FR2839061A1 - Micromechanical component comprising a substrate with an insulating layer and provided with a furrowed zone and a three layer closing zone for the furrowed structure - Google Patents

Abstract

A micromechanical component includes a substrate (1) with: (a) an electrical and/or thermal insulating layer (4) provided in the substrate and adjacent to the leading face of the substrate; (b) a furrowed structure (2', 3') provided in the insulation zone (4) and having an aspect ratio greater than one; and (c) a closing zone (6, 8, 9) provided on the insulation zone for closing the furrowed structure. An Independent claim is also included for a method for the fabrication of this micromechanical component.

Description

Field of the invention The present invention relates to a component

micromeca

picnic with a substrate.

  The invention also relates to a manufacturing method

s of such a component.

  State of the art Although the present invention can be applied to micromechanical components and micromechanical structures which conches, in particular sensors and actuators? it will be described 0 in the case of its basic problem related to a chemical sensor in micromechanics achievable according to the technique of the silicon surface mechanics as for example: an air quality sensor The old air quality sensors were made with a gas sensitive material on a ceramic. The gas sensitive material changes resistance and / or dielectric property according to the concentration of the detected gas. To have a good sensitivity it is necessary to heat the gas-sensitive material. The downside is the use of ceramic and relatively large space from the point of view

  clean heating to use and long response time.

  Recently, chemical sensors based on thermal effects have been manufactured, applying bulk micromechanical methods. In these block micromechanical processes, a membrane is produced for example by a complicated etching process from the rear side. Such a membrane is necessary to ensure insulation.

  2s thermal resistances by heating wires on the front face of the sensor.

  The setting up of the membrane is usually done by an etching process by wet chemistry with KOH potash. According to this process, the plate must be mounted in an engraving box. This process, with a back side, integrated process, or KOH etching process, is very

  complicates and entails considerable costs.

  AIM OF THE INVENTION The aim of the present invention is to develop a micromechanical component according to a simpler and more economical manufacturing process with an isolated front face zone making it possible to receive by

  ss example a sensor installation.

  To this end, the invention relates to a micromechanical component of the type defined above, characterized by a layer of electrical and / or thermal insulation provided in the substrate and adjacent to the front face of the substrate, a grooved structure provided in the insulation zone and having an aspect ratio greater than the unit and a closing zone

  provided on the insulation zone to close the structure in grooves.

  The invention also relates to a method for manufacturing such a component, a method characterized in that it forms a groove structure on a main surface of the substrate, comprising grooves and a corresponding number of spacers between the grooves, form one

  insulation zone on the resulting structure adjacent to the main surface

  blade of the substrate and a modified groove structure and a

  0 closing zone to close the modified groove structure.

  The object of the present invention is particularly suitable for the manufacture of a chemical sensor for detecting CO, NOx or other gases. According to this process, the thermal insulation between the heating resistors and the substrate is carried out by a front face insulation layer produced according to the invention. In this embodiment described by way of example, an air quality sensor is obtained having the following advantages: - low power consumption due to the good thermal decoupling, integration of a sensor element on a chip, o - integration possible of a circuit on the sensor element, - very small footprint with any geometric of the insulation range, - response time reduced due to the low mass that must be brought to temperature, - operation possible by capacitive or resistive flight, - different material for the resistance or the heating and / or measurement electrode,

  - several materials sensitive to gases can be used on a substrate.

  To make such a sensor, all you need is steps

  process in surface micromechanics, that is to say only processes

  treatment of the front panel. This eliminates common processes

  tents for treatment of the rear face such as for example etching by

  KOH using an engraving box to give structure to the mem-

  brane. The removal of the engraving step by KOH from the rear face

  also allows miniaturization of micromechanical components.

  Another advantage lies in the use of scratches or particles on

  the front of the plate because it is no longer necessary to provide

reverse cedes.

  Another advantage lies in the replacement of the mem-

  brane needed until now for insulation by an insulation block plus

  compact. This will prevent ruptured membranes when applied

  than the front face sensor structure, for example in the form of a chemically sensitive paste. Finally, only a few stages of layer generation and photolithography are necessary to obtain the

  front face insulation block according to the invention.

  According to an advantageous development, the substrate is made of silicon.

  cium and the silicon dioxide insulation zone or a combination o of silicon diode and cavities (these are put under vice or

  found under normal conditions).

  According to another characteristic, the closure zone comprises a first layer of silicon dioxide and above

  this one a layer of silicon nitride.

  According to another preferential development, the layer of silicon nitride is integrated into a second layer of silicon dioxide.

  According to another preferential development, the iron zone

  meture includes a sensor installation to detect a property

  electric of a medium planned at this place.

  According to another preferential development, the iron zone

  meture includes a heating system to heat the environment.

  According to another preferential development, the component is an air quality sensor and the medium is a medium sensitive to 2s gas and the sensor installation is a capacity detection installation.

and / or resistance detection.

  Drawings The present invention will be described below in more detail with the aid of an exemplary embodiment shown schematically in the accompanying drawings in which:

  - Figures la-lg show steps for manufacturing a chi-

  mique in the form of an air quality sensor correspond to a first embodiment of the invention, - Figure 2 is a top view of a chemical sensor according to Figure 1.

  Description of implementation examples

  In the figures we will use the same references to de-

  sign the same components or components of the same function.

  Figures la-g show the stages of manufacturing a chemical sensor in the form of an air quality sensor according to a

  first embodiment of the present invention.

  According to FIG. 1 a, the reference 1 designates a substrate in

  s silicon in the form of a silicon wafer. The substrate is not ne-

  a silicon wafer. I1 can for example also form the upper layer of a multi-layer substrate by

  example of a plate and an epitaxial layer.

  Using habitual photolithography pro cedes and a

  0 anisotropic etching step, for example by reac ion etching

  tive, we make grooves 2 in the substrate 1. Between the grooves 2 we

  leaves partitions 3 in the material of the substrate. Characteristic thickness

  ristic of the substrate is between 200 m and 600, um; a depth

  the characteristic groove 2 is between 20 µm and 200 µm.

  Depending on the application, the grooves 2 can have any shape. We can choose for example a structure in which the

  grooves 3 wind columns remain from the substrate 1 in this area.

  Other possibilities are for example spacers in the form of partitions or spacers in the form of arcs of a circle. Such process steps

  lead to the state represented in FIG.

  According to FIG. 1b, the structure re- thermally oxidized

  sultante to form an insulating layer of oxide 4. In this context, the expression <insulating N means thermal and / or electrical insulation according to the intended application for the micromechanical component. In the second case of the component described here, it is a chemicLue sensor so that

  the thermal insulation effect has priority.

  The width of the spacers 300 in FIG. 1a is chosen so that it can be completely oxidized by thermal oxidation and so that the modified spacers 3 ′ are made entirely of silicon dioxide. The 2-channel grooves transformed into modified 2 'grooves, of smaller width, by thermal oxidation. In this context it should be noted that the width of the grooves 2 can also be chosen so that they are completely closed by the thermal oxidation step and that there are no grooves 2 ', shrunk, as in

the example presented here.

  According to FIG. 1c, during the following stages of the process

  of, we realize ['air isolation of modified grooves 2' by realizing zo-

  closing nes 6, 8, 9 in the form of a succession of layers s covering the modified groove structure 2 ', 3'. The closing zone is obtained by depositing a first layer of oxide 6 followed by depositing a layer of nitride 8 covering the first layer of edge 6 as well as by depositing a second layer of oxide 9 covering the nitride layer

s of silicon 8.

  In a subsequent process step described in relation

  tion with FIG. 1d, the second oxide layer 9 is polished and the silicon nitride layer 8 constitutes a polishing stop layer so as to obtain a surface of planar structure. The oxide residue! of the second

  io layer of silicon dioxide 9 remains only in the troughs

above the grooves 2 '.

  According to figure lc, we then form on the resulting structure

  a chemical sensor in the form of a known air quality sensor.

  The main sensor elements are formed by platinum resistors and include thermal sensors 10, a heating installation and a distribution of electrodes 20. The manufacture of these elements

  sensor is generally known and does not require description

detailed here.

  In a following step of the process represented in FIG. 1f, a new layer of silicon oxide 16 is deposited and it is put into structure. In the present case, this layer covers all the sensor elements including the electrode device 20 and protects these means. Next to the electrode device 20 there are obviously also the contacts (not shown) of the connection paths (which do not wind

  no longer shown) sensor elements.

  It should be noted that the sensor elements may

  can be made not only in platinum but also for example

  made of conductive silicon. Such silicon substrate sensor elements

  cium can form a heating wire at the same time, a distribution

electrodes and thermosensors.

  According to FIG. Lg, a sensitive paste 30 is then applied.

  chemically on the resulting structure and we cultivate it. The dough 30 is ap-

  pliquee in particular over the electrode device 20 and touches the layer of silicon nitride 8 or the o2gid remains of the layer of

  3s silicon dioyde 9 between the electrodes.

  It should be noted that the wind sensor elements

  preferably arranged above the grooves 2 'which guarantees a cut

  thermal range as efficient as possible. In particular, it follows that

  the thermal sensors 10 measure the temperature of the iron zone

  temperature, the heating installation 50 regulating this temperature and the chemically sensitive paste 30 is coupled to the distribution in electrodes 20, thermally, only in the closing zone and not at the level of the substrate 1.

  For the rest of the process steps, especially the training

  tion of connection paths, etc ..., we proceed in a known way not detailed here. The process according to the invention can be integrated in particular into existing processes so that, for example, from the plane of the

  o sensor elements it is possible to totally use existing methods.

  Figure 2 is a top view of a chemical sensor

according to figure 1.

  Figure 2 is a top view of a sensor structure made according to the method of Figures la-lg. As shown in FIG. 2, the electrodes 20a, 20b of the distribution of electrodes 20 have an interdigitated comb structure, the branching branches of which go towards the outside. The connections 50a, 50b of the heating installation 50 are vented towards the outside by a ring surrounding in a form of meandres the distribution of electrodes 20. The contact to the outside can be done in any way. As thermal sensor 10, in this example, two platinum resistors 10a, 10b are used, not described

detailed manner.

  Although the present invention has been described above using a preferential embodiment, it is not limited to this.

  s example but allows multiple variants.

  In the above examples, the micromechanical component according to the invention is presented in simple forms for the description of its basic principles. Essentially complicated developments using the same basic principles can obviously be envisaged. For example, instead of changing the dielectric characteristics, it is also possible to modify the electrical resistance of the medium, for example of the medium sensitive to gas, by means of corresponding measurement electrodes. It is also possible to provide different media on the insulation layer, sensitive to different gases. This allows detec

  ter several gases with the same sensor element.

  Finally, we can also use any basic micromechanical materials, without being limited to a silicon support given by way of example. The closure zone can also have other successions of layers, for example another layer of silicon dioxide in place of the layer of silicon nitride.

NOMENCLATURE

  1 substrate 2, 2 'grooves 3, 3' spacer / partition 4 layer of thermal oaryde 6 layer of oxide 8 layer of nitride lo 9 layer of oxide, lea, lob thermal sensor fit heater to, 50b connection of the heater fit 50 distribution of electrodes} 5 20a, 20b electrodes 16 layer of chemically sensitive paste oxide t '

R EVE N D I CATI O N S

  1) Micromechanical component comprising a substrate (l), characterized by an electrical insulation layer (4) and / or thermal provided in the substrate (l) and adjacent to the front face of the substrate (1), a grooved structure ( 2 ', 3') provided in the insulation zone (4) and having an aspect ratio greater than ['unit, and a closing zone (6, 8, 9) provided on the insulation zone (4 ) for iron

  sea structure in grooves (2 ', 3').

  2) micromechanical component according to claim l, characterized in that the substrate (1) is made of silicon and the insulation zone (4) is made of silicon dioxide. 3) micromechanical component according to claim 2, characterized in that the closing zone (6, 8, 9) comprises a first layer of silicon dioxide (6) and above this a layer of silicon nitride or

  o a layer of silicon dioxide (8).

  4) micromechanical component according to claim 3, characterized in that the layer of silicon nitride or silicon dioxide (8) is integrated

  in a second layer of silicon dioxide (9).

   ) Micromechanical component according to one of the preceding claims

  tes, characterized by a sensor installation (20; 20a, 20b) provided on the closure zone (6, 8, 9) to detect an electrical property of a medium (30) provided at this location. 6) micromechanical component according to claim 5, characterized by a heating installation (70) provided on the closing zone (6, 8, 9)

to heat the medium provided (30).

  7) micromechanical component according to one of the preceding claims

  tes 5 or 6, characterized in that the component is an air quality sensor, the medium 130) is a gas-sensitive medium and the sensor installation (20; 20a, 20b) is a detection installation capacity and / or a resistance detection installation. 8) Method for manufacturing a micromechanical component characterized by the following steps: - a substrate (1) is produced, - a groove structure (2 ′, 3 ′) is formed on a main surface of the substrate (1), comprising grooves (2) and a corresponding number of spacers (3) between the grooves, - an insulation zone (4) is formed on the resulting structure adjacent to the main surface of the substrate (1) and a groove structure (2 ', 3') modified and - a closing zone (6, 8, 9) is created to close the structure of

modified grooves (2 ', 3').

  9) Method according to claim 8, characterized in that the insulation zone (4) is preferably formed by thermal oxidation of

the groove structure (2, 3).

   ) Method according to claim 9, characterized in that the modified groove structure (2 ', 3') comprises spacers (3 ') having

  completely undergoes thermal oxidation.

  11) Method according to claim 9 or 10, characterized in that the modified groove structure (2 ', 3') has grooves (2 ') at least in

shrunk part.

  12) Method according to claim 9 or 10, characterized in that the modified groove structure (2 ', 3') comprises grooves (2 ') at least

completely firm.

  13) Method according to claim 9 or 10, characterized in that the closure zone (6, 8, 9) comprises the deposition of a first layer of silicon dioxide (6) and a layer of silicon nitride placed over it or a layer of silicon dioyde (8) on the structure

of modified grooves (2 ', 3').

  14) Method according to claim 13, characterized in that the silicon nitride layer (8) is planarized by a deposit followed by a po

  smoothing a second layer of silicon dioyde (9).

   ) Method according to any one of claims 1 to 14,

  characterized in that the closing range 16, 8, 9) comprises a sensor installation (20; a, 20b) for capturing an electrical property of a medium (30) provided thereon. 16) Method according to claim 15, characterized by a heating installation (70) provided on the closing zone (6, 8, 9)

to heat the medium (30) provided.

  17) Method according to one of claims 15 or 16,

  characterized in that the component is an air quality sensor, the medium (30) being a gas-sensitive medium and the sensor installation (20; 20a, 20b) is an installation

  Capacity input lation and / or resistance input facility.

  18) Method according to one of claims 8 to 17,

  characterized in that the substrate (1) is made of silicon and the insulation zone (4) is made of silicon dioxide