JPH0352211B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a deflection distortion correction method in an electron beam or ion beam exposure apparatus.

[Prior Art] In an electron beam or ion beam exposure apparatus, correction of deflection distortion must be performed with high precision in order to connect and overlay drawn patterns with high precision. Several methods of this type have been devised in the past, and FIG. 1 shows the principle of a typical one. In the figure, 1 is a mark for measuring deflection distortion on the top surface, 2 is a mark for measuring deflection distortion on the bottom surface,
3 indicates a sample, and 4 indicates a beam deflector.

In the above configuration, mark detection is first performed for the distortion measurement marks 1 and 2 on the upper and lower surfaces to measure the amount of deflection distortion, and after determining the deflection distortion correction coefficient based on the measurement results, the height of the sample surface 3 is determined. Measure Z. Since the height difference H between the upper and lower surfaces is known in advance, the deflection distortion correction coefficient for sample surface 3 can be easily determined by interpolation from the deflection distortion correction coefficients for the upper and lower surfaces obtained previously. be able to. Therefore,
In this method, the key point is how accurately the height Z of the sample surface can be measured.

FIG. 2 shows the method for measuring the height of the sample surface. In the figure, 5 is a light generator, 6 is a positioning light receiving element, 7 is an optical axis, 8 is a semiconductor integrated circuit chip, and 9 is a light receiving element for positioning.
is a beam deflection field, and the height of the sample surface can be measured by the irradiation position where the light receiving element 6 is irradiated with the light reflected from the sample surface. The semiconductor integrated circuit chip 8 consists of one or more beam deflection fields 9. A pattern is drawn for each deflection field, and when the chip 8 is drawn by connecting two or more deflection fields, the pattern is sequentially drawn for each deflection field while moving the sample by moving the stage. In that case, the height of the sample surface is conventionally measured at the center of the deflection field or the center of the chip.

However, in semiconductor integrated circuits, patterns for different layers are drawn several to more than ten times over layers that have already been drawn and undergone a predetermined process, resulting in unevenness on the surface of the chip. As a result, the light for height measurement is scattered especially in areas where fine patterns are densely packed.
Since the amount of light decreases significantly, it becomes impossible to accurately measure the height of the sample surface. The inside of a semiconductor integrated circuit chip is usually filled with minute patterns, and with conventional methods, it is difficult to accurately measure the height of the sample surface as the process progresses. According to experiments, the difference in height between areas with dense patterns and areas with no patterns is over 200 μm.
Pattern overlay and connection accuracy is 0.5μm
I found out that it also works.

[Object and structure of the invention]

The present invention has been made in view of the above circumstances, and its purpose is to provide a deflection distortion correction method that can accurately determine the height of a sample surface and perform highly accurate deflection distortion correction. be.

In order to achieve such an objective, the present invention
The height of the sample surface is determined by flattening the sample surface in a specific positional relationship with the alignment mark, and then calculating the height inside the chip based on the measurement results for that sample surface. It is.

In other words, avoid measuring areas in the chip where drawing patterns are densely packed, measure using the optical method described above on flat areas with few or no drawing patterns, and based on the results, measure the inside of the chip. The height is calculated, and in this case, marks for beam alignment are used to determine the measurement position. Hereinafter, the present invention will be explained in detail using Examples.

〔Example〕

The semiconductor integrated circuit chip 8 is placed on the surface of the sample 3, which is a wafer, as shown in FIG. The area around the chip is normally
A scribe line 10 having a width of 100 to 200 μm is configured. Reference numeral 11 denotes an alignment mark provided in this scribe line, and during actual drawing, the beam is positioned while detecting this mark 11.

FIG. 5 is a block diagram of a beam exposure apparatus showing one embodiment of the present invention. In the figure, 12 is a height measuring device, 13 is a height calculation circuit, 14 is a backscattered electron detector, 15 is a mark detection circuit, 16 is a control computer, 17 is an interface, and 18 is a deflection distortion correction coefficient for the upper and lower surfaces. Memory, 19 is a correction coefficient calculation circuit, 20 is a drawing sequencer, 21 is a sample surface correction coefficient memory, 22 is a pattern data memory, 23
2 is a pattern data processing circuit, 24 is a beam deflection circuit, and 25 is a memory for height measurement results.

In the above configuration, prior to drawing a pattern of a semiconductor integrated circuit, etc., the deflection distortion of the two upper and lower surfaces is measured using the deflection distortion measurement marks on the upper and lower surfaces, as in the past, and the deflection distortion correction coefficient is calculated based on the measurement results. is determined by the control computer 16, and the correction coefficient is stored in the memory 1.
Remember it in 8. Next, the stage is moved so that the alignment mark 11 at the lower left of the chip 8 is at the center of the beam, and the height of the sample surface at that point is measured by the height measuring device 12, and the measurement results are is stored in the memory 25. Thereafter, the position of the mark is detected by the reflected electron detection circuit 14 and the mark detection circuit 15, and the stage is moved to the next mark. Here, the height of the sample surface is measured again, and the measurement results are stored in the memory 25. This operation is performed for the marks at the four corners surrounding the chip 8, and the mark positions are also detected. As for the height information at the four corners of the chip, the height calculation circuit 13 calculates the average value of the two excluding the maximum and minimum values, and the result is stored in the internal memory of the control computer 16 as the height inside the chip. be done. This chip height information is transmitted through the interface 17.
Furthermore, the deflection distortion correction coefficients for the upper and lower surfaces of the memory 18 are entered into a correction coefficient calculation circuit 19, where they are converted into correction coefficients corresponding to the height of the sample surface using a linear interpolation method. This converted correction coefficient is stored in the correction coefficient memory 21. Mark position information is also calculated in a similar manner, and correction coefficients for sample distortion are stored in the correction coefficient memory 21. These height and mark position calculations are performed by the drawing sequencer 20.
This is done in an orderly manner under the control of

On the other hand, pattern data for semiconductor integrated circuits is stored in a pattern data memory 22, and when a drawing command is received from the control computer 16, the data enters the pattern data processing circuit 23, where it is stored in the memory 22.
A distortion correction calculation is performed with the sample surface correction coefficient transferred from 1, resulting in correct pattern position data. The pattern position data is sent to the beam deflection control circuit 24, and as a result, the beam is correctly deflected.

In this example, the height was measured around the four corners of each chip, and the average value of the measurement results at two points excluding the maximum and minimum values was taken as the height of the entire chip. normal
For samples that have undergone the LSI process, the amount of deformation on the wafer is at most 50 μm, and between chips it is less than 10 μm. If the beam landing angle is 2.5 mrad, the beam position shift due to a 10 μm height change is
It is 0.025 μm, which poses no practical problem. For samples with particularly large deformations, the height change within the chip is determined by plane or curved surface approximation based on the height measurement results around the chip as described above, and the deflection is performed in units of deflection fields that divide the chip. It is sufficient to perform distortion correction calculations. Conversely, if the sample is flat, the height around each chip may be measured for each chip, and the measured data may simply be averaged to determine the height of each chip.

In addition, in the above-mentioned embodiment, the height was measured on the alignment mark around the chip, but it is not necessary to measure the height on the alignment mark. You can also create a file and do it there.

〔Effect of the invention〕

As explained above, according to the present invention, the height of the sample surface is measured on the alignment mark provided around the drawing chip or inside the chip, or on a flat part in the vicinity, thereby making it possible to improve the drawing pattern. There is no disturbance to the height measuring device due to unevenness, unlike when directly measuring in the central area where there is a high density of trees, and extremely reliable height measurement is possible. Therefore, highly accurate deflection distortion correction can be performed.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the principle of the deflection distortion correction method, Fig. 2 is a diagram for explaining the conventional method for measuring the height of the sample surface, Fig. 3 is an arrangement diagram of semiconductor integrated circuit chips, FIG. 4 is a detailed enlarged view showing the vicinity of the chip, and FIG. 5 is a block diagram of a beam exposure apparatus showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Mark for measuring deflection distortion on the top surface, 2... Mark for measuring deflection distortion on the bottom surface, 3... Sample, 4... Beam deflector, 5... Light generator, 6... Light receiving element for positioning, 7 ...Optical axis, 8...Semiconductor integrated circuit chip, 9...Beam deflection field, 10...Scribe line, 11...Alignment mark, 1
2...Height measuring device, 13...Height calculation circuit, 14
...Backscattered electron detector, 15...Mark detection circuit,
16... Control computer, 17... Interface, 18... Upper and lower deflection distortion correction coefficient memory,
19... Correction coefficient calculation circuit, 20... Drawing sequencer, 21... Correction coefficient memory for sample surface, 22
... Pattern data memory, 23 ... Pattern data processing circuit, 24 ... Beam deflection circuit, 25 ... Memory for height measurement results.

Claims (1)

[Claims] 1 Using deflection distortion measurement marks attached to the upper and lower surfaces with a known level difference prepared in advance,
Deflection distortion is measured by detecting marks on the surface, and based on the measurement results, the deflection distortion correction coefficients for the upper and lower surfaces are calculated.The height of the sample surface is determined and the deflection distortion correction coefficients for the upper and lower surfaces are used to calculate the deflection distortion correction coefficients for the above-mentioned two surfaces. In a deflection distortion correction method in an electron beam or ion beam exposure apparatus that calculates a deflection distortion correction coefficient according to the height of a surface, the height of the sample surface is determined by each of the integrated circuits that constitute the integrated circuit to be drawn on the sample surface. The height is measured on the flattened sample surface in a specific positional relationship with the reference mark provided for each chip or multiple chips, and the height inside the drawing chip is calculated based on the measurement results. A deflection distortion correction method characterized in that the deflection distortion is corrected by