JP3327175B2 - Detection unit and wafer polishing apparatus provided with the detection unit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device
At least an interlayer insulating layer or a metal electrode film
Polishing device that removes part of
The present invention relates to a detection unit used in a wafer polishing apparatus.

[0002]

2. Description of the Related Art Densification of semiconductor devices has been progressing without limitation and some of various obstacles accompanying the densification are being overcome by various techniques and methods. One of the major challenges is the flattening of global (relatively large) device surfaces. As the degree of integration of devices increases, further lamination of electrodes and the like is inevitable. In view of the reduction in the depth of focus during exposure accompanying the shortening of the wavelength of lithography, there is a great demand for accurately flattening the interlayer layer at least in the range of the exposure area. In addition, there is a high demand for so-called inlay (plug, damascene) in which the metal electrode layer is embedded, and in this case, removal and flattening of an extra metal layer after lamination are required as essential.

Conventionally, many methods for locally planarizing an interlayer layer by improving a film forming method and the like have been proposed and implemented, but efficient planarization in a larger area, which is further required in the future, has been proposed. CMP is attracting attention as a technology.
(Chemical Mechanical Polishing or Planarizatio
This is a polishing process called n).

[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. ing. Specifically, a wafer called a slurry using a slurry called a slurry in which abrasive particles (generally silica, alumina, cerium oxide, etc.) are dispersed in a soluble solvent of a polishing material such as an acid or an alkali, and the wafer is coated 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.

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 step is greatly demanded for improving the process efficiency.

As one of the methods for detecting the end of the polishing step, a method of detecting a change in friction when polishing proceeds to a layer different from the target polishing layer by a change in torque of a motor for rotating a wafer or a pad is used. ing.

Further, an optical path is provided on the polishing pad to irradiate the wafer surface with light, or an optical path is provided on the wafer carrier to irradiate light (infrared light) that is transparent to the wafer from the back surface of the wafer. A method for measuring the thickness of a thin film being polished due to interference is also being developed for practical use.

In this method, when measuring an interlayer insulating film to be polished, a laser beam is applied to a polished surface, and a change in intensity of reflected light with time is monitored. The change in the interference condition of the irradiation light due to the change in the film thickness causes a change in the light quantity (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]

However, the technique for monitoring the amount of polishing and the end point of polishing during CMP during polishing as described above has established a decisive solution in spite of increasing demand. It has not been.

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.

Also, in the method of measuring the film thickness using interference (method of irradiating a laser beam and tracking the time variation of the reflected light amount), uncertainties depending on patterns, errors due to measurement positions, and the like have been pointed out. I have.

That is, one of the problems with this method is that the polished wafer does not have optically uniform properties. The reason will be described with reference to FIG. In general, as shown in FIG. 6A, the interlayer insulating film 101 is polished in a state where the metal wiring layer 102 and the like are under the polishing wafer 1, or in the state shown in FIG. The upper metal film 102 is polished.

Since such a device pattern (base pattern) exists, reflected light or transmitted light of the probe light is variously affected by the light. To give a simple example, if there is a pattern of the metal electrode 102 on the base, there is no transmitted light (at a normal wavelength) in that part, and the reflected light becomes large.

In the case shown in FIG. 6 (a), the film thickness often fluctuates not only on the whole surface of the wafer but only on the convex portion which is a part thereof. Only fluctuations are detected. Furthermore, in the case where unevenness is present, the progress of polishing often progresses in a non-uniform manner, not in a form in which the polishing is performed in a planar manner. Cannot be obtained.

For this reason, the interference film thickness measuring mechanism which shows a good film thickness measuring performance on a blank wafer (one-side film-forming wafer having no pattern) also has a noise on a signal on a patterned wafer provided with electrodes. It has also been reported that a large amount of manganese is mixed, and in some cases, measurement becomes difficult.

Simultaneous measurement during polishing (in-situ measurement)
In order to perform the measurement, the moving wafer must be measured, the signal becomes more complicated, and the measured value (reflected light intensity, etc.) is increased due to the presence of the slurry, which is an abrasive, on the light beam. There is a problem of increasing instability.

As described above, since the technique for monitoring the polishing amount and the polishing end point during polishing is insufficient, the actual process is often dealt with by controlling the polishing time or the like. The film thickness is to be formed more than necessary.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is intended to remove at least a part of an interlayer insulating layer or a metal electrode film from a wafer on which semiconductor elements are formed by polishing. It is an object of the present invention to provide a wafer polishing apparatus capable of accurately and simply detecting a quantity or a polishing end point during or after polishing.

[0019]

A first means for solving the above-mentioned problems is that a semiconductor element is formed and a top layer is made of metal.
A wafer polishing apparatus for removing at least a part of the metal film in a wafer having two or more layers by polishing, the metal film being on a polished surface of a wafer on which a semiconductor element is formed.
A probe light irradiating unit that irradiates a part or all of the probe light with the probe light reflected from the wafer surface or the spectral reflectance or the spectral transmittance of the probe light transmitted through the wafer .
A wafer polishing apparatus (Claim 1), comprising a detection unit for detecting a polishing end point from a change .

The reflected light and the transmitted light from the polished surface of the wafer on which the semiconductor element is formed are reflected on each layer of the device (laminated thin film),
This can be seen as the superposition of light waves from each part, and the waveform of the wavelength dependency (spectral reflectance or spectral transmittance) changes depending on the thickness of the layer being polished (uppermost layer). This change is more stable (has reproducibility) than changes in the amount of reflected light and the amount of transmitted light, and is less susceptible to intervening slurries, non-uniform film thickness, surface / interface irregularities, and the like. Therefore,
According to the apparatus, the wafer thickness, the amount of polishing, or the polishing end point can be accurately detected regardless of these noise factors. The polishing amount is measured indirectly from the initial thickness of the wafer and the measured wafer thickness.

Interlayer insulation in a wafer on which semiconductor elements are formed
At least a part of the edge layer or the metal electrode film is removed by polishing.
A wafer polishing apparatus, comprising a wafer on which a semiconductor element is formed.
C. A probe that irradiates a part or all of the polished surface with probe light.
Probe light irradiator and probe light reflected from wafer surface
Or the spectral reflectance or spectrum of the probe light transmitted through the wafer
A detection that detects the polishing amount or polishing end point based on the change in transmittance.
A detection unit , wherein the detection unit detects at least one maximum point or minimum point in the spectral curve of reflectance or transmittance, or a change in the wavelength of both, or a maximum point, the appearance or disappearance of a minimum point. Thus, a wafer polishing apparatus (claim 2) for detecting a polishing amount or a polishing end point.

Among the changes in the wavelength dependence (spectral reflectance or spectral transmittance) of the probe light reflected from the wafer surface or the probe light transmitted through the wafer, at least one local maximum in the reflectance or transmittance spectral curve. Fluctuations in the position (wavelength) of the point or the minimum point, or both, or the appearance or disappearance of the maximum point / minimum point are particularly correlated with the thickness of the layer being polished (the uppermost layer), and provide stable reproducibility. It is a signal with. Therefore, accurate measurement becomes possible by using this signal as a signal for detecting the polishing amount or the polishing end point.

Interlayer insulation in a wafer on which semiconductor elements are formed
At least a part of the edge layer or the metal electrode film is removed by polishing.
A wafer polishing apparatus, comprising a wafer on which a semiconductor element is formed.
C. A probe that irradiates a part or all of the polished surface with probe light.
Probe light irradiator and probe light reflected from wafer surface
Or the spectral reflectance or spectrum of the probe light transmitted through the wafer
A detection that detects the polishing amount or polishing end point based on the change in transmittance.
Having a sensing unit , the detection unit, the waveform of the spectral reflectance or spectral transmittance at the polishing end point calculated or measured in advance,
A wafer polishing apparatus according to claim 3, wherein a polishing end point is detected by comparing the measured spectral reflectance or spectral transmittance waveform.

Generally, at the polishing end point, the waveform of the spectral reflectance or the spectral transmittance has a significantly different pattern from the waveform of the spectral reflectance or the spectral transmittance before the polishing is completed. The polishing end point can be accurately detected by comparing the actually measured value with the spectral reflectance or the spectral transmittance at the polishing end point obtained in advance.

A fourth means for solving the above-mentioned problem is as follows.
A wafer polishing apparatus according to any one of the first to third means, wherein the probe light is applied to a pattern structure portion of the wafer with a spot diameter sufficiently larger than the minimum structure of the device of the wafer. ).

A wafer to be polished has a large number of periodic structures which are aggregates of small individual elements, and the wafer is not uniform when viewed finely. Therefore, when the spot diameter of the probe light to be irradiated is small, the reflected light or the transmitted light is affected by the fine structure and changes depending on the irradiation position, which may cause noise. However, by setting the spot diameter of the probe light to be irradiated to be sufficiently larger than the minimum structure of the device on the wafer, the reflected light or the transmitted light becomes constant regardless of the irradiation position of the probe light, and a stable signal can be obtained.

A fifth means for solving the above problem is as follows.
In any one of the first to third means,
The probe light is more than the minimum structure of the device on the wafer
Irradiates the pattern structure portion of the wafer with a large spot diameter
Probe light reflected from the wafer surface or
The probe light transmitted through the wafer is transmitted to each part of the device.
A superposition of light waves from
A polishing apparatus (Claim 5). A sixth means for solving the above-mentioned problem is the fourth or fifth means, wherein the detection unit is polished using only a signal when only the pattern structure portion of the wafer is irradiated with the probe light. A wafer polishing apparatus for detecting an amount or a polishing end point (Claim 6 )
It is.

As described above, in the present wafer polishing apparatus, the principle of detecting the polishing amount or the polishing end point is that reflected light and transmitted light from the wafer polished surface on which the semiconductor element is formed are converted into a device (laminated thin film). Can be viewed as the superposition of light waves from each layer and each part. Therefore, when the probe light is applied to a portion having no pattern structure, a significant detection signal cannot be obtained. Therefore,
By detecting the polishing amount or the polishing end point using only the signal when only the pattern structure portion of the wafer is irradiated with the probe light, the detection can be performed using only a significant signal, and the measurement can be performed. The result will be accurate.

[0029] A seventh means for solving the above problem is as follows.
In any of the sixth means from the first means, the probe light, a wafer polishing apparatus which is irradiated on the wafer through the light transmitting member provided in the polishing table and the polishing pad (claim 7).

Usually, polishing is performed by pressing a wafer held by a wafer carrier against a polishing pad provided on a rotating polishing platen and swinging while rotating. Therefore, by providing a light-transmitting member on the polishing platen and the polishing pad and irradiating the wafer surface with probe light through the light-transmitting member, measurement can be performed even during polishing (in-situ).

An eighth means for solving the above-mentioned problem is as follows.
In any of the sixth means from the first means, the probe light, a wafer polishing apparatus which is irradiated on the wafer portion protruding from the polishing pad (claim 8).

Thus, the measurement can be performed while the polishing is in progress while the wafer is temporarily protruded from the polishing pad, so that accurate measurement can be performed even while the polishing is in progress.

A ninth means for solving the above-mentioned problems is as follows:
In any one of the first to eighth means, the probe light applied to the wafer has a wide range of wavelength components, and a spectroscope that separates reflected light or transmitted light, or reflected light or transmitted light. a wafer polishing apparatus having a filter for selecting a specific wavelength in the transmitted light (claim 9).

[0034] Thus, compared to an apparatus that spectrally irradiates the irradiating light into light of a single wavelength, sequentially irradiates light of different wavelengths, and detects reflected light or transmitted light to detect spectral characteristics. Thus, the polishing amount or the polishing end point can be detected in a short time. A tenth means for solving the above-mentioned problem is that a semiconductor element is formed and the uppermost layer is a metal film.
In polishing the wafer, at least a part of the metal film in the wafer having the upper layer is removed by polishing, the probe light irradiating section is formed by polishing the metal film on the wafer polishing surface on which the semiconductor element is formed.
Irradiating a portion or the probe light of the wavelength of all the multicomponent
Change in the spectral reflectance or spectral transmittance of the probe light reflected from the wafer surface or the probe light transmitted through the wafer
From a detection unit and detecting the polishing endpoint (claim 10). The first to solve the above problems
One means is to provide interlayer insulation in a wafer on which semiconductor elements are formed.
At least a part of the edge layer or the metal electrode film is removed by polishing.
When polishing the wafer, the probe light irradiation unit
Multi-component waves on part or all of the formed wafer polishing surface
Irradiates a long probe light, and the probe reflected from the wafer surface
Spectral reflectance of lobe light or probe light transmitted through wafer
Or, among the changes in spectral transmittance, at least one local maximum or local minimum in the spectral curve of reflectance or transmittance,
Or variation in the wavelength of both, or maximum point, by detecting the appearance or disappearance of local minimum point, the detection unit and detecting the amount of polishing or polishing endpoint (claim 11)
It is. Twelfth means for solving the above problem, the semi
An interlayer insulating layer or metal electrode in a wafer on which conductive elements are formed
When polishing wafers to remove at least part of the polar film by polishing
As a result, the probe light irradiating part is
Probe light of multi-component wavelength on part or all of the polished surface
And the probe light or the wafer reflected from the wafer surface
Spectral reflectance or transmittance of probe light transmitted through wafer
Of the changes in the above, the polishing end point is detected by comparing the waveform of the spectral reflectance or spectral transmittance at the polishing end point calculated or measured in advance with the waveform of the actually measured spectral reflectance or spectral transmittance. A detecting unit (claim 12 ). A thirteenth means for solving the above-mentioned problem is the device according to any one of claims 10 to 12 , wherein the probe light has a spot diameter sufficiently larger than a minimum structure of a device of the wafer and a pattern structure portion of the wafer. The detecting unit (claim 13 ) irradiates the. The task
A fourteenth means for solving the problems is defined in claims 10 to
12. In any one of the above 12, wherein the probe light
With a spot diameter sufficiently larger than the minimum structure of the device,
Irradiated on the pattern structure part of c, from the wafer surface
Reflected probe light or probe transmitted through the wafer
Light is a superposition of light waves from each part of the device
A detection unit (claim 14).
A fifteenth means for solving the above-mentioned problem is defined in claim 13
(14 ) In the detecting section ( 14 ), a detecting section for detecting the polishing amount or the polishing end point by using only a signal when only the pattern structure portion of the wafer is irradiated with the probe light. A sixteenth means for solving the above-mentioned problem is defined in the claims.
In any one of claims 15 to 10, the probe light, a detecting portion to be irradiated on the wafer through the light transmitting member provided in the polishing table and the polishing pad or the wafer carrier (claim 16). A seventeenth means for solving the above-mentioned problem is the detector according to any one of claims 10 to 15 , wherein the probe light is applied to a wafer portion protruding from the polishing pad (claim 17 ). .

[0035]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an example of an embodiment of the present invention.

In FIG. 1, a wafer 1 to be polished is held by a wafer carrier 2. A polishing pad 4 is provided on the surface of the polishing platen 3, and the polishing platen 3 is rotated around its central axis. The wafer carrier 2 rotates and reciprocates while pressing the wafer 1 on the polishing pad 4, and polishes the wafer 1 with the polishing pad 4. The polishing platen 3 and the polishing pad 4 are provided with a quartz light transmitting window 5. Light emitted from the irradiation light source 6 is projected on the surface of the wafer 1 through the quartz light transmitting window 5. The reflected light from the wafer 1 is spectrally processed by an optical system as shown in FIG. 2 and data processed by a personal computer 7 to detect the polishing amount or the polishing end point.

FIG. 2 is a diagram showing details of an example of the optical system used in the embodiment shown in FIG. In FIG. 2, light from a xenon lamp 8, which is an irradiation light source, is converted into a parallel light beam by a lens 9, passes through a slit 10, and is condensed on a beam splitter 12 by a lens 11. The light that has passed through the beam splitter 12 is
The light beam is again converted into a parallel light beam by 3 and projected on the surface of the wafer 1 through the quartz light transmitting window 5 in FIG.

The reflected light is condensed on the beam splitter 12 again through the quartz light transmitting window 5 and the lens 13. In the beam splitter 12, the reflected light has its direction changed by 90 ° and is converted into a parallel light by the lens 14. Then, the light is reflected by the reflecting mirror 15 and condensed on the pinhole 17 by the lens 16. Then, noise components such as scattered light and diffracted light are removed, and the light is projected on the diffraction grating 19 via the lens 18 and separated. The split light enters the linear sensor 20, and the spectral intensity is measured.

The personal computer 7 detects a change in the distribution of the spectral intensity, and detects the thickness of the layer to be polished (uppermost layer) and the polishing end point based on a predetermined algorithm. The polishing amount is determined from the initial thickness of the wafer and the thickness of the layer being polished (the uppermost layer).

According to this method, it is possible to measure the polishing amount or the polishing end point in both the polishing of the interlayer insulating film and the polishing of the metal electrode film without changing the apparatus.

When the irradiation light is applied to a portion of the wafer having no pattern, the spectral reflectance or the spectral transmittance becomes a simple waveform that can be easily predicted, and is realized by the existing film thickness detecting device. Thus, the calculation of the film thickness is also easy. However, in general, areas without patterns are very small in area, and
Since the position is not constant depending on the wafer, it is difficult to perform high-speed measurement with a simple mechanism using this method.

A feature of the present invention is that measurement can be performed not only by irradiating such a blank surface but also by irradiating an electrode pattern or an uneven portion.

The reflected light from the non-blank structural part is
It can be considered as a superposition of light waves from each layer and each part of the device (laminated thin film), and the wavelength-dependent (spectral characteristic) waveform usually has a large number of local minimums (peaks) due to complicated interference effects. ).

If the structure (two-dimensional structure and film thickness) of the device being measured is known in advance, it is possible to obtain the film thickness of the polished layer (top layer) by analyzing this waveform. It is possible.

There are various factors that disturb the absolute value of the reflected light signal. For example, interstitial slurry in the case of in-situ, variations in optical constants due to inhomogeneous film quality, and irregularities on the surface or film interface. Therefore, when the polishing amount or the polishing end point is detected from the absolute value of the reflected light signal as in the related art, an error increases.

In the present invention, in consideration of these noise factors, in the invention according to the first aspect, the change in the wavelength dependency (spectral reflectance or spectral transmittance) is changed. The position (wavelength) of the maximum and minimum in the spectral characteristics is used as important judgment data. The present inventors have found that these data are not very sensitive to the various error factors mentioned above. Compared with the conventionally proposed method of detecting the polishing end point from the time change of the absolute value of the reflected light amount,
The reason why the present invention is a strong detection method that is strong against noise effects is as follows.
The point is to use the change in the wavelength dependence, particularly the maximum and minimum positions of the spectral characteristics.

When the device has a multilayer structure and a complicated structure,
It may not be easy to use this method (calculation of the film thickness from the spectral characteristics). In such a case, a spectral reflection waveform from a device structure having a predetermined film thickness that is desirable as the end of polishing is calculated in advance (this is much easier than back calculation from the waveform), and the shape of this waveform is calculated. It is effective that the polishing end point is determined by the fact that the shapes of the measured waveforms coincide with each other, and typically, that the maximum and minimum positions of the measured values coincide with the maximum and minimum positions of the calculated waveform.

Further, if the actual measured value of the spectral reflectance of the wafer polished to the desired end point can be obtained by the dummy wafer polishing usually performed in the device polishing, the actual measured value is used as a reference to finish the polishing. Judging a point is more practical and convenient.

Although the above description has been made with the thickness measurement of a dielectric film (interlayer insulating film) causing interference exclusively in mind, the present invention can be applied to metal film polishing in the same manner. That is, in general, when polishing the metal laminated on the entire surface of the electrode layer embedded (inlaid), as the polishing progresses, a portion with and without a metal layer appears. The spectral curve of the reflected light is usually smooth in the case of a metal film (this is not always the case when the surface unevenness is large). When the metal film disappears and a pattern appears, the spectral waveform changes greatly due to the influence of the underlying dielectric layer (many maxima and minima appear). By observing this change, the end of the metal film polishing, that is, the appearance of the base can be detected.

The wafer to be polished in CMP is
It is an integrated device.
However, structurally, there are quite a number of periodic structures of small individual elements (wiring patterns). 64M DR
Taking AM as an example, it is an integrated body of cells of about 1 μm square, and the cells are further arranged with one chip spread over about 1 cm ² to constitute a wafer. Therefore, when viewed finely, even if it looks uneven, it can often be seen as uniform (generally from several mm to several cm) when viewed macroscopically.

By irradiating such a structure with light of a spot sufficiently larger than the minimum unit of the cell, it is possible to perform control without irradiating position control or very simple control (for example, a special position such as an edge). ), A uniform signal can be obtained, and the measurement according to the present invention becomes possible.

These measurements are of course effective in so-called in-line or off-line measurement after the polishing step.
It is more effective if measurement can be performed in-situ while polishing is in progress. In an ordinary polishing apparatus, the polishing pad is larger than the wafer. To realize this, as shown in FIG. It is conceivable to perform measurement or to make the wafer protrude from the pad, and perform irradiation and reflected light measurement there.

It should be noted that measurement is performed during polishing, as both the wafer and the polishing pad are constantly moving. Since both the pad and the wafer (carrier) are rotating, and the wafer (carrier) usually swings, the wafer (carrier) moves unless a considerably complicated mechanism (irradiation light source moves synchronously with the wafer) is used. It is difficult to observe a certain position of the camera. In such a case, the optical signal to be observed is naturally affected by the change of the irradiation place. However, as described above, as long as an average signal is obtained in a relatively large spot, it is possible to suppress the influence of movement.

However, it is possible that part or all of the illuminated portion may deviate from the average structural portion. For example, the wafer itself may deviate from the detection irradiation part, or irradiation light may be irradiated to a part that largely includes an edge part (a part without a pattern structure).

Since the fluctuation due to the reflected light from the inhomogeneous portion seen in the macro is often discontinuous and large in quantity, it is often possible to eliminate it at the signal processing stage. It is also conceivable to eliminate the effect by performing measurement while measuring. This can be done by observing the wafer surface with an imaging device such as a CCD and irradiating a predetermined structure with appropriate probe light while recognizing the pattern to perform measurement. In this case, it is also effective to provide a mechanism for changing the irradiation position.

Further, when the irradiation is not properly performed, the signal acquisition may not be performed. In this method, a pattern on an irradiation surface is recognized, and a signal is detected only during a period in which irradiation is appropriately performed on a predetermined periodic structure. The problem with this method is that the polishing proceeds while the signal cannot be detected, and the polishing exceeds the required accuracy of the polishing. The time required for polishing is tp, and the required accuracy of polishing is p
(%), The time required to polish the required precision of polishing is
tp × p / 100. If the signal undetectable time is sufficiently shorter than this value, it is possible to avoid extra polishing during the unmeasurable time as described above.

When measuring from a fixed position while polishing is in progress while the wafer is rotating at high speed, the time required for the measurement is also important. It is desirable to do it as fast as possible. In order to meet this requirement, in the embodiment of the present invention shown in FIG. 1, light having a multi-component wavelength is used as irradiation light. Specifically, it is conceivable to irradiate white light (or a component obtained by dividing the light). It is conceivable that light containing light in a wide wavelength range is incident as incident light, the reflected light is spectrally processed using an element such as a diffraction grating or a hologram, and the intensity of each wavelength is received by a multi-division light receiving sensor.

According to this method, only the reflected light is obtained as the measurement, and the spectral processing can be performed immediately, so that the measurement can be performed quickly. When measuring spectral characteristics by this method, naturally consider the wavelength distribution of the light source (measurement is made in advance, or measurement is performed on a branch optical path).
There is a need.

Although the amount of information as an acquisition signal decreases,
A configuration that uses a color selection filter or a dichroic mirror to obtain wavelength distribution information of reflected light is also considered as an example of high-speed measurement.

Of course, if time permits, it is also possible to sequentially irradiate light of a single wavelength having a different wavelength and measure the reflected light to determine the spectral characteristics.

In the above, the method of irradiating the probe light from the front side (polishing surface side) of the wafer as shown in FIG. 1 has been described. For example, the light source is embedded in the wafer carrier 2 in FIG. The probe light may be irradiated from the back surface of the substrate. In this method, the polishing state is known by observing the wavelength dependence of the reflected light from the polished surface of the wafer, that is, the spectral characteristics. In this case, a multi-component wavelength light source in the infrared region transmitting through the wafer is required.

Further, in FIG. 1, a quartz light transmitting window is also provided in the wafer carrier 2 so that light transmitted through the wafer 1 is received by a light receiving section provided on the wafer carrier 2 side to measure spectral characteristics. You may. Conversely, wafer carrier 2
A light transmitting unit may be provided on the side of the polishing table 3 and a light receiving unit may be provided on the side of the polishing platen 3 to measure the spectral transmission characteristics.

[0063]

【Example】

(Example 1) In the actual polishing system shown in FIG.
The interlayer insulating film SiO ₂ of the imaging device on the 6-inch wafer was polished, and the end point of the polishing was detected. The polished image sensor has a minimum periodic structure of about 10 μm square. Light irradiation is performed on the polishing pad 4 (epoxy polishing cloth) on the lower surface and the polishing platen 3
Then, a circular hole of about 2 cmφ was opened, and a light transmitting window 5 made of quartz was provided on the same surface as the polishing pad surface.

The irradiation optical system is an optical system for making light from the xenon lamp 8 as shown in FIG.
After the scattered light and the diffracted light are removed from the reflected light by the pinhole 17, the wavelength is decomposed by the diffraction grating 19, and the light of the different wavelength is directed to the different direction, so that the photodiode type linear sensor 20 (50) Element). The measurement wavelength range is approximately 400 nm to 800 nm, and the irradiation spot system is about 2 mmφ. The output from the sensor is processed by the personal computer 7 after amplification. At that time, the spectral intensity information of the light source light measured in advance is used as a coefficient at the time of processing.

As the abrasive (slurry), silica particles dispersed in an alkaline solvent were used and polished at a polishing pressure of about 100 g / cm ² . The effect on the light quantity (mainly scattering loss) due to the presence of the slurry was 1% or less.

Observation of the obtained spectral reflectance shows that when the cell portion is irradiated, there is almost no change (difference) even if the irradiation position is moved, and the waveform as shown in FIG. Obtained. In FIG. 3, the solid line and the dotted line show the waveforms of the reflected light from the portions where the irradiation positions are different, but both of them almost overlap, indicating that there is no change (difference) due to the irradiation position.

When the irradiation light is applied to a portion other than the cell, that is, a portion around the cell called a scribe line or a portion without a cell near the wafer edge, the waveform is greatly different, and the absolute value of the reflectance is about twice. It became. In the present example, the effect of these special parts could be eliminated by using an algorithm that does not perform signal acquisition (does not process the acquired signal) when the light amount of the specific wavelength becomes a certain value or more.

On the outermost surface of the device, a CVD
The formed insulating film SiO ₂ is polished and polished to a polishing thickness of about 150 nm. First, a sample subjected to predetermined polishing was measured as a dummy, a spectral characteristic waveform as shown in FIG. 4 was obtained, and the maximum and minimum positions thereof were extracted (using a peak search program). A signal was obtained by actually performing polishing, and polishing was terminated when a state where the maximum and minimum positions of the spectral characteristic waveform coincided with the extracted positions (circles in the figure). By actually observing some wafers for which polishing was determined to have been completed, it was confirmed that the surface was flattened and polished with an error of about 10% of the target polishing thickness.

(Embodiment 2) In the present embodiment, while performing the same measurements as in Embodiment 1, the reflected light spectral characteristics of the structure at the polishing end point are calculated in advance, and the calculated maximum and minimum values are compared with the actually measured values. I did that. The calculated reflected light waveform did not fit in the measured waveform and its absolute value, but showed good agreement at the local maximum and local minimum positions. By detecting the polishing end point using the calculated maximum and minimum positions, the polishing end can be detected with an accuracy of about 10% of the film thickness.

(Example 3) The measurement of Example 1 and the monitoring of the polishing of the metal layer (Al) were performed by the same mechanism arrangement.
When the polishing is started, the entire surface is covered with metal, and when the reflected light is observed, a substantially flat spectral characteristic waveform as shown in FIG. 5A is obtained. As the polishing progresses and the insulating layer is exposed, the absolute value of the amount of reflected light decreases, and a waveform b having a maximum value and a minimum value appears due to the interference effect. By terminating the polishing when the waveform b becomes stable, it is possible to detect the termination with an accuracy of about 10% in the polishing step of about 300 nm.

[0071]

As described above, according to the present invention, there is provided a wafer polishing apparatus for removing at least a part of an interlayer insulating layer or a metal electrode film in a wafer having a semiconductor element formed thereon by polishing, wherein the semiconductor element is A probe light irradiator that irradiates a part or all of the formed wafer polished surface with probe light, and a wavelength dependence of the probe light reflected from the wafer surface or the probe light transmitted through the wafer (spectral reflectance or spectral transmittance) ), A detection unit for detecting a polishing amount or a polishing end point is provided.
The detection of the polishing amount or the polishing end point during or after polishing is performed with a high sensitivity and a simple mechanism. This device is immune to noise and less affected by signal disturbances.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of an example of an optical system used in the apparatus shown in FIG.

FIG. 3 is a diagram showing measured waveforms before the end of polishing in Example 1.

FIG. 4 is a diagram showing a waveform at a polishing end point in the first embodiment.

FIG. 5 is a diagram showing a measurement waveform on a metal surface and a measurement waveform at a polishing end point in Example 3.

FIG. 6 is a schematic view of a polishing process by CMP. (A)
Shows polishing of an interlayer insulating layer, and (b) shows polishing of a metal layer (inlaid). In each case, the upper figure is before polishing and the lower figure is after polishing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Wafer 2 ... Wafer carrier 3 ... Polishing surface plate 4 ... Polishing pad 5 ... Quartz translucent window 6 ... Irradiation light source 7 ... Personal computer 8 ... Xenon lamp 9, 11, 13, 14, 16, 18 ... Lens 10 ... Slit DESCRIPTION OF SYMBOLS 12 ... Beam splitter 15 ... Mirror 17 ... Pinhole 19 ... Diffraction grating 20 ... Linear sensor 101 ... Interlayer insulating layer 102 ... Metal electrode film

──────────────────────────────────────────────────の Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/304 B24B 37/04 B24B 49/12 G01B 11/06

Claims (17)

(57) [Claims] A semiconductor element is formed, and a top layer is a metal film
A wafer polishing apparatus for removing at least a part of the metal film in a wafer having two or more layers by polishing,
A probe light irradiating unit for irradiating a part or all of the metal film on the polished surface of the wafer on which the semiconductor element is formed, and a spectral reflectance of the probe light reflected from the wafer surface or the probe light transmitted through the wafer or Changes in spectral transmittance
And a detecting unit for detecting a polishing end point . 2. An interlayer in a wafer on which semiconductor elements are formed.
At least a part of the insulating layer or the metal electrode film is removed by polishing.
A wafer polishing apparatus, in which a semiconductor element is formed.
A probe for irradiating a part or all of the polished surface with probe light
Lobe light irradiator and probe reflected from wafer surface
Spectral reflectance or fraction of light or probe light transmitted through the wafer
Detects polishing amount or polishing end point based on change in light transmittance
Having a detection unit, the detection unit, at least one maximum point or minimum point in the reflectance or transmittance spectral curve,
A wafer polishing apparatus for detecting a polishing amount or a polishing end point by detecting a change in wavelength of both of them, or the appearance or disappearance of a maximum point or a minimum point. 3. An interlayer in a wafer on which semiconductor elements are formed.
At least a part of the insulating layer or the metal electrode film is removed by polishing.
A wafer polishing apparatus, in which a semiconductor element is formed.
A probe for irradiating a part or all of the polished surface with probe light
Lobe light irradiator and probe reflected from wafer surface
Spectral reflectance or fraction of light or probe light transmitted through the wafer
Detects polishing amount or polishing end point based on change in light transmittance
Having a detection unit, the detection unit compares the waveform of the spectral reflectance or spectral transmittance at the polishing end point calculated or measured in advance with the waveform of the actually measured spectral reflectance or spectral transmittance. A wafer polishing apparatus for detecting a polishing end point. 4. The method according to claim 1, wherein the probe light has a spot diameter sufficiently larger than a minimum structure of a device on the wafer and a pattern on the wafer.
The wafer polishing apparatus according to any one of claims 1 to 3, wherein the wafer is irradiated to a wafer structure portion. 5. The method according to claim 1, wherein the probe light is a device of a wafer.
With a spot diameter sufficiently larger than the minimum structure,
Irradiated on the wafer structure and reflected from the wafer surface
The probe light or the probe light transmitted through the wafer is
Superposition of light waves from each part of the device
The method according to any one of claims 1 to 3, wherein
Wafer polishing equipment. 6. The polishing apparatus according to claim 1, wherein the detecting section detects the polishing amount or the polishing end point using only a signal when only the pattern structure portion of the wafer is irradiated with the probe light. wafer polishing apparatus according to claim 4 or 5. Wherein said probe light, any one of the claims 1 to 6, characterized in that it is irradiated on the wafer through the light transmitting member provided in the polishing table and the polishing pad or the wafer carrier 3. The wafer polishing apparatus according to claim 1. Wherein said probe light, the wafer polishing apparatus according to any one of claims 1 to 6, characterized in that it is irradiated on the wafer portion protruding from the polishing pad. 9. A probe light applied to the wafer has a wide range of wavelength components, and a spectroscope for separating reflected light or transmitted light, or selection of a specific wavelength in reflected light or transmitted light. The wafer polishing apparatus according to any one of claims 1 to 8 , further comprising a filter for performing the operation. 10. A semiconductor device is formed, and a top layer is formed of a metal.
In polishing a wafer having at least a part of the metal film in a wafer having two or more layers, which is a film, a probe light irradiating part is partially or wholly part of the metal film on a wafer polishing surface on which a semiconductor element is formed. Is irradiated with probe light having a multi-component wavelength, and the spectral reflectance or transmittance of the probe light reflected from the wafer surface or the probe light transmitted through the wafer is irradiated.
A detection unit that detects a polishing end point from a change in the excess rate . 11. A layer in a wafer on which a semiconductor element is formed.
Polishing at least a part of the inter-insulation layer or the metal electrode film
During wafer polishing, the probe light irradiation part is
Multi-component on part or all of wafer polished surface on which wafers are formed
Irradiates a probe light with a wavelength of
Of the probe light transmitted through the wafer or the probe light transmitted through the wafer
Iritsu or of the change in the spectral transmittance, detecting at least one maximum point or minimum point, or variation in the wavelength of both, or maximum point, the appearance or disappearance of local minimum points in the spectral curve of reflectance or transmittance A detection unit for detecting a polishing amount or a polishing end point. 12. A layer in a wafer on which a semiconductor element is formed.
Polishing at least a part of the inter-insulation layer or the metal electrode film
During wafer polishing, the probe light irradiation part is
Multi-component on part or all of wafer polished surface on which wafers are formed
Irradiates a probe light with a wavelength of
Of the probe light transmitted through the wafer or the probe light transmitted through the wafer
By comparing the waveform of the spectral reflectance or spectral transmittance at the polishing end point calculated or measured in advance, and the measured spectral reflectance or spectral transmittance waveform among the changes in the emissivity or spectral transmittance. A detecting unit for detecting a polishing end point. Wherein said probe light, a sufficiently large spot diameter than the minimum structure of the wafer of devices, patterns of wafer - claim 10, characterized in that is applied to the down structural part
Detection unit according to any one of claims 12 to. 14. The device according to claim 1, wherein the probe light is a wafer device.
With a spot diameter sufficiently larger than the minimum structure of
And is reflected from the wafer surface.
Probe light or probe light transmitted through the wafer,
The superposition of light waves from each part of the device.
13. The method according to claim 10, wherein:
The detection unit according to the item. 15. The polishing apparatus according to claim 15, wherein the detection section detects the polishing amount or the polishing end point using only a signal when only the pattern structure portion of the wafer is irradiated with the probe light. The detection unit according to claim 13 . 16. The probe light, any one of claims 15 to be irradiated on the wafer through the light transmitting member provided in the polishing table and the polishing pad or the wafer carrier from claim 10, wherein The detection unit according to 1. 17. The probe light, the detection unit according to any one of claims 15 claim 10, characterized in that it is irradiated on the wafer portion protruding from the polishing pad.