MEMS suspended structure cavity release etching method

Abstract

The invention relates to the field of semiconductor processing and manufacturing, in particular to an MEMS suspended structure cavity release etching method, which specifically comprises the following steps that the back surface of an etched wafer is coated with a protective layer, and the protective layer comprises photoresist and a UV film; carrying out vacuum heating on the etched wafer; performing etching processing on the front surface of the etching wafer; the photoresist on the back of the etched wafer is removed, meanwhile, a bonding layer is arranged on the surface, away from the etched wafer, of the protective layer, a substrate wafer is arranged on the surface, away from the etched wafer, of the bonding layer, and the substrate wafer is placed on an electrostatic chuck, so that the phenomenon of membrane bulging or glue bulging caused by large air pressure difference on the two sides of the protective layer is not prone to occurring; and the possibility that the normal operation of the processing technology is influenced by helium detection alarm is reduced.

Description

Technical Field

[0001] The present application relates to the field of semiconductor processing and manufacturing, and in particular to a cavity release etching method for a MEMS suspended structure. Background Art

[0002] MEMS, or micro-electromechanical system, requires processing on a wafer to form a variety of devices, and in order to further improve the performance of the devices, some devices are suspended between the substrate via a supporting structure or by forming a cavity on the substrate.

[0003] At the same time, the wafer is fixed by adsorption by the electrostatic chuck during processing. An air duct for helium flow is also formed on the electrostatic chuck. On the one hand, the flowing helium is used to take away the heat of the wafer during processing. On the other hand, if the sealing between the wafer and the electrostatic chuck is poor, helium leakage will occur, which will increase the helium flow in the electrostatic chuck. For this reason, helium detection can be used to determine whether the wafer is well fixed. Once the helium flow in the electrostatic chuck is too large during the helium detection, the processing process needs to be stopped. For example, the electrostatic chuck with publication number CN117672943A.

[0004] Regarding the above-mentioned related technologies, some suspended release processing requires the formation of a structure with a high aspect ratio, for which the wafer needs to be etched through. If the air channel of the electrostatic chuck is directly opposite to the wafer etched through position, it will cause a helium detection alarm and stop the processing process. Summary of the invention

[0005] In order to ensure that the wafer can be etched through smoothly and that helium detection does not easily cause the processing process to be stopped, the present application provides a MEMS suspended structure cavity release etching method.

[0006] The present application provides a MEMS suspended structure cavity release etching method using the following technical solution.

[0007] A MEMS suspended structure cavity release etching method specifically comprises the following steps.

[0008] S1, coating the back side of the etched wafer with a protective layer, the protective layer comprising a photoresist and a UV film; S2, vacuum heating the etched wafer; S3, performing etching processing on the front side of the etched wafer; S4. Remove the photoresist on the back side of the etched wafer.

[0009] By adopting the above technical solution, after the wafer is etched through, due to the presence of the protective layer, the helium gas sent out by the electrostatic chuck is not likely to leak too much, so that the helium gas detection is not likely to alarm, and the processing technology can proceed smoothly.

[0010] Optionally, in S1, an adhesive layer is disposed on a surface of the protective layer away from the etching wafer, a substrate wafer is disposed on a surface of the adhesive layer away from the etching wafer, and the substrate wafer is placed on an electrostatic chuck.

[0011] By adopting the above technical scheme, when a separate protective layer is attached to the etching wafer, it is easy to cause the stress in the suspended structure where the stress is already concentrated to further increase, causing the suspended structure to bend or even break. In addition, when etching is performed in a vacuum environment and the cavity is formed, the air pressure difference on both sides of the protective layer is large, resulting in bulging membrane or glue bulging. The helium flow in the electrostatic chuck increases instantly, causing the helium detection to easily alarm, affecting the normal progress of the processing technology. In addition, directly placing the protective layer of photoresist or UV film on the electrostatic chuck is likely to cause contamination, affecting the service life of the equipment. For this reason, using an adhesive layer on the protective layer and setting the substrate wafer can solve the above problems.

[0012] Optionally, the adhesive layer comprises paraffin.

[0013] By adopting the above technical solution, paraffin wax can be dissolved in 70°C water or degumming liquid, and can also be removed by oxygen plasma with strong removal performance, so that the substrate wafer and the etched wafer can be separated after etching is completed.

[0014] Optionally, the substrate wafer is first heated to 70-120° C., and then an adhesive layer is coated on the substrate wafer, and then the surface of the substrate wafer coated with the adhesive layer is bonded to the protective layer of the etching wafer.

[0015] By adopting the above technical solution, the adhesive layer is first coated on the heated substrate wafer to melt the adhesive layer, and then the etching wafer and the substrate wafer are aligned and closely bonded together. The coating of the protective layer on the etching wafer and the coating of the adhesive layer on the substrate wafer can be carried out simultaneously to improve the overall etching efficiency.

[0016] Optionally, after the adhesive layer of the substrate wafer and the protective layer of the etching wafer are aligned and bonded, the substrate wafer and the adhesive layer are naturally cooled to room temperature before performing S2.

[0017] By adopting the above technical solution, the possibility that the position of the etching wafer and the substrate wafer may be offset due to incompletely solidified paraffin during the wafer transfer process, thereby affecting the subsequent etching quality, can be reduced.

[0018] Optionally, the substrate wafer is heated to 100°C.

[0019] By adopting the above technical solution, the fluidity and bonding strength of the paraffin when coated at 100°C, as well as the defects and overflow during subsequent vacuum heating, can be better balanced and controlled.

[0020] Optionally, the vacuum heating temperature in S2 is 100°C.

[0021] By adopting the above technical solution, the photoresist can be smoothly cured while the paraffin wax is not prone to excessive overflow and defects, which helps the paraffin wax to provide sufficient bonding force after vacuum heating.

[0022] Optionally, after the vacuum heating in S2, the bonded wafers are inspected for any adhesive layer overflow, and if so, acetone is used to remove the overflowed adhesive layer.

[0023] By adopting the above technical solution, the possibility of the adhesive layer overflowing during the etching process contacting the electrostatic chuck and causing contamination is reduced.

[0024] Optionally, in S3, the wafer after etching is placed into a degumming solution.

[0025] By adopting the above technical solution, the photoresist is initially removed, which facilitates the subsequent ion removal of the remaining small amount of photoresist.

[0026] Optionally, the degumming solution is heated to 70-120°C.

[0027] By adopting the above technical solution, the adhesive layer can be melted and removed simultaneously in the debonding liquid.

[0028] In summary, the present application includes at least the following beneficial effects.

[0029] After the wafer is etched through, due to the presence of the protective layer, the helium gas sent out by the electrostatic chuck is not likely to leak too much, so that the helium gas detection is not likely to alarm, and the processing technology can proceed smoothly. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flowchart of the main steps of this application. DETAILED DESCRIPTION

[0031] The present application is further described in detail below in conjunction with the accompanying drawings.

[0032] The present application embodiment discloses a MEMS suspended structure cavity release etching method, referring to Figure 1 , specifically including the following steps.

[0033] S1. Coating a protective layer on the back of the etched wafer. The protective layer includes a photoresist and a UV film. In this embodiment, the protective layer is photoresist.

[0034] S2. Heat the substrate wafer to 70-120°C. A single-polished wafer may be used for the substrate wafer. Then, an adhesive layer is coated on the polished surface of the substrate wafer. The adhesive layer may be paraffin, acrylate or polyvinyl alcohol, etc. In this embodiment, paraffin may be used for the adhesive layer. Then, the surface of the substrate wafer coated with the adhesive layer is bonded to the protective layer of the etched wafer.

[0035] S3, the substrate wafer and the bonding layer are naturally cooled to room temperature.

[0036] S4. The etched wafer and the substrate wafer are vacuum heated at a temperature consistent with the heating temperature of the substrate wafer in S2. The vacuum degree is 1 Mbar and maintained for 15 minutes.

[0037] S5. After vacuum heating, check whether there is any adhesive layer overflow on the wafers that have been bonded. If so, use acetone to remove the overflowed adhesive layer.

[0038] S6. Place the substrate wafer on an electrostatic chuck and fix it, and perform etching on the front side of the etched wafer.

[0039] S7, placing the etched wafer into a degumming solution, which may be acetone, isopropyl ketone or a mixture of the two. The degumming solution is heated to 70-120°C. In this embodiment, the degumming solution is heated to 70°C.

[0040] S8. Use oxygen plasma to remove the photoresist remaining on the back side of the etched wafer and the paraffin remaining on the front side of the substrate wafer.

[0041] The following is a demonstration of the optimal value selection of the substrate wafer heating temperature in a MEMS suspended structure cavity release etching method in combination with several embodiments.

[0042] Embodiment 1:

[0043] S1. Coat the back of the etched wafer with photoresist as a protective layer.

[0044] S2. Heat the substrate wafer to 70° C. A single-polished wafer may be used as the substrate wafer. Then, paraffin wax is applied as an adhesive layer to the polished surface of the substrate wafer. Then, the surface of the substrate wafer coated with the adhesive layer is bonded to the protective layer of the etched wafer.

[0045] S3, the substrate wafer and the bonding layer are naturally cooled to room temperature.

[0046] S4. Vacuum heat the etched wafer to 70°C with a vacuum degree of 1 Mbar for 15 minutes.

[0047] Embodiment 2:

[0048] The difference from the first embodiment is that the substrate wafer heating temperature in S2 and the vacuum heating temperature in S4 are 80°C.

[0049] Embodiment three:

[0050] The difference from the first embodiment is that the substrate wafer heating temperature in S2 and the vacuum heating temperature in S4 are 90°C.

[0051] Embodiment 4:

[0052] The difference from the first embodiment is that the substrate wafer heating temperature in S2 and the vacuum heating temperature in S4 are 100°C.

[0053] Embodiment five:

[0054] The difference from the first embodiment is that the substrate wafer heating temperature in S2 and the vacuum heating temperature in S4 are 110°C.

[0055] Embodiment six:

[0056] The difference from the first embodiment is that the substrate wafer heating temperature in S2 and the vacuum heating temperature in S4 are 120°C.

[0057] Each of the above examples was subjected to the following same tests after vacuum heating to obtain corresponding sample parameters.

[0058] The coating uniformity was observed by a combination of naked eye observation and microscope observation. Each example was observed by three people and scored on a scale of 1-5, with 1 being the worst and 5 being the best. The final score of the coating uniformity of each example was the average of the three scores.

[0059] Bonding strength: The bonding force between the adhesive layer and the substrate wafer and the protective layer is detected by tensile testing.

[0060] Bubble density: the more voids there are at the paraffin bonding interface, the more bubbles are formed after vacuum heating, that is, the more bubbles there are per unit area, which reflects the poorer bonding strength between the paraffin, the wafer and the protective layer.

[0061] The paraffin overflow rate is as follows: after the paraffin coating is completed, the total mass of the coating paraffin is recorded in each example; after vacuum heating, the overflowed paraffin is collected and weighed; the paraffin overflow rate can be calculated by dividing the mass of the overflowed paraffin by the total mass of the coating paraffin.

[0062] The paraffin residual rate, the mass M1 of the paraffin used for coating and the mass M2 of the substrate wafer are recorded in each example. The paraffin and the substrate wafer after vacuum heating in each example are placed in a degumming solution formed by 90% concentration of acetone, and the degumming solution is heated to 70°C and allowed to stand for 15 minutes. Then the substrate wafer is taken out and dried to obtain M3 by weighing. The residual rate after degumming is (M3-M2) / M1. The higher the paraffin residual rate, the more difficult it is to clean the corresponding paraffin.

[0063] The specific results of each example are shown in the following table.

[0064]

[0065] It can be seen from this that when the substrate wafer is heated to 100°C, the coated paraffin can be controlled at the best state in terms of uniformity, bonding strength, and defects formed after vacuum heating. There is a certain amount of paraffin overflow at 100°C, and the residual paraffin can also be well controlled at 100°C. If the temperature is too low, the paraffin will not melt fully, and if the temperature is too high, there will be too many volatile components in the paraffin, and the paraffin will be more difficult to clean up later.

[0066] The implementation principle of a MEMS suspended structure cavity release etching method in an embodiment of the present application is: when the wafer needs to be etched through during the suspended structure molding process, a protective layer can be coated on the back of the etching wafer and an adhesive layer can be coated on the front of the substrate wafer, and then the etching wafer and the substrate wafer are bonded together so that the protective layer and the adhesive layer are combined, and then the substrate wafer is placed on an electrostatic chuck, so that during the etching process of the wafer, helium detection is not easy to alarm, and the processing technology can proceed normally. In addition, the substrate wafer is heated to 100°C, so that the paraffin as an adhesive layer has good bonding strength and is also convenient for subsequent cleaning.

[0067] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A MEMS suspended structure cavity release etching method, characterized in that: The specific steps include: S1, coating the back side of the etched wafer with a protective layer, the protective layer comprising a photoresist and a UV film; S2, vacuum heating the etched wafer; S3, performing etching processing on the front side of the etched wafer; S4, removing the photoresist on the back side of the etched wafer; In S1, an adhesive layer is arranged on the surface of the protective layer away from the etching wafer, a substrate wafer is arranged on the surface of the adhesive layer away from the etching wafer, and the substrate wafer is placed on an electrostatic chuck.

2. A MEMS suspended structure cavity release etching method according to claim 1, characterized in that: The adhesive layer includes paraffin wax.

3. A MEMS suspended structure cavity release etching method according to claim 2, characterized in that: The substrate wafer is first heated to 70-120° C., then an adhesive layer is coated on the substrate wafer, and then the surface of the substrate wafer coated with the adhesive layer is bonded to the protective layer of the etching wafer.

4. A MEMS suspended structure cavity release etching method according to claim 3, characterized in that: After the adhesive layer of the substrate wafer and the protective layer of the etching wafer are aligned and bonded, the substrate wafer and the adhesive layer are naturally cooled to room temperature before S2 is performed.

5. A MEMS suspended structure cavity release etching method according to claim 3, characterized in that: The substrate wafer is heated to 100°C.

6. A MEMS suspended structure cavity release etching method according to claim 5, characterized in that: The vacuum heating temperature in S2 is 100°C.

7. A MEMS suspended structure cavity release etching method according to claim 2, characterized in that: After the S2 vacuum heating, the bonded wafers are inspected for any adhesive layer overflow, and if so, acetone is used to remove the overflowed adhesive layer.

8. A MEMS suspended structure cavity release etching method according to claim 2, characterized in that: In S3, the etched wafer is placed into a degumming solution.

9. A MEMS suspended structure cavity release etching method according to claim 8, characterized in that: The degumming solution is heated to 70-120°C.

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