WO2003027002A2

WO2003027002A2 - Method for the production of a micromechanical structure

Info

Publication number: WO2003027002A2
Application number: PCT/DE2002/002111
Authority: WO
Inventors: Frank Fischer; Lars Metzger
Original assignee: Robert Bosch Gmbh
Priority date: 2001-09-01
Filing date: 2002-06-10
Publication date: 2003-04-03
Also published as: WO2003027002A3

Abstract

The invention relates to a method for the production of a micromechanical structure, comprising the following steps: a micromechanical structure is provided with a first micromechanical structural element (MS) made of a first material and a second micromechanical structure element (OS) made of a second material; a gaseous etching medium (G) is conducted over the micromechanical structure, said etching medium (G) being constituted in such a way that it etches the second material selectively as opposed to the first material in a first temperature range above room temperature; the micromechanical structure is brought to the first temperature range for selective etching of the second material as opposed to the first material.

Description

Manufacturing process for a micromechanical structure

STATE OF THE ART

The present invention relates to a manufacturing method for a micromechanical structure.

Although applicable to any micromechanical components and structures, in particular sensors and actuators, the present invention and the problem on which it is based are explained in relation to a micromechanical structure that can be produced in the technology of silicon surface micromechanics.

In AE Franke, Y. Jiao,. T. Wu, T.-J. King, RT Howe, POST-CMOS MODÜLAR INTEGRATION OF POLY-SIGE MICORSTRUCTURES USING POLY-GE SACRIFICIAL LAYERS, Solid-State Sensor and Actuator Workshop, Hilton Kead Island, South Carolina, June 4-8, 2000 will be a process for manufacturing Surface micromechanical structures are described in which freely movable or functional structures consist of polycrystalline silicon / germanium (poly-SiGe) and in which polycrystalline germanium (poly-Ge) is used for the sacrificial layer. The materials used in this process make the integration of surface micromechanical generated structures in a standard CMOS process.

Integration is not possible when generating MΞMS (MΞMS = Micro Electromechanical Systems) structures from polycrystalline silicon, since very high temperatures of up to 1100 ° C are required for the layer deposition and the subsequent doping process. See DE 195 37 814 AI. These high temperatures are not compatible with the aluminum or copper materials of a CMOS process.

In standard MEMS processes, Si0 ₂ serves as a sacrificial layer. The sacrificial layer is removed in hydrofluoric acid or by a hydrofluoric acid gas phase etching process. Both methods attack the materials of the CMOS process and are therefore not compatible. In order to be able to integrate MEMS structures in a CMOS process, the materials for the micromechanical structures and the processes for structuring them must be compatible.

According to the article by AE Franke et al. shows that polycrystalline silicon / germanium (poly-SiGe) and polycrystalline germanium (poly-Ge) meet the above requirements. Both materials are deposited in an LPCVD reactor at temperatures around 450 ° C (poly-SiGe) and 375 ° C (poly-Ge). The deposited layers have a low layer resistance and have low voltages, which means that temperature treatment after the deposition is not necessary. The polycrystalline The silicon / germanium layer can be structured using the plasma etching processes known in semiconductor technology. The germanium sacrificial layer can be etched selectively to the silicon / germanium layer with hot hydrogen peroxide (H ₂ 0 ₂ ). Since Si0 ₂ and aluminum are not attacked by the etching solution H ₂ O ₂ , this etching process can be integrated into the CMOS process. The disadvantages of this method are the wet chemical structuring of the germanium sacrificial layer.

5a-d show an illustration of the essential process steps of a known method.

In FIG. 5a, S denotes a substrate, MS a micromechanical structural element in the form of an asymmetrical T bar made of polysilicon and OS a sacrificial layer made of germanium. Using said liquid etching medium EM in the form of H ₂ 0 ₂ . the sacrificial layer OS is etched, as illustrated in FIG. 5b. 5c, d during the drying process, there may be "sticking" between the free-standing structures and the substrate S. This is due to the fact that capillary forces KK occur between the micromechanical structural element MS and the substrate S due to residues of the liquid etching medium EM, which cause permanent ADH adhesion.

To avoid this, a very complex drying process is necessary, such as drying with CO? (also known as C0 ₂ critical point drying). It is also with wet chemical etching processes not possible to etch out narrow and long structures, such as channels, because the capillary forces KK severely impair the media flow.

The general problem underlying the present invention is therefore to provide a dry etching method which does not have the disadvantages of the known wet etching method mentioned.

ADVANTAGES OF THE INVENTION

The idea underlying the present invention according to claim 1 is to provide a dry etching process in which a micromechanical material can be etched selectively in relation to another micromechanical material in a predetermined temperature range above room temperature. Due to the selectivity, no passivation layers are necessary. The first micromechanical material is preferably germanium and the second micromechanical material is silicon, silicon oxide, silicon nitride or silicon germanium. In this case, molecular chlorine (Cl ₂ ) is preferably used as the etching medium. Since germanium does not react spontaneously with chlorine, the etching process must be activated thermally. This can be done either by a heating process or by a thermal absorption process.

The selectivity of the etching medium with respect to the first material is achieved in that for the etching of the second Materials lower temperatures than are required for the etching of the first material. This provides a temperature window in which the second material can be selectively etched relative to the first material. Regarding the materials germanium / silicon, the possibility of selective etching was reported in K. Ikeda, S. Imai, M. Matsumara, Atomic layer etching of germanium, Applied Surface Science, Volume 112, 1997, pages 87-91.

"Sticking" can therefore not occur in the method according to the invention, since the second material is etched out of the gas phase.

Advantageous developments and improvements of the subject matter of the invention can be found in the subclaims.

According to a preferred development, the first micromechanical structural element is a T-bar, e.g. made of polysilicon.

According to a further preferred development, the first material is selected from the following group: silicon, in particular polysilicon, silicon oxide, silicon nitride, silicon germanium.

According to a further preferred development, the second micromechanical structural element is a sacrificial layer. According to a further preferred development, the second material is germanium. This material can be etched with the etching medium chlorine gas particularly well, thermally activated, selectively with respect to silicon and silicon compounds.

According to a further preferred development, the micromechanical structure is provided on a substrate.

According to a further preferred development, the entire micromechanical structure is brought to a temperature in the first temperature range.

According to a further preferred development, the second micromechanical structural element is brought selectively to a temperature in the first temperature range by radiation absorption.

According to a further preferred development, the conduction of the gaseous etching medium over the micromechanical structure is started at room temperature before the micromechanical structure is brought into the first temperature range.

DRAWINGS

Embodiments of the invention are shown in the drawing and explained in more detail in the following description. Show it :

1 shows a schematic illustration of an etching reactor for carrying out a first embodiment of the method according to the invention;

2a-ά a representation of the essential process steps of the first embodiment of the method according to the invention;

3 shows a schematic representation of an etching freak for carrying out a second embodiment of the method according to the invention;

4a-d show the essential process steps of the second embodiment of the method according to the invention; and

5a-d show the essential process steps of a known method.

DESCRIPTION OF THE EMBODIMENTS

In the figures, identical reference symbols designate identical or functionally identical components.

1 shows a schematic representation of an etching reactor for carrying out a first embodiment of the method according to the invention. In FIG. 1, in addition to the reference symbols R already introduced, denote an etching reactor, E a gas inlet for an etching gas G, here Cl ₂ , A a gas outlet, SH a substrate holder and WH a resistance heater with which the etching reactor R is surrounded.

The etching reactor R is connected to a gas supply system (not shown) for the inlet of the etching gas G in the form of CL ₂ and to a vacuum unit (not shown). The substrate S, here in the form of a wafer, can be heated by the resistance heater WH or by heating the substrate holder SH, not shown.

2a-d show a representation of the essential process steps of the first embodiment of the method according to the invention.

According to FIG. 2a, the dry etching process begins with the inlet of chlorine gas into the etching reactor R, in which the micromechanical structure is located on the substrate holder SH. This happens at room temperature. The chlorine gas located in the etching reactor R adsorbs on the germanium surface of the sacrificial layer OS and forms a GeCl _x layer there, ie various stoichiometric compounds with chlorine, such as GeCl and GeCl ₂ . These reaction products can j ^'edoch at room temperature does not desorb. In order to then activate the etching process, the etching reactor is heated by means of the resistance heater WH to a temperature in the temperature range 300 ° C. <T <600 ° C., preferably 400 ° C. The result of the thermally supplied energy is that the reaction products in the form of GeCl _{2 can} desorb from the germanium surface or the reaction products in the form of GeCl are converted into reaction products in the form of GeCl _Ξ . Of course, the chlorine gas also adsorbs on the micromechanical structural element MS in the form of the T-bar. However, a lower temperature is required for the desorption of GeCl ₂ than for the desorption of SiCl ₂ . The latter requires a temperature of at least 600 ° C. Because of this behavior, a large temperature window 300 ° C <T <600 ° C is available, in which one can selectively etch the germanium of the sacrificial layer OS against the silicon of the T-beam MS.

If the resistance heater WH is kept constant at the elevated temperature of, for example, 400 ° C. and chlorine gas G is continuously introduced into the etching reactor R, then a continuous etching of the germanium sacrificial layer OS takes place, as illustrated in FIG. 2d, which ultimately results in FIG 2e shows the state in which the sacrificial layer OS has been completely removed.

3 show a schematic illustration of an etching reactor for carrying out a second embodiment of the method according to the invention. The embodiment of the etching reactor R shown in FIG. 3 differs from the embodiment shown in FIG. 1 in that, instead of the resistance heater WH, a light source LQ for emitting radiation of a certain one

Energy hv is provided.

4a-d show the essential process steps of the second embodiment of the method according to the invention.

B and 4b begin in the same way as in the first exemplary embodiment explained above in connection with FIG. 2.

According to FIG. 4c, however, the entire micromechanical structure is then not heated by a heater, but rather the heating takes place selectively through the absorption of the light radiation by the light source LQ.

Due to the smaller band gap of germanium compared to silicon, the wavelength of the incident light hv can be selected such that the light passes through the silicon of the micromechanical structural element MS and the sacrificial size OS is absorbed in the germanium. This leads to local heating of the sacrificial layer OS. In other words, in order for the light energy to be absorbed by the germanium sacrificial layer OS, the energy of the radiation must be greater than the bandgap of the germanium. However, in order to To prevent silicon from heating up, the energy of the radiation must be less than the bandgap of the silicon.

The aforementioned radiation absorption also makes it possible to set a temperature in the range 300 ° C. <T <600 ° C., preferably 400 ° C., which leads to the etching behavior already described, which is illustrated for this embodiment in FIGS. 4d and 4e.

Although the present invention has been described above on the basis of preferred exemplary embodiments, it is not restricted to these but can be modified in a variety of ways.

In particular, the method according to the invention is of interest not only for the sacrificial layer etching illustrated above, but generally for the selective structuring of a certain material, e.g. Germanium, compared to other materials known in semiconductor technology.

Claims

Manufacturing process for a micromechanical structure

1. Manufacturing method for a micromechanical structure with the steps:

Providing a micromechanical structure with a first micromechanical structure element (MS) made of a first material and a second micromechanical structure element (OS) made of a second material;

Guiding a gaseous etching medium (G) over the micromechanical structure, the etching medium (G) being such that it selectively etches the second material with respect to the first material in a first temperature range above room temperature;

Bring the micromechanical structure into the first temperature range for selective etching of the second material compared to the first material.

2. The method according to claim 1, characterized in that the first micromechanical structural element (MS) is a T bar.

3. The method according to claim 1 or 2, characterized in that the first material is selected from the following group: silicon, in particular polysilicon, silicon oxide, silicon nitride, silicon germanium.

4. The method according to any one of the preceding claims, characterized in that the second micromechanical structural element (OS) is a sacrificial layer.

5. The method according to any one of the preceding claims, characterized in that the second material is germanium.

6. The method according to any one of the preceding claims, characterized in that the etching medium (G) is chlorine gas.

7. The method according to any one of the preceding claims, characterized in that the micromechanical structure is provided on a substrate (1).

8. The method according to any one of the preceding claims, characterized in that the entire micromechanical structure is brought to a temperature in the first temperature range.

9. The method according to any one of the preceding claims, characterized in that the second micromechanical structural element (OS) selectively by radiation absorption is brought to a temperature in the first temperature range.

10. The method according to any one of the preceding claims, characterized in that the conduction of the gaseous etching medium over the micromechanical structure is started at room temperature before the micromechanical structure is brought into the first temperature range.