerstand einer sensitiven, meist Metalloxide umfassenden, Schicht mit Hilfe einer Auswertestruktur, den Elektroden, auswertbar ist, sind insbesondere als Gas- oder Feuchtesensoren in vielen Ausführungen bekannt. Als sensitive Schichten zur Gasdetekti- on werden in der Regel poröse Keramikschichten, zum Beispiel Sn02 oder W03, eingesetzt, deren elektrische Oberflächenleitfähigkeit sich bei Adsorption von Gasen ändert. Die porösen Keramikschichten können durch Dotierstoffe selektiv empfindlich für bestimmte Gase gemacht werden.Chemical sensors in which the electrical resistance of a sensitive layer, usually comprising metal oxides, can be evaluated with the aid of an evaluation structure, the electrodes, are known in many designs, in particular as gas or moisture sensors. Porous ceramic layers, for example Sn0 2 or W0 3 , are generally used as sensitive layers for gas detection, the electrical surface conductivity of which changes when gases are adsorbed. The porous ceramic layers can be made selectively sensitive to certain gases by means of dopants.
Die Resistivitäten solcher Keramiken sind sehr hoch. Dies führt dazu, dass die Messwiderstände ebenfalls groß werden. Die Auswertestruktur besteht deshalb üblicherweise aus einer Interdigitalstruktur (IDT; "Interdigitated Transducers") , al- so aus zwei koplanaren, fingerartig ineinander greifenden E- lektroden. Dies entspricht einer Parallelschaltung der lateral zwischen den einzelnen Fingern unterschiedlicher Polarität gebildeten Widerstände und damit einem verringerten Sensor-Innenwiderstand bzw. einer erhöhten Empfindlichkeit des Sensors. Häufig wird neben den Elektroden und dem Heizwiderstand noch ein Temperaturmesswiderstand auf dem Sensor vorgesehen, wobei alle Elemente der Metallisierung beispielsweise aus Platin in einer Metallisierungsebene strukturiert werden können. Um ein "Nachaltern" insbesondere des Temperaturmesswiderstandes zu verhindern, wird auf der Metallisierungsebene vielfach eine Passivierungsschicht, typischerweise Siliziumoxid, vorgesehen. Die Passivierungsschicht ist durch Kontaktlöcher zu strukturieren, um den Kontakt zwischen den Elektroden und der auf der Passivierungsschicht aufgebrachten sensitiven Schicht zu ermöglichen.The resistivities of such ceramics are very high. This means that the measuring resistances also become large. The evaluation structure therefore usually consists of an interdigital structure (IDT; "Interdigitated Transducers"), that is to say of two coplanar, interdigitated electrodes. This corresponds to a parallel connection of the resistances formed laterally between the individual fingers of different polarity and thus a reduced internal sensor resistance or an increased sensitivity of the sensor. In addition to the electrodes and the heating resistor, a temperature measuring resistor is often also provided on the sensor, it being possible for all elements of the metallization to be structured, for example from platinum, in one metallization level. In order to prevent "aging" in particular of the temperature measuring resistor, a passivation layer, typically silicon oxide, is often provided on the metallization level. The passivation layer is to be structured through contact holes in order to enable contact between the electrodes and the sensitive layer applied to the passivation layer.
Während die Strukturen der Metallisierung und die sensitive Schicht herkömmlicherweise auf einem Aluminiumoxid-Substrat aufgebracht werden, sind inzwischen auch mikromechanisch, auf der Basis eines Silizium-Substrats, gefertigte Membran- Sensoren bekannt. Durch die thermische Abkoppelung der auf der Membran angeordneten Sensorstrukturen vom Substrat ergibt sich eine verringerte Leistungsaufnahme des Sensors.While the structures of the metallization and the sensitive layer are conventionally applied to an aluminum oxide substrate, membrane sensors manufactured on the basis of a silicon substrate are also known micromechanically. The thermal decoupling of the sensor structures arranged on the membrane from the substrate results in a reduced power consumption of the sensor.
Ein mikrostrukturierter Silizium-Membransensor mit einer auf einer Si02, Si3N Membran aufgebrachten sensitiven Schicht ist zum Beispiel aus der DE 197 10 358 AI bekannt. Bei dem bekannten Sensor werden allerdings, anders als beim gattungsge- mäßen Sensor, nur die Heiz- und Temperaturmessstrukturen mittels einer Siliziumoxid-Schicht passiviert, auf die dann eine interdigitale, dreidimensionale Elektrodenstruktur aufgebracht wird, in die eine sensitive Schicht siebdrucktechnisch eingefüllt wird.A microstructured silicon membrane sensor with a sensitive layer applied to an Si0 2 , Si 3 N membrane is known, for example, from DE 197 10 358 AI. In the known sensor, however, unlike the generic sensor, only the heating and temperature measurement structures are passivated by means of a silicon oxide layer, to which an interdigital, three-dimensional electrode structure is then applied, into which a sensitive layer is filled using screen printing technology.
Generell muss bei der siebdrucktechnischen Erzeugung der sensitiven Keramikschicht diese nach dem Aufbringen als Dickschicht-Paste noch versintert werden. Dabei auftretende oder verbleibende mechanische Spannungen, insbesondere Grenzflä- chenspannungen, können zur Ablösung von Schichtmaterial und Partikelgeneration führen. Die Auswirkungen von z.B. Sn02 o- der W03 auf andere mikromechanische Prozesse sind unklar, so dass allgemein eine Kontaminationgefahr besteht. Die Porosität der beim Sintern entstehenden Metalloxid-Keramik ist einerseits wünschenswert, da die hohe Empfindlichkeit der Keramik eben durch das hohe Oberflächen-zu-Volumen-Verhältnis be- dingt wird. Gleichzeitig wirkt sich die Porosität jedoch negativ auf die mechanische Stabilität der Schicht aus. Die wichtigste Forderung an die Stabilität besteht darin, dass die Keramikschichten auf dem Untergrund und den Elektroden über die Lebensdauer des Sensors haften. Außerdem darf der elektrische Kontakt zwischen Keramik und Elektroden nicht degenerieren.In general, when the sensitive ceramic layer is produced by screen printing, it has to be sintered after it has been applied as a thick-layer paste. Any mechanical tensions that occur or remain, in particular interfacial tensions, can lead to the detachment of layer material and particle generation. The effects of eg Sn0 2 or W0 3 on other micromechanical processes are unclear, so that there is a general risk of contamination. The porosity of the metal oxide ceramic produced during sintering is desirable on the one hand because the high sensitivity of the ceramic is due to the high surface-to-volume ratio. At the same time, however, the porosity has a negative effect on the mechanical stability of the layer. The most important requirement for stability is that the ceramic layers adhere to the substrate and the electrodes over the life of the sensor. In addition, the electrical contact between ceramic and electrodes must not degenerate.
Derzeit werden die Keramikschichten direkt auf den Passivie- rungsschichten erzeugt. Dabei hat es sich gezeigt, dass die Haftung der Keramiken vielfach ungenügend ist. Die Aufgabe der Erfindung besteht darin, die Situation hinsichtlich der Haftung zu verbessern.The ceramic layers are currently produced directly on the passivation layers. It has been shown that the adhesion of the ceramics is often insufficient. The object of the invention is to improve the situation with regard to liability.
Diese Aufgabe wird erfindungsgemäß durch einen chemischen Sensor gemäß Anspruch 1 gelöst. Weiterbildungen und bevorzugte Maßnahmen ergeben sich aus den Unteransprüchen.This object is achieved according to the invention by a chemical sensor according to claim 1. Further training and preferred measures result from the subclaims.
Die Erfindung baut auf dem gattungsgemäßen chemischen Sensor dadurch auf, dass eine Haftvermittlerschicht vorgesehen ist, die als zweite Metallisierungsebene ausgebildet ist und die zwischen der Passivierungsschicht und der Keramikschicht angeordnet ist.The invention is based on the generic chemical sensor in that an adhesion promoter layer is provided which is designed as a second metallization level and which is arranged between the passivation layer and the ceramic layer.
Durch die obere der in zwei Lagen aufgebrachten Metallisie- rung ist es möglich, die porösen sensitiven Keramikschichten besser an den durch die Passivierungsschicht gegebenen Untergrund anzubinden. Gleichzeitig führt die in der oberen Ebene jeweils zwischen zwei Kontaktlochöffnungen angeordnete metallische Haftvermittlerschicht zu einer starken räumlichen Ein- grenzung der elektrischen Feldlinien, damit auch der Strompfade zwischen zwei Interdigitalelektrodenfingern, wodurch letztlich eine starke Eingrenzung der aktiven Zone in der sensitiven Keramik bedingt ist, was mit dem Vorteil eines verbesserten Schutzes vor Sensorvergiftung, zum Beispiel durch Silikon, einhergeht. Darüber hinaus eröffnet sich erfindungsgemäß die Möglichkeit einer aktiven elektrischen Nut- zung der zweiten Metallisierungsebene, insbesondere, aber nicht nur, im Zusammenhang mit den Sensorelektroden. Die Haftvermittlerschicht kann im übrigen — bei Eignung als Bondmaterial — auch im Bondbereich des Sensors eingesetzt werden.The upper metallization applied in two layers makes it possible to better bind the porous, sensitive ceramic layers to the substrate provided by the passivation layer. At the same time, the metallic adhesion promoter layer arranged between two contact hole openings in the upper level leads to a strong spatial limitation of the electrical field lines, and thus also to the current paths between two interdigital electrode fingers, which ultimately strongly limits the active zone in the sensitive ceramics, which is associated with the advantage of improved protection against sensor poisoning, for example through silicone. In addition, according to the invention, there is the possibility of active electrical use of the second metallization level, in particular, but not only, in connection with the sensor electrodes. The adhesion promoter layer can also be used in the bond area of the sensor - if it is suitable as a bonding material.
Vorzugsweise ist die zweite Metallisierungsebene so aufgebracht, dass sie in den Kontaktlöchern auf der ersten Metallisierungsebene zu liegen kommt.The second metallization level is preferably applied in such a way that it comes to lie in the contact holes on the first metallization level.
Es kann nützlich sein, wenn eine weitere Passivierungsschicht zwischen der Haftvermittlerschicht und der Keramikschicht angeordnet und so strukturiert ist, dass die Haftvermittlerschicht teilpassiviert ist.It can be useful if a further passivation layer is arranged between the adhesion promoter layer and the ceramic layer and is structured such that the adhesion promoter layer is partially passivated.
Es kann vorgesehen sein, dass in der Elektrodenstruktur der ersten Metallisierungsebene zwei koplanare Elektroden strukturiert sind, und dass die zweite Metallisierungsebene nicht auf definiertem elektrischen Potenzial liegt. In diesem Fall resultieren die erwähnten Vorteile hinsichtlich der Verbesserung der Haftung und der Eingrenzung der funktioneilen Kera- mikzone durch Äquipotenzialflachen.It can be provided that two coplanar electrodes are structured in the electrode structure of the first metallization level, and that the second metallization level is not at a defined electrical potential. In this case, the advantages mentioned result in the improvement of the adhesion and the narrowing of the functional ceramic zone by means of equipotential surfaces.
Alternativ kann aber auch vorgesehen sein, dass die Elektrodenstruktur der ersten Metallisierungsebene eine erste Elektrode bildet, und dass die zweite Metallisierungsebene als zweite Elektrode ausgebildet ist und auf definiertem elektrischen Potenzial liegt, so dass die sensitive Keramikschicht mit einer vertikalen Elektrodenanordnung versehen ist. Dadurch ergibt sich ein erheblich verkürzter Elektrodenabstand gegenüber dem sonst üblichen, lithografisch vorgegebenen la- teralen Elektrodenabstand. Andererseits ist damit auch die laterale Ausdehnung der Keramikschicht nicht mehr durch mess- technische Anforderungen vorgegeben und kann gegebenenfalls verringert werden.Alternatively, it can also be provided that the electrode structure of the first metallization level forms a first electrode, and that the second metallization level is designed as a second electrode and is at a defined electrical potential, so that the sensitive ceramic layer is provided with a vertical electrode arrangement. This results in a considerably shorter electrode spacing compared to the otherwise customary, lithographically specified, lateral electrode spacing. On the other hand, the lateral expansion of the ceramic layer can no longer be determined by technical requirements and can be reduced if necessary.
In diesem Zusammenhang ist es besonders nützlich, die Elekt- roden als Interdigitalelektroden auszubilden, was jedoch auch bei allen anderen Ausführungsformen möglich ist.In this context, it is particularly useful to design the electrodes as interdigital electrodes, but this is also possible in all other embodiments.
Vorzugsweise sind in der ersten Metallisierungsebene zusätzlich zur Elektrodenstruktur eine Heizstruktur und eine Tempe- raturmessstruktur ausgebildet.In addition to the electrode structure, a heating structure and a temperature measurement structure are preferably formed in the first metallization level.
Bevorzugt sind die Strukturen der Metallisierung auf der Vorderseite eines Si-Substrats aufgebracht, das eine Membran aufweist .The structures of the metallization are preferably applied to the front of an Si substrate which has a membrane.
Die Erfindung wird im Folgenden anhand von Ausführungsbeispielen mit Bezug auf die Figuren näher erläutert. Es zeigen:The invention is explained in more detail below on the basis of exemplary embodiments with reference to the figures. Show it:
Figur 1 einen Querschnitt eines erfindungsgemäßen Sensors,FIG. 1 shows a cross section of a sensor according to the invention,
Figur 2, in gleicher Darstellung, eine Variante des Sensors,FIG. 2, in the same representation, a variant of the sensor,
Figur 3, in gleicher Darstellung, einen schematisch vereinfachten Ausschnitt aus dem Querschnitt gemäß Figur 1 bzw. 2.FIG. 3, in the same representation, shows a schematically simplified section of the cross section according to FIGS. 1 and 2.
Figur 1 zeigt ein Silizium-Substrat 1 in dem, beispielsweise durch Ätzen einer Kavität 2 von der Rückseite des Substrats 1 her, eine dielektrische Membran 3 erzeugt ist, die aus einer Schichtenfolge von zum Beispiel Siliziumdioxid und Silizium- nitrid bestehen kann. Über der Membran 3 befindet sich eine erste Metallisierungsebene, beispielsweise aus dem Material Platin. Diese Metallisierung ist so strukturiert, dass die Heizstruktur 4 und die Interdigitalelektrodenfinger unterschiedlicher Polarität IDT 1 und IDT 2, sowie gegebenenfalls ein Temperaturwiderstand 5 für den chemischen Sensor ausgebildet sind. Zur besseren Haftung der Platin-Metallisierung der ersten Metallisierungsebene ist es vorteilhaft, die o- berste Membranschicht, hier Siliziumnitrid, oberflächlich in eine Siliziumoxidschicht 3' umzuwandeln.FIG. 1 shows a silicon substrate 1 in which, for example by etching a cavity 2 from the back of the substrate 1, a dielectric membrane 3 is produced, which can consist of a layer sequence of, for example, silicon dioxide and silicon nitride. A first metallization level, for example made of platinum, is located above the membrane 3. This metallization is structured in such a way that the heating structure 4 and the interdigital electrode fingers of different polarity IDT 1 and IDT 2, and optionally a temperature resistor 5, are formed for the chemical sensor. For better adhesion of the platinum metallization of the first metallization level, it is advantageous to converting the burst membrane layer, here silicon nitride, into a silicon oxide layer 3 'on the surface.
Oberhalb der ersten Metallisierungsebene liegt eine Passivie- rungsschicht 6 (Zwischenisolationsschicht) aus z. B. CVD-Above the first metallization level there is a passivation layer 6 (intermediate insulation layer) made of z. B. CVD
Oxid, -Nitrid oder -Oxynitrid. In der Passivierungsschicht 6 befinden sich Löcher 7, die zur Kontaktierung der Keramikschicht 9 und der Bondlands dienen. Auf der Passivierungsschicht 6 liegt eine zweite Metallisierungsebene, die Haft- vermittlerschicht 8, die zur Haftvermittlung für die Keramikschicht 9 dient, und die, wie weiter unten im Zusammenhang mit Figur 3 beschrieben, optional auf ein definiertes Potenzial gelegt werden und dann als zweite Interdigitalelektrode IDT 2 dienen kann, wobei in diesem Fall die erste Metallisie- rungsebene bezgl. der Auswertestruktur nur Interdigitalelekt- rodenfinger IDT 1 gleicher Polarität aufweist.Oxide, nitride or oxynitride. There are holes 7 in the passivation layer 6, which serve for contacting the ceramic layer 9 and the bondlands. On the passivation layer 6 there is a second metallization level, the adhesion promoter layer 8, which serves to promote adhesion for the ceramic layer 9, and which, as described further below in connection with FIG. 3, is optionally set to a defined potential and then as a second interdigital electrode IDT 2 can serve, in which case the first metallization level with respect to the evaluation structure has only interdigital electrode fingers IDT 1 of the same polarity.
Wie Figur 2 zeigt, kann die zweite Metallisierungsebene so aufgebracht sein, dass sie in den Kontaktlochöffnungen 7 auf der ersten Metallisierungsebene zu liegen kommt. Eine weitere Passivierungsschicht 10 kann optional auf der zweiten Metallisierung 8 liegen. Sie enthält wiederum Löcher zu Anschlusszwecken.As FIG. 2 shows, the second metallization level can be applied in such a way that it comes to lie in the contact hole openings 7 on the first metallization level. A further passivation layer 10 can optionally lie on the second metallization 8. It in turn contains holes for connection purposes.
Zur Herstellung des erfindungsgemäßen Sensors wird der Sili- zium-Rohwafer zunächst thermisch oxidiert. Anschließend erfolgt die Abscheidung eines LPCVD-Nitrids bzw. die Erzeugung eines Oxids. Danach erfolgt auf der Vorderseite des Wafers die Abscheidung der ersten Metallisierung und deren Struktu- rierung in Heizer 4, Temperaturfühler 5 und Interdigitalelektrode IDT. Danach wird eine Passivierungsschicht 6 aufgebracht, beispielsweise ein CVD-Oxid. Auf der Rückseite des Wafers wird die Ätzmaske für das Kavernenätzen zum Erzeugen der Membran 3 definiert. Durch die verringerte Wärmeableitung ist der Sensor schneller ansteuerbar. Als Nächstes erfolgt das Aufbringen der Haftvermittlerschicht 8 bzw. der zweiten Metallisierungsebene, beispielsweise aus den Materialien Au, Cr/Au, Pt, Pd, W oder Sn. Die Haftvermittlerschicht 8 wird darauf folgend so strukturiert, dass sie nur in dem Bereich zwischen den Interdigitalelektrodenfingern verbleibt, auf dem hinterher die Keramik haften soll sowie gegebenenfalls noch auf den Bondlands.To produce the sensor according to the invention, the silicon raw wafer is first thermally oxidized. An LPCVD nitride is then deposited or an oxide is produced. The first metallization and its structuring into heater 4, temperature sensor 5 and interdigital electrode IDT are then deposited on the front of the wafer. A passivation layer 6 is then applied, for example a CVD oxide. The etching mask for the cavern etching for producing the membrane 3 is defined on the back of the wafer. The sensor can be controlled more quickly due to the reduced heat dissipation. Next, the adhesion promoter layer 8 or the second metallization level, for example made of the materials Au, is applied. Cr / Au, Pt, Pd, W or Sn. The adhesion promoter layer 8 is subsequently structured in such a way that it only remains in the area between the interdigital electrode fingers on which the ceramic is intended to adhere afterwards and, if appropriate, still on the bondlands.
Auf der Vorderseite des Wafers werden dann die Kontaktlöcher 7 in die Passivierungsschicht 6 hinein geätzt, dabei kann die Haftvermittlerschicht 8 teilweise als Ätzmaske dienen. Das Aufbringen der Haftvermittlerschicht 8 und Ätzen der Kontaktlöcher 7 kann auch in umgekehrter Reihenfolge erfolgen. Schließlich wird auf der Vorderseite einen Schutzlack aufgebracht und die Kavernen 2 von hinten durch anisotropes Ätzen hergestellt. Abschließend wird der Pastendot aufgebracht und in einem Ofen zur porösen Keramikschicht 9 gesintert. Weitere Details zu den an sich bekannten Verfahrensschritten lassen sich der oben genannten DE 197 10 358 AI entnehmen.The contact holes 7 are then etched into the passivation layer 6 on the front of the wafer, and the adhesion promoter layer 8 can partially serve as an etching mask. The application of the adhesive layer 8 and etching of the contact holes 7 can also be carried out in the reverse order. Finally, a protective lacquer is applied to the front and the caverns 2 are produced from the rear by anisotropic etching. Finally, the paste dot is applied and sintered in an oven to form the porous ceramic layer 9. Further details on the known process steps can be found in DE 197 10 358 AI mentioned above.
Figur 3 zeigt zur Erläuterung der über die verbesserte Haft- Vermittlung hinausgehenden Funktion des erfindungsgemäßenFIG. 3 shows to explain the function of the invention that goes beyond the improved mediation
Sensors einen Ausschnitt aus dem Querschnitt des Sensors. Die z-Skala ist stark überhöht dargestellt. Ebenfalls zur besseren Übersichtlichkeit ist die keramische Funktionsschicht 9 nicht abgebildet:Sensor a section of the cross section of the sensor. The z-scale is shown very high. The ceramic functional layer 9 is also not shown for better clarity:
Zwischen den beiden Interdigitalelektroden IDT 1 und IDT 2 wird eine Spannung angelegt. Das Messsignal wird als Strom abgegriffen. Falls die obere, zweite Metallisierungsebene, also die strukturierte Haftvermittlerschicht 8, nicht auf de- finiertem Potenzial liegt, das heißt floatet, sind beide IDTs in der unteren, ersten Metallisierungsebene realisiert. Ohne die zusätzliche zweite Metallisierung bzw. Haftvermittlerschicht 8 würden die Strompfade zwischen den IDTs ausschließlich über die Keramikschicht laufen, wie in der Figur 3 durch den gestrichelt dargestellten Pfeil angedeutet. Mit der erfindungsgemäßen Haftvermittlerschicht 8 verlaufen sie hingegen, wie dargestellt, zwischen dieser und den beiden IDTs. Der Strompfad führt dann außerhalb der Kontaktlöcher 7 über die Haftvermittlerschicht 8. Eine Veränderung der Leitfähigkeit in der Peripherie des Keramikdots bzw. der Keramikschicht 9, zum Beispiel durch eine Vergiftung, spielt bei dieser Konfiguration vorteilhafterweise praktisch keine Rolle mehr, da die elektrischen Feldlinien und damit die Strompfade stark räumlich eingegrenzt sind.A voltage is applied between the two interdigital electrodes IDT 1 and IDT 2. The measurement signal is tapped as current. If the upper, second metallization level, that is to say the structured adhesion promoter layer 8, is not at a defined potential, that is to say floating, both IDTs are implemented in the lower, first metallization level. Without the additional second metallization or adhesion promoter layer 8, the current paths between the IDTs would run exclusively over the ceramic layer, as indicated in FIG. 3 by the arrow shown in broken lines. With the adhesion promoter layer 8 according to the invention, however, they run, as shown, between the latter and the two IDTs. The current path then leads outside the contact holes 7 via the adhesion promoter layer 8. A change in the conductivity in the periphery of the ceramic dot or ceramic layer 9, for example due to poisoning, advantageously plays practically no role in this configuration, since the electrical field lines and thus the current paths are very limited in space.
Falls die obere, zweite Metallisierungsebene (Haftvermittler- Schicht 8) auf ein definiertes Potenzial (z.B. 0V) gelegt wird, kann sie als IDT 2 verwendet werden. Der Elektrodenabstand ist in diesem Fall effektiv etwa halb so groß wie bei floatender Haftvermittlerschicht 8. If the upper, second metallization level (bonding agent layer 8) is set to a defined potential (e.g. 0V), it can be used as IDT 2. In this case, the electrode spacing is effectively approximately half as large as in the case of a floating adhesive layer 8.

Claims

Patentansprüche claims
1. Chemischer Sensor, mit einer auf einem Substrat (1) angeordneten ersten Metallisierungsebene, in der eine Elektrodenstruktur (IDT) ausgebildet ist, einer auf der ersten Metallisierungsebene aufgebrachten, durch Kontaktlöcher (7) struktu- rierten Passivierungsschicht (6), und mit einer auf der Passivierungsschicht (6) und in den Kontaktlöchern (7) erzeugten sensitiven Keramikschicht (9), dadurch gekennzeichnet, dass eine Haftvermittlerschicht (8) vorgesehen ist, die als zweite Metallisierungsebene ausgebildet ist und die zwischen der Passivierungsschicht (6) und der Keramikschicht (9) angeordnet ist.1. Chemical sensor, with a first metallization level arranged on a substrate (1), in which an electrode structure (IDT) is formed, a passivation layer (6) applied on the first metallization level and structured through contact holes (7), and with a sensitive ceramic layer (9) produced on the passivation layer (6) and in the contact holes (7), characterized in that an adhesion promoter layer (8) is provided which is designed as a second metallization level and which is between the passivation layer (6) and the ceramic layer ( 9) is arranged.
2. Chemischer Sensor nach Anspruch 1, dadurch gekennzeichnet, dass die zweite Metallisierungsebene so aufgebracht ist, dass sie in den Kontaktlöchern (7) auf der ersten Metallisierungsebene zu liegen kommt.2. Chemical sensor according to claim 1, characterized in that the second metallization level is applied such that it comes to lie in the contact holes (7) on the first metallization level.
3. Chemischer Sensor nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass eine weitere Passivierungsschicht (10) zwischen der Haftvermittlerschicht (8) und der Keramikschicht (9) angeordnet und so strukturiert ist, dass die Haftvermittlerschicht (8) teilpassiviert ist.3. Chemical sensor according to claim 1 or 2, characterized in that a further passivation layer (10) is arranged between the adhesion promoter layer (8) and the ceramic layer (9) and is structured such that the adhesion promoter layer (8) is partially passivated.
4. Chemischer Sensor nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass in der Elektrodenstruktur (IDT) der ersten Metallisierungsebene zwei koplanare Elektroden (IDT 1, IDT 2) strukturiert sind, und dass die zweite Metallisierungsebene nicht auf definiertem elektrischen Potenzial liegt.4. Chemical sensor according to one of claims 1 to 3, characterized in that two coplanar electrodes (IDT 1, IDT 2) are structured in the electrode structure (IDT) of the first metallization level, and that the second metallization level is not at a defined electrical potential.
5. Chemischer Sensor nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass die Elektrodenstruktur (IDT) der ersten Metallisierungsebene eine erste Elektrode (IDT 1) bildet, und dass die zweite Metallisierungsebene als zweite E- lektrode (IDT 2) ausgebildet ist und auf definiertem elektri- sehen Potenzial liegt, so dass die sensitive Keramikschicht (9) mit einer vertikalen Elektrodenanordnung versehen ist.5. Chemical sensor according to one of claims 1 to 3, characterized in that the electrode structure (IDT) of the first metallization level forms a first electrode (IDT 1), and that the second metallization level is designed as a second electrode (IDT 2) and is at a defined electrical potential, so that the sensitive Ceramic layer (9) is provided with a vertical electrode arrangement.
6. Chemischer Sensor nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, dass die Elektroden (IDT 1, IDT 2) als Interdigitalelektroden ausgebildet sind.6. Chemical sensor according to one of claims 1 to 5, characterized in that the electrodes (IDT 1, IDT 2) are designed as interdigital electrodes.
7. Chemischer Sensor nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, dass in der ersten Metallisierungsebene zusätzlich zur Elektrodenstruktur (IDT) eine Heizstruk- tur (4) und eine Temperaturmessstruktur (5) ausgebildet sind.7. Chemical sensor according to one of claims 1 to 6, characterized in that a heating structure (4) and a temperature measurement structure (5) are formed in the first metallization level in addition to the electrode structure (IDT).
8. Chemischer Sensor nach einem der Ansprüche 1 bis 7, dadurch gekennzeichnet, dass die Strukturen (4, 5, IDT) der Metallisierung auf der Vorderseite eines Si-Substrats (1) aufgebracht sind, das eine Membran (3) aufweist.8. Chemical sensor according to one of claims 1 to 7, characterized in that the structures (4, 5, IDT) of the metallization are applied to the front of a Si substrate (1) which has a membrane (3).
9. Chemischer Sensor nach einem der Ansprüche 1 bis 8, dadurch gekennzeichnet, dass das Material für die zweite Metallisierungsebene Au, Cr/Au, Pt, Pd, W oder Sn umfasst.9. Chemical sensor according to one of claims 1 to 8, characterized in that the material for the second metallization level comprises Au, Cr / Au, Pt, Pd, W or Sn.
10. Chemischer Sensor nach einem der Ansprüche 1 bis 9, dadurch gekennzeichnet, dass das Aufbringen der sensitiven Keramikschicht (9) mittels Siebdruck-, Dispens- oder Inkjet-Ver- fahren erfolgen kann. 10. Chemical sensor according to one of claims 1 to 9, characterized in that the application of the sensitive ceramic layer (9) can take place by means of screen printing, dispensing or inkjet methods.
PCT/DE2004/001647 2003-07-25 2004-07-23 Microstructured chemical sensor WO2005012893A1 (en)

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EP1319943A2 (en) * 2001-12-14 2003-06-18 Stiftung Caesar Center of Advanced European Studies and Research Impedance sensor for analytes in liquid solution
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