JPH0321952A - Photomask and production thereof - Google Patents

Abstract

PURPOSE:To prevent a change in the line width of a continuous pattern at the connected part by reducing the light transmissivity of the dividing boundary regions of the substrates of photomasks. CONSTITUTION:When a continuous pattern 4 is formed in a resist film 5 with the Cr patterns 2, 2' of 2 photomasks, the light transmissivity of the terminal regions 3 of the quarts glass substrates 1 of the photomasks is reduced to about 1/2 by implanting Ga ions and exposure in sections is carried out with the treated photomasks to form a pattern 4 with no change in the line width. The resist film 5 is positive and the region 6 is a double-exposed region. Since the total quantity of energy applied to the resists by double exposure is made equal to the quantity of energy applied to the other parts, the pattern is not thickened or thinned at the boundary region.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a photomask for divided exposure that projects and transfers continuous patterns to each other, and an object of the present invention is to avoid changes in pattern width in areas that are printed in duplicate. The light transmittance of the mask substrate is set to 1 so that the total amount of effective light energy for overlapping exposure is approximately equal to the non-overlapping area.
It is assumed that it is extinct.

The method of the present invention utilizes ion implantation to reduce optical transmission.

[Industrial application field]

The present invention is a reticle used in the manufacture of semiconductor devices.
It is related to masks, especially photomasks that divide a single pattern and project and transfer it.

The use of photolithography technology in the manufacture of semiconductor devices. Initially, it was started by transferring patterns one wafer at a time. In other words, one photomask has 1
All of the patterns of a plurality of chips included in a single wafer were provided, and the pattern was exposed in close contact with a photoresist film.

Later, as integrated circuits became more highly integrated and the patterns to be transferred became finer, high-quality masks for each chip were prepared, and the wafer was repeatedly printed while shifting the chip size in the X/Y directions. It became so. This is a process called step-and-repeat, and the mask used is called a reticle mask. In order to make a reticle mask defect-free, it is advantageous to enlarge the pattern to be transferred onto the object, so a method is generally adopted in which the pattern is reduced and printed at the time of transfer.

If we further advance the idea of dividing the mask structure from a wafer into chips, we will arrive at a method in which the pattern for one chip is also divided and step-and-repeat exposure is performed. One of the features of this method is that even if the chip size increases, the mask pattern can be magnified at a high rate without deteriorating its quality. An example of this is that the parts where are repeatedly arranged can be processed with one mask.

Since this chip division method sequentially transfers continuous Bakun, in order to avoid discontinuities in the pattern at the division boundary, the division boundary area is included in both adjacent masks, and that part is Duplicate printing is usually done. The photomask handled by the present invention is related to such a chip division method.

[Prior art and the problem to be solved by the invention] In photolithography, the effective boundary between exposure and non-exposure, which determines the position of the edge of the resist pattern after development, changes slightly depending on the amount of exposure. It is well known to those skilled in the art to do so. For example, g for novolac resists
In lithography with line ultraviolet light, an expansion of the photosensitive area of 2 to lOnn+ occurs per millijoule. In the above-described tinop division method, the division boundary area is exposed twice, so if left as is, the pattern width passing through the division boundary area will change. This state is illustrated in FIG. 3, where the width of the strip-shaped continuous pattern 4' cut in the resist film 5 is
It is narrow in the double exposure amount area 6.

This narrowing of the pattern width is due to the
When a window is opened in a negative resist using a mask as shown in the figure, and when a band-shaped window is opened in a positive resist, the pattern width is partially expanded.

An object of the present invention is to provide a photomask that does not cause pattern dimension changes in multiple exposure areas in chip-divided photolithography, thereby facilitating the manufacture of semiconductor devices with larger chip sizes. It's about getting used to it.

[Means to solve the problem]

In order to achieve the above object, the photomask of the present invention is a photomask used in a process of dividing a pattern to be shaped by projection transfer and completing one pattern by projecting and transferring each divided pattern, and comprising: The light transmission of the division boundary area of the photomask substrate is controlled such that the total amount of light energy irradiated to the division boundary area overlapped in the process is approximately equal to the amount of light energy irradiated to the non-overlapping area. The ratio is reduced.

Further, claim (2) is a method for manufacturing the photomask.
The invention is characterized in that ions are implanted into a region of the substrate where the light transmittance is reduced.

[For production]

Usually, the above boundary area, ie the seam part of the pattern, is 2
Since the resist is exposed twice, the light energy supplied to the resist is twice that of the other parts. If the light transmittance of this part of the mask substrate is reduced by 1/2, the total amount of energy given to the resist by two exposures will be the same as the amount of energy given to the other parts, and the No enlargement or thinning of the pattern will occur.

The above discussion suggests that the light energy should be applied to the entire wavelength range that sensitizes the resist, but approximately the same effect can be obtained by reducing the transmittance of the wavelength light representative of the wavelength range to 1/2. . Furthermore, even if the total amount of energy given to the overlapping exposure areas is not the same, a corresponding effect can be expected by reducing the amount each time.

If you think about it in terms of pattern seams, there are 4 in the shape of a square.
When multiple patterns are arranged, a region exposed four times occurs in the center, so the transmittance of this region is set to 1/4 of that of the non-overlapping region. However, the purpose of the present invention is to
The goal is not to accurately equalize the total amount of light energy, but to keep the enlargement or thinning of the pattern within an allowable range, so there is no problem in increasing the amount of irradiation light even in multiple exposure areas as long as it is within the allowable range. .

In this specification, the amount of energy is concerned only with light in a wavelength range that sensitizes the resist, and it goes without saying that light energy in a wavelength range that does not sensitize the resist is also considered a problem. "Effective" in the claims has this meaning.

In the photomask manufacturing method of the present invention, ions such as Ga'' are implanted into the glass substrate of the photomask. This is shown in Figure 2. In the figure, the horizontal axis is the wavelength of light, and the vertical axis is the light transmittance after implantation, and the implantation conditions are an acceleration voltage of 20 KeV and a dose of 2 XIO15cr6.
−”.

As is clear from the figure, the light transmittance of the g-line (434 nm) commonly used in ultraviolet lithography is approximately 76
%, and by increasing the dose, the light transmittance can be adjusted to a desired value.

〔Example〕

FIG. 1 shows the edge of a photomask for forming a continuous pattern. 3A shows the right end of the first photomask, and FIG. 1A shows the left end of the second photomask. These may be the right and left ends of the same mask.

Cr patterns 2 and 2' provided on both masks
As a result, a continuous pattern 4 as shown in FIG. 3(C) is formed on the resist film 5. At the end of the substrate 1 made of quartz glass, the light transmittance of the region 3 is reduced by implanting Ga ions to approximately N'l/2.

When divisional exposure is performed using a photomask treated in this manner, a pattern material with no change in line width is formed as shown in FIG. 1(C). Here, the resist film 5 is of a positive type, and a region 6 is a double exposed portion.

In this example, selective ion implantation using a mask is performed as a process to reduce the light transmittance of the substrate.
Although the implantation is performed uniformly in all the overlapping parts, if the implantation is performed using a focused ion beam, the required time can be shortened by limiting the process to the part adjacent to the Cr pattern.

In addition, in the present invention, a semi-transparent film is provided on the edge region of the glass substrate to absorb light in a predetermined wavelength range, or a thin metal film is deposited to reflect a part of the irradiated light. A similar effect can also be obtained.

[Effects of the Invention] As described above, according to the present invention, even in photolithography using a divided mask, the line width of the continuous pattern does not change at the connection portion.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the processing of the present invention, Figure 2 is a diagram showing the change in light transmittance due to ion implantation. FIG. 3 is a diagram showing line width changes in the divided mask method, In the diagram 1 is glass base t anti, 2, 2′ is Cr pattern, 3 is a low transmittance region at the edge of the substrate, 4,4' is a continuous pattern, 5 is a resist film; 6 is double exposure area It is. Schematic diagram showing the process of the present invention No. 1 figure

Claims (2)

[Claims] (1) A photomask used in the process of dividing a pattern formed by projection transfer and completing one pattern by projecting and transferring each divided pattern, and dividing boundary areas that are exposed repeatedly in the process. The light transmittance of the division boundary area of the photomask substrate is reduced so that the total amount of effective light energy irradiated to the photomask substrate is approximately equal to the amount of effective light energy irradiated to the non-overlapping area. photomask. (2) A method for manufacturing a photomask according to claim (1), characterized in that ion implantation is performed into a region of the substrate where light transmittance is to be reduced.