KR101118007B1 - Micro cantilever and method of manufacturing the same and silicon thin film and method of manufacturing the same - Google Patents

Abstract

Disclosed is a method of fabricating a silicon thin film of a micromechanical structure for stress gradient relaxation and surface resistance reduction. A Cu-thin film is deposited on the silicon thin film and subjected to a heat treatment to cause Cu-silicide at the silicon thin film surface. The silicon thin film includes Cu-silicide on the top surface.

Description

Microcantilever and its manufacturing method and silicon thin film and its manufacturing method {MICRO CANTILEVER AND METHOD OF MANUFACTURING THE SAME AND SILICON THIN FILM AND METHOD OF MANUFACTURING THE SAME}

It relates to micromechanics.

Low-Pressure Chemical Vapor Deposition (LPCVD) polysilicon thin films are frequently used to form micromechanical structures due to their excellent mechanical properties. LPCVD polysilicon thin films are also applicable to simple resistors, gates of MOS transistors, dynamic random access memory cell plates, and surface micromachining MEMS devices.

However, polysilicon has the disadvantage of having a high residual stress gradient and high resistance. In the fabrication of MEMS devices, most silicon thin films have residual stresses due to differences in coefficients of thermal expansion, non-uniform plastic deformation, inadequate lattice arrangement, and uneven growth conditions. Residual stress is a stress that remains on an object even after the original cause of pressure such as external force and thermal gradient is eliminated. In general, microstructures made of thin films are affected by residual stress, which is different from the intended structure. There are many variations.

In particular, the development of silicon micromachining technology among microelectromechanical system (MEMS) technology enables the fabrication of microcantilevers capable of measuring extremely fine displacements, which are used as probes of atomic force microscopes, and recently as physical, chemical and biological sensors. If the application is active, but can not control the shape shift of the cantilever, precise measurement is impossible.

For example, when the microcantilever has a positive residual stress gradient, a tensile stress is generated on the upper surface of the cantilever, and a compressive stress is generated on the lower surface of the cantilever, so that the cantilever changes shape in a direction away from the substrate. If the tensile stress is excessively large, cracks or interlayer separation may occur in the thin film, and if the compressive stress is excessively large, buckling may occur. Thus, mitigating this residual stress is one of the major challenges in the fabrication of silicon thin films, and the study of this problem is based on the finding that "the MEMS device having a support structure configured to minimize the stress associated with deformation and its manufacturing method is Korean Patent Laid-Open Publication No. 2008-0055851.

In addition, since the high surface resistance of the thin film is an obstacle to performing a function as a component of the micromechanical structure, it is an important task to reduce the surface resistance of the thin film.

In order to alleviate the stress gradient of the silicon thin film, furnace annealing may be generally used. The thermal treatment eliminates the residual stress of the thin film through the rearrangement of the crystal by exposing the thin film for a long time at high temperature. Indeed, the compressive stress of low pressure chemical vapor deposition (LPCVD) polycrystalline silicon decreases with increasing heat treatment temperature.

Rapid thermal annealing (RTA) can be used as another method for solving the residual stress and stress gradient of the silicon thin film. Unlike heat treatment, RTA is a method of relieving residual stress by exposing the thin film to high temperature for several tens of seconds. Indeed, the compressive stress of polycrystalline silicon decreases with increasing RTA annealing time or with increasing annealing temperature. Heat treatment at a temperature higher than the deposition temperature can reduce the residual stress of the polysilicon thin film.

The surface resistance of thin films can generally be reduced using high concentration ion implantation procedures and heat treatments. However, about 10 ²⁰ cm ^- resistance even at very high doping of ³ can still be high for the application. In addition, conventional furnace treatments, ie long time treatments at high temperatures, are difficult to use in integrated systems of electrical circuits with low melting points.

Metal silicide may be introduced into the silicon thin film. Metal silicides are characterized by low resistivity (tens of μΩ-cm), low contact resistance, the ability of self-aligned forms through selective etching, and elastic properties. These properties can be applied to micromechanical structures.

1 shows a conventional cantilever with a positive stress gradient.
FIG. 2 illustrates the relaxation mechanism of the cantilever undergoing a positive stress gradient and the stress gradient of the cantilever through Cu-silicided.
3 shows another embodiment of a cantilever manufacturing process using Cu-silicided.
4 illustrates an embodiment of a method for stress gradient mitigation when the cantilever structure has a positive stress gradient and a negative stress gradient.

In particular, Cu-silicide has excellent electrical properties in polysilicon micromachining, and low-thermal-budget control of stress gradients is possible through built-up stresses generated from Cu-silicided processes. In addition, the silicided temperature of Cu-silicide is lower than the silicided temperature of other metal silicides (about 200 ° C.), and it is easy to form a state in which Cu ₃ Si predominates, thereby generating a significant magnitude of compressive residual stress. Can be.

In one embodiment, in order to fabricate a microcantilever having a low stress gradient and low resistance, a process of preparing a substrate, depositing a sacrificial layer on the substrate, etching to remove a portion of the sacrificial layer, and part of the sacrificial layer may be performed. Depositing a cantilever structure layer on the removed and exposed substrate portion, sacrificial layer, depositing a Cu-thin film on the cantilever structure layer, and performing a thermal treatment on the Cu-thin film to form Cu-silicide on the cantilever structure layer The microcantilever may be manufactured through a process of removing the sacrificial layer.

In another embodiment, the method may further include removing a native oxide on the cantilever structure layer using an aqueous hydrogen fluoride fluoride solution after etching the cantilever structure layer and before depositing the Cu-thin film.

In another embodiment, the method may further include removing Cu remaining without reacting before removing the sacrificial layer after the heat treatment.

In another embodiment, a cantilever device using Cu-silicide is formed on the substrate and the substrate, and includes a cantilever portion extending outward from the substrate and floating above the substrate, wherein the top surface of the cantilever portion is made of Cu-silicide, It is also possible to implement a microcantilever.

Specific details of other embodiments are included in the detailed description and the drawings. Advantages and features of the present technology, and methods of accomplishing the same will be apparent with reference to embodiments described below in detail with the accompanying drawings. However, the present technology is not limited to the embodiments disclosed below, but may be implemented in various forms, and the present embodiments merely provide a complete description of the present technology, and have ordinary skill in the art to which the present technology belongs. It is provided to fully inform the technical scope of the technology. The size and relative size of layers and regions in the figures may differ from the actual for clarity of explanation. Like reference numerals refer to like elements throughout.

Embodiments described herein will be described with reference to plan and cross-sectional views, which are ideal schematic diagrams of the present technology. Accordingly, shapes of the exemplary views may be modified by manufacturing techniques and / or tolerances. Accordingly, the embodiments are not limited to the specific forms shown, but also include variations in forms produced by manufacturing processes. Thus, the regions illustrated in the figures have schematic attributes, and the shape of the regions illustrated in the figures is intended to illustrate a particular form of region of the device or device, and is not intended to limit the scope of the techniques. Hereinafter, a method for manufacturing a microcantilever according to an embodiment will be described with reference to the drawings by taking a cantilever of an LPCVD polysilicon film as an example.

FIG. 1 shows a conventional microstructure whose shape changes with residual stresses caused by differences in coefficients of thermal expansion, non-uniform plastic deformation, inadequate alignment of the lattice, uneven growth conditions, and the like. 1 shows a cantilever with a positive stress gradient. Tensile stress is generated on the upper surface of the cantilever having a positive stress gradient, and compressive stress is generated on the lower surface of the cantilever, and the cantilever is bent in a direction away from the substrate.

In FIG. 2, a process of mitigating a stress gradient by depositing and silicidating a polysilicon cantilever 20 and a Cu-thin film 30 having a positive stress gradient on the polysilicon cantilever 20 is illustrated. As shown on the left side of FIG. 2A, the polysilicon cantilever 20 having a positive stress gradient is bent in a direction away from the substrate 10. This bending is caused by having a compressive stress in the lower part of the cantilever 20 and a tensile stress in the upper part as shown in the stress distribution diagram of the cantilever 20 on the right side of FIG.

On this polysilicon cantilever 20, a Cu-thin film 30 is deposited as shown in Fig. 2 (b). In one embodiment, the Cu-thin film 30 may be deposited to a thickness of about 90 nm, and upon deposition of the Cu-thin film 30, a pressure low enough to prevent oxygen contamination, for example 5.0 x 10 ^The Cu-thin film 30 may be deposited using a thermal evaporator at a deposition pressure of ^-6 torr, but is not limited to such thickness and pressure. After the Cu-thin film 30 is deposited, a heat treatment may be performed to proceed with Cu-silicide formation. The temperature for the silicideation of the Cu-thin film 30 is lower than that of the other metal silicides, and the heat treatment can be performed even at about 200 ° C. The polysilicon cantilever 20 in which the Cu-silicide 40 is formed can restore flatness like the polysilicon cantilever 20 shown in the upper end of Fig. 2 (c). At the lower end of Fig. 2 (c), the cantilever flattened by the tensile stress on top of the polysilicon cantilever 20, which had a positive stress gradient before Cu-silicide formation, canceled out with the built-up stress of the compressive stress due to Cu-silicide formation. The stress distribution which 20 has is shown. The built-up stress resulting from Cu-silicided can be controlled according to the silicided temperature. Therefore, it is possible to reduce the shape variation of the cantilever 20 by adjusting the silicided temperature. In addition to the case disclosed in FIG. 2A, when the cantilever has a negative stress gradient, the curved cantilever may be flattened by depositing a Cu-thin film on the lower part of the cantilever, adjusting the temperature, and performing a heat treatment.

When using a Cu-thin film, since the silicided temperature is lower than that of other metals, damage to the integrated circuit may be less, and the surface resistance may be reduced due to the low resistivity of Cu. After Cu-silicided, Cu and Cu oxide which have not reacted with the polysilicon cantilever 20 may remain on the surface of the cantilever, and thus can be selectively removed through a Cu etchant. As an example, the Cu etchant may be a solution mixed with sulfuric acid, hydrogen peroxide, and deionized water at 1: 23: 2000, but is not limited thereto. In addition, the removal of such Cu and Cu oxide may use other methods well known in the art.

3 is another embodiment of a method for producing cantilevers using Cu-silicides. First, the silicon substrate 110 is prepared. About 200 nm thick LPCVD Si ₃ N ₄ may be deposited as the insulating layer 120 on the silicon substrate 110. As shown in FIG. 3A, a 2 μm-thick tetraethylorthosilane (TEOS) film may be deposited as the sacrificial layer 130 on the insulating layer 120. FIG. 3B illustrates a process of etching a portion of the outer end of the sacrificial layer 130. On the insulating layer 120 and the sacrificial layer 130 exposed due to etching, as shown in FIG. 3 (c), 2 µm thick LPCVD polysilicon is used as the cantilever structure layer 140 such as high temperature thermal treatment. It can be deposited without a process. To form the cantilever shape, a portion of the outward end of the cantilever structure layer on the sacrificial layer 130 may be etched away using inductively coupled plasma (ICP) etching to the cantilever structure layer 140. . Since the natural oxide film may be formed on the cantilever structure layer 140 when the external atmosphere is contacted, the natural oxide film on the cantilever structure layer may be removed by immersing the substrate on which the cantilever structure layer 140 is formed in an aqueous hydrogen fluoride fluoride solution. After the oxide film is removed, as shown in Fig. 3 (d), the Cu-thin film 150 having a thickness of about 90 nm is sufficiently low to prevent oxygen contamination, for example, 5.0 x 10 ^-6 torr. The deposition pressure may be deposited on the cantilever structure layer 140 using a thermal evaporator. The above-described pressures and thicknesses are merely selected to describe the embodiments, and the disclosed technique is not limited to the above-described thicknesses and pressures. After the deposition of the Cu-thin film 150, a heat treatment may be performed to form the Cu-silicide 160, as shown in FIG. 3 (e). The lower part of the cantilever, which has a positive stress gradient before silicidation, has a compressive stress and the upper part has a tensile stress. A large compressive stress is generated on the upper part of the cantilever due to the growth of Cu ₃ Si generated by the heat treatment. And the built-up compressive stress due to the formation of Cu ₃ Si can attenuate this tensile stress. Therefore, by controlling the heating temperature in the furnace treatment, it is possible to control the degree of silicidation, thereby controlling the state where the stress is zero. The furnace treatment is possible not only at low temperatures of about 200 ° C. or lower, but also at higher temperatures, for example, about 500 to 700 ° C. The effect of stress due to the formation and growth of Cu-silicide can be investigated using continuous wafer-curve measurements. As described above, when Cu is used, silicidation may be performed at low temperatures, thereby allowing low-thermal-budget control. In addition, when Cu-silicide is used, since Cu-silicided changes in single phase, it is easier to control silicided. In addition, Cu may have low resistance and good electromigration properties such that the cantilever has low surface resistance (about 0.5 μm-cm to 1 μm-cm) through Cu-silicided. This low surface resistance allows the cantilever to have suitable electrical properties for polysilicon micromachining.

Since unreacted Cu or Cu-oxide may remain even after the heat treatment, the residue may be selectively removed from the surface of the cantilever structure layer 140 using a Cu etchant. Subsequently, the substrate may be immersed in an aqueous fluoric acid fluoride solution, and the sacrificial layer 130, the TEOS layer, may be removed. Removal of such sacrificial layer 130 may use methods well known in the art. As the sacrificial layer 130 is removed, as shown in FIG. 3 (f), the cantilever structure layer 140 extends outward from the upper side of the silicon substrate 110, so that a portion thereof floats from the silicon substrate 110. It can be done.

4 illustrates an embodiment of a method for stress gradient mitigation when the cantilever structure has a positive stress gradient and a negative stress gradient. In one example, the cantilever structure may be composed of a support layer 210, an insulation layer 220, and a cantilever layer 230. First, FIG. 4 (a) shows the case where the cantilever layer 230 has a positive stress gradient, that is, when the cantilever layer 230 is bent away from the support layer 210, among the surfaces of the cantilever layer 230. The Cu-thin film 240 may be deposited on the surface opposite to the support layer 210. Thereafter, the thermal treatment may be performed on the Cu-thin film 240, and the thermal treatment temperature may be about 300 ° C. or less, and may be maintained at about 200 ° C. or less. However, the heat treatment temperature is not limited to the above-described range, but may be selected in a higher temperature range. The Cu-thin film 240 and the cantilever layer 230 react through the thermal treatment to form the Cu-silicide 250, and as described in FIG. 2, the stress gradient is relaxed to bend away from the support layer 210. The flatness of layer 230 can be restored.

As shown in FIG. 4B, when the cantilever layer 230 has a negative stress gradient, that is, when the cantilever layer 230 is bent to approach the support layer 210, the surface of the cantilever layer 230 is out of the surface of the cantilever layer 230. Cu-thin film 240 may be deposited on the surface in the direction of support layer 210. Thereafter, the thermal treatment may be performed on the Cu-thin film 240, and the thermal treatment temperature may be about 300 ° C. or less, or may be maintained at about 200 ° C. or less. Cu-silicide 240 and cantilever layer 230 react with each other to form Cu-silicide 250, and the stress gradient is relaxed according to the principle as described in FIG. 2 to approach the support layer 210. The flatness of the bent cantilever layer 230 can be restored. Therefore, the manufacturer of the cantilever structure can restore the cantilever structure to the desired shape by selecting a method more suitable for various shape variations of the cantilever.

Meanwhile, the present embodiment has been described using the cantilever structure of the silicon thin film as an example, but the above description merely illustrates the cantilever structure as an example showing a reduction in stress gradient and surface resistance obtained through Cu-silicide formation. 'S technique is applicable to other silicon thin films and is not limited to cantilever structures only.

Although the embodiments have been described with reference to the accompanying drawings, it will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or features of the present technology. . Accordingly, the above-described embodiments may be modified in arrangement and detail in accordance with the spirit disclosed herein. For example, the material of the cantilever structure is not limited to polysilicon, and various structural layers, insulating layers, and the like are not limited to specific materials. Therefore, the embodiments described above are to be understood in all respects as illustrative and not restrictive, and formal changes and modifications from the disclosed description are considered to be within the scope of the following claims.

Claims (6)

As a method of manufacturing a micromechanical structure comprising a thin film,
Depositing a Cu-thin film on the thin film according to the bending direction of the thin film; And
Performing a thermal treatment on the Cu-thin film to Cu-silicide the thin film surface,
The said heat treatment temperature is 200 degrees C or less, The micromechanical structure manufacturing method. Preparing a substrate on which a cantilever structure layer is formed;
Depositing a Cu-thin film on the cantilever structure layer according to the bending direction of the cantilever structure layer;
Performing a thermal treatment on the Cu-thin film to form Cu-silicide on the cantilever structure layer;
The said heat treatment temperature is 200 degrees C or less, The microcantilever manufacturing method. Preparing a substrate;
Depositing a sacrificial layer on the substrate;
Etching the sacrificial layer to remove a portion of the sacrificial layer;
Depositing a cantilever structure layer on the exposed portion of the substrate and the sacrificial layer by removing a portion of the sacrificial layer;
Depositing a Cu-thin film on the cantilever structure layer according to the bending direction of the cantilever structure layer;
Thermally treating the Cu-thin film to form Cu-silicide in the cantilever structure layer; And
Removing the sacrificial layer;
The said heat treatment temperature is 200 degrees C or less, The microcantilever manufacturing method. The method of claim 3, wherein
And depositing the cantilever structure layer and then removing the native oxide on the cantilever structure layer using an aqueous hydrogen fluoride solution before depositing the Cu-thin film. The method of claim 3, wherein
Before the step of removing the sacrificial layer, further comprising the step of removing Cu and Cu-oxide remaining unsilicided, microcantilever manufacturing method. A method of forming a thin film on a substrate structure having a support layer and a cantilever layer,
The method comprises:
Depositing a sacrificial layer on the support layer;
Etching at least a portion of the sacrificial layer to form the substrate structure;
Removing the native oxide on the cantilever layer with hydrofluoric acid;
When the cantilever layer is bent in a direction away from the support layer, a Cu-thin film is deposited on the surface of the cantilever layer opposite to the support layer, and when the cantilever layer is bent in the direction of the support layer, the cantilever in the direction of the support layer. Depositing a Cu-thin film on the layer surface;
Subjecting the substrate structure to a temperature of 200 ° C. or lower; And
A method of forming a thin film, comprising the step of removing unsilicided Cu or Cu-oxide.

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