WO2023078137A1 - 具有弧形底角的凹槽的制备方法、mems麦克风的制备方法 - Google Patents

具有弧形底角的凹槽的制备方法、mems麦克风的制备方法 Download PDF

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Publication number
WO2023078137A1
WO2023078137A1 PCT/CN2022/127652 CN2022127652W WO2023078137A1 WO 2023078137 A1 WO2023078137 A1 WO 2023078137A1 CN 2022127652 W CN2022127652 W CN 2022127652W WO 2023078137 A1 WO2023078137 A1 WO 2023078137A1
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Prior art keywords
groove
layer
arc
window
photoresist layer
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PCT/CN2022/127652
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English (en)
French (fr)
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陈家伟
宋健
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绍兴中芯集成电路制造股份有限公司
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Publication of WO2023078137A1 publication Critical patent/WO2023078137A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R31/00—Apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/005—Electrostatic transducers using semiconductor materials
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/04—Microphones
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2201/00—Details of transducers, loudspeakers or microphones covered by H04R1/00 but not provided for in any of its subgroups
    • H04R2201/003—Mems transducers or their use

Definitions

  • the invention relates to the technical field of semiconductors, in particular to a method for preparing a groove with an arc-shaped bottom angle and a method for preparing a MEMS microphone.
  • gate trenches need to be formed in trench field effect transistors
  • isolation trenches need to be formed in trench isolation structures
  • cavities need to be formed in MEMS devices.
  • the preparation method for the groove generally includes: forming a photoresist layer on the layer to be etched, and performing an etching process to form the groove in the layer to be etched.
  • the wet etching process is usually used in the existing process, but the wet etching process is isotropic etching, which leads to the etching accuracy of the layer to be etched It is difficult to control, and the size of the formed grooves is also prone to deviation.
  • the purpose of the present invention is to provide a method for preparing grooves with arc-shaped bottom angles, so as to solve the problem that the etching precision is difficult to control in the existing technology.
  • the present invention provides a method for preparing grooves with arc-shaped bottom angles, comprising: forming a photoresist layer on the layer to be etched, and opening a first size opening in the photoresist layer and performing a plasma etching process to form a groove in the layer to be etched, comprising: sequentially consuming the layer to be etched exposed to the window through the window to first etch step to form a groove with the first opening size; the photoresist material of the photoresist layer gradually extends to the center of the window, and the opening size of the window is gradually reduced, so as to reduce the opening size of the groove in the second etching stage
  • the consumption at the bottom corner position gradually increases from the edge of the groove to the center, and the bottom corner of the groove is modified into an arc shape.
  • the etching selectivity ratio of the layer to be etched and the photoresist layer is greater than or equal to 10.
  • the etching gas used in the plasma etching process includes fluorine-containing gas.
  • the fluorine-containing gas includes, for example, carbon tetrafluoride. It may further include: argon, oxygen and carbon monoxide.
  • etchant is deposited on the top surface of the photoresist layer until the second etching stage deforms the photoresist layer to extend toward the center of the window .
  • the thickness of the photoresist layer is greater than or equal to 2.8 ⁇ m.
  • the depth of the groove is greater than or equal to 2 ⁇ m.
  • the material of the layer to be etched at least corresponding to the depth region of the bottom corner includes silicon oxide.
  • the bottom angle of the groove formed in the first etching stage is a right angle.
  • an etch stop layer is further formed at the bottom of the layer to be etched, and the plasma etching process is performed and the etching stops at the etch stop layer.
  • Another object of the present invention is to provide a method for forming a MEMS microphone, comprising:
  • the etching selectivity ratio between the first sacrificial layer and the photoresist layer is greater than or equal to 10.
  • the etching gas used in the plasma etching process includes fluorine-containing gas.
  • the fluorine-containing gas includes carbon tetrafluoride.
  • the substrate is sequentially etched in the first etching stage, and etched into the first sacrificial layer.
  • the first etching stage of the plasma etching process can accurately copy the groove pattern in the photoresist layer to the layer to be etched, and
  • the second etching stage by extending the photoresist material of the photoresist layer toward the direction of the window, the opening size of the window can be automatically reduced, so that the opening size of the window can be expanded with the extension of the photoresist material
  • grooves with arc-shaped bottom corners are formed. That is, in the preparation method of the groove provided by the present invention, not only the size of the formed groove (that is, the opening size of the groove) can be precisely controlled, but also the arc bottom angle can be automatically formed.
  • a back cavity with an arc-shaped bottom angle can be formed, thereby helping to reduce the stress of the microphone product and improve the signal-to-noise ratio of the product.
  • 1-4 are structural schematic diagrams of grooves with arc-shaped bottom corners during their preparation process in an embodiment of the present invention.
  • 5 to 7 are structural schematic diagrams of the MEMS microphone in an embodiment of the present invention during its manufacturing process.
  • the reference signs are as follows: 110-layer to be etched; 120-etching stop layer; 100a-first groove; 100b-second groove; 100c-third groove; 200-photoresist layer; 200a -window; 10-substrate; 10a-back cavity; 21-first sacrificial layer; 22-second sacrificial layer; 30-vibrating film; 31-first insulating layer; 32-first conductive layer; 33-second Insulating layer; 40-back plate; 41-third insulating layer; 42-second conductive layer; 50-photoresist layer.
  • FIG. 1-4 are structural schematic diagrams of grooves with arc-shaped bottom corners during their preparation process in an embodiment of the present invention.
  • the method for preparing a groove with an arc-shaped bottom angle in this embodiment specifically includes the following processes.
  • a photoresist layer 200 is formed on the layer to be etched 110, and a window 200a with a first opening size CD1 is opened in the photoresist layer 200. It can be considered that the photoresist layer 200 The initial size of the window 200a in is the first opening size CD1.
  • the material of the layer to be etched 110 includes, for example, silicon or silicon dioxide, and the photoresist layer 200 is, for example, a photoresist layer.
  • a plasma etching process is performed to copy the window pattern in the photoresist layer 200 to the layer to be etched 110 to form a groove.
  • the depth of the groove can reach 2 ⁇ m, for example, that is, the depth of the groove is greater than or equal to 2 ⁇ m.
  • the selectivity ratio is greater than or equal to 10, for example. In this way, the consumption of the photoresist layer 200 in the etching process can be reduced, and even the consumption of the photoresist layer 200 can be avoided.
  • the photoresist layer 200 is a photoresist layer
  • the etching gas of the plasma etching process can be selected from, for example, a fluoride gas, and the fluoride gas has an effect on the photoresist layer. Very low etch rate.
  • the material of the layer to be etched 110 includes, for example, silicon oxide, and the etching gas of the plasma etching process, for example, may be carbon fluoride gas (C 4 F 8 ), so as to ensure that the layer to be etched 110 has a higher etch rate.
  • the etching gas in the plasma etching process further includes argon (Ar), so as to further improve the etching selectivity of the layer to be etched 110 and the photoresist layer 200 .
  • the etching gas in the plasma etching process may include the following components: carbon fluoride gas (C 4 F 8 )/argon (Ar)/oxygen (O 2 )/carbon monoxide (CO) .
  • the plasma etching process may specifically include the following etching stages.
  • the layer to be etched 110 exposed in the window is sequentially consumed through the window 200a, so as to form an opening having the same opening size as the initial size of the window in the first etching stage.
  • groove ie, the first groove 100a. That is, in the initial stage of the plasma etching process, the photoresist layer 200 can still maintain its original shape, and the opening size of the window 200a is correspondingly maintained at the first opening size CD1, so in the initial etching stage , the first groove 100a having the first opening size CD1 can be formed in the layer to be etched 110 .
  • the plasma etching process is specifically an anisotropic etching process, so that the bottom angle of the formed first groove 100a can be formed at a right angle or close to a right angle in the first etching stage. And, through the first etching stage, the groove bottom of the first groove 100a is etched as a whole to the first depth position of the layer to be etched 110, for example, the first etching stage formed
  • the depth of a groove 100a is 80%-95% of the depth of the final groove.
  • the photoresist material of the photoresist layer 200 will gradually extend toward the center of the window, and the opening of the window will The size gradually decreases, so that the consumption of the bottom corner of the groove in the second etching stage gradually increases from the edge to the center of the groove, so that the bottom corner of the groove is modified into an arc shape.
  • an extension portion is formed as the photoresist material gradually extends toward the center of the window.
  • the photoresist layer 200 can be made
  • the opening size of the window is reduced to the second opening size CD2, and the second groove 100b is formed by etching.
  • the bottom of the second groove 100b is further etched to a second depth within the range corresponding to the second opening size CD2, and the second groove 100b
  • the bottom of the groove within the range from the first opening size CD1 to the second opening size CD2 corresponds to forming an arc-shaped bottom angle.
  • the photoresist material further extends toward the center of the window to form an extension.
  • the window in the photoresist layer 200 can be The opening size is further reduced to a third opening size CD3, and the third groove 100c is formed by etching. Relative to the first groove 100a, the bottom of the third groove 100c is further etched to a third depth within the range corresponding to the third opening size CD3, and the third groove 100c The bottom of the groove within the range from the first opening size CD1 to the third opening size CD3 corresponds to forming an arc-shaped bottom angle.
  • the etchant will not etch the photoresist layer 200, and will continue to accumulate on the top surface of the photoresist layer 200 until the second etching stage , so that the photoresist layer 200 is deformed and extended toward the center of the window.
  • the thickness of the photoresist layer 200 at least near the window gradually decreases accordingly.
  • the depth of the groove prepared in this embodiment is relatively large (for example, the depth of the groove is greater than or equal to 2 ⁇ m), the corresponding etching time is relatively long, so that the performed plasma etching process can at least meet the first requirement. the first etching stage, and at least reach the second etching stage to form grooves with required depth.
  • a thicker photoresist layer (photoresist layer) is also provided. The thicker photoresist layer will be easily deformed in the long-time etching process. Specifically, the photoresist layer The thickness can be, for example, greater than or equal to 28000 angstroms.
  • an etching stop layer 120 is further disposed under the layer to be etched 110 , so that etching can be stopped on the etching stop layer 120 .
  • FIG. 3 and FIG. 4 are taken as examples.
  • the size of the curved bottom angle of the groove can be controlled by adjusting the etching depth of the first etching stage, the extension size of the photoresist layer, etc. according to requirements.
  • this embodiment also provides a method for manufacturing a MEMS microphone.
  • 5-7 are structural schematic diagrams of the MEMS microphone in an embodiment of the present invention during its preparation process. As shown in FIGS. 5-7 , the preparation method of the MEMS microphone in this embodiment includes the following steps.
  • Step 1 specifically referring to FIG. 5 , provides a substrate 10 , and a first sacrificial layer 21 , a vibrating membrane 30 , a second sacrificial layer 22 and a back plate 40 are sequentially formed on the front side of the substrate 10 .
  • the vibrating membrane 30 may further include a first conductive layer 32 and a first insulating layer 31 and a second insulating layer 33 located on the upper and lower sides of the first conductive layer 32 .
  • the material of the first conductive layer 32 may include polysilicon, and the materials of the first insulating layer 31 and the second insulating layer 33 may include silicon nitride.
  • the back plate 40 may include a second conductive layer 42 and a third insulating layer 41 , and the third insulating layer 41 is located on a side of the second conductive layer 42 close to the second sacrificial layer 22 .
  • the material of the second conductive layer 42 of the back plate 40 may also include polysilicon, and the material of the third insulating layer 41 may include silicon nitride.
  • the material of the first sacrificial layer 21 may include silicon oxide.
  • the material of the second sacrificial layer 22 may also include silicon oxide.
  • a photoresist layer 50 is formed on the back side of the substrate 10, and a window with a first opening size is formed in the photoresist layer 50 to define the MEMS device. dorsal area.
  • the photoresist layer 50 is specifically a photoresist layer.
  • Step 3 specifically referring to FIG. 6 , performs a plasma etching process to sequentially etch the substrate 10 and the first sacrificial layer 21 to form a back cavity 10a.
  • the etching selectivity ratio of the first sacrificial layer 21 and the photoresist layer 50 is greater than or equal to 10.
  • the etching gas used in the plasma etching process may include a fluorine-containing gas, such as carbon tetrafluoride.
  • the plasma etching process includes: a first etching stage and a second etching stage.
  • the substrate 10 exposed in the window and the first sacrificial layer 21 are sequentially consumed through the window to form a groove with a first opening size in the first etching stage.
  • the substrate 10 is sequentially etched into the first sacrificial layer 21, that is, the bottom of the groove formed through the first etching stage located in the first sacrificial layer 21 , and the groove does not penetrate through the first sacrificial layer 21 yet.
  • the photoresist material of the photoresist layer 50 is gradually extended to the center of the window, so that the opening size of the window is gradually reduced, so that in the second etching stage, the groove
  • the amount of consumption at the bottom corner gradually increases from the edge of the groove to the center, and the bottom corner of the groove is modified into an arc, thus forming the back chamber 10a with an arc bottom corner.
  • the etchant that has almost no etching rate for the photoresist layer will accumulate on the surface of the photoresist layer 50, and with the increase of the accumulation content
  • the photoresist material of the photoresist layer is extended toward the direction of the window, thereby realizing the automatic reduction of the size of the window.
  • the first sacrificial layer 21 is etched into the first sacrificial layer 21 through the first etching stage, so the etching of the first sacrificial layer 21 is continued in the second etching stage, and the curved bottom Corners are formed in the first sacrificial layer 21 .
  • the side of the vibrating membrane 30 close to the first sacrificial layer 21 is the first insulating layer 31 (for example, a silicon nitride layer), so that the etching can stop at the first insulating layer in the second etching stage. 31, and under the protection of the first insulating layer 31, the first conductive layer 32 in the vibrating membrane 30 is protected from etching damage.
  • the bottom angle of the back cavity 10a close to the vibrating membrane 30 is an arc bottom angle, which can effectively reduce the stress of the microphone product and improve the signal-to-noise ratio of the product.
  • the manufacturing method of the MEMS microphone further includes: Step 4, specifically referring to FIG. 7 , at least partially removing the second sacrificial layer 22 to provide A cavity is formed.
  • a plurality of openings are opened in the back electrode plate 40, and the openings expose the second sacrificial layer 22, so the etchant can pass through during the release process of the second sacrificial layer.
  • the opening etches the second sacrificial layer 22 .
  • the second sacrificial layer 22 may be etched by a dry etching process (VHF) containing hydrogen fluoride gas.
  • VHF dry etching process
  • the dry etching process adopted in this embodiment will help overcome the problem that etching residues are difficult to remove.
  • the plasma etching process is used to enable the first etching stage to accurately copy the groove pattern in the photoresist layer to the groove to be etched.
  • the photoresist material of the photoresist layer is extended toward the direction of the window to automatically reduce the opening size of the window, so that the second etching stage can follow the photolithography
  • the extension of the adhesive material gradually forms a groove with an arc bottom corner.

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Abstract

本发明提供了一种具有弧形底角的凹槽的制备方法、MEMS麦克风的制备方法。通过等离子刻工艺使光刻胶层中的凹槽图形能够精确的复制至待刻蚀层中，并且随着刻蚀的进行使光刻胶层的光刻胶材料往窗口的方向延展，以自动缩减窗口的开口尺寸，从而能够随着光刻胶材料的延展而逐步形成具有弧形底角的凹槽。可见，本发明提供的凹槽的制备方法，不仅可以精确的控制所形成的凹槽尺寸，并可以自动形成弧形底角。

Description

具有弧形底角的凹槽的制备方法、MEMS麦克风的制备方法 技术领域
本发明涉及半导体技术领域，特别涉及一种具有弧形底角的凹槽的制备方法及MEMS麦克风的制备方法。
背景技术
在半导体的加工工艺中，常常需要制备凹槽以进一步形成对应的器件。例如，沟槽型场效应晶体管中需要形成栅极沟槽，沟槽隔离结构中需要形成隔离沟槽，以及MEMS器件中即需要形成腔体等。
目前，针对凹槽的制备方法一般包括：在待刻蚀层上形成光刻胶层，并执行刻蚀工艺以形成凹槽在所述待刻蚀层中。其中，为了使所形成的凹槽具有弧形底角，现有工艺中通常采用湿法刻蚀工艺，然而湿法刻蚀工艺为各向同性刻蚀，从而导致对待刻蚀层的刻蚀精度难以控制，所形成的凹槽的尺寸也容易产生偏差。
发明内容
本发明的目的在于提供一种具有弧形底角的凹槽的制备方法，以解决现有工艺存在的刻蚀精度难以控制的问题。
为解决上述技术问题，本发明提供一种具有弧形底角的凹槽的制备方法，包括：在待刻蚀层上形成光刻胶层，所述光刻胶层中开设有第一开口尺寸的窗口；以及，执行等离子刻蚀工艺，以在所述待刻蚀层中形成凹槽，包括：通过所述窗口依次消耗暴露于所述窗口中的待刻蚀层，以在第一刻蚀阶段形成第一开口尺寸的凹槽；所述光刻胶层的光刻胶材料逐步往所述窗口的中心延展，所述窗口的开口尺寸逐步缩减，以在第二刻蚀阶段对凹槽的底角位置的消耗量由凹槽的边缘至中心方向逐步增加，而将凹槽的底角修饰为弧形。
可选的，所述等离子刻蚀工艺中，对所述待刻蚀层和所述光刻胶层的刻蚀选择比大于等于10。
可选的，所述等离子刻蚀工艺所采用的刻蚀气体包括含氟气体。其中， 所述含氟气体例如包括四氟化碳。还可进一步包括：氩气、氧气和一氧化碳。
可选的，在所述等离子刻蚀工艺中，刻蚀剂堆积于所述光刻胶层的顶表面上，直至第二刻蚀阶段使所述光刻胶层发生形变而朝向窗口的中心延展。
可选的，所述光刻胶层的厚度大于等于2.8μm。以及，所述凹槽的深度大于等于2μm。
可选的，所述待刻蚀层至少对应于底角的深度区域的材料包括氧化硅。
可选的，在所述第一刻蚀阶段形成的凹槽的底角为直角。
可选的，所述待刻蚀层的底部还形成有刻蚀停止层，以及执行所述等离子刻蚀工艺并刻蚀停止于所述刻蚀停止层。
本发明的又一目的在于提供一种MEMS麦克风的形成方法，包括：
在衬底的正面上依次形成第一牺牲层、振动膜、第二牺牲层和背极板；
在所述衬底的背面形成光刻胶层，所述光刻胶层中形成有第一开口尺寸的窗口；以及，执行等离子刻蚀工艺，依次刻蚀所述衬底和所述第一牺牲层以形成背腔，包括：通过所述窗口依次消耗暴露于所述窗口中的衬底和第一牺牲层，以在第一刻蚀阶段形成第一开口尺寸的凹槽；所述光刻胶层的光刻胶材料逐步往所述窗口的中心延展，所述窗口的开口尺寸逐步缩减，以在第二刻蚀阶段对凹槽的底角位置的消耗量由凹槽的边缘至中心方向逐步增加，而将凹槽的底角修饰为弧形构成所述背腔。
可选的，所述等离子刻蚀工艺中，对所述第一牺牲层和所述光刻胶层的刻蚀选择比大于等于10。
可选的，所述等离子刻蚀工艺所采用的刻蚀气体包括含氟气体。例如，所述含氟气体包括四氟化碳。
可选的，在所述第一刻蚀阶段依次刻蚀所述衬底，并刻蚀至所述第一牺牲层中。
在本发明提供的具有弧形底角的凹槽的制备方法中，利用等离子刻工艺使其第一刻蚀阶段能够将光刻胶层中的凹槽图形精确复制至待刻蚀层中，并在第二刻蚀阶段通过使光刻胶层的光刻胶材料往窗口的方向延展，以自动缩减窗口的开口尺寸，从而可以在第二刻蚀阶段即能够随着光刻胶材料的延展而相应形成具有弧形底角的凹槽。即，本发明提供的凹槽的制备方法中，不 仅可以精确的控制所形成的凹槽尺寸(即，凹槽的开口尺寸)，并可以自动形成弧形底角。在将本发明提供的凹槽的制备方法应用于MEMS麦克风中，例如能够形成具有弧形底角的背腔，从而有利于降低麦克风产品的应力，提高产品的信噪比。
附图说明
图1-图4是本发明一实施例中具有弧形底角的凹槽在其制备过程中的结构示意图。
图5-图7为本发明一实施例中的MEMS麦克风在其制备过程中的结构示意图。
其中，附图标记如下：110-待刻蚀层；120-刻蚀停止层；100a-第一凹槽；100b-第二凹槽；100c-第三凹槽；200-光刻胶层；200a-窗口；10-衬底；10a-背腔；21-第一牺牲层；22-第二牺牲层；30-振动膜；31-第一绝缘层；32-第一导电层；33-第二绝缘层；40-背极板；41-第三绝缘层；42-第二导电层；50-光刻胶层。
具体实施方式
以下结合附图和具体实施例对本发明提出的具有弧形底角的凹槽的制备方法、MEMS麦克风的制备方法作进一步详细说明。根据下面说明，本发明的优点和特征将更清楚。需要说明的是，附图均采用非常简化的形式且均使用非精准的比例，仅用以方便、明晰地辅助说明本发明实施例的目的。以及附图中所示的诸如“上方”，“下方”，“顶部”，“底部”，“上方”和“下方”之类的相对术语可用于描述彼此之间的各种元件的关系。这些相对术语旨在涵盖除附图中描绘的取向之外的元件的不同取向。例如，如果装置相对于附图中的视图是倒置的，则例如描述为在另一元件“上方”的元件现在将在该元件下方。
图1-图4是本发明一实施例中具有弧形底角的凹槽在其制备过程中的结构示意图。如图1-图4所示，本实施例中的具有弧形底角的凹槽的制备方法具体包括如下过程。
首先参考图1所示，在待刻蚀层110上形成光刻胶层200，所述光刻胶层 200中开设有第一开口尺寸CD1的窗口200a，可以认为，所述光刻胶层200中的窗口200a的初始尺寸即为第一开口尺寸CD1。其中，所述待刻蚀层110的材料例如包括硅或二氧化硅等，所述光刻胶层200例如为光刻胶层。
接着参考图2-图4所示，执行等离子刻蚀工艺，以将所述光刻胶层200中的窗口图形复制至所述待刻蚀层110中而形成凹槽。其中，所述凹槽的深度例如可达到2μm，即，所述凹槽的深度大于等于2μm。
进一步的，所述等离子刻蚀工艺中，对所述待刻蚀层110和所述光刻胶层200具有较高的刻蚀选择比，其选择比例如大于等于10。如此，以降低所述光刻胶层200在刻蚀过程中的消耗量，甚至可以避免所述光刻胶层200被消耗。
本实施例中，所述光刻胶层200为光刻胶层，则所述等离子刻蚀工艺的刻蚀气体例如可选自氟化物气体，所述氟化物气体对所述光刻胶层具备极低的刻蚀速率。以及，所述待刻蚀层110的材料例如包括氧化硅，则所述等离子刻蚀工艺的刻蚀气体例如可选用氟化碳气体(C 4F 8)，以确保对所述待刻蚀层110具备较高的刻蚀速率。可选的，所述等离子刻蚀工艺中的刻蚀气体还包括氩气(Ar)，以进一步提高对所述待刻蚀层110和所述光刻胶层200的刻蚀选择比。具体的实施例中，所述等离子刻蚀工艺中的刻蚀气体可包括如下组份：氟化碳气体(C 4F 8)/氩气(Ar)/氧气(O 2)/一氧化碳(CO)。
其中，所述等离子刻蚀工艺具体可包括如下刻蚀阶段。
第一刻蚀阶段，具体参考图2所示，通过所述窗口200a依次消耗暴露于所述窗口中的待刻蚀层110，以在第一刻蚀阶段形成开口尺寸与窗口的初始尺寸相同的凹槽(即，第一凹槽100a)。即，在等离子刻蚀工艺的初始阶段，所述光刻胶层200仍能保持其原有形貌，其窗口200a的开口尺寸也相应的保持为第一开口尺寸CD1，因此在初始刻蚀阶段，能够在所述待刻蚀层110中形成具有第一开口尺寸CD1的第一凹槽100a。
本实施例中，所述等离子刻蚀工艺具体为各向异性刻蚀工艺，从而在第一刻蚀阶段可使所形成的第一凹槽100a的底角呈现为直角或接近直角。以及，通过所述第一刻蚀阶段，使所述第一凹槽100a的凹槽底部整体刻蚀至待刻蚀层110的第一深度位置，例如可使第一刻蚀阶段所形成的第一凹槽100a的深 度值为最终形成的凹槽的深度值的80％-95％。
第二刻蚀阶段，具体参考图3和图4所示，随着刻蚀的进行，所述光刻胶层200的光刻胶材料将逐步往所述窗口的中心延展，所述窗口的开口尺寸即呈逐步缩减的趋势变化，以在第二刻蚀阶段对凹槽的底角位置的消耗量由凹槽的边缘至中心方向逐步增加，从而将凹槽的底角修饰为弧形。
具体结合图2和图3所示，在所述第二刻蚀阶段中，随着光刻胶材料逐步往窗口的中心延展而形成有延伸部，此时，例如可使光刻胶层200中的窗口的开口尺寸缩减至第二开口尺寸CD2，并刻蚀形成第二凹槽100b。相对于所述第一凹槽100a而言，所述第二凹槽100b在对应于第二开口尺寸CD2的范围内凹槽底部进一步刻蚀至第二深度位置，以及所述第二凹槽100b在第一开口尺寸CD1至第二开口尺寸CD2的范围内的凹槽底部即对应于形成弧形底角。
接着结合图3和图4所示，随着刻蚀的进行，所述光刻胶材料进一步往窗口的中心延展而形成有延伸部，此时，例如可使光刻胶层200中的窗口的开口尺寸进一步缩减至第三开口尺寸CD3，并刻蚀形成第三凹槽100c。相对于所述第一凹槽100a而言，所述第三凹槽100c在对应于第三开口尺寸CD3的范围内凹槽底部进一步刻蚀至第三深度位置，以及所述第三凹槽100c在第一开口尺寸CD1至第三开口尺寸CD3的范围内的凹槽底部即对应于形成弧形底角。
需要说明的是，在等离子刻蚀工艺中，刻蚀剂不会刻蚀光刻胶层200，并且还会持续的堆积在所述光刻胶层200的顶表面上，直至第二刻蚀阶段，使得光刻胶层200发生形变而朝向窗口的中心延展。此外，随着光刻胶材料逐步往窗口的中心延展，相应的使得光刻胶层200至少靠近窗口的部分的厚度逐步减薄。
此外，由于本实施例中所制备的凹槽的深度较大(例如，凹槽的深度大于等于2μm)，其对应的刻蚀时间较长，从而使得所执行的等离子刻蚀工艺至少能够满足第一刻蚀阶段，并至少抵达至第二刻蚀阶段方能够形成所需深度的凹槽。以及，本实施例中还设置厚度较大的光刻胶层(光刻胶层)，厚度较大的光刻胶层将容易在长时间的刻蚀过程发生形变，具体的，光刻胶层的厚 度例如可大于等于28000埃。
本实施例中，所述待刻蚀层110的下方还设置有刻蚀停止层120，进而可刻蚀停止于所述刻蚀停止层120上。
应当认识到，本实施例中为了清楚的解释凹槽的弧形底角的形成过程，因此以图3和图4作为示例。然而在具体应用中，可根据需求通过调整第一刻蚀阶段的刻蚀深度、光刻胶层的延展尺寸等控制凹槽的弧形底角的尺寸。
基于如上所述的凹槽的制备方法，本实施例中还提供了一种MEMS麦克风的制备方法。图5-图7为本发明一实施例中的MEMS麦克风在其制备过程中的结构示意图，如图5-图7所示，本实施例中的MEMS麦克风的制备方法包括如下步骤。
步骤一，具体参考图5所示，提供衬底10，所述衬底10的正面上依次形成有第一牺牲层21、振动膜30、第二牺牲层22和背极板40。
其中，所述振动膜30可进一步包括第一导电层32以及位于所述第一导电层32上下两侧的第一绝缘层31和第二绝缘层33。所述第一导电层32的材料可包括多晶硅，所述第一绝缘层31和所述第二绝缘层33的材料可包括氮化硅。以及，所述背极板40可包括第二导电层42和第三绝缘层41，所述第三绝缘层41位于所述第二导电层42靠近所述第二牺牲层22的一侧。其中，所述背极板40的第二导电层42的材料也可包括多晶硅，所述第三绝缘层41的材料可包括氮化硅。
进一步的，所述第一牺牲层21的材料可包括氧化硅。以及，所述第二牺牲层22的材料也可包括氧化硅。
步骤二，继续参考图5所示，在所述衬底10的背面形成光刻胶层50，所述光刻胶层50中形成有第一开口尺寸的窗口，以界定出所述MEMS器件的背腔区域。本实施例中，所述光刻胶层50具体为光刻胶层。
步骤三，具体参考图6所示，执行等离子刻蚀工艺，依次刻蚀所述衬底10和所述第一牺牲层21以形成背腔10a。其中，在所述等离子刻蚀工艺中，对所述第一牺牲层21和所述光刻胶层50的刻蚀选择比大于等于10。具体的，所述等离子刻蚀工艺所采用的刻蚀气体可包括含氟气体，例如四氟化碳。
进一步的，所述等离子刻蚀工艺包括：第一刻蚀阶段和第二刻蚀阶段。
在第一刻蚀阶段中，通过所述窗口依次消耗暴露于所述窗口中的衬底10和所述第一牺牲层21，以在第一刻蚀阶段形成第一开口尺寸的凹槽。本实施例中，通过所述第一刻蚀阶段以依次刻蚀所述衬底10并刻蚀至所述第一牺牲层21中，即，通过第一刻蚀阶段所形成的凹槽的底部位于所述第一牺牲层21中，并且凹槽仍未贯穿所述第一牺牲层21。
在第二刻蚀阶段中，所述光刻胶层50的光刻胶材料逐步往所述窗口的中心延展，使得所述窗口的开口尺寸逐步缩减，以在第二刻蚀阶段对凹槽的底角位置的消耗量由凹槽的边缘至中心方向逐步增加，而将凹槽的底角修饰为弧形，如此即形成具有弧形底角的背腔10a。具体而言，随着刻蚀的不断进行，对所述光刻胶层几乎无刻蚀率的刻蚀剂即会堆积于所述光刻胶层50的表面上，并随着堆积含量的增加使得光刻胶层的光刻胶材料往窗口的方向延展，进而实现窗口尺寸的自动缩减。
本实施例中，经由第一刻蚀阶段而刻蚀至所述第一牺牲层21中，因此在第二刻蚀阶段即继续对所述第一牺牲层21进行刻蚀，并使弧形底角形成在第一牺牲层21中。此外，所述振动膜30其靠近第一牺牲层21的一侧为第一绝缘层31(例如，氮化硅层)，从而使得第二刻蚀阶段可刻蚀停止于所述第一绝缘层31，并在所述第一绝缘层的31的保护下，避免振动膜30中的第一导电层32受到刻蚀损伤。
需要说明的是，所述背腔10a靠近振动膜30的底角为弧形底角，从而可以有效的降低麦克风产品的应力，提高产品的信噪比。
进一步的，所述MEMS麦克风的制备方法还包括：步骤四，具体参考图7所示，至少部分去除所述第二牺牲层22，以在所述振动膜30和所述背极板40之间形成空腔。
具体而言，在所述背极板40中开设有多个开孔，所述开孔暴露有所述第二牺牲层22，因此在所述第二牺牲层释放工艺中刻蚀剂即可通过所述开孔刻蚀所述第二牺牲层22。其中，可采用含氟化氢气体的干法刻蚀工艺(VHF)刻蚀所述第二牺牲层22。与采用湿法刻蚀工艺去除所述第二牺牲层22相比，本实施例中所采用的干法刻蚀工艺将有利于克服刻蚀残留物难以清除的问题。
综上所述，本实施例提供的具有弧形底角的凹槽的制备方法中，利用等离子刻工艺使其第一刻蚀阶段能够将光刻胶层中的凹槽图形精确复制至待刻蚀层中，并在第二刻蚀阶段通过使光刻胶层的光刻胶材料往窗口的方向延展，以自动缩减窗口的开口尺寸，从而可以在第二刻蚀阶段即能够随着光刻胶材料的延展而逐步形成具有弧形底角的凹槽。可见，如上所述的凹槽的制备方法中，不仅可以精确的控制所形成的凹槽尺寸(即，凹槽的开口尺寸)，并可以自动形成弧形底角。
需要说明的是，虽然本发明已以较佳实施例披露如上，然而上述实施例并非用以限定本发明。对于任何熟悉本领域的技术人员而言，在不脱离本发明技术方案范围情况下，都可利用上述揭示的技术内容对本发明技术方案作出许多可能的变动和修饰，或修改为等同变化的等效实施例。因此，凡是未脱离本发明技术方案的内容，依据本发明的技术实质对以上实施例所做的任何简单修改、等同变化及修饰，均仍属于本发明技术方案保护的范围。
还应该认识到，此处描述的术语仅仅用来描述特定实施例，而不是用来限制本发明的范围。必须注意的是，此处的以及所附权利要求中使用的单数形式“一个”和“一种”包括复数基准，除非上下文明确表示相反意思。例如，对“一个步骤”或“一个装置”的引述意味着对一个或多个步骤或装置的引述，并且可能包括次级步骤以及次级装置。应该以最广义的含义来理解使用的所有连词。以及，词语“或”应该被理解为具有逻辑“或”的定义，而不是逻辑“异或”的定义，除非上下文明确表示相反意思。此外，本发明实施例中的方法和/或设备的实现可包括手动、自动或组合地执行所选任务。

Claims (17)

  1. 一种具有弧形底角的凹槽的制备方法，其特征在于，包括：
    在待刻蚀层上形成光刻胶层，所述光刻胶层中开设有第一开口尺寸的窗口；
    执行等离子刻蚀工艺，以在所述待刻蚀层中形成凹槽，包括：通过所述窗口依次消耗暴露于所述窗口中的待刻蚀层，以在第一刻蚀阶段形成第一开口尺寸的凹槽；所述光刻胶层的光刻胶材料逐步往所述窗口的中心延展，所述窗口的开口尺寸逐步缩减，以在第二刻蚀阶段对凹槽的底角位置的消耗量由凹槽的边缘至中心方向逐步增加，而将凹槽的底角修饰为弧形。
  2. 如权利要求1所述的具有弧形底角的凹槽的制备方法，其特征在于，所述等离子刻蚀工艺中，对所述待刻蚀层和所述光刻胶层的刻蚀选择比大于等于10。
  3. 如权利要求1所述的具有弧形底角的凹槽的制备方法，其特征在于，所述等离子刻蚀工艺所采用的刻蚀气体包括氟化物气体。
  4. 如权利要求3所述的具有弧形底角的凹槽的制备方法，其特征在于，所述等离子刻蚀工艺所采用的刻蚀气体还包括：氩气、氧气和一氧化碳。
  5. 如权利要求1所述的具有弧形底角的凹槽的制备方法，其特征在于，在所述等离子刻蚀工艺中，刻蚀剂堆积于所述光刻胶层的顶表面上，直至所述第二刻蚀阶段使所述光刻胶层发生形变而朝向窗口的中心延展。
  6. 如权利要求1所述的具有弧形底角的凹槽的制备方法，其特征在于，所述光刻胶层的厚度大于等于2.8μm。
  7. 如权利要求1所述的具有弧形底角的凹槽的制备方法，其特征在于，所述凹槽的深度大于等于2μm。
  8. 如权利要求1所述的具有弧形底角的凹槽的制备方法，其特征在于，所述待刻蚀层至少对应于底角的深度区域的材料包括氧化硅。
  9. 如权利要求1所述的具有弧形底角的凹槽的制备方法，其特征在于，在所述第一刻蚀阶段形成的凹槽的底角为直角。
  10. 如权利要求1所述的具有弧形底角的凹槽的制备方法，其特征在于， 所述待刻蚀层的底部还形成有刻蚀停止层，以及执行所述等离子刻蚀工艺并刻蚀停止于所述刻蚀停止层。
  11. 如权利要求1所述的具有弧形底角的凹槽的制备方法，其特征在于，所述等离子刻蚀工艺为各向异性刻蚀工艺。
  12. 如权利要求1所述的具有弧形底角的凹槽的制备方法，其特征在于，在所述第二刻蚀阶段中，所述光刻胶层中的窗口的开口尺寸缩减至第二开口尺寸，所述凹槽的底部在对应于所述第二开口尺寸的范围内进一步刻蚀至第二深度位置。
  13. 如权利要求12所述的具有弧形底角的凹槽的制备方法，其特征在于，所述光刻胶层中的窗口的开口尺寸进一步缩减至小于所述第二开口尺寸的第三开口尺寸，所述凹槽的底部在对应于所述第三开口尺寸的范围内进一步刻蚀至大于所述第二深度位置的第三深度位置。
  14. 一种MEMS麦克风的形成方法，其特征在于，包括：
    在衬底的正面上依次形成第一牺牲层、振动膜、第二牺牲层和背极板；
    在所述衬底的背面形成光刻胶层，所述光刻胶层中形成有第一开口尺寸的窗口；以及，
    执行等离子刻蚀工艺，依次刻蚀所述衬底和所述第一牺牲层以形成背腔，包括：通过所述窗口依次消耗暴露于所述窗口中的衬底和第一牺牲层，以在第一刻蚀阶段形成第一开口尺寸的凹槽；所述光刻胶层的光刻胶材料逐步往所述窗口的中心延展，所述窗口的开口尺寸逐步缩减，以在第二刻蚀阶段对凹槽的底角位置的消耗量由凹槽的边缘至中心方向逐步增加，而将凹槽的底角修饰为弧形构成所述背腔。
  15. 如权利要求14所述的MEMS麦克风的形成方法，其特征在于，所述等离子刻蚀工艺中，对所述第一牺牲层和所述光刻胶层的刻蚀选择比大于等于10。
  16. 如权利要求14所述的MEMS麦克风的形成方法，其特征在于，所述等离子刻蚀工艺所采用的刻蚀气体包括含氟气体。
  17. 如权利要求14所述的MEMS麦克风的形成方法，其特征在于，在所述第一刻蚀阶段依次刻蚀所述衬底，并刻蚀至所述第一牺牲层中。
PCT/CN2022/127652 2021-11-05 2022-10-26 具有弧形底角的凹槽的制备方法、mems麦克风的制备方法 WO2023078137A1 (zh)

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