TWI420808B - The Manufacturing Method of Bending Plate Wave Micro - sensor - Google Patents

Description

Method for manufacturing curved flat wave micro sensor

The present invention relates to a method of manufacturing a sensor, and more particularly to a method of manufacturing a curved flat wave microsensor.

In conventional MEMS technology, isotropic or anisotropic etch 矽 wafers are key technologies for micro-sensor and actuator processes. Dry and wet etching is most common in conventional etching techniques. Dry etching requires a high vacuum environment and the price of the machine is higher than that of wet etching. Conventional wet etching machines often use time as the basis for evaluating the depth, but when the temperature and concentration of the etching solution are shifted, it is easy to cause The sample produced an undesirable etch depth.

When the thickness of the conventional flexural plate wave (FPW) element is equal to 6 μm, the conventional FPW element has a mass sensitivity of 17200 cm ² g ^-1 and a center frequency of 22.675 MHz, so that its sensing capability is not good. In addition, the conventional FPW device uses a non-electrochemical etching technique to etch the germanium wafer, so that it is difficult to control the etching depth of the FPW device. Furthermore, in the conventional etching technique, the yttrium wafer is etched using a KOH solution, which tends to cause uneven etching surface.

Therefore, it is necessary to provide an innovative and progressive method of manufacturing a curved plate wave micro-sensor to solve the above problems.

The invention provides a method for manufacturing a curved flat wave micro sensor, which comprises the following steps: (a) providing a surface acoustic wave (SAW) element, one side of which is externally and sequentially included a barrier layer, a P-type germanium layer and an N-type epitaxial layer, the barrier layer comprising an opening, the opening revealing a portion of the P-type germanium layer; and (b) performing an electrochemical germanium etch stop process, etching through After the P-type germanium layer, one passivation time of etching the N-type epitaxial layer is controlled, and the thickness of the N-type epitaxial layer after etching is within 3 micrometers (μm).

The manufacturing method of the invention adopts an electrochemical 矽 etch stop process to etch the N-type epitaxial layer of the surface acoustic wave device to within 3 μm to form a curved flat wave micro sensor, thereby reducing the suspended thin plate (N-type Lei The thickness of the wafer layer is such that the operating frequency of the curved plate wave microsensor is lowered and the sensing capability of the curved plate wave microsensor is improved. Moreover, the invention adopts the electrochemical 矽 etch stop process, which can make the product have excellent repetitive process capability, and can precisely control the etch depth to improve the process yield of the curved plate wave micro sensor.

1 is a flow chart showing a manufacturing method of a flexural plate wave (FPW) micro-sensor of the present invention; FIG. 2 is a schematic view showing a surface acoustic wave (SAW) element; and FIG. 3 is a curved plate wave of the present invention. A schematic of a miniature sensor. With reference to FIG. 1 and FIG. 2, first referring to step S11, a surface acoustic wave element 1 is provided. One side of the surface acoustic wave element 1 includes a resistive layer 11, a P-type germanium layer 12 and an N-type from the outside to the inside. The epitaxial layer 13 includes an opening 111, and the opening 111 exposes a portion of the P-type germanium layer 12.

In this embodiment, the barrier layer 11 comprises a layer of thickness 5000. The cerium oxide (SiO ₂ ) film 112 and a layer of thickness 1500 A low stress tantalum nitride (Si ₃ N ₄ ) film 113 is formed on the surface of the P type germanium layer 12.

Referring to FIG. 1 to FIG. 3, referring to step S12, an electrochemical etch stop process is performed. After the P-type germanium layer 12 is etched through, the passivation time of one of the N-type epitaxial layer 13 is controlled to be etched. The thickness of the N-type epitaxial layer 13 is within 3 micrometers (μm) to complete a curved plate wave microsensor 2.

Referring to Figure 4, there is shown a system configuration diagram of the electrochemical etch stop process of the present invention. In FIG. 4, only the P-type germanium layer 12 and the N-type epitaxial germanium layer 13 which are etched in the electrochemical germanium etch stop process are shown.

With reference to FIG. 1 to FIG. 4, in the embodiment, step S12 includes the following steps: step S121, encapsulating the surface acoustic wave component 1 with a fixture 3 (with reference to FIG. 2) and revealing the P-type germanium layer 12, And electrically connecting the N-type epitaxial layer 13 to the negative electrode of the potentiostat 4 such that the P-type germanium layer 12 and the N-type epitaxial layer 13 serve as a working electrode (Work Electrode, WE); step S122 The surface acoustic wave device 1, a counter electrode (CE) and a reference electrode (RE) are packaged in an etching solution 5, and the auxiliary electrode CE is electrically connected to the potentiostat 4 The positive electrode, the reference electrode RE is electrically connected to the potentiostat 4 to provide a stable potential of the etching solution 5; in step S123, the distance between the working electrode WE and the reference electrode RE (indicated by SWR) is adjusted to 1~5 a centimeter, a distance between the reference electrode RE and the auxiliary electrode CE (indicated by SRC) of 1 to 5 cm, an etching potential of -0.3 to -1.5 volts (V), an etching temperature of 60 to 90 ° C, and an etching solution 5 The concentration is 30% by weight (wt%); and in step S124, a peak current appears after etching through the P-type germanium layer 12 (in FIG. 5, = T at room), to control the etching of the N-type epitaxial silicon layer 13 of the passivation time ΔT in 5 to 50 minutes, to complete an electrochemical etch stop silicon process, to complete the production of micro-wave sensor 2 is bent plate.

Preferably, in step S121, the surface acoustic wave element 1 is encapsulated by a Teflon fixture; in step S122, potassium hydroxide (KOH) is selected as the etching liquid 5; in step S123, the working electrode WE is controlled. The distance between the reference electrodes RE is 2 cm, the distance between the reference electrode RE and the auxiliary electrode CE is 2 cm, the etching potential is -0.75 volts, and the etching temperature is 80 ° C. The passivation time ΔT is 37 minutes in step S124. The peak current is 0.6 mA, and the passivation current after etching through the passivation time ΔT is 0.4 mA. The passivation current is a current that exhibits a steady state, which represents that the P-type germanium layer 12 has been etched through the N-type epitaxial layer 13.

In the present invention, the potentiostat 4 can be provided with a voltage source for the electrochemical etch stop process. It is understood that in other applications, the voltage source of the electrochemical 矽 etch stop process can be any device that provides a stable voltage.

The present invention is illustrated by the following examples, which are not intended to be limited to the details disclosed herein.

Example:

In this example, a three-electrode (working electrode WE, auxiliary electrode CE, and reference electrode RE) electrochemical etching system is used to perform an electrochemical etching stop process. The system configuration diagram is as shown in FIG. 4, wherein the etching liquid 5 is Potassium hydroxide (KOH). In the electrochemical etching, in order to prevent the KOH etching solution from eroding the definition pattern of the surface acoustic wave element 1 (refer to FIG. 2), the surface acoustic wave element 1 is protected by a Teflon tool, and the electrochemical device is provided by the potentiostat 4.矽 etching stops the voltage source of the process, and connects the negative electrode of the voltage source to the N-type epitaxial layer 13 in an ohmic contact manner, so that the P-type germanium layer 12 and the N-type epitaxial layer 13 serve as the working electrode WE And the positive electrode of the voltage source is connected to the auxiliary electrode CE via an ammeter, and the reference electrode RE is responsible for providing a stable potential of the KOH etching solution.

In the overall etching process, the control parameters include: the distance between the working electrode WE and the reference electrode RE (SWR), the distance between the reference electrode RE and the auxiliary electrode CE (SRC), the etching potential, the etching temperature, and the passivation time ΔT. The preferred parameter setting range of the overall etching process and the preferred parameter setting values are shown in Table 1.

In the present example, the preferred parameters are set such that the applied voltage is fixed at -0.75 V; the concentration of the KOH etching solution is 30 wt%; the etching temperature is fixed at 80 ° C; and the pitch SWR and the pitch SRC are both set to 2 cm.

After 5 hours of etching, the current versus time relationship shown in FIG. 5 is known to have been etched to the interface between the P-type germanium layer 12 and the N-type epitaxial layer 13 (PN interface), and an obvious result will be produced. The anode current (current peak is about 0.6 mA, followed by a passivation current of 0.4 mA). After a passivation time ΔT for about 37 minutes, the current enters a steady state (about 0.4 mA), which means that the P-type germanium layer 12 has been etched through and etched to a portion of the N-type epitaxial layer 13.

After the electrochemical etching stop process is completed, the thickness of the N-type epitaxial layer 13 after etching is 3 μm, and the roughness thereof is less than ±100 nm. The actual measurement results show that the curved plate wave micro-sensor 2 manufactured by the manufacturing method of the present invention has a mass sensitivity of -8.52×10 ⁷ cm ² g ^-1 and an actual center frequency of 8.75 MHz, so Good quality sensitivity.

The manufacturing method of the invention adopts an electrochemical 矽 etch stop process to etch the N-type epitaxial layer of the surface acoustic wave device to within 3 μm to form a curved flat wave micro sensor, thereby reducing the suspended thin plate (N-type Lei The thickness of the wafer layer is such that the operating frequency of the curved plate wave microsensor is lowered and the sensing capability of the curved plate wave microsensor is improved. Moreover, the invention adopts the electrochemical 矽 etch stop process, which can make the product have excellent repetitive process capability, and can precisely control the etch depth to improve the process yield of the curved plate wave micro sensor.

The above embodiments are merely illustrative of the principles and effects of the invention and are not intended to limit the invention. Therefore, those skilled in the art can make modifications and changes to the above embodiments without departing from the spirit of the invention. The scope of the invention should be as set forth in the appended claims.

1. . . Surface acoustic wave component

2. . . Curved plate wave micro sensor of the invention

3. . . Fixture

4. . . Potentiostat

5. . . Etching solution

11. . . Blocking layer

12. . . P-type layer

13. . . N-type epitaxial layer

111. . . Opening

112. . . Cerium oxide film

113. . . Tantalum nitride film

CE. . . Auxiliary electrode

RE. . . Reference electrode

WE. . . Working electrode

1 is a flow chart showing a manufacturing method of a flexural plate wave (FPW) micro sensor of the present invention;

Figure 2 shows a schematic diagram of a surface acoustic wave (SAW) component;

Figure 3 is a schematic view showing a curved flat wave microsensor of the present invention;

4 is a system configuration diagram showing an electrochemical etch stop process of the present invention; and

Figure 5 is a graph showing current versus time for an electrochemical ruthenium etch stop process in an example of the present invention.

(no component symbol description)

Claims (9)

A method for manufacturing a curved plate wave micro-sensor comprises the steps of: (a) providing a surface acoustic wave (SAW) element, one side of the surface acoustic wave element comprising a barrier layer externally and sequentially; a P-type germanium layer and an N-type epitaxial layer, the barrier layer comprising an opening, a thin film of germanium dioxide and a thin film of tantalum nitride, the opening revealing a portion of the p-type germanium layer, the germanium dioxide film is located Between the P-type ruthenium layer and the tantalum nitride film; and (b) performing an electrochemical etch stop process, after etching the P-type ruthenium layer, controlling etching of a passivation time of the N-type epitaxial layer, etching The thickness of the N-type epitaxial layer is then within 3 micrometers (μm). The method of claim 1, wherein the thickness of the N-type epitaxial layer in the step (a) is 20 μm. The method of claim 1, wherein in the step (b), the surface roughness of the N-type epitaxial layer after etching is within ±100 nanometers (nm). The method of claim 1, wherein the step (b) comprises the steps of: (b1) encapsulating the surface acoustic wave device with a fixture and exposing the P-type germanium layer, and electrically connecting the N-type epitaxial layer to a constant potential a negative electrode of the device such that the P-type germanium layer and the N-type epitaxial layer serve as a working electrode; (b2) the surface acoustic wave device, an auxiliary electrode (Counter Electrode) and a reference after encapsulation The electrode (Reference Electrode) is placed in an etchant, and the auxiliary electrode is electrically connected to the positive potentiometer The reference electrode is electrically connected to the potentiostat to provide a stable potential of the etching solution; (b3) adjusting the distance between the working electrode and the reference electrode to be 1 to 5 cm, and the distance between the reference electrode and the auxiliary electrode 1 to 5 cm, an etching potential of -0.3 to -1.5 volts, an etching temperature of 60 to 90 ° C, a concentration of the etching solution of 30% by weight (wt%); and (b4) when the P-type layer is etched through After a peak current occurs, the passivation time for etching the N-type epitaxial layer is controlled to be 5 to 50 minutes to complete the electrochemical etch stop process. The method of claim 4, wherein the surface acoustic wave element is encapsulated in the step (b1) with a Teflon fixture. The method of claim 4, wherein in the step (b2), the etching liquid is selected from potassium hydroxide (KOH). The method of claim 4, wherein in step (b3), the distance between the working electrode and the reference electrode is 2 cm, the distance between the reference electrode and the auxiliary electrode is 2 cm, the etching potential is -0.75 volt, and etching is performed. The temperature is 80 °C. The method of claim 4, wherein the passivation time is 37 minutes in step (b4). The method of claim 4, wherein the peak current is 0.6 mA in the step (b4), and one passivation current after the passivation time is 0.4 mA.