JP2000260840A - Method and device for measuring semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid a leveling error in a scan type stepper by, at measuring flatness for examining an exposure focal point plane with a semiconductor substrate tilted, measuring the flatness of the semiconductor substrate for each measurement unit region whose area is that of an exposure unit region or less. SOLUTION: An exposure unit region has a horizontal length X mm and vertical length Y mm, while a measurement unit region is a region S21 having a horizontal length L1 mm which is a scanning direction for scan exposure and a vertical length L2 mm. LTV-measurement is performed for each measurement unit region S21 to determine a leveling reference plane for each measurement unit region S21, and the measurement unit region is sequentially shifted from S21a to S21b, and then to S21c for measurement likewise, determining a leveling reference plane. Related to shifting of measurement unit region, the measurement unit regions S21a and S21b, for example, as well as S21b and S21c, are performed to overlap by at least 1/2 of horizontal length. Thus, a high-precision leveling control is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for measuring a semiconductor substrate, and more particularly to a method and an apparatus for measuring the flatness of a semiconductor substrate when scanning and exposing a circuit pattern on the semiconductor substrate.

[0002]

2. Description of the Related Art In a semiconductor device manufacturing process, a lithography step is a step of projecting a circuit pattern drawn on a reticle onto a semiconductor substrate in a reduced size by an exposure apparatus called a stepper and printing the circuit pattern. The printing of the circuit pattern is performed by one exposure of a chip group or a chip group including a plurality of chips, and the exposure part is sequentially moved to perform exposure of a subsequent chip or a chip group. This operation is repeated to print a circuit pattern on the entire surface of the semiconductor substrate.

By the way, when the exposure in the lithography process is performed, if the thickness of the semiconductor substrate varies, the distance between the lens and the surface of the semiconductor substrate fluctuates. Occurs and the circuit pattern is blurred. The range in which this defocus does not occur is called the depth of focus D. Between the depth of focus D, the resolution R, the aperture ratio NA of the stepper, and the wavelength λ of the light source, R = K1 / NA D = K2 × λ / (NA) ^{There are two} relationships. Here, K1 and K2 are constants. The resolution R depends on the minimum line width that can be drawn, and the minimum line width has been reduced with higher integration of semiconductor devices. Therefore, in order to make the resolution R fine, it is necessary to shorten the wavelength λ of the light source, and as a result, the depth of focus D becomes small. That is, a more accurate flatness is required for the semiconductor substrate.

Therefore, in the range where the circuit pattern is exposed, an operation of inclining the semiconductor substrate with respect to the focal plane so as to minimize the height difference caused by the uneven thickness of the semiconductor substrate, that is, leveling is introduced. A mechanism for reducing the flatness required for a semiconductor substrate is incorporated in a stepper.

FIG. 4 is an explanatory view schematically showing a state in which leveling of a semiconductor substrate is performed in a conventional stepper.

As shown in FIG. 4, conventionally, the flatness of the front surface of the semiconductor substrate 41 is measured in advance, and the exposed surface S41 over the entire surface of the substrate 41 is compared with the substrate 41.
The entire surface of the substrate 41 has been exposed at one time while performing leveling for inclining the substrate 41 at an angle that minimizes the defocus at each part.

On the other hand, since the rate of progress of high integration of semiconductor devices is high, even if the minimum line width that can be drawn is reduced, the chip area is increasing. Therefore, it becomes necessary to draw a region having a larger area with a stepper with a smaller resolution, and it is necessary to use a lens having a larger diameter and less aberration. However, this not only places a heavy burden on the design of the stepper lens system, but also greatly increases the cost of the stepper.

Therefore, when a certain circuit pattern is exposed on a semiconductor substrate, a scan exposure method has been devised in which a pattern on a reticle is exposed while scanning a part of the pattern instead of exposing the pattern at once. By this scanning exposure, a small lens can be used for the stepper, and the substantial flatness of the semiconductor substrate can be improved by reducing the exposure unit area.

However, in the case of scanning exposure, if the exposure is performed while performing the above-described leveling, the semiconductor substrate is tilted so as to conform to the surface shape because the unit area of the exposure is small. The inclination angle of the substrate may increase. That is, even if the thickness unevenness of the semiconductor substrate is almost the same, the leveling angle may be larger than that of a conventional stepper that does not perform scanning.

FIG. 5 is an explanatory diagram schematically showing a state in which a semiconductor substrate is leveled in a scan exposure stepper.

In the conventional scan exposure, the flatness of the whole semiconductor substrate is measured in advance, and FIG.
As shown in the figure, based on the measurement results,
The leveling is performed by tilting the semiconductor substrate 51 so as to minimize the defocus with respect to the exposure surface S51A.
However, as shown in FIG. 5B, the exposure target area moves for scan exposure, and the flatness of the entire semiconductor substrate is measured in advance in a portion where the surface of the semiconductor substrate 51 has a steep gradient, as described above. Based on the result, the exposure surface S51
If an attempt is made to perform leveling in order to minimize the defocus with respect to B, the inclination angle of the semiconductor substrate 51 becomes extremely large.

However, the leveling angle of the stepper is
It is not unlimited to ensure a predetermined level of throughput, and has a limit of, for example, 40 μrad.
Therefore, leveling cannot cope with a change in surface shape, and a leveling error occurs in which the focal plane cannot be adjusted to the optimum plane of the target unit exposure plane, which may result in pattern blur due to defocus. That is,
It is necessary to consider not only the thickness unevenness but also the gradient of the surface shape.

On the other hand, the flatness of the semiconductor substrate is defined as LTV (Local Thickness Variation) representing the absolute value of the thickness unevenness of the semiconductor substrate with respect to the back surface, and S-TIR (Surface Total Indicator) with reference to the front surface.
r), S-FPD (Surface Focal Plane Deviation) is widely used. Corresponding to a stepper with the leveling mechanism described above is S-TIR, which is a reference for a given square or rectangle such that the difference (distance) from one surface to the other with respect to the surface is minimized. A plane is set, and the sum of the height difference of the surface with respect to the reference plane (peak to va
lley). However, since this is a value for a fixed area, it corresponds to a conventional stepper that does not perform scanning, but does not correspond to scanning. That is, they represent the flatness of a fixed area, and do not take into account the case where the area moves like scanning exposure. In addition, in the scan type stepper, as described above, the leveling angle and, therefore, the gradient of the surface of the semiconductor substrate are important. In the method of directly measuring the gradient, the back surface of the semiconductor substrate needs to coincide with an absolute reference plane. However, if minute particles adhere to the back surface of the semiconductor substrate, the portion rises and accurate measurement cannot be performed. . In this case, the problem can be solved by using a semiconductor substrate holding jig of a stepper, but introduction of a new one into the semiconductor substrate manufacturing process causes an increase in inspection cost, and as a result, a semiconductor substrate price rises Leads to.

Further, the surface of the semiconductor substrate is mirror-finished, and is polished on a polishing cloth such as urethane or non-woven fabric using an abrasive represented by colloidal silica. At this time, since a load is applied, the semiconductor substrate is more or less immersed in the polishing cloth, and the outer peripheral portion of the semiconductor substrate is more selectively polished, so-called "sagging" occurs. Due to the sagging, the peripheral portion of the semiconductor substrate has the above-mentioned gradient steep, and the possibility of occurrence of a leveling error increases.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method and an apparatus for measuring the flatness of a semiconductor substrate which can avoid a leveling error in a scan type stepper. is there.

[0016]

According to a method and an apparatus for measuring a semiconductor substrate according to the present invention, when exposing a circuit pattern while sequentially moving an exposure unit area for exposing the circuit pattern on the semiconductor substrate, In a semiconductor substrate measuring method for measuring the flatness of a semiconductor substrate to incline the semiconductor substrate so as to reduce the height difference of the semiconductor substrate surface with respect to the focal plane and to determine an exposure focal plane, an area equal to or less than an area of an exposure unit region It is characterized by measuring the flatness of the semiconductor substrate for each measurement unit region, and according to this configuration, as the period of the irregularities on the surface of the semiconductor substrate becomes smaller,
Since the inclination angle of the leveling is reduced, it is possible to measure the flatness of the surface of the semiconductor substrate without modifying the conventionally used thickness measuring device, which is a parameter based on the back surface of the entire semiconductor substrate. The leveling error occurrence rate can be reduced as compared with the LTV measurement.

In order to accurately define the leveling reference plane, the measurement unit area has a length in a second direction perpendicular to the first direction in which the exposure unit area is moved, and a length in the first direction. The length should be longer than the above.

Further, it is preferable to measure the flatness of the semiconductor substrate while sequentially moving the measurement unit area in the first direction in which the exposure unit area is moved in response to the scan exposure.

In order to perform high-precision leveling control,
The first measurement unit region and the second measurement unit region in which measurement is performed next to the first measurement unit region may have at least half of each area overlapping each other.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a method and an apparatus for measuring a semiconductor substrate according to the present invention will be described below with reference to the drawings.

In the method and apparatus for measuring a semiconductor substrate according to the present invention, the measurement of the flatness of the surface of the semiconductor substrate for leveling is performed for each measurement unit area having an area equal to or less than the area of the exposure unit area.

First, the relationship between the leveling and the period of the irregularities on the semiconductor substrate surface in the method and apparatus for measuring a semiconductor substrate according to the present invention will be described. Here, a one-dimensional case will be described for simplicity.

FIG. 1 is an explanatory diagram schematically showing the relationship between the leveling and the period of irregularities on the surface of a semiconductor substrate in the method and apparatus for measuring a semiconductor substrate according to the present invention.

It is assumed that the period of the unevenness on the surface of the semiconductor substrate is X, the amplitude is A, the length of the exposure unit area is L, and the length of the measurement unit area is equal to the length L of the exposure unit area. The steepest slope of the substrate surface is in the middle between the concave and convex parts,
The gradient is 2Aπ / X. Further, since LTV = 2A, the gradient can also be expressed as LTVπ / X. As shown in FIG. 1A, when the period X of the irregularities on the surface of the semiconductor substrate 11 is sufficiently long with respect to the exposure unit region length L, the reference surface S11 for leveling the surface irregularities is located between the concave portion and the convex portion. Equal to the gradient of the part. As shown in FIG. 1B, as the period X of the irregularities on the surface of the semiconductor substrate 12 becomes shorter, the gradient of the leveling reference surface S12 becomes smaller than the gradient (LTVπ / X) between the concave portion and the convex portion. As shown in FIG. 1C, when the period X of the irregularities on the surface of the semiconductor substrate 13 becomes smaller than the exposure unit region length L, the leveling reference plane S13 becomes horizontal.

As described above, in the method and apparatus for measuring a semiconductor substrate according to the present invention, the measurement of the flatness of the surface of the semiconductor substrate for leveling is performed in a measurement unit area having an area equal to or less than the area of the exposure unit area. The leveling reference plane is determined every time, so that the flatness of the semiconductor substrate surface can be measured without modifying the conventionally used thickness measuring device, and the entire semiconductor substrate can be measured. Compared to the LTV measurement, which is a parameter based on the back side,
The leveling error occurrence rate can be reduced.

In practice, the measurement of the flatness of the surface of the semiconductor substrate for leveling is performed in a two-dimensional measurement unit area.

FIG. 2 is an explanatory view schematically showing the measurement of the flatness of the surface of the semiconductor substrate for leveling in the method and apparatus for measuring a semiconductor substrate according to the present invention.

As shown in FIG. 2A, here, the exposure unit area has a width of X mm and a length of Y mm, and the measurement unit area has a length of L1 mm (L1 = L1 mm) in the scanning direction in the scanning exposure. X), the length in the vertical direction perpendicular to the scanning direction is L2 mm (L2 ≦
A region S21 in FIG. That is, the measurement unit region has an area equal to or less than the exposure unit region area. However, in order to accurately determine the reference plane for leveling, the length in the vertical direction should be longer than the length in the horizontal direction.

An LTV measurement is performed for each measurement unit area S21 to determine a leveling reference plane for each measurement unit area S21. As shown in FIG.
1a, S21b, and S21c are sequentially moved, measurement is performed in the same manner, and a leveling reference plane is determined. The movement of the measurement unit area is performed, for example, so that the measurement unit areas S21a and S21b and the measurement unit areas S21b and S21c overlap at least an area having a length L1 / 2 in the horizontal direction.
Thus, highly accurate leveling control can be performed.

Assuming that there are irregularities on the substrate surface only in the horizontal direction in FIG. 2, the inclination angle θ of leveling is given by θ = LTV
/ L1.

[0031]

Embodiments of the present invention will be described below in detail. A silicon single crystal was pulled up by the Czochralski method, and this single crystal was processed into 100 single-sided mirror-surface semiconductor substrates having a diameter of 200 mm and a target thickness of 725 μm by slicing, lapping, etching, and mirror polishing. Next, the flatness was evaluated by measuring the thickness distribution of the semiconductor substrate using a capacitance type thickness measuring instrument for these semiconductor substrates. The evaluation condition is LT in which an area of 8 mm in width and 8 mm in height is set as a measurement unit area.
The measurement of V and the measurement of S-TIR using an area of 8 mm in width and 24 mm in length as a measurement unit area were performed. Further, in correspondence with the leveling of the scanning exposure, an area of 8 mm in width and 8 mm in height is used as a measurement unit area, and the LTV is moved while moving the measurement unit area by 1 mm in the scanning direction at the time of subsequent exposure.
Was measured.

The S-TIR measurement value of each semiconductor substrate is 0.2 μm or less, and no defocus occurs. On the other hand, with respect to the LTV measurement value, when the measurement unit area of 8 mm in width and 8 mm in height was sequentially measured as in the past, the LTV
There were 10 semiconductor substrates that did not satisfy the condition of ≦ 0.32 μm (this is referred to as Group A). Next, the remaining 9
For 0 sheets, the measurement unit area of 8 mm wide and 8 mm long is
When the measurement was performed while moving by 1 mm in the scanning direction at the time of the subsequent exposure, there were 40 semiconductor substrates that did not satisfy the condition of LTV ≦ 0.32 μm (this is referred to as Group B). LTV ≦
Even if the semiconductor substrate satisfies the condition of 0.32 μm,
When the measurement unit area is moved by 1 mm at a time, a portion having poor flatness may be included in one measurement unit area, so this occurs. Further, the remaining 50 semiconductor substrates are set as a C group.

Next, a line having a width of 0.20 μm is
A circuit pattern drawn at a pitch was exposed on a semiconductor substrate using a scan type stepper. The unit exposure area is horizontal 8
mm, 24 mm long, 32 mm wide, 24 m long
Exposure was performed with the area of m being one shot. After that, the presence or absence of pattern blurring due to defocus was checked with respect to the measured flatness. The pattern blurring occurred where the LTV measurement value was poor. That is, in the semiconductor substrate of the group A, a leveling error has occurred and a pattern blur has occurred. In the semiconductor substrate of the B group, pattern blurring due to defocus due to a leveling error has occurred in a region where the condition of LTV ≦ 0.32 μm was not satisfied in the measurement while moving the measurement unit region by 1 mm in the scanning direction. Was. No leveling error occurred in the semiconductor substrate of Group C, and no pattern blur due to the unevenness of the surface of the semiconductor substrate occurred.

FIG. 3 is a graph showing the relationship between the LTV measurement value and the occurrence rate of circuit pattern blur in the method and apparatus for measuring a semiconductor substrate according to the present invention.

In the above embodiment, the measurement unit area for LTV measurement for leveling is L1 = 8 mm in width and L2 in length.
= Mm, and the maximum inclination angle of the leveling of the scan exposure stepper is 40 μrad. Therefore, if there is unevenness on the substrate surface only in the lateral direction, LTV = θ × L1
Therefore, when the LTV measurement value is θ × L1 = 0.32 μm or less, the circuit pattern blur does not occur. However, when the LTV measurement value exceeds θ × L1 = 0.32 μm, the circuit pattern blur occurrence rate sharply increases. You can see that.

[0036]

According to the method and the apparatus for measuring a semiconductor substrate according to the present invention, when exposing a circuit pattern while sequentially moving an exposure unit area for exposing the circuit pattern on the semiconductor substrate, the semiconductor is positioned with respect to the exposure focal plane. In a method of measuring the flatness of a semiconductor substrate, in which a semiconductor substrate is inclined so that a difference in height of the substrate surface is reduced so as to define an exposure focal plane, a measurement unit having an area equal to or less than an area of an exposure unit region. Since the flatness of the semiconductor substrate was measured for each region, in the lithography process,
It is possible to prevent the occurrence of a leveling error and the occurrence of pattern blur due to defocus due to the influence of the gradient on the back surface of the substrate surface as well as within the flatness in the shot region at the time of exposure. As a result, even in the planarization (CMP) of the interlayer insulating film, uneven polishing due to the ability to follow the polishing cloth is suppressed, and the occurrence of characteristic defects in semiconductor device manufacturing such as uniform film thickness distribution is suppressed, and high yield is achieved. Thus, a highly reliable device can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a relationship between leveling and a period of irregularities on a semiconductor substrate surface in a method and an apparatus for measuring a semiconductor substrate according to the present invention.

FIG. 2 is an explanatory view schematically showing the measurement of the flatness of the surface of the semiconductor substrate for leveling in the method and apparatus for measuring a semiconductor substrate according to the present invention.

FIG. 3 is a graph showing a relationship between an LTV measurement value and a circuit pattern blurring occurrence rate in the method and apparatus for measuring a semiconductor substrate according to the present invention.

FIG. 4 is an explanatory view schematically showing a state in which leveling of a semiconductor substrate is performed in a conventional stepper.

FIG. 5 is an explanatory view schematically showing a state where leveling of a semiconductor substrate is performed in a scan exposure stepper.

[Explanation of symbols]

 11, 12, 13, 21, 41, 51 Semiconductor substrate S11, S12, S13 Reference surface for leveling S21, S21a, S21b, S21c Measurement unit area S41, S51A, S51B Exposure surface

Claims (8)

[Claims] When a circuit pattern is exposed while sequentially moving an exposure unit area for exposing the circuit pattern to the semiconductor substrate, the semiconductor substrate is tilted so that a height difference of the semiconductor substrate surface with respect to an exposure focal plane is reduced. In the semiconductor substrate measuring method for measuring the flatness of the semiconductor substrate to determine the exposure focal plane, the flatness of the semiconductor substrate is measured for each measurement unit region having an area equal to or less than the area of the exposure unit region. A method for measuring a semiconductor substrate, comprising: 2. The measurement unit area has a length in a second direction perpendicular to a first direction in which the exposure unit area is moved, which is equal to or longer than the length in the first direction. The method for measuring a semiconductor substrate according to claim 1, wherein: 3. The flatness of the semiconductor substrate is measured while sequentially moving the measurement unit region in a first direction in which the exposure unit region is moved. The method for measuring a semiconductor substrate according to the above. 4. The first measurement unit region and the second measurement unit region in which measurement is performed next to the first measurement unit region have at least half of their respective areas overlapping each other. 4. The method for measuring a semiconductor substrate according to claim 3, wherein: 5. When exposing a circuit pattern while sequentially moving an exposure unit area for exposing the circuit pattern on the semiconductor substrate, the semiconductor substrate is tilted so that a height difference of the semiconductor substrate surface with respect to an exposure focal plane is reduced. In the semiconductor substrate measuring apparatus for measuring the flatness of the semiconductor substrate to determine the exposure focal plane, the flatness of the semiconductor substrate is measured for each measurement unit area having an area equal to or less than the area of the exposure unit area. An apparatus for measuring a semiconductor substrate, comprising: 6. The measurement unit area has a length in a second direction perpendicular to the first direction in which the exposure unit area is moved, which is equal to or longer than the length in the first direction. The apparatus for measuring a semiconductor substrate according to claim 5, wherein: 7. The semiconductor device according to claim 5, wherein the flatness of the semiconductor substrate is measured while sequentially moving the measurement unit area in a first direction in which the exposure unit area is moved. The apparatus for measuring a semiconductor substrate according to claim 1. 8. The first measurement unit region and the second measurement unit region in which measurement is performed next to the first measurement unit region have at least half of their areas overlapping each other. The apparatus for measuring a semiconductor substrate according to claim 7, wherein: