BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a cross-sectional view of an exemplary deep trench formed by conventional DRIE process.
FIGS. 2 to 5 are schematic diagrams illustrating a method of deep etching according to a preferred embodiment of the present invention.
FIG. 6 shows the steps involved in the method of deep etching according to the present invention.
DETAILED DESCRIPTION
In the following detailed description, reference is made to the accompanying drawings, which form a part of this application. The drawings show, by way of illustration, specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.
FIGS. 2 to 5 are schematic diagrams illustrating a method of deep etching according to a preferred embodiment of the present invention. As shown in FIG. 2, a wafer 20 is provided. A patterned mask 22 having at least an opening 26 is formed on a surface 22 of the wafer 20. The opening 26 exposes the surface 22 of the wafer and defines the position of a deep opening formed in the following processes. The wafer 22 is a silicon wafer and other kinds of wafers can also be used, for instance, a single crystalline silicon wafer, an amorphous crystalline silicon wafer, or a poly crystalline silicon wafer. The patterned mask 24 disposed on the surface 22 of the wafer may comprise photoresist, metal, silicon nitride, tetra-ethyl-ortho-silicate (TEOS), or other materials of high-selectivity and anisotropic features.
As shown in FIG. 3, the wafer 20 is transferred into a chamber and is disposed on a lower electrode of the chamber. A deposition process is performed. In this preferred embodiment, the deposition process uses octafluorocyclobutane (C4F8) as a precursor to form a polymer layer 28 of fluorocarbon (nCFx). The deposition may use tetrafluoromethane (CF4) or other kinds of precursors to form the polymer layer 28. The deposition process uses a deposition gas preferably comprising 70-120 standard cubic centimeters per minute (sccm) of C4F8 at a chamber pressure between 35-55 mT. And the deposition gas is preferably generated by supplying 500-1500 W of RF power to the upper electrodes and 0 W to the lower electrode.
A plasma etching process is performed after the polymer layer 28 formation. The plasma etching process uses an etching gas including a precursor to form halogen, an inert gas to enhance bombardment, and oxygen (O2) reactant. In this preferred embodiment, the halogen precursor and the inert gas are sulfur hexafluoride (SF6) and argon (Ar), respectively. The etching gas preferably comprises 180-260 sccm of SF6, 40-80 sccm of O2 and 100-400 sccm of Ar, and is preferably generated by supplying 1500-2500 W of RF power to the upper electrode and 18-30 W of RF power to the lower electrode. As shown in FIG. 4, the etching gas uses fluoride (F−) released from SF6 while utilizing Ar bombardment to remove the polymer layer (not shown) formed in the prior deposition process. The etching gas also etches the surface 22 of the wafer through the opening 26 to form a deep opening 30. Thereafter, the wafer 20 is oxidized by oxygen reactant and an oxide layer 36, for instance, silicon oxide, is formed on a sidewall of the deep opening 30 after the polymer layer (not shown) is removed. The plasma etching process is a physical etching process using Ar bombardment to remove the surface 22 of the wafer 20 perpendicular to the direction of Ar bombardment. However, the plasma etching process merely removes the sidewall 34, the polymer layer (not shown) on the sidewall 34, or the oxide layer 36 on the sidewall 34, which are parallel to the direction of the Ar bombardment. Therefore, the oxide layer 36 protects the sidewall 34 during the plasma etching process, and the method of the invention etches the wafer 20 anisotropically.
The method of the present invention alternatively repeats the aforementioned deposition process and the plasma etching process until the deep opening 30 has a predetermined depth. As shown in FIG. 5 the profile of the sidewall 34 is substantially vertical, and the deep opening 30 has an aspect ratio greater than approximately 10:1, even greater than approximately 35:1. It should be noticed that the method of the present invention uses the polymer layer formed in the deposition process to protect the sidewall of the deep opening, and then uses the oxide layer formed in the plasma etching process to protect the sidewall from etching. The method of the invention will not be affected by the lattice structure of the wafer, and therefore the deep opening or a hole formed by the method of the invention will have a high aspect ratio, respectively.
To facilitate the method of the invention, FIG. 6 shows the steps involved in the method of deep etching according to the present invention. The method starts at step 100 and begins at step 102 when a wafer having a patterned mask on the top surface thereof is provided. A deposition process is performed at step 104 and a plasma etching process is performed to form a deep opening on the top surface at step 106. Ajudging step is performed at step 108. The procedure of the method returns to step 104 and repeats step 104 and step 106 when the deep opening has a depth less than the predetermined depth. Otherwise, the procedure will continue and the method ends at step 110. Since the method of the invention repeats steps of deposition and etching, proper gases should be used to keep balance between deposition and etching to the deep opening having a vertical profile.
Instead of the described precursors, such as C4F8 and CF4 for the deposition process, other precursors of the polymer layer are allowed to be used in the deposition process, for example, perfluorinated compounds (PFC), styrene-like monomer, or ether-like fluorine compounds. In addition, other etching gases, for example, nitrogen trifluoride (NF3), CF4, or other compounds capable of releasing F−, are used for the plasma etching process. The plasma etching process may be performed with other kinds of halogens instead of F−; for instance, chloride (Cl−) can be used in the plasma etching process. The precursor of the halogen will be selected depending on the species of the halogen.
According to the aforementioned embodiment, the method of the deep etching uses the polymer layer formed the deposition process to increase the selectivity between the patterned mask and the wafer and the oxide layer formed during the plasma etching process, and alternatively repeats the deposition process and the plasma etching process to form a deep opening having a hydrophilic surface of the sidewall and high aspect ratio. The deep opening formed by the method of the invention has less CD bias and the profile of the sidewall is approximately vertical. The parameters of the method are flexible and can be adjusted depending on the type of the wafer or other requirements. It should be noticed that the deep opening formed by the method of the invention not only has a vertical profile of the sidewall, but also has a hydrophilic surface. Moreover, the method of the invention is suitable to manufacture ink jet heads, blood cell counters, biochips, or the products having deep openings.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
Patent Application
20080023441
