1. Field of the Invention
The present invention relates to a plasma processing apparatus, and more specifically, relates to a plasma processing apparatus capable of suppressing the occurrence of particles caused by reaction products.
2. Description of the Related Art
In the field of manufacturing semiconductor devices, plasma processing apparatuses using plasma are adopted as means for realizing microfabrication to respond to the increasing demands for highly precise high-speed microfabrications (such as dry etching), to realize enhanced performance of semiconductor integrated circuit elements and cut down costs. Among such arts, the art of dry etching is often applied, in which processing gas is used to process films deposited on the sample and evacuate the residual gas in the processing chamber via a turbo-molecular pump or the like to the exterior. Various kinds of gases (such as Ar, Cl2 and HBr) can be used as the processing gases, but some gases are not sufficiently evaporated, depending on the kind of films deposited on the sample being processed. In such cases, gases are not sufficiently discharged and become the cause of reaction products, which deposit on the inner wall of the vacuum processing chamber and on the inner wall of an inductive vacuum processing chamber lid disposed on the upper portion of the vacuum processing chamber. When excessive reaction products are deposited on the inner wall of the vacuum processing chamber and the inner wall of the vacuum processing chamber lid, deposition films may fall off from the surface of the inner wall and attach to the surface of the sample as particles.
One type of prior art plasma processing apparatuses is an inductive plasma processing apparatus having a high frequency power supply connected to a coil-like induction antenna disposed on an outer circumference of a vacuum processing chamber lid for supplying high frequency power to the coil-like induction antenna, to thereby generate plasma. The drawback according to this type of plasma processing apparatus adopting an induction antenna is that the bonding state of the induction antenna and the plasma within the vacuum processing chamber lid is varied by the reaction products deposited on the inner wall of the vacuum processing chamber and the vacuum processing chamber lid, by which the etching rate, the uniformity of etching, the perpendicularity of the etching profile and the state of deposition of reaction products on the etched side walls is varied with time.
Next, Japanese patent application laid-open publication No. 2004-235545 (patent document 1) discloses the following method as the method for preventing reaction products from depositing on the inner wall of the vacuum processing chamber lid. A Faraday shield capacitively coupled with plasma is arranged between induction antennas disposed at the outer circumference of a vacuum processing chamber lid and plasma, and high frequency power is supplied to the Faraday shield to generate self bias to the inner wall of the vacuum processing chamber lid, drawing ions in the plasma by the electric field within the ion sheath and sputtering the surface of the inner wall of the vacuum processing chamber lid. The sputtering is used to suppress or remove the deposition of reaction products on the inner wall of the vacuum processing chamber lid, and perform cleaning of the inner wall of the vacuum processing chamber lid. In the present specification, the vacuum processing chamber lid is airtightly fixed to the upper portion of the vacuum processing chamber.
As described, a self bias is generated on the surface of the inner wall of the vacuum processing chamber lid via the high frequency voltage applied to the Faraday shield, by which the electric field of the ion sheath is increased and the energy of ions reaching the inner wall of the vacuum processing chamber lid is enhanced. Therefore, ion sputtering via ions becomes prominent, enabling more reaction products to be cleaned. Further, most appropriate cleaning becomes possible by controlling the high frequency voltage supplied to the Faraday shield.
Further, the following method is disclosed in Japanese patent application laid-open publication No. 2005-259836 (patent document 2) as a method for cleaning the whole surface of the inner wall of the vacuum processing chamber lid in a uniform manner. Patent document 2 discloses a plasma etching apparatus having a Faraday shield divided into multiple parts and providing independent high frequency power supplies respectively to each of the divided Faraday shields, to thereby enable control of the voltages applied to the respective Faraday shields.
According to the disclosed plasma processing apparatus, in order to remove the reaction products generated from samples during etching and thickly deposited on a center portion of the vacuum processing chamber lid (top plate) closest to the sample surface, a high frequency power which is higher than the power supplied to the outer circumference portion of the top plate is supplied to the divided Faraday shield disposed at the center portion of the top plate. According to this arrangement, reaction products deposited both on the center portion and the outer circumference portion of the top plate can be cleaned appropriately.
FIG. 10 shows the state of deposition of reaction products attached to the inner wall of the vacuum processing chamber lid in a plasma processing apparatus. When etching is performed, a large amount of reaction products is generated from the sample being processed, and the generated reaction products are attached to and deposited on the inner wall of the vacuum processing chamber lid (hereinafter referred to as a window 12) and the inner wall surface of a vacuum processing chamber 2 as a film (18).
In contrast, at an outermost circumference portion (portion B) of the inner wall surface of the window 12, the self bias is reduced since the vacuum processing chamber 2 is grounded, so that the energy of ions with respect to portion B is reduced. Ion sputtering rarely occurs in portion B, and therefore, reaction products remain in portion B. As a result, the inner wall surface of the window 12 is divided into a region (portion A) where the reaction products are completely removed, and a region (portion B) where reaction products easily remain.
In order to eliminate residual reaction products in portion B, it is necessary to set the high frequency voltage applied to the Faraday shield 17 (Faraday shield voltage: hereinafter abbreviated as FSV) as high as possible to remove the reaction products deposited on the inner wall of the window 12. According to this method, however, the inner wall surface of the window 12 of portion A is chipped excessively.
As described, if the inner surface of the window 12 is chipped and the speed of consumption of the window 12 itself is increased, the replacement cycle of the window 12 is shortened. Further, the chipped window 12 becomes the source of reaction products and re-deposits on the wafer surface, causing instability of etching rate of the process performance and in-plane unevenness of the wafer etching rate and the like. Another drawback is that the chipped surface of the window 12 turns into particles and attach to the sample surface. Therefore, in order to overcome the above-mentioned problems, it is necessary to remove the reaction products deposited on the whole inner wall surface of the window 12 in a most suitable manner.
Prior arts such as that disclosed in patent document 2 enables to remove the reaction products deposited on the whole inner wall surface of the window 12 in a suitable manner, but since independent high frequency power supplies must be disposed in response to the divided Faraday shields and antennas, the application thereof to industrially-applied plasma processing apparatuses causes increase of costs and requires a large mounting space.
Furthermore, there is a drawback that cannot be solved by the prior art disclosed in patent document 2. This drawback will be described with reference to FIG. 5. Since the present drawback is not related to the division number of Faraday shields, the plasma processing apparatus illustrated in FIG. 5 has a Faraday shield that is not divided into multiple parts.
In FIG. 5, the dotted lines with arrows show high frequency currents flowing from a Faraday shield 17 into the vacuum processing chamber 2 during plasma processing. The Faraday shield 17 is capacitively coupled with plasma, and the high frequency current from the Faraday shield 17 flows through the plasma as shown by the arrows into the vacuum processing chamber 2 being grounded.
Now, when the high frequency voltage applied to the Faraday shield 17 is denoted by Va, the area of the Faraday shield 17 is denoted by Sa, the high frequency voltage generated in the ion sheath on the surface of the inner wall of the vacuum processing chamber 2 is denoted by Vb, and the surface area of the ion sheath is denoted by Sb, the following expression is satisfied, as taught in cited document (Michael A. Lieberman, Allan J. Lichetenberg, ED Research, “Principles of Plasma Discharges and Materials Processing” Chapter 11).
                                          V            b                                V            a                          =                              (                                          S                a                                            S                b                                      )                    n                                    [                  Expression          ⁢                                          ⁢          1                ]            
Expression 1 shows that a self bias is not only generated at the inner wall surface of the window 12 by the high frequency voltage applied to the Faraday shield 17, but also generated at the inner wall surface of the vacuum processing chamber 2 into which high frequency current flows.
Therefore, the inner wall of the vacuum processing chamber 2 is sputtered via the ions accelerated by Vb. As described, when the inner wall of the vacuum processing chamber 2 is sputtered, the lifetime of the respective parts composing the interior of the vacuum processing chamber 2 is reduced, and the frequency of replacement of the parts is increased. Thus, the running costs of the plasma processing apparatus cased by replacement of parts is increased. Even further, the chipped inner wall of the vacuum processing chamber 2 becomes the source of particles, by which the mass production performance of the plasma processing apparatus is deteriorated.