JP3380941B2 - Line width management pattern and line width management method using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line width management pattern used for manufacturing a semiconductor device and a line width management method using the same, and more particularly to a surface step difference of a pattern (actual pattern) formed in a chip, The present invention relates to a line width management pattern that faithfully reflects the height of a photoresist surface and the density of patterns, and a method of using the line width management pattern with higher accuracy than ever.

[0002]

2. Description of the Related Art In the semiconductor industry, mass production of 64M DRAM, which is a next-generation LSI, is imminent, and a stable fine processing technique having a minimum processing dimension of 0.30 μm is required. In such fine processing, pattern dimension measurement, that is, line width management is extremely important. Even if the processing accuracy is ± 20%, the allowable dimensional error is 0.06 μm
Therefore, the measurement accuracy is 0.01 to 0.
A level of 005 μm is required. As a measuring device,
A length-measuring SEM (scanning electron microscope) is generally used.

However, it is difficult to manage such a fine line width based on the measurement of an actual pattern.
This is because it is very difficult for the operator of the length-measuring SEM to find out the pattern processed with the minimum processing size from the patterns in the chip. In particular, A
In an integrated circuit in which the layout of transistors and wiring is random such as SIC (IC for a specific application), line width management based on actual pattern measurement is almost impossible. Therefore, conventionally, a pattern dedicated to line width management, that is, a line width management pattern is formed on a substrate (wafer) at a position where it does not interfere with chip fabrication, and this line width management pattern is measured by a length measurement SEM.
A method of estimating the line width of the pattern in the chip by observing at is adopted. A space for dividing a plurality of chips completed on a substrate (wafer) is often used as a place for forming a line width management pattern.
That is the scribe line.

FIG. 6 shows a configuration example of a conventional line width management pattern 40. The figure (a) is a top view and the figure (b) is YY.
It is a line sectional view. This line width management pattern 40 is, for example, a single resist pattern formed simultaneously on a scribe line when a resist pattern that is an etching mask for the Al-based wiring film 43 is formed on the substrate 42 in a chip. 41.

[0005]

By the way, a pattern formed in a chip is roughly classified into a resist pattern formed by photolithography and a dry etching using the resist pattern as a mask. There are circuit patterns, but the line width of these patterns varies due to various factors. The main factors are (a) pattern density, (b) photoresist surface height, and (c) underlying surface step. First, the line width variation of the resist pattern will be described.

Regarding the above (a) pattern sparseness and denseness, first, FIG. 3 shows the variation of the resist pattern due to the sparse and denseness of the pattern. This graph shows a resist pattern obtained after development by transferring a line pattern and a hole pattern, which have the same size on the photomask but different densities, to the photoresist film on the wafer by using an i-line stepper. Is a plot of the results of measurement of the line width or the opening width (hole diameter) of the above with a length-measuring SEM, where (a) is a line pattern and (b) is a hole pattern. The photoresist material used is a chemically amplified positive photoresist.

In the case of the line pattern shown in (a), the line width variation of the resist pattern is not uniform, and the line width increases when the pattern is very dense and decreases once when the pattern becomes slightly sparse. After that, it tends to increase gradually again as the pattern becomes sparse. This is because the degree of diffraction of the exposure light at the edge portion of the pattern on the photomask depends on the distance between the adjacent patterns. Particularly, on the dense side, the resolution in the non-formation portion is reduced due to the decrease in resolution. The resist removal becomes worse and the line width remarkably increases. On the other hand, in the case of the hole pattern shown in FIG. 6B, if the holes are separated by a certain amount or more, the light intensity in the peripheral portion of the holes becomes less than the exposure threshold value, and a constant hole diameter is maintained. However, if the image contrast deteriorates as the holes approach each other, the light intensity around the holes increases due to the overlapping of the skirts of the light intensity curve (proximity effect), and the hole diameter increases when this reaches the exposure threshold. Like

The height of the (b) photoresist surface affects defocus. FIG. 4 shows how the line width variation of the resist pattern with respect to the focus shift amount of the exposure apparatus depends on the height of the photoresist surface. Here, the height of the photoresist surface refers to the distance from the Si substrate to the center of the film thickness of the resist film, and the surface at a height just between the high portion and the low portion is the just focus surface (focus shift amount). Is set to 0). From this figure, it can be seen that the allowable range of defocus for achieving the desired resist pattern line width is significantly different between the high portion and the low portion. Normally, in order to correct this focus shift, an optimum focus / offset value is input to the exposure apparatus to perform the exposure operation, but this optimization is effective only for the pattern in the chip.

The above-mentioned (c) surface step of the underlying layer causes the halation and the standing wave effect to be manifested in the lithography. As is well known, in a semiconductor device manufactured according to a highly miniaturized design rule such as a recent VLSI or a future ULSI, the number of layers of various circuit patterns is laminated as the device structure becomes three-dimensional. However, if there is a step in the underlying material layer of the photoresist film, the light intensity of a specific region becomes high due to the reflected light from this portion, which may cause halation. This manifests itself as a waist in a positive photoresist pattern, for example. On the other hand, the standing wave effect means that the reflected lights due to multiple reflection in the photoresist film or between the base film interfere with each other,
This is a phenomenon in which a light intensity distribution occurs in the thickness direction of the photoresist film. As a result, a difference in sensitivity occurs between a portion where the resist film thickness is large and a portion where the resist film thickness is small on the substrate surface, causing a line width variation as shown in FIG. Here, (a) shows the case of a line pattern, and (b) shows the case of a hole pattern. These line width variations are λ / 2n
(Where λ is the wavelength of exposure light and n is the refractive index of the photoresist film). In addition, as the actual damage due to the standing wave effect, wavy deformation of the side wall surface of the contact hole pattern is also known.

The line width variation of the resist pattern has been discussed above. Needless to say, the line width variation directly affects the line width of the circuit pattern formed by anisotropic dry etching using the line width variation as a mask. To do. In dry etching, in addition to this, there is a possibility that a microloading effect may appear due to the density of the pattern. This is because the supply of etchant to the surface to be etched is hindered or the vapor pressure of the etching reaction product is reduced in the inside of minute holes or in the dense parts of the pattern such as minute lines and spaces. The phenomenon is that the etching rate decreases. At this time, the etching reaction product excessively deposited on the sidewall surface of the resist pattern acts in the direction of thickening the line width of the circuit pattern. As described above, various factors are intertwined with the line width variation, and it is considered that a factor for thickening the line width and a factor for thinning the line width simultaneously act on a certain region, and the action mechanism thereof is very complicated.

Looking at the conventional line width management pattern shown in FIG. 6 based on the above discussion, it can be seen that this line width management pattern shows the unevenness of the actual pattern, the height of the photoresist surface, and the surface step of the base. It is obvious that the line width variation due to these factors cannot be generated in the same manner as the actual pattern. That is, since the conventional line width management pattern has only a single thin line pattern,
In the first place, we cannot see the effect of the density difference. Further, since the height of the photoresist surface is also different from that of the actual pattern portion, even if the focus / offset is optimized for the actual pattern portion, the effect of the optimization does not extend to the line width management pattern. Absent. Further, since the layout of the underlying step is different from that of the actual pattern portion, the halation and the standing wave effect do not occur similarly. Therefore, even if the line width of the conventional line width management pattern is measured, the line width of the pattern in the chip cannot be correctly estimated from this measurement result. In recent years, there are many conditions that increase line width fluctuations due to three-dimensional and complicated semiconductor device structures, shorter exposure wavelengths, and finer patterns themselves. This causes a significant deterioration in the quality and yield of semiconductor devices.

Therefore, the present invention solves the above-mentioned problems, and reflects the factors affecting the line width variation of the pattern inside the chip as they are in the line width management pattern outside the chip, so that the accurate line width information according to the reality is obtained. Line width management pattern, which gives
And it aims at providing the line width management method using this.

[0013]

The present invention is proposed to achieve the above objects.

First, the line width management pattern of the present invention is arranged on a scribe line for dividing a plurality of chips formed on a substrate into each other, and the pattern formed in the chip has the maximum vertical profile. The upper and lowermost surfaces, the densest area and the sparsest area in the horizontal profile, and the maximum portion and the minimum portion of the resist film thickness generated based on the mutual relationship between the vertical profile and the horizontal profile are formed in a plurality of patterns. It has a reproduced basic cell. Then, the basic cells are formed at least at the corners and the center of the exposure area on the substrate for one shot by the projection exposure apparatus including a plurality of chips divided by the scribe line.

In order to easily manufacture this basic cell, it is preferable to use a representative pattern of each layer constituting the above pattern. The representative pattern at this time does not have to be completely the same as the in-chip pattern, and may be representative of the density of the pattern in the chip, the height of the photoresist surface, and the surface step of the base. Typically, a part of the circuit pattern formed in the chip in each layer can be used. The basic cell may be only one,
By arranging a plurality of them regularly, the line width management pattern becomes similar to the actual pattern as a whole, so that more accurate length measurement can be performed. In addition, all the basic cells that configure the line width management pattern in the same layer do not have to be the same. For example, a basic cell that performs centralized management of the gate length and a basic cell that manages the most severe step difference or sparseness. It is also possible to mix.

On the other hand, the line width management method of the present invention manages the line width of the pattern formed in the chip based on the measured value of the line width obtained by irradiating the above-mentioned line width management pattern with an electron beam. To do. The current mainstream reduction projection exposure apparatus is designed to perform batch exposure of several chips in one exposure (one shot), depending on the chip area. This one
It is a boundary line of the exposure area on the substrate for the shot. Within this exposure area, the closer to the corner, the greater the influence of the aberration of the projection lens and the more prominent the line width variation appears. Therefore, for accuracy, the basic cells are arranged at the corners and the center of the exposure area.

The line width management method of the present invention can be applied to the line width management of a photoresist pattern, or to the line width management of a circuit pattern formed using this as an etching mask. The latter circuit pattern is not always composed of a single layer. For example, in the case of W-polycide wiring processing, the WSi _x film and the polysilicon film are etched in a common pattern. Further, the "line width" referred to in the present invention is not limited to the width of an elongated structure such as a wiring pattern, and can be broadly interpreted as a "pattern dimension" including the diameter of a connection hole (hole). For hole processing,
The interlayer insulating film to be processed is not limited to a single film, and for example, in order to connect the third layer wiring and the first layer wiring, it is necessary to etch the two layers of the interlayer insulating film.
Alternatively, the single-layer interlayer insulating film is a non-doped silicate glass) film, an SOG (spin on glass) film, B
Si such as PSG (boron phosphorus silicate glass) film
It may be composed of an O _x type multilayer film.

[0018]

The basic cell of the line width management pattern of the present invention is the representative pattern of each layer constituting the pattern in the chip,
For example, by including a part of the pattern formed in the chip, the thickness direction profile and the sparse / dense profile of the actual pattern in the chip are reproduced as they are. Therefore, when the line width of the pattern changes in the chip due to the density of the pattern, the height of the photoresist surface, and the surface step of the underlying layer as shown in FIGS. appear. Therefore, it is possible to perform accurate line width management in accordance with reality. Of course, the ease of detection due to the formation of the basic cell on the scribe line is the same as in the past. Further, if the number of basic cells arranged is increased, a line width evaluation pattern close to an actual pattern can be obtained, so that the measurement accuracy can be improved.

The line width of the line width management pattern can be measured by irradiating an electron beam by applying the principle of SEM. At this time, in the exposure area on the substrate for one shot by the projection exposure apparatus, by arranging the basic cell in the corner where the line width variation is most prominent, extremely accurate measurement can be performed. By this line width management method, the line width of both the photoresist pattern and the circuit pattern can be
Can be managed accurately.

[0020]

EXAMPLES Specific examples of the present invention will be described below.

Example 1 In this example, an example of the structure of the line width management pattern of the present invention will be described with reference to FIGS. 1 and 2.

FIG. 1A shows an exposure area 10 on the substrate for one shot when a reduction projection exposure apparatus capable of exposing four chips 1 at one shot is used. A line width management pattern 20 is arranged on a scribe line 2 that runs vertically and horizontally on the substrate to separate the chips 1 from each other.

An enlarged view of one of the line width management patterns 20 is shown in FIG. One line width management pattern 2
0 is a plurality (4 in this case) regularly arranged in a grid pattern.
It is composed of zero basic cells 30. The microstructure of each basic cell 30 is the same.

Further, an enlarged view of one of the basic cells 30 is shown in FIG. Here, the shaded portion is the resist pattern forming the outermost layer of this basic cell. The resist pattern is formed here as a mask for etching the polysilicon film (see reference numeral 36 in FIG. 2) immediately thereunder, and two thick resist patterns running in the central portion in the vertical direction. 32 and two thin resist patterns 31 vertically arranged on both sides thereof in a vertical direction, that is, eight thin resist patterns 31 in total. The resist patterns 31 and 32 have different sparse densities. The polysilicon film 36 in a semiconductor device is used for wiring as a gate electrode of a MOS transistor or as a constituent material of a word line or a bit line of a memory element. In the former case, the minimum processing size of the device of the generation, For the latter, the minimum processing size of one generation before that is usually applied. Also in the figure,
A region shown by a broken line that overlaps the formation region of two adjacent resist patterns 33 is an opening of the element isolation pattern 33 formed on the lower layer side of the polysilicon film 36.

FIG. 2 is a sectional view taken along line XX of FIG.
From this figure, in this basic cell 30, not only the horizontal profile such as the line width of the pattern and the sparse / dense profile, but also the surface step s generated by the formation of the element isolation region 33 in the Si substrate 35, and the poly step reflecting this Step difference of the silicon film 36, height difference of the photoresist surface, thickness difference of the photoresist film | t ₁ −t ₂ | (where t ₁ is the film thickness of the resist pattern 31 and t ₂ is the film of the resist pattern 32) It can be seen that vertical profiles such as (representing thickness) are reproduced in the same manner as the actual pattern. However, the layout of the pattern in the basic cell 30 is not exactly the same as the layout of the actual pattern formed in the chip 1, and a part of the actual pattern is adopted.

In the above-mentioned FIG. 1 (c), the small square patterns arranged between the resist patterns 31 and on both sides thereof are added for reference only. , 32 are used as masks to form an electrode pattern by dry etching of the polysilicon film 36, and then a contact hole pattern 3 is opened in an interlayer insulating film covering the electrode pattern.
It is 4. That is, in the basic cell 30, patterns representing each layer are sequentially formed in the subsequent steps.

Embodiment 2 In this embodiment, the line width management method of the present invention will be described separately for each item of (i) selection of a length measurement pattern and (ii) line width management place in a shot.

(I) Selection of Measurement Pattern For a pattern that requires the strictest line width control such as the gate length of a MOS transistor, the resist pattern 31 formed in the basic cell 30 is selected as the measurement pattern. To do. Further, even if the line width control is not so strict, a portion where the resolution performance is likely to deteriorate due to the standing wave effect or halation is also selected as the measurement pattern. That is, where the minimum processing dimension is applied, where the ideal image plane is most distant from the just focus surface (top and bottom surfaces), where the resist film is thickest, where there is a step in the underlying material layer, etc. Is the target of selection. By this selection, it is possible to manage and prevent abnormal formation of the resist pattern such as disconnection or short circuit of the wiring pattern or defective hole removal.

Further, although patterns having various sparse densities are mixed in the actual pattern portion, the tendency of the line width variation with time is different between the dense part and the sparse part of the pattern. Therefore, if a pattern representing the densest part and the sparsest part is also selected as the measurement pattern, the tendency of the line width variation can be known for the sparse density with all of the actual patterns.

(Ii) Line Width Management in Shot The tendency of line width fluctuation in the on-substrate exposure area 10 for one shot is not normally uniform due to the influence of the aberration of the projection lens of the stepper. The influence of aberration is most likely to appear in the area corresponding to the peripheral portion of the lens, so that the exposure area on the substrate 10
Of the line width management patterns 20 arranged at the four corners of the substrate are individually measured, and the line width management pattern 2 arranged at the center of the on-substrate exposure area 10 corresponding to the center of the lens with the least aberration.
Measure 0.

By the way, when the line width management patterns are arranged at the four corners of the on-substrate exposure area 10 as shown in FIG. 1A, the line width management patterns 20 at the four corners are step-and-step. -It is necessary to consider measures to prevent overlapping exposure due to adjacent shots in repeat exposure. One of the possible measures is to set the step pitch in the exposure device so that the scribe lines do not overlap. In this case, the scribe line width between the adjacent on-substrate exposure areas 10 is twice as wide as the conventional one. When it is not desired to change the scribe line width, as another measure, it is possible to expose the line width management patterns 20 existing on the same side by different shots. That is, for example, in FIG. 1A, when the line width management pattern 20 in the upper right corner is exposed by this shot, the line width management pattern 20 in the lower right corner is exposed by the adjacent shot on the right side or another shot. However, in this case, a plurality of exposure areas 10 on the substrate are finally combined on the board in a jigsaw puzzle manner, and if the arrangement shown in FIG. Since the number of line width management patterns 20 that can be used in the inside decreases, it is desirable to appropriately increase the number of arrangements.

In the line width management method of the present invention,
If all measurement patterns are selected, the measurement accuracy will improve, but the man-hours required for management will inevitably increase. Therefore, the point is how to improve the accuracy while minimizing the increase in man-hours. In the case of the present invention, even if the measurement location is limited to the portion that represents the gate length of the MOS transistor, the maximum underlying step that can occur in the actual pattern inevitably occurs around it, so that the wiring pattern Abnormality of resist pattern such as short circuit or disconnection
It can be detected at the same time when measuring the gate length.

The line width management of the present invention as described above is performed by the length measurement SEM.
As a result of actually using, the following merits were obtained. First, in the present invention, the line width variation in the actual pattern portion appears in the line width management pattern as it is. Therefore, for example, when the line width abnormality of the resist pattern is detected, the resist pattern may be recreated and the subsequent etching process may be performed. did it. On the other hand, conventionally, even if the line width variation exceeds the allowable range in the actual pattern part, if the measurement result of the line width management pattern is within the allowable range, the process proceeds to the next step, There was a problem that a trouble was not noticed until a defect was judged during a typical device operation check. In mass production, parameters such as the film thickness and reflectance of the underlying film that affect the focus shift and exposure sensitivity shift may change over a long period of time. We were able to.

The specific embodiment of the present invention has been described above, but the present invention is not limited to this embodiment. For example, the line width management of the resist pattern has been described in the above embodiment, but the line width management of the circuit pattern of the underlying material film etched by using the resist pattern as a mask can be performed in exactly the same manner.
Further, the arrangement and the number of line width management patterns in the exposure area on the substrate for one shot can be appropriately changed. For example, in the above-described embodiment, the line width management pattern is arranged only at the four corners and the center. However, when the number of chips in one shot is larger, if the line width management pattern is provided at each lattice point of the scribe line running in the vertical and horizontal directions, the chip It is possible to know in detail the variation in line width variation between them. Alternatively, when the area of one chip is large and variations in line width can occur within the chip, it is advisable to add the line width management pattern to the region along the sides of the chip. In addition, the number of basic cells forming one line width management pattern and the shape and structure of the pattern forming the basic cells can be changed without departing from the spirit of the present invention.

[0035]

As is apparent from the above description, according to the present invention, it is possible to observe the line width management pattern which directly reflects the line width variation occurring in the actual pattern in the chip. It is possible to dramatically improve the accuracy of line width management. Therefore, the present invention greatly contributes to high performance, high integration, and high reliability of semiconductor devices through line width management.

[Brief description of drawings]

FIG. 1 is a schematic plan view showing a structure of a line width management pattern of the present invention, FIG. 1A is an arrangement of line width management patterns in an exposure area on a substrate for one shot, and FIG. 1B is each line width. The arrangement of the basic cells in the management pattern, and FIG. 7C shows the layout of the pattern in each basic cell.

FIG. 2 is a sectional view taken along line XX in FIG.

3A and 3B are graphs showing variations in a resist pattern due to a difference in pattern density, where FIG. 3A shows a line pattern and FIG. 3B shows a hole pattern.

FIG. 4 is a graph showing variations in line width of a resist pattern with respect to a focus shift amount of an exposure apparatus.

5A and 5B are graphs showing a standing wave effect, wherein FIG. 5A shows the case of a line pattern, and FIG. 5B shows the case of a hole pattern.

6A and 6B are schematic diagrams showing a structure of a conventional line width management pattern, wherein FIG. 6A is a plan view and FIG. 6B is a cross-sectional view taken along the line YY.

[Explanation of symbols]

1 chip 2 scribe line 10 Exposure area on substrate (for one shot by exposure device) 20 line width management pattern 30 basic cells 31,32 resist pattern 33 element isolation pattern 34 contact hole pattern 35 Si substrate 36 Polysilicon film

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Claims (7)

(57) [Claims] 1. A top surface, a bottom surface, and a horizontal profile in a vertical profile of a pattern formed in the chip and arranged on a scribe line for dividing a plurality of chips formed on a substrate from each other. A basic cell in which a maximum portion and a minimum portion of the resist film thickness, which are generated based on the mutual relationship between the densest area and the sparsest area in the above, and the vertical profile and the horizontal profile, are reproduced in a plurality of patterns. has the basic cell was divided by the scribe line
One shot with a projection exposure apparatus that includes multiple chips
A line width management pattern formed at least in the corners and center of the exposure area on the substrate . 2. The line width management pattern according to claim 1, wherein the basic cell includes a representative pattern of each layer forming the pattern. 3. The line width management pattern according to claim 1, wherein the representative pattern is a part of a pattern formed in the chip in each of the layers. 4. The line width management pattern according to claim 1, wherein a plurality of the basic cells are regularly arranged. 5. A pattern formed in the chip based on a line width measurement value obtained by irradiating the line width management pattern according to claim 1 with an electron beam. Line width management method to manage line width. 6. The line width management method according to claim 5, wherein the pattern formed in the chip is a photoresist pattern. 7. The line width management method according to claim 5, wherein the pattern formed in the chip is a pattern formed in at least the uppermost layer of the circuit pattern.