JP3164758B2 - Exposure apparatus focus management method and exposure apparatus focus management apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus focus management method and a focus management apparatus for an exposure apparatus used in a semiconductor manufacturing process or the like.

[0002]

2. Description of the Related Art Conventionally, an apparatus for performing pattern exposure in a lithography process or the like in the manufacture of a semiconductor has been used, and is called an exposure apparatus. A reduction projection type exposure apparatus is known as one type of the exposure apparatus, and is generally called a stepper. In this stepper, light from a light source passes through a reticle on which an exposure pattern is drawn, is reduced by an optical system, and is projected on a semiconductor wafer.

In this stepper, in order to accurately perform high-resolution pattern exposure, it is necessary that the focus value of the optical system is always maintained at an optimum value.

Conventionally, focus adjustment of a stepper is performed by 1
The operation of the apparatus is temporarily stopped for each lot or for a plurality of lots, and is manually performed using a test wafer.

In this focus adjustment, a test
As a wafer, a bare wafer (wafer having no surface formed thereon) on which a photoresist is formed is used, and as a reticle, line and space exposure is performed at a predetermined interval (for example, 0.6 μm). Use a pattern drawn. Then, while changing the focus value of the optical system, at each focus value,
The pattern is transferred to the photoresist on the test wafer.

At this time, if the focus of the optical system is near the optimum value, the photoresist is line-and-
Space patterns can be transferred. But,
If the focus value deviates from the optimum value by a predetermined distance in the short distance direction or the long distance direction, the line cannot be transferred. Therefore, conventionally, when determining the optimum value of the focus, the maximum value and the minimum value of the focus value at which the line-and-space pattern can be transferred are determined by visual observation with a microscope or the like, and these values are determined. The average value was adopted as the optimal value.

For example, the standard focus value of a stepper is set to "0", and the maximum and minimum focus values at which a line and space pattern can be transferred are -0.8 μm and +0.6 μm, respectively. Then
The optimum value is determined to be -0.1 [mu] m.

Conventionally, the precision of pattern exposure has been ensured by obtaining the optimum value of focus and manually adjusting the focus value.

[0009]

As described above, conventionally, in order to measure the focus shift and adjust the focus value, the operation of the apparatus must be stopped once for each lot or for each of a plurality of lots. did not become. Also, the work of replacing the bare wafer every time the focus value is changed, the work of checking the pattern transferred to the bare wafer, the work of adjusting the focus of the stepper after determining the optimum focus value, etc. are all performed manually. Since it was a task, it took a long time. For this reason, the conventional focus management method has a disadvantage that the operation rate of the stepper is reduced.

Furthermore, in the conventional focus management method,
Since the measurement and adjustment of the focus shift had to be performed after a certain period of time, even if the focus shift became large during that period, it could not be discovered. For this reason, since the quality within the same lot cannot be made constant, there is also a disadvantage that the reliability of the quality inspection performed by extracting wafers for each lot is low.

In addition, in the conventional focus management method,
An error may occur in the focus measurement result due to the influence of the photoresist on the bare wafer, and the reliability of the focus adjustment result is low.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the prior art, and it is possible to make the quality within the same lot constant without lowering the operation rate of an exposure apparatus, and to improve the focus. It is an object of the present invention to provide a focus management method for an exposure apparatus and a focus management apparatus for an exposure apparatus, which can improve the reliability of a result of the adjustment.

[0013]

[Means for Solving the Problems]

(1) A focus management method for an exposure apparatus according to a first aspect of the invention is directed to an exposure apparatus that transmits light to a reticle on which an exposure pattern is drawn, reduces the transmitted light by an optical system, and projects the reduced light on a substrate to be processed. A step of forming a step on the surface of the substrate to be processed, and writing an exposure pattern on the reticle such that transmitted light having the same cross-sectional dimension is projected onto each of the steps. A reticle drawing step, an exposure step of projecting light of the same cross-sectional dimension onto each of the steps formed on the surface of the substrate to be processed using the reticle drawn in the reticle drawing step, and an exposure step A measuring step of measuring the dimensions of the pattern transferred to each of the steps, and a measurement result of the measuring step and an optical path difference of the steps. A data generating step of determining a shift amount of the focus and generating correction data for correcting the focus of the optical system based on the shift amount; and the optical system based on the correction data obtained in the data generating step. Adjusting the focus of the system. (2) A focus management apparatus for an exposure apparatus according to a second aspect of the invention is an exposure apparatus that transmits light to a reticle on which an exposure pattern is drawn, reduces the transmitted light by an optical system, and projects the reduced light on a substrate to be processed. An exposure apparatus focus management apparatus for managing the focus of the optical system,
Using the reticle, an exposure unit that projects light having the same cross-sectional dimension on a step formed on the surface of the substrate to be processed,
Measuring means for measuring the dimension of the pattern transferred to each of the steps by the exposing means; determining the amount of focus shift from the measurement result of the measuring means and the optical path difference of the steps; and Data generating means for generating correction data for correcting the focus of the optical system, and adjusting means for adjusting the focus of the optical system based on the correction data obtained by the data generating means. Features.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a focus management method for an exposure apparatus and a focus management apparatus for an exposure apparatus according to the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram conceptually showing a configuration of a stepper provided with a focus management device according to the present embodiment.

In FIG. 1, an XY stage 11 includes:
The silicon wafer 12 is placed. The light emitted from the light source 13 passes through the reticle 14 on which the exposure pattern is drawn, is reduced by the optical system 15, and is projected on the silicon wafer 12.

A pattern measuring device (corresponding to “measuring means” of the present invention) 16 measures the length of the pattern transferred to the step of the silicon wafer 12 as described later. This pattern measuring device 16 is, for example, a silicon wafer 12
An electron gun that scans the upper step with an electron beam and a detector that detects the electron beam reflected on the silicon wafer 12 and reads the waveform can be used.

A CPU (Central Processing Unit) 17 corresponds to the “pattern judging means” of the present invention.
6. Input the measurement result. Further, the CPU 17 calculates the optical path difference based on the step on the silicon wafer 12 described above.
It is stored in advance. Then, the amount of focus shift of the optical system 15 is determined from the measurement result of the pattern measuring device 16 and the optical path difference. Further, the CPU 17 has an internal memory (not shown) for storing the shift amount obtained by this determination. Then, by statistically processing the shift amount stored in the internal memory, a subsequent occurrence of a focus shift is predicted, and correction data is calculated based on the prediction. Statistical methods include:
For example, there is a method of calculating an average value of shift amounts generated in one exposure process from shift amounts obtained by a plurality of past detections.

Focus adjuster ("adjustment means" of the present invention)
The correction data 18 is input from the CPU 17 to the correction data. Then, the focus value of the optical system 15 is adjusted based on the correction data.

FIG. 2A is a diagram conceptually showing an example of the entire configuration of the reticle 14 used in the stepper according to the present embodiment. In the figure, a region 21 is a region where an exposure pattern for a normal lithography process, that is, an exposure pattern for forming an integrated circuit on the silicon wafer 12 is drawn. On the other hand, in the area 22,
An exposure pattern for transferring a pattern to a step formed on the silicon wafer 12 is drawn.

FIG. 2B is a conceptual diagram showing the region 22 in an enlarged manner. As shown in the figure, in the area 22, rhombic exposure patterns 22a, 22b and 22c of the same shape (length is L and width is W) are drawn. By these exposure patterns 22a, 22b, and 22c, rhombic patterns can be transferred to the steps of the silicon wafer 12, respectively.

FIG. 3A is a front view conceptually showing an example of a transfer pattern formed on the silicon wafer 12. FIG. 3B shows the region 32 shown in FIG.
It is a conceptual expansion side view of. In the figure, a region 31 of the reticle 14 (FIG.
The exposure pattern drawn in (a) is transferred.
On the other hand, in the resist region 32, three resist surfaces 32a, 32b, and 32c that form steps are formed. Then, with respect to these resist surfaces 32a, 32b, and 32c, rhombic exposure patterns 22a, 22b, and 22c drawn in the region 22 of the reticle 14 (see FIG. 2B).
Is transferred. Here, the difference between the heights of the resist surface 32a and the resist surface 32b is Δh ₁ ,
Assuming that the height difference between 2b and the resist surface 32c is Δh ₂ , these values Δh ₁ and Δh ₂ correspond to optical path differences at the time of exposure.

Next, a method of causing the CPU 17 to determine the amount of defocus of the optical system 15 in this embodiment will be described.

When pattern exposure is performed on the silicon wafer 12, the minimum line width that can be transferred by this exposure increases as the amount of focus shift increases. Therefore, when a rhombic pattern (see FIG. 2B) drawn on the reticle 14 is transferred to a certain plane (a step is not considered here), if there is a shift in focus, a portion having a small width W is obtained. Is not transferred, the length L of the transferred rhombic pattern is reduced. FIG. 4 shows the relationship between the pattern length L of the pattern transferred onto the silicon wafer 12 and the amount of focus shift. As can be seen from the figure, by comparing the pattern length L with the length L when the focus is at the optimum value, the amount of this focus shift can be known.

However, from FIG. 4, although the absolute value of the focus shift amount can be known, whether the shift is a shift in the positive direction (a direction in which the focal length becomes longer) or a negative direction (the focal length becomes longer). It is not possible to know whether the shift is in the direction of shortening.

On the other hand, in the present embodiment, three rhombic patterns of the silicon wafer 12 are to be transferred, and three resist surfaces 32a, 32b, 32 to be transferred are used.
Since steps (that is, optical path differences) Δh ₁ and Δh ₂ are provided in c, not only the absolute value of the focus shift amount but also the direction of the shift can be known.

FIG. 5 is a graph showing an example of each pattern length L when a rhombic pattern is transferred to three resist surfaces 32a, 32b, 32c of the silicon wafer 12.
In the figure, the resist surface 32 of the silicon wafer 12 is
L ₁ the length of the pattern to be transferred to a, the resist surface 32
the length of the pattern transferred to b L _2, the resist surface 32
the length of the pattern transferred to c are indicated by L _3. Here, assuming that the absolute values of the steps Δh ₁ and Δh ₂ are the same, as illustrated in FIG.
₂ ) is a negative value when L ₁ > L ₃ .
When L ₁ <L ₃ , the value is a positive value. When the shift amount of L ₂ is zero (that is, when the focus is an optimum value), L ₁ = L.
It becomes ₃ .

Therefore, according to the present embodiment, it is possible to make the CPU 17 determine the absolute value and the sign of the focus shift amount by one measurement.

Further, by measuring three types of pattern lengths, it is possible to increase the measurement accuracy.

Although the absolute values of Δh ₁ and Δh ₂ are the same in FIG. 5, the same determination can be made even if the absolute values are different.

Here, each of the resist surfaces 32a, 32b, 3
The lengths L ₁ , L ₂ and L ₃ of the transfer pattern in 2c are
As described above, it is measured by the pattern measuring device 16. As a measuring method at this time, for example, there is a method of scanning the resist surfaces 32a, 32b, and 32c in the length direction with an electron beam. Each resist surface 3
When 2a, 32b, and 32c are scanned with an electron beam, the reflected beam has a different waveform between a region altered by exposure and an unexposed region. Therefore, the area to be exposed (that is, the area where the pattern has been transferred) can be determined from the waveform of the reflected beam, and the pattern lengths L ₁ , L ₂ , and L ₃ can be measured by the number of dots at the time of scanning.

Next, a procedure for managing the focus state of the stepper shown in FIG. 1 using such a principle will be described.

Before performing the actual exposure step, first, a photoresist is applied to the surface of the silicon wafer 12. Then, using, for example, a normal etching technique, a step composed of resist surfaces 32a, 32b, 32c is formed on the surface of the resist (see FIG. 3B; substrate processing process).

When drawing an exposure pattern used in a normal lithography process on the reticle 14, a rhombic exposure pattern for focus management as shown in FIG. 2B is also drawn. (See FIG. 2 (a);
Reticle drawing process).

Next, the above-described silicon wafer 12 and reticle 14 are set on a stepper, and the same exposure as in a normal lithography process is performed (exposure process). As a result, normal pattern transfer can be performed on the photoresist formed on the silicon wafer 12, and a focus management pattern can be transferred onto each of the resist surfaces 32a, 32b, and 32c.

Subsequently, the pattern measuring device 16 measures the lengths L ₁ , L ₂ , L ₃ of the patterns transferred to the resist surfaces 32a, 32b, 32c as described above (measurement process).

Thereafter, the CPU 17 inputs the measurement data L ₁ , L ₂ , L ₃ and calculates the amount of focus shift as described above. Then, the correction data is generated by performing statistical processing using the shift amount and the shift amount already stored in the internal memory (the shift amount calculated by past measurement). The correction data can be constituted by, for example, the timing of performing the focus correction, the correction amount at that time, and the like (data generation process).

Then, the focus adjuster 18 adjusts the focus of the optical system 15 based on the correction data (adjustment process).

As described above, according to the present embodiment, the focus adjustment can be performed in parallel with the normal lithography process, so that there is no need to stop the operation of the stepper for the focus adjustment. Therefore, it is possible to improve the operation rate of the stepper.

Further, since it is possible to prevent the focus shift amount from gradually increasing in the same lot, it is possible to make the quality in the same lot constant, and therefore, it is possible to set the wafer for each lot. Can be extracted to improve the reliability of the quality inspection.

In addition, since the correction data is generated by statistical processing of the shift amount, the reliability of the focus adjustment result can be improved.

Note that the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can be implemented with appropriate modifications.

For example, in the present embodiment, the correction data is generated by using the statistical processing of the shift amount. However, for example, without using the statistical processing, the focus data is generated in accordance with the detected shift amount. Even when the adjustment is performed, it is possible to perform a more useful focus management than before.

Further, even when the exposure step for focus management is performed separately from a normal lithography step, useful focus management can be performed.

[0045]

As described in detail above, according to the present invention, the quality within the same lot can be kept constant without lowering the operation rate of the exposure apparatus, and the focus adjustment result can be obtained. It is possible to provide an exposure apparatus focus management method and an exposure apparatus focus management apparatus that can improve reliability.

[Brief description of the drawings]

FIG. 1 is a diagram conceptually showing a configuration of an exposure apparatus provided with a focus management apparatus according to an embodiment of the present invention.

FIG. 2A is a view conceptually showing an example of the entire configuration of a reticle used in the exposure apparatus shown in FIG. 1;
FIG. 2B is a conceptual diagram showing an enlarged part of the reticle shown in FIG.

3A is a front view conceptually showing an example of a transfer pattern formed on a silicon wafer, and FIG. 3B is a conceptual enlarged side view of a step forming region of the silicon wafer shown in FIG. FIG.

FIG. 4 is a graph showing a relationship between a pattern length of a pattern transferred onto a silicon wafer and a focus shift amount.

FIG. 5 is a graph showing an example of each pattern length when a rhombic pattern is transferred to a step of a silicon wafer.

[Explanation of symbols]

 Reference Signs List 11 XY stage 12 Silicon wafer 13 Light source 14 Reticle 15 Optical system 16 Pattern measuring device 17 CPU 18 Focus adjuster

Claims (6)

(57) [Claims] 1. A focus management method for an optical system in an exposure apparatus for transmitting light to a reticle on which an exposure pattern is drawn, reducing the transmitted light by an optical system, and projecting the reduced light on a substrate to be processed. A substrate processing step of forming a step on the surface of the processing substrate; a reticle drawing step of drawing an exposure pattern on the reticle such that transmitted light having the same cross-sectional dimension is projected onto each of the steps; drawing in the reticle drawing step An exposing step of projecting light having the same cross-sectional dimension onto each of the steps formed on the surface of the substrate to be processed, using the reticle obtained, and a dimension of a pattern transferred to each of the steps by this exposing step. And measuring the focus deviation from the measurement result of the measurement process and the optical path difference of the step, and determining the deviation amount of the focus. A data generation step of generating correction data for correcting the focus of the optical system based on the correction data, and an adjustment step of adjusting the focus of the optical system based on the correction data obtained in the data generation step. And a focus management method for an exposure apparatus. 2. The method according to claim 1, wherein the data generation step predicts a subsequent shift amount by statistically processing a plurality of shift amounts obtained in the past, and generates the correction data based on the prediction result. 2. The focus management method for an exposure apparatus according to claim 1, wherein: 3. A focus management method for an exposure apparatus according to claim 1, wherein said exposure step is a step of simultaneously performing projection on said step and exposure for a normal lithography step. . 4. An exposure apparatus for transmitting light to a reticle on which an exposure pattern is drawn, reducing the transmitted light by an optical system, and projecting the reduced light on a substrate to be processed. An exposure unit for projecting light having the same cross-sectional dimension onto a step formed on the surface of the substrate to be processed, using the reticle, and transferring the light to each of the steps by the exposure unit. Measuring means for measuring the dimensions of the patterned pattern, and correction data for determining the amount of focus shift based on the measurement result of the measuring means and the optical path difference of the step, and correcting the focus of the optical system based on the amount of shift. And data adjusting means for adjusting the focus of the optical system based on the correction data obtained by the data generating means. An exposure device for focus management apparatus characterized by was e. 5. A data generating means for statistically processing a plurality of shift amounts obtained in the past to predict a subsequent shift amount, and for generating the correction data based on the prediction result. 5. A focus management device for an exposure apparatus according to claim 4, wherein: 6. A focus management apparatus for an exposure apparatus according to claim 4, wherein said exposure means simultaneously performs projection on said step and exposure for a normal lithography step.