A large-angle MEMS biaxial micromirror and its fabrication method

Abstract

This invention discloses a large-angle MEMS biaxial micromirror, comprising a bonded first SOI sheet and a second SOI sheet. A lens is disposed on the second SOI sheet, a first comb tooth group is disposed below the second SOI sheet, and second comb tooth groups are disposed on both sides of the lens. Unlike existing technologies, this solution only requires the bonding of two SOI sheets to fabricate the micromirror, ensuring quality while effectively controlling costs.

Description

Technical Field

[0001] This invention belongs to the field of MEMS biaxial micromirror technology, and particularly relates to a large-angle MEMS biaxial micromirror and its fabrication method. Background Technology

[0002] In modern communication technology, fiber optic communication plays a crucial role, and optical switches, as fundamental components in optical communication systems, are currently the most actively developed passive optoelectronic devices. Among various types of optical switches, electrostatically driven MEMS micromirrors (MEMS micromirrors) have advantages such as low crosstalk, fast switching speed, small size, and ease of large-scale integration, making them the mainstream optical switch in recent years. MEMS micromirrors are also widely used in digital displays and laser scanning. Based on the structural complexity of MEMS micromirrors, they can be divided into single-axis micromirrors, dual-axis micromirrors, and micromirror arrays. Dual-axis MEMS micromirrors, due to their ability to rotate in four directions across two dimensions within a plane, have wider applications. However, for vertically comb-driven dual-axis MEMS micromirrors, the vertical comb-driven structure is generally located around the mirror surface. The distances of the comb teeth from the central axis of the mirror surface differ between the two dimensions, resulting in different maximum deflection angles in the two dimensions, making it difficult to achieve equal maximum deflection angles across both axes.

[0003] For example, Chinese patent CN113820851A discloses a novel method for fabricating a biaxial vertical comb-tooth MEMS micromirror. It uses multiple silicon wafers to combine and finally obtain a biaxial micromirror. During the research process, the user found that there were risks in the fabrication of the first movable comb tooth using this method. Since the bonding area has requirements, it is difficult to guarantee the bonding if the bonding area is too small. At the same time, it uses multiple SOI wafers, which require multiple bonding processes, making the processing technology complex and the cost high. Summary of the Invention

[0004] The purpose of this invention is to provide a large-angle MEMS biaxial micromirror and its fabrication method, so as to solve the problems of complex fabrication process, high cost, difficulty in guaranteeing quality, and inability to achieve large-angle deflection of existing biaxial micromirrors.

[0005] This invention discloses a large-angle MEMS biaxial micromirror, comprising a bonded first SOI sheet and a second SOI sheet. A lens is disposed on the second SOI sheet, a first comb tooth group is disposed below the second SOI sheet, and second comb tooth groups are disposed on both sides of the lens. Unlike existing technologies, this method only requires the bonding of two SOI sheets for fabrication, ensuring quality while effectively controlling costs. This invention proposes two fabrication schemes:

[0006] This invention discloses a method for fabricating a large-angle MEMS biaxial micromirror, comprising the following steps:

[0007] S11. The lower comb teeth and isolation trenches are fabricated using the first SOI wafer. The SOI wafer includes a substrate layer, a dielectric layer BOX, and a device layer.

[0008] S12. Using the second SOI wafer, complete the preparation of the upper comb teeth of the mirror comb pair, the thinning of the rotating shaft, and the preparation of the lower half of the upper comb teeth of the mirror side comb pair.

[0009] S13. Bond the first SOI wafer and the second SOI wafer together, remove the substrate and BOX layer of the second SOI wafer, complete the preparation of the mirror, the preparation of the rotating shaft, the preparation of the upper half of the comb teeth next to the mirror, and define the overall boundary of the micromirror.

[0010] This invention discloses another method for fabricating large-angle MEMS biaxial micromirrors, comprising the following steps:

[0011] S21. The lower comb teeth and isolation trenches are fabricated using the first SOI wafer. The SOI wafer includes a substrate layer, a dielectric layer BOX, and a device layer.

[0012] S22. Use the second SOI wafer to complete the fabrication of all upper comb teeth, fabricate the rotating shaft, and define the overall boundary of the micromirror.

[0013] S23. Bond the first SOI wafer and the second SOI wafer together, remove the substrate and BOX layer of the second SOI wafer, and use a shadowmask as a mask to complete the preparation of the mirror.

[0014] Both schemes involve the same steps, that is, steps S11 and S21 are identical, both including the following steps:

[0015] S111, Clean the SOI wafer;

[0016] S112, deposit SiO2 medium on the surface of the first SOI wafer;

[0017] S113, First layer photolithography, lower comb teeth and isolation trench photoresist patterning;

[0018] S114, etching medium SiO2, defines the lower comb teeth and isolation groove pattern;

[0019] S115, Second layer photolithography, isolation trench photoresist patterning;

[0020] S116, Etch Si to define the isolation trench pattern;

[0021] S117, Remove the adhesive, use SiO2 as a mask, and etch down to the BOX layer;

[0022] S118. Remove the medium SiO2 to complete the preparation of the isolation groove and the lower comb teeth;

[0023] Preferably, step S12 includes the following steps:

[0024] S121, the third layer of photolithography on the surface of the second SOI wafer, patterning of photoresist for the upper comb teeth, micromirror boundaries and square grooves in the rotating shaft area;

[0025] S122, Etch Si, define the upper comb pattern, and the etching morphology of the rotating shaft area is a square groove;

[0026] Preferably, step S13 includes the following steps:

[0027] S131, the device layers of the first SOI wafer and the second SOI wafer are opposite each other, and silicon-silicon bonding is performed;

[0028] S132, Remove the bottom silicon and BOX layer of the second SOI wafer;

[0029] S133, deposited mirror-finish metal;

[0030] S134, fourth layer of photolithography, patterning of photoresist in the mirror and pad areas;

[0031] S135, Etch the metal to define the mirror and pad patterns;

[0032] S136, fifth layer photolithography, patterning of photoresist at the boundaries of the upper comb teeth, rotating shaft and micromirrors;

[0033] S137, Etching Si, defines the rotation axis, micromirror boundary, and upper comb teeth of the mirror side comb pair.

[0034] Preferably, step S22 includes the following steps:

[0035] S221. Deposit SiO2 dielectric on the surface of the second silicon wafer;

[0036] S222, the third layer of photolithography on the surface of the second SOI wafer, patterning of the upper comb teeth, micromirror boundaries and rotating axis photoresist;

[0037] S223, Etch SiO2 to define the upper comb teeth, micromirror boundary and rotation axis pattern;

[0038] S224, fourth layer of photolithography, patterning of comb teeth, micromirror boundaries and rotating axis photoresist around the mirror surface;

[0039] S225, Etch Si, Define the comb teeth around the mirror, the micromirror boundary and the rotation axis pattern;

[0040] S226, remove the adhesive, use SiO2 as a mask, etch Si, add comb teeth, micromirror boundary and rotation axis to BOX around the mirror;

[0041] S227, removes SiO2.

[0042] Preferably, step S23 includes the following steps:

[0043] S231, the device layers of the first SOI wafer and the second SOI wafer are opposite each other, and silicon-silicon bonding is performed;

[0044] S232. Remove the bottom silicon and BOX layer of the second SOI wafer. BOX removal is performed using Vapor HF.

[0045] S233, using a shadow mask to sputter mirror metal.

[0046] Compared with the prior art, the beneficial effects of the present invention are:

[0047] This invention discloses a large-angle MEMS biaxial micromirror, comprising a bonded first SOI sheet and a second SOI sheet. A lens is disposed on the second SOI sheet, a first comb tooth group is disposed below the second SOI sheet, and second comb tooth groups are disposed on both sides of the lens. This achieves equal large-angle deflection in two dimensions, effectively improving the duty cycle of the micromirror and reducing its volume. Unlike existing technologies, this solution only requires the bonding of two SOI sheets, ensuring quality while effectively controlling costs. The first fabrication method primarily allows for adjustment of the axis of rotation, making it highly practical. The second fabrication method utilizes a shadow mask to fabricate the mirror surface, simplifying the comb tooth fabrication steps and reducing fabrication difficulty, thus enhancing operability. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the large-angle MEMS biaxial micromirror structure of the present invention;

[0049] Figure 2 This is a schematic diagram of the structure corresponding to step S111 of the present invention;

[0050] Figure 3 This is a schematic diagram of the structure corresponding to step S112 of the present invention;

[0051] Figure 4 This is a schematic diagram of the structure corresponding to step S113 of the present invention;

[0052] Figure 5 This is a schematic diagram of the structure corresponding to step S114 of the present invention;

[0053] Figure 6 This is a schematic diagram of the structure corresponding to step S115 of the present invention;

[0054] Figure 7 This is a schematic diagram of the structure corresponding to step S116 of the present invention;

[0055] Figure 8 This is a schematic diagram of the structure corresponding to step S117 of the present invention;

[0056] Figure 9 This is a schematic diagram of the structure corresponding to step S118 of the present invention;

[0057] Figure 10 This is a schematic diagram of the structure corresponding to step S121 of the present invention;

[0058] Figure 11 This is a schematic diagram of the structure corresponding to step S122 of the present invention;

[0059] Figure 12 This is a schematic diagram of the structure corresponding to step S131 of the present invention;

[0060] Figure 13 This is a schematic diagram of the structure corresponding to step S132 of the present invention;

[0061] Figure 14 This is a schematic diagram of the structure corresponding to step S135 of the present invention;

[0062] Figure 15 This is a schematic diagram of the structure corresponding to step S136 of the present invention;

[0063] Figure 16 This is a schematic diagram of the structure corresponding to step S147 of the present invention;

[0064] Figure 17 This is a schematic diagram of the structure corresponding to step S221 of the present invention;

[0065] Figure 18 This is a schematic diagram of the structure corresponding to step S222 of the present invention;

[0066] Figure 19 This is a schematic diagram of the structure corresponding to step S223 of the present invention;

[0067] Figure 20 This is a schematic diagram of the structure corresponding to step S224 of the present invention;

[0068] Figure 21 This is a schematic diagram of the structure corresponding to step S225 of the present invention;

[0069] Figure 22 This is a schematic diagram of the structure corresponding to step S226 of the present invention;

[0070] Figure 23 This is a schematic diagram of the structure corresponding to step S227 of the present invention;

[0071] Figure 24 This is a schematic diagram of the structure corresponding to step S231 of the present invention;

[0072] Figure 25 This is a schematic diagram of the structure corresponding to step S232 of the present invention;

[0073] Figure 26This is a schematic diagram of the structure corresponding to step S233 of the present invention.

[0074] Figure descriptions: 11. Mirror-faced lower comb teeth to lower comb teeth; 12. Mirror-faced side comb teeth to lower comb teeth; 21. Mirror-faced lower comb teeth to upper comb teeth; 22. Mirror-faced side comb teeth to upper comb teeth; 23. Mirror surface; 24. Mirror-faced lower comb teeth to rotating shaft; 25. Mirror-faced side comb teeth to rotating shaft. Detailed Implementation

[0075] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0076] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front end," "rear end," "both ends," "one end," and "the other end," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0077] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0078] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0079] Example 1

[0080] like Figure 1As shown, this invention discloses a large-angle MEMS biaxial micromirror, comprising a first SOI sheet and a second SOI sheet bonded together. A lens is disposed on the second SOI sheet, and a first comb tooth group is disposed below the second SOI sheet. The first comb tooth group includes a lower comb tooth pair 11 and a lower comb tooth pair 21. Second comb tooth groups are disposed on both sides of the lens. The second comb tooth groups include a lower comb tooth pair 12 and a higher comb tooth pair 22. This arrangement allows for equal large-angle deflection in both dimensions, effectively improving the duty cycle of the micromirror and reducing its volume. Unlike existing technologies, this solution only requires the bonding of two SOI sheets, ensuring bonding quality and effectively controlling costs.

[0081] Example 2

[0082] This embodiment discloses a method for fabricating a large-angle MEMS biaxial micromirror, characterized by the following steps:

[0083] S11. The lower comb teeth and isolation trenches are fabricated using the first SOI wafer. The SOI wafer includes a substrate layer, a dielectric layer BOX, and a device layer.

[0084] S111, Clean the SOI wafer to obtain the following: Figure 2 The silicon wafer shown.

[0085] S112, deposit SiO2 dielectric on the surface of the first SOI wafer; to obtain as shown in the figure. Figure 3 The structure shown.

[0086] S113, First layer photolithography, lower comb teeth and isolation trench photoresist patterning; resulting in... Figure 4 The structure shown.

[0087] S114, using SiO2 as the etching medium, defines the lower comb teeth and isolation trench pattern; resulting in... Figure 5 The structure shown.

[0088] S115, Second layer photolithography, isolation trench photoresist patterning; resulting in... Figure 6 The structure shown.

[0089] S116, Etch Si to define the isolation trench pattern; obtain as follows: Figure 7 The structure shown.

[0090] S117, Remove the adhesive, using SiO2 as a mask, and etch down to the BOX layer; to obtain... Figure 8 The structure shown.

[0091] S118, Remove the medium SiO2 to complete the fabrication of the isolation groove and lower comb teeth; obtain as follows Figure 9 The structure shown.

[0092] S12. Using the second SOI wafer, complete the preparation of the upper comb teeth of the mirror comb pair, the thinning of the shaft, and the preparation of the lower half of the upper comb teeth of the mirror side comb pair.

[0093] S121, the third layer of photolithography on the surface of the second SOI wafer, patterning the upper comb teeth, micromirror boundaries, and square grooves in the rotation axis region with photoresist; resulting in... Figure 10 The structure shown.

[0094] S122, Etch Si, define the upper comb pattern, and etch the rotation axis region into a square groove; obtain as follows: Figure 11 The structure shown.

[0095] S13. Bond the first SOI wafer and the second SOI wafer together, remove the substrate and BOX layer of the second SOI wafer, complete the preparation of the mirror, the preparation of the rotating shaft, the preparation of the upper half of the comb teeth next to the mirror, and define the overall boundary of the micromirror.

[0096] S131, the device layers of the first SOI wafer and the second SOI wafer are aligned, and silicon-silicon bonding is performed; thus, as shown in... Figure 12 The structure shown.

[0097] S132, Remove the bottom silicon and BOX layer of the second SOI wafer; to obtain as follows Figure 13 The structure shown.

[0098] S133, deposited mirror metal.

[0099] S134, fourth layer of photolithography, patterning of photoresist in the mirror and pad areas.

[0100] S135, Etch the metal, defining the mirror and pad patterns; obtain as follows: Figure 14 The structure shown.

[0101] S136, fifth layer photolithography, patterning of photoresist at the upper comb teeth, rotating axis, and micromirror boundaries; resulting in... Figure 15 The structure shown.

[0102] S137, Etch Si, defining the rotation axis, micromirror boundary, and the upper comb teeth of the mirror-side comb pair. The result is as follows: Figure 16 The structure shown.

[0103] This embodiment can reduce the thickness of the pivot axis in key parts of the micromirror, making it more practical. To illustrate the thinning effect, only the pivot axis of the comb tooth pair below the mirror surface is thinned in the illustration; the pivot axis of the comb tooth pair beside the mirror surface is not thinned. If needed, the pivot axis of the comb tooth pair beside the mirror surface can also be thinned.

[0104] Example 3

[0105] This embodiment discloses a method for fabricating a large-angle MEMS biaxial micromirror, including the following steps:

[0106] S21. The lower comb teeth and isolation trenches are fabricated using the first SOI wafer. The SOI wafer includes a substrate layer, a dielectric layer BOX, and a device layer.

[0107] S211. Clean the SOI wafer to obtain the following result: Figure 2 The silicon wafer shown.

[0108] S212, deposit SiO2 on the surface of the first SOI wafer; to obtain... Figure 3 The structure shown.

[0109] S213, First layer photolithography: lower comb teeth and isolation trench photoresist patterning; resulting in... Figure 4 The structure shown.

[0110] S214, using SiO2 as the etching medium, defines the lower comb teeth and isolation groove pattern; resulting in... Figure 5 The structure shown.

[0111] S215, Second layer photolithography, isolation trench photoresist patterning; resulting in... Figure 6 The structure shown.

[0112] S216, Etch Si to define the isolation trench pattern; obtain as follows: Figure 7 The structure shown.

[0113] S217, Remove the adhesive, use SiO2 as a mask, and etch down to the BOX layer; obtain as follows: Figure 8 The structure shown.

[0114] S218, Remove the medium SiO2 to complete the preparation of the isolation groove and lower comb teeth; obtain as follows Figure 9 The structure shown.

[0115] S22. Use the second SOI wafer to complete the fabrication of all upper comb teeth, fabricate the rotating shaft, and define the overall boundary of the micromirror.

[0116] S221, deposit SiO2 dielectric on the surface of the second silicon wafer; to obtain as shown in the figure. Figure 17 The structure shown.

[0117] S222, the third layer of photolithography on the surface of the second SOI wafer, patterning of the upper comb teeth, micromirror boundaries, and rotating axis photoresist; resulting in... Figure 18 The structure shown.

[0118] S223, Etch SiO2 to define the upper comb teeth, micromirror boundary, and rotation axis pattern; obtain as follows: Figure 19 The structure shown.

[0119] S224, fourth layer photolithography, patterning of the comb teeth, micromirror boundaries, and rotation axis photoresist around the mirror surface; resulting in... Figure 20 The structure shown.

[0120] S225, etch Si, define the comb teeth around the mirror, the micromirror boundary, and the rotation axis pattern; obtain as follows: Figure 21 The structure shown.

[0121] S226, remove the resist, use SiO2 as a mask, etch Si, add comb teeth around the mirror, micromirror boundary and rotation axis to the BOX; obtain as shown. Figure 22 The structure shown.

[0122] S227, Remove SiO2. The result is as follows: Figure 23 The structure shown.

[0123] S23. Bond the first SOI wafer and the second SOI wafer together, remove the substrate and BOX layer of the second SOI wafer, and use a shadowmask as a mask to complete the preparation of the mirror.

[0124] S231, the first SOI wafer and the second SOI wafer have their device layers facing each other, and are bonded together with silicon; thus, a silicon-silicon bond is obtained. Figure 24 The structure shown.

[0125] S232, Remove the bottom silicon and BOX layer of the second SOI wafer. BOX removal is performed using Vapor HF. Figure 25 The structure shown.

[0126] S233, using a shadow mask, sputter mirror metal. The result is... Figure 26 The structure shown.

[0127] This embodiment utilizes a shadow mask to prepare the mirror surface, which simplifies the preparation steps and reduces the difficulty of preparing the comb teeth, making it more operable.

[0128] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics of the solutions is not described in detail here. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the present invention is defined by the appended claims rather than the foregoing description. Therefore, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for fabricating a large-angle MEMS biaxial micromirror, characterized in that, Includes the following steps: S11. The lower comb teeth and isolation trenches are fabricated using the first SOI wafer. The SOI wafer includes a substrate layer, a dielectric layer BOX, and a device layer. S12. Using the second SOI wafer, complete the fabrication of the upper comb teeth of the mirror-side comb pair, the thinning of the rotating shaft, and the fabrication of the lower half of the upper comb teeth of the mirror-side comb pair; including: S121, the third layer of photolithography on the surface of the second SOI wafer, patterning of photoresist for the upper comb teeth, micromirror boundaries and square grooves in the rotating shaft area; S122, Etch Si, define the upper comb pattern, and the etching morphology of the rotating shaft area is a square groove; S13. Bond the first SOI wafer and the second SOI wafer, remove the substrate and BOX layer of the second SOI wafer to complete the fabrication of the mirror, the fabrication of the rotating shaft, the fabrication of the upper half of the mirror side comb teeth, and define the overall boundary of the micromirror, including: S131, the device layers of the first SOI wafer and the second SOI wafer are opposite each other, and silicon-silicon bonding is performed; S132, Remove the bottom silicon and BOX layer of the second SOI wafer; S133, deposited mirror-finish metal; S134, fourth layer of photolithography, patterning of photoresist in the mirror and pad areas; S135, Etch the metal to define the mirror and pad patterns; S136, fifth layer photolithography, patterning of photoresist at the boundaries of the upper comb teeth, rotating shaft and micromirrors; S137, Etching Si, defines the rotation axis, micromirror boundary, and upper comb teeth of the mirror side comb pair.

2. A method for fabricating a large-angle MEMS biaxial micromirror, characterized in that, Includes the following steps: S21. The lower comb teeth and isolation trenches are fabricated using the first SOI wafer. The SOI wafer includes a substrate layer, a dielectric layer BOX, and a device layer. S22. Using the second SOI wafer, complete the fabrication of all upper comb teeth, fabricate the rotating shaft, and define the overall boundary of the micromirror; including: S221. Deposit SiO2 dielectric on the surface of the second silicon wafer; S222, the third layer of photolithography on the surface of the second SOI wafer, patterning of the upper comb teeth, micromirror boundaries and rotating axis photoresist; S223, Etch SiO2 to define the upper comb teeth, micromirror boundary and rotation axis pattern; S224, fourth layer of photolithography, patterning of comb teeth, micromirror boundaries and rotating axis photoresist around the mirror surface; S225, Etch Si, Define the comb teeth around the mirror, the micromirror boundary and the rotation axis pattern; S226, remove the adhesive, use SiO2 as a mask, etch Si, add comb teeth, micromirror boundary and rotation axis to BOX around the mirror; S227, Remove SiO2; S23. Bond the first SOI wafer and the second SOI wafer together, remove the substrate and BOX layer of the second SOI wafer, and use a shadow mask as a mask to complete the fabrication of the mirror, including: S231, the device layers of the first SOI wafer and the second SOI wafer are opposite each other, and silicon-silicon bonding is performed; S232. Remove the bottom silicon and BOX layer of the second SOI wafer. BOX removal is performed using Vapor HF. S233, using a shadow mask to sputter mirror metal.

3. The preparation method according to claim 1, characterized in that: Step S11 includes: S111, Clean the SOI wafer; S112, deposit SiO2 medium on the surface of the first SOI wafer; S113, First layer photolithography, lower comb teeth and isolation trench photoresist patterning; S114, etching medium SiO2, defines the lower comb teeth and isolation groove pattern; S115, Second layer photolithography, isolation trench photoresist patterning; S116, Etch Si to define the isolation trench pattern; S117, Remove the adhesive, use SiO2 as a mask, and etch down to the BOX layer; S118. Remove the medium SiO2 to complete the preparation of the isolation groove and the lower comb teeth.

4. The preparation method according to claim 2, characterized in that: Step S21 includes: S211, Clean the SOI wafer; S212, deposit SiO2 dielectric on the surface of the first SOI wafer; S213, First layer photolithography, lower comb teeth and isolation trench photoresist patterning; S214, etching medium SiO2, defines the lower comb teeth and isolation groove pattern; S215, Second layer photolithography, isolation trench photoresist patterning; S216, Etch Si to define the isolation trench pattern; S217, Remove the adhesive, use SiO2 as a mask, and etch down to the BOX layer; S218. Remove the medium SiO2 to complete the preparation of the isolation groove and the lower comb teeth.

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