JPH0325010B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to an overlapping exposure method when a portion of a marker cannot be detected.

(b) Technology background As semiconductor ICs become smaller and more dense, pattern width,
As pattern spacing has become finer, electron beam exposure is being used instead of conventional ultraviolet exposure.

For semiconductor IC pattern formation, conductor layers,
IC chips with multilayer structures are being created by combining thin film formation technology such as insulating layers with photolithography using photoresist.

When the semiconductor substrate material is silicon (Si), the thickness of the semiconductor substrate (hereinafter referred to as wafer) is approximately 500 (μm) and the diameter varies from 3 [inches] to 6 [inches]. The maximum size of an IC chip is 10 mm square, so a large number of IC chips can be made from a single wafer. Now IC
Chips are formed with a multilayer structure of 10 or more layers, but in this case extremely high weight and alignment accuracy are required. For example, 10 layers are placed on a 10 mm square pattern.
[mm] Even when overlapping square patterns, 0.1 [μ
An accuracy of about 100 m is required.

Therefore, this positioning method is performed by providing a marker on the wafer and detecting the marker for positioning, but there are cases where this cannot be detected.

The present invention relates to an alignment method in such a case.

(c) Prior Art and Problems FIG. 1 shows the relationship between a main field and a marker when a pattern is drawn on a wafer 1 using an electron beam exposure device.

In an electron beam device, the electron beam emitted from the electron gun is aligned by an alignment coil, the beam shape is determined by multiple slits provided on the axis, the beam is focused by multiple lenses, and the sharpness is ensured by an aperture. However, before reaching the wafer 1, a deflection coil is provided which is integrated with a lens 2 and mutually orthogonal X and Y coils 3 and 4, as shown in FIG. 5, which allows electron beams to be swung over a certain area of the wafer surface,
This drawable area is called the main field. In other words, when drawing a 5 [mm] square IC chip pattern on a wafer, if a 10 [mm] square is secured as the main field, four IC chip patterns can be drawn for each alignment. Then, by repeating the operation of moving the wafer 10 mm, positioning it, and exposing it to light, IC chip patterns are drawn in units of four in this example. Here, alignment markers are etched at the four corners of the main field for overlapping exposure.

FIG. 1 shows this state, in which drawing is performed on the wafer 1 in units of main fields.
Positioning markers 7 are made at these four corners by etching.

Figure 2 shows a plan view A and a cross-sectional shape B of the marker. Although this shape can be arbitrary, for example, 10 [μ
m] angle and depth dimension 8 are 5000 [Å] to 1 [μm].

Now, pattern formation is repeated using the wafer 1 shown in Fig. 1 to form a multilayer IC chip.The method is to use the main field that is first projected when the wafer 1 set in a wafer holder is placed in an electron beam device. The center position 9 shown in FIG. 2A is determined by scanning four marker positions with an electron beam and detecting backscattered electrons with a backscattered electron detector.

Fig. 2B shows a method for determining the center position 9 by scanning the marker 7 from the left and right and above and below with an electron beam. The center position 9 can be detected by detecting it and scanning it also from the orthogonal direction. Note that the thin layer formed on the wafer 1 including the marker recesses represents the photoresist film 11.

After the positions of the markers 7 at the four corners have been detected in this way, overlay exposure should be performed in accordance with the detection, but the wafer pattern may expand or contract due to the temperature coefficient of the wafer material. Due to curvature of the wafer 1, misalignment of the position of the wafer 1 set in the wafer holder and inserted into the electron beam device, etc., the predicted position of the marker and the marker position on the wafer do not necessarily match when viewed from the electron beam device. Therefore, it is necessary to adjust the electron beam writing program to the four marker positions on the wafer 1 and perform pattern correction as shown in the following equation.

ΔX=G _x X+R _x Y+H _x XY+O _x ...(1) ΔY=G _Y Y+R _Y X+H _Y XY+O _Y ...(2) Here, X...X coordinate value predicted by the electron beam device.

Y...Y coordinate value predicted by the electron beam device.

ΔX...Distance in the X direction representing the difference between the expected position of the marker and the marker position on the wafer ΔY...Distance in the Y direction representing the difference between the expected position of the marker and the marker position on the wafer G _x , G _y ...Gain Correction coefficients R _x , R _y ... Rotation correction coefficients H _x , H _y ... Trapezoidal correction coefficients O _x , O _y ... Offset correction coefficients Figure 3 shows how the pattern programmed in the electron beam device is converted into a pattern on the wafer. It shows the deformation operation necessary for superimposition, and when the program pattern is a rectangular pattern 12 shown by a solid line, a rectangular pattern 13 surrounded by a broken line in FIG.
This occurs when the wafer 1 is stretched and curved, and the program pattern is changed to this rectangular pattern 1.
In order to overlap with 3, it is necessary to correct it using gain correction coefficients G _x and G _y . Further, the parallelogram pattern 14 surrounded by a dotted line in FIG. 3A occurs when the pattern on the wafer is more twisted than the program pattern and must be corrected using rotation correction coefficients R _x and R _y . Further, a trapezoidal pattern 15 shown by a broken line in FIG. 3B appears when the wafer is curved, and in this case, it is necessary to correct the program pattern using trapezoidal correction coefficients H _x and H _y to make it match. Furthermore, the rectangular pattern 16 indicated by a dotted line in FIG. 3B is laterally shifted from the predicted position of the program 12, and needs to be corrected using rotation correction coefficients O _x and O _y .

Here you can actually modify the program pattern and
To perform overlapping exposure with the pattern formed on the wafer, set ΔX and ΔY for the four markers.
Measure the value of , find eight correction coefficients from equations (1) and (2), and then find and from the following equation.

=X+G _x X+R _x Y+H _x XY+O _x ...(3) =Y+G _y Y+R _y X+H _y XY+O _y ...(4) Here...the value of the X coordinate axis to be inserted into the electron beam device.

……〃Y coordinate axis value.

These measurements and calculations are automatically performed using an electron beam device and a computer as shown in FIG.
In other words, X data and Y data are ADD (adder) 1
After adding the correction term in step 7, digital, analog,
The signal is converted into a signal by a converter (DAC) 18, amplified by an amplifier 19, and applied to the X coil 3 and Y coil 4 of the deflection coil 5.

As described above, when overlapping exposure is performed using an electron beam device, markers at the four corners of the main field are detected. However, there are cases where four markers 7 are not found in the main field. The reason for this is that, as shown at 6' in Figure 1, the main field is located at the edge of the wafer, or the marker 7 may be forgotten or damaged during pattern formation of the first layer. In this case, if one marker 7 is not found, only three markers can be detected. In such cases, conventionally, the correction coefficients of the main field 6 where there are four adjacent markers are used as they are for drawing. However, in this case, there was a problem because the overlay accuracy decreased.

(d) Purpose of the Invention The present invention provides a method for overlapping exposure using an electron beam exposure device without reducing accuracy when only three out of four markers are found in the main field. The purpose is to

(e) Structure of the Invention The above object is to provide an IC chip having a multilayer structure in which a marker provided on a semiconductor substrate is detected and positioned, and a new pattern is repeatedly drawn on the substrate by electron beam exposure. In the group-forming electron beam exposure method, when only three of the four markers that should be at the expected positions in the main field to be drawn with the electron beam can be detected, gain, rotation, trapezoid, and Among the four types of offset correction coefficients, for the trapezoid correction coefficient, the value obtained when drawing the adjacent main field is used, and for the gain, rotation, and offset correction coefficients, the value obtained when drawing the main field to be drawn is used. This can be realized by an electron beam exposure method characterized in that positioning is determined based on the positions of three markers detected in .

(f) Embodiments of the Invention The present invention provides gain peak correction coefficients G _x and G _y that correct the amount of deformation due to expansion and contraction of the wafer, and rotation peak correction coefficient R that corrects the twist of the wafer set in the wafer holder. Compared to _x , R _y and offset length correction coefficients O _x , O _y that correct deviations in movement position, trapezoidal apex correction coefficients H _x , H _y that correct the amount of deformation due to wafer warping have relatively little influence. This method focuses on the fact that the accuracy does not deteriorate to this extent even if the previous value is used as is. In fact, the method for calculating the values of is G _x , G _y , R _x , _Ry ,
The values of O _x and O _y are determined, and the values of H _x and H _y are determined from equations (3) and (4) using the previous values as they are.
Note that there may be cases where only 2 out of 4 markers can be detected, but in this case, the offset top correction coefficient
It is preferable to obtain only O _x and O _y and use the other three types of correction coefficients by fixing the values used in the superposition of adjacent main fields.

By employing the above method, it becomes possible to perform overlapping exposure with much higher precision than in the past.

(g) Effects of the invention The present invention requires high overlay accuracy as patterns become more complex and finer in IC chip manufacturing, but in many cases not all markers can be seen during electron beam exposure. By implementing the present invention, the overlay accuracy is improved compared to the conventional method, and therefore the yield can be improved.

[Brief explanation of the drawing]

Figure 1 is a plan view showing the relationship between the wafer and the main field, Figure 2 A is a plan view of the marker, Figure B is a sectional view, and Figures 3 A and B are the relationship between the program pattern and the correction pattern. FIG. 4 is a configuration diagram illustrating the mechanism of the deflection coil. In the figure, 1 is the wafer, 3 and 4 are the X and Y deflection coils, 6 and 6' are the main field, and 7
is a marker.

Claims (1)

[Claims] 1. Detecting and positioning a marker provided on a semiconductor substrate, and repeatedly drawing a new pattern on the substrate by electron beam exposure to form a group of IC chips having a multilayer structure. In the electron beam exposure method, when only three of the four markers that should be at the expected positions in the main field to be drawn with the electron beam can be detected, four types of markers are used: gain, rotation, trapezoid, and offset. Among the correction coefficients, for the trapezoid correction coefficient, the value obtained when drawing the adjacent main field is used, and for the gain, rotation, and offset correction coefficients, the three values detected in the main field to be drawn are used. An electron beam exposure method characterized in that positioning is determined based on the position of a marker.