Mask plate absorption layer preparation method, mask plate and preparation method thereof

Abstract

The disclosure provides a mask plate absorption layer preparation method, a mask plate and a preparation method thereof, and relates to the field of photolithography technology. The mask plate absorption layer preparation method comprises the following steps: obtaining a mask substrate; preparing a transition film layer on the surface of the mask substrate; and preparing an actual absorption layer on the surface of the transition film layer. The transition film layer is used to offset the stress of the actual absorption layer on the surface of the mask substrate, so as to control the deformation amount and / or surface figure PV of the surface of the mask substrate.

Description

Technical Field

[0001] This disclosure relates to the field of photolithography, and in particular to a method for preparing an absorption layer of a photomask, a photomask, and the method for preparing the same. Background Technology

[0002] In the fabrication of micro / nano lithography masks, the deposition of the absorption layer is a crucial step and forms the basis for mask patterning. In practical applications, the absorption layer material deposited on the mask substrate often possesses residual stress. If this residual stress is high, it can cause deformation of the mask substrate, increasing positional errors and linewidth inhomogeneities in the mask patterning process, thus negatively impacting the lithography process. Summary of the Invention

[0003] In view of the above, a first aspect of the present disclosure provides a method for preparing a mask absorption layer, which includes obtaining a mask substrate; preparing a transition film layer on the surface of the mask substrate; and preparing an actual absorption layer on the surface of the transition film layer; wherein the transition film layer is used to counteract the stress of the actual absorption layer on the surface of the mask substrate, so as to control the deformation and / or surface shape PV of the mask substrate surface.

[0004] According to embodiments of this disclosure, the method further includes: obtaining a first surface shape of a mask substrate on which no predetermined absorption layer is formed; preparing different types of predetermined absorption layers on the mask substrate to obtain second surface shapes of mask substrates on which various types of predetermined absorption layers are formed; calculating the stress magnitude of the corresponding type of predetermined absorption layer on the surface of the mask substrate based on the change in surface curvature between the second surface shape and the first surface shape corresponding to each type of predetermined absorption layer; determining the first stress type of each type of predetermined absorption layer on the surface of the mask substrate and the second stress type of the required transition film layer for each type of predetermined absorption layer based on the stress magnitude of each type of predetermined absorption layer on the surface of the mask substrate, wherein the first stress type of the predetermined absorption layer on the surface of the mask substrate is opposite to the second stress type of the required transition film layer for the predetermined absorption layer.

[0005] According to embodiments of this disclosure, preparing a transition film layer on the surface of a mask substrate includes: determining an actual absorption layer and a first stress type of the actual absorption layer on the surface of the mask substrate from various types of predetermined absorption layers; obtaining a second stress type of the transition film layer required for the actual absorption layer based on the first stress type, as a target stress type; and preparing a transition film layer on the surface of the mask substrate with the stress type being the target stress type.

[0006] According to embodiments of this disclosure, fabricating a transition film layer with a target stress type on the surface of a mask substrate includes: determining a predetermined etching selectivity range between the actual absorption layer and the transition film layer with the target stress type, wherein the predetermined etching selectivity range should satisfy the requirement that the transition film layer with the target stress type can serve as a hard masking layer for the actual absorption layer; selecting a transition film layer with the target stress type based on the predetermined etching selectivity range and fabricating the transition film layer with the target stress type on the surface of the mask substrate.

[0007] According to embodiments of this disclosure, preparing a transition film layer on a mask substrate includes: preparing a transition film layer on the mask substrate with a second stress type of tensile stress when the first stress type of the actual absorbing layer on the surface of the mask substrate is compressive stress; or preparing a transition film layer on the mask substrate with a second stress type of compressive stress when the first stress type of the actual absorbing layer on the surface of the mask substrate is tensile stress.

[0008] According to embodiments of this disclosure, the transmittance of the transition film layer in the application band is greater than 80%.

[0009] According to embodiments of this disclosure, the material of the actual absorption layer includes at least one of Cr, Ta, and Mo, and the material of the transition film layer includes at least one of SiO2, Si, and TiO2. The thickness of the transition film layer is 90 nm to 100 nm, and the thickness of the actual absorption layer is 38 nm to 42 nm.

[0010] According to embodiments of this disclosure, the deposition process for the transition film includes at least one of chemical vapor deposition, physical vapor deposition, plasma-enhanced chemical vapor deposition, and ion beam deposition.

[0011] A second aspect of this disclosure provides a method for preparing a mask, wherein an absorber layer of the mask is prepared using the above-described preparation method; and a mask is prepared when the deformation and / or surface shape PV of the mask substrate surface meets preset conditions.

[0012] A third aspect of this disclosure provides a mask prepared using the above-described preparation method.

[0013] The mask absorption layer preparation method, mask, and preparation method thereof provided in the embodiments of this disclosure have at least the following technical effects:

[0014] Before preparing the absorption layer on the mask substrate, a transition film layer is prepared in advance, and then the absorption layer is prepared on the transition film layer. The transition film layer offsets the influence of the absorption layer stress on the mask surface shape, greatly reducing the change in the mask surface shape before and after the absorption layer is coated.

[0015] This method is universal and is not limited to the adjustment of stress in the mask absorption layer and the control of mask surface shape. For a wider range of substrate deformation control needs, this method can also be applied to select appropriate control films with suitable stress types and values ​​for surface shape control. Attached Figure Description

[0016] The above and other objects, features and advantages of this disclosure will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0017] Figure 1 A flowchart illustrating a method for preparing a mask absorption layer according to an embodiment of the present disclosure is shown schematically.

[0018] Figure 2 The diagram illustrates a structure corresponding to a mask absorption layer prepared using existing methods and a schematic diagram corresponding to a mask absorption layer prepared using the method of the present disclosure.

[0019] Figure 3A The stress diagram of a conventional Cr film prepared by conventional radio frequency sputtering is illustrated.

[0020] Figure 3B The diagram illustrates the stress profile of a Cr film prepared using the preparation method of embodiments of the present disclosure.

[0021] Figure 4 The diagram illustrates the repeatability verification results of the Cr film stress control process according to an embodiment of the present disclosure.

[0022] Figure 5 The diagram illustrates a comparison of the effect of the stress control scheme according to embodiments of the present disclosure on suppressing the PV increment of the mask surface shape before and after coating.

[0023] Figure 6 The diagram schematically illustrates the surface shape measurement results of the 6mm × 6mm graphic area at the center of the front of the mask after employing the stress control method according to an embodiment of the present disclosure. Detailed Implementation

[0024] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein, indicate the presence of said features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components. All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0026] In the process of developing this disclosure, it was discovered that metallic chromium (Cr) layers are often used as absorber layer materials in photomasks due to their high absorption rate of ultraviolet light. Typically, to facilitate photomask patterning, the Cr film thickness must be as thin as possible while ensuring that the ultraviolet light transmittance remains below a certain value. This necessitates that the prepared Cr film have the highest possible density. To improve the density of the Cr film, radio frequency sputtering is commonly used to prepare it. However, Cr films prepared by this method usually have high residual stress, which can cause significant deformation of the substrate, compromising the control of positional errors and the uniformity of the pattern on the photomask.

[0027] The residual stress of chromium films prepared by magnetron sputtering can be reduced by increasing the sputtering chamber pressure, using a DC power supply for sputtering, and post-annealing. However, these methods have limited adjustment range for stress values ​​and can lead to a decrease in the density of the deposited chromium layer. This results in problems such as increased transmittance of the chromium layer of the required thickness under incident light at a specific wavelength and increased surface roughness, thus reducing its excellent performance as an absorption layer in a photomask.

[0028] In view of this, the embodiments of this disclosure aim to provide a method for preparing an absorption layer of a photomask, a photomask, and the method thereof, which reduces the influence of absorption layer stress on the deformation of the photomask substrate before and after coating, while ensuring that the absorption rate of the absorption layer remains unchanged. This provides a new technical approach for effectively suppressing the influence of absorption layer stress on the surface shape of the photomask substrate. Specific embodiments are described in detail below.

[0029] Figure 1 A flowchart illustrating a method for preparing a mask absorption layer according to an embodiment of the present disclosure is shown schematically.

[0030] like Figure 1 As shown, the mask absorption layer preparation method of this embodiment may include operations S110 to S120.

[0031] By operating S110, a mask substrate is obtained.

[0032] In operation S120, a transition film layer is prepared on the mask substrate, and an actual absorption layer is prepared on the transition film layer. The transition film layer is used to counteract the stress exerted by the actual absorption layer on the surface of the mask substrate, thereby controlling the deformation of the mask substrate surface.

[0033] In some embodiments of this disclosure, the mask substrate may include, for example, sapphire or fused quartz of any facet shape. The specific type of mask substrate can be selected according to actual application requirements, and this disclosure does not impose any limitations. The actual absorption layer can be understood as the absorption layer that needs to be prepared during the preparation of the finished mask.

[0034] In some embodiments of this disclosure, the first stress type of the transition film layer may be opposite to the second stress type of the actual absorption layer, and the stress magnitude of the transition film layer may be comparable to that of the absorption layer.

[0035] Therefore, before fabricating the mask for the finished product, it is necessary to pre-determine the required transition film layers corresponding to the absorbing layers for various stress types. As one possible implementation, determining the required transition film layers corresponding to the absorbing layers for various stress types may include:

[0036] Obtain the first surface profile of a mask substrate on which no predetermined absorption layer has been formed.

[0037] Different types of predetermined absorption layers are prepared on the mask substrate to obtain the second surface shape of the mask substrate with various types of predetermined absorption layers formed on its surface.

[0038] The stress on the mask substrate surface of the corresponding type of predetermined absorption layer is calculated based on the change in surface curvature between the second surface shape and the first surface shape corresponding to each type of predetermined absorption layer.

[0039] Based on the stress magnitude of each type of predetermined absorption layer on the mask substrate surface, the first stress type of each type of predetermined absorption layer on the mask substrate surface and the second stress type of the transition film layer required for each type of predetermined absorption layer are determined. The first stress type of the predetermined absorption layer on the mask substrate surface is opposite to the second stress type of the transition film layer required for the predetermined absorption layer.

[0040] For example, various types of predetermined absorber layers are deposited on a mask substrate. Before and after deposition, the surface shape of the mask is measured using a stress meter. The stress meter calculates the type and magnitude of the stress exerted by the deposited predetermined absorber layer on the substrate based on the change in curvature of the mask surface before and after deposition. If the stress value calculated by the stress meter is positive, it indicates that the stress exerted by the deposited predetermined absorber layer on the mask substrate is compressive stress; if the stress value calculated by the stress meter is negative, it indicates that the stress exerted by the deposited predetermined absorber layer on the substrate is tensile stress. The predetermined absorber layer can be understood as the absorber layer that needs to be prepared in the process of pre-determining the required transition film layer corresponding to various stress types of absorber layers.

[0041] In some embodiments of this disclosure, fabricating a transition film layer on a mask substrate may include:

[0042] The actual absorption layer and the first stress type of the actual absorption layer on the mask substrate surface are determined from various types of predetermined absorption layers.

[0043] The second stress type of the transition film layer required for the actual absorption layer is obtained based on the first stress type, and is used as the target stress type.

[0044] A transition film layer with the stress type of the target stress type is prepared on the surface of the mask substrate.

[0045] Further, a transition film layer with a stress type of the target stress type is prepared on the surface of the mask substrate, including: determining a predetermined etching selectivity range between the actual absorption layer and the transition film layer with the target stress type, wherein the predetermined etching selectivity range should satisfy that the transition film layer with the target stress type can serve as a hard mask layer for the actual absorption layer; selecting a transition film layer with the stress type of the target stress type based on the predetermined etching selectivity range and preparing the transition film layer with the stress type of the target stress type on the surface of the mask substrate.

[0046] Because the etching selectivity between the actual absorption layer and the transition layer is considered during the fabrication of the transition layer, the transition layer can serve as a hard masking layer for the actual absorption layer, thereby enabling high-quality transfer of the actual absorption layer.

[0047] In some embodiments of this disclosure, fabricating a transition film layer on a mask substrate may include:

[0048] When the first stress type of the actual absorption layer on the surface of the mask substrate is compressive stress, a transition film layer with a second stress type of tensile stress is prepared on the mask substrate.

[0049] According to embodiments of this disclosure, the first stress type on the surface of the mask substrate of the predetermined absorption layer being opposite to the second stress type of the required transition film layer of the predetermined absorption layer can be understood as follows: if the first stress type is compressive stress, then the second stress type can be tensile stress; or, if the first stress type is tensile stress, then the second stress type can be compressive stress. Based on this, in some other embodiments of this disclosure, the fabrication of the transition film layer on the mask substrate may further include:

[0050] When the first stress type of the actual absorption layer on the surface of the mask substrate is tensile stress, a transition film layer with the second stress type of compressive stress is prepared on the mask substrate.

[0051] As one possible implementation, the material of the absorber layer may include at least one of Cr, Ta, and Mo, and the material of the transition film layer may include at least one of SiO2, Si, and TiO2.

[0052] Figure 2 The diagram illustrates a structure corresponding to a mask absorption layer prepared using existing methods and a schematic diagram corresponding to a mask absorption layer prepared using the method of the present disclosure.

[0053] like Figure 2 As shown, taking a Cr film as the actual absorption layer as an example, a SiO2 film with the opposite stress type to the required transition film, whose stress value can cancel out that of the Cr film and has high transmittance at the desired wavelength (e.g., 365 nm), can be selected as the transition film based on the pre-determined absorption layers of various stress types. This allows for the control of the stress in the Cr film without affecting the transmittance of the mask. By pre-depositing the SiO2 film before preparing the Cr film, the SiO2 film can counteract the stress of the Cr film on the mask substrate, reducing the change in the mask surface shape before and after the Cr film deposition.

[0054] Taking the Mo film as the actual absorption layer as an example, the stress of the Mo film can be controlled by selecting a Si film with the opposite stress type to the Mo film, whose stress value can be canceled by the Mo film, and which has high transmittance at the used wavelength (e.g., 193 nm) based on the required transition film layer corresponding to the absorption layer of various stress types in advance.

[0055] During the fabrication process, a transition film layer can be deposited first on the surface of the mask substrate, and then the actual absorption layer required can be deposited after cooling.

[0056] In some embodiments of this disclosure, the transmittance of the transition film layer in the applied wavelength band can be greater than 80% to ensure better light transmission in the applied wavelength band.

[0057] In some embodiments of this disclosure, the deposition process and thickness of the transition film can be controlled to adjust the stress of the absorber layer material to the required range, thereby suppressing the influence of absorber layer stress on the mask surface shape.

[0058] As one possible implementation, the thickness of the transition film can be 90 nm to 100 nm, and the thickness of the actual absorption layer can be 38 nm to 42 nm.

[0059] As another possible implementation, the deposition process of the transition film includes at least one of chemical vapor deposition, physical vapor deposition, plasma-enhanced chemical vapor deposition, and ion beam deposition.

[0060] Embodiments of this disclosure also provide a method for preparing a photomask, which may include:

[0061] The absorption layer of the mask is prepared using the above-described method for preparing the mask absorption layer.

[0062] A mask is prepared when the deformation and / or surface shape PV on the surface of the mask substrate meets preset conditions.

[0063] The specific details of the absorption layer fabrication for the mask are not elaborated here. After the absorption layer is fabricated, the actual stress and surface deformation (PV) of the mask substrate are verified. If they meet the requirements, a mask with satisfactory stress and surface shape is obtained through further processing.

[0064] The embodiments of this disclosure also provide a mask, which is prepared using the mask preparation method described above, and the specific details will not be repeated here.

[0065] To more clearly illustrate the effectiveness of the above-mentioned mask absorption layer preparation method and mask preparation method, some specific examples are given below.

[0066] Example 1

[0067] In this embodiment, a Cr film with a thickness of 40 nm can be deposited on the surface of a 6-inch square photomask as the absorption layer.

[0068] To address the issue of mask shape changes caused by Cr film stress, a SiO2 layer prepared by chemical vapor deposition can be used as a control layer. Specifically, before depositing the Cr film, a 100 nm thick SiO2 film is deposited on the substrate as a transition layer using chemical vapor deposition. The stress value of the deposited SiO2 film is measured to be -1000 MPa using a stress meter. After the substrate cools, it is placed in the chamber of an RF sputtering deposition apparatus, and a 40 nm thick Cr film is deposited on top of the SiO2 film. The stress value of the Cr film is then measured after the substrate is removed.

[0069] Figure 3A The stress diagram of a Cr film prepared by conventional radio frequency sputtering is schematically shown. Figure 3B The diagram illustrates the stress profile of a Cr film prepared using the preparation method of embodiments of the present disclosure.

[0070] like Figure 3A and 3B As shown, the stress value of the dense Cr film prepared by radio frequency sputtering is +1800 MPa. After adjustment, the stress value of the Cr layer is reduced to +140 MPa, which meets the stress index requirement of +50 MPa to +200 MPa.

[0071] Example 2

[0072] Based on Example 1, the same process was used to perform stress adjustment on the mask substrate multiple times.

[0073] Figure 4 The diagram illustrates the repeatability verification results of the Cr film stress control process according to an embodiment of the present disclosure.

[0074] like Figure 4 As shown, the mask absorption layer preparation method provided in this embodiment has certain process stability, and the film layers prepared in different batches can meet the stress index requirements of +50 MPa to +200 MPa.

[0075] Example 3

[0076] Based on Example 1, experiments were conducted on a 6-inch square quartz mask substrate with protrusions. Figure 5 This diagram schematically illustrates a comparison of the effect of the stress control scheme according to embodiments of the present disclosure on suppressing the PV increment of the mask surface shape before and after coating. Figure 6 The diagram schematically illustrates the surface shape measurement results of the 6mm × 6mm graphic area at the center of the front of the mask after applying the stress control method according to an embodiment of the present disclosure.

[0077] like Figure 5 and Figure 6 As shown, before the coating process, the PV value of the substrate increased by more than 500 nm, which adversely affected the accuracy control of the mask's positional error and the linewidth uniformity control of the high-resolution pattern. However, after using the method disclosed in this paper, the results show that the stress control scheme of this paper suppressed the deformation of the 6-inch mask caused by the stress of the Cr film layer, and the PV increase of the substrate before and after coating decreased from 500 nm to 100 nm. Figure 5 The PV on the 6mm×6mm front boss surface can be controlled to around 4 nm. Figure 6 The impact of the absorption layer deposition step on the positional error accuracy of the mask and the linewidth uniformity of the high-resolution pattern is reduced to negligible levels.

[0078] In summary, the experimental data fully verify that the stress control scheme disclosed herein can effectively reduce the stress of the Cr film layer and reduce the mask surface shape change caused by the stress of the Cr film layer, providing a good foundation for technical indicators such as the position error of the direct writing pattern of the mask and CDU control.

[0079] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of this disclosure is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A method for preparing a mask blank absorption layer, characterized by, The method comprises the following steps: obtaining a mask substrate; preparing a transition film layer on the surface of the mask substrate, and preparing an actual absorption layer on the surface of the transition film layer; wherein the transition film layer is used to offset the stress of the actual absorption layer on the surface of the mask substrate, so as to control the deformation amount and / or surface shape PV of the surface of the mask substrate; wherein the step of preparing the transition film layer on the surface of the mask substrate comprises: determining the actual absorption layer and a first stress type of the actual absorption layer on the surface of the mask substrate from various types of predetermined absorption layers; and obtaining a second stress type of the transition film layer required by the actual absorption layer as a target stress type based on the first stress type; preparing the transition film layer with the target stress type on the surface of the mask substrate; wherein the first stress type of the predetermined absorption layer on the surface of the mask substrate is opposite to the second stress type of the transition film layer required by the predetermined absorption layer.

2. The method of claim 1, wherein, The method further comprises the following steps: obtaining a first surface shape of the mask substrate without a predetermined absorption layer on the surface; preparing different types of predetermined absorption layers on the mask substrate to obtain respective second surface shapes of the mask substrate with various types of predetermined absorption layers on the surface; calculating the stress of the corresponding type of predetermined absorption layer on the surface of the mask substrate according to the surface shape curvature change amount between the corresponding second surface shape of the various types of predetermined absorption layers and the first surface shape; determining the first stress type of the various types of predetermined absorption layers on the surface of the mask substrate and the second stress type of the transition film layer required by the various types of predetermined absorption layers respectively according to the stress of the various types of predetermined absorption layers on the surface of the mask substrate.

3. The method of claim 1, wherein, The step of preparing the transition film layer with the target stress type on the surface of the mask substrate comprises: determining a predetermined etching selectivity range between the actual absorption layer and the transition film layer with the target stress type, wherein the predetermined etching selectivity range should meet the requirement that the transition film layer with the target stress type can be used as a hard mask layer of the actual absorption layer; selecting the transition film layer with the target stress type based on the predetermined etching selectivity range and preparing the transition film layer with the target stress type on the surface of the mask substrate.

4. The method according to claim 1 or 2, characterized in that, The step of preparing the transition film layer on the mask substrate comprises: in the case that the first stress type of the actual absorption layer on the surface of the mask substrate is compressive stress, preparing a transition film layer with a second stress type of tensile stress on the mask substrate; or, in the case that the first stress type of the actual absorption layer on the surface of the mask substrate is tensile stress, preparing a transition film layer with a second stress type of compressive stress on the mask substrate.

5. The method according to claim 1 or 2, characterized in that, The transmittance of the transition film layer in the application wave band is greater than 80%.

6. The method of claim 1 or 2, wherein, The material of the actual absorption layer comprises at least one of Cr, Ta and Mo, and the material of the transition film layer comprises at least one of SiO2, Si and TiO2. The thickness of the transition film layer is 90 nm-100 nm, and the thickness of the actual absorption layer is 38 nm-42 nm.

7. The method according to claim 1 or 2, characterized in that, The deposition process of the transition film layer includes at least one of chemical vapor deposition, physical vapor deposition, plasma enhanced chemical vapor deposition and ion beam deposition.

8. A method for manufacturing a mask blank, comprising: manufacturing the absorption layer of the mask blank by using the method according to any one of claims 1-7; manufacturing the mask blank when the deformation amount and / or the surface profile PV of the surface of the mask substrate meet the preset condition.

9. A reticle, characterized by, The mask blank is manufactured by using the method according to claim 8.

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