Vacuum measurement device

Details Vacuum measurement device Vacuum measurement device

2001-08-27

2004-05-11

Gray, David (Department: 2851)

Optics: measuring and testing

By polarized light examination

Of surface reflection

Reexamination Certificate

active

06734969

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a device to carry out measurements in a vacuum chamber, in particular to measure thin layers, with a case, exhibiting at least one measurement window, to receive a measurement system.
Furthermore, the invention relates to a vacuum adapter for mechanisms to carry out optical measurements in a vacuum chamber.
Measurements in the vacuum, in particular for quality control, are quite important, for example, in the production of semiconductors. The most frequent variables to be measured are, for example, the thickness of the thin functional layers ranging from a few nanometers to some micrometers and the size and distribution of the particles. With the transition to smaller structures and larger wafer diameters, the demand for process-accompanying quality control increases. The goal is the early detection of errors and the correction of process parameters to increase the yield and the productivity of the production process. The higher the requirements of the quality control are, the more often the wafers have to leave the production process in order to be subjected to a random measurement.
BACKGROUND OF THE INVENTION
The state of the art includes the so-called stand alone measuring machines, which are installed at central points of the plant. Due to the high cost of these systems and the relatively high space requirement, only a few of these systems can be installed. One drawback is also the additional paths, the additional loading and unloading steps of the wafers from the transport boxes and back again. Moreover, much time is lost between the detection of a defect and the reaction, a state that can result in enormous losses as the process speed increases and the value of the individual wafers increases dramatically.
To improve the yield and to reduce the production cycles precisely in thin film production, the layer properties of the thin films should be measured as process oriented as possible. One preferred method for measuring the refractive index and the thickness of thin layers is ellipsometry. It exploits the change in the polarization state of the light after its reflection on the sample surface. In addition, the collimated and fully polarized light is focused on the sample at a specific angle of incidence. In addition to the reflection, the polarization state of the radiation changes as a function of the properties of the sample.
In the case of ellipsometric measurements for determining the coating parameters in production processes not only stand alone machines have been used, but there has also been an attempt to measure the coating parameters in situ. The EP 0 527 150 B1 proposes an arrangement for ellipsometric in situ measurements in an industrial coating system. The ellipsometer, according to the EP 0 527 150 B1, exhibits a so-called paddle, on which not only the wafers to be measured are disposed but also the analyzing and the polarizing unit as well as the beam deflecting units are disposed in the form of prisms. Both for the incident beam and for the reflected beam a tube is provided as the beam tube. In a preferred embodiment these two tubes are also fastened to the paddle.
This ellipsometer arrangement has grave drawbacks. To carry out the measurement with an adequately good angle of incidence (usually between 65 and 75 degrees), it is a drawback with respect to production engineering that the coating furnace, which was optimized for a high throughput, cannot be fully filled, because minimum spacing must be maintained between the wafer to be measured and its neighboring wafer. Since the coating furnace is filled differently than what would correspond to the optimized state, the flow conditions in the furnace change and thus the quality of the coating.
From the view point of measurement technology it is quite disadvantageous that the pumps, which are typical in a vacuum chamber, excite the tube and the paddle to self sustained oscillation, the results of which are falsified measurements. The high temperatures and gases, generated during production, have a negative impact on the measurement results, since prism wall deposits and thermally induced stresses can be expected.
SUMMARY OF THE INVENTION
The object of the invention is to provide a device to carry out the measurements in the vacuum. Said device ought not to exhibit either the drawbacks of the stand alone devices or the in situ measuring devices, but rather permit a process oriented measurement under optimal measurement conditions.
This problem is solved by a device, according to claim
1
. In addition, the problem is solved by a vacuum adapter, according to claim
14
.
The case of the inventive device is divided into two parts, of which the first part projects into the vacuum chamber or defines with at least one surface the vacuum of the vacuum chamber; and the second part of the case is located outside the vacuum chamber.
The vacuum chambers are not the process vacuum chambers, but, for example, transfer or lock chambers of the production system. Special measurement chambers, to which the inventive device can also be attached, can also be integrated into the production system. The samples to be measured are brought to the device for measurement purposes by means of the transport means, such as robots, which are present in the production system in any event. Then said samples are positioned in the immediate vicinity of the first part of the case.
The inventive device exhibits at least one adjusting device, which engages with the case and whose purpose is to change the position relative to the vacuum chamber or relative to the sample to be measured. Thus, it is guaranteed that the device can be adjusted prior to each measurement, a condition that can be necessary for many a measuring method. It is necessary especially when the demands on the measuring accuracy are high or when the positioning of the sample by the transport means in the process system is too inaccurate.
It is possible to adjust the device prior to every measurement without interrupting the production process by means of the means to dispose sealingly and moveably the case in the wall of the vacuum chamber. In addition, with these means the device can be uncoupled mechanically from the vacuum chamber. Furthermore, the device can be assembled and tested independently of the vacuum chamber.
The inventive device exhibits a counterpull device, which engages with the second part of the case and permits a force to act that acts against the force, acting on the device owing to the negative pressure of the vacuum of the vacuum chamber. Thus, the goal of a force-free and tension-free state of the device is achieved, a state that leads to a better operating mode of the individual components and a higher reliability and measuring accuracy. In particular, it makes it easier to adjust the device. Even the mechanical uncoupling of the device from the vacuum chamber is thus increased. A special advantage lies in the fact that the arrangement eliminates the need to use especially heavy duty motors for the adjusting device. Consequently small motors and correspondingly weak spindle drives, which have to be designed only to compensate for any reset forces of the means to dispose the case in a sealed and moveable manner in the wall of the vacuum chamber, are sufficient.
It has proved advantageous to install, among other things, bellows as the means for the sealing and moveable arrangement of the case in the wall of the vacuum chamber. Since the bellows do not exhibit any rigid expansion, they permit the position of the device to be adjusted in relation to the vacuum chamber or to the sample to be measured without having to accept any losses in the sealing effect. In addition, said bellows damp possible oscillations of the vacuum chamber relative to the device. In the event of lower vacuum and minimum adjustment paths, elastic seals are also conceivable.
To apply the counterforce, a spring suspension or a magnetic suspension is, for example, also conceivable. Preferred is a negative pressure chamber that is formed

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