JPH03248477A - Infrared sensor element and it's manufacture - Google Patents

Abstract

PURPOSE:To make a subminiature and highly precise element which can perform a rapid temperature measurement by laying bridges on which infrared sensors are mounted over a groove section formed on a substrate in advance. CONSTITUTION:Four parallel bridges 7 are laid at nearly regular intervals over a groove section 2. Each of the bridges 7 is an insulated layer 6 which was originally formed on an area other than the groove section 2 of a silicon substrate 1 and which was extended over the groove section 2 and is composed of three layers; silicon oxide 3b, silicon nitride 4b and another silicon oxide 5b. Each of the bridges 7 is 3.3mum in thickness, 60mum in width and 2mm in length. Each of the bridges is extremely long in proportion to its thickness and width. Since the bridges 7 are multilayer-structured and are made of the plural number of material having complementarity, the strength of the bridges is raised. This can make the bridges long. The long bridges remarkably contributes to the improvement of a response sensitivity of an infrared sensor element.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an infrared sensor element and a method for manufacturing the same;
In particular, the present invention relates to an ultra-small infrared sensor element suitable for use in a non-contact thermometer that can measure body temperature without contacting the human body, and a method for manufacturing the same.

[Prior Art] Thermometers used in hospitals, for example, are desirably inexpensive and capable of quickly and accurately measuring a patient's body temperature.

However, even if the thermometers currently in use are electronic thermometers, it takes more than 5 minutes to measure temperature with a direct indicator needle (the sensor waits until the temperature of the substance to be measured before taking the measurement). Furthermore, even a so-called predictive thermometer that measures the temperature at thermal equilibrium based on the actual temperature and elapsed time requires about 1 minute. Such temperature measurement time is too long for infants and critically ill patients.

On the other hand, at present, the armpit or sublingual area is generally selected as the temperature measurement site, and such areas cannot be said to display the accurate temperature of the entire body, making it difficult to obtain more accurate temperature measurement results. In order to achieve this, it is necessary to measure the temperature at a temperature closer to the brain temperature, and such temperature measurement sites include areas within the auditory canal that are less affected by wind and outside air, especially the thalamus, which is closer to the brain temperature. A site near the eardrum that reflects the temperature of the lower part has been found to be optimal.

Therefore, an extremely small infrared sensor that can accurately detect the amount of heat emitted from the eardrum is used to measure body temperature in an extremely short time (for example, within 3 seconds) and with high precision (for example,
There has been a demand for the development of a so-called tympanic membrane thermometer that can measure temperature at 100° C./looo C.).

By the way, as an ultra-compact and highly sensitive infrared sensor that can be used in such a tympanic membrane thermometer, for example, there is
As disclosed in Japanese Patent Application Laid-open No. 178149 and Japanese Patent Application Laid-Open No. 62-277528, a structure in which a heat-sensitive portion of a sensor element is formed on a bridge floating above a substrate has been proposed.

When manufacturing such an infrared sensor element, first an insulating film made of silicon oxide or silicon nitride is formed on a silicon substrate or a metal substrate, metal wiring is applied thereon, and then a film material sensitive to infrared rays is formed. After forming the infrared rays in a predetermined pattern, the substrate is selectively etched to form a cavity, and a bridge on which an infrared sensitive section is placed is suspended above the cavity. I had obtained a sensor element.

[Problems to be Solved by the Invention] However, such conventional infrared sensor elements,
In the manufacturing process, after forming an insulating film, wiring, and an infrared sensitive part on a substrate, in the final step, the part of the substrate exposed to the side of the infrared sensitive part is etched in the depth direction using an etching solution. By removing the part of the substrate below the insulating film on which the infrared sensitive part is mounted to form a cavity, a bridge was built above this cavity, so when forming the cavity, etching to the bottom of the resist film was avoided. It has been extremely difficult or impossible to control the dimensional accuracy of the cavity portion to 10 μm or less, which is required for a minute infrared sensor element that can be used in a tympanic membrane thermometer, while avoiding wraparound.

Therefore, in conventional infrared sensor elements of this type, the length of the bridge part is not constant due to variations in the dimensions and shape of the cavity part of each element, and as a result, the thermal characteristics of each sensor element vary. Due to this variation, it was not possible to obtain an infrared sensor element with uniform thermal characteristics, and there was a limit to miniaturization and high precision of the element.

The present invention has been made in view of these problems, and provides an infrared sensor element that is ultra-small, highly accurate, capable of rapid temperature measurement, and has uniform thermal characteristics, and a method for manufacturing the same. The purpose is to

[Means for Solving the Problems] In order to achieve the above-mentioned object, the infrared sensor element according to the present invention is provided by forming a hollow portion in a predetermined region of a substrate prior to forming the bridge. This feature is characterized in that the infrared sensitive portion is accurately created in advance, and then a bridge on which an infrared sensitive portion is placed is provided over the dug portion.

Furthermore, when manufacturing the infrared sensor element according to the present invention,
Generally, a silicon substrate is used, but there are no particular restrictions on the electrical characteristics, thickness, surface shape, etc. of this silicon substrate, and a silicon wafer, which is usually easily available, can be used.

A metal film such as titanium, molybdenum, tungsten, chromium, copper, nickel, or aluminum is deposited on such a silicon substrate by vapor deposition, sputtering, plating, or
It is formed using a CVD method or the like. The thickness of the film is sufficient as long as it can withstand etching of silicon by reactive ion etching (RIE) in a subsequent process, and is preferably 10 μm or less. Using this metal film as a mask,
For example, if a silicon substrate is etched using an etching method with good controllability, such as reactive ion etching (RIE), a recessed portion having a desired size and shape can be accurately formed.

Next, this dug portion is filled with a metal film that becomes a sacrificial layer for forming a bridge, and the upper surface of the substrate is again made flat. This sacrificial layer can be formed by etching or lift-off. When forming the sacrificial layer by etching, select a metal material with a coefficient of thermal expansion close to that of silicon of the substrate, form a pattern with resist, and use an etching solution suitable for the metal material to dissolve the metal film and remove the sacrificial layer. Form so as to leave a layer. In addition, when forming the sacrificial layer by the lift-off method, it is necessary to select a metal material for the sacrificial layer that can withstand the etching solution that etches the metal material used as a mask to form the trench. For example, molybdenum, tungsten, titanium, Chromium or the like is suitable, and a film made of these metal materials is formed in the same manner as described above. When using the lift-off method, there is no need to pattern the resist, and the metal film that was previously used as a mask to form the trench is used again as a mask, self-lining is performed to form a sacrificial layer within the trench, and then a sacrificial layer is formed within the trench. Etching is performed using an etching solution capable of dissolving only the metal film used as the mask, thereby removing the underlying mask layer and lifting off the metal film deposited on the upper surface of this mask layer. At this time, if the substrate is vibrated using ultrasonic waves, etching of the underlying metal film will proceed rapidly.
Can be easily lifted off.

Next, a silicon oxide film (S 10 x), a silicon nitride film (SiNY), and an organic material such as polyimide,
A film of negative resist is deposited as a bridge material to form an insulating layer having a multilayer structure. The thickness of each film is preferably 10 μm or less from the viewpoint of bridge strength and thermal conductivity. In terms of the simplicity of the film formation process, silicon oxide film/silicon nitride film structure, silicon oxide film/silicon nitride film/silicon oxide film structure, silicon oxide film/polyimide film structure, silicon oxide film/silicon nitride film/polyimide film structure Although a multilayer structure such as a silicon oxide film/negative resist film structure is recommended, it does not necessarily have to be a multilayer structure as long as a predetermined bridge strength can be obtained. Further, in order to increase the strength of the root portion of the bridge, polyimide, a negative resist, or even a metal film may be formed.

In particular, a multilayer structure in which a silicon oxide film and a silicon nitride film are combined, as shown in the examples below, is suitable for film formation because they mutually relieve stress (tensile, compressive) that occurs after each film is formed. Moreover, since silicon oxide has a low thermal conductivity, it is suitable for improving the sensitivity of an infrared sensor element.

A metal film wiring and an infrared sensitive film are formed on an insulating layer that allows such a multilayer structure, and an etching solution is applied thereon to dissolve a metal film or a sacrificial layer made of the same material as the sacrificial layer described above. A mask with a bridge pattern is formed using a metal film made of a material that is soluble in the sacrificial layer.The insulating layer is etched using this mask, and the bridge on which the infrared sensitive part is mounted is formed by extending it over the sacrificial layer. Etching in this case is also preferably performed by reactive ion etching.

Finally, by etching away the sacrificial layer together with the mask layer on the bridge, a bridge can be formed on the substrate.

[Function] In the conventional manufacturing method of an infrared sensor element having a bridge structure, a bridge is formed by extending it on a substrate, and then the substrate below the portion corresponding to the beam is removed by wet etching to create a cavity. Because the method of forming a bridge was adopted, it was difficult to control the cavity to a shape of 10 μm or less, and as a result, when forming minute infrared sensor elements, the thermal characteristics of individual sensor elements varied and were not uniform. It has been difficult to obtain an infrared sensor element with suitable thermal characteristics.

However, in the present invention, since the trench is formed in advance in a predetermined area of the substrate, it is possible to use an etching method with good controllability such as RIE to form the trench. With this, it was possible to easily obtain a dimensional accuracy of 10 μm or less. Therefore, even if the infrared sensor element is miniaturized, the thermal characteristics of each sensor element can be made uniform, and as a result, an ultra-small infrared sensor element can be obtained.

Furthermore, by forming the bridge beam into a multilayer structure, the mechanical strength of the bridge can be increased, and it has become possible to produce a large number of infrared sensor elements with a high yield.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

1 to 3 show the structure of an infrared sensor element according to the present invention, in which FIG. 1 is a plan view, and FIGS. 2 and 3 are taken along lines ■-■ and m-■ in FIG. 1, respectively. FIG.

In the figure, reference numeral 1 denotes a substantially square silicon substrate with dimensions of about 3 mm on one side, and this silicon substrate 1 has a trench in a predetermined area in the center thereof, with a nearly vertical inner wall and a flat bottom wall. It has a built-in part 2. In addition, silicon substrate 1
The area other than the groove 2 on the upper surface of the silicon oxide (Si
An insulating layer 6 formed by laminating a silicon nitride (SiaN,) film 3a, a silicon oxide (S102) film 4a, and a silicon oxide (S102) film 5a in this order is deposited. Digging part 2
Above, four bridges 7 that are parallel to each other are bridged at approximately equal intervals across the trenches 2, and each bridge 7 is connected to an insulating layer on a region of the silicon substrate 1 other than the trenches 2. A three-layer structure including a silicon oxide film 3b, a silicon nitride film 4b, and a silicon oxide film 5b is provided, with the layer 6 extending above the trench 2. An infrared sensing section 8 made of a silicon film is placed on the center of each bridge 7. As shown in FIG. 4, electrode wires 9.9 made of titanium are led out from both sides of each infrared sensitive section 8, and these electrode wires 9.9
electrode pads 10. extend along the bridge 7 and are made of an aluminum film formed on the left and right ends of the insulating layer 6.
10, respectively.

The infrared sensor element configured in this manner can be used as a temperature measuring element because the resistance value of the infrared sensing section 8 made of a silicon film changes depending on the amount of heat of the infrared rays that the sensing section 8 receives.

The bridge 7 in the infrared sensor element according to this example has a thickness of 3.3 μm, a width of 60 μm, and a length of 2 mm. In this example, the bridge 7 is formed to be extremely long compared to its thickness and width, but as described above, the bridge 7 has a multilayer structure made of a plurality of complementary materials. As a result, the strength of the bridge 7 can be increased, making it possible to increase the length of the bridge. This greatly contributes to improving the response sensitivity of the infrared sensor element.

Note that the dimensional ratios of the bridge 7 in FIGS. 1 to 4 do not represent the actual dimensional ratios, but are illustrated with the thickness particularly enlarged.

Next, a method for manufacturing the infrared sensor element shown in FIGS. 1 to 3 will be specifically described with reference to FIGS. 5(A) to 5(M). Note that FIGS. 5(A) to 5(M) show the manufacturing process of the cross-sectional structure shown in FIG. 3.

First, a silicon substrate 1 as shown in FIG. 5(A) is prepared, and a titanium film 11 is deposited on the silicon substrate 1 to a thickness of about 5 μm by vapor deposition as shown in FIG. 5(B). Form. Subsequently, a sacrificial layer pattern, which will be described later, is formed on the titanium film 11 using a photoresist, and then an etching solution for titanium, such as hydrofluoric acid:nitric acid:water=1:1, is applied.
: A hole was made in a predetermined area of the titanium film 11 using an etching solution having a composition of 50, as shown in FIG. 5(C).
As shown in FIG. 2, a mask lla for forming a sacrificial layer is formed of a titanium film. When the above etching solution is used, the time required to dissolve the titanium film 11 with a thickness of 5 μm is about 3 minutes.

Next, the silicon substrate 1 is etched by reactive ion etching (RIE) using a mask lla made of a titanium film, and as shown in FIG. Form to a depth of . In this case, the amount of etching that wraps around to the bottom of the mask material (titanium mask 11a in this example) (underetch) changes depending on the RIE conditions, and the RIE conditions also vary depending on the RIE apparatus, but the inventors In the RIE apparatus used, when etching was carried out under the following conditions, the spread of etching to the lower part of the mask could be suppressed to a negligible extent.

Etching gas: CF4+02 (approximately 5%) Gas flow rate: 2 20~50 SCCM Operating pressure: 0.01~0. I TorrRF output: 50 to 200 W Etching speed under the above conditions is 0.01 to 01 μm/
When the dug portion 2 was formed to a depth of about 3 μm, the amount of underetching was 0.2 μm or less.

Next, by sputtering molybdenum, as shown in Fig. 5(E).
As shown in FIG. 2, a molybdenum film 12a having a thickness of about 3 μm is formed in each of the dug portions 2. As shown in FIG.

In this case, the molybdenum film 12 formed inside the dug portion 2
The upper surface of a is made to be on the same plane as the upper surface of the substrate 1.

At the same time, a molybdenum film 12b is also deposited on the titanium mask 11a.

The molybdenum film 12a in the dug portion 2 is called a sacrificial layer because it is removed after the bridge 7 is formed thereon. The molybdenum film 12a serving as the sacrificial layer is formed by self-alignment using the titanium mask lla used to form the recessed portion 2, so that when the recessed portion 2 is formed, the etching does not substantially extend to the lower part of the mask lla. If the molybdenum film 1 is not suitable for use as a sacrificial layer,
2a is accurately filled into the dug portion 2.

Next, the titanium mask 11a underlying the molybdenum film 13 is etched using an etching solution containing hydrofluoric acid and water in a ratio of 1:9. At this time, ultrasonic waves or the like are used to make it easier for the etching solution to enter the lower part of the molybdenum film 12b. By etching for about 30 minutes, the titanium mask 11a
The upper molybdenum film 12b is peeled off and lifted off, and as shown in FIG.
A substrate 21 having a flat upper surface with a molybdenum film 12a as a sacrificial layer buried therein is obtained.

Next, a silicon oxide film 13 is formed on the upper surface of the substrate 21 to a thickness of 1 μm by the CVD method, and a silicon nitride film 14 is formed thereon to a thickness of about 0.3 μm by the same method. A silicon oxide film 15 is again formed to a thickness of about 2 μm to form an insulating layer 16 having a multilayer structure on the substrate 21 as shown in FIG. 5(G).

Next, on the entire surface of the insulating layer 16, a titanium film 19, which will become the electrode wires 9 in a later step, is formed by sputtering to a thickness of about 0.6 μm, as shown in FIG. is selectively etched to form electrode wires 9 along the portions of the insulating layer 16 that will become the bridges 7, as shown in FIG. 5(I). Note that in FIG. 5(I), a part of the electrode wire 9 is also shown at the left and right ends of the upper surface of the insulating layer 16, and this part is connected to the electrode pad 10 in FIG. This part is actually located in a position that cannot be seen in the figures from FIG. 5(1) onwards. however,
In order to simplify the drawings from FIG. 5(I) onwards, they are shown at the left and right ends.

Next, as shown in FIG. 5(J), the bridge 7 of the insulating layer 16 is
A silicon film, which will become the infrared sensitive part 8, is formed in the central part on the part where it is connected to the electrode wires 9.9, and electrode pads 1 made of aluminum are further formed on the electrode wires 9 at both ends.
form 0.

Next, a molybdenum film 22 with a thickness of about 1 μm is formed on the entire surface by sputtering, and as shown in FIG. 5(K), a pattern of bridges 7 is formed on the upper surface of the molybdenum film 22 using a photoresist film 23. Then, using this photoresist film 23 as a mask, the molybdenum film 22 is etched using an etching solution of, for example, nitric acid: sulfuric acid: water - 1:1:3, and as shown in FIG. 5(L), the bridge 7 is created. An etching mask 22a is formed for etching. Next, using the molybdenum mask 22a, the insulating layer 16 is etched as shown in FIG.
2a and form it.

Finally, using an etching solution of nitric acid: sulfuric acid: water = 1 + 1: 3, the molybdenum film 22a on the surface and the molybdenum film 1 as a sacrificial layer in the trench 2 of the silicon substrate 1 are removed.
By etching and removing 2a, the structure shown in FIG.
It is possible to obtain an infrared sensor element in which four bridges 7 are suspended above the dug portion 2 as shown in N).

[Effects] As is clear from the above explanation, in the method for manufacturing an infrared sensor element according to the present invention, a trench is formed in a predetermined region of a substrate in advance by using an etching method with excellent controllability such as RIE. After that, the trench is filled with a sacrificial layer to flatten the top surface of the substrate, and then a bridge is formed on the flat top surface of the substrate by extending over the sacrificial layer.
The feature is that the bridge is built floating above the excavation by removing the sacrificial layer.
Although the infrared sensor element obtained by this manufacturing method is extremely small, it has high precision and uniform thermal characteristics, so it is suitable as an infrared sensor element for the eardrum thermometer mentioned at the beginning. It will be easily understood that

[Brief explanation of drawings]

FIG. 1 is a plan view of an infrared sensor element according to the present invention, and FIG.
The figure and Figure 3 are the n-■ line and ■- line of Figure 1, respectively.
■A sectional view taken along the line; FIG. 4 is an enlarged perspective view of the infrared sensing portion; FIGS. 5(A) to (N) are sectional views showing the sequential manufacturing process of the infrared sensor element in FIG. 1. .

Claims (1)

[Scope of Claims] 1. An infrared sensor element, characterized in that a bridge on which an infrared sensitive section is placed is provided on a recessed section formed in advance in a substrate. 2. The bridge is constituted by a laminate of at least one layer of a first material with compressive stress properties and at least one layer of a second material with tensile stress properties. Item 1. The infrared sensor element according to item 1. 3. The substrate is made of silicon, and the first material is S.
The infrared sensor element according to claim 3, wherein the infrared sensor element is made of iO_2 and the second material is made of Si_3N_4. 4. The infrared sensor element according to claim 1, wherein the bridge is made of an organic material. 5. The infrared sensor element according to claim 4, wherein the organic material is made of polyimide. 6. The infrared sensor element according to claim 1, wherein the bridge is made of a laminate of different organic materials. 7. Form a dug portion in advance in a predetermined area on the substrate, fill this dug portion with a sacrificial layer made of a metal material, and place a bridge on which an infrared sensitive part is placed on the sacrificial layer. 1. A method for manufacturing an infrared sensor element, characterized in that the sacrificial layer is etched in such a manner that the bridge is formed on the recessed portion. 8. The manufacturing method according to claim 7, wherein the dug portion is formed by reactive ion etching using a mask film deposited on a region other than the predetermined region on the substrate. 9. The manufacturing method according to claim 8, wherein the sacrificial layer is filled into the dug portion by self-alignment using the mask film. 10. The manufacturing method according to claim 8 or 9, wherein molybdenum is used as the metal material forming the sacrificial layer. 11. insoluble in the substrate and the sacrificial layer;
and by etching the mask film using an etchant that is soluble in the mask film, a sacrificial layer material is deposited on the mask film as the sacrificial layer is filled into the dug portion. Claim 8~
10. The manufacturing method described in one of 10. 12. The manufacturing method according to claim 9, wherein the mask film is made of titanium.