RU2511272C1 - Method of making micro-electromechanical relays - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to microsystem engineering and can be used in making micro-electromechanical relays. The method of making micro-electromechanical relays involves successively forming on a substrate a contact plating consisting of a control electrode, two bottom switched contacts placed on two sides of the control electrode at a certain distance, a sacrificial layer, a top movable contact placed over the control electrode and bottom switched contacts and supports for suspending the top movable contact. The sacrificial layer is formed from at least three sacrificial sublayers in several steps using two positive photoresists with different viscosity; holes are formed for the bottom switched contacts and the supports for suspending the top movable contact by photolithography, and the sacrificial layer is heat treated at the final step.

EFFECT: high planarity of the sacrificial layer, which improves efficiency of the process of manufacturing micro-electromechanical relays.

5 cl, 9 dwg

Description

Technical field

The invention relates to a microsystem technique (MCT), in particular to a technology for forming “sacrificial” layers, and can be used in the manufacture of microelectromechanical (MEMS) relays.

State of the art

In micromechanics, the technology of surface microprocessing using “sacrificial” layers currently prevails. It is based on two main processes of applying the “sacrificial”, and then the working layers and removing through the holes in the working layer of the “sacrificial” for the formation of volumetric cavities between the working layer and the substrate [1]. Such parameters of the “sacrificial” layer, such as roughness, planarity, height, mechanical stress, affect the performance of the actuating element, which is formed on it, and, accordingly, of the entire device as a whole [2].

From the prior art it is known that as a "sacrificial" layer spread:

- silicon dioxide obtained by thermal oxidation or pyrolytic deposition from the gas phase and soluble in hydrofluoric acid;

- aluminum soluble with acid reagents;

- polysilicon, precipitated from the gas phase at low pressure and soluble in potassium hydroxide [3].

As the material of the “sacrificial” layer, polyimide was widely used. The advantages of this material are: the possibility of forming thin layers, good surface adhesion and selectivity of etching, etching of polyimide is possible by dry method in oxygen plasma [4].

Also, photoresists are used as a “sacrificial” layer. The use of photoresists as “sacrificial” layers, in contrast to the frequently used polyimide layers, can significantly reduce the temperature and time of the formation and removal of the “sacrificial” layer. Photoresists fit well with existing planar technology [5].

The closest in essence and the achieved effect technical solution is a method of manufacturing MEMS switch, presented in patent RU 2417941 "Method for manufacturing MEMS switch". The inventive method for manufacturing a MEMS switch on the substrate is applied stepwise to an electrode layer in which a lower control electrode and a lower contact are formed. On top of the electrode layer, a first “sacrificial” layer is applied, the thickness of which is the sum of the heights of the upper and lower contacts, and the relief is etched in the “sacrificial” layer to form an opening to the surface of the lower contact. Then perform the second "sacrificial" layer, the thickness of which is equal to the calculated value of the contact gap. Next, the upper contact, the movable part of the required design, the upper control electrode are formed and the entire “sacrificial” layer is etched [6]. A disadvantage of the known technical solution is the low reproducibility of the process due to the low planarity of the relief of the "sacrificial" layer.

Disclosure of invention

The technical result of the claimed invention is to obtain a high level of planarity of the "sacrificial" layer, which increases the reproducibility of the manufacturing process of microelectromechanical relays.

The technical result is achieved by the fact that the method of manufacturing microelectromechanical relays, including the sequential formation on the substrate of contact metallization, consisting of a control electrode, two lower switched contacts located on both sides of the control electrode at a certain distance, a "sacrificial" layer, the upper movable contact located above the control electrode and the lower switched contacts, supports for hanging the movable upper contact, characterized in that "sacrificial the th ”layer is formed from at least three“ sacrificial ”sublayers in several stages using two positive photoresists with different viscosities, holes are formed for the lower switched contacts and supports for suspending the movable upper contact by photolithography, and the“ sacrificial ”layer is heat treated at the final stage , the thickness of the lower first “sacrificial” sublayer is equal to the height of the lower switched contacts. The lower first “sacrificial” sublayer is subjected to heat treatment, at which the edges shrink, formed by the method of photolithography of the holes for the lower switched contacts. The thickness of the second and third "sacrificial" sublayer is equal to 2/3 of the gap between the upper movable and lower switched contacts. At the final stage, a two-stage heat treatment of the “sacrificial” layer is carried out: the first stage of heat treatment is carried out at + 105 ± 10 ° C for 8-12 minutes, the second stage - at + 160 ± 20 ° C for 9-11 minutes.

Two-stage heat treatment leads to evaporation of the residual solvent, absorbed water, developer and rinse aid, shrinkage and fusion of the positive photoresist, which improves the degree of planarization of the relief of the "sacrificial" layer. The degree of planarization of the “sacrificial” layer is calculated by the following formula [7]:

Degree of planarization,

where d _a - the height of the steps of the relief formed on the substrate,

d _s - the height of the "sacrificial" layer above the step.

Brief Description of the Drawings

The features and essence of the claimed invention are explained in the following detailed description, illustrated by drawings, which shows the following:

Figure 1 presents the substrate with the formed lower layer of contact metallization and the first "sacrificial" sublayer.

Figure 2 presents the substrate with the holes formed in the first "sacrificial" sublayer, opening the lower switched contacts.

Figure 3 presents the substrate with the holes formed in the first "sacrificial" sublayer, the edges of which have settled as a result of heat treatment.

Figure 4 presents the substrate with the formed first and second "sacrificial" sublayers.

Figure 5 presents the substrate with the formed first, second and third "sacrificial" sublayers.

Figure 6 presents the substrate with the holes formed in the "sacrificial" layer, opening the supports for suspension of the upper movable contact.

7 shows a substrate with a formed upper movable contact.

On Fig presents a substrate with an etched "sacrificial" layer.

In figures 1 to 8, the following is indicated:

1 - the first "sacrificial" sublayer;

2 - lower switched contacts;

3 - control electrode;

4 - substrate;

5 - supports for hanging the upper movable contact;

6 - holes in the "sacrificial" layer, opening the lower switched contacts;

7 - the second "sacrificial" sublayer;

8 - the third "sacrificial" sublayer;

9 - holes in the "sacrificial" layer, opening supports for hanging the upper movable contact;

10 - upper movable contact.

Figure 9 is the percent yield of suitable crystals.

The implementation of the invention and example implementation

The claimed method of manufacturing a microelectromechanical relay is as follows: on the substrate (4), a lower contact metallization layer is formed, consisting of a control electrode (3), lower switched contacts (2) and supports for hanging (5) the upper movable contact (8). Next, on the substrate (4), the first “sacrificial” sublayer is applied - positive photoresist FP2550 (1), with a thickness equal to the height of the lower switched contacts (2) (Fig. 1); using the method of photolithography in the first "sacrificial" sublayer (1), holes are formed that open the lower switched contacts (2) (figure 2); heat treatment of the first “sacrificial” sublayer into a heating cabinet is carried out, during the heat treatment, the edges of the holes formed by the photolithography method shrink (6) (Fig. 3). Next, a second “sacrificial” sublayer is applied to the substrate (4) - positive photoresist FP9120-1 (7), with a thickness equal to 2/3 of the gap between the upper (10) and lower (2) switched contacts, and dried in an IR heat treatment unit (figure 4). On top of the second “sacrificial” sublayer (7), a third “sacrificial” sublayer is applied - positive photoresist FP9120-1 (8), with a thickness equal to 2/3 of the gap between the movable upper (10) and lower switched contact (2), and is also dried in the installation of infrared heat treatment (figure 5). Then, using the photolithography method, holes are formed in the layer consisting of the first (1) and second “sacrificial” sublayers (7), which open the supports for suspending the upper movable contact (9) (Fig. 6). Next, a two-stage heat treatment of the formed “sacrificial” sublayers (1, 7, 8) is carried out in a heating cabinet: the first stage of heat treatment is carried out at + 105 ± 10 ° C for 9-11 minutes, the second stage - at + 160 ± 20 C for 9- 11 minutes At the first stage of the heat treatment, evaporation of the residual solvent, absorbed water, developer and rinse aid occurs. At the second stage of heat treatment, shrinkage and fusion of the positive photoresist occurs, which increases the degree of planarization of the relief of the “sacrificial” layer from 75% to 90% (calculated by formula 1). Next, the upper movable contact is formed (10) (Fig. 7) and the “sacrificial” sublayers (1, 7, 8) are etched (Fig. 8).

The claimed method is applied in the manufacture of a high-frequency microelectromechanical relay. The manufacture was carried out as follows: on the substrate (4), a lower contact metallization layer is formed, consisting of a control electrode (3), lower switched contacts (2) and supports for suspension (5) of the upper movable contact (8) (Fig. 1); then on the substrate (4) are applied "sacrificial" sublayers (1, 7, 8) with a thickness equal to the specified distance between the control electrode and the movable contact (Fig.2-7); then a two-stage heat treatment of the formed “sacrificial” layers is carried out (1, 7, 8); then the upper movable contact is formed (10) (Fig. 7) and the “sacrificial” sublayers (1, 7, 8) are etched (Fig. 8).

The application of the claimed method in the manufacture of high-frequency micromechanical relays allowed to increase the percentage of yield of suitable crystals by 25% (Fig. 9).

Thus, the use of the proposed method allows to solve the problem of improving the planarization of the "sacrificial" layer with the achievement of the expected technical result.

Bibliography

1. Pyatnyshev E.N., Lurie M.S., Popova I.V. Specificity of the technology of micromechanical devices. - Microsystem technology, 2001, No. 6, p. 32-34.

2. Soloviev Yu.V., Volkov VV, Aleksandrov S.E., Speshilov A.B. MEMS switch of resistive-capacitive type. - Nano- and microsystem technology. 2007, No. 7, pp. 65-68.

3. Varadan V., Vinoy K., Joseph K. HF MEMS and their application.-Moscow. Technosphere, 2004 .-- 528 s.

4. Zhukov A.A., Zdobnikov A.E., Tarasov V.V. Micromachine technology for the formation of bridge structures of a 64x64 microbolometric matrix. - Applied Physics, 2003.p. 48-51.

5. Takacs T., Pulskamp J., Polcawich R. UV baked / cured photoresist used as a sacrificial layer in MEMS fabrication. - Army Research Laboratory notes, 2005.http: //www.dtic.mil.

6. Patent RU 2417941 "A method of manufacturing a MEMS switch."

7. Moro, W. Microlithography: In 2 hours, Part 2: Transl. From English. - M.: Mir, 1990 .-- 632 p.

Claims (5)

1. A method of manufacturing microelectromechanical relays, including the sequential formation on the substrate of contact metallization, consisting of a control electrode, two lower switched contacts located on both sides of the control electrode at a certain distance, a "sacrificial" layer, an upper movable contact located above the control electrode and lower switched contacts, supports for hanging the movable upper contact, characterized in that the "sacrificial" layer is formed of at least three "germs governmental "sublayers in several steps using two positive photoresists with different values of viscosity, to form a lower opening of switched contacts and supports for the suspension of the movable upper contact photolithography, the final heat treatment step is carried out" sacrificial "layer. 2. The manufacturing method according to claim 1, characterized in that the thickness of the lower first "sacrificial" sublayer is equal to the height of the lower switched contacts. 3. The manufacturing method according to claim 2, characterized in that the lower first “sacrificial” sublayer is subjected to heat treatment, in which the edges of the holes formed by the photolithography method for the lower switched contacts are shrunk. 4. The manufacturing method according to claim 3, characterized in that the thickness of the second and third "sacrificial" sublayer is equal to 2/3 of the gap between the upper movable and lower switched contacts. 5. The manufacturing method according to any one of claims 1 to 4, characterized in that at the final stage a two-stage heat treatment of the “sacrificial” layer is carried out: the first heat treatment stage is carried out at +105 ± 10 ° C for 8-12 minutes, the second stage - at + 160 ± 20 ° C for 9-11 minutes.

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