A method for removing static charge accumulation of MEMS chip

Abstract

The present invention relates to a method for removing the accumulation of static charge of a MEMS chip, comprising: a. evacuating a closed chamber to a degree of vacuum of 1Pa-1.2Pa and a temperature of 40°C-50°C; allowing the static charge of the MEMS device to accumulate on the surface of the dielectric layer; b. introducing a mixed gas of nitrogen and gaseous alcohol at a temperature of 40°C-50°C to make it fully contact with the surface of the dielectric layer and remove water vapor particles adsorbed on the surface of the dielectric layer of the wafer; c. introducing a mixed gas of nitrogen, gaseous alcohol and gaseous hydrogen fluoride at a temperature of 40°C-50°C to strip a certain thickness of the dielectric layer in the MEMS device structure; then introducing nitrogen to completely remove the residual gaseous hydrogen fluoride gas in the chamber; d. vacuum sealing and packaging between the MEMS device and the silicon cover plate. The present invention uses gas cleaning to remove the accumulated charge in the MEMS device, avoids leakage between the electrodes of the MEMS device, improves the insulation resistance between the electrodes of the MEMS device, and improves the yield and long-term reliability of the MEMS device.

Description

Technical Field

[0001] The invention relates to the technical field of MEMS device manufacturing, and in particular to a method for removing static charge accumulation from a MEMS chip. Background Art

[0002] During the manufacturing process of MEMS devices, the accumulation of static charge on the wafer surface is mainly caused by the following reasons: static charge accumulation caused by the contact and separation process between objects, such as static charge accumulation during the loading and lifting operation of the wafer on the electrostatic chuck, static charge accumulation on the wafer during the photoresist coating process, static charge accumulation during the spin drying process of the wafer; the radio frequency plasma effect in the vacuum process equipment (CVD, PVD, etc.) causes static charge accumulation on the wafer surface; static charge accumulation during the high-pressure rinsing process of the wafer, etc.

[0003] During the manufacturing process of MEMS chips, static charges will inevitably accumulate. The accumulated static charges will move in the silicon dioxide dielectric layer (hereinafter referred to as the dielectric layer) of the device under the action of electric field or temperature, causing leakage between electrodes of the MEMS device, which seriously affects the yield and long-term reliability of the MEMS device. Therefore, it is of great significance to study how to eliminate the accumulation of static charges.

[0004] After searching existing patents, the Chinese patent "Method for Removing Movable Ion Charges in Chips" (patent number CN104835733B) adopts a solution to bake the chip to gather the accumulated charges on the upper surface of the dielectric layer; remove a certain thickness of the surface dielectric layer with HF acid solution, and finally rinse and dry the chip to achieve the purpose of removing the accumulated surface charges; however, this method is not suitable for removing the electrostatic charge accumulation of MEMS devices: on the one hand, MEMS devices often have movable microstructures, and the cleaning of the microstructures in hydrofluoric acid solution and the subsequent flushing and drying processes will cause the MEMS movable microstructures to have problems of attraction and fracture. On the other hand, the lead-out position of the silicon electrode structure of the MEMS device is usually made with a conductive metal pattern, and cleaning with hydrofluoric acid solution will corrode the conductive metal, which directly affects the electrical performance and packaging reliability of the device. Summary of the invention

[0005] The purpose of the present invention is to provide a method for removing the electrostatic charge accumulation of a MEMS chip, remove the charge accumulated in the MEMS device, and improve the yield and long-term reliability of the MEMS device.

[0006] The present invention adopts the following technical solution:

[0007] A method for removing static charge accumulation of a MEMS chip, characterized by comprising the following steps:

[0008] a. Place the wafer with the MEMS device structure in a closed chamber, evacuate the chamber to a vacuum degree of 1Pa-1.2Pa, and raise the chamber temperature to 40℃-50℃; after the wafer temperature is raised, the static charge of the dielectric layer in the MEMS device gradually accumulates on the surface of the dielectric layer;

[0009] b. Introduce a mixture of nitrogen and gaseous alcohol at a temperature of 40°C-50°C into the closed chamber. The flow rate of the mixed gas is: 1000sccm of nitrogen and 200sccm of gaseous alcohol. The introduction time is 300s. After the mixed gas is fully in contact with the surface of the dielectric layer, the gas in the chamber is discharged through the exhaust port. Repeat the above operation twice to remove the water vapor particles adsorbed on the surface of the wafer dielectric layer using the mixed gas of nitrogen and gaseous alcohol.

[0010] c. A mixture of nitrogen, gaseous alcohol and gaseous hydrogen fluoride at a temperature of 40°C-50°C is introduced into the sealed chamber to remove a certain thickness of the dielectric layer in the MEMS device structure; then nitrogen is introduced into the sealed chamber to completely remove the residual gaseous hydrogen fluoride in the chamber;

[0011] d. The MEMS device after the accumulated charge is removed is vacuum sealed and packaged with the silicon cover in a vacuum environment.

[0012] The further technical solution is:

[0013] In step c, a mixed gas of nitrogen, gaseous alcohol and gaseous hydrogen fluoride is introduced into the closed chamber. The flow rate of the mixed gas is: nitrogen 1000sccm, gaseous alcohol 200sccm, gaseous hydrogen fluoride 200sccm, and the introduction time is 10s. The dielectric layer in the MEMS device structure is stripped of a certain thickness by gaseous hydrogen fluoride. The entire cleaning process consumes a dielectric layer thickness of Gaseous hydrogen fluoride removes the remaining charge on the surface of the dielectric layer while stripping off a dielectric layer of a certain thickness. Finally, nitrogen gas is introduced into the closed chamber with a nitrogen flow rate of 1000 sccm, an introduction time of 150 s, and a temperature of 45°C. The residual gaseous hydrogen fluoride in the chamber is completely removed by nitrogen gas.

[0014] The advantages of the present invention are as follows: the present invention is applicable to MEMS devices with movable microstructures, and utilizes gas cleaning to remove the accumulated charges in the MEMS devices, thereby avoiding leakage between the electrodes of the MEMS devices, and improving the insulation resistance between the electrodes of the MEMS devices, thereby improving the yield and long-term reliability of the MEMS devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 A flow chart of a method for removing static charge accumulation in a MEMS device structure according to the present invention;

[0017] Figure 2 It is a schematic diagram of the surface charge distribution and adsorbed water vapor particles of the dielectric layer of the MEMS device structure that has not been gas cleaned in the present invention;

[0018] Figure 3 A schematic diagram of the charge distribution on the dielectric layer surface of the MEMS device structure after chamber heating according to the present invention;

[0019] Figure 4 A schematic diagram of the charge distribution on the surface of the dielectric layer of the MEMS device structure after cleaning by a mixture of nitrogen and gaseous alcohol according to the present invention;

[0020] Figure 5 It is a schematic diagram of the surface charge distribution of the dielectric layer of the MEMS device structure after being cleaned by a mixed gas of nitrogen, gaseous alcohol and gaseous hydrofluoric acid in the present invention;

[0021] Figure 6 This is a schematic diagram of vacuum sealing and packaging of a MEMS device structure and a cover plate after gas cleaning according to the present invention;

[0022] Figure 7 The insulation resistance test result between electrodes of the MEMS device before gas cleaning of the present invention;

[0023] Figure 8 This is a test result of the insulation resistance between electrodes of the MEMS device after cleaning by the implementation method of the present invention.

[0024] In the figure, 1. silicon substrate, 2. dielectric layer, 3. silicon movable structure, 4. water vapor particles, 5. accumulated static charge, 6. conductive metal, 7. conductive metal, 8. silicon electrode, 9. silicon packaging cover, 10. glass sauce. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0026] like Figure 2As shown, in the MEMS device structure, charges are usually accumulated 5 on the surface of the dielectric layer 2. The charge accumulation in the dielectric layer is caused by the presence of a large number of electron or hole traps inside and on the surface of the dielectric material. At the same time, the MEMS device is exposed to the air in the early process, and water vapor particles 4 are often adsorbed on the surface of the dielectric layer. Figure 2 Shown is a schematic diagram of the charge distribution and adsorbed water vapor particles on the dielectric layer of a MEMS device.

[0027] Figure 1 is a flow chart of a method for removing static electricity from a MEMS structure in an embodiment of the present invention;

[0028] like Figure 1 As shown, the specific steps of this method for removing static electricity accumulation in MEMS structures are as follows:

[0029] 1. Place the wafer with MEMS device structure (hereinafter referred to as wafer) in a closed chamber, evacuate the closed chamber to a certain vacuum degree; increase the chamber temperature; introduce a mixture of nitrogen and gaseous alcohol until the chamber reaches a fixed pressure value, and then discharge the gas in the chamber through the exhaust port after maintaining it for a period of time. Repeat the above inflation and deflation process several times.

[0030] Specifically: Place the MEMS wafer with the dielectric layer in a sealed chamber in a gaseous hydrogen fluoride device (equipment manufacturer: SPTS, model: uEtch), and evacuate the sealed chamber until the vacuum reaches 1 Pa. Set the chamber temperature to 45°C; heat the wafer. When the wafer temperature rises, the static charge of the dielectric layer in the MEMS device gradually accumulates on the surface of the dielectric layer, such as Figure 3 As shown, Figure 3 The present invention provides a diagram of the electrostatic charge distribution on the surface of the dielectric layer of the MEMS device after cavity heating.

[0031] Second, introduce a mixture of nitrogen and gaseous alcohol into the closed chamber (mixed gas flow rate: nitrogen 1000sccm, gaseous alcohol 200sccm; introduction time 300s, temperature 45°C), so that the mixed gas is fully in contact with the surface of the dielectric layer, and then exhaust the gas in the chamber through the exhaust port; repeat the above operation twice, and use the mixed gas of nitrogen and gaseous alcohol to remove the water vapor particles adsorbed on the surface of the wafer dielectric layer. Figure 4 As shown, it is a schematic diagram of water vapor adsorbed on the surface of the MEMS device and the distribution of static charges after cleaning with a mixed gas of nitrogen and gaseous alcohol provided by the present invention, wherein the water vapor is removed.

[0032] 3. A mixture of nitrogen, gaseous alcohol and gaseous hydrogen fluoride is introduced into a closed chamber until a fixed pressure value is reached in the chamber and maintained for a period of time to remove a certain thickness of the dielectric layer in the MEMS device structure; nitrogen is introduced into the closed chamber to completely remove the residual gaseous hydrogen fluoride in the chamber with nitrogen.

[0033] Specifically, a mixed gas of nitrogen, gaseous alcohol and gaseous hydrogen fluoride is introduced into a closed chamber (the mixed gas flow rate is: nitrogen 1000sccm, gaseous alcohol gas 200sccm, gaseous hydrogen fluoride 200sccm, the introduction time is 10s, and the temperature is 45°C). The dielectric layer in the MEMS device structure is stripped of a certain thickness using gaseous hydrogen fluoride. The entire cleaning process consumes a dielectric layer thickness of Gaseous hydrogen fluoride removes the remaining charge on the surface of the dielectric layer while stripping off a dielectric layer of a certain thickness. Figure 5 The electrostatic charge distribution diagram of the surface of the MEMS device after the wafer surface is cleaned and stripped of a certain thickness of the dielectric layer provided by the present invention. Finally, nitrogen gas is introduced into the closed chamber (nitrogen flow rate is 1000sccm, introduction time is 150s, temperature is 45°C), and the residual gaseous hydrogen fluoride gas in the chamber is completely removed by nitrogen gas.

[0034] 4. In a vacuum environment, the MEMS device after the accumulated charge is removed is vacuum-sealed and packaged with the silicon cover plate.

[0035] Specifically: After gas cleaning, the MEMS device will continue to absorb water vapor particles and electrostatic charges in the air when placed in the air, and should be immediately vacuum sealed and packaged for no more than 2 hours. In this implementation case, glass slurry 10 is used as a bonding agent in a vacuum environment (vacuum degree is 1pa) to bond the MEMS device structure and the silicon cover plate 9 with a cavity structure together to achieve the purpose of vacuum sealing packaging. The vacuum sealing packaging process is not limited to the use of any other sealing materials, and is mainly to isolate the outside air and prevent the MEMS device from continuing to absorb charges in the air. Figure 6 A schematic diagram of the implementation of the present invention, in which the MEMS device is vacuum sealed and packaged after the wafer surface is cleaned by a gas environment.

[0036] Test comparison results:

[0037] 1. Use a resistance group tester to test the resistance between the electrodes of a MEMS device with accumulated static charge, such as Figure 7 The test result is shown in the figure. It can be seen from the figure that the resistance between the electrodes is 270.471Mohm, indicating that there is leakage between the electrodes, resulting in conduction between the electrodes.

[0038] 2. The MEMS device with accumulated static charge is cleaned with gas using the process method for removing static electricity from the MEMS structure provided in this embodiment. After cleaning, the resistance between the electrodes is tested. Figure 8 The figure shows the test results. It can be seen from the figure that the resistance between the electrodes is 12.0937 Gohm, which means that the leakage problem between the electrodes is significantly improved and the insulation performance between the electrodes is significantly improved.

[0039] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for removing static charge accumulation from MEMS chips, Features The following steps are involved: a. Place the wafer with the MEMS device structure in a closed chamber, evacuate the chamber to a vacuum degree of 1Pa-1.2Pa, and raise the chamber temperature to 40℃-50℃; after the wafer temperature is raised, the static charge of the dielectric layer in the MEMS device gradually accumulates on the surface of the dielectric layer; b. Introduce a mixture of nitrogen and gaseous alcohol at a temperature of 40°C-50°C into the closed chamber. The flow rate of the mixed gas is: 1000sccm of nitrogen and 200sccm of gaseous alcohol. The introduction time is 300s. After the mixed gas is fully in contact with the surface of the dielectric layer, the gas in the chamber is discharged through the exhaust port. Repeat the above operation twice to remove the water vapor particles adsorbed on the surface of the wafer dielectric layer using the mixed gas of nitrogen and gaseous alcohol. c. A mixture of nitrogen, gaseous alcohol and gaseous hydrogen fluoride at a temperature of 40°C-50°C is introduced into the sealed chamber to remove a certain thickness of the dielectric layer in the MEMS device structure; then nitrogen is introduced into the sealed chamber to completely remove the residual gaseous hydrogen fluoride in the chamber; d. The MEMS device after the accumulated charge is removed is vacuum sealed and packaged with the silicon cover in a vacuum environment.

2. A method for removing static charge accumulation of a MEMS chip according to claim 1, Features: In step c, a mixed gas of nitrogen, gaseous alcohol and gaseous hydrogen fluoride is introduced into the closed chamber. The flow rate of the mixed gas is: nitrogen 1000sccm, gaseous alcohol 200sccm, gaseous hydrogen fluoride 200sccm, and the introduction time is 10s. The dielectric layer in the MEMS device structure is stripped of a certain thickness by gaseous hydrogen fluoride. The entire cleaning process consumes a dielectric layer thickness of Gaseous hydrogen fluoride removes the remaining charge on the surface of the dielectric layer while stripping off a dielectric layer of a certain thickness. Finally, nitrogen gas is introduced into the closed chamber with a nitrogen flow rate of 1000 sccm, an introduction time of 150 s, and a temperature of 45°C. The residual gaseous hydrogen fluoride in the chamber is completely removed by nitrogen gas.

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