Semiconductor device manufacturing: process – Chemical etching – Combined with coating step
Reexamination Certificate
2000-02-10
2001-08-21
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Chemical etching
Combined with coating step
C438S044000, C438S243000, C438S444000
Reexamination Certificate
active
06277756
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon Japanese Patent Application No. Hei. 11-34671 filed on Feb. 12, 1999, and Hei. 11-353393 filed on Dec. 13, 1999, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to methods of manufacturing a semiconductor device. More specifically, the invention relates to a method of manufacturing a semiconductor device having a trench.
2. Related Art
A semiconductor acceleration or angular velocity sensor typically includes a small comb-shaped beam structure formed on a substrate for detecting a physical quantity. The comb-shaped structure is formed so that the physical quantity is detected by way of electrostatic force. The distance between each comb-like element must be narrow, and the thickness of the structure must be set to a particular value in order to downsize the sensor and achieve a high detection performance.
The typical comb-shaped structure is created by forming a mask on the substrate and by dry-etching the substrate through the mask. The aspect ratio of the trench, which is the depth of a trench with respect to an opening width of the trench, is typically set to a large number.
A large trench aspect ratio can be a limitation from a process technology viewpoint. In the case of normal dry etching, if high anisotropy anisotropic etching (in which an etching rate for a vertical direction of the substrate is higher than that for the other directions) is used, the etching is typically gradually advanced in a width direction of the trench from a surface portion of the substrate in the trench. Therefore, when the etching is performed for a long time, a sectional shape of the trench may be a V-shape because the trench width is gradually enlarged, so that the aspect ratio is saturated at a certain degree.
A method of solving the above problem is disclosed in U.S. Pat. No. 5,501,893 to Laermer. Laermer discloses a dry-etching method including two steps including (1) plasma etching having a high anisotropy; and (2) deposition of a polymer-based thin film.
During thin film deposition, the polymer-based thin film is deposited on each sidewall of the etched trenches in order to serve as a protection film and to prevent the sidewall of the trench from being etched during plasma etching. In this manner, it can prevent the opening of the trench from being etched toward the opening width direction and improve an upper limitation of the aspect ratio of the trench shape compared to normal dry etching.
However, this method fails to completely protect the sidewalls from being etched because the trench width is slightly enlarged. The limitation of the aspect ratio is also present.
FIG. 9
shows the relationship between process time and aspect ratio when the trench is experimentally processed in a reactive dry etching (RIE) apparatus based on the above-described method. As shown from this figure, the aspect ratio never exceeds 25 even when the etching is performed for a long time.
Another method to solve the above-described inconvenience is disclosed in U.S. Pat. No. 5,658,472 to Bartha. Bartha also divides an etching process into an etching step and a step for forming a protection film on a sidewall of a trench, and alternately performs these two steps. In this technology, the step for forming the protection film is performed by depositing a thermal oxide film (SiO
2
) in a chamber different from that in which the etching is performed, or by depositing a thin ice film in the chamber in which the etching is performed. In comparison to the polymer-based film, the aspect ratio is improved because the films disclosed in Bartha have durability for sidewall etching.
However, it would take a long time to unload the substrate and to form the thermal oxide film every time the protection film is deposited. Furthermore, the temperature of the substrate needs to rise and fall after every unloading. Therefore, it is not preferable from a viewpoint of process throughput. Also, the substrate needs to be below the freezing point during the etching in order to use the ice film as the protection film. These limitations cause the apparatus to be complicated.
SUMMARY OF THE INVENTION
This invention has been conceived in view of the background thus far described and its first object is to effectively form a trench having a high aspect ratio with relatively simple steps.
Its second object is to provide a method of manufacturing a semiconductor device having a trench whose aspect ratio can be easily increased.
According to the present invention, a method of manufacturing a semiconductor device includes: loading a semiconductor substrate having a mask thereon to a chamber; forming a trench in the semiconductor substrate by using a reactive ion etching using the mask; forming a protection film on an inside surface of the trench, and; etching a part of the protection film positioned at a bottom portion of the trench, and for etching the semiconductor substrate through the bottom portion of the trench by using a reactive ion etching to deepen the trench. The protection film forming and bottom surface etching are performed under a plasma of gas introduced into the chamber. The type of gas is changed based upon the particular step. The protection film forming and the bottom surface etching are done repeatedly in order to form the final trench.
According to the above-described method, after an initial trench is formed, a protection film is formed on the inside surface of the initial trench. The reactive ion etching is then performed. In this method, the protection film on the bottom surface of the trench is removed prior to the sidewall of the trench because of the etching anisotropy. The etching is then advanced to a depth direction of the trench. Repeatedly performing the above prevents the opening width of the trench from being enlarged and achieves a high aspect ratio.
The present method is an improvement over the prior art methods. In the present method it is unnecessary to remove the semiconductor substrate from the chamber to form the protection film, or to repeatedly rise or lower the temperature of the semiconductor substrate.
According to another aspect of the present invention, a method of manufacturing a semiconductor device includes: forming a trench in the semiconductor substrate by using a reactive ion etching, and forming a polymer film as a first protection film on an inside surface of the trench; and forming a second protection film that has a high durability for etching compared to the polymer film on the inside surface of the trench after the trench and first protection film are formed. This method is repeatedly performed to form a final trench.
The above-described method can increase durability for a laterally advancing etching by covering the sidewall of the trench with the first and second protection film. The method controls etching in the depth direction by forming a polymer film on the bottom surface of the trench and subsequently removing the film. As a result, it can prevent both the width of the trench from being enlarged and the etching from stopping due to the trench becoming tapered.
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E.M. Young, et al. “UV light stimulated thermal oxidation of silicon”, APL 50 (2), pp. 80-82. Date unknown.*
M. Niwano et al. “UV ozone oxidation of Si surface studied by photoemission an
Kano Kazuhiko
Ohara Junji
Ohya Nobuyuki
Yoshihara Shinji
Denso Corporation
Law Office of David G. Posz
Niebling John F.
Simkovic Viktor
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