Method for patterning metal in MEMS etching deep hole

Abstract

The invention discloses a method for patterning metal in a deep hole etched by an MEMS (Micro Electro Mechanical System). The method comprises the following steps: S1, forming a deep hole in the surface of a wafer by adopting a composite mask process, and then carrying out metal deposition to form a metal layer; s2, EPR is coated on the surface of the metal layer in the S1 to form an EPR layer, then photoresist is sprayed on the surface of the EPR layer to form a photoresist layer, after the contact time of the photoresist layer and the EPR layer is longer than or equal to 10 s, spin coating is carried out to form a photoresist layer, exposure and corrosion are carried out to remove the metal layer in other areas except the deep hole, and then the photoresist layer in the deep hole is removed. According to the method, the surface of the metal layer is coated to form the EPR layer, so that the photoresist can be effectively promoted to quickly and fully fill the space above the metal layer in the deep hole, and the thickness difference is formed between the photoetching layer in the deep hole region and the photoetching layer in other regions, thereby ensuring that the protective layer is formed on the surface of the metal layer in the deep hole after the developing process, and further realizing the metal patterning in the deep hole.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, and more particularly, to a method for metal patterning in deep holes of MEMS etching. Background Art

[0002] Microelectromechanical systems (MEMS) refer to micro-devices or systems with characteristic dimensions between 1 nm and 1 mm, integrating micro-mechanisms, micro-sensors, signal processing circuits, signal control circuits, and micro-actuators. With the increasing requirements of consumer electronics for increasing storage capacity and reducing package size, traditional silicon surface processing such as etching or microfabrication in MEMS technology is difficult to meet the actual application needs. The processing of silicon-based substrates is no longer limited to their surfaces, but is developing towards more complex three-dimensional structures, and high aspect ratio structures are an important direction.

[0003] The high aspect ratio structure in MEMS refers to a structure with vertical sidewalls where the ratio of the height to the width of the micro-structure or the ratio of the depth to the width of the hole is relatively large. Currently, high aspect ratio structures are mainly fabricated by deep silicon etching, and then a metal film is formed at the bottom of the high aspect ratio structure by combining photoresist and thin film deposition. This method generally first forms a patterned structure with deep holes by using a composite mask process (mainly including processes such as wafer cleaning, thin film deposition, lithography, etching, and photoresist removal), and deposits a metal film in all regions, then spins on photoresist as a whole, and then removes the photoresist to expose the metal film, and then obtains metal patterning in the deep holes by etching away the metal film on the surfaces of other regions except the deep hole regions; however, it is found in actual application that the photoresist is difficult to fully fill the deep holes, resulting in the metal film at the bottom being etched away together during the etching process of some deep holes, and thus metal patterning in the deep holes cannot be achieved. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for metal patterning in deep holes of MEMS to overcome the defects or deficiencies that the existing methods are difficult to achieve metal patterning in high aspect ratio structures in MEMS.

[0005] The above object of the present invention is achieved by the following technical solutions:

[0006] The present invention protects a method for metal patterning in deep holes of MEMS etching, including the following steps:

[0007] S1. Form deep holes on the surface of the wafer by using a composite mask process, and then deposit a metal layer.

[0008] S2. Coat the surface of the metal layer in S1 with EPR to form an EPR layer, then spray photoresist on the surface of the EPR layer to form a photoresist layer, and spin-coat to form a photoresist layer after the contact time between the photoresist layer and the EPR layer is ≥ 10 s, then expose and etch to remove the metal layer in other areas except the deep holes, and then remove the photoresist layer in the deep holes; wherein, the EPR is a photoresist stripping solution.

[0009] The inventors' research found that during the metal patterning process in the deep holes of MEMS etching, before coating the photoresist on the surface of the metal layer, first coating a layer of EPR (photoresist stripping solution) can effectively promote the subsequent coated photoresist to quickly and fully fill the space above the metal layer in the deep holes, making the thickness difference between the photoresist layer in this deep hole area and that in other areas, so as to ensure that a protective layer is formed on the surface of the metal layer in the deep holes after the development process, avoiding the damage of the metal layer in the deep holes when etching and removing the metal layer in other areas, and thus realizing the metal patterning in the deep holes. Moreover, it was further found that the contact time between the photoresist layer and the EPR layer plays a key role in the final metal patterning in the deep holes. When the contact time between the two layers is too short, it is difficult to effectively promote the photoresist to enter the deep holes to form a protective layer, resulting in the damage of the metal layer in some deep holes during the process of etching and removing the metal layer in other areas, and it is difficult to realize the metal patterning in the deep holes.

[0010] Optionally, the contact time between the photoresist layer and the EPR layer in S2 is 10 - 45 s, preferably 10 - 30 s, more preferably 10 - 15 s, and specifically can be 11 s, 12 s, 13 s or 14 s.

[0011] Optionally, the mass ratio of the EPR to the photoresist in S2 is (10 - 100):(3 - 15); wherein, by weight, the EPR can be 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, 75 parts, 80 parts, 85 parts, 90 parts or 95 parts, and the photoresist can be 4 parts, 6 parts, 8 parts, 10 parts, 12 parts or 14 parts.

[0012] Optionally, the depth of the deep holes in S1 is 30 - 400 μm, and the hole diameter of the deep holes is 50 - 60 μm.

[0013] Generally, the thickness of the metal layer in S1 is less than the depth of the deep holes; optionally, the thickness of the metal layer in S1 is 10 nm - 5 μm. The metal layer is a metal film obtained by using evaporation or sputtering thin film deposition technology, and for example, it can be an Au film, an Al film or a Cr film.

[0014] Optionally, the photoresist stripping solution described in S2 is at least one of an acidic stripping solution, an alkaline stripping solution, or a solvent-based stripping solution; preferably, it is a mixture composed of propylene glycol monomethyl ether and propylene glycol monomethyl ether acetate in a mass ratio of (65 wt% to 75 wt%):(25 wt% to 35 wt%). Among them, the propylene glycol monomethyl ether can specifically be 66 wt%, 68 wt%, 70 wt%, 72 wt%, or 74 wt%, and the propylene glycol monomethyl ether acetate can specifically be 26 wt%, 28 wt%, 30 wt%, 32 wt%, or 34 wt%.

[0015] Optionally, the photoresist described in S2 is at least one of an ultraviolet positive photoresist or an ultraviolet negative photoresist; preferably, it is an ultraviolet positive photoresist.

[0016] Preferably, the rotation speed of spin coating in S2 is 50 to 1800 U / min. The rotation speed of spin coating can be selected according to actual production requirements.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] In the method for metal patterning in the deep holes of MEMS etching of the present invention, before coating the photoresist on the surface of the metal layer, a photoresist stripping solution is first coated, which can effectively promote the subsequent coated photoresist to quickly and fully fill the space above the metal layer in the deep holes, so that a thickness difference is formed between the deep hole area and the photoresist layer in other areas, thereby ensuring that a protective layer is formed on the surface of the metal layer in the deep holes after the development process, avoiding damage to the metal layer in the deep holes when etching and removing the metal layer in other areas, and thus realizing metal patterning in the deep holes. Description of the Drawings

[0019] Figure 1 It is a schematic flow chart of the method for metal patterning in the deep holes of MEMS etching of the present invention.

[0020] Figure 2 It is a schematic diagram of steps S1 to S3 in Example 1.

[0021] Figure 3 It is a schematic diagram of steps S4 to S7 in Example 1.

[0022] Figure 4 It is the metal-patterned SOI wafer (a) after step S4 in Example 1 and an enlarged view (b) of a local deep hole.

[0023] Figure 5 It is the SOI wafer (a) after step S6 in Comparative Example 2 and an enlarged view (b) of a local deep hole.

[0024] Figure 6 It is the SOI wafer (a) after step S6 in Comparative Example 1 and an enlarged view (b) of a local deep hole.

[0025] Figure 7 It is a magnified view of the SOI wafer (a) and the local deep holes (b) after the completion of step S6 in Example 1. Detailed implementation manners

[0026] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the technical field.

[0027] Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0028] The thickness of the top silicon oxide layer of the SOI wafer is 1 μm, and the thickness of the buried oxide layer is 1 μm;

[0029] The EBR is the diluent OK73 THINNER produced by Changchun Institute of Applied Chemistry (Changshu) Co., Ltd., and its composition is: 70 wt% of propylene glycol monomethyl ether and 30 wt% of propylene glycol monomethyl ether acetate;

[0030] The photoresist is the ultraviolet positive photoresist with the model of KMP C7510 produced by Beijing Kehua Microelectronics Co., Ltd.

[0031] Example 1

[0032] A method for patterning metal in deep holes of MEMS etching, comprising the following steps (as Figure 1 shown):

[0033] S1. Using a positive photoresist process, spin-coat the surface of the SOI wafer automatically to form a photoresist layer with a thickness of 3 μm, perform patterning exposure and development using a lithography machine, and then perform RIE etching (etching parameters: CHF 3 :Ar = 1:1 sccm, pressure of 32 mTorr, etching time of 24 min for three cycles) to etch the SiO 2 barrier layer on the top silicon of the SOI wafer to 0.1 - 0.4 μm below the silicon surface, and use NMP (N-methylpyrrolidone) as a photoresist remover to remove the photoresist, forming an oxidized layer patterned SOI wafer;

[0034] S2. Use the positive photoresist process to automatically spin coat the surface of the patterned SOI wafer with an oxide layer (photoresist thickness is 10 μm). Use a lithography machine to expose and develop the secondary overlay pattern, and then etch it using the DRIE-Bosch process to etch the secondary overlay pattern to the required depth (400 μm). Remove the photoresist and clean the SOI wafer;

[0035] S3. Use the surface oxide layer as the secondary barrier layer and the buried oxide layer as the etch stop layer (composite mask process). The etch depth is 50 μm. Continue to use the DRIE-Bosch process to etch the exposed silicon surface for a second time to form an SOI wafer with deep hole steps;

[0036] S4. Use the electron beam evaporation process to deposit a metal layer on the surface of the SOI wafer to form a metal-patterned SOI wafer; among them, the metal deposition layer in the stepped deep hole is at the deep hole pattern, and the metal layer thickness is for metal patterning;

[0037] S5. Fix the metal-patterned SOI wafer on an automatic spin coater, and use EBR to evenly coat the surface of the metal-patterned SOI wafer and rotate it at a low speed (100 U / min) for 3 seconds so that EBR is evenly distributed on the surface of the SOI wafer; then evenly spray photoresist onto the surface of the EBR layer to form a photoresist layer. After contacting for a certain time, form a metal-patterned SOI wafer covered with photoresist at a high speed (3000 U / min);

[0038] S6. Use flood exposure to expose the entire wafer (light intensity is 350 mJ / mm 2 ², exposure time is 17 s), and then perform development processing (developer is NMD-3, development time is 50 s) to obtain a photoresist layer that has formed a protective metal pattern at the bottom of the deep hole covered with photoresist;

[0039] S7. Use the wet etching process (etchant is Au etchant, etchant temperature is 70 °C, etching time is 3 min) to etch away the metal layer in areas other than the deep hole area, and then use NMP to dissolve the photoresist in the deep hole area and clean it to obtain the formed metal pattern at the bottom of the deep hole.

[0040] Among them, the above steps S1 to S3 are as Figure 2 shown, and steps S4 to S7 are as Figure 3 shown.

[0041] Example 2

[0042] A method for patterning metal in deep holes of MEMS etching, including the following steps (as Figure 1 shown):

[0043] S1. Use the positive photoresist process to automatically spin-coat a photoresist layer with a thickness of 3 - 10 μm on the surface of the SOI wafer. Use a lithography machine for patterning exposure and development processing, and then perform RIE etching (etching parameters: CHF 3 :Ar = 1:1 sccm, pressure of 32 mTorr, etching time of 24 min for three cycles) to etch the SiO 2 barrier layer on the top silicon of the SOI wafer to 0.1 - 0.4 μm below the silicon surface. Use NMP as the photoresist remover to remove the photoresist and form an oxidized layer patterned SOI wafer;

[0044] S2. Use the positive photoresist process to automatically spin-coat (photoresist thickness is 10 μm) on the surface of the oxidized layer patterned SOI wafer. Use a lithography machine to expose and develop the secondary overlay pattern, and then etch it with the DRIE - Bosch process to etch the secondary overlay pattern to the required depth (400 μm), and remove the photoresist and clean the SOI wafer;

[0045] S3. Use the surface oxide layer as the secondary barrier layer and the buried oxide layer as the etching stop layer (composite mask process), with an etching depth of 50 μm. Continue to use the DRIE - Bosch process to etch the exposed silicon surface for secondary etching to form an SOI wafer with deep hole steps;

[0046] S4. Use the electron beam evaporation process to deposit a metal layer on the surface of the SOI wafer to form a metal patterned SOI wafer; among them, the metal deposition layer in the stepped deep hole is at the deep hole pattern, and the metal layer thickness is for metal patterning;

[0047] S5. Fix the metal patterned SOI wafer on an automatic spin coater, and apply EBR evenly on the surface of the metal patterned SOI wafer and rotate it at a low speed (100 U / min) for 3 seconds to make the EBR evenly distributed on the surface of the SOI wafer; then evenly spray photoresist onto the surface of the EBR layer to form a photoresist layer. After contacting for a certain time, form a metal patterned SOI wafer covered with photoresist at a high speed (3000 U / min);

[0048] S6. Perform exposure processing on the entire wafer using flood exposure (light intensity is 300 - 700 mJ / mm 2 ², exposure time is 17 s), and then perform development processing (developer is NMD - 3, development time is 50 s) to obtain a photoresist layer that protects the metal pattern at the bottom of the deep hole covered with photoresist;

[0049] S7. Use the wet etching process (etching solution is Au etching solution, etching solution temperature is 70 °C, etching time is 3 min) to etch the metal layer in areas other than the deep hole area, and then use NMP to dissolve the photoresist in the deep hole area and clean it to obtain the metal pattern formed at the bottom of the deep hole.

[0050] Example 3

[0051] A method for metal patterning in deep holes of MEMS etching, comprising the following steps (as Figure 1 shown):

[0052] S1. Using a positive photoresist process, spin-coat the surface of the SOI wafer automatically to form a photoresist layer with a thickness of 3 - 10 μm. Use a lithography machine for patterned exposure and development, and then perform RIE etching (etching parameters: CHF 3 :Ar = 1:1 sccm, pressure of 32 mTorr, etching time of 24 min for three cycles) to etch the SiO 2 barrier layer on the top silicon of the SOI wafer to 0.1 - 0.4 μm below the silicon surface. Use NMP as the photoresist remover to remove the photoresist, forming an oxidized layer patterned SOI wafer;

[0053] S2. Using a positive photoresist process, spin-coat the surface of the oxidized layer patterned SOI wafer automatically (photoresist thickness is 10 μm). Use a lithography machine to expose and develop the secondary overlay pattern, and then etch using the DRIE - Bosch process to etch the secondary overlay pattern to the required depth (400 μm). Remove the photoresist and clean the SOI wafer;

[0054] S3. Using the surface oxide layer as the secondary barrier layer and the buried oxide layer as the etch stop layer (composite mask process), etch to a depth of 50 μm. Continue to use the DRIE - Bosch process to etch the exposed silicon surface for secondary etching, forming an SOI wafer with deep hole steps;

[0055] S4. Use an electron beam evaporation process to deposit a metal layer on the surface of the SOI wafer, forming a metal patterned SOI wafer; among them, the metal deposition layer in the stepped deep hole is at the deep hole pattern, and the metal layer thickness is for metal patterning;

[0056] S5. Fix the metal patterned SOI wafer on an automatic spin coater, and use EBR to evenly coat the surface of the metal patterned SOI wafer and rotate at a low speed (100 U / min) for 3 seconds to make the EBR evenly distributed on the surface of the SOI wafer; then evenly spray photoresist onto the surface of the EBR layer to form a photoresist layer. After contacting for a certain time, form a metal patterned SOI wafer covered with photoresist at a high speed (3000 U / min);

[0057] S6. Perform exposure treatment on the entire wafer using flood exposure (light intensity is 300 - 700 mJ / mm 2 ², exposure time is 17 s), and then perform development treatment (developer is NMD - 3, development time is 50 s) to obtain a photoresist layer that has formed a protected metal pattern at the bottom of the deep hole covered with photoresist;

[0058] S7. Use a wet etching process (the etching solution is an Au etching solution, the temperature of the etching solution is 70 °C, and the etching time is 3 min) to etch the metal layer in areas other than the deep hole area, and then use NMP to dissolve the photoresist in the deep hole area and clean it to obtain the metal pattern at the bottom of the formed deep hole.

[0059] Comparative Example 1

[0060] A method for patterning metal in MEMS etched deep holes includes steps substantially the same as those in Example 1, except that: after uniformly spraying photoresist onto the surface of the EBR layer to form a photoresist layer in step S5, a metal-patterned SOI wafer covered with photoresist is directly formed at a high rotation speed (3000 U / min).

[0061] Comparative Example 2

[0062] A method for patterning metal in MEMS etched deep holes includes steps substantially the same as those in Example 1, except that step S5 is: fixing the metal-patterned SOI wafer on an automatic spin coater, uniformly spraying photoresist onto the surface of the metal-patterned SOI wafer to form a photoresist layer, and then forming a metal-patterned SOI wafer covered with photoresist at a high rotation speed (3000 U / min).

[0063] Table 1 EBR, photoresist, deep holes, and metal layers in Examples 1 to 3

[0064]

[0065]

[0066] Performance test

[0067] Use an Olympus metallographic optical microscope to observe the coverage of the photoresist in the deep holes of the metal-patterned SOI wafers in each example and comparative example in step S6 to evaluate the effect of patterning metal in MEMS etched deep holes.

[0068] According to Figure 4 It can be seen that the metal-patterned SOI wafer in step S4 of Example 1 has a comb-shaped deep hole structure, and the deep hole structures in Examples 2 and 3 and Comparative Examples 1 and 2 are the same as those in Example 1. According to Figure 5 It is known that when simply coating photoresist onto the surface of the metal-patterned SOI wafer, the photoresist cannot fill into the comb-shaped deep hole structure to form a photoresist layer; according to Figure 6It can be found that even if an EBR layer is first formed on the surface of a metal-patterned SOI wafer and then photoresist is uniformly sprayed onto the surface of the EBR layer to form a photoresist layer, if the contact time between the two layers is too short, the photoresist can only partially fill the comb-shaped deep holes and it is difficult to completely cover the deep holes, and an effective photoresist layer cannot be formed either. According to Figure 7 It can be seen that an EBR layer is first formed on the surface of a metal-patterned SOI wafer, then photoresist is uniformly sprayed onto the surface of the EBR layer to form a photoresist layer, and the two layers are allowed to contact for a certain period of time (greater than or equal to 10 s) before the photoresist can quickly fill and completely cover the comb-shaped deep holes to form an effective photoresist layer, thereby preventing the metal layer in the deep holes from being corroded and further realizing metal patterning in the deep holes.

[0069] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for patterning metal in MEMS deep hole etching, characterized in that: The following steps are involved: S1. Use a composite mask process to form deep holes on the surface of the wafer, and then perform metal deposition to form a metal layer; S2. Coat EPR on the surface of the metal layer in S1 to form an EPR layer, then spray photoresist on the surface of the EPR layer to form a photoresist layer, and after the contact time between the photoresist layer and the EPR layer is ≥10s, spin coat to form a photoresist layer, expose and corrode to remove the metal layer in other areas outside the deep hole, and then remove the photoresist layer in the deep hole; wherein, the EPR is a photoresist stripping liquid.

2. The method according to claim 1, characterized in that: The contact time between the photoresist layer and the EPR layer in S2 is 10 to 15 seconds.

3. The method according to claim 1, characterized in that: The mass ratio of EPR to photoresist in S2 is (10-100):(3-15).

4. The method according to claim 1, characterized in that: The depth of the deep hole in S1 is 30 to 400 μm.

5. The method according to claim 4, characterized in that: The diameter of the deep hole in S1 is 50 to 600 μm.

6. The method according to claim 1, characterized in that: The thickness of the metal layer in S1 is smaller than the depth of the deep hole.

7. The method according to claim 6, characterized in that: The thickness of the metal layer in S1 is 10 nm to 5 μm.

8. The method according to any one of claims 1 to 3, characterized in that: The photoresist stripping solution is at least one of an acidic stripping solution, an alkaline stripping solution or a solvent stripping solution.

9. The method according to any one of claims 1 to 3, characterized in that: The photoresist in S2 is at least one of a UV positive photoresist and a UV negative photoresist.

10. The method according to claim 1, characterized in that: The rotation speed of the spin coating in S2 is 50 to 1800 U / min.

Images