Plasma processing apparatus capable of suppressing variation of processing characteristics

This application is a Continuation of U.S. application Ser. No. 10/934,510, filed Sep. 7, 2004, which claims priority from Japanese Patent Application No. 2004-236532, filed on Aug. 16, 2004, the contents of which are incorporated herein by reference.

The present invention relates to a plasma processing apparatus, or in particular to a technique for suppressing the variation of the processing characteristics of the plasma processing apparatus.

With the increased degree of miniaturization, the increased integration and the increased variety of the component materials of devices, not only the higher processing accuracy, but the long-lasting stability of the processing characteristics of each single plasma processing apparatus and the suppression of the difference in the processing characteristics between a plurality of plasma processing apparatuses are required as a crucial factor for mass production of the semiconductor.

In the plasma etching apparatus, for example, repeated processing operations cause the deposits on and the wear of the inner wall of the reaction chamber. With the progress of these deposits and wear, the wafer processing characteristics continue to undergo a change over a long period of time and finally come to deviate from the reference level of the tolerable variation of the processing characteristics for fine etching patterns and fail to meet the performance requirements of the devices fabricated. Also, the separation of the deposits generates undesirable fine particles, and the wear of the parts of the processing chamber induces the abnormal electric discharge or the like leading to a device defect.

For these reasons, the plasma processing apparatuses have recently come to be monitored continuously for many parameters (emission spectrum, peak-to-peak voltage Vpp of the bias waveform, behavior of the reflected wave, etc.) considered to affect the processing conditions. In this way, the advisability of the continued production is determined on the one hand, and various measures have been studied to utilize the plasma cleaning to reduce the deposit or to use a new inner material to prevent the wear on the other hand. As a result, the process can be suspended before occurrence of a product defect or the time required before the occurrence of a defect can be lengthened.

Nevertheless, the plasma processing apparatus follows the everlasting trend toward stricter criteria of the tolerable variation in the processing characteristics for fine pattern etching (for example, the gate length in 45-nm node has reached the order of 20 nm, of which the variation of 2 nm or more is not permitted). Even in the case where the mass production continues to be monitored based on the various parameters of the apparatus, therefore, only a small change in the processing characteristics may cause the deviation from a tolerable criterion.

In each of these cases, the cleaning of the whole reaction chamber or the replacement of the consumable parts is required, resulting in shorter cycles of the overall cleaning operation or an increased frequency of change of the consumable parts. This leads to a lower utilization rate and an increased cost of the consumable parts. Although the method of removing the deposits of Si, C, Al, etc. by plasma cleaning is also utilized, it is impossible to remove only the predetermined deposits and leave nothing extraneous on the inner wall surface of the reaction chamber or never to wear the inner wall surface of the reaction chamber in the cleaning process (perfect plasma cleaning). It is therefore difficult to reset the interior of the reaction chamber completely.

For this reason, it has become crucial to develop a technique to maintain constant wafer processing characteristics by the diagnosis or by the status monitor, with high accuracy, on the delicate variations of the inner wall conditions of the reaction chamber or the delicate differences between the apparatuses. The parameters for determining the wafer processing characteristics include the pressure, gas flow rate, wall surface and wafer temperatures and the power matching. A technique for increasing the accuracy of each of these parameters is now under development. Examples of patent documents concerning the monitor and diagnosis of the reaction chamber and the operation of controlling the power and the matching unit are described below.

JP-A-9-260096 discloses a method in which the plasma is ignited after moving the stub of the impedance matching unit to a preset ignition point, and after securely igniting the plasma, the stub is moved to a match point where the plasma is stabilized. To control the tracking, an operation track is plotted from an initial setting through a plasma ignition point to a plasma stabilizing point.

In JP-A-2003-174015, on the other hand, a sensor is mounted midway of the route from the matching unit to the electrode in the plasma processing apparatus, so that the processing characteristics and the variation thereof are detected with high sensitivity.

Also, U.S. Patent Application Publication No. 2004/0003896A1 discloses a technique in which the impedance is measured during the processing of the wafer and stored as a data base together with the information on the wafer processing. In this way, the empirical information are accumulated and related to the wafer processing characteristics.

It is essential to operate the same plasma processing apparatus with stable processing characteristics over a long period of time and to minimize the difference of the processing characteristics between different reaction chambers. Nevertheless, the increase in the deposits on the inner wall and the wear of the inner wall of the apparatus cause variations in the processing characteristics. Also, even in the case where the component parts of the reaction chambers are fabricated with very high accuracy, delicate differences develop between the component parts thus fabricated, with the occasional result that the difference of the processing characteristics between a plurality of apparatuses fail to meet the tolerance.

Also, the characteristics of even the same component part, if removed provisionally and reassembled for the purpose of maintenance, undergo a change due to the difference in the assembly conditions.

As described above, in the plasma processing apparatus, even after securing a predetermined plasma density, a predetermined impedance or a predetermined effective input power, the processing characteristics cannot always be kept constant.

To cope with these problems, this invention has been achieved based on the knowledge that for securing constant processing characteristics by stabilizing the internal conditions of the plasma processing apparatus, the essential prerequisite is to control the ambient conditions such as the pressure and flow rate of the processing gas with high accuracy and thus to control the matching between the power supply and the plasma. In view of this, the object of the invention is to provide a plasma processing technique for detecting and suppressing the variation of the processing characteristics of the plasma processing apparatus.

In order to achieve this object, according to this invention, there is provided a plasma processing apparatus comprising a reaction chamber with an insulated inner side wall, a sample rest arranged in the reaction chamber and an antenna, wherein the high-frequency power from a plasma-generating power supply is supplied to the antenna so that the processing gas introduced into the reaction chamber is converted into a plasma and the sample placed on the sample stage is processed with the plasma, wherein a matching unit for impedance matching, arranged between the plasma-generating power supply and a load circuit having the antenna, includes a sensor for measuring the impedance characteristic of the load circuit and a means for changing the match point of the matching unit as viewed from the input terminal toward the load side of the matching unit and the match operation track leading to the match point in accordance with the measurement of the sensor.

According to this invention having the aforementioned configuration, the variation in the processing characteristic of the plasma processing apparatus is detected and suppressed.

Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.