Capacitive humidity sensor with nanoporous hydrophilic dielectric and fabrication process therefor

The present invention relates to the field of humidity detection devices and / or measurement devices, and specifically to capacitive humidity sensors.

The present invention relates to an improved humidity sensor device using a nanoporous dielectric material capable of detecting low levels of humidity and a method of manufacturing said sensor.

The present invention also provides a differential device for measuring humidity using the sensor.

The present invention is particularly suitable for detecting humidity in encapsulated components such as integrated circuits, MEMS or NEMS.

There are a number of existing techniques and components for performing humidity level measurements.

The components used are generally suitable for measuring 0% to 100% RH relative humidity.

Throughout this description, the term relative humidity RH refers to the ratio between the amount of water vapor contained in a given medium at a given temperature and the maximum amount (saturation point) that can be contained therein. This ratio is indicated by the number of RHs that vary between 0 and 100.

Commonly used hygrometers for measuring RH between 0% and 100% include lithium chloride hygrometers, psychrometers, mass spectrometers, condensed hygrometers, and humidity measuring devices that measure changes in impedance. is there.

Measuring relative humidity by measuring changes in impedance is most often used because it is the easiest to carry out.

Specifically, there are two categories of sensors that measure changes in impedance.

The first category relates to sensors for resistance changes, where changes in surface conductivity are measured.

Capacitive sensors provided with a layer of sensitive dielectric material to absorb ambient moisture can also be distinguished. In the sensor, a layer of dielectric material is arranged between the two electrodes to form a capacitor. As the humidity changes, so does the amount of water absorbed by the layer of dielectric material, resulting in a change in the dielectric constant of this layer and a change in the capacitance of the capacitor being measured. This change may be due to the dielectric constant of water, which is as high as about 80.

In capacitive sensors, the electrodes of the capacitors can be comb-shaped, for example made of a metal such as AlCu, AlSi, or CrNiAu. The two electrodes of the capacitor may be placed on one coplanar surface, as described in literature such as US Patent Application 2004/0 177 685 or US Patent Application 2003/0 179 805. it can. The literature of US Pat. No. 6,356 087 discloses a capacitive sensor that is located on another surface and has electrodes facing each other.

In capacitive humidity sensors, one of the electrodes can be permeable to humidity, allowing water vapor to move into the dielectric material layer of the capacitor. This permeable electrode has a slight thickness, eg, between about 10 nm and 20 nm, to crack the material, thereby facilitating faster diffusion of water vapor and improving sensor response time. It can be gold or a constrained Cr (Cr).

An example of a humidity sensor containing a polymer with an upper Cr electrode is described in French Patent No. 2 486 656, and "Polymer Based Capacitive Hygrometers", H. Grange and G. Delapierre, Chemical Sensor Technology, Vol. 3, N. It is shown in the literature of Yamazoe, Ed., Kodansha Ltd., pp. 147-162, (1991).

In general, the main criteria required for humidity sensors are: --Very short response time --Linear response to relative humidity (RH) between 0% and 100% RH --There is little hysteresis --Low temperature coefficient -Preferably have a wide operating temperature range between -20 ° C and 80 ° C --Measurement is stable for a long period of time, including in harsh media.

Some humidity sensors are typically provided to measure very low humidity levels from 10ppm (0.001%) to 1,000ppm (0.1%).

For example, a humidity value of 40% RH in air at 23 ° C corresponds to 1% or 10,000 ppm of moisture in the air.

Depending on the application, accurate measurement or accurate detection of a small amount of humidity may be required.

A technique used to carry out the detection is mass spectrometry. This method is not easy to use and cannot be used on an industrial scale.

A surface conductivity sensor can also be used to measure low humidity. In that case, the measurement principle is based on the detection of inter-electrode leakage current from a polarized sensor under a thermal cycle. The dew point corresponds to the start of conduction. The corresponding temperature can be converted to a moisture content of ppmv. The disadvantage of this method is that it is necessary to set up a cooling system on the component in order to obtain a gradual decrease in surface temperature.

The literature "Porous Silicon Oxide layer formation by the electrochemical treatment of a porous silicon layer" by Yamana et al., Electrochemical Society, vol.137, 1990, is a microporous SiO designed to measure low humidity.₂Shows a humidity sensor with layers.

Salonen et al., Sub ppm trace moisture detection with a simple silicon carbide porous silicon sensor, Elsevier, 2005, discloses a humidity sensor with a microporous layer of SiC intended to perform low-level humidity measurements. doing.

All of these sensors have pore diameters where water saturation is not achieved for intermediate humidity levels between 55% and 97%. At RH below 55%, the sensitivity of these sensors is not sufficient.

The challenge arises of finding a new, more sensitive humidity sensor designed to detect low humidity levels, without the aforementioned drawbacks.

<p num="0026"><patcit num="1"><text>U.S. Patent Application No. 2004/0 177 685</text></patcit><patcit num="2"><text>U.S. Patent Application No. 2003/0 179 805</text></patcit><patcit num="3"><text>U.S. Pat. No. 6,356 087</text></patcit><patcit num="4"><text>French Patent No. 2 486 656</text></patcit></p>

<p num="0027"><nplcit num="1"><text>H. Grange and G. Delapierre, "Polymer Based Capacitive Hygrometers", Chemical Sensor Technology, N. Yamazoe, Ed., Kodansha Ltd., (1991), Vol. 3, pp. 147-162,</text></nplcit><nplcit num="2"><text>Yamana et al., "Porous Silicon Oxide layer formation by the electrochemical treatment of a porous silicon layer", Electrochemical Society, 1990, vol.137,</text></nplcit><nplcit num="3"><text>Salonen et al., "Sub ppm trace moisture detection with a simple carbonized porous silicon sensor", Elsevier, 2005</text></nplcit></p>

<p num="0028"> The present invention relates to the provision of a sensitive humidity detection device and / or measurement device, and specifically to the detection and / or measurement of low level humidity.</p><p num="0029"> "Low humidity level" means the relative humidity of less than 55% RH, more specifically less than 20% RH.</p>

<p num="0030"> To this end, the present invention proposes a capacitive detector with at least one dielectric material located between at least one first electrode and a second electrode and having a hole with a radius of less than 2 nm. ..</p><p num="0031"> The sensitivity can be improved by using the dielectric.</p><p num="0032"> The nanoporous dielectric may be a "low k" dielectric, such as those commonly used in the field of interconnection.</p><p num="0033"> The nanoporous dielectric may be, for example, MSQ or SiOCH. The nanoporous dielectric material has high sensitivity to low humidity relative humidity between 0% and 20%.</p><p num="0034"> Nanoporous materials can include hydrophilic regions. The nanoporous material may be treated, for example, to make it hydrophilic or more hydrophilic. For example, hydrophilic treatment may be performed by oxidizing the nanoporous material.</p><p num="0035"> The oxidation of the nanoporous material can be carried out using an oxidation plasma treatment. N₂Plasma with O can be used advantageously.</p><p num="0036"> The hydrophilic region may be, specifically, SiO, SiOH or Si * type (free radical Si) when the nanoporous dielectric is MSQ or SiOCH.</p><p num="0037"> By increasing the hydrophilic nature of the sensor, its sensitivity can be improved.</p><p num="0038"> The sensor may further include at least one floating electrode that is placed on the nanoporous material and is permeable to humidity, the floating electrode facing the first electrode and the second electrode. And are placed.</p><p num="0039"> One application of this sensor is the detection of leaks in integrated circuit type encapsulated components, MEMS or NEMS with sealed or sealed cavities where humidity is measured.</p><p num="0040"> According to one possible embodiment, the sensor can include several layers of various nanoporous materials between the electrodes.</p><p num="0041"> The present invention comprises a capacitive sensor with at least one nanoporous dielectric material disposed between the at least one first electrode and a second electrode, and a capacitor with a non-porous dielectric material for humidity. Also related to devices for measurement or detection.</p><p num="0042"> The pores of the nanoporous dielectric material can have a radius of less than 2 nm.</p><p num="0043"> The non-porous dielectric material means that it does not contain any open pores.</p><p num="0044"> The capacitor can be configured to share a common electrode with the capacitance sensor.</p><p num="0045"> The nanoporous dielectric material of the sensor of the device may be MSQ or SiOCH.</p><p num="0046"> The nanoporous dielectric material may be subjected to a hydrophilic treatment using an oxide plasma.</p><p num="0047"> The present invention --The step of forming at least one first electrode and at least one second electrode on the substrate, Including a step of forming at least one nanoporous dielectric material between the first electrode and the second electrode, wherein the nanoporous dielectric material has holes with a radius of less than 2 nanometers. It also relates to the method of manufacturing a capacitive humidity sensor.</p><p num="0048"> According to one possible embodiment, the nanoporous dielectric material may be MSQ or SiOCH.</p><p num="0049"> This method can further include the step of forming a hydrophilic region on the nanoporous material.</p><p num="0050"> This step can be performed, for example, by performing a processing step of oxidizing the nanoporous material.</p><p num="0051"> The formation of hydrophilic regions on the nanoporous material is N₂This can be done by oxidizing the material with O-plasma.</p><p num="0052"> This method can further include the step of forming at least one floating electrode having permeability to humidity by facing the first electrode and the second electrode on the nanoporous material.</p><p num="0053"> The present invention will be better understood by reading the description of examples, which are shown for illustration purposes only and are by no means limiting, with reference to the accompanying drawings.</p>

<figref num="1A">FIG. 5 illustrates a first embodiment of a capacitive humidity sensor mechanism having at least one capacitor with comb-shaped electrodes in which a nanoporous dielectric material is placed between the teeth.</figref><figref num="1B">FIG. 5 illustrates a first embodiment of a capacitive humidity sensor mechanism having at least one capacitor with comb-shaped electrodes in which a nanoporous dielectric material is placed between the teeth.</figref><figref num="2A">FIG. 5 illustrates a second embodiment of a capacitive humidity sensor mechanism having at least one capacitor with comb-shaped electrodes with nanoporous dielectric material placed between and above the teeth.</figref><figref num="2B">FIG. 5 illustrates a second embodiment of a capacitive humidity sensor mechanism having at least one capacitor with comb-shaped electrodes with nanoporous dielectric material placed between and above the teeth.</figref><figref num="3A">FIG. 6 illustrates a third embodiment of a capacitive humidity sensor mechanism having at least one capacitor with a comb electrode and a floating electrode and a nanoporous dielectric material disposed between the floating electrode and the comb electrode. is there.</figref><figref num="3B">FIG. 6 illustrates a third embodiment of a capacitive humidity sensor mechanism having at least one capacitor with a comb electrode and a floating electrode and a nanoporous dielectric material disposed between the floating electrode and the comb electrode. is there.</figref><figref num="4A">FIG. 5 illustrates a fourth embodiment of a capacitive humidity sensor mechanism having at least one capacitor with comb electrodes and a porous dielectric material disposed between the rectangular floating electrodes and the comb electrodes. ..</figref><figref num="4B">FIG. 5 illustrates a fourth embodiment of a capacitive humidity sensor mechanism having at least one capacitor with comb electrodes and a porous dielectric material disposed between the rectangular floating electrodes and the comb electrodes. ..</figref><figref num="5A">FIG. 5 illustrates a fifth embodiment of a capacitive humidity sensor mechanism having at least one capacitor with rectangular and floating electrodes and a nanoporous dielectric material disposed between the floating and comb electrodes. is there.</figref><figref num="5B">FIG. 5 illustrates a fifth embodiment of a capacitive humidity sensor mechanism having at least one capacitor with rectangular and floating electrodes and a nanoporous dielectric material disposed between the floating and comb electrodes. is there.</figref><figref num="6A">It is a figure which shows the statistical pore distribution curve of a SiOCH dielectric.</figref><figref num="6B">It is a figure which shows the statistical pore distribution curve of a SiOCH dielectric.</figref><figref num="7A">It is a figure which shows the statistical pore distribution curve of MSQ dielectric.</figref><figref num="7B">It is a figure which shows the statistical pore distribution curve of MSQ dielectric.</figref><figref num="8A">It is a figure which shows the 2nd Example of the method of manufacturing the capacitive humidity sensor which comprises a nanoporous dielectric material.</figref><figref num="8B">It is a figure which shows the 2nd Example of the method of manufacturing the capacitive humidity sensor which comprises a nanoporous dielectric material.</figref><figref num="8C">It is a figure which shows the 2nd Example of the method of manufacturing the capacitive humidity sensor which comprises a nanoporous dielectric material.</figref><figref num="8D">It is a figure which shows the 2nd Example of the method of manufacturing the capacitive humidity sensor which comprises a nanoporous dielectric material.</figref><figref num="8E">It is a figure which shows the 2nd Example of the method of manufacturing the capacitive humidity sensor which comprises a nanoporous dielectric material.</figref><figref num="8F">It is a figure which shows the 2nd Example of the method of manufacturing the capacitive humidity sensor which comprises a nanoporous dielectric material.</figref><figref num="8G">It is a figure which shows the 2nd Example of the method of manufacturing the capacitive humidity sensor which comprises a nanoporous dielectric material.</figref><figref num="8H">It is a figure which shows the 2nd Example of the method of manufacturing the capacitive humidity sensor which comprises a nanoporous dielectric material.</figref><figref num="9A">It is a figure which shows the 2nd Example of the method of manufacturing the capacitive humidity sensor which comprises a nanoporous dielectric material.</figref><figref num="9B">It is a figure which shows the 2nd Example of the method of manufacturing the capacitive humidity sensor which comprises a nanoporous dielectric material.</figref><figref num="9C">It is a figure which shows the 2nd Example of the method of manufacturing the capacitive humidity sensor which comprises a nanoporous dielectric material.</figref><figref num="9D">It is a figure which shows the 2nd Example of the method of manufacturing the capacitive humidity sensor which comprises a nanoporous dielectric material.</figref><figref num="9E">It is a figure which shows the 2nd Example of the method of manufacturing the capacitive humidity sensor which comprises a nanoporous dielectric material.</figref><figref num="9F">It is a figure which shows the 2nd Example of the method of manufacturing the capacitive humidity sensor which comprises a nanoporous dielectric material.</figref><figref num="10">It is a figure which shows the result of the test performed on the Example of the humidity sensor produced by this invention.</figref><figref num="11">It is a figure which shows the result of the test performed on the Example of the humidity sensor produced by this invention.</figref><figref num="12">It is a figure which shows an Example of the differential device for humidity measurement which comprises a capacitance sensor which has a capacitor which has a nanoporous derivative and a non-porous dielectric.</figref>

Identical, similar or equivalent parts of separate drawings are numbered the same for ease of interpretation across the drawings.

The separate parts shown in the drawing are not necessarily drawn in proportion to their actual size to make the drawing easier to read.

An example of a capacitive humidity sensor manufactured by the present invention is shown in FIGS. 1A to 1B.

The humidity sensor is formed on a substrate or wafer 100, which can be, for example, a Si semiconductor material.

The upper surface and the lower surface of the wafer 100 are coated with insulating layers 102 and 104, respectively. These insulating layers 102 and 104 can be formed, for example, by thermal oxidation of the substrate.

The sensor comprises at least one capacitor electrodes 105a, 105b, each of which can have a comb-shaped pattern. In FIG. 1B, the comb electrodes 105a, 105b have teeth combined with each other (see, respectively, 106 and 107).

The insulating layer 102 formed on the upper surface of the substrate can avoid the formation of a short circuit between the electrodes.

The nanoporous dielectric material 108 is placed between the electrodes 105a and 105b, and in this embodiment it is placed on the same surface as the latter. Therefore, the thickness e of layer 109 of nanoporous dielectric material 108 and the thickness of electrodes 105a, 105b are substantially equal (thickness e is the orthogonal reference defined in FIGS. 1A and 1B).

<maths num="1"><img id="000002" he="18" wi="49" file="JP5744729B2_D0001.tif" img-format="tif" img-content="drawing" /></maths>

Vector

<maths num="2"><img id="000003" he="18" wi="49" file="JP5744729B2_D0001.tif" img-format="tif" img-content="drawing" /></maths>

Dimensions measured along a direction parallel to). For example, layer 109 of the nanoporous dielectric material 108 can have a thickness e between 100 nanometers and 500 nanometers, such as about 150 nanometers.

As the humidity level in the atmosphere around the capacitor changes, the permittivity of layer 109 of the dielectric material 108 that absorbs humidity changes in relation to the amount of moisture absorbed. As long as the dielectric constant of water (ε = 80) is much higher than the dielectric constant of the selected dielectric material 108, this change can be significant even at low humidity levels.

The nanoporous dielectric material 108 can effectively have a dielectric constant ε of less than 5, for example about 3.

The dielectric material 108 has a large open porosity of, for example, 30% to 50%, the porosity of which is slightly larger than that of a water molecule having a radius of 0.132 nm.

Nanoporous dielectric material 108 is a material designed with holes with a maximum radius of less than 2 nanometers. The average radius of the holes in the nanoporous material 108 is, for example, between 0.2 nanometers and 1.5 nanometers. The nanoporous material 108 may be SiOCH or methylsilsesquioxane (MSQ).

Nanoporous Dielectric Material 108 is N₂It may be subjected to hydrophilic treatment using O plasma. In the above treatment, when the nanoporous material 108 is SiOCH, for example, holes of about 0.6 nanometers can be obtained in the nanoporous material 108. By the above treatment, for example, an open porosity of about 32% can be obtained.

If the nanoporous material 108 is MSQ, then N₂By hydrophilic treatment using O-plasma, for example, nanoporous material 108 having holes having an average radius of about 0.7 nanometer can be obtained. In this case, an open porosity of about 46% can be obtained by this hydrophilic treatment.

In this mechanism, since the layer 109 of the nanoporous dielectric material 108 does not protrude beyond the surfaces of the electrodes 105a and 105b, the change in water content contained in the dielectric 108 can be completely measured. Humidity is effectively present between the comb teeth 106, 107. The capacitance value of the capacitor depends on the parameters shown by the following equation.

<maths num="3"><img id="000004" he="24" wi="49" file="JP5744729B2_D0001.tif" img-format="tif" img-content="drawing" /></maths>

During the ceremony S is the surface area of the electrode (S = h × ld × Ne), d₀Is the distance between the gaps or the teeth of the electrodes, ε₀Is the permittivity of the vacuum, εr is the permittivity of the porous material e is the thickness of the electrode h is the height of the tooth ld is the length of the comb tooth, Nd is the total number of comb teeth Ne is the number of voids (Ne = Nd-1).

For the capacitor, the shorter the value of the distance between the comb teeth 106, 107, the higher the capacitance. The void may be about 1 to 2 μm. The number Nd and length ld of the comb teeth may be designed, for example, to obtain a capacitor capacity of about 1 pF or more corresponding to the dielectric layer of the capacitor which does not contain any moisture.

2A and 2B show another embodiment of the capacitive humidity sensor.

In this other embodiment, the nanoporous dielectric material 108 has a different distribution than one of the previous embodiments and is in the form of a layer 209 covering the teeth 106, 107 of the electrodes 105a and 105b (FIGS. 2A and 2B). ). The high open porosity of material 108 allows moisture to diffuse between the teeth 106 and 107.

By "open pores" is meant that the pores of the material can communicate with each other and communicate with the outside of the material.

According to one embodiment of any one dimension of the sensor described above, the length of the comb-shaped fingers may be, for example, about 1,000 μm, the number of fingers combined with each other may be, for example, about 300, and the distance between the gaps. For example, may be about 1.5 μm.

3A and 3B show another embodiment of the humidity sensor embodiment. In this embodiment, the sensor further comprises additional electrodes in the form of floating electrodes 215. The floating electrode 215 is provided on a part of the electrodes 105a and 105b, specifically on the comb teeth 106 and 107.

In this case, the nanoporous dielectric material 108 may be distributed in the form of at least one block 309 present on the electrodes 105a, 105b and is located between the latter and the floating electrode 215. The composition and thickness of the floating electrode 215 is designed to be permeable to humidity.

The floating electrode 215 may be, for example, Cr or Au, and has a thickness as small as, for example, between 5 nanometers and 20 nanometers, for example, about 10 nanometers. The upper floating electrode 215 is designed to have a thickness capable of reaching conductivity while maintaining sufficient permeability.

The floating electrode 215 may have a pattern that reproduces a pattern of a part of the electrodes 105a and 105b, specifically, a part of the comb-shaped electrodes 105a and 105b, or may trace the same pattern.

The block 309 of the dielectric material 108 may also trace the pattern of the floating electrode 215.

The sensor is designed to allow moisture to enter the porous dielectric 108 through the floating electrode 215 and through the surface of block 309 of the porous dielectric 108.

Another embodiment of the sensor is shown in FIGS. 4A and 4B.

In this embodiment, the sensor is equipped with an upper permeable floating electrode 315 formed of a rectangular metal region located on block 409 of the porous dielectric material 108. The block 409 of the dielectric material may trace the same pattern as the pattern of the electrode 315, and covers the comb-shaped electrodes 105a and 105b.

In this case, moisture enters the dielectric 108 through the permeable electrode 315.

The change in the capacitance of the capacitor due to the change in the humidity level in the dielectric 108 is due to the space d existing between the teeth 106 and 107 of the electrodes 105a and 105b.₀The first element due to the change in the dielectric constant of the material 108 inside, and the space d between the comb of electrodes 105a, 105b and the floating electrode 315.₁There are two other elements due to the change in the permittivity of the dielectric material 108 inside.

Another embodiment of the sensor is shown in FIGS. 5A and 5B.

In this embodiment, two rectangular electrodes 205a, 205b are formed on the insulating layer 102 of the substrate 100, which are separated by a region of block 509 of the nanoporous dielectric material 108. Block 509 of the nanoporous dielectric material 108 also covers a portion of electrodes 205a, 205b. On the block 509 of the dielectric material 108, there is also a permeable floating electrode 415 that can have a rectangular shape. In this embodiment, the change in capacitance due to humidity is due to the space d between the upper part of the lower electrodes 205a, 205b and the upper part of the floating electrode 415.₁There is one factor due to the change of ε along.

To carry out any of the devices described above, nanoporous dielectric material 108, eg, by deposition by chemical vapor deposition (CVD) if this material is, for example, SiOCH, or if this material is eg MSQ. In the case of, it can be formed by applying annealing after spin coating.

A mask, such as a resin mask, is then formed and etched through the mask to form one or more patterns in the material 108.

Removal of the resin mask can be accomplished by stripping techniques. This stripping can use the RIE plasma method in an oxygen / argon mixture to remove a portion of the resin, and then a helium / hydrogen mixture to remove the rest of the resin without damaging the nanoporous material. it can.

When the nanoporous material 108 is SiOCH, it simultaneously deposits the precursor of the organic substrate and the pore-forming sacrificial material by plasma-enhanced chemical vapor deposition (PECVD), followed by the removal of the pore-forming organic phase. It can be formed by using a method consisting of performing a process for the purpose. Then, for example, SiOCH material 108 having a porosity of about 34% and having holes having an average radius of about 0.8 nanometers can be obtained.

If the nanoporous material 108 is MSQ, this is polymethyselsis quioxane mixed with an organic pore-forming agent containing methacrylate in a solution of methylpropylene glycol acetate (PGMEA) deposited, for example by spin coating. ) Can be formed using a solution of (MSQ).

In this way, for example, an MSQ material 108 having a hole having an average radius of about 1.2 nanometers and having a porosity of about 46% can be obtained.

Once the material 108 is deposited, a hydrophilic treatment can be performed to create a hydrophilic region on the nanoporous material 108.

For this, the process is, for example, pure or Ar, N₂, Diluted with He, N₂O plasma, or CO₂Plasma, or O₂Oxidized plasma, which is a plasma, can be used. In this way, the size of the pores and open pores can be reduced.

The material treated in this way will have a very large developed surface, i.e. the entire surface of the pores, occupied by a first adsorption layer or Langmuir layer (a monomolecular layer covers the surface). It makes it possible to obtain a very large number of adsorption sites, where RH is generally filled with a relative humidity of less than 20%. The pores of material 108 can be saturated at relative humidity of less than 50% or 55%.

With MSQ or SiOCH-based nanoporous materials 108, very high sensor sensitivity can be achieved for very small amounts of water (as much as a few ppm or ppb).

The sensitivity of the sensor according to the invention with a layer of nanoporous material 108 is a mesoporous material or for the measurement of low humidity levels, specifically 0% to 20% RH, especially 0% to 10% RH. Higher than prior art sensors for microporous materials.

The nanoporous material 108 has a specific adsorption mechanism. This adsorption mechanism can be monomolecular and poly-molecular.

The amount of water adsorbed in the pores of the nanoporous material 108 can be estimated using the following equation (BET) of "Brunauer, Emmett, Teller".

<maths num="4"><img id="000005" he="24" wi="86" file="JP5744729B2_D0001.tif" img-format="tif" img-content="drawing" /></maths>

N is the absolute amount (mol) of adsorbed gas, Nm is the amount (mol) of adsorbed gas per single layer

<maths num="5"><img id="000006" he="24" wi="86" file="JP5744729B2_D0001.tif" img-format="tif" img-content="drawing" /></maths>

q is the heat of adsorption qc is heat of condensation, R is the ideal gas constant T is the temperature P is pressure, P0 is the saturated vapor pressure at temperature T.

This equation can be used to describe polymolecular adsorption and to define the number of adsorption layers under a given pressure.

Since nanoporous material 108 has holes with an average radius of about 1 nanometer, this material saturates well before reaching 50% to 55% RH.

According to one aspect of the invention, capacitive humidity sensors such as those described above with hydrophilic nanoporous dielectric material 108 are encapsulated or sealed, eg, accelerometers or pressure sensors protected by components or, for example, covers. It can be used to detect leaks in encapsulated electronic devices.

As previously shown, the porous dielectric material 108 may be, for example, SiOCH.

Next, an embodiment of a method for producing a layer of a nanoporous SiOCH material will be described.

This material can be formed using PECVD (Plasma Accelerated Chemical Vapor Deposition), preferably the so-called "pore formation method".

For this, a two-phase material can be deposited, the first phase containing Si, O, C, H, intended to form the backbone of the porous dielectric material, and also C, H and optional. The second organic so-called "pore-forming" phase, which optionally contains O, acts as a sacrificial phase. The sacrificial phase deteriorates throughout the treatment period resulting in the formation of a thin nanoporous layer.

The precursor used for deposition may be, for example, diethoxymethylsilane for the phase intended to form the backbone and trivertal® from PCAS for the pore-forming phase.

According to one embodiment, the deposition conditions for a capacitance sensor suitable for a 200 mm wafer are, for example, a pressure of about 7 torr, a power of about 350 W, and a deposition temperature of, for example, about 200 ° C. Next, annealing in the oven may be performed at a temperature of, for example, about 450 ° C. for, for example, about 8 hours.

For example, it is possible to obtain an open porosity of about 34% with an average pore radius of about 0.8 nm by measuring on a SiOCH layer having a thickness of 0.35 μm (for example, FIG. 6A).

Next, the layer of the SiOCH nanoporous material can be treated so as to become hydrophilic.

In FIG. 6A, curves C1 and C2 show the distribution of pore radii in the porous SiOCH material for adsorption (curve C1) and desorption (C2), respectively.

These curves represent the statistical distribution of holes of various radii with respect to radii. The vertices of these Gaussian curves are centered on the average hole radius.

Curve C1 shows this distribution calculated from adsorption measurements of measurement liquids such as toluene.

Curve C2 shows this distribution calculated from the desorption measurements of a measurement liquid such as toluene.

Curves C10 and C20 correspond to pore diameters calculated using Kelvin's law.

The curve represents the statistical distribution of the hole diameter, and dV / d (lnR) is the probability of existence of a hole with a given radius.

The treatment of forming a hydrophilic region on the nanoporous material 108 is, for example, N for applying the hydrophilic treatment to the nanoporous material.₂O plasma can be used.

After the treatment, an open porosity of about 32% of the nanoporous layer can be obtained, with an average pore radius of about 0.6 nanometers.

In FIG. 6B, the measurement curves C3 and C4 show the distribution of pore radii in the SiOCH porous material for adsorption measurements (curve C3) and desorption measurements (curve C4), respectively, when the material is subjected to a hydrophilic treatment. Shown.

Curves C30 and C40 correspond to pore diameters calculated using Kelvin's law.

The curve represents the statistical distribution of the hole diameter, and dV / d (lnR) is the probability of existence of a hole with a given radius.

Next, an example of a method for producing a layer of MSQ nanoporous material will be described.

This material deposits an organic pore-forming agent containing a solution containing a sacrificial material, for example polymethyl cersicioxane, and a methacrylate in a solvent, the entire solution being, for example, PGMEA (propylene glycol monomethyl ether acetate). However, it can be deposited using, for example, a spin coating method.

The solvent is then removed on the hot plate, for example, at a first temperature of, for example, 100 ° C. over an initial period of 30 seconds, and then at a higher temperature, for example, 200 ° C., over a time of, for example, about 4 minutes. Can perform material annealing at.

The sample is then placed in the oven at a temperature of, for example, about 450 ° C. for 1 hour. The applied treatment results in the total extraction of the pore-forming phase and the formation of pores with radii less than 2 nanometers in the material.

An open porosity of, for example, about 46.1% can be obtained on a layer having a thickness of 0.35 μm with an average pore radius of, for example, an adsorption layer of about 2.2 nm.

In Figure 7A, curves C50 and C60 show the distribution of pore radii in porous MSQ materials.

A hydrophilic treatment can then be applied to the MSQ material.

After this treatment, an open porosity of, for example, about 35.8% can be obtained with an average pore radius of the adsorption layer of about 0.7 nm.

In FIG. 7B, curves C70 and C80 show the distribution of pore radii in the MSQ nanoporous material after hydrophilic treatment for the measurement of toluene adsorption and toluene desorption, respectively.

The nanoporous materials described above have large developed surfaces, i.e. large pore surfaces and many absorption regions.

For example, a layer of MSQ dielectric material having a pore ratio of about 35.8% and an average pore diameter of 1.4 nm can be obtained.

Layers of nanoporous materials 108, such as those described above, saturate with water as soon as two to three molecular layers of water are adsorbed for a relative humidity value of less than 55%.

Therefore, a slight increase in the ambient humidity of the nanoporous material 108 can result in a very large increase in the permittivity of the layer of the dielectric material 108 due to the strong concentration of moisture in the nanoporous material 108, even at low pressures.

This allows for very early detection of leaks in the cavities of encapsulated components left in the surrounding atmosphere, in a medium with a humidity generally corresponding to a value of RH of about 20% to 60%. Can be done.

Next, an embodiment of the method for manufacturing the capacitive humidity sensor according to the present invention will be described with reference to FIGS. 8A to 8H.

The starting material for this method may be a substrate 100 or a wafer 100 of a Si wafer semiconductor material having a thickness of, for example, about 525 μm, which may have a polished front surface (FIG. 8A).

Insulating layers are formed on both sides of the wafer. These insulating layers 102 and 104 can be formed, for example, by oxidizing the substrate 100, and can have a thickness of about several micrometers, for example, about 2 μm (FIG. 8B).

One or more electrodes of at least one capacitor are then formed.

For this purpose, a metal layer 105 is first deposited on the insulating layer 102 (Fig. 8C). The deposit may be a stack formed of, for example, an AlCu with a thickness of about 150 nanometers, or a layer of, for example, a Cr with a thickness of about 10 nanometers and a layer of gold, for example, about 150 nanometers.

A pattern is then formed on the metal layer 105 by, for example, photolithography followed by etching.

In this way, for example, comb-shaped coplanar electrodes 105a, 105b combined with each other can be formed (Fig. 8D).

Next, a layer of nanoporous dielectric material 108 having a thickness between, for example, 250 nanometers and 500 nanometers is formed on the metal electrode. The porous dielectric material 108 may be, for example, SiOCH or MSQ and can be deposited, for example, by PECVD (Plasma Accelerated Chemical Vapor Deposition) (FIG. 8E).

Nanoporous materials are formed with holes with radii between 0.6 nanometers and 2 nanometers.

The nanoporous material can be formed by using the above-mentioned method or the like.

Then N₂Hydrophilic treatment of nanoporous material 108 is performed using O-plasma.

Then, for example gold or Cr, a thin layer 110 of metallic material is deposited. The thickness of the thin layer 110 of the metallic material may be between 5 nanometers and 20 nanometers, for example, about 10 nanometers (Fig. 8F). The thickness and material of the metal layer 110 can be designed so that this layer is permeable to humidity.

For example, a layer of gold as thick as 10 nanometers does not last completely seamlessly.

A layer of Cr about 10 nanometers thick is constrained, especially when deposited by vacuum deposition, and tends to crack the material on which this layer is deposited. Water vapor can enter the cracks.

Next, at least one top electrode is formed on the metal layer 110 of the capacitor. This is accomplished by etching layers 110 of metallic materials and layers of nanoporous materials.

According to one possibility, a comb-shaped pattern with teeth combined with each other can be formed in these layers 108, 110 (Fig. 8G).

According to one variant, the electrodes may be in the shape of a rectangular pattern (Fig. 8H).

Next, a modified embodiment of the method for manufacturing the capacitive humidity sensor according to the present invention described above will be described with reference to FIGS. 9A to 9H.

The starting material of this method may also be a semiconductor material substrate 100 or a wafer 100, and insulating layers 102 and 104 are formed on both sides.

Next, a layer of nanoporous dielectric material with a thickness between, for example, 250 nanometers and 500 nanometers is formed on the metal electrode (Fig. 9A). The porous dielectric material may be, for example, SiOCH or MSQ, and can be formed, for example, by using the method described above.

A nanoporous material with holes with radii between 0.6 nanometers and 2 nanometers is formed.

Then, for example, N₂A hydrophilic treatment is applied to the material using O-plasma. Oxidation can occur over the entire surface of the pores.

The insulating layer 209 is then formed on the porous material layer 208. The insulating layer 210 is SiO₂The base may be, for example, a TEOS type, and may have a thickness of, for example, about 100 nanometers (Fig. 9B).

Subsequently, a plurality of openings 213 are created in the insulating layer 209 and the porous material layer 208 in order to expose the insulating layer 102 (FIG. 9C).

The openings are then filled with a metallic material 215, eg, AlCu or Cu. The thickness of the metallic material can be, for example, between 450 and 800 nanometers (Fig. 9D).

Polishing, for example chemical mechanical polishing (CMP), is then performed to remove the thickness of the metallic material 215 protruding beyond the aperture. For example, a thickness of about 200 nanometers can be removed to form the metal electrodes 205a, 205b of the capacitor (Fig. 9E).

The insulating layer 209 can then be removed (Fig. 9F).

At least one first capacitor with nanoporous dielectric material 108 and at least one second capacitor with almost non-porous or non-porous dielectric material used as a reference for more accurate measurements. Differential pressure measuring devices equipped with and can also be used.

FIG. 12 shows an embodiment of the device. In this embodiment, the first capacitor C₁Has a hole with a radius of less than 2 nanometers, N₂It is provided with a layer of nanoporous dielectric material such as MSQ or SiOCH (not shown in FIG. 22) that may undergo a hydrophilic treatment to oxidize, such as treatment with O. The nanoporous dielectric is placed between the first electrode 505a and the second electrode 505b, which acts as a reference electrode and the second capacitor C.₂It is a common electrode shared by.

Second capacitor C₂Is a non-porous, TEOS type SiO₂Alternatively, it is provided with another layer of dielectric material such as a polyether sulfone type polymer. Non-porous material means a material that does not contain any open pores.

Second capacitor C₂The other dielectric material of is placed between the common electrode 505b and the other electrode 505c. Thus, the second capacitor C₂Is formed of a dielectric material whose dielectric properties do not change with low humidity, specifically changes between 0 ppm and 500 ppm. Second capacitor C₂Acts as a reference capacitor.

Therefore, when the humidity changes, the first capacitor C₁The value of changes, but the second capacitor remains unchanged. Changes C over the range 0-500 ppm to measure changes in humidity₂-C₁Can be taken into account.

The differential pressure measuring device can be used to overcome so-called "surface" parasitic phenomena, for example due to moisture on electrodes and / or conductor wires. Reference capacitor C₂The dielectric material can be deposited from a liquid source of tetraethyl orthosilicate and oxygen, for example using LPCVD (Low Pressure Chemical Vapor Deposition), and the reaction is carried out at a temperature of about 380 ° C.

Sensors according to the invention are of encapsulated components, specifically electronic components or microelectronic components or microsystems, such as, generally, resin, soluble glass or co-fused gold beads, or integrated polysilicon. It can be used to detect leaks in sensors of accelerometers, gyros or pressure detectors of the type protected by a cover-sealed silicon cover.

Generally vacuum or N₂For these types of components encapsulated in, capacitors with a layer of nanoporous dielectric material may be able to detect leaks of one digit or more in ppm.

Humidity sensors according to the invention can be used to measure the amount of water vapor contained in the gas or air of a sealed or sealed component.

The component can be a MEMS component, for example an accelerometer or gyro or seismograph.

The sensor according to the invention has many uses. Among these applications are humidity measurement to control the drying of items before burning in the pottery manufacturing industry, in addition to the detection of humidity of sealed components, the paper industry, the food industry, the electronics industry, and drying or preferably. Can be mentioned for humidity measurement in areas where low humidity levels are controlled.

Since the porous material contains an amount of moisture that can be high in the surrounding air, to optimize the performance level with respect to the sensitivity of the sensor according to the invention integrated into an encapsulated or sealed component. The humidity of the nanoporous dielectric material is removed prior to sealing or encapsulation. This desorption can depend on the humidity in the air, with RH of less than 30% in cold winter climates and RH of more than 60% in summer, for example. The desorption can be carried out, for example, by vacuum heating, at a temperature of, for example, about 200 ° C. and under pumping.

Various results of sensitivity tests performed on examples of capacitive humidity sensors according to the invention are described below.

In the test, for example, a sealed container placed under vacuum after heat treatment at about 200 ° C for about 10 minutes was subjected to a temperature of about 23 ° C and a relative humidity of about 50% at the stage of pressure rise. This was done by adding a volume of air. Each device was tested using a Hewlett-Packard LCR-type device 4284A by plotting a curve of capacitance change ΔC / C with respect to humidity concentration.

In Figure 10, curve C₁₀₂, C₁₀₄Is a frequency of 1 kHz performed on the capacitance sensor according to the present invention formed of the nanoporous hydrophilic dielectric of MSQ and the capacitance sensor according to the present invention having a similar structure but the nanoporous hydrophilic dielectric is SiOCH. Represents the test of.

For comparison, curve C₁₀₆Shows the sensitivity of sensors similar in mechanism but with TEOS dielectric, while curve C₁₀₈Indicates the sensitivity of a sensor with a polymer-based dielectric of the polyether sulfone type.

Figure 11 shows the SiOCH capacitive humidity sensors tested in a moist air atmosphere and in a nitrogen atmosphere at a pressure of 800 mbar with moist air containing a relative humidity of about 50% at the pressure rise stage. Curve C of change in capacitance with respect to relative humidity C₁₃₂, C₁₃₄Is shown.

100 boards 102 Insulation layer 104 Insulation layer 105 metal layer 105a electrode 105b electrode 106 comb-shaped electrode teeth 107 Comb-shaped electrode teeth 108 Nanoporous Dielectric Material 109 Nanoporous Dielectric Material Layer 110 metal layer 205a metal electrode 205b metal electrode 208 Layer of porous material 209 layers 210 Insulation layer 213 opening 215 Floating electrode 309 blocks 315 Floating electrode 409 blocks 415 Floating electrode 509 blocks