JP2001088008A - Polishing method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable good polishing and extension of service life of polishing pad in dressing the pad at the polishing work. SOLUTION: Setting of termination time of dressing a polishing pad by a polishing pad dresser 15a is carried out based on measurement of a current value of a motor 7a driving a surface plate 9a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing technique for a semiconductor wafer or the like, and more particularly to a polishing technique in which a dressing technique for a polishing pad used in polishing is improved.

[0002]

2. Description of the Related Art As LSIs become more highly integrated, the depth of focus of exposure equipment used in LSI manufacturing processes becomes smaller year by year. Accordingly, the exposure margin has been reduced. Therefore, it is necessary to reduce the flatness of the interlayer film formed on silicon, which is a semiconductor wafer. Since there is a limit in a method combining a coated green film and reactive etching, CMP (Chemical) is used as a planarization method.
Mechanical Polishing) has been introduced.

FIG. 8 is a schematic perspective view showing the outline of the Kenmaro method by CMP. Polishing pad 5 made of polyurethane foam
1 is rotated on a surface plate 52 fixed to the upper surface, and the polishing pad 51 is rotated while the semiconductor wafer 54 is fixed on a wafer carrier 53 provided facing the polishing pad 51.
The semiconductor wafer 54 is pressed against the polishing pad 51 with a predetermined load and polished while a polishing slurry (polishing liquid) 55 in which silica abrasive grains are turbid is dropped on the surface of the semiconductor wafer 54. During or before polishing, the surface of the polishing pad 51 is shaved using a polishing pad dresser (grinding stone on which diamond is electrodeposited) 56 and fluffed to dress the polishing pad 51.

The dressing of the polishing pad 51 is performed for the purpose of stabilizing the polishing efficiency, and is always performed for maintaining the surface of the polishing pad 51 in a good and fuzzy state suitable for polishing. . In the polishing process, the polishing efficiency fluctuates due to poor dressing of the polishing pad 51 or the like. As a result, the thickness of the interlayer film varies on the surface of the semiconductor wafer 54, and the film thickness varies on the surface of the semiconductor wafer 54. These cause over-etching and contact failure in a step after the semiconductor manufacturing process.

[0005] Regarding the dressing time, the amount of shaving the polishing pad 51 is different depending on each polishing slurry 55 and the like. Therefore, dressing is performed experimentally before processing, and the dressing time is defined based on the data. I have.

[0006]

However, in the above-mentioned dressing method, the dressing state is not constantly monitored during the dressing, and data fixed in advance using data obtained by experiments is used. When a difference between the data and the actual polishing state occurs, the predetermined polishing cannot be performed on the semiconductor wafer, the consumption of the pad cannot be grasped, and the life of the pad cannot be extended.

The present invention has been made on the basis of these circumstances. In dressing a polishing pad in polishing a semiconductor wafer or the like, the dressing time is optimized, good polishing is performed, and the life of the polishing pad is improved. It is an object of the present invention to provide a polishing method and apparatus capable of extending the polishing time.

[0008]

According to the first aspect of the present invention, a wafer held by a wafer carrier is brought into contact with a polishing pad attached to a surface plate at a predetermined pressure for polishing, and the polishing is performed. The polishing method, wherein the pad is dressed by pressing with a polishing pad dresser, wherein the dressing with the polishing pad dresser is terminated based on a measurement result of a current value of a motor that drives the surface plate. is there.

According to the second aspect of the present invention,
The dressing end time of the polishing pad dresser is set to be longer than a time when a current value of a motor for driving the surface plate becomes a constant value in a saturated state.

According to the third aspect of the present invention,
In the polishing method, the dressing is performed by the polishing pad dresser, and the wafer carrier is separated from the polishing pad.

According to the means of the invention of claim 4,
In a polishing apparatus having a surface plate on which a polishing pad for polishing a wafer held by a wafer carrier is mounted, and a polishing pad dresser for dressing the polishing pad, a motor for driving the surface plate includes a motor And a motor current detection circuit for detecting a current flowing through the polishing apparatus.

Further, according to the means of the invention of claim 5,
The polishing apparatus is characterized in that the motor is controlled by a controller based on a detection result of a current value by the motor current detection circuit.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1A and 1B are schematic diagrams of a CMP apparatus used in accordance with the method of the present invention.
1 is a front view, and FIG. 1B is a plan view.

[0015] CMP apparatus, a wafer carrier 2 for holding the semiconductor wafer 1 is mounted to rotate continuously by a driving motor 3 about the axis A ₁ in the direction indicated by the arrow 4. The wafer carrier 2 is arranged such that a force indicated by an arrow 5 is applied to the semiconductor wafer 1. CMP apparatus arrows, also by the drive motor 7 about an axis _{A 2} 8
The surface plate 9 is attached so as to rotate continuously in the direction shown by. The surface of the surface plate 9 is inflated,
A polishing pad 10 made of a material such as polyurethane is attached. A polishing slurry containing a polishing liquid such as silica or alumina polishing particles suspended in a basic or acidic solution is supplied to the surface of the polishing pad 10 from a reservoir 11 via a conduit 12.

The polishing pad dresser 15 has a holder 17 to which a polishing and grinding layer 16 such as a dresser pad (grindstone on which diamond is electrodeposited) impregnated with diamond particles is attached. The holder 17 rotates continuously in the direction indicated by the arrow 19 by a drive motor 18 about the axis A _3, the holder 17 is further as a load to force abrasive grinding layer 16 shown by an arrow 20 It is set so.

FIG. 2 is a block diagram relating to the detection of the end of the polishing pad dresser. The surface plate 9a composed of a turntable having a polishing pad 10a attached to the surface,
It is rotationally driven at about 100 rpm by the motor 7a.
The motor 7a is driven by a driver 31 receiving a control signal from the controller 30. A motor current detection circuit 32 is connected to the motor 7a, and detects a current value of the motor 7a. The output side of the motor current detection circuit 32 is connected to the controller 30. That is, the controller 3
In the case of 0, the output signal from the motor current detection circuit 32 is received, the operation is calculated based on the output signal, and the control signal is sent to the driver 31 to control the motor 7a.

A wafer carrier 2a provided at a position facing the polishing pad 10a has an outer diameter of about 200 mm, and is suction-fixed to a semiconductor wafer 1a as a workpiece and is rotationally driven at about 100 rpm by a motor A3a. A3a is a driver A that has received a signal from the controller 30.
Drive control is performed by the control unit 33. Further, in a state where the wafer carrier 2a and the motor A3a are integrated, the wafer carrier 2 is moved up and down by the wafer carrier up-down mechanism 34 so as to make contact with and separate from the polishing pad 10a on the surface plate 9a. At the time of polishing, the semiconductor wafer 1a held by the wafer carrier 2a is placed on the polishing pad 10a at a predetermined polishing pressure, for example, 1 mm.
Polish for about 20 seconds. When the polishing is completed, the wafer carrier 2a moves upward by the wafer carrier vertical mechanism 34 and separates from the polishing pad 10a. The wafer carrier vertical mechanism 34 is a linear moving mechanism and is a ball screw (not shown).
Is guided by a linear guide (not shown) and linearly moves.

The wafer carrier up-down mechanism 34 is driven up and down by a driver B35 which receives a signal from the controller 30. In other words, the rotation of the wafer carrier 2a and the contact with the polishing pad 10a operate under the control of the controller 30 at a predetermined timing.

A polishing pad dresser 15a having an outer diameter of about φ200 mm provided at a position facing the polishing pad 10a has a polishing and grinding layer 16a formed on the lower surface side, and is rotationally driven at about 20 rpm by a motor B18a. Is a driver C that has received a signal from the controller 30
The drive is controlled by 36. In a state in which the polishing pad dresser 15a and the motor B18a are integrated, the dresser up / down mechanism 37 moves up and down to perform a contact / separation operation with respect to the polishing pad 10a on the surface plate 9a. When dressing the polishing pad 10a with the polishing and grinding layer 16a,
Polish polishing layer 16a is applied to polishing pad 10a for about 20 seconds.
Comes in contact with each other to bring the polishing and grinding layer 16a to about 10 to 100 rpm.
And rotate the polishing pad 10a to about 0.07031-
Dressing is performed by applying a pressure of 0.7031 kgf / cm ² (about 1 to 10 psi) to fluff the surface of the polishing pad 10a.

During dressing of the polishing pad 10a, the wafer carrier 2a is separated from the polishing pad 10a, and the semiconductor wafer 1a does not contact the polishing pad 10a. During dressing of the polishing pad 10a,
The polishing pad 10a rotates at about 10 to 100 rpm.

When the dressing is completed, the dresser vertical mechanism 37 moves the polishing pad dresser 15a upward and separates from the polishing pad 10a. The dresser up / down mechanism 37 is a linear movement mechanism, and linearly moves with movement by a ball screw (not shown) guided by a linear guide (not shown). The dresser up / down mechanism 37 is driven in the up / down direction by a driver D38 receiving a signal from the controller 30. That is, the rotation of the polishing pad dresser 15a and the polishing pad 10
The contact with “a” operates under the control of the controller 30 at a predetermined timing.

During the dressing of the polishing pad, the polishing of the semiconductor wafer and the dressing can be performed simultaneously in parallel without separating the wafer carrier from the polishing pad. The polishing pad slides with the semiconductor wafer via a medium called an abrasive (not shown). The abrasive has a particle size of about 30-50n
m, and the silica abrasive grains interposed in the sliding portion of the semiconductor wafer and the polishing pad are involved in the polishing, and the surface of the polishing pad is brought into contact with the semiconductor wafer. Deformed and smoothed. In addition, it is damaged by the product of polishing and the adhesion of slurry.

If such damage occurs, the polishing efficiency is reduced. Therefore, the surface of the polishing pad is scraped with a polishing pad dresser using a grindstone on which diamond abrasive grains are electrodeposited, and the damage is recovered by fluffing.

It is considered that the polishing pad surface is smoothed and the polishing efficiency is reduced because clogging due to polishing damage is larger than the effect of dressing, and the polishing amount is reduced. Therefore, the operation of the polishing pad dresser needs to be set so that the effect of dressing is greater than the damage of polishing.

FIG. 3A shows a dressing pattern of the polishing pad dresser, and FIG. 3B shows a corresponding grinding efficiency (μm / min). FIG.
(C) shows the uniformity of the polished surface of the semiconductor wafer by the corresponding polishing. These are all 19
Fall 1998: Proceedings of the Japan Society of Applied Physics, page 751, paper number 16p-ZL-19, "High Polishing Rate Insulating Film C"
Optimization of dress sequence of MP "is disclosed in FIG.

That is, as shown in FIG. 3A, the dressing patterns are A (100%), B (50%), C
(50% division), D (25%) and E (0%), the polishing efficiency is as follows, when 25 semiconductor wafers are processed as shown in FIG. 3B, and the dressing pattern is E. , The dressing patterns are A to D
Is almost the same.

On the other hand, regarding the uniformity of the polished surface by polishing, as shown in FIG. 3C, a considerable difference occurs depending on the dressing pattern. A is best, C is next, and the rest are less preferred.

The relationship between the dressing time (number of processed sheets) and the polishing efficiency (μm / min) is as shown in FIG. It transits. That is, when a predetermined number of pieces of polishing are performed, the surface of the polishing pad becomes smooth and constant, so that the polishing efficiency also becomes constant.

FIG. 5 shows the surface roughness Ra of the polishing pad.
3 is a graph showing (μm) and polishing efficiency (μm / min). The two have a substantially linear relationship. In addition,
FIG. 5 is disclosed on page 10 of a paper published in “Journal of the Japan Society of Abrasive Processing” issued in November 1998 as “FIG. 3” of “Planarization of Interlayer Film by CMP”.

Therefore, based on the results shown in FIGS. 4 and 5, the relationship between the dressing time and the surface roughness of the polishing pad is as shown in FIG. In other words, the surface roughness of the polishing pad does not change after the dressing time has passed the predetermined value, and remains at a substantially constant value.

That is, after the lapse of a predetermined time, the surface roughness of the polishing pad becomes substantially constant (this is a state where the surface of the polishing pad is crushed, which is not preferable for polishing). The load on the motor that rotates the attached platen is also constant, and the current flowing through the motor is changed from the initial state _I0 by a predetermined time t, as shown in FIG.
After _one course does not change becomes constant value I _s it becomes saturated.

From these facts, it is always necessary to check the surface of the polishing pad.
To polish in a fluffy state before the surface is smoothed,
For the dressing end time T, the predetermined time shown in FIG.
Interval t ₁Is related to t₁<Dressing within T
The only thing to do is to end it. That is, the surface plate
The motor current value is always detected by the motor current detection circuit,
Predetermined time t₁Detection, and drain for a longer time.
Perform good polishing by terminating the washing
be able to. Also, polishing can be performed without deteriorating polishing performance.
It is also possible to extend the life of the polishing pad.

In the above-described embodiment, the motor current detecting circuit is connected to the motor for driving the surface plate to detect the end point of the dressing. However, as another method, the motor current detecting circuit drives the polishing pad dresser. It may be connected to a motor and the end point of the dressing may be detected based on the detection result.

[0035]

According to the present invention, the load on the polishing pad is reduced.
Since it is detected by the value of the current flowing to the motor driving the turntable to which it is attached, and the dressing end time of the polishing pad is set thereby, the polishing can always be performed with the polishing pad in a good condition.

In addition, the life of the polishing pad can be extended without lowering the polishing performance.

[Brief description of the drawings]

1A is a schematic front view of a CMP apparatus, and FIG. 1B is a schematic plan view thereof.

FIG. 2 is a block diagram relating to detection of the end of the polishing pad dresser of the present invention.

FIG. 3 (a) is a dressing pattern diagram of a polishing pad dresser, and FIG. 3 (b) is a corresponding grinding efficiency (μm / m).
(c) is a graph showing the uniformity of the polished surface corresponding to the graph.

FIG. 4 is a graph showing a relationship between dressing time and polishing efficiency.

FIG. 5 is a graph showing the relationship between the polishing pad surface roughness and polishing efficiency.

FIG. 6 is a graph showing a relationship between a dressing time and a surface roughness of a polishing pad.

FIG. 7 is a graph illustrating a dressing end time.

FIG. 8 is an explanatory diagram of a CMP method.

[Explanation of symbols]

1, 1a: semiconductor wafer, 2, 2a: wafer carrier,
7, 7a: motor, 9, 9a: platen, 10, 10a: polishing pad, 15, 15a: polishing pad dresser, 30 ...
Controller, 32 ... Motor current detection circuit

Claims (5)

[Claims] 1. A polishing method in which a wafer held by a wafer carrier is polished by bringing a wafer into contact with a polishing pad attached to a surface plate at a predetermined pressure, and the polishing pad is dressed by applying pressure by a polishing pad dresser. The polishing method according to claim 1, wherein the dressing by the polishing pad dresser is terminated based on a measurement result of a current value of a motor for driving the surface plate. 2. The dressing end time of the polishing pad dresser is set to be longer than a time when a current value of a motor for driving the surface plate becomes a constant value in a saturated state. The polishing method according to claim 1. 3. The polishing method according to claim 1, wherein, when dressing by said polishing pad dresser, said wafer carrier is separated from said polishing pad. 4. A polishing apparatus, comprising: a platen on which a polishing pad for polishing a wafer held by a wafer carrier is mounted; and a polishing pad dresser for dressing the polishing pad, a motor for driving the platen. , A motor current detection circuit for detecting a current flowing through the motor is connected to the polishing apparatus. 5. The polishing apparatus according to claim 4, wherein said motor is controlled by a controller based on a detection result of a current value by said motor current detection circuit.