JP2001274126A - Polishing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing apparatus, capable of detecting the thickness of a conductive film, such as Cu layer, Al layer, etc., formed on the surface to be polished on a semiconductor substrate in real-time basis as a continuous measured value by placing a sensor, such as eddy current sensor, etc., at a turn table having a polishing cloth or fixed abrasive plate. SOLUTION: The polishing apparatus has a top ring 3 for holding a substrate and a turntable 1 having a polishing surface. The apparatus polishes a surface to be polished on the substrate, on which a semiconductor devices is formed, with the polishing surface is slidably contacted to the surface to be polished, and comprises at least a sensor 10 formed below the polishing surface of the turntable 1. The sensor is capable of measuring the thickness of a conductive film formed on the surface to be polished on the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing apparatus, and more particularly to a polishing apparatus for polishing a substrate such as a semiconductor wafer without exposing the surface to be polished while the substrate is mounted on a top ring. The present invention relates to a polishing apparatus capable of continuously detecting the thickness of a conductive film formed on a surface in real time.

[0002]

2. Description of the Related Art Conventionally, in order to form a wiring circuit on a semiconductor substrate, a conductor is formed on the substrate surface by sputtering or the like, and then a chemical dry etching is performed using a pattern mask such as a resist. Unnecessary portions of the film were removed. In general, aluminum (Al) or an aluminum alloy has been used as a material for forming a wiring circuit. However, as the degree of integration of the semiconductor increases, the wiring becomes thinner, the current density increases, and thermal stress and temperature rise occur. This becomes more remarkable as the thickness of Al or the like becomes thinner due to stress migration or electromigration, and finally, there is a risk of disconnection or short circuit.

Therefore, in order to avoid excessive heat generation due to energization, a material such as copper having higher conductivity is required to be used for forming the wiring. However, it is difficult to dry-etch copper or its alloy, and it is difficult to adopt the above-described method of forming a pattern after forming a film on the entire surface of the substrate.
Therefore, a process of forming a wiring groove in a predetermined pattern in advance and filling the groove with copper or an alloy thereof may be considered. According to this, a step of removing the film by etching is unnecessary, and a polishing step for removing a surface step may be performed. In addition, there is an advantage that a portion called a wiring hole connecting the upper and lower sides of the multilayer circuit can be formed at the same time.

However, such a shape of the wiring groove or the wiring hole has a considerably high aspect ratio (ratio of depth to diameter or width) as the wiring width becomes finer. Was difficult. In addition, a vapor phase growth (CVD) method is used as a film forming means of various materials. However, it is difficult to prepare an appropriate gaseous raw material with copper or its alloy, and when an organic raw material is used. However, there is a problem that carbon (C) is mixed into the deposited film to increase the migration property.

Therefore, a method has been proposed in which a substrate is immersed in a plating solution to perform electroless or electrolytic plating of, for example, copper (Cu), and then unnecessary portions of the surface are removed by chemical mechanical polishing (CMP). In such film formation by plating, it becomes possible to uniformly fill a wiring groove having a high aspect ratio with a metal having a high conductivity. The CMP process presses a semiconductor wafer held by a top ring on a polishing cloth stuck on a turntable, and simultaneously polishes a Cu layer on the semiconductor wafer while supplying a polishing slurry containing abrasive grains. Is what you do.

When the Cu layer is polished by a CMP process, it is necessary to selectively remove the Cu layer from the semiconductor substrate while leaving only the Cu layer formed in the wiring groove. That is, in the places other than the wiring grooves, the Cu layer is
Removal is required until the oxide film (SiO ₂ ) is exposed. In this case, if the Cu layer in the trench for wiring is polished together with the oxide film (SiO ₂ ) due to excessive polishing, the circuit resistance increases, and the entire semiconductor substrate must be discarded. Damage. On the contrary, polishing is insufficient,
If the Cu layer remains on the oxide film, circuit isolation will not be successful and short circuits will occur, which will require repolishing and increase manufacturing costs. This situation is not limited to the Cu layer.
Another conductive film such as an L layer is formed, and this conductive film is formed by CMP.
The same applies to polishing in a process.

Therefore, an end point detection method using an eddy current sensor has been proposed to detect the end point of the CMP process. FIG. 7 is a diagram showing a main part of a conventional polishing apparatus. The polishing apparatus has a polishing cloth 4 on the upper surface.
2 is provided with a rotating turntable 41 on which a semiconductor wafer 43 as a semiconductor substrate is rotatably and pressably held, and a polishing liquid supply nozzle 48 for supplying a polishing liquid Q to the polishing pad 42. . The top ring 45 is connected to a top ring shaft 49. The top ring 45 has an elastic mat 47 made of polyurethane or the like on the lower surface thereof, and holds the semiconductor wafer 43 in contact with the elastic mat. Further, the top ring 45 is provided with a cylindrical retainer ring 46 on the outer peripheral edge so that the semiconductor wafer 43 does not come off from the lower surface of the top ring 45 during polishing.

Here, the retainer ring 46 is fixed to the top ring 45, the lower end surface thereof is formed so as to protrude from the holding surface of the top ring 45, and the semiconductor wafer 43 is held in the holding surface. Polishing cloth 42 during polishing
It does not fly out of the top ring due to the frictional force with it. An eddy current sensor 50 is embedded in the top ring 45, and the eddy current sensor 5
0 is connected to an external controller (not shown) through the inside of the top ring shaft 49 via the wiring 51.

The semiconductor wafer 43 is held under the elastic mat 47 on the lower surface of the top ring 45, and the turntable 4
A semiconductor wafer 43 on the polishing cloth 42 on the top ring 4
5, and the turntable 41 and the top ring 45 are rotated so that the polishing pad 42 and the semiconductor wafer 43 are moved relative to each other for polishing. At this time, the polishing liquid Q is supplied from the polishing liquid supply nozzle 48 onto the polishing pad 42. When polishing Cu (copper), for example, when polishing abrasives composed of fine particles such as alumina and silica in an oxidizing agent, a polishing liquid is used, and while the Cu surface is oxidized by a chemical reaction, mechanical polishing by the abrasives is performed. The semiconductor wafer is polished by a combined action with the action.

During the above-mentioned polishing, the eddy current sensor 50
Formed on the surface to be polished of the semiconductor wafer 43 by the
The change in the thickness of the conductive film such as a layer is continuously detected. Then, the signal of the eddy current sensor 50 is monitored, and the frequency at which the conductive film on the oxide film (SiO ₂ ) is removed, leaving only the conductor such as the Cu layer formed in the wiring groove. The change detects the end point of the CMP process.

[0011]

However, in the method using the eddy current sensor shown in FIG. 7, since the eddy current sensor is provided on the top ring side, a conductive layer such as a Cu layer formed on a semiconductor wafer is not provided. There is a disadvantage that the thickness of the film can be measured only directly below the eddy current sensor. In this case, if the number of sensors embedded on the top ring side is increased,
Although the number of measurement points of the film thickness increases, the problem is still that only intermittent measurement values at a plurality of points (or many points) apart from each other are obtained, and measurement values as a continuous profile cannot be obtained. There was a point. Further, as the number of sensors increases, there is a problem that the cost of the apparatus increases and the signal processing becomes complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and a sensor such as an eddy current sensor is arranged on a turntable side provided with a polishing cloth or a fixed abrasive plate, so that a surface to be polished on a semiconductor substrate is provided. Cu layer or Al formed on
An object of the present invention is to provide a polishing apparatus capable of detecting the thickness of a conductive film such as a layer as a continuous measurement value in real time.

[0013]

In order to achieve the above object, the present invention comprises a top ring for holding a substrate and a turntable having a polished surface, wherein the surface on which a semiconductor device is formed on the substrate is polished. In a polishing apparatus for polishing by sliding contact with a surface, at least one sensor capable of measuring a thickness of a conductive film formed on a surface to be polished on the substrate is provided below a polishing surface of the turntable. It is a feature. The polishing surface comprises a polishing cloth or a fixed abrasive plate. When the polishing surface is made of polishing cloth,
The sensor is installed in the turntable. If the polished surface comprises a fixed abrasive plate, the sensor is located within the fixed abrasive plate.

According to the present invention, the conductive film is polished by bringing the substrate into sliding contact with the polishing surface. During this polishing, the eddy current sensor passes immediately below the surface to be polished of the semiconductor substrate every time the turntable makes one rotation. In this case, since the eddy current sensor is installed on the track passing through the center of the semiconductor substrate, it is possible to continuously detect the film thickness on the arc-shaped track of the polished surface of the semiconductor substrate as the sensor moves. is there.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a polishing apparatus according to the present invention will be described below with reference to FIGS.
FIG. 1 is a longitudinal sectional view showing the entire configuration of the polishing apparatus of the present invention. As shown in FIG. 1, the polishing apparatus includes a turntable 1 and a top ring 3 that presses the turntable 1 while holding the semiconductor wafer 2. The turntable 1 is connected to a motor 7 and is rotatable around its axis as indicated by an arrow. On the upper surface of the turntable 1, a polishing cloth 4
Is affixed.

The top ring 3 is connected to a motor (not shown) and to a lifting cylinder (not shown). As a result, the top ring 3 can be moved up and down as shown by the arrow and rotatable around its axis, so that the semiconductor wafer 2 can be pressed against the polishing cloth 4 with an arbitrary pressure. ing. The top ring 3 is connected to a top ring shaft 8, and the top ring 3 has an elastic mat 9 made of polyurethane or the like on a lower surface thereof. A guide ring 6 for preventing the semiconductor wafer 2 from coming off is provided on a lower outer peripheral portion of the top ring 3. A polishing liquid nozzle 5 is provided above the turntable 1, and the polishing cloth 4 attached to the turntable 1 by the polishing liquid nozzle 5 is provided.
The polishing liquid Q is supplied thereon.

As shown in FIG. 1, an eddy current sensor 10 is embedded in the turntable 1. The wiring 14 of the eddy current sensor 10 passes through the turntable 1 and the turntable support shaft 1a, and
It is connected to a controller 12 via a rotary connector (or slip ring) 11 provided at the shaft end of a. The controller 12 is a display device (display) 1
3 is connected.

FIG. 2 is a plan view of the polishing apparatus shown in FIG. As shown, the eddy current sensor 10 is
It is installed at a position passing through the center Cw of the semiconductor wafer 2 being polished held by the top ring 3. Reference symbol _CT is the center of rotation of the turntable 1. Eddy current sensor 1
0 indicates that the film thickness of the conductive film such as the Cu layer of the semiconductor wafer 2 can be continuously detected on the passage locus while passing below the semiconductor wafer 2.

FIG. 3 is an enlarged sectional view of a main part showing an embedded state of the eddy current sensor 10, FIG. 3 (a) shows a case where an abrasive cloth is stuck on a turntable, and FIG. This shows a case where a fixed abrasive plate is set on a table. As shown in FIG.
When the polishing cloth 4 is stuck on the eddy current sensor 10
Is embedded in the turntable 1. As shown in FIG. 3B, the fixed abrasive plate 15 is placed on the turntable 1.
Is installed, the eddy current sensor 10 is embedded in the fixed abrasive plate 15.

3A and 3B, the polishing surface of the upper surface of the polishing pad 4 or the polishing surface of the upper surface of the fixed abrasive plate 15, that is, the surface to be polished of the semiconductor wafer. The distance L to the upper surface of the eddy current sensor 10 is 1.
It may be 3 mm or more. FIGS. 3A and 3B show a semiconductor wafer 2 in which a conductive film 2b made of a Cu layer or an Al layer is formed on an oxide film (SiO ₂ ) 2a.

As the polishing cloth, for example, a nonwoven fabric such as Politex manufactured by Rodale or IC100
A foamed polyurethane such as 0 is used. The fixed abrasive plate 15 is formed by solidifying fine abrasive particles (for example, CeO ₂ ) having a particle size of several μm or less using a resin as a binder and forming the particles into a disk shape.

In the polishing apparatus having the above structure, the semiconductor wafer 2 is held on the lower surface of the top ring 3, and the semiconductor wafer 2 is pressed against the polishing cloth 4 on the upper surface of the rotating turntable 1 by a lifting cylinder. On the other hand, the polishing slurry Q is held by the polishing cloth 4 by flowing the polishing slurry Q from the polishing slurry nozzle 5, and the polishing polishing liquid is held between the polishing surface (lower surface) of the semiconductor wafer 2 and the polishing cloth 4. Polishing is performed with the liquid Q present. During this polishing, the eddy current sensor 10 passes immediately below the surface to be polished of the semiconductor wafer 2 every time the turntable 1 makes one rotation. In this case, since the eddy current sensor 10 is installed on the track passing through the center Cw of the semiconductor wafer 2, the film thickness is continuously formed on the arc-shaped track of the surface to be polished of the semiconductor wafer 2 with the movement of the sensor. Detection is possible. In addition, in order to shorten the detection time interval,
As shown by the imaginary line in FIG. 2, the eddy current sensor 10 may be added, and two or more sensors may be provided on the table.

Next, using an eddy current sensor, a Cu layer
The principle of detecting the thickness of the conductive film on the semiconductor wafer composed of one layer will be briefly described. The system principle of the eddy current type process monitor is that high-frequency current flows through the sensor coil,
An eddy current is generated in the conductive film (metal film) of the wafer,
The eddy current changes depending on the film thickness, and the end point is detected by monitoring the combined impedance with the sensor circuit. That is, when a high-frequency current flows through the sensor coil, an eddy current is generated in the conductive film (metal film). Then, the impedance in the circuit is monitored. The impedance in the circuit is such that L and C of the sensor unit and R of the conductive film are connected in parallel, and Z changes when R in the following equation (1) changes. At this time, the resonance frequency also changes, and the end point of the CMP process can be determined by monitoring the degree of the change.

(Equation 1) Here, Z: combined impedance, j: square root of −1 (imaginary number), L: inductance, f: resonance frequency, C:
Capacitance of capacitor, R: resistance of conductive film (metal film), ω = 2πf.

FIG. 4 is a graph showing the result of processing the detection signal of the eddy current sensor 10 obtained during polishing of the semiconductor wafer by the controller 12 based on the above-described principle.
In FIG. 4, the horizontal axis represents the polishing time, and the vertical axis represents the resonance frequency (Hz). FIG. 4A shows a change in resonance frequency while the eddy current sensor 10 passes a plurality of times immediately below the semiconductor wafer 2 during polishing, and FIG. 4B is an enlarged view of a portion A in FIG. FIG. FIG. 4 (a) and FIG.
(B) shows the case where the conductive film formed on the semiconductor wafer is Cu (copper).

As shown in FIG. 4 (a), as the polishing progresses, the signal of the eddy current sensor
The value treated in 2 gradually decreases. That is, as the thickness of the conductive film decreases, the resonance frequency which is a value obtained by processing the signal of the eddy current sensor 10 by the controller 12 decreases. In FIG. 4A, the initial 6800 (H
It gradually decreases from z). Therefore, if the value of the resonance frequency when the conductive film is removed except for the wiring portion is checked in advance, the end point of the CMP process can be detected by monitoring the value of the resonance frequency. In FIG. 4A, the value of the resonance frequency when the conductive film is removed except for the wiring portion is 6620 (Hz). If a certain frequency before reaching the polishing end point is set as a threshold, the fixed abrasive plate 15 having a high polishing rate (polishing rate) (see FIG. 3B) is used until the threshold is reached. After the polishing is performed, the polishing is performed using the polishing pad 4 (see FIG. 3A) having a polishing rate lower than that of the fixed abrasive plate 15 after reaching the threshold, and when the polishing end point is reached, the CMP process may be terminated.

In the eddy current sensor, the measurement sensitivity of the conductive film thickness varies depending on the frequency of the high-frequency current supplied to the sensor coil. For example, when a high-frequency current having a frequency of 20 MHz is supplied to the sensor coil, the conductive film thickness is 0 to 10
While it can be measured over a wide area of Å
When a high-frequency current having a frequency of 160 MHz is supplied to the sensor coil, the conductive film becomes a sensor sensitive to a narrow range of 0 to 1000 °. As described above, by selecting the frequency of the high-frequency current supplied to the eddy current sensor depending on the polishing process (the film thickness or film type to be measured), or by combining a plurality of eddy current sensors, the conductive film thickness can be accurately determined. Measurement can be performed, and the efficiency of the process can be improved. Further, the eddy current sensor may be changed depending on the polishing process.

As shown in FIG. 4B, when the eddy current sensor 10 passes just below the semiconductor wafer 2, a change in the resonance frequency in the surface to be polished can be detected. That is, the change in frequency corresponds to the change in film thickness, and the eddy current sensor 10 is installed at a position passing through the center Cw of the semiconductor wafer 2 being polished. In addition, it is possible to detect the polishing uniformity of the semiconductor wafer in the diameter direction. By inputting the detected in-plane uniformity of the surface to be polished to the control unit of the polishing apparatus, it is possible to change the polishing conditions such as changing the pressing force of the top ring and the distribution of the pressure applied to the upper surface of the semiconductor wafer. As a result, the in-plane uniformity of the polished surface can be improved.

FIG. 5 is a graph showing a change in resonance frequency obtained by processing a signal of an eddy current sensor by a controller when a plurality of semiconductor wafers are polished by one polishing cloth. In FIG. 5, the horizontal axis represents the polishing time, and the vertical axis represents the resonance frequency (Hz). The polishing cloth consumes 0.7 mm from the state in which the first semiconductor wafer is polished due to a plurality of dressings and a plurality of polishing. As shown in FIG. 5, the frequency obtained by processing the signal of the eddy current sensor at the start of polishing for each polishing increases when the polishing cloth is repeatedly used and consumed as compared to when the polishing cloth is used. are doing. That is, from 6800 (Hz) at the start of use of the polishing cloth to 690
It has risen to 0 (Hz). Therefore, by monitoring the value of the resonance frequency at the start of each polishing, the degree of consumption of the polishing cloth can be determined, and therefore, the time for replacing the polishing cloth can be accurately known.

FIG. 6 is a view showing another embodiment of the polishing apparatus of the present invention. FIG. 6 (a) is a plan view of a turntable of the polishing apparatus, and FIG. 6 (b) is a sectional view of the polishing apparatus. It is. As shown in FIGS. 6A and 6B, an optical sensor 30 is provided adjacent to the eddy current sensor 10 in the polishing apparatus of the present embodiment. The optical sensor 30 includes a light projecting element and a light receiving element, and is configured to irradiate light to the surface to be polished of the semiconductor wafer from the light projecting element, and to receive light reflected from the surface to be polished by the light receiving element. I have. In this case, the light emitted from the light emitting element is a laser light or an LED. When the conductive film such as a Cu layer or an Al layer becomes a thin film having a predetermined thickness, a part of light emitted from the light emitting element to the surface to be polished passes through the conductive film, There are two types of reflected light: reflected light reflected from the oxide film below the conductive film and reflected light reflected from the surface of the conductive film. The two types of reflected light are received by the light receiving element, and the signal from the light receiving element is processed by the controller 32, whereby the thickness of the conductive film remaining on the oxide film can be detected more accurately than by the eddy current sensor.

As described above, by mounting the two types of film thickness measuring sensors on the polishing apparatus, the signal of the eddy current sensor 10 is processed until the conductive film becomes a thin film having a predetermined thickness. The thickness of the thin film is monitored by processing the signal of the optical sensor 30 when the thickness of the thin film becomes a predetermined thickness and the optical sensor 30 can detect the thickness. As a result, it is possible to accurately detect that the conductive film has been removed except for the wiring portion using the optical sensor 30 having high measurement sensitivity for the thin film.
The end point of the P process can be determined. Of course, the eddy current sensor 10 and the optical sensor 30 can be used together until the end point of the CMP process. That is, the eddy current sensor 10 and the optical sensor 3 remove the conductive film except for the wiring portion.
0 can be processed and monitored to detect and determine the end point of the CMP process. In the present embodiment, Cu and Al have been described as the conductive films, but other metals such as Cr, W, and Ti may be used.

[0031]

As described above, according to the present invention, by arranging a sensor such as an eddy current sensor on the side of a turntable provided with a polishing cloth or a fixed abrasive plate, a surface to be polished on a semiconductor substrate is provided. The thickness of the formed conductive film such as the Cu layer or the Al layer can be detected as a continuous measurement value in real time.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing the overall configuration of a polishing apparatus according to the present invention.

FIG. 2 is a plan view of the polishing apparatus of the present invention.

FIG. 3 is an enlarged sectional view of a main part showing an embedded state of an eddy current sensor. FIG. 3 (a) shows a case where an abrasive cloth is stuck on a turntable, and FIG. The case where a fixed abrasive plate is installed is shown.

FIG. 4 is a graph showing a result of processing a detection signal of an eddy current sensor obtained during polishing of a semiconductor wafer by a controller, and FIG. 4 (a) shows that a plurality of eddy current sensors are directly under the semiconductor wafer during polishing. FIG. 4 (b) is an enlarged view of a portion A in FIG. 4 (a).

FIG. 5 is a graph showing a change in frequency obtained by processing a signal of an eddy current sensor by a controller when a plurality of semiconductor wafers are polished by one polishing cloth.

6 is a view showing another embodiment of the polishing apparatus of the present invention, FIG. 6 (a) is a plan view of a turntable of the polishing apparatus, and FIG. 6 (b) is a cross-sectional view of the polishing apparatus. .

FIG. 7 is a diagram showing a main part of a conventional polishing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Turntable 1a Turntable support shaft 2 Semiconductor wafer 3 Top ring 4 Polishing cloth 5 Polishing abrasive nozzle 6 Guide ring 7 Motor 8 Top ring shaft 9 Elastic mat 10 Eddy current sensor 11 Rotary connector (or slip ring) 12 Controller 13 Display Device (display) 14 Wiring 15 Fixed abrasive plate 30 Optical sensor 32 Controller 41 Turntable 42 Polishing cloth 43 Semiconductor wafer 45 Top ring 46 Retainer ring 47 Elastic mat 48 Abrasive liquid supply nozzle 49 Top ring shaft 50 Eddy current sensor 51 Wiring

Continued on the front page (72) Inventor Kazuo Shimizu 11-1 Haneda Asahimachi, Ota-ku, Tokyo Inside Ebara Corporation (72) Inventor Hiroyuki Osawa 11-1 Haneda Asahi-cho, Ota-ku, Tokyo Inside Ebara Corporation F term (reference) 3C034 AA08 AA13 BB92 BB93 CA22 CB03 CB14 3C058 AA07 AB01 AB04 AB06 AC02 AC04 BA01 BB01 BB09 BC02 CB05 DA17

Claims (4)

[Claims] 1. A polishing apparatus, comprising: a top ring for holding a substrate; and a turntable having a polished surface, wherein the polishing device polishes the surface by forming a semiconductor device on the substrate in contact with the polished surface. A polishing apparatus, wherein at least one sensor capable of measuring the thickness of a conductive film formed on the surface to be polished on the substrate is provided below the polished surface. 2. The polishing apparatus according to claim 1, wherein said sensor is an eddy current sensor. 3. The polishing apparatus according to claim 1, wherein the sensor is installed in the turntable. 4. The polishing apparatus according to claim 2, wherein at least one optical sensor is provided in addition to said eddy current sensor.