Inattentive HF Concentration Vapors Phase Release of Micro-electro-mechanical Systems and Optical Systems

Abstract

A low-cost, conventional release using low concentrations of HF to overcome the stiction of MEMS structure.

Claims

1. A method to release micro-electro-mechanical structure (MEMS) from a sacrificial substrate comprising the steps of: providing an aqueous solution comprised of a predetermined concentration of HF; locating said substrate a predetermined distance from said aqueous solution of HF; and exposing said substrate to vapors released from said aqueous solution of HF until said MEMS structure is released from said substrate.

2. The method of claim 1 wherein said concentration of HF in said aqueous solution is 48% or less.

3. The method of claim 1 wherein said concentration of HF in said aqueous solution is 25% or less.

4. The method of claim 1 wherein said concentration of HF in said aqueous solution is 1% or less.

5. The method of claim 2 wherein said predetermined distance around 5 cm.

6. The method of claim 3 wherein said predetermined distance around 5 cm.

7. The method of claim 4 wherein said predetermined distance around 5 cm.

8. The method of claim 5 wherein said predetermined time is around 10 minutes.

9. The method of claim 5 wherein said predetermined time is around 16 minutes.

10. The method of claim 6 wherein said predetermined time is around 25 minutes.

11. The method of claim 7 wherein said predetermined time is around 35 minutes.

12. The method of claim 5 wherein said sacrificial substrate is SiO.sub.2 or an insulating material that can be chemically etched by HF.

13. The method of claim 5 wherein said sacrificial substrate is a metal.

14. The method of claim 5 wherein said sacrificial substrate is Titanium, Aluminum, Copper, or a metal that is chemically etched by HF.

15. The method of claim 6 wherein said sacrificial substrate is SiO2 or an insulating material that can be chemically etched by HF.

16. The method of claim 6 wherein said sacrificial substrate is a metal.

17. The method of claim 6 wherein said sacrificial substrate is Titanium, Aluminum, Copper or a metal that is chemically etched by HF.

18. The method of claim 3 wherein said substrate is a wafer having a diameter of 8 inches or less.

19. The method of claim 4 wherein said substrate is a wafer having a diameter of 8 inches or less.

20. The method of claim 5 wherein said predetermined time is equal to or greater than 16 minutes.

21. The method of claim 5 wherein said predetermined time is equal to or greater than 25 minutes.

22. The method of claim 5 wherein said predetermined time is equal to or greater than 35 minutes.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0012] In the drawings, which are not necessarily drawn to scale, like numerals may describe substantially similar components throughout the several views. Like numerals having different letter suffixes may represent different instances of substantially similar components. The drawings illustrate generally, by way of example, but not by way of limitation, a detailed description of certain embodiments discussed in the present document.

[0013] FIG. 1 illustrates a MEMS device Vapor Release for 10 minutes with 48% concentration HF. Release region (shaded) is about 50 microns with no damage to the upper layer.

[0014] FIG. 2 illustrates a MEMS device Vapor Release for 5 minutes with 24% concentration HF.

[0015] FIG. 3 shows a hydrofluoric (HF) acid Vapor Phase Etching (VPE) system that may be used with the embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed method, structure, or system. Further, the terms and phrases used herein are not intended to be limiting, but rather to provide an understandable description of the invention.

[0017] In one embodiment, the present invention provides a low-cost, conventional release using low concentration HF to overcome the stiction of MEMS structure. In one preferred embodiment, 48% or 25% HF concentrations may be used. The 48% concentration of HF released a 220 nm structure in 16 minutes at room temperature. The wafer and HF solution is separated at a distance of approximately 5 cm. The 48% HF released a structure of up to 220 ?m without collapsing the structure.

[0018] A 25% of HF concentration produced a very uniform and controlled release in which the release region can be controlled with respect to time. The 25% or a lesser concentration HF may be used for the micro-scale structural release up to 250 ?m. The release region is not limited to that value as it may depend on the thickness of top material film, the concentration of HF and the distance between the sample and solution.

[0019] It has also been found that there is a higher degree of control over the release using lower concentrations. Lower concentrations have a higher level of uniform release all over the features of the structure as compared to a higher concentration. The lower concentration also protects features from collapsing.

[0020] In another embodiment, the present invention provides a process wherein the concentration of HF may be <1% HF. At this lower concentration, the process of the present invention has several advantages over the use of higher concentrations which are greater than 48%.

[0021] The embodiments of the present invention are not limited to the sample size. The embodiments of the present invention may also be used for wafer-scale release processes as well. The embodiments of the present invention are also scalable to 12 inches wafers or larger.

[0022] The low concentration controlled released can also be used for Nano-electro-mechanical-systems. The release process is not only limited to HF release but also may applied to the release of III-V sacrificial material layers using Tetramethylammonium hydroxide (TMAH) vapors as silicon has very good selective etching with TMAH.

[0023] The sacrificial layer needs to be reactive with HF vapors for dissolving to separate the substrate from MEMS and optical system. In one exemplary case, a SiO2 sacrificial layer was used, but the embodiments of the present invention are not limited to SiO2 and may be used with metal sacrificial layer materials like Titanium, Aluminum, and Copper.

[0024] In one embodiment, the present invention used 48% and 24% of HF concentration in an aqueous solution which may include water, DI water and other dilutants. For this embodiment, SiO2 was used as the sacrificial layer. A

[0025] FIGS. 1 and 2 show the results of the present invention. FIG. 1 shows the results of MEMS device Vapor Release for 10 minutes with 48% concentration HF. Release region 100 is about 50 microns with no damage to the upper layer. FIG. 2 shows the results of MEMS device Vapor Release for 5 minutes with 24%. Release region 200 is about 50 microns with no damage to the upper layer. concentration HF.

[0026] In other preferred embodiments of the present invention, the predetermined time is around 10 minutes, around 16 minutes. around 25 minutes or around 35 minutes. In other preferred embodiments of the present invention, the predetermined time is equal to or greater than 10 minutes, 16 minutes, 25 minutes or 35 minutes.

[0027] In one preferred embodiment, the present invention provides a method to release a micro-electro-mechanical structure (MEMS) from a sacrificial substrate comprising the steps of providing an aqueous solution comprised of a predetermined concentration of HF; locating the substrate a predetermined distance from said aqueous solution of HF; and exposing the substrate to vapors released from the aqueous solution of HF until the MEMS structure is released from said substrate.

[0028] The concentration of HF in the aqueous solution may be 48% or less, 25% or less, or 1% or less and the predetermined distance is around 5 cm.

[0029] FIG. 3 shows a hydrofluoric (HF) acid Vapor Phase Etching (VPE) system 300 that may be used with the embodiments of the present invention. System 300 include a first container 310 which may be closed and holds the desired concentration of HF in liquid form, First container is in communication with Teflon chamber 320 that is used to treat a wafer or substrate with the desired HF concentration in liquid form. Chamber 320 is configured to hold substrate or wafer 330 a predetermined distance d above the top surface of liquid 340 in chamber 330 by use of holder 350. Valve 360 controls the level of liquid 340 and vents 360-361 permit the vapor from liquid 340 to flow into contact with substrate or wafer 330.

[0030] While the foregoing written description enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The disclosure should therefore not be limited by the above-described embodiments, methods, and examples, but by all embodiments and methods within the scope and spirit of the disclosure.