A method of manufacturing a micromechanical devices

 

(57) Abstract:

Usage: for fabrication of micromechanical devices, in particular microgyroscopes, microaccelerometers, microswitches, pressure of the silicon-containing semiconductor structures. The method involves the fabrication of micromechanical devices from silicon-containing semiconductor structure, providing a coating on a substrate film made of conductive monocrystalline silicon-containing material is separated from the substrate by a dielectric layer, followed by etching areas of the film for forming the measuring node, removing dielectric layer to release the movable elements of the measuring site and the creation of electrical contacts for measuring. As the source material used bipolar grown semiconductor sandwich structure containing film of silicon carbide, separated from the substrate by a layer of aluminum nitride. To establish the end of the operation of etching the dielectric film of the semiconductor optionally form a stand-alone test plot with the linear dimensions of the calculation of the floating semiconductor film test uchastki remaining parts of manufactured products. The technical result of the invention is the improvement of mechanical, thermal and radiation stability of micromechanical devices. 2 C.p. f-crystals, 3 tab., 4 Il.

The invention relates to microelectronics and relates to a technology for manufacturing micromechanical devices, in particular, microgyroscopes, microaccelerometers, microswitches, pressure of the silicon-containing semiconductor structures.

A known method of manufacturing a micromechanical explosive devices by etching a thin epitaxial film and the subsequent epitaxial growth film on a substrate coated with her auxiliary layer formed in the epitaxial film of the picture elements of the epitaxial layer with open sides, cover the sides of the bearing layer, grazing auxiliary layer, separating the base layer from the device layer from the substrate, and then removing the base layer in the staging environment and transfer epitaxial layer of the intermediate medium at the stationary substrate (U.S. patent N 5244818, H 01 L 31/18, 1993). In the manufacture of the movable microstructure on a substrate applied a temporary layer and selectively removing areas of this layer, exposing the holes in the layer to create columns in the composition Mick is a structure selective etching with subsequent removal of individual sections of the temporary layer. Next, on the substrate, a temporary layer and the second layer precipitated photosensitive polymer (FP), filling in the gaps in the second layer and the temporary layer. After selective removal plots AF a certain amount of this polymer leave gaps temporary layer for the formation of columns between the substrate and the second layer. Then a temporary layer and unused OP remove (U.S. patent N 5314572, H 01 L 21/306, 44 1/22, 29 37/00, C 03 C 15/00, 1994).

These methods are complex and have low reliability because of the possibility of damage to the microstructure with numerous treatments, especially when transferring epitaxial layer from the source substrate at the stationary. In addition, there arises the problem of fixing the epitaxial layer on the stationary substrate.

To improve the manufacturability of the micromechanical elements on a substrate precipitated layer of aluminum nitride (AIN), spraying aluminum target in a vacuum chamber filled with nitrogen and the reaction gas. Then on a layer of aluminum nitride is precipitated by the dielectric layer and using photolithography to form the dielectric layer of the contact window exposing the surface of aluminum nitride, which is used as a table-layer etching. In conclusion, delete the second method is the impossibility of forming a conductive configuration of the formed epitaxial layer.

There is also known a method of manufacturing a micromechanical devices on the example of the semiconductor pressure sensor by epitaxial extension silicon film on a substrate of monocrystalline sapphire, followed by formation of a film of the diffusion resistor. Using a silicon film as a stop layer, selective etching of the hot phosphoric acid to remove the area of the substrate corresponding to only the diffusion resistor, thus forming a membrane structure. As the mask for etching use a film of silicon dioxide (Japan patent N 5-10830, H 01 L 29/84, 1993).

However, this method has a low-fidelity geometric dimensions of micromechanical elements, formed by deep etching of sapphire. In addition, etching of the substrate reduces the strength of the structure and requires sealing of cavities formed during Assembly.

Closest to the claimed is a method for manufacturing micromechanical devices on the example of the manufacture of microaccelerometer providing for application on a substrate film made of conductive monocrystalline silicon, separated from the substrate layer dialecting node, the creation of electrical contacts for measuring and partial removal of the dielectric layer to release the movable elements of the measuring site (French patent N 2700065, H 01 L 49/02, G 01 P 15/08, 15/125, 1994).

However, the devices manufactured by this method have low mechanical, thermal and radiation resistance.

The objective of the proposed method of increasing the mechanical, thermal and radiation stability of the produced products.

The solution of the stated problem is that in the method of manufacturing a micromechanical devices, providing the application to the substrate film of conductive monocrystalline silicon-containing material is separated from the substrate by a dielectric layer, followed by etching areas of the film for forming the measuring node, removing dielectric layer to release the movable elements of the measuring site and the creation of electrical contacts for measuring the quality of the film of conductive monocrystalline silicon-containing material on a substrate is applied epitaxial film of silicon carbide (SiC), separated from the substrate with the epitaxial dielectric layer of aluminum nitride is logicheskih changes to improve the quality of manufactured products is that among a significant number of possible pairs of conductive materials epitaxial films and epitaxial layers of dielectrics having a high wear resistance, mechanical strength and close coefficients of thermal expansion (what is important to eliminate deformation of the micromechanical elements) pair of "silicon carbide - aluminum nitride has the best crystal-chemical compatibility that provides reliable to obtain a sandwich structure.

When the technical realization of the proposed method, it is advisable to remove sections of aluminum nitride to produce etching in hot concentrated phosphoric acid. This provide the Etchant is the most selective in the processing of used a sandwich structure, does not cause outgassing and does not form a ballast connections, distorting the generated patterns.

When forming the elements of the micromechanical device requiring high-fidelity design elements, the most acceptable is a variant of the method, additionally providing for the formation of isolated test section processed a sandwich structure with the linear dimensions of the calculation splarka at the moment ensure achievement of specified dimensions of the formed elements of the device. At this point, the etching of the dielectric cease.

This option is most appropriate when forming the support sensitive element microgyroscope because there is not enough deep etching dramatically reduces the sensitivity of the measurements, and overexposure etching can lead to detachment of the sensor element from the substrate.

The AIN layer can be accomplished with Windows shielding required portions of the layer of SiC formed microstructure directly with the substrate.

In Fig. 1 is a diagram of a micromechanical pressure sensor to example 1.

In Fig. 2 shows a diagram of the MEMS accelerometer for example 2.

In Fig. 3 is a diagram of a micromechanical gyroscope to example 3.

In Fig. 4 is a diagram of an isolated test section to determine the time of etching of the layer of AIN to example 3.

The method is illustrated by the following examples.

Example 1. Fabrication of micromechanical pressure sensor

On a substrate 1 (Fig. 1) made of silicon orientation (III) put 2 layers of AIN and film 3 of SiC sequential deposition in ostroski areas. In the first working zone is aluminum plate, and the second silicon target.

The deposition is carried out at 5% excess flows of Al and Si, respectively. Each layer is precipitated for 30 min under vacuum at the temperature of the substrate in the range from 900 to 950oC. first substrate 1 precipitated layer 2 AIN from the first working area target in nitrogen-argon environment, then block the flow of nitrogen into the chamber and precipitated film 3 SiC of the second working zone target, etc. Get epitaxial sandwich structure of SiC (8 μm) on the AIN (1 μm).

On the external surface of the film 3 of SiC is applied photoresistive mask, through which plasma etched in this film through the window 4 3x3 µm. Then the mask is removed by dissolving in dimethylformamide and produce etching of the layer of AIN, located in the area of Windows, using heated to 75oC aqueous KOH solution (33 wt%), coming into the zone etching through the window 4 made in the SiC film. Etching vacuumized membrane cavity 5 in the layer 4 AIN produce over 45 minutes the reaction Products and unreacted ingredients are removed by rinsing in deionized water and dried processed structure with a layer 6 of Nickel from thermal spraying in a vacuum. In this case, the substrate is placed at an angle of 45othe direction of flow of the sprayed metal to prevent it in the formed membrane cavity in the AIN layer through the window in the film. The result of this operation is the sealing membrane of the cavity 5, with the applied sealing conductive layer 6 in contact with the formed above the cavity 5 a flexible membrane made of SiC, is one of the plates is formed membrane capacitive pressure sensor. The second contact 7 sprayed outside on a silicon substrate 1, which serves as the other plate of the capacitive sensor. Contacts connected to the input capacitance meter, programmirovanie in units of pressure. Served on top of the pressure sensor is perceived membrane cavity by changing the capacitance of the sensor due to a change in the distance between its plates. The resulting microdata has the following specifications:

- measured pressure range from 0 to 500 kPa;

- accuracy of 0.5%.

For comparison fabricate micromechanical pressure sensors, including the SiC film separated from the substrate by a layer of AIN, where the substrate using high-temperature oxide - beryllium ceramic PLA the substrate epitaxial deposition is impossible). In addition, make the sensors of the epitaxial SiC/Al2O3/Si, Si/AlN/Al2O3(French patent N 2700065) and epitaxially patterns SiO2/AlN/Si (U.S. patent N 5270263).

Take into account the percentage of the manufacture of good products in relation to geometric forms and sizes and degassing membrane cavity (under the microscope), the drift electrical characteristics and the sensitivity of the measurement.

Suitable sensors are subjected to thermal testing by keeping at a temperature of 700oC for 3 h and radiation treatment based 1,41015neutrons/cm2and reveal a save percentage of good products in respect of the above characteristics. The data results of 20-300 tests are given in table. 1 (see the end of the description).

As can be seen from the table, the yield of a micromechanical pressure sensors, the proposed method is 30%, and in prototype - 27,7% (difference not statistically significant). At the same time, the sensors obtained by the proposed method have a significantly higher performance, as evidenced by 84% preservation of their health after heat treatment compared with 37% in prototype sposo quality indicators exceed the corresponding values of other ways.

Example 2. Fabrication of micromechanical accelerometer

On a substrate 1 (Fig. 2) sapphire bipolar put a layer 2 of aluminum nitride and a film 3 of silicon carbide, in which the etched through-process window 4, as in example 1. The film 3 is also etched outer contour of the formed flexible hinged element of the device according to the plotted drawing photoresistive mask. Later in the film 3 in the zone of maximum bending stress (located near the site of the fastening forming a hinged element) create a piezoresistive bridge circuit 5 by ion implantation of boron with subsequent plating of Nickel-titanium contacts 6 for connection to the transmitter. Then etched through in the film 3 window 4 and the circuit forming the rolling element produce etching of the layer 2 of AlN for the formation of a beam structure of the rolling element with the cavity 7.

Etching portions of the layer of AlN in different batches of manufactured devices with a volume of 50 to 200 products produced within 30-120 minutes at a temperature of from 60 to 95oC using the following reagents: concentrated phosphoric, fluoride-hydrogen and nitric acids, KOH (33% solution), re is h table, etching portions of the layer of AlN heated with concentrated phosphoric acid provides maximum product yield (32%). The rest of the tested reagents damage or sapphire substrate 1, or the sensitive elements of the device that dramatically reduces product yield. This fluoride-hydrogen acid layer AlN virtually no poison.

The product is sealed in a protective ceramic body.

Under the action of acceleration applied perpendicular to the substrate 1, the movable element deforms, which is fixed by means of piezoresistive circuit 5.

Technical characteristics of the fabricated MEMS accelerometers:

- measuring range from 0 to 100 m/s2;

- accuracy - 0.5% of measuring range.

As a result of thermal and radiation tests accepted items in example 1 efficiency save 83 and 89% of the devices, respectively.

Example 3. Fabrication of micromechanical gyroscope

On a substrate 1 (Fig. 3) sapphire, metallic plates 2 serving also collector items, bipolar put a layer 3 of aluminum nitride and a film 4 of silicon carbide, in which the etched smoga hanging sensitive element microgyroscope, according to the plotted drawing photoresistive mask, providing for the formation of a capacitive bridge between the plates of the moving element and the stationary base. Then etched through in the film 4 window 5 and the circuit formed of the rolling element produce etching of the layer 3 AIN for education design of the rolling element with the cavity 6 and a Central pillar formed neitralnym plot layer 3.

Due to technological difficulty strict adherence to the prescribed shape and size of support sensitive element microgyroscope to establish the end of the operation AlN etching the SiC film 4 advanced form isolated test site (Fig. 4) with the linear dimensions of the calculation of the floating semiconductor film of the test section when the etching on the underlying dielectric layer at a time to guarantee the achievement of a given size bearing. For this purpose, two vacant plots of the original structure photolithographically form the test objects in blocks with a square (Fig. 4A) and round (Fig. 4B) bases. The feasibility of performing the test object in the form of block shapes is to render its buoyancy and used the Rhone square or diameter round base). In this example, the optimum is A= 50 µm (table. 3), providing maximum product yield (24%). When A<50 μm is naturalmania site support, and when A>50 μm is pietrapiana AlN in this area, up to the breakage of the sensing element.

Etching portions of the layer of AlN cease at the moment of ascension test section detected by color change in the location of the tear film, because the opened area of the sapphire substrate is different from a dark film of SiC.

The seal device as in example 2.

When changing the angular velocity in roll and/or pitch change occurs Coriolis forces acting on the plates of the rolling element vibrating in the plane of the substrate, which leads to changes in the balance capacities in different shoulders formed bridge and taken into account by measuring transducer connected to the plates.

Specifications made of a micromechanical gyroscope:

- measurement range angular velocity from 0 to 100 o;

- accuracy - 1%.

As a result of thermal and radiation tests accepted items in example 1 performance retain 82 and 92%redlagaemyi method in comparison with the known allows to increase the precision and strength of micromechanical devices, that allows them to operate in extreme conditions, characterized by high temperatures (700oC) and radiation (1,41015neutrons/cm2).

1. A method of manufacturing a micromechanical devices from silicon-containing semiconductor structure, providing a coating on a substrate film made of conductive monocrystalline silicon-containing material is separated from the substrate by a dielectric layer, followed by etching areas of the film for forming the measuring node, removing portions of the layer of dielectric to release the movable elements of the measuring site and the creation of electrical contacts for measuring, characterized in that as a film of conductive monocrystalline silicon-containing material on a substrate is applied epitaxial film of silicon carbide, separated from the substrate with the epitaxial dielectric layer is aluminum nitride, forming a semiconductor sandwich structure.

2. The method according to p. 1, characterized in that the removal of sections of aluminum nitride is produced by etching in hot concentrated phosphoric acid.

3. The method according to p. 1 or 2, characterized in that for ostanovochnyy insulated test section with the linear dimensions of the calculation of the floating semiconductor film of the test section when you delete on the underlying dielectric layer at a time ensure achievement of specified dimensions of the remaining parts of manufactured products.

 

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