CN1245662C - Reticle and method for reducing lens aberration and pattern shift - Google Patents

Abstract

A light shield capable of reducing lens aberration and pattern shift comprises a transparent substrate and a light shield layer, wherein the light shield layer is arranged on the transparent substrate and is provided with a plurality of groups of pattern areas and a plurality of auxiliary patterns, the auxiliary patterns are arranged in the groups of pattern areas, each auxiliary pattern is equidistant to the two groups of patterns above and below the auxiliary pattern, and the length of each auxiliary pattern is equal to the width of the corresponding group of patterns. A method for reducing lens aberration and pattern shift, comprising: providing a semiconductor substrate, covering a photoresist layer on the semiconductor substrate, forming patterns in the photoresist layer by a photomask, wherein each pattern is equidistant to the upper and lower arrays of patterns, the length of the pattern is equal to the width of the arrays of patterns, and performing an etching step by using the patterned photoresist as a mask to form an array of trench regions in the semiconductor substrate. According to the photomask and the method of the invention, the critical dimension among the array patterns can obtain better consistency, and the phenomenon of pattern shift can be effectively reduced.

Description

Reticle and method for reducing lens aberration and pattern shift

technical field

The present invention relates to the design of a photomask and the process method of applying the photomask, in particular to a method for reducing lens aberration (lens aberration) to improve the consistency of critical dimensions (CD) between array patterns (array patterns) A photomask and method for eliminating pattern displacement caused by off-axis illumination (OAI).

Background technique

In the semiconductor manufacturing process, lithography uses a step-by-step or scan-by-scan exposure program to expose a wafer in sections to gradually complete the exposure of the entire wafer. Before lithography, the parameters that affect the lithography results must be fine-tuned and optimized. These lithography process parameters include photoresist thickness, baking/cooling temperature and time, development method and time, exposure dose, focal length compensation and numerical value. Aperture (Numerical Aperture, NA), etc. Next, etching is used to transfer the photoresist pattern produced by the lithography process to the material under the photoresist. Similarly, etching parameters such as: gas ratio, gas flow rate, bias power, temperature and etching mode, etc., also need to be passed in advance. Fine-tuning so that the final desired key size is achieved. However, in the traditional process, during the post-etching inspection (After Etching Inspection, AEI), it will be found that there are differences between the CDs of the array pattern area in the wafer, and this difference will cause some irreparable defects, such as in The open circuit phenomenon of the contact hole (contact hole) obtained by the electrical acceptance test (Wafer Acceptance Test, WAT), these defects will seriously affect the yield.

One of the reasons for the CD difference between the array patterns in the wafer is the lens (lens) of the optical system in the lithography equipment, which produces lens aberrations. Common lens aberrations such as spherical aberration (spherical), Astigmatism, coma, field curvature and distortion, etc. The formation of the above-mentioned various lens aberrations is not only due to the inherent defects in the design and manufacture of the lens material itself, but also due to the diffraction phenomenon generated when the irradiated light passes through the mask pattern and the lack of light transmittance of the mask pattern itself. Also related.

In addition, the off-axis luminescence technology that can increase the depth of focus (DOF) and improve the resolution without changing the mask design and maintaining the original resist parameters is a major progress in improving the quality of lithography. Axial lighting became standard equipment on new steppers. However, as the depth of focus increases, the light intensity of off-axis luminescence must also be continuously increased. As a result of continuously increasing the light intensity, the received dose on the resist is often difficult to control, and the exposure pattern shift deviation occurs. Phenomenon. If this phenomenon cannot be effectively improved, in the process of making wafers in the future, such as when aligning the position of the previous underlying layer (previous underlying layer) components, it will inevitably cause so-called overlap errors, and Unexpected openings or shorts occur, resulting in serious loss of product.

Contents of the invention

The purpose of the present invention includes designing a photomask and a process method using the photomask so as to obtain better critical dimension consistency among array patterns and effectively reduce pattern shifting.

Therefore, the present invention designs a photomask that improves CD consistency and reduces pattern shift, including a light-transmitting substrate and a light-shielding layer, the light-shielding layer is disposed on the light-transmitting substrate, and has an array of pattern regions and multiple Auxiliary patterns (assist patterns), the above-mentioned auxiliary patterns are arranged in the array pattern area and wherein each auxiliary pattern is equidistant from the two array patterns above and below, and the length of the above-mentioned auxiliary patterns is equal to the width of the above-mentioned array patterns.

Wherein, the light-transmitting base of the photomask is made of quartz material, and the light-shielding layer is a chromium metal layer.

The present invention also provides a method for reducing lens aberration and pattern shift, which includes the following steps: providing a semiconductor substrate, covering a photoresist layer on the semiconductor substrate, and forming pattern, wherein the photomask has an array pattern area and a plurality of auxiliary patterns, the auxiliary patterns are arranged in the array pattern area and wherein each auxiliary pattern is equidistant from the two array patterns above and below, and make the above auxiliary patterns The length is equal to the width of the array pattern, and an etching step is performed to form an array trench region in the semiconductor substrate by using the patterned photoresist as a mask.

According to the photomask of the present invention, since the auxiliary patterns are added between the array patterns, the light transmittance of the array patterns is indirectly increased, and the setting of the auxiliary patterns can also effectively compensate for the problem of light intensity degradation at the edge of the pattern caused by light diffraction. , resulting in better consistency of critical dimensions among array patterns.

Furthermore, the auxiliary pattern also helps to control the obtained dose. If the pattern on the resist has the same and stable obtained dose, it can effectively reduce the occurrence of pattern shift and facilitate the alignment of the next layer.

Description of drawings

FIG. 1 is a schematic diagram showing a conventional photomask;

FIG. 2 is a schematic diagram showing a photomask of the present invention;

Figure 3 is a sectional view showing Figure 2;

Figure 4A is a schematic diagram showing a lithography process;

Figure 4B is a schematic diagram showing the etching process;

FIG. 5A shows the difference in critical dimensions between array patterns after the etching process using a traditional photomask (based on the 3θ deformation aberration as an evaluation basis);

FIG. 5B is a diagram showing the CD difference between array patterns after the etching process using the mask of the present invention (based on the 3θ deformation aberration as the evaluation basis);

FIG. 6A shows the CD difference between array patterns after the etching process using a traditional photomask (based on coma aberration as an evaluation basis);

FIG. 6B is a diagram showing CD differences among patterns in the array after the etching process using the mask of the present invention (coma aberration is used as an evaluation basis).

Symbol Description:

10-Reticle substrate

102-array pattern area

103-translucent substrate

104-shading layer

106-auxiliary pattern

112-Reticle

118-Wafer

120-photoresist

Detailed ways

In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, a preferred embodiment is specifically cited below, together with the accompanying drawings, and described in detail as follows:

First, a photomask substrate 10 is provided, which is composed of a light-transmitting base 103 and a light-shielding layer 104 (as shown in FIG. 3 ). The light-transmitting substrate 103 is made of, for example, quartz, and the light-shielding layer 104 is made of, for example, chromium metal.

Next, as shown in FIG. 2 , a photomask pattern is transferred onto the photomask substrate 10 by electron beam direct writing to form an array of pattern regions 102 , and an auxiliary pattern 106 is also transferred onto the photomask substrate 10 at the same time. Outside the array pattern area 102 and the auxiliary pattern 106 is the area of the light-shielding layer 104 that is not directly written and developed by the electron beam. The array pattern in this embodiment is an array pattern of grooves, but the present invention is not limited thereto, and may also be an array pattern specified by other process steps. The auxiliary patterns 106 are disposed in the array pattern area 102 and each auxiliary pattern maintains equidistant distances from the two array patterns above and below it. The width of the auxiliary pattern 106 is generally between 60-80 nanometers, preferably 70 nanometers, which is based on the principle that no additional patterns will be produced in the photoresist layer after exposure, and the length of the auxiliary pattern 106 makes it consistent with the above-mentioned array patterns. equal in width.

A general common lithography process is shown schematically in FIG. 4A. The light L generated by a light source generator (not shown) passes through the pattern areas 102, 106 in the mask 112, and is focused and imaged on the photoresist 120 on the wafer 118. . Afterwards, using the patterned photoresist 120 as a mask, a developing step is performed to form a pattern area 102, 106 in the photoresist 120 on the wafer 118, and then conventional wet etching or dry etching techniques can be used, The pattern on the photoresist is transferred into the substrate, as shown in FIG. 4B, to form, for example, an array of trenches.

It can be seen from the mask structure of the present invention (as shown in FIG. 2 ), that due to the addition of the auxiliary pattern 106, the light transmittance of the array pattern area on this mask is higher than that of the same array on the traditional mask (as shown in FIG. 1 ). The light transmittance of the pattern area is slightly increased. After the etching process, using the mask of the present invention, the CD consistency of each pattern in the array pattern area is better than that of the traditional mask. The following is a further explanation with the test data.

Among the five kinds of lens aberrations mentioned above, distortion aberration and coma aberration have the greatest impact on the results of this test, and among them, distortion aberration has the most significant impact on the results of 3θ. Therefore, this test is Using these two lens aberrations as the evaluation basis, two sets of test data were respectively obtained: the first set of test data (this test was conducted based on the 3θ deformation aberration as the evaluation basis) is as follows, and is illustrated in detail with Figures 5A and 5B. Using a traditional photomask, after exposure and etching, the measured key dimensions of the trenches are as follows: the left trench is 138.2nm; the right trench is 120nm, and the size difference between the two is 18.2nm (as shown in FIG. 5A ). Using the photomask of the present invention, after exposure and etching, the measured key dimensions of the trenches are as follows: the left trench is 140.5nm; the right trench is 132.2nm, and the size difference between the two is 8.3nm (as shown in FIG. 5B ). According to the above test data, if the photomask of the present invention is used, the 3θ deformation aberration can be effectively reduced by about 40%-60%.

The second set of test data (this test was conducted based on the evaluation of coma aberration) is as follows, and is described in detail with reference to Figs. 6A and 6B. Using a traditional photomask, after exposure and etching, the measured key dimensions of the trenches are as follows: the left trench is 134.2nm; the right trench is 145.8nm, and the size difference between the two is 11.6nm (as shown in FIG. 6A ). In addition, using the photomask of the present invention, after exposure and etching, the measured key dimensions of the grooves are as follows: the left groove is 134.5 nm; the right groove is 141.1 nm, and the size difference between the two is 6.6 nm (as shown in FIG. 6B ). According to the above test data, if the photomask of the present invention is used, the coma aberration can be effectively reduced by about 30%-50%.

In addition, the pattern displacement phenomenon caused by off-axis light emission has been significantly improved after using the mask of the present invention, and the displacement phenomenon of each pattern in the pattern area of the array is much less than that of the traditional mask. . The test data will be described in detail below. Using a traditional photomask, after exposure and etching, the deviation distance between the measured groove position and the original groove set position is as follows: the left groove is 10nm; the right groove is 10nm. In addition, using the photomask of the present invention, after exposure and etching, the deviation distance between the measured groove position and the original groove set position is as follows: left groove 2.5nm; right groove 2.5nm. According to the above test data, if the photomask of the present invention is used, the phenomenon of pattern shift can be effectively reduced by about 75%.

Claims (12)

1. A photomask that can reduce lens aberration and pattern shift, is characterized in that: described photomask comprises: a light-transmitting substrate; A light-shielding layer arranged on the light-transmitting substrate, wherein the light-shielding layer has a pattern area of an array and a plurality of auxiliary patterns, and the auxiliary patterns are arranged in the pattern area of the array, and each auxiliary pattern is connected with two sets of patterns above and below The patterns are equidistant, and make the length of the aforementioned auxiliary pattern equal to the width of the aforementioned array pattern. 2 . The mask capable of reducing lens aberration and pattern shift according to claim 1 , wherein the transparent substrate is a quartz substrate. 3 . The mask capable of reducing lens aberration and pattern shift according to claim 1 , wherein the light-transmitting substrate is a calcium fluoride substrate. 4 . 4. The mask capable of reducing lens aberration and pattern shift according to claim 1, wherein the light-shielding layer is a chrome metal layer. 5 . The mask capable of reducing lens aberration and pattern shift according to claim 1 , wherein the thickness of the light-shielding layer is between 150-200 nanometers. 6 . The mask capable of reducing lens aberration and pattern shift according to claim 1 , wherein the auxiliary pattern has a width of 60-80 nanometers. 7. A method capable of reducing lens aberration and pattern shift, comprising the following steps: providing a semiconductor substrate covered with a photoresist layer; A pattern is formed in the photoresist layer by means of the photomask, wherein the photomask has an array pattern area and a plurality of auxiliary patterns. The two array patterns are equidistant, and the length of the above-mentioned auxiliary pattern is equal to the width of the above-mentioned array pattern; Using the patterned photoresist as a mask, an etching step is performed to form a group of trench regions in the semiconductor substrate. 8. The method for reducing lens aberration and pattern shift according to claim 7, wherein the semiconductor substrate is a silicon substrate. 9. The method for reducing lens aberration and pattern shift according to claim 7, wherein the width of the auxiliary pattern is between 60-80 nanometers. 10. The method capable of reducing lens aberration and pattern shift according to claim 7, wherein when the photomask is used to form a pattern in the photoresist layer, substantially the auxiliary pattern is not generated on the photoresist layer Additional patterns. 11. The method capable of reducing lens aberration and pattern displacement according to claim 7, after etching, the line width difference between the obtained array patterns is the same as the line width between the array patterns obtained without the above-mentioned auxiliary pattern mask Difference comparison, 40%-60% reduction. 12. The method capable of reducing lens aberration and pattern shift according to claim 7, after etching, compared with the pattern shift caused by not setting the auxiliary pattern mask, the pattern shift is reduced by 40% -80%.

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