KR0161593B1 - A photomask and a method of making the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask used in a photolithography process in a manufacturing process of a semiconductor device, the configuration of which is a first etching pattern 41 and a phase inversion region, which are phase inversion regions, on a transparent quartz substrate 40. An etching pattern 42, and the second etching pattern 42 has a phase of (2n + 1) π times the phase of light passing through the unetched substrate surface and has an etch depth that allows light to pass therethrough. It is formed to have. According to the above-mentioned phase inversion mask, the area | region which interferes while light cancels between the phase inversion area | region and a phase inversion area | region becomes wide, and the space | interval between patterns becomes large.

Description

Photomask and its manufacturing method

1A is a cross-sectional view showing the structure of a substrate-etched chromium-free mask as an example of a conventional photomask.

Figure 1b is a cross-sectional view showing the structure of a half-lon PSM (phase shift mask) as another example of a conventional photomask.

2A to 2D are enlarged cross-sectional views showing a partial structure of the chromium-free PSM when the photoresist pattern is formed using the substrate-etched chromium-free PSM of FIG. 1a, and a phase profile of a transmissive exposure source. , A graph showing the intensity of the exposure source and the profile of the exposed photoresist pattern, respectively.

3A to 3D are enlarged cross-sectional views showing a partial structure of the PSM when forming the photoresist pattern using the halftone PSM of FIG. 1B, a phase profile of a transmitting source, intensity of the exposure source, and photoresist Graph showing each profile's profile.

FIG. 4A is a cross-sectional view showing the structure of a conventional substrate-etched chromium-free PSM having uneven portions repeatedly formed with minute widths on a substrate surface corresponding to a patternless pattern.

4B is a cross-sectional view showing the structure of a conventional rim type PSM in which a light shielding film is formed on a substrate corresponding to a patternless pattern.

5A to 5C are cross-sectional views showing the structure of the PSM when the pattern is formed using the substrate-etched chromium-free PSM of FIG. 4A, the phase profile of the transmissive exposure source, and the intensity profile of the exposure source. Showing graph.

6 is a cross-sectional view showing the structure of a substrate-etched chromium-free PSM according to the first embodiment of the present invention.

FIG. 7 is a partial cross-sectional view illustrating a loss state of light transmitted through each etched groove when exposed using the PSM of FIG. 6. FIG.

8A to 8C are cross-sectional views showing the structure of the PSM when the pattern is formed using the substrate-etched chromium-free PSM of FIG. 6, the phase profile of the light source to pass through, and the intensity profile of the light source. Section showing.

9 is a cross-sectional view showing the structure of a substrate-etched chromium-free PSM according to a second embodiment of the present invention.

10A to 10C are cross-sectional views showing a structure of a PSM according to a third embodiment of the present invention, and a graph showing a phase profile and an intensity profile of an exposure source for an exposure source passing through the PSM.

11A and 11B are sequential manufacturing process diagrams illustrating a process of manufacturing a PSM according to a third embodiment.

* Explanation of symbols for main parts of the drawings

40: transparent quartz substrate 41: etching part

42,42a: phase inversion part

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a photomask used in a photolithography process of a semiconductor device manufacturing process. More specifically, the substrate is formed by etching a substrate to form a region that does not invert the phase of light and a region that inverts the phase It relates to an etch-free chromium phase inversion mask (a Cr-less phase mask of substrate etching type).

As semiconductor devices are highly integrated, in order to form fine patterns, the use of a phase inversion mask (hereinafter referred to as PSM) is inevitable. Such PSMs are classified into two types of masks. One is a PSM having a structure etched such that the surface of the transparent quartz substrate 10a has a predetermined pattern 11a as shown in FIG. 1a (hereinafter referred to as substrate etched PSM), and the other is shown in FIG. 1b. As shown in Fig. 2, the half-tone PSM has a structure in which the semi-transmissive film 11b is formed on the quartz substrate 10b instead of the light shielding film. Although this half-tone PSM transmits light through the transflective film 11b, its transmittance is in the range of about 5-20% and the light transmitted through the transflective film 11b is 180 to the incident light. It has a phase inversion of °. This semi-transmissive film 11b is called a half-tone film.

Of the two types of PSMs described above, substrate-etched PSMs, especially substrate-etched Cr-less masks, have a much better effect than the half-tone PSMs in forming patterns. That is, by using the chromium-free substrate etching mask, a pattern profile superior to the half-tone PSM can be formed on the wafer.

2A to 2D show a partial structure of the chromium-free mask, the phase profile of the exposure source to pass through, the intensity of the exposure source, and the case where the chromium-free mask of FIG. 1a is used. This is a graph showing the profiles of the photoresist pattern.

Conventional substrate-etched chromium-free PSMs (see FIG. 1a) are shown in FIG. 2a and FIG. 2b, where light is transmitted with a phase of 0 ° (convex non-etched portions) and 180 °. It has a mask pattern 11a which is divided into a region (concave etching part) having a phase inverted and transmitted.

When the photoresist pattern is formed on the wafer using such a mask, the photoresist pattern 21a is formed on the substrate 20a corresponding to both regions as shown in FIG. 2D. However, in the case of the half-tone PSM, the photosensitive film pattern is not formed corresponding to the region (halftone film) inverted by 180 degrees.

As described above, the substrate-etched chromium-free PSM has a distinct interface between the pattern and the pattern in forming the pattern, so that the best pattern profile of the PSM developed to date can be realized as shown in FIG. However, in the case of the mask it was difficult to adjust the pattern spacing.

Referring back to Figure 2b, the spacing between the pattern and the pattern (i.e., the concave and convex portions in the mask pattern) is the region where the phase inverted lights between the two patterns disappear due to the destructive interference. In this way, it is an area that is extinguished by offset interference. This canceled and extinguished region is the same as the unexposed region because the energy of light appears as zero as shown in FIG. 2C. That is, in the interval between patterns, the energy of light passing through the interface between the non-inverted region (non-etched portion) and the inverted region (substrate etched portion) is represented by zero. And the width of this interval (w = w1 + w2 = 2w1) is theoretically constant. This is because the spacing between the two patterns is large or small on both sides. Therefore, it is difficult to manage the line width between patterns.

If the two patterns are far apart, since no pattern should be formed between the patterns, the light should be blocked. However, the substrate-etched chromium-free PSM also has a problem of weakening in the above-described case.

3A to 3D are cross-sectional views showing a partial structure of the PSM in the case of using the halftone PSM of FIG. 1B, a phase profile for a light source that passes through, an intensity of the light source, and a profile of the photoresist pattern, respectively. This graph is shown.

A conventional halftone PSM (see FIG. 1B) is a half-transmitted half having a phase of 0 ° and a phase inverted to 180 ° as shown in FIGS. 3A and 3B. It has a mask pattern divided by the tone film 11b.

When the photoresist pattern is formed on the wafer using the halftone mask, as illustrated in FIG. 3D, the photoresist pattern 21b is formed on the substrate 20b corresponding to the region having the phase of 0 ° and being transmitted. Is formed. However, in response to the halftone film 11b inverted by 180 °, the photosensitive film pattern is not formed because the intensity of transmitted light is relatively small as shown in FIG. 3C.

Referring back to FIG. 3b, at the interval between the pattern and the pattern, i.e., the region having a phase of 0 ° and the halftone film 11b inverted to 180 °, the phase inverted lights disappear due to mutual interference. Since the intensity of light passing through the halftone film 11b is much smaller than the region transmitted with the phase of 0 °, the interval becomes narrower as the intensity of light is weaker.

That is, as shown in FIG. 3d, the interface between the region transmitted through the phase of 0 ° and the halftone film 11b inverted to 180 ° corresponds to the region transmitted through the phase of 0 ° as shown in FIG. 3d. Although the distance w1 of the photosensitive film pattern 21b formed on the substrate 20b is wide, the distance w2 between patterns formed corresponding to the halftone film 11b transmitted by inverting to 180 ° is relatively larger than w1. As a result, the spacing (w1 + w2, w1w2) between the patterns becomes relatively narrow. As described above, the halftone PSM has an advantage of easily controlling the spacing between the patterns than the substrate-etched chromium-free PSM. However, as described above, the halftone PSM has a problem in that the halftone PSM is less than the substrate-etched chromium-free PSM. have. Therefore, in order to achieve high integration of the semiconductor device, it is preferable to use a substrate-etched chromium-free PSM.

In addition, as can be seen from FIGS. 2b and 3b, when the substrate-etched chromium-free PSM is used, the pattern area closer to zero with the phase of integration at the interface of the pattern is closer than that of the halftone PSM. Since it can be formed widely, the overlap between the patterns is reduced, so that the proximity effect is also small, and thus a finer pattern can be formed.

As such, it is well known in the art that the substrate-etched chromium-free PSM has the most excellent effect among the various PSMs in forming the micropattern. have.

For example, in the case of forming a fine pattern using a substrate-etched chromium-free PSM, it is particularly difficult to control the space between the pattern and the pattern.

Therefore, recently, two mask formation techniques for managing the spacing of patterns have been developed. One is a technique of forming a mask by etching the substrate at minute intervals to form a minute uneven portion on the surface of the substrate, and the other is a technique of forming a mask by forming a light shielding film on the substrate. Masks formed by the latter technique are commonly referred to as rim type PSMs.

FIG. 4a shows the structure of the substrate-etched chromium-free PSM formed by the former technique, and FIG. 4b shows the structure of the rim-type PSM formed by the latter technique.

As shown in FIGS. 4A and 5A to 5C, the surface of the substrate 30a has a PSM substrate (Fig. 4a or 5a) having uneven portions 31a repeatedly etched at minute intervals. When the photosensitive film pattern is formed by using the light emitting pattern, light is not sufficiently transmitted through the uneven portion 31a formed on the substrate 30a (see FIG. 5C). It becomes low and the pattern of the photosensitive film is not formed. That is, since the intensity of light transmitted through the uneven portion 31a is very low, the photosensitive film pattern is not formed corresponding to the uneven portion. Thus, the area | region in which the photosensitive film pattern is not formed is called a no pattern hereafter.

When the photosensitive film pattern is formed using the rim type PSM shown in FIG. 4B, the light shielding film 31b is formed on the surface of the substrate 30b so as to correspond to the area where the pattern is not to be formed. The light is blocked by 31b) so that no pattern is formed in correspondence to the light shielding film.

On the other hand, when the exposure process is performed using a substrate-etched PSM having a fine uneven pattern corresponding to the non-pattern, when the short wavelength of light is used as the exposure source, the gap between the uneven patterns should be made smaller.

In general, light used as an exposure source of a wafer is changing from a G-line (λ = 483 nm) to an i-line (λ = 365 nm) and a DUV (deep ultra-violet = KrF: λ = 248 nm). ArF excimer laser (λ = 193 nm) is expected to be used. Therefore, the uneven pattern must be formed very finely.

However, the light used to manufacture the photomask (including the phase inversion mask) is a photomask manufactured by using a laser or an electron-beam than the photomask manufactured using the ArF excimer laser beam described above. The resolution of wafer exposure is poor. Therefore, as the wavelength of light used for exposure becomes shorter, inevitably, the uneven pattern in the photomask must be further refined, which causes a problem of making the photomask more difficult.

Such a problem makes it difficult to design a photomask, to a manufacturing process including a data processing, a capacitance, an exposure, a development and an etching, and an inspection process, and thus it is difficult to expect a proper yield of a semiconductor device. In addition, the manufacturing cost has been significantly increased, it was a problem that it is difficult to put to practical use.

In addition, there is a method of using X-rays as a method of manufacturing a photomask with shorter wavelengths of light shorter than lasers and electron beams currently in use. This method has a problem that it is very difficult to manufacture a photomask because the lens system can not be designed to implement a pattern size of 1: 1 with the wafer.

In addition, the photomask in which the light shielding film is formed has an advantage of excellent light shielding effect and easier manufacturing than a method of forming a fine concavo-convex pattern, but it is possible to form the light shielding film only when there is no pattern in a wide area, and Where a pattern is needed, there is a problem that the effect cannot be expected. Moreover, when using the photomask in which the light shielding film was formed, there was also a problem that the trouble of having to perform alignment exposure again in the exposure process was followed.

Accordingly, an object of the present invention is proposed to solve the problem that the above-described disadvantages of the conventional substrate-etched chromium-free PSM cannot be used in a highly integrated pattern. To provide a substrate-etched chromium-free PSM that can obtain a gap of.

According to one aspect of the present invention for achieving the above object, the first etching pattern 41 formed between the phase non-etched phase inversion region on the transparent quartz substrate 40 and the second etching pattern formed of the phase inversion region In the photomask having 42, the second etching pattern 42 includes a plurality of irregular patterns repeatedly formed, and the etching portions of each of the irregular patterns have a phase of light that passes through the unetched substrate surface. It has a phase of (2n + 1) π times and has an etching depth set to transmit light.

In this photomask, a light shielding film 43 is formed on the non-etched phase non-etching region between the respective patterns of the first etching pattern 41.

In this photomask, the light shielding film 43 is a chrome film.

In this photomask, an etching depth of an etching portion of each of the uneven patterns is relatively deeper than that of the first etching pattern 41.

In the photomask, sidewalls of the second etching patterns 42 are inclined with respect to the surface of the quartz substrate 40.

In this photomask, the inclination is set within a range of about 70 ° to 90 °.

According to another feature of the present invention, a method of manufacturing a photomask having a first etching pattern 41, which is a phase inversion region, and a second etching pattern 42, which is a phase inversion region, on a transparent quartz substrate 40, Applying a photoresist film (45) to only the first etching pattern (41) except for the second etching pattern (42); And etching the second etching pann 42 to be deeper than the etching depth of the first etching pattern 41 by performing dry etching.

In this method, the dry etching process of the second etching pattern has a phase of (2n + 1) π relative to the phase of light passing through the unetched substrate surface until the light has an etching depth to allow light to pass therethrough. Is executed.

In this method, the sidewall of each pattern of the second etching pattern is formed to have a slope by the dry etching process.

In this method, the dry etching process uses a mixed gas obtained by mixing a gas of CHF ₃ or CF ₄ with O ₂ gas as an etchant.

In this method, the mixing ratio of the mixed gas is set within the range of about 10: 1 to 4: 1.

In this method, the dry etching process is performed under conditions of low pressure of about 150 m Torr or less and high power of about 400 W or more.

According to the above-mentioned phase inversion mask, the area | region which interferes while light cancels between the phase inversion area | region and phase inversion area | region becomes large, and the space | interval between patterns becomes large.

Best Mode for Carrying Out the Invention Embodiments of the present invention will be described below with reference to FIGS. 6 to 11.

Example 1

Referring to FIG. 6, the novel photomask of the present invention includes a mask pattern having an etching portion 41 formed on the surface of the substrate 40 and a phase inversion portion 42 for forming a patternless pattern on the wafer. However, the phase inversion portion 42 is formed of a concave-convex pattern having a plurality of fine repeating patterns and is etched deeper than the etching depth of the etching portion 41. A portion which is not etched between the etching portions 41 is a phase non-inverting region through which light is transmitted without phase inversion. In general, the deeper the etching depth of the substrate, the poorer the an intensity profile of light appears, which is why the light passing through the substrate 40 is lost, as shown in FIG. Because.

That is, FIG. 7 shows that light is lost in an etching portion having a larger etching depth among the various etching portions formed on the substrate 40, and the phase inversion portion 42 removes one etching portion of the uneven pattern. As an example. Specifically, light passing through the substrate 40 is diffracted as it is emitted into the air, and is reflected and refracted on the sidewall of the substrate 40 which is partially etched in the diffracted light. At this time, the light passing through the above-described photomask has a phase and intensity profile as shown in FIGS. 8B and 8C due to the loss of light in the phase inversion portion 42.

As shown in FIG. 8B, the profile of the intensity of light passing through the photomask of the present invention is lowered as a whole although the integral value thereof does not change. Therefore, between the etching portion 41 and the phase inverting portion 42 adjacent to each other, the area where the light interferes with each other becomes wider, thereby increasing the distance between the patterns. That is, as can be seen in FIG. 8, the interval w2 or w3 between the etching portion 41 and the phase inversion portion 42 adjacent thereto is wider than the interval w1 between the etching portions 41. do. As such, if the etching depth of the phase inversion part is deep, the loss of light increases due to diffraction and dispersion of the light, and thus the pattern interval is widened. The etching depth may be formed such that light passing through the phase inversion region has a phase difference of 180 ° (π) with light passing through the non-inversion region. That is, the light passing through the phase inversion region 42 is 3π, 5π, 7π,... As such, the etching depth of the phase inversion region 42 is determined so that the phase can be transmitted with an odd multiple of pi.

In addition, the etching depth is usually dependent on the material of the substrate. In the case of quartz substrates, which are most commonly used, etching portions may be formed to have a depth similar to the wavelength of light used as an exposure source. In other words, the substrate may be etched to a depth of about 3650 Å (365 nm = 0.365 μm) in the i-line (exactly 361 mm).

Where D is the etching depth,? Is the light source wavelength used, n is the refractive index of the substrate, and n _QZ = 1.51.

Accordingly, the photomask according to the present invention is a substrate etched micro mask set to an integer multiple of the wavelength of the exposure source corresponding to the etching depth of the substrate.

When the fine photoresist pattern is formed using the photomask according to the above-described embodiment, the gap between the pattern and the pattern can be effectively controlled by adjusting the etching depth of the phase inversion region of the photomask.

In addition, the phase inversion mask according to the present invention can be effectively used even in a highly integrated pattern, since a fine pattern interval can be obtained on the wafer even without a mask pattern that is not fine.

Example 2

Referring to FIG. 9, the photomask according to Embodiment 2 includes a chromium film 43, which is a light shielding film, between the etching portions 41 in the structure of the photomask according to Embodiment 1 (the structure shown in FIG. 6). The structure is the same as that of FIG. 6 except that it is formed on a region, that is, an unetched region. In FIG. 9, components having the same functions as those shown in FIG. 6 are given the same reference numerals, and description thereof will be omitted.

Specifically, in this embodiment, the photomask includes an etching portion 41 and a phase inversion portion 42 formed on the surface of the substrate 40, the phase inversion portion 42 is formed of a plurality of etching portions And etched deeper than the etch depth of the etched portion 41, and the light shielding film 43 is formed on an unetched portion (phase inversion region) between the etched portions 41. Has The light shielding film 43 is made of chromium.

Referring back to FIG. 9, light is lost in an etching portion having a larger etching depth among various etching portions formed in the substrate 40. That is, light passing through the substrate 40 is diffracted as it exits into the air, and is reflected and refracted on the sidewall of the substrate 40 which is partially etched in the diffracted light. At this time, loss of light passing through the phase inversion region occurs. Therefore, the area where the light is canceled and aroused at the interface between the phase non-phase inversion area and the phase inversion area becomes wider. Therefore, the effect of widening the spacing between patterns can be expected.

Example 3

Referring to FIG. 10A, the photomask according to Embodiment 3 is a photomask according to Embodiment 1 except that an etching portion of each uneven pattern of the phase inversion region 42 is formed with a slope. Is the same as the structure). In FIG. 10A, the same reference numerals are given to components having the same functions as the components shown in FIG. 6, and the description thereof is omitted.

In this embodiment, the photomask includes an etching portion 41 and a phase inversion portion 42a formed on the surface of the substrate 40, wherein the phase inversion portion 42a is formed of a plurality of uneven patterns. Each uneven pattern is etched deeper than the etch depth of the etched portion 41, and the uneven pattern is etched to have a slope inclined at a predetermined angle with respect to the surface thereof.

Referring back to FIG. 10B, since the phase inversion portion 42a of the photomask is formed of a plurality of grooves (grooves) having an inclination, light diffracted while passing through the grooves is dispersed. This scattered light affects adjacent patterns (usually offsetting interference), resulting in much lost light. As a result, the offset interference generated at the boundary portion with the adjacent pattern occurs in a considerably wide range. Therefore, the distance from the adjacent pattern becomes wider. This means that the deeper the etching depth of the phase inversion part 42a (if the phase of the light passing through it is inverted by 180 ° with the adjacent pattern), the wider the range of offset interference becomes, and thus the gap between the patterns. Also means widening. In the drawing, reference numeral 44 denotes a reduction projection lens for focusing light passing through the mask.

Meanwhile, referring to FIGS. 11A and 11B, a method of manufacturing a photomask according to this embodiment is a phase inversion region on a photomask in a conventional method of manufacturing a structure of a conventional substrate etched phase inversion mask. Etching the etching pattern of the step further includes.

Specifically, in FIG. 11A, the photosensitive film is applied and developed on the substrate 40, whereby the photosensitive film pattern 45 is formed so that only the phase inversion portion 31a of the conventional substrate etch type phase shift mask is lean. Next, a dry etching process using a mixed gas obtained by mixing a gas of CHF ₃ or CF ₄ with O ₂ gas is used as an etchant. At this time, it is carried out under conditions of low pressure (about 150 m Torr or less), high power (about 400 W or more), and the mixing ratio of the mixed gas (CHF ₃ or CF ₄ gas: O ₂ gas) than the normal dry etching process. Determined in the range of approximately 10: 1 to 4: 1.

When dry etching is performed in this way, as shown in FIG. 11B, an etching pattern having a slope is formed in the phase inversion region 42a. The inclination is set within a range of about 70 ° to 90 ° with respect to the surface of the quartz substrate 40.

As described above, in this embodiment, the phase inversion region is composed of an etch pattern having a slope, so that the area where the phase inversion region interferes while light cancels between the phase inversion regions is widened, and thus, the spacing between patterns is widened. Effect.

In addition, the phase inversion mask having a phase inversion pattern having a slope according to the present invention can be effectively used to implement a high integration pattern because a finer pattern interval can be obtained on a wafer even without a mask pattern that is not fine.

Furthermore, since the phase inversion mask formed according to the manufacturing method of the present invention can control the etching depth and the etch shape of the phase inversion region by etching the substrate, it is possible to use a fine mask pattern having a fine pattern, a pattern interval, or an uneven pattern. It is possible to form a fine pattern on the wafer without forming.

Claims (11)

A photomask comprising a first etching pattern 41 formed between an unetched phase non-etching region on a transparent quartz substrate 40 and a second etching pattern 42 formed of a phase inversion region. The pattern 42 has a plurality of uneven patterns repeatedly formed, and the etched portion of each uneven pattern has a phase of (2n + 1) π times the phase of light passing through the unetched substrate surface and the light passes through A photomask having an etching depth set to be. The photomask according to claim 1, wherein a light shielding film (43) is formed on said unetched phase non-etching region between said patterns of said first etching pattern (41). The photomask of claim 2, wherein the light shielding film (43) is a chromium film. The photomask according to claim 1, wherein an etching depth of an etching portion of each of the uneven patterns is relatively deeper than that of the first etching pattern (41). The photomask according to claim 1, wherein the second etching pattern (42) has sidewalls formed with an inclination with respect to the surface of the quartz substrate (40). The photomask of claim 5, wherein the inclination is set within a range of 70 ° to 90 °. In the method of manufacturing a photomask having a first etching pattern 41, which is a phase inversion region, and a second etching pattern 42, which is a phase inversion region, on a transparent quartz substrate 40, on the quartz substrate 40. Forming a photoresist pattern (45) for opening only the second etching pattern (42) by application and development of the photoresist layer on the substrate; And etching the second etching pattern (42) deeper than the etching depth of the first etching pattern (41) by performing dry etching. The method of claim 7, wherein the dry etching of the second etching pattern has a phase of (2n + 1) π times the phase of light passing through the unetched substrate surface and has an etching depth such that the light is transmitted. Method of manufacturing a photomask, characterized in that executed to. The method of claim 8, wherein the sidewalls of the patterns of the second etching pattern are inclined by the dry etching process. The method of claim 9, wherein the dry etching process comprises using a mixed gas of a mixture of CHF ₃ or CF ₄ gas and O ₂ gas in a ratio of 10: 1 to 4: 1 as an etchant. Way. The method of claim 10, wherein the dry etching process is performed under a condition of low pressure of 150 m Torr or less and high power of 400 W or more.