JP4442555B2 - Polishing method - Google Patents

Description

  The present invention relates to a polishing method, and more particularly, to a polishing method for repeatedly performing electrolytic polishing and chemical mechanical polishing performed when a buried wiring is formed by flattening the concavo-convex surface of a copper plating film surface associated with copper wiring formation. .

  The detection of the end point in the electrolytic polishing of the copper plating film used for the copper wiring was controlled by the polishing time.

  However, in electropolishing, the area of the remaining copper film is reduced, and the copper elution and removal speed is locally accelerated due to the electrolytic concentration on the fine wiring. However, there are still problems such as disappearance of fine wiring and remaining huge wiring.

  Furthermore, the current value at the end point is much smaller than when the entire surface is covered with copper, and a local resistance value change due to current concentration is also added, and the removal amount is estimated from the accumulated value of the integrated current (for example, Patent Documents) 1)), it is difficult to accurately determine the end point.

  As a result, the surface to be polished of the copper film is formed on an unstable surface with a rough surface roughness, the copper embedded in the groove wiring portion is over-polished, and the wiring cross-sectional area is insufficient due to the receding of the copper wiring surface, Problems such as dishing and erosion have occurred. In this way, short-circuiting and opening of the wiring occur due to local non-uniformity due to copper residue, over-polishing and the like.

  In particular, when the electrolytic polishing at the end point is only for the trench wiring portion, the copper film is covered from the 100% state where the copper film is formed on the entire surface to the pattern density. The polishing area is decreasing. For this reason, since the electropolishing easily concentrates on the copper in the fine trench wiring portion, the polishing rate difference between the remaining huge remaining portion or wide wiring portion and the independent fine wiring portion increases, and the independent fine wiring portion The polishing speed increases at an accelerated rate. Further, the electropolishing conditions fluctuate due to an extreme change in the anode current density, and the glossy electropolishing conditions deviate, thereby causing defects such as surface roughening.

Japanese Patent Laid-Open No. 2001-077177

  The problem to be solved is that the polishing rate cannot be increased without degrading the quality of the surface to be polished.

  An object of the present invention is to increase the polishing rate without degrading the quality of the surface to be polished by using electrolytic polishing and chemical mechanical polishing or chemical buffing in combination.

The polishing method of the present invention, patterns of irregularities on the wafer surface is formed, a polishing method of polishing a metal film formed on the wafer surface so as to fill the recess, polishing gold Shokumaku includes electrolytic polishing, 6.9kPa have chemical mechanical polishing or row alternately chemically buffing or lower polishing pressure, and these electrolytic polishing, chemical mechanical polishing or a set of polishing two or more times the chemical buffing It is characterized by performing .

  In the polishing method of the present invention, the surface of the metal film surface is roughened by electrolytic polishing because the metal film is alternately polished by electrolytic polishing and chemical mechanical polishing or chemical buff polishing. In the chemical mechanical polishing or chemical buffing, the polishing rate is increased. In addition, since the surface after electropolishing is polished by chemical mechanical polishing or chemical buffing, the surface to be polished is the same as when polished by chemical mechanical polishing or chemical buffing alone. Can be obtained, and the polishing rate can be increased. Since the electrolytic polishing and the chemical mechanical polishing or the chemical buffing are alternately performed, the polishing rate can be increased without degrading the quality of the surface to be polished.

  In the polishing method of the present invention, the polishing of the metal film is alternately performed by electrolytic polishing and chemical mechanical polishing or chemical buffing, so that the smoothness equivalent to that obtained by only chemical mechanical polishing or chemical buffing is used. The quality of the surface to be polished can be obtained, the in-plane uniformity of the surface to be polished is excellent, and the polishing rate can be increased. Alternatively, polishing can be performed at a low pressure at an equivalent polishing rate. Therefore, there is an advantage that the fine wiring can be prevented from disappearing due to the electrolytic concentration and the surface to be polished of the metal film can be prevented from being rough due to the change of the electrolytic polishing conditions.

  An example of one embodiment according to the polishing method of the present invention will be described.

  The polishing method of the present invention is a polishing method for polishing a metal film formed on a wafer surface so as to fill a recess formed on the wafer surface. In the polishing method, the metal film is polished by electrolytic polishing and CMP or chemical buff polishing. This is an alternate polishing method. As the end point of this electropolishing, an end point detection method described later can be used in the electropolishing step in the final step among the electropolishing performed a plurality of times. In the electrolytic polishing before the final process, for example, the polishing end point is determined by the polishing time. Further, it is desirable that the optimum number of times of electrolytic polishing and CMP is obtained in advance through experiments.

  As the CMP, for example, loose abrasive CMP using a slurry containing abrasive grains, CMP using a fixed abrasive pad, CMP using abrasive-free slurry can be employed.

  In the polishing method of the present invention, the polishing of the metal film is carried out alternately by electrolytic polishing and CMP or chemical buff polishing. Therefore, as shown in FIG. As shown in (2) of FIG. 1, the surface of the metal film is roughened by electropolishing, so that the surface roughness becomes rough. Since such a surface state is polished by CMP or chemical buffing, the polishing rate in CMP or chemical buffing is increased. At this time, the polishing pressure of CMP can be reduced to 1/7 to 1/10 as compared with normal CMP. Therefore, even if a fragile film such as a general low dielectric constant organic film or a porous low dielectric constant insulating film is used as the base, CMP can be performed without destroying the base. . As a result of performing low-pressure CMP, the surface of the metal film 32 is finished as a smooth surface as shown in FIG.

  For example, in normal CMP, the polishing pressure is 27.5 kPa to 48.1 kPa, the polishing rate is 200 nm / min to 600 nm / min, and the flatness of the surface to be polished is not good or normal, and the surface is uniform. Sex is 3% to 5%. On the other hand, in CMP with a low polishing pressure, the polishing pressure is 6.9 kPa or less and the polishing rate is 100 nm / min or less, but the flatness of the surface to be polished is good and the in-plane uniformity is about 5%. is there.

In addition, when the voltage / current density was as high as 50 mA / cm ² or more, the dissolution rate of electropolishing was a maximum dissolution rate of 800 nm / min and an in-plane uniformity of 3% or less. On the other hand, when the voltage / current density was as low as 20 mA / cm ² or less, the elution rate was 200 nm / min or less, and the in-plane uniformity was 3% or less.

  From the above results, it was found that a layer having a rough surface (hereinafter referred to as an altered layer) formed by electrolytic polishing can be polished at a relatively high speed even at a low polishing pressure. Therefore, efficient polishing can be performed by alternately performing electrolytic polishing and CMP a plurality of times.

  In addition, as shown in FIG. 2A, when the formation of the altered layer 33 of the metal film 32 by electropolishing is balanced with the polishing of the altered layer 33 by CMP, that is, the metal roughened by electropolishing. When the surface of the film 32 is smoothed by CMP, a smooth and glossy good polished surface can be obtained. On the other hand, as shown in (2) of FIG. 2, when the altered layer 33 of the metal film 32 is formed thick by electrolytic polishing, the altered layer 33 cannot be completely polished even by polishing by CMP. That is, the surface of the metal film 32 roughened by electropolishing is not smoothed by CMP. If electrolytic polishing and CMP are repeated in such a state, the surface to be polished becomes very rough and no polishing effect is obtained. Further, as shown in (3) of FIG. 2, if the formation of the altered layer 33 of the metal film 32 by electropolishing is too thin, the altered layer 33 can be easily polished by CMP, but a desired thickness is polished. Therefore, it takes too much time, and a sufficient improvement in polishing throughput cannot be expected.

  As described above, in the above polishing method, the surface having a rough surface after electropolishing is polished by CMP or chemical buffing, so that it is equivalent to polishing by CMP or chemical buffing alone. A smooth and polished surface can be obtained, and the polishing rate can be increased. As described above, since electrolytic polishing and CMP or chemical buff polishing are alternately performed, the polishing rate can be increased without degrading the quality of the surface to be polished, so that the polishing throughput can be improved. .

  Next, examples of various polishing sequences will be described with reference to FIG. In FIG. 3, (1) and (2) show the polishing sequence of the prior art, and (3) shows the polishing sequence of the present invention.

  A sample for performing the polishing sequence has the following structure. That is, an insulating film is formed on the wafer surface, and a wiring groove is formed in the insulating film. A tantalum nitride film is formed as a barrier layer on the inner surface of the wiring groove and the insulating film surface. Further, a copper film is formed on the barrier layer so as to fill the wiring groove by a normal copper plating technique. The copper film in the portion other than the wiring trench has a thickness of 1.200 μm.

FIG. 3 (1) shows a case where the copper film is polished by only normal CMP. The polishing pressure P is set to 0.280 kgf / cm ² and CMP for 3 minutes is performed four times. Since the removal amount of the copper film by one CMP is 0.300 μm, the 1.200 μm copper film was removed by four CMPs. In this process, since electropolishing is not performed, the removal amount by electropolishing is zero. In the above process, the tantalum nitride film was exposed as indicated by black triangles. Therefore, the last CMP is over-polishing.

FIG. 3B shows a case where the copper film is polished only by low-pressure CMP. The polishing pressure P is set to 0.060 kgf / cm ² and CMP for 3 minutes is performed 16 times. Since the removal amount of the copper film by one CMP is 0.075 μm, the 1.200 μm copper film was removed by 16 CMPs. In this process, since electropolishing is not performed, the removal amount by electropolishing is zero. In the above process, the tantalum nitride film was exposed as indicated by black triangles. Therefore, the 13th and subsequent CMPs are over-polished.

FIG. 3 (3) shows a polishing method according to an embodiment of the present invention, in which low-pressure CMP and electrolytic polishing are alternately performed, and after the tantalum nitride film is exposed, the copper film is polished only by low-pressure CMP. The polishing pressure P was set to 0.060 kgf / cm ² (≈5.88 kPa) , CMP for 3 minutes was performed 8 times in total, and electrolytic polishing was performed 5 times in total. Since the removal amount of the copper film by one CMP is 0.075 μm, the 0.600 μm copper film was removed by eight CMPs. In addition, since the polishing amount by one electrolytic polishing is 0.0167 μm, the 0.0833 μm copper film is removed by five electrolytic polishings.

  In the case of (3) above, the total of the polishing amount by CMP and the polishing amount by electrolytic polishing does not match the thickness of the copper film for the following reason. That is, in the electrolytic polishing, the entire surface to be polished is not uniformly polished, but is deeply polished in the depth direction more than the polishing amount. That is, the altered layer is formed deeper than the polishing amount. For this reason, since this deteriorated layer is easily formed when polished by CMP, even the low-pressure CMP is polished more than the polishing amount of CMP itself. As a result, even if the sum of the polishing amount by CMP and the polishing amount by electrolytic polishing does not coincide with the thickness of the copper film, the excess copper film is completely removed.

  In the process (3), the barrier layer was exposed when indicated by black triangles. Therefore, the last three CMPs are over-polished. In the final electrolytic polishing, the end point was detected by the end point detection method by the polishing method described later.

  In FIG. 3, the normal pressure CMP has a polishing time of 3 minutes, the polishing rate is about 0.100 μm / min, and the polishing amount of one CMP is 0.300 μm. The low pressure CMP has a polishing time of 3 minutes, the polishing rate is about 0.025 μm / min, and the polishing amount of one CMP is 0.075 μm. Electrolytic polishing has a polishing time of 10 seconds, a polishing rate of 0.100 μm / min, and a polishing amount of 0.0167 μm. In each of the above processes, over-polishing was performed at the time when the barrier layer was exposed, and the amount of polishing was equivalent to 30% of the amount of polishing so far.

Next, the results are summarized in FIG. As shown in FIG. 4, the polishing time was 12 minutes in CMP at a normal polishing pressure. However, the problems described in the background art have occurred. In CMP using a low polishing pressure, the polishing time was 48 minutes, and the throughput was significantly reduced. On the other hand, in the polishing method in which electrolytic polishing and low-pressure CMP are alternately performed, the total polishing time is 24 minutes when one electropolishing time is 5 seconds, and the total polishing time when one electropolishing time is 10 seconds. It was found that the polishing time was 21 minutes, the surface to be polished was good, and efficient polishing could be realized.

  Next, an example of an electrolytic polishing apparatus that realizes the polishing method of the present invention will be described with reference to the schematic configuration diagram of FIG.

  As shown in FIG. 5, the electropolishing apparatus 1 includes an electropolishing chamber 11 in which an electropolishing liquid 12 is stored. A wafer holder (not shown) is provided in the electropolishing chamber 11 so that the metal film 32 formed on the surface of the wafer 31 is immersed in the electropolishing liquid 12. Further, a power source 21 having a cathode connected to the wafer 31 side and an anode connected to the electrolyte solution 12 side is provided. In addition, a current detector 22 for detecting a current flowing between the power source 21 and the cathode or anode is connected. Connected to the current detector 22 is an end point determination unit 23 that determines an electropolishing end point of the metal film 32 based on a change in current obtained by the current detector 22. Further, the end point determination unit 23 is connected to the power source 21 and instructs to stop the voltage application of the power source 21 when the end point of electropolishing is determined. The electropolishing end point of the metal film 32 in the end point determination unit 23 is obtained, for example, by differentiating a change in current waveform during electropolishing.

  Next, the relationship between the current flowing during electropolishing and the polishing time will be described with reference to FIG. This electropolishing uses the electropolishing apparatus described with reference to FIG.

  This polishing method is a polishing method in which a metal film formed on the wafer surface is electropolished so as to fill a recess formed in the wafer surface, and the electropolishing of the metal film is performed by changing the current waveform obtained during the polishing. Determine the end point.

  For example, a wiring groove pattern is formed in the insulating film formed on the wafer surface, and a barrier layer is formed on the inner surface of the wiring groove and the insulating film surface. Further, a metal film (for example, a copper film) is formed on the barrier layer so as to fill the wiring groove.

  When the metal film having such a configuration is electropolished with a constant applied voltage, for example, the current waveform during electropolishing is characteristic when the underlying barrier layer is exposed, as shown in FIG. The current waveform is shown. Therefore, the electropolishing end point is detected by monitoring the current waveform.

  As the detection method, for example, the change in the current waveform during electropolishing is differentiated. The point at which the slope of the current waveform at the end point position (or change in slope) obtained in advance matches the slope of the measured current waveform (or change in slope) is taken as the polishing end point. Thus, the end point of electropolishing can be accurately determined by monitoring the current waveform.

  Normally, a conductive base pattern is formed in the lower layer of the trench wiring, and the metal film in each wiring trench is connected by the base pattern, so that the current fluctuation as described later with reference to FIG. The current value drops rapidly without causing

  Further, as shown in (1) of FIG. 6, after the current is suddenly reduced, the rate of current reduction is reduced (part B). That portion may be the polishing end point. In addition, when the metal film on the so-called solid film formed on the flat surface is electropolished, as shown in (2) of FIG. 6, when the current starts to rapidly decrease, only for a predetermined time, The current value varies greatly (part C in the drawing). This is because since the pattern is not formed on the base, when the metal film is polished and remains in an island shape, the resistance fluctuates rapidly.

  Further, the entire surface of the wafer is covered with a metal film at the initial stage of electropolishing. For example, in the case of electropolishing where a constant voltage is applied, the current value increases as the thickness of the remaining copper film decreases. Since it decreases in proportion to the resistance value, the approximate remaining film amount of the metal film can be estimated. The transition to detailed current waveform monitoring can be simplified by setting the resistance value from an appropriate value.

  Similarly, in the case of electrolytic polishing in which a constant current is applied, an approximate remaining film value can be estimated from a change in voltage value.

It is a schematic cross section explaining one embodiment concerning the polishing method of the present invention. It is a schematic cross section explaining the form of the grinding | polishing state concerning the grinding | polishing method of this invention. It is a figure explaining an example of the actual grinding | polishing sequence concerning each grinding | polishing method. It is a comparison figure of polish time by each polish method. It is a schematic block diagram which shows one Embodiment which concerns on an electropolishing apparatus. FIG. 6 is a relationship diagram between current flowing during electropolishing and polishing time.

Explanation of symbols

  32 ... Metal film

Claims (6)

In a polishing method for polishing a metal film formed on the wafer surface so that a concave-convex pattern is formed on the wafer surface and the concave portion is embedded,
The polishing of the metal film, and electrolytic polishing, have alternating row following a chemical mechanical polishing or chemical buffing low polishing pressure 6.9 kPa, the electrolytic polishing, the chemical mechanical polishing or chemical buff A polishing method in which a set of polishing steps with polishing is performed twice or more . The electrolytic polishing makes the surface of the metal film rough,
The chemical mechanical polishing or chemical buffing, the said metal film surface roughened by electrolytic polishing, the polishing method of the 請 Motomeko 1, wherein you smooth every electropolishing process. It said plurality endpoints of electrolytic polishing in the final step of electropolishing step, the polishing method according to 請 Motomeko 1 or 2 you determined by changes in the current waveform obtained when the electrolytic polishing the metal film. The end point of the electropolishing is the gradient of the current waveform obtained by differentiating the change of the current waveform, or the change of the gradient is the gradient of the current waveform at the end point of electropolishing that has been obtained in advance, or the gradient請 Motomeko 3 polishing method according to the point that matches the change. The polishing method according to any one of claims 1 to 4, wherein the electrolytic polishing and the chemical mechanical polishing or the chemical buff polishing are obtained in advance by experiments in an optimum number of times. The said uneven | corrugated pattern is formed on the base layer which consists of a low dielectric constant organic film or a porous low dielectric constant insulating film provided on the wafer surface. Polishing method.

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