Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
2000-12-20
2003-01-14
Powell, William A. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S728000, C438S732000, C156S345420, C156S345460, C156S345480, C156S345510, C156S915000, C216S067000, C216S070000
Reexamination Certificate
active
06506687
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dry-etching apparatus for fine-etching a semiconductor device and a method of fabricating a semiconductor device by forming interconnection and the like by dry etching.
2. Description of the Related Arts
One of techniques for fine-etching a semiconductor device is a dry etching technique. In dry etching, an etching gas is introduced into a vacuum chamber, a high-frequency bias or &mgr; wave is applied to the gas to generate a plasma, the plasma of the etching gas is generated, and a thin film such as a polysilicon film or an Al—Cu—Si film formed on a semiconductor wafer is etched by radicals and ions generated in the plasma. A photoresist film on which a mask pattern is transferred is formed on the thin film, and only the portion which is not covered with the photoresist film is removed by dry etching, thereby forming a semiconductor device structure in which interconnections, electrodes, and the like are integrated on the wafer.
An etching mechanism in dry etching will be briefly described by using an example of etching an Si film with chlorine gas. The chlorine gas introduced in an etching apparatus and chlorine radicals generated in the plasma are adhered on the surface of Si. Cations generated in the plasma are also incident on the surface, so that the surface is locally heated. By the heating, Si reacts with chlorine to form a reaction by-product and is desorbed. By repeating the above, etching on the Si film progresses.
In a pressure region where etching is usually performed, since the mean free path of the reaction by-product is equal to or shorter than 1 cm and is short as compared with the size (height of about 20 cm) of the etching apparatus, the reaction by-product generated on the surface of the wafer has a diffusion phenomenon by collision with other gas molecules. Consequently, the reaction by-product has the probability that it is incident on the wafer. When the incident reaction by-product is adhered, the progress of etching is disturbed. In the case where an incident flux of the reaction by-product has a distribution in the wafer surface, since etch rate decreases where the incident amount is large, it is difficult to perform uniform etching in the wafer surface.
With respect to the incident flux of the reactive by-product in the center portion and that in a peripheral portion of the wafer, although the center portion is surrounded by a reaction by-product generating portion, the peripheral portion has the reaction by-product generating portion only on one of the sides. The incident flux of the reaction by-product in the wafer center portion is less than that in the wafer peripheral portion. As a result, in an etching apparatus of a uniform ion incident amount, the etch rate in the wafer peripheral portion is higher than that in the peripheral portion. Further, the reaction by-products are adhered on side faces of a pattern. When the adhering amount is large, the pattern becomes thick. When the adhering amount is small, side-etching occurs. In order to uniform an etched shape in the wafer surface, it is therefore necessary to uniform the incident amount of the reaction by-products. To be more accurate, since a chip is not formed in the region of about 3 mm of the periphery of the wafer, it is necessary to uniform the incident amount of the reaction by-products in the region except for the periphery of 3 mm of the wafer.
In a conventional etching apparatus, the distribution of the incident flux of the reaction by-products is controlled by optimizing a gas flow, installing a focusing ring, and the like. However, as the gas pressure in the etching process is becoming lower, it is becoming difficult to improve the uniformity only by the gas flow. When a focusing ring is installed to distribute plasma density, in association with increase in wafer diameter, an excessive distribution occurs in the plasma density, a charge distribution occurs in the wafer surface, and the probability that the semiconductor device is destroyed increases. Further, as the diameter of the wafer increases, the height of the focusing ring has to be increased. When the height is increased, however, the reaction by-product is adhered to the focusing ring and becomes a cause of a foreign matter and a particle. That is, in the conventional etching apparatus, it is difficult to uniformly process a wafer having a large diameter of about 12 inches.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a dry etching apparatus capable of obtaining a uniform etch rate and a uniform etched shape in a wafer surface by uniforming the number of re-incident times of a reaction by-product and a method for fabricating a semiconductor device, having such a dry etching process.
The object is achieved by uniforming the thickness of a near-surface region. Specifically, at the time of etching a wafer of a large diameter, the distance between the wafer and a member facing the wafer to a predetermined value, thereby uniforming a distribution in the surface, of the thickness of the near-surface region.
First, the incident mechanism of the reaction by-product will be described. The reaction by-product generated on the wafer moves according to a diffusion phenomenon. To be specific, since the mean free path of the product generated on the wafer is about 1/100 of the size of the etching apparatus, the product collides with gas molecules in the apparatus. By the collision, the moving direction of the reaction by-products changes and a part of the reaction by-products moves toward the wafer. Even if the movement can be maintained in the direction of moving apart from the wafer, the reaction by-products again collide with the gas molecules. As a result, the moving direction of the reaction by-products changes and the reaction by-products are incident on the wafer again and again. By such a diffusion phenomenon, the concentration of the reaction by-products becomes high near the wafer and decreases with distance from the wafer. According to the diffusion theory, the distance of the region in which the concentration of the reaction by-products from the wafer is equal to about the radius of the wafer. On the other hand, the distribution of the reaction by-products is almost uniform in a region apart from the wafer by the radius of the wafer. The concentration of the reaction by-products in the region apart from the wafer is determined substantially by residence time of the reaction by-products. The region near the wafer in which the concentration of the reaction by-products is higher than the concentration determined by the residence time will be called a near-surface region. The thickness of the near-surface region changes, as will be described hereinlater, depending on the position of the wafer, gas pressure, and gas flow rate.
As described above, by forming the near-surface region, the reaction by-products are incident on the wafer again and again. The number of colliding times of the reaction by-products with the gas molecules in the near-surface region is obtained by a mean free path (L) to the thickness (D) of the near surface region, that is, D/L. Since the probability that the reaction by-products move in the direction toward the wafer and the probability that the reaction by-products move in the direction apart from the wafer by a single collision are equal to each other, in the half of the D/L times of collisions, the reaction by-products are incident on the wafer. That is, the number of re-incident times is obtained by D/2L from the thickness (D) of the near-surface region and the mean free path (L).
In the case where the portion facing the wafer has a shower-plate structure for introducing gas, when the gas flow rate increases, the near-surface region becomes smaller, and the number of re-incident times of the reaction by-products (re-incident number of times) decreases according to a diffusion equation. When the gas pressure is increased, the diffusion coefficient of the reaction by-products becomes smaller
Izawa Masaru
Tachi Shinichi
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Powell William A.
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