Method and apparatus for process control in semiconductor manufacture

#The present invention is generally in the field of optical monitoring techniques, and relates to the control of semiconductor processing by measuring parameters of thin films, e.g. within processing equipment (the so-called “integrated metrology”).

#Optical methods for on-line or integrated measurement of the parameters of dielectric films (e.g., film thickness) are known in the art. Most of these techniques are based on reflectometry in broaden spectral range, e.g. from DUV to NIR spectral range.

#The NanoSpec 9000 spectrophotometric device commercially available from Nanometrics Inc., USA (that is installed on the CVD production cluster tool Producer commercially available from Applied Materials, USA) utilizes a configuration that allows measurements of a wide range of dielectric films just after deposition within the CVD cluster tool before a processed wafer goes to an out-put cassette. The device includes a measuring tool installed in a load/unload block, outside a vacuum part of the cluster tool. This configuration suffers from that it applies measurements to a wafer a certain time after the wafer moves out of a reaction deposition chamber. During this time period, which is needed for transferring the wafer within the vacuum part of the cluster tool and out of this vacuum part towards the cassette block, other wafers of the lot pass through the deposition chamber. This time delay impedes appropriate control of the manufacturing process. Actually, in case of malfunction or drift effect in the deposition process, measurements by a tool located out of the vacuum environment of the CVD tools arrangement will recognize this effect with a certain delay, and wafers of the lot processed after the first measured wafer will be scrapped.

#In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

#FIG. 1 schematically illustrates an optical system according to one embodiment of the present invention, combining “small spot” and “large spot” operational modes in a common light directing assembly;

#FIG. 2 more specifically illustrates a beam expanding unit suitable to be used in the system of the present invention for implementing the “large spot” operational mode;

#Referring to FIG. 1, there is illustrated an optical system, generally designated OS, according to one embodiment of the invention, applied to a wafer W. The system OS comprises a broad-band (white) light source 10, an imaging detector 26 (CCD camera) the provision of which is optional, a spectrophotometer 30, and a light directing assembly, generally at 31. As will be described more specifically further below, the light directing assembly is operable so as to selectively provide “large spot” or “small spot” measurement modes.

#The light directing assembly 31 defines an illumination channel for the propagation of light produced by the light source to the wafer's plane, and a light detection channel for the propagation of light returned from the wafer to the detectors 26 and 30, and defines two optical paths for illuminating and returned beams propagation, a first optical path for realizing the “small spot” operational mode and the second optical path for realizing the “large spot” operational mode. Optical elements of the assembly 31 accommodated in the illumination channel include a condenser lens 14 optionally connected to the light source via an optic fiber 12; a beam splitter 16; a tube lens 18; and an objective lens 20 that may and may not be translatable. A pinhole mirror 22 located at the other side of the beam splitter 16 and a relay lens 24 define the light detection channel part associated with the CCD camera 26. Another relay lens 27 and optionally a mirror 28 define the detection channel part associated with the spectrophotometer 30. All the above elements define the optical path for spectroscopic measurements with a small measuring area (“small-spot” operational mode), as used for example in the NovaScan 840 ITM, commercially available from Nova Measuring Instruments, Rehovoth, Israel. Preferably, only the objective lens 20 along with the light beam deflecting element, such as a beam-splitter or mirror (not shown) is translated in the X-Y plane parallel to the wafer's plane in combination with mirrors deflecting the collimated light beam along X and Y axes (see U.S. Pat. No. 5,764,365 assigned to Nova Measuring Instruments. Ltd.). Also, the wafer W may be moved relative the optical system OS; the movement may be carried out by X, Y or R-Θ stage or any other two-coordinate motion system.

#Further provided in the light directing assembly 31 of the optical system OS is an optical arrangement including mirrors 32 and 34, wherein mirror 32 is stationary mounted and mirror 34 is movable between its inoperative and operative positions 34 and 34′ (shown in dashed line) to be, respectively, out of and in the optical path passing through the objective lens 20. Any suitable drive (not-shown) can be used, being operated by a control unit (not shown), for providing the movement of the mirror 34, e.g. reciprocal, rotating, tilting, etc. Generally speaking, this optical arrangement of the light directing assembly provides selective propagation of the illuminating and reflected light beams through the first optical path passing through the objective lens 20, or through the second optical path that does not pass through the objective lens 20. The mirrors 32 and 34, when in the operative position of the mirror 34, direct a wide collimated light beam to the wafer W along the second optical path without the beam passage through the objective lens 20, thus providing spectroscopic measurements with a relatively large measuring area (“large-spot” operational mode of the system 10). The system 10 thus can operate with two operational modes, i.e., with relatively small and large illuminating spots.