TWI397959B - Method for making microstructure of polycrystalline silicon - Google Patents

Description

Method for making a composite crystal microstructure

The invention relates to a method for fabricating a microcrystalline structure of a polycrystalline silicon, in particular to a post-processing method for fabricating a component of a polycrystalline silicon as a structural layer in a CMOS process.

In recent years, many advanced countries have used CMOS processes to fabricate MEMS components, and manufacture and integrate various types of micro-sensors, μ-actuators, μ-processors, and micro-optics. Components such as μ-optical devices and electronic circuits are modularized on a single wafer, and MEMS technology is used to miniaturize components and bring many advantages such as high responsivity, high accuracy, and low power loss.

Optical MEMS is a key development area in MEMS. Various micro-optical components manufactured by surface micromachining technology are used to enable successful actuation of microstructures in post-process (Release). ) is the most important process, how to release the microstructure before it is destroyed without destroying the specific structural layer, and the release result directly affects the performance of the component. When the volume of the component is smaller (<0.18 μm), the wafer size is more Large (>8吋), etching selectivity and uniformity are more important, so the complete release microstructure will be the key to the success of using a common process to make MEMS components.

Etching technology can be divided into dry etching (Dry Etching) and wet etching (Wet Etching). Dry etching is anisotropic etching, which has better directivity but is more than wet etching. Poor selectivity, and wet etching is mainly isotropic etching, which has the advantages of simple process, cheap equipment and mass production. To release components of a CMOS-MEMS process using wet etching, The choice between the etchant and the structure and the thickness of the etched material must be considered.

In general, CMOS processes mostly use poly-silicon as the layout of the circuit. However, if a polysilicon is used to fabricate the MEMS microstructure, a high selectivity etching solution must be used in order to perform the etching sacrifice. Layers do not harm the microstructure. However, the selection of a higher etching liquid shortens the etching time, but when the sacrificial layer structure is not completely etched clean, the microstructure of the polycrystalline germanium is also subjected to severe etching. From another point of view, if the sacrificial layer of the component is too thick or the etching rate of the etching solution is slow, resulting in an increase in etching time, the microstructure is excessively etched and damaged.

In view of the above problems, the main object of the present invention is to provide a method for fabricating a germanium germanium microstructure by using a CMOS-MEMS process metal layer capable of blocking the characteristics of dry etching to reduce the thickness of the sacrificial layer and the etching time. The microstructure of the polycrystalline germanium material is successfully released and the integrity of the component is maintained.

Therefore, in order to achieve the above object, the method for fabricating a germanium germanium microstructure disclosed in the present invention is applied to a MEMS device fabricated by a CMOS process, and the MEMs device is a polycrystalline germanium as a structural layer and a metal layer. As an etch barrier to reduce the thickness of the sacrificial layer, the sacrificial layer is etched to the metal layer by dry etching in the first post-process, then the etching is stopped, and then the second post-process is wet-etched first. In addition to the metal layer, removing the sacrificial layer protecting the polysilicon structure layer will shorten the time for etching the sacrificial layer, and also avoid excessive etching to impair the integrity of the structural layer.

In addition, the present invention can utilize the photomask of the side opening design in the first post-process, and etch the sacrificial layer to avoid the process error directly eroding the metal layer and causing the polycrystalline germanium structure layer to be affected. damage. In addition, in the second post-process, the exposed metal layer of the side layer can also be etched, and the sacrificial layer above the metal layer is peeled off, and the sacrificial layer of the protective polysilicon structure layer is etched, thereby greatly reducing the thickness of the sacrificial layer and etching. Time increases the integrity of the component after complete release and the likelihood of successful actuation.

In order to further understand the purpose, features and functions of the present invention, the drawings are described in detail as follows:

Please refer to FIG. 1A to FIG. 1D for a schematic flow chart of a method for fabricating a polysilicon structure according to a first embodiment of the present invention.

In this embodiment, a MEMS device is formed by using a CMOS process as a structural layer. As shown in FIG. 1A, the MEMS device is mainly composed of a germanium-containing substrate 10, a germanium germanium structure layer 20, and an aluminum metal layer 30. The germanium dioxide sacrificial layer 40 and the field oxide layer 50 are formed, and the germanium germanium structure layer 20 is separated from the germanium-containing substrate 10 by the field oxide layer 50, and the metal layer 30 is located above the germanium germanium structure layer 20, and sacrificed. The layer 40 covers the germanium-containing substrate 10, the germanium germanium structure layer 20, the metal layer 30 and the field oxide layer 50, and isolates the metal layer 30 from the germanium germanium structure layer 20. When the MEMS component is fabricated via a CMOS-MEMS shared process platform, a subsequent post-process step is required to release the polysilicon structure layer 20 from the sacrificial layer 40 for successful actuation.

As shown in FIG. 1B, the anisotropic etching by Reactive Ion Etching (RIE) of the first post-process, plus the metal layer 30 can be used as an etch barrier layer, and the dioxide is oxidized. The sacrificial layer 40 is etched to the metal layer 30 above the polysilicon structure layer 20 and then etched to reduce the thickness of the cerium oxide sacrificial layer 40.

As shown in Figure 1C, the second post-process is the use of phosphoric acid that does not react with the cerium oxide material. In accordance with the characteristics, the metal layer 30 protecting the polysilicon structure layer 20 is etched.

Finally, as shown in FIG. 1D, the sacrificial layer 40a around the polysilicon structure layer 20 and the field oxide layer 50 are etched by a cerium oxide etching solution (hydrofluoric acid (HF) or Silox Vapox III) to complete the release. .

This embodiment utilizes the characteristics of the metal barrier RIE etching in the CMOS-MEMS process and the manner in which the germanium is used to protect the microstructure, which can reduce the thickness of the sacrificial layer above the polycrystalline germanium structure layer, and at the same time, the metal layer is sacrificed. The layer thickness is greatly reduced, and this method will successfully release the microstructure in a short time and maintain the integrity of the component.

Furthermore, please refer to FIG. 2A to FIG. 2D, which are schematic flowcharts of a method for fabricating a polysilicon structure according to a second embodiment of the present invention.

This embodiment utilizes a MEMS device fabricated by a CMOS process, as shown in FIG. 2A. Then, in the reactive ion etching process of the first post-process, in order to avoid the process error, the reactive ion etching directly breaks the metal layer 30 to damage the polysilicon structure layer 20, and the side of the photomask is opened by the side. The holes are subjected to reactive ion etching to etch the sacrificial layer 40, and only the side of the metal layer 30 is exposed, that is, the metal layer 30 above the polysilicon structure layer 20 is still subjected to the sacrificial layer 40b over the metal layer 30. The metal layer 30 is protected and utilized to protect the integrity of the germanium structure layer 20, as shown in FIG. 2B.

Then, as shown in FIG. 2C, the second post-process is to first etch the metal layer 30 with phosphoric acid and remove the sacrificial layer 40b over the metal layer 30. Finally, the sacrificial layer 40a and the field oxide layer 50 are etched with a cerium oxide etching solution (hydrofluoric acid (HF) or Silox Vapox III) to release the polycrystalline germanium structure layer 20 as shown in FIG. 2D.

In summary, according to the method for fabricating the microcrystalline structure of the germanium provided by the present invention, the use of the polycrystalline germanium as the main structure of the component can greatly improve the yield and feasibility of the component fabrication.

Although the present invention has been disclosed above in the foregoing embodiments, it is not intended to limit the invention. It is within the scope of the invention to be modified and modified without departing from the spirit and scope of the invention. Please refer to the attached patent application for the scope of protection defined by the present invention.

10‧‧‧Inorganic substrate

20‧‧‧Multilayer structure layer

30‧‧‧metal layer

40‧‧‧ Sacrifice layer

40a‧‧‧ sacrificial layer

40b‧‧‧sacrificial layer

50‧‧‧ field oxide layer

1A to 1D are schematic flow charts showing a method of fabricating a polycrystalline germanium microstructure according to a first embodiment of the present invention.

2A to 2D are schematic flow charts showing a method of fabricating a germanium germanium microstructure according to a second embodiment of the present invention.

10‧‧‧Inorganic substrate

20‧‧‧Multilayer structure layer

30‧‧‧metal layer

40‧‧‧ Sacrifice layer

40a‧‧‧ sacrificial layer

50‧‧‧ field oxide layer

Claims (10)

A method for fabricating a germanium germanium microstructure, the method comprising: providing a MEMS device by using a CMOS process, the MEMS device comprising at least a germanium-containing substrate, a field oxide layer, a germanium germanium structure layer, a metal layer and a a sacrificial layer, the polycrystalline germanium structure layer is separated from the germanium-containing substrate by the field oxide layer, the metal layer is located above the germanium germanium structure layer, and the sacrificial layer covers the germanium-containing substrate, The field oxide layer, the polycrystalline germanium structure layer and the metal layer are separated from the metal germanium structure layer and the metal layer; the sacrificial layer is etched to the metal layer by dry etching to expose the metal layer Removing the metal layer by wet etching; and removing the sacrificial layer and the field oxide layer around the polysilicon structure layer by wet etching. The method for producing a polycrystalline germanium microstructure according to claim 1, wherein the dry etching for exposing the metal layer is reactive ion etching (RIE). The method for fabricating a polycrystalline germanium microstructure according to claim 1, wherein the step of exposing the metal layer is performed by etching a sacrificial layer by using a photomask that is opened at one side, and only exposing the metal layer side The metal layer above the polysilicon structure layer is still protected by the sacrificial layer above the metal layer. A method of fabricating a germanium germanium microstructure as described in claim 3, wherein the step of removing the metal layer removes the sacrificial layer over the metal layer. The method for fabricating a germanium germanium microstructure according to claim 1, wherein the step of removing the metal layer removes a portion of the sacrificial layer above the germanium germanium structure layer. A method of fabricating a germanium germanium microstructure as described in claim 1, wherein the step of removing the metal layer uses phosphoric acid. A method of fabricating a germanium germanium microstructure as described in claim 1, wherein the step of removing the sacrificial layer and the field oxide layer around the germanium germanium structure layer is performed using a cerium oxide etching solution. The method for producing a polycrystalline germanium microstructure according to claim 7, wherein the cerium oxide etching solution is hydrofluoric acid (HF) or Silox Vapox III. The method for producing a polycrystalline germanium microstructure according to claim 1, wherein the sacrificial layer is made of silica dioxide. The method for producing a polycrystalline germanium microstructure according to claim 1, wherein the metal layer is made of aluminum metal.