WO2014094538A1

WO2014094538A1 - Deep silicon etch method

Info

Publication number: WO2014094538A1
Application number: PCT/CN2013/088450
Authority: WO
Inventors: 蒋中伟
Original assignee: 北京北方微电子基地设备工艺研究中心有限责任公司
Priority date: 2012-12-20
Filing date: 2013-12-03
Publication date: 2014-06-26
Also published as: CN103887164A; CN103887164B; TW201426866A; TWI514470B

Abstract

A deep silicon etch method comprises: a deposition step (S101), generating a protection layer to protect an etch side wall; an etch step (S102), etching an etch bottom and the etch side wall; and repeating the deposition step (S101) and the etch step (S102) until the whole deep silicon etch process is finished; and further comprises a bottom smoothing step (S103), the bottom smoothing step (S103) being: performing plasma processing by using a fluoride gas to remove polymers generated on the etch bottom because of deposition, a process pressure used in the bottom smoothing step (S103) being less than a process pressure used in the etch step (S102), and the bottom smoothing step (S103) being performed at least once in the whole deep silicon etch process. By means of the deep silicon etch method, in the deep silicon etch process, polymers on the etch bottom are suppressed from gradually increasing, and micro masks or silicon grass is suppressed from generating, so as to improve an etch speed and a selection ratio of the deep silicon etch, and improve the roughness of the etch bottom.

Description

Deep silicon etching method

Technical field

The present invention relates to the field of semiconductor fabrication, and more particularly to a deep silicon etching method. Background technique

MEMS (Micro-Electro-Mechanical Systems) devices and MEMS systems are increasingly used in automotive and consumer electronics, as well as TSV (Through Silicon Etch) technology in future packaging applications. The broad prospects, dry plasma deep silicon etching process has gradually become one of the mainstream processes in the field of MEMS processing and TSV technology.

The main difference between the deep silicon etching process and the general silicon etching process is that the etching depth of the deep silicon etching process is much larger than that of the general silicon etching process, and the etching depth of the deep silicon etching process is generally several tens of micrometers. Even hundreds of microns, and the etching depth of the general etch process is less than 1 micron. In order to etch a silicon material having a thickness of several tens of micrometers, a deep silicon etching process is required to have a faster etching rate, a higher selectivity ratio, and a larger aspect ratio.

The typical deep silicon etching process is the Bosch process. In the Bosch process, the entire etching process is an alternating cycle of the etching step and the deposition step. 1 shows a flow chart of the Bosch process. As shown in FIG. 1, the Bosch process includes: step S1, a deposition step; step S2, an etching step; step S3, determining whether the etching reaches a predetermined depth, and if so, ending Etching; if no, go to step S1 and repeat steps S1 to S3. The process gas in the etching step S2 is usually SF ₆ (sulfur hexafluoride). Although the gas has a high etching rate in etching the silicon substrate, it is difficult to be characterized by isotropic etching. Control the sidewall morphology. In order to reduce the etching of the sidewalls, the process is added to the deposition step S1, the process gas of the deposition step S1 is usually C ₄ F ₈ (carbon tetrafluoride), and the deposition step S1 deposits a polymer protective layer on the sidewalls. The protective sidewalls are not etched, thereby enabling etching only on the vertical plane.

During plasma deep silicon etching, F (fluorine) radicals and 8 plasmas are generated, of which The etching of silicon is mainly performed by the process of reacting F radicals and silicon to form SiF ₄ to complete the wind, 3⁄4 禹T chemical etching; at the same time, SF _X plasma has physical bombardment effect on silicon, that is, physical etching The etching of silicon is only a small contribution to the silicon etching compared to the chemical etching of the F radical.

In the etching step S2, in order to obtain a faster silicon etching rate, a higher process pressure (usually between 50 and 500 mT) is usually employed. This is because the etching of silicon is mainly based on the chemical etching of F radicals, and higher density F radicals can be obtained under higher process pressure, and more F radicals lead to higher silicon. Etching rate. However, the etching of the polymer produced in the deposition step S1 is mainly based on the bombardment of ions, and the collision of various particles increases under a high process pressure, and the energy of the ions is significantly lower, thereby This results in a significantly lower etch rate of the polymer. Due to the decrease of the etching rate of the polymer, the polymer produced in the deposition step S1 is difficult to be completely etched and removed, and gradually increases in the subsequent process steps. After a plurality of deposition steps S1 and etching steps S2, a polymer is formed. Similar to the "micro-mask" morphology, even in the case of severe siliceous, Figure 2 shows an electron micrograph of the silicon grass produced in deep silicon etching. The generation of a micromask or silica will increase the roughness of the etched bottom and reduce the quality of the deep silicon etch.

In order to avoid the generation of micro-mask or silicon grass, in the prior art, the etching step is usually performed at a lower process pressure, but the lower process pressure causes a decrease in the etching rate of the silicon, which in turn leads to etching. The choice is lower than the ratio. Summary of the invention

The invention provides a deep silicon etching method for suppressing the gradual increase of the etched bottom polymer during the deep silicon etching process, thereby suppressing the generation of the micromask or the silicon grass, thereby improving the etching rate of the deep silicon etching. And choose the ratio and improve the roughness of the etched bottom.

In order to achieve the above object, an embodiment of the present invention provides a deep silicon etching method, the method comprising:

a deposition step of forming a protective layer to protect the etched sidewalls; Etching step of etching the etched bottom and the etched sidewall;

Repeating the deposition step and the etching step until the end of the entire deep silicon etching process;

The bottom smoothing step further includes: performing a plasma treatment using a fluorine-containing gas to remove a polymer generated by deposition at the bottom of the etching; and, the bottom smoothing step adopts a process pressure less than The process pressure used in the etching step,

The bottom smoothing step is performed at least once throughout the deep silicon etch process.

Preferably, the bottom smoothing step is performed once every N deposition steps and etching steps, N being a positive integer.

Preferably, the bottom smoothing step is performed after the etching step.

Preferably, the process pressure used in the etching step is 40 to 500 mT.

Preferably, the process pressure is 50 to 300 mT.

Preferably, the process pressure used in the bottom smoothing step is 2 to 50 mT.

Preferably, the upper radio frequency power used in the bottom smoothing step is 50 ~ 1000W, the lower radio frequency power is 0 ~ 50W, and the flow rate of the fluorine-containing gas is 5 ~ 500sccm.

Preferably, the fluorine-containing gas used in the bottom smoothing step is CF ₄ , SF ₆ , NF ₃ , or

One of CHF ₃ .

Preferably, the process time of the bottom smoothing step is 0.5 ~ 10S.

Advantageous effects of the present invention include:

In one embodiment, the deep silicon etching method provided by the embodiment of the present invention has a bottom smoothing step, and a smaller process pressure is used in the step, so that the energy of the plasma increases, and the energy increase of the plasma can improve the deposition. The etching rate of the polymer produced in the step is etched, which in turn enhances the etching of the polymer and inhibits the increase of the polymer at the bottom of the etching.

Secondly, the deep silicon etching method provided by the embodiment of the present invention can remove the residual polymer at the bottom of the etching in time due to the introduction of the bottom smoothing step, and effectively improve the excessive etching under the high process pressure. The bottom unevenness caused by the rate can suppress the increase of the roughness of the bottom of the etching and improve the smoothness of the bottom of the etching. Thirdly, the deep silicon etching method provided by the embodiment of the present invention can suppress the increase of the etched bottom polymer and improve the roughness of the etched bottom, thereby suppressing the etching due to the introduction of the bottom Τ ^. The increase in the bottom polymer leads to the formation of micro-masks and even silice.

Fourthly, the deep silicon etching method provided by the embodiment of the present invention can effectively suppress the formation of the micro-mask or even the silicon grass by introducing the bottom smoothing step, so that a higher process pressure can be adopted in the etching step. The etching rate and the etching selectivity ratio are improved. DRAWINGS

The above and/or additional aspects and advantages of the present invention will become apparent and readily understood from

Figure 1 is a flow chart of a Bosch process in the prior art;

2 is an electron micrograph of a silicon grass produced in a prior art deep silicon etching;

3 is a flowchart of a deep silicon etching method according to an embodiment of the present invention;

FIG. 4 is an effect diagram of deep silicon etching according to an embodiment of the present invention. detailed description

In order to enable those skilled in the art to better understand the technical solutions of the present invention, the deep silicon etching method provided by the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Embodiments of the present invention provide a deep silicon etching method, the method comprising: a deposition step of forming a protective layer to protect an etched sidewall; and an etching step of etching the etched bottom and the etched sidewall; The deposition step and the etching step are repeated until the entire deep silicon etching process is completed. In the deep silicon etching method, a bottom smoothing step is further included, the bottom smoothing step is: performing a plasma treatment using a fluorine-containing gas to remove a polymer generated by deposition at the bottom of the etching; and the bottom smoothing step is adopted The process pressure is less than the process pressure used in the etching step, and the bottom smoothing step is performed at least once throughout the deep silicon etching process.

During the above-described alternate cycle of performing the deposition step and the etching step, the sinking can be performed each time After the stacking step and the etching step, the bottom smoothing step is performed once; the bottom smoothing step may also be interlaced by one ,1, for example, after each N deposition steps and etching steps, the bottom smoothing step is performed, N It is a positive integer; in addition, the bottom smoothing step may be performed at non-fixed intervals depending on the degree of bottom roughness of the entire process or the amount of polymer remaining at the bottom of the etch.

Wherein, the size of N may be set according to actual etching needs, for example, according to the amount of polymer remaining at the bottom of the etching, for example, setting N to 2, and performing the above after each deposition step and etching step is performed. Bottom smoothing step. For example, if N is set to 3, the deposition step and the etching step are performed three times, and the bottom smoothing step is performed once.

In the embodiment of the present invention, for the bottom smoothing step for reducing the bottom roughness, the bottom smoothing step is preferably performed after the etching step. In order to better achieve smoothness of the etched bottom, more preferably, a bottom smoothing step is performed after each deposition step and etching step.

The deep silicon etching method provided by the embodiment of the present invention will be described below with reference to a specific example. Referring to FIG. 3, a flow chart of a deep silicon etching method according to an embodiment of the present invention is shown. The deep silicon etching method includes:

Step S101, a deposition step. The depositing step is: creating a protective layer to protect the etched sidewalls.

Step S102, an etching step. The etching step is: etching the etched bottom and the etched sidewall.

Step S103, a bottom smoothing step. The bottom smoothing step is: performing a plasma treatment using a fluorine-containing gas to remove a polymer generated by deposition at the bottom of the etching; and, the bottom smoothing step employs a process pressure lower than a process pressure employed in the etching step.

Step S104: determining whether the etching reaches a predetermined depth, and if yes, ending the etching; if not, proceeding to step S101, and repeating steps S101 to S104.

In the embodiment of the present invention, the residual polymer is removed in time due to the introduction of the bottom smoothing step. The micro-mask or the silicon grass formed by the polymer of the A field is not smoothed by the higher process pressure in the prior art, so that a higher process pressure can be used in the etching step. The process pressure used in the etching step is 40-500 mT, and preferably, the process pressure is 50-300 mT. The deep silicon etching method provided by the embodiment of the present invention adopts a high process pressure in the etching step. It is possible to increase the etching rate and the etching selectivity while suppressing the formation of the micro-mask or the silicon grass.

For the bottom smoothing step provided by the embodiment of the present invention, the process pressure used is 2 to 50 mT. At lower process pressures in the bottom smoothing step, the bottom irregularities due to the higher etch rate can be removed by the fluorine-containing gas, so that better uniformity can be obtained at lower process pressures. At the same time, at lower pressure, the energy of the plasma is higher, and the etching effect on the polymer is stronger, and the formation of the micro-mask or the silicon grass caused by the polymer residue can be effectively suppressed.

In the bottom smoothing step provided by the embodiment of the present invention, the power of the upper radio frequency power source used is

50 ~ 1000W, the lower RF power supply is 0 ~ 50W, and the flow rate of the fluorine-containing gas is 5 ~ 500sccm.

Further, the fluorine-containing gas used in the bottom smoothing step may be one of CF ₄ , SF ₆ , NF ₃ , or CHF ₃ , or may be another fluorine-containing gas. The fluorine-containing gas can effectively react with C (carbon), so that the fluorine-containing gas in the bottom smoothing step can effectively remove the residual polymer and improve the smoothness of the bottom of the etching.

The process time for the bottom smoothing step is 0.5 ~ 10S. Generally, the etching time and deposition process are both 0.5 to 20 seconds. In the actual process, the process time of the bottom smoothing step can be adjusted according to the length of the process time of the etching step. The adjustment principle is as follows: If the process time of the bottom smoothing step is too short, the bottom smoothing effect is affected; If the process time of the step is too long, it will affect the production efficiency of the entire deep silicon etching process.

Please refer to FIG. 4 , which illustrates an effect diagram of deep silicon etching provided by an embodiment of the present invention. As shown in FIG. 4, the deep silicon etching method is performed by the deep silicon etching method provided by the embodiment of the present invention, and the etching bottom is smooth, and no silicon grass phenomenon occurs. The deep silicon etching method provided by the embodiment of the invention has the following advantages:

First, the deep silicon etching method provided by the embodiment of the present invention can suppress the increase of the polymer at the bottom of the etching during the deep silicon etching process. This is because: a smaller process pressure is used in the bottom smoothing step, so the energy of the plasma increases, and the energy increase of the plasma can increase the etching rate of the polymer produced in the deposition step, thereby enhancing The etching of the polymer and the increase in the polymer at the bottom of the etch.

Secondly, the deep silicon etching method provided by the embodiment of the invention can improve the roughness of the bottom of the etching. As described in the prior art, the residual polymer in the deposition step will cause the bottom of the etching to be unsmooth, and cause uneven etching of the silicon at the bottom of the etching, thereby increasing the roughness of the bottom of the etching. The increased roughness of the etched bottom will make it possible to: even if the polymer formed at the bottom of the etch step in the deposition step is etched by extending the process time of the etching step, the etched bottom is not uniformly etched due to the silicon surface. However, it still has a large roughness. In this case, even if the etching is continued, the silicon surface at the bottom of the etching cannot be made smooth. In the embodiment of the present invention, the introduction of the bottom smoothing step can remove the residual polymer at the bottom of the etching in time, and effectively improve the bottom unevenness caused by the excessive etching rate under a high process pressure. Thereby, it is possible to suppress an increase in the roughness of the bottom of the etching and maintain the smoothness of the bottom of the etching. Therefore, the deep silicon etching method provided by the embodiment of the present invention can improve the roughness of the etching bottom at a lower process pressure.

Thirdly, the deep silicon etching method provided by the embodiment of the present invention can suppress the formation of a micromask or even a silicon grass. Since the introduction of the bottom smoothing step can suppress the increase of the etched bottom polymer and improve the roughness of the etched bottom, the formation of the micro-mask or even the silice due to the increase of the etched bottom polymer is suppressed.

Fourthly, the deep silicon etching method provided by the embodiment of the invention can improve the etching rate and the etching selectivity. In the prior art, in order to avoid the formation of a micromask or even a silicon grass, deep silicon etching is required at a lower process pressure, thereby causing a decrease in etching rate and etching selectivity. In the embodiment of the present invention, since the bottom smoothing step can effectively suppress the formation of the micro-mask or even the silicon grass, a higher process pressure can be used in the etching step, thereby improving the etching rate and etching selection. Choose ratio.

It is to be understood that the above embodiments are merely illustrative embodiments employed to illustrate the principles of the invention, but the invention is not limited thereto. Various modifications and improvements can be made by those skilled in the art without departing from the spirit and scope of the invention. These modifications and improvements are also considered to be within the scope of the invention.

Claims

claims

1. A deep silicon etching method, characterized in that the method includes:

Deposition step, generating a protective layer to protect the etched sidewalls;

Etching step: etching the etching bottom and etching sidewalls;

Repeat the deposition step and the etching step until the entire deep silicon etching process is completed;

Wherein, a bottom smoothing step is also included, and the bottom smoothing step is: using fluorine-containing gas to perform plasma treatment to remove the polymer produced by deposition at the bottom of the etching; and, the process pressure used in the bottom smoothing step is less than the The process pressure used in the etching step,

Perform the bottom smoothing step at least once throughout the deep silicon etch process.

2. The deep silicon etching method according to claim 1, wherein the bottom smoothing step is performed once every N times of deposition steps and etching steps, where N is a positive integer.

3. The deep silicon etching method according to claim 2, wherein the bottom smoothing step is performed after the etching step.

4. The deep silicon etching method according to claim 1, characterized in that the process pressure used in the etching step is 40 ~ 500mT.

5. The deep silicon etching method according to claim 4, wherein the process pressure is 50 ~ 300mT.

6. The deep silicon etching method according to claim 1, wherein the process pressure used in the bottom smoothing step is 2 ~ 50mT.

7. The deep silicon etching method according to claim 1, wherein the bottom smoothing step The power of the upper RF power supply used in this step is 50~1000W, the power of the lower RF power supply is U~5UW, and the flow rate of the fluorine-containing gas is 5~500sccm.

8. The deep silicon etching method according to claim 1, wherein the fluorine-containing gas used in the bottom smoothing step is one of CF ₄ , SF ₆ , NF ₃ , or CHF3.

9. The deep silicon etching method according to claim 1, wherein the process time of the bottom smoothing step is 0.5~10S.