JP3550594B2 - Apparatus for measuring thickness of multilayer sample and polishing apparatus having the same - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a film thickness measuring device for measuring the film thickness of a multilayer film sample having fine irregularities on the surface in the process of manufacturing a semiconductor substrate, a micro machine, and the like, and to a polishing device having the device. is there.
[0002]
[Prior art]
2. Description of the Related Art Densification of semiconductor devices continues to advance without showing any limitations, and some of the various obstacles associated with densification are being overcome by various techniques and methods. One of the major challenges is the flattening of global (relatively large area) device surfaces. As the degree of integration of the device increases, further lamination of electrodes and the like is inevitable. Considering a reduction in the depth of focus at the time of exposure, which accompanies a reduction in the wavelength of lithography, there is a great demand for accurately flattening the interlayer layer at least in the range of the exposure area.
[0003]
Conventionally, many methods of locally planarizing an interlayer layer by improving a film forming method and the like have been proposed and implemented, but are attracting attention as an efficient planarization technique for a larger area, which is required in the future. Is a polishing process called CMP (Chemical Mechanical Polishing or Planarization).
[0004]
CMP is a process for removing the surface irregularities of a wafer by using a chemical action (dissolution with an abrasive or a solution) in combination with physical polishing, and is the most promising candidate for global planarization technology. Specifically, a polishing agent called a slurry in which abrasive grains (typically silica, alumina, cerium oxide, etc.) are dispersed in a soluble solvent of a polishing material such as an acid or an alkali is used, and the wafer is polished with an appropriate polishing cloth. Polishing proceeds by pressing the surface and rubbing by relative motion. By making the pressure and the relative movement speed uniform over the entire surface of the wafer, it is possible to uniformly polish the surface.
[0005]
Although this process still has many problems in terms of matching with the conventional semiconductor process, etc., one of the general required problems is to detect the end of the polishing process. In particular, the detection of the polishing end point (in-situ) while performing the polishing process is greatly demanded for improving the process efficiency.
[0006]
As one method of detecting the end of the polishing process, a method of detecting a fluctuation in friction when polishing proceeds to a layer different from a target polishing layer by a change in torque of a motor for rotating a wafer or a pad is used.
[0007]
Also, an optical path is provided on the polishing pad to irradiate light to the wafer surface, or an optical path is provided to the wafer carrier to irradiate light (infrared light) that is permeable to the wafer from the back surface of the wafer. A method for measuring the thickness of a thin film being polished has also been developed for practical use.
[0008]
This is to irradiate a laser beam to a polished surface when measuring an interlayer insulating film to be polished, and to monitor a temporal change in the intensity of the reflected light. The change in the interference condition of the irradiation light due to the change in the film thickness causes a change in the light amount (a normal sinusoidal change if the film thickness reduction rate is constant). This makes it possible to calculate the film thickness, that is, the polishing amount.
[0009]
[Problems to be solved by the invention]
However, as to the technique for monitoring the polishing amount and the polishing end point during CMP during polishing as described above, a definitive solution has not yet been established despite increasing demands.
[0010]
For example, the method of detecting the polishing end point by the motor torque is effective at present only for detecting the start of polishing of a clearly different layer, and is insufficient in accuracy.
[0011]
One of the problems with the method of measuring the film thickness using interference is that minute irregularities exist on the surface of the polished wafer. FIG. 5 is a schematic diagram showing a polished wafer. In the polished wafer, an SiO ₂ film 2 is formed on a Si substrate 1, and a metal wiring layer 3 and the like are present in the SiO ₂ film 2. Generally, fine irregularities exist on the surface of the polished wafer before or during polishing as shown in FIG.
[0012]
Therefore, the reflected light obtained by projecting the light on the surface of the polished wafer has the following light components superimposed.
(a) Interference light components due to the laminated films (generated at concave portions and convex portions, respectively, FIG. 5A)
(b) A component where the interference light at the concave portion and the interference light at the convex portion further interfere (FIG. 5B).
(c) Diffracted light component due to phase change of uneven portion
In film thickness detection using ordinary optical interference, the light receiving surface is assumed to be flat, and the film thickness is determined from the positions of the peaks and valleys of the amount of reflected light obtained by the interference of the laminated film and the optical constants (refractive index and absorption coefficient). Ask. That is, the film thickness is determined assuming that there are no components (b) and (c). Therefore, when a polished wafer having irregularities on the surface is measured, there is a problem that the components (b) and (c) cause an error and accurate measurement cannot be performed.
[0014]
For this reason, conventionally, it was necessary to take measures such as searching for a flat portion having no unevenness on the surface and performing measurement at that portion, but it is difficult to search for a flat portion during polishing and perform measurement. Was not practical.
[0015]
As described above, the technology for monitoring the polishing amount during polishing is insufficient, and in the actual process, it is often dealt with by controlling the polishing time or the like. I was forced to film.
[0016]
The present invention has been made in order to solve such problems, even in a multilayer sample having minute irregularities on the surface, a film thickness measurement device capable of accurately measuring the film thickness, and An object of the present invention is to provide a polishing apparatus having this apparatus.
[0017]
[Means for Solving the Problems]
A first means for solving the above problem is an apparatus for measuring the thickness of a multilayer sample having fine irregularities on the surface, wherein the difference between the height of the concave portion and the convex portion is H , Where d is the width of d, a light projecting unit that projects light obliquely on the surface of the multilayer sample at an incident angle θ larger than tan ⁻¹ d / ( 2H ) , and a multilayer film that has a reflection angle substantially equal to the incident angle. A multilayer film comprising: a light receiving unit that receives light reflected from a sample surface; and a film thickness measuring unit that detects an interference pattern of light detected by the light receiving unit and measures a film thickness. This is a sample thickness measuring device (claim 1).
[0018]
In this film thickness measuring apparatus, light is obliquely projected on the surface of the multilayer sample and light reflected from the multilayer sample surface is received at a reflection angle substantially equal to the incident angle. The light according to (c) is not received because of the shadow of the convex portion. Therefore, only the light according to (a) is received, and the film thickness can be measured by the same principle as when the surface is flat.
[0019]
A second means for solving the above-mentioned problem is a polishing apparatus having the first means (claim 2).
[0020]
This polishing apparatus has a multilayer film sample thickness measuring apparatus capable of accurately measuring the film thickness, so that the polishing can be accurately completed.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a measurement principle when the film thickness measuring apparatus according to the present invention is applied to a semiconductor wafer. In the polished wafer, an SiO ₂ film 2 is formed on a Si substrate 1, and a metal wiring layer 3 and the like are present in the SiO ₂ film 2.
[0022]
Light is projected onto the polished wafer obliquely, and light reflected from the multilayer sample surface is received at a reflection angle substantially equal to the incident angle. Assuming that the height difference between the concave portion and the convex portion is H, the width of the concave portion is d, and the incident angle and the reflection angle are θ, when θ ≧ tan ⁻¹ d / (2H), the light incident on the concave portion is It does not directly reach the detection unit by hitting the side wall of the projection. The light that hits the side wall is absorbed and reflected by the metal wiring layer 3 and does not reach the detection unit, or enters the detection unit as stray light due to multiple reflection. Light that has entered the detection unit as stray light due to multiple reflection does not contribute to interference. This is because the optical path length becomes longer than the coherent length due to multiple reflection.
[0023]
Therefore, according to this method, the light reflected by the concave portion does not interfere with the reflected light from the convex portion in the detection portion, and thus information on only the reflected light from the convex portion (light interference only from the reflected light from the convex portion). Can be selected, and the signal can be treated as if it were a signal from a flat surface with no irregularities.
[0024]
FIG. 2 is a schematic diagram of a light projecting unit of the device according to the embodiment of the present invention. Light from a Xe lamp (light source) 11 is condensed by a condenser lens 12 and converted to monochromatic light by a monochromator 13. Then, the light is collimated by the collimator lens 14 and is incident on the goniometer 16 via the reflection mirror 15. Then, the incident angle is defined by the goniometer 16 and the object 17 is irradiated obliquely. Various monochromatic lights are generated by the monochromator 13 and interference data is obtained for each of them. The light receiving device and the measuring circuit are the same as those of the conventional optical interference type film thickness measuring device, and the description is omitted.
[0025]
FIG. 3 shows an embodiment of a polishing apparatus having a multilayer film thickness measuring apparatus according to the present invention. In FIG. 3, a material to be polished (wafer) 21 is held by a wafer carrier 22. A polishing pad 24 is provided on the surface of the polishing platen 23, and the polishing platen 23 rotates around its central axis. The wafer carrier 22 rotates while reciprocating while pressing the wafer 21 onto the polishing pad 24, and polishes the wafer 1 with the polishing pad 24. The quartz platen 23 and the polishing pad 24 are provided with a quartz transmission window 25. Reference numeral 26 denotes an apparatus for measuring the thickness of the multilayer film sample as described above, which projects light onto the surface of the wafer 1 through the quartz transmission window 25 and processes the reflected light to measure the film thickness. Then, the polishing is finished when the film thickness reaches the specified thickness.
[0026]
In addition to the method of irradiating light through the quartz transmission window 25 as described above, the wafer is protruded outside the polishing platen 23 and the polishing pad 24 at the time of measurement, and the light is projected onto the protruding wafer portion to perform measurement. Is also good.
[0027]
【Example】
A sample as shown in FIG. 4 was prepared and measured. First, the Si substrate 31 was heated to form a 573 nm SiO ₂ thermal oxide film 32. On top of this, aluminum 33 was laminated by 700 nm sputtering. A photoresist was applied on the formed laminated film (Si / SiO ₂ thermal oxide film / aluminum), a photomask was provided, and the photoresist was exposed to light. Thereafter, the aluminum was etched and the photoresist was removed. Finally, the sample was completed by laminating a 390 nm SiO ₂ film 34 by plasma CVD. The sample thus prepared is a laminated film in which aluminum is patterned at a pitch of 1 μm.
[0028]
Light was obliquely projected on this sample by the optical system shown in FIG. 2, and the specularly reflected light from the sample was received by the detector, and the luminous intensity of the reflected light was measured. Although not shown, the detector is simultaneously moved by the goniometer so that the specular reflected light can be received.
[0029]
As the angle of incidence was changed by the goniometer, the reflection spectrum showed the following changes.
When the incident angle was small, the obtained spectral reflection spectrum was complicated and greatly different from that obtained from a flat laminated film.
However, when the incident angle was 35 ° or more, the amount of received light decreased, but the spectral reflection spectrum was the same as that of a flat film in which a 573 nm SiO ₂ thermal oxide film, 700 nm aluminum, and 390 nm SiO ₂ films were stacked on a Si substrate. Was obtained. That is, by using the obliquely incident light beam, the same spectral reflection spectrum was observed in the region having the unevenness as in the region having no unevenness.
[0030]
【The invention's effect】
As described above, in the apparatus for measuring the thickness of a multilayer sample according to the present invention, light is obliquely projected onto the surface of the multilayer sample and reflected from the multilayer sample surface at a reflection angle substantially equal to the incident angle. Since the light is received, the reflected light from the concave portion is not received because it is shaded by the convex portion. Therefore, only the light reflected from the surface of the convex portion is received, and the film thickness can be measured by the same principle as when the surface is flat.
[0031]
In addition, the polishing apparatus according to the present invention includes the apparatus for measuring the thickness of a multilayer film sample that can accurately measure the film thickness, so that the polishing can be accurately completed.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a measurement principle of a film thickness measuring device according to the present invention.
FIG. 2 is a schematic view showing an example of a light projecting unit of the film thickness measuring device according to the present invention.
FIG. 3 is a view showing an example of an embodiment of a polishing apparatus according to the present invention.
FIG. 4 is a diagram showing a sample used in an example of the present invention.
FIG. 5 is a schematic view showing a polished wafer.
[Explanation of symbols]
1 ... Si substrate 2 ... SiO ₂ film 3 ... metal wiring layer 11 ... Xe lamp 12 ... condenser lens 13 ... monochromator 14 ... collimator lens 15 ... reflecting mirror 16 ... goniometer 17 ... object to be measured 21 ... object to be polished (wafer )
22 ... wafer carrier 23 ... polishing platen 24 ... polishing pad 25 ... a quartz transmission window 26 ... film thickness measuring device 31 ... Si substrate 32 ... SiO ₂ thermal oxide film 33 ... aluminum 34 ... SiO ₂ film

Claims (2)

An apparatus for measuring the thickness of a multilayer sample having fine irregularities on its surface, wherein a difference in height between the concave portion and the convex portion is H , and a width of the concave portion is d, and the surface of the multilayer sample is measured. A light projecting unit that projects light obliquely at an incident angle θ larger than tan ⁻¹ d / ( 2H ) , and a light receiving unit that receives light reflected from the multilayer sample surface at a reflection angle substantially equal to the incident angle. A film thickness measuring unit for measuring a film thickness by detecting an interference pattern of light detected by a light receiving unit. A polishing apparatus comprising the apparatus for measuring a film thickness of a multilayer film sample according to claim 1.

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