阅读说明：本技术 一种mems悬浮结构的深硅刻蚀方法 (Deep silicon etching method for MEMS suspension structure ) 是由 喻磊 曹卫达 丁景兵 黄斌 于 2021-09-23 设计创作，主要内容包括：本发明涉及一种MEMS悬浮结构的深硅刻蚀方法,其特征在于将MEMS悬浮结构的深硅刻蚀程序设置为两个刻蚀阶段：刻蚀第一阶段,采用n次沉积步骤—刻蚀步骤的循环,其中n大于20；刻蚀第二阶段,采用m次沉积步骤—刻蚀步骤—停止冷却步骤的循环,其中m大于20。本发明提高MEMS悬浮可动结构深硅刻蚀时的散热效果,避免刻蚀局部温度过高导致的结构损伤,提升MEMS悬浮可动结构释放的可靠性。(The invention relates to a deep silicon etching method of an MEMS (micro-electromechanical system) suspension structure, which is characterized in that a deep silicon etching program of the MEMS suspension structure is set into two etching stages: etching the first stage by adopting n cycles of deposition step-etching step, wherein n is more than 20; and in the second stage of etching, the circulation of the deposition step, the etching step and the cooling step is stopped for m times, wherein m is more than 20. The invention improves the heat dissipation effect of the MEMS suspension movable structure during deep silicon etching, avoids the structural damage caused by overhigh etching local temperature and improves the reliability of the release of the MEMS suspension movable structure.)

1. A deep silicon etching method of an MEMS suspension structure is characterized in that a deep silicon etching program of the MEMS suspension structure is set to be two etching stages:

etching the first stage by adopting n cycles of deposition step-etching step, wherein n is more than 20;

and in the second stage of etching, the circulation of the deposition step, the etching step and the cooling step is stopped for m times, wherein m is more than 20.

2. The deep silicon etching method for the MEMS suspension structure, as recited in claim 1, wherein the cycle of the deposition step, the etching step and the cooling step is stopped, and the automatic control is performed by the program setting of the etching device, and the program setting in the etching device is: 1. step0, plasma ignition and stabilization; 2. step1, passivation deposition step, setting passivation gas flow, passivation time, coil power and the like; 3. step2, etching step, setting etching gas flow, passivation time, coil power and the like, step3, stopping the cooling step, setting the gas flow and the coil power to be 0, and setting step 1-step 3 circulation, wherein the circulation frequency is m.

Technical Field

The invention belongs to the technical field of semiconductors, and relates to a deep silicon etching method for releasing a suspended movable structure.

Background

Deep silicon etching is a key technology for realizing the MEMS suspension movable structure. At present, a Bosch process is mainly adopted for deep silicon etching, and the etching process is carried out by alternately and circularly carrying out a passivation step and an etching step, wherein the passivation step is used for depositing a layer of polymer on the side wall and the bottom of a groove to be used as a protective layer to protect the side wall from being corroded, and the etching step is used for removing the passivation layer at the bottom of an etching opening and carrying out a physical and chemical reaction with exposed silicon to etch the silicon.

When the movable structure of the suspended silicon is etched, heat generated in the etching process is conducted through silicon which is not completely etched in the etching opening and is conducted to the cooled bottom through the anchor point, so that the surface temperature of the movable structure of the silicon is kept stable. Once the large etching opening is completely etched through, the heat load in etching is completely loaded on the structure with the smaller critical dimension of the etching opening, and the heat can only be conducted through the part of the suspended silicon structure, and when the conduction path of the part of the suspended silicon structure is too long, the problem of too high etching local temperature is easily caused. Observation results show that as etching is nearly finished, the critical dimension is etched through, the thermal conductivity of the suspension structure is remarkably reduced, the etching equipment cools the silicon wafer substrate by using helium back cooling and is not enough to rapidly cool the suspension structure, and accumulated heat cannot be conducted out in time, so that the local temperature of the structure is overhigh. The passivation layer is volatilized quickly due to overhigh temperature, the side wall cannot be protected, and the etching reaction is aggravated due to overhigh temperature, so that the bottom of the structure is seriously damaged by etching, and the device is badly influenced, so that the problem of overhigh local temperature becomes a limiting factor in the deep silicon etching of the structure.

In some documents, a solution is a step etching process, that is, an etching procedure is manually paused, cooled for a certain time, and then restarted, so that multiple manual pausing and restarting etching procedures are performed to help heat dissipation to achieve the purpose of improving local overheating.

Disclosure of Invention

The invention aims to provide a deep silicon etching method, which improves the heat dissipation effect of an MEMS suspension movable structure during deep silicon etching, avoids structural damage caused by overhigh etching local temperature and improves the reliability of release of the MEMS suspension movable structure.

In order to achieve the purpose, the invention adopts the following technical scheme:

the deep silicon etching procedure of the MEMS suspension structure is set into two stages, wherein in the first stage, the structure is large in size and not completely etched, the heat dissipation is good, and the cycle of passivation step-etching step is adopted; in the second stage, the large size of the structure is completely etched, the key size is not completely etched, at the moment, the heat dissipation of the suspension structure begins to gradually deteriorate, the etching heat begins to accumulate on the suspension silicon structure, a cooling stopping step is added after the etching step in each cycle, and a cycle of passivation step, etching step and cooling stopping step is formed, namely, cooling stopping is carried out after each etching step, plasma stops generating during the cooling stopping step, the etching heat can be conducted out within the stopping time, the problem of overhigh local temperature can be remarkably avoided, and therefore the damage to the back of the sensitive structure is eliminated. In the second stage of the deep silicon etching method, the cooling stopping step is a part of an etching program, and the etching program does not need to be manually paused; and the cooling and heat dissipation time is set after each etching cycle, so that the heat dissipation effect is good, and the damage of the bottom of the structure caused by overhigh local temperature can be obviously avoided.

In order to illustrate the invention more clearly, the drawings that are needed in the description of the embodiments will be briefly described below, it being apparent that the drawings in the description below are only some embodiments of the invention, and that other drawings may be derived from these drawings by a person skilled in the art without inventive effort.

Description of the drawings:

FIG. 1 is a flow chart of a deep silicon etching method in an embodiment of the present invention;

FIG. 2 is a scanning electron micrograph of a MEMS annular suspension structure subjected to typical localized overheating resulting in bottom damage;

FIG. 3 is a scanning electron microscope image of the bottom of the MEMS annular suspension structure in the embodiment of the invention.

Detailed Description

In order to make the technical solutions of the present invention better understood, the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

As shown in fig. 1, the deep silicon etching method for the MEMS suspension structure provided by the present invention sets the deep silicon etching procedure of the MEMS suspension structure as two stages:

in the first stage of etching, the MEMS suspension structure is large in size, not completely etched and good in heat dissipation, and the cycle of 'deposition step-etching step' is adopted;

in the second stage of etching, the MEMS suspension structure is completely etched in large size, the critical dimension is not completely etched, at the moment, the heat dissipation of the suspension structure begins to gradually deteriorate, etching heat begins to accumulate on the suspension silicon structure, a cooling stopping step is added after the etching step in each cycle, and a cycle of a deposition step, the etching step and the cooling stopping step is formed, namely, cooling stopping is carried out after each etching step, plasma stops generating during the cooling stopping step, the etching heat can be conducted out within the stopping time, the problem of overhigh local temperature can be remarkably avoided, and therefore the damage to the back of the sensitive structure is eliminated. In the second stage of the deep silicon etching method, the cooling stopping step is a part of an etching program, and the etching program does not need to be manually paused; and the cooling and heat dissipation time is set after each etching cycle, so that the heat dissipation effect is good, and the damage of the bottom of the structure caused by overhigh local temperature can be obviously avoided.

An example of a 50 micron thick MEMS gyroscope suspension deep silicon etch procedure is as follows:

the first stage of etching comprises 200 cycles of deposition step-etching step, wherein in the deposition step, gases are all octafluorocyclobutane, the gas flow is 300sccm, the upper radio frequency power is 2500W, the lower radio frequency power is 0W, the process gas pressure is 30mT, the substrate temperature is 15 ℃, and the deposition time is 1.0 s-1.1 s; in the etching step, the gas is sulfur hexafluoride, the etching time is 2.0 s-2.2 s, the gas flow is 400sccm, the upper radio frequency power is 2500W, the lower radio frequency power is 50W-55W, and the etching duty ratio is 50%.

The second stage of etching comprises 150 cycles of 'deposition step-etching step-cooling stopping step', wherein in the deposition step, deposition gas is octafluorocyclobutane, the gas flow is 300sccm, the upper radio frequency power is 2500W, the lower radio frequency power is 0W, the process gas pressure is 50mT, the substrate temperature is 15 ℃, and the deposition time is 1.1 s-1.2 s; in the etching step, the gas is sulfur hexafluoride, the etching time is 2.2 s-2.4 s, the gas flow is 400 sccm-430 sccm, the upper radio frequency power is 2500W, the lower radio frequency power is 55W-60W, and the etching duty ratio is 50%; in the cooling stopping step, the gas flow is 0, the upper radio frequency power and the lower radio frequency power are both 0, and the time is 5 s. The "deposition step-etching step-cooling stop step" is cyclically automatically controlled by the program settings of the etching apparatus, the program settings in the etching apparatus being: 1. step0, plasma ignition and stabilization; 2. step1, passivation step, setting passivation gas flow, passivation time, coil power and the like; 3. step2, etching step, setting etching gas flow, passivation time, coil power and the like; 4. step3, stop the cooling step, set the gas flow and the coil power to 0, set step 1-step 3 cycles with the number of cycles of 150.

Second, an example of a 80 micron thick MEMS ring gyroscope suspension deep silicon etch procedure is as follows:

the first etching stage comprises 420 cycles of deposition step-etching step, wherein in the deposition step, gases are all octafluorocyclobutane, the gas flow is 300sccm, the upper radio frequency power is 2500W, the lower radio frequency power is 0W, the process gas pressure is 30mT, the substrate temperature is 15 ℃, and the deposition time is 1.0 s-1.1 s; in the etching step, the gas is sulfur hexafluoride, the etching time is 2.0 s-2.4 s, the gas flow is 400sccm, the upper radio frequency power is 2500W, the lower radio frequency power is 50W-60W, and the etching duty ratio is 50%.

The second stage of etching comprises 150 cycles of 'deposition step-etching step-cooling stopping step', wherein in the deposition step, the gas deposition gas is octafluorocyclobutane, the gas flow is 300sccm, the upper radio frequency power is 2500W, the lower radio frequency power is 0W, the process gas pressure is 50mT, the substrate temperature is 15 ℃, and the deposition time is 1.1 s-1.2 s; in the etching step, the gas is sulfur hexafluoride, the etching time is 2.4 s-2.6 s, the gas flow is 400 sccm-450 sccm, the upper radio frequency power is 2500W, the lower radio frequency power is 60W-65W, and the etching duty ratio is 50%; in the cooling stopping step, the gas flow is 0, the upper radio frequency power and the lower radio frequency power are both 0, and the time is 5 s.

FIG. 2 shows the etching effect of a suspension structure of a MEMS ring gyroscope with the thickness of 80 microns by adopting the conventional Bosch process, and the damage to the edge of the bottom of the suspension structure is started to occur due to the local overheating effect in the deep silicon etching of the suspension structure.

FIG. 3 shows the etching effect of the optimized 'deposition step-etching step-cooling stopping step' cyclic deep silicon etching process for a certain MEMS annular gyroscope suspension structure with the thickness of 80 microns, and the bottom edge of the suspension structure is smooth and free of damage.

It will be understood that the above embodiments are merely exemplary embodiments taken to illustrate the principles of the present invention, which is not limited thereto. It will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the spirit and substance of the invention, and these modifications and improvements are also considered to be within the scope of the invention.