DE102004003341B4 - Halftone phase mask with multiple transmissions and process for their preparation - Google Patents

Abstract

A halftone phase mask for projecting a pattern of features formed on the mask onto a photosensitive layer in the fabrication of integrated circuits on a semiconductor wafer, comprising:
A transparent mask substrate (10);
A first portion (12) of a pattern having first structural elements (14) as raised ridges having a first height (16) of a semi-transparent phase-shifting material disposed on the planar surface (11) of the transparent mask substrate (10); are formed in such a way that a light beam penetrating the mask substrate (10) within the first structural elements (14) has a phase jump in the range of 160 ° to 200 ° with respect to a mask substrate (10) outside the first structural elements (14) in the region of the planar surface (14). 11) of the mask substrate (10) undergoes penetrating light beam; and
- a second portion (18) of the pattern, wherein the second structural elements (20) are raised webs having a second height (22) of the same semitransparent phase-shifting material of the first structural elements (14) formed on the planar surface.

Description

The The invention relates to a halftone phase mask with multiple transmissions for projecting a pattern of structural elements formed on the mask on a photosensitive layer in the manufacture of integrated Circuits on a semiconductor wafer and process for their preparation.

integrated Circuits are made by photolithographic projection of Patterns formed on photomasks on semiconductor wafers produced. For Each layer is usually a mask with the circuit level corresponding pattern used.

photomasks or reticles are used in the field of semiconductor manufacturing, by means of lithographic projection on one with a photosensitive Lacquer-coated semiconductor wafers in the paint a pattern of structural elements to build. The choice of the lateral extent of the on the semiconductor wafer to be formed structural elements is due to a particular Restricted by the projection system predetermined lower resolution limit. The resolution limit depends from the exposure wavelength, the aperture size of the lens system, or, for example, the type of illumination source of the projection system, Etc.

highly integrated Circuits, such as dynamic or non-volatile memory as well as logic devices, are currently being manufactured with circuit elements, whose width extends down to 70 nm. In the example of the memory modules this applies, for example, to the very dense and periodically arranged patterns of narrow word or bit lines and, where appropriate, the corresponding contacts or trenches.

there It can often happen that the corresponding highly integrated Structure pattern in a circuit plane with the structural elements electrically subsequent Peripheral area are arranged together. Structural elements, for example Tracks, such peripheral areas are usually relaxed Requirements for the structure width. On the for the formation of the circuit level Accordingly, photomasks to be used together are dense, often Periodic arrays of structural elements as well as isolated or semi-insulated, larger-sized Structural elements arranged together in a pattern.

It it is known that in the lithographic projection structural elements, their width each near the resolution limit of the relevant exposure device is different because of the optical imaging characteristics larger sized, transfer non-periodic structure elements into the image plane become. This is partly because of the limited numerical Aperture of the exposure device, on the other hand, s.den individual exposure settings in the device. In the presence of lens aberrations, for example due to of lens defects, can the different imaging effects intensify, which in particular Linewidth variations or positional accuracy errors in the Structural pattern shares become visible.

The resolution limit of a projection system but also by the use of modern lithographic techniques the for reduce an exposure used masks. This concerns before in particular the area of the phase masks, which also phase shift masks be called (English: Phase Shift Masks).

One special type is the so-called halftone phase mask (English: Attenuated Phase Shift Mask). The on conventional chrome masks Structural elements formed as opaque layers on a transparent carrier substrate become semipermeable in the half-tone masks, i. semitransparent, and phase-shifting. The term "semipermeable" is somewhat misleading since the transmittance, i. that portion of the incident light, which penetrate the semitransparent layer and the transparent one carrier substrate can reach, depending on the application in a wide range between a few percent (e.g., 3%) of the intensity of the incident light beam and over 50% can amount. The acted upon with a phase deviation of typically 180 ° and due to the low transmissivity attenuated light beam causes an opposite conventional chrome structural elements increased contrast enhancement at the edges of transparent and semitransparent sections. In the halftone phase masks can therefore semitransparent structural elements with high dimensional stability be imaged on a semiconductor wafer.

In US 2003/0152844 A1 a phase mask is shown in which a quartz substrate in a first area a structured semitransparent Layer and above a structured phase shift layer adjacent to one Depression on the surface of the substrate are attached. In a second area is a structured semitransparent layer applied to the quartz substrate.

In the US 6,326,107 B1 a phase shift mask is shown in which are arranged in a first region around a recess structure elements made of semitransparent material and in egg In the second area above the transparent mask substrate, further structural elements made of semitransparent material are arranged.

One particular problem with halftone phase masks is that that the contrast-enhancing Effect for dense regions of features different from those isolated structural elements is. In general, it tries to in very dense areas, the transmittance of semitransparent Structural elements very high, i. in the range of about 50%, to choose. In the environment isolated or semi-isolated structural elements introduces high transmittance too additional existing diffraction images, which arise due to higher diffraction orders. This phenomenon is known in the art as side-lobe printing and can by a reduced transmission can be eliminated. This results However, the problem is that the concurrent optimization for dense and isolated structural elements is difficult and the existing one Process window is disadvantageously reduced.

It It is therefore an object of the invention to provide a halftone phase mask, in both dense and isolated structural arrangements together with high dimensional accuracy can be imaged on a semiconductor wafer, as well as to provide a method the simple production of a halftone phase mask with several Transmission allows.

• – ein transparentes Maskensubstrat;
• – einen ersten Anteil eines Musters, bei dem erste Strukturelemente als erhabene Stege mit einer ersten Höhe aus einem semitransparenten phasenschiebenden Material, das auf der ebenen Oberfläche des transparenten Maskensubstrats angeordnet ist, derart gebildet sind, dass ein das Maskensubstrat innerhalb der ersten Strukturelemente durchdringender Lichtstrahl einen Phasensprung im Bereich von 160° bis 200° gegenüber einem das Maskensubstrat außerhalb der ersten Strukturelemente im Bereich der ebenen Oberfläche des Maskensubstrats durchdringenden Lichtstrahl erfährt; und
• – einen zweiten Anteil des Musters, bei dem zweite Strukturelemente als erhabene Stege mit einer zweiten Höhe aus dem gleichen semitransparenten phasenschiebenden Material der ersten Strukturelemente, das auf der ebenen Oberfläche des transparenten Maskensubstrats angeordnet ist, und benachbart zu den zweiten Strukturelementen angeordnete Gräben in der Oberfläche des Maskensubstrats mit einer Tiefe derart gebildet sind, dass ein das Maskensubstrat innerhalb der zweiten Strukturelemente durchdringender Lichtstrahl einen Phasensprung im Bereich von 160° bis 200° gegenüber einem das Maskensubstrat außerhalb der zweiten Strukturelemente im Bereich der Gräben in der Oberfläche des Maskensubstrats durchdringenden Lichtstrahl erfährt, wobei die erste Höhe größer als die zweite Höhe (22) ist, so dass im ersten Anteil des Musters ein das Maskensubstrat innerhalb der ersten Strukturelemente durchdringender Lichtstrahl einen geringeren Transmissionsgrad aufweist als ein das Maskensub strat innerhalb der zweiten Strukturelemente durchdringender Lichtstrahl.

This object is achieved according to the invention by a halftone phase mask for projecting a pattern of structural elements formed on the mask onto a photosensitive layer in the manufacture of integrated circuits on a semiconductor wafer, comprising:

• A transparent mask substrate;
• A first portion of a pattern in which first features are formed as raised lands having a first height of a semi-transparent phase shift material disposed on the planar surface of the transparent mask substrate, such that a light beam penetrating the mask substrate within the first feature Experiences phase jumps in the range of 160 ° to 200 ° with respect to a light beam penetrating the mask substrate outside the first structural elements in the region of the planar surface of the mask substrate; and
• A second portion of the pattern comprising second features as raised lands having a second height from the same semitransparent phase shift material of the first features disposed on the planar surface of the transparent mask substrate and trenches disposed adjacent to the second features in the surface the mask substrate is formed with a depth such that a light beam penetrating the mask substrate within the second structural elements undergoes a phase jump in the range of 160 ° to 200 ° with respect to a light beam passing through the mask substrate outside the second structural elements in the region of the trenches in the surface of the mask substrate, wherein the first height is greater than the second height ( 22 ) is such that in the first portion of the pattern, a light beam penetrating the mask substrate within the first structural elements has a lower transmittance than a light beam penetrating the mask sub-strate within the second structural elements.

The Halftone phase mask according to the invention has structural elements of a first portion and a second portion of the pattern, with semitransparent phase shifting Material of different thickness are executed. advantageously, the structural elements are arranged on the same mask substrate, at which the height of the first structural element is selected so that a phase jump in the range of 160 ° to 200 °, preferably 180 °, results. This value leaves also for reach the second structural elements, since the height of the second structural elements based on the needed Transmittance is given, while the necessary phase-rotating component through the depth of the trenches is determined. Thus, it is possible a halftone phase mask, each with optimized conditions for the first and to form the second structural elements.

According to one preferred embodiment is in the Halftone phase mask the transmittance of a mask substrate less within the first structural elements of the penetrating light beam than 10%, preferably about 6%, and the transmittance of a mask substrate within the second structural elements penetrating light beam between 10% and 70%, preferably between 20% and 60%.

In order to assigns the halftone phase mask to the optimized projection of the components of the pattern transmissions, which are clearly different from each other differ. For example, in a pattern whose first Share associated with low transmission, the amount of the first Structure elements based on the desired Transmission executed be. For the second parts of the pattern are on the same mask substrate second structural elements provided with the high transmission.

According to a further preferred Ausfüh In the case of the halftone phase mask, the mask substrate consists of quartz, ie of silicon dioxide, or of calcium fluoride.

at Use of a mask substrate made of quartz, preferably of silicon dioxide, is the use commercially available Mask blanks possible. This can be cost-effective Produce halftone phase masks with high yield.

According to one another preferred embodiment in the halftone phase mask comprises the semitransparent phase shift Material molybdenum silicide.

The Use of molybdenum silicide as a semitransparent phase-shifting material is in commercial available mask blanks usual. In order to can be cost-effective Halftone phase masks based on commercially available Make mask blanks.

According to one another preferred embodiment In the halftone phase mask, the first portion of the pattern is included semi-isolated structures.

at semi-isolated structures is often a low-level projection Transmittance desired, to eliminate the so-called side-lobe printing. advantageously, let yourself this with the halftone phase mask according to this embodiment realize.

According to one another preferred embodiment In the halftone phase mask, the second portion of the pattern is included a dense line-column pattern.

at dense line-column patterns is often a high-profile projection Transmittance desired, one as possible high picture quality to reach. Advantageously, this can be done with the halftone phase mask realize.

According to one another preferred embodiment For the halftone phase mask, the pattern corresponds to a plane of a Circuit pattern of dynamic random access memory.

One dynamic random access memory is in the range of Memory cells have dense structures (line-column patterns) in the manufacture the integrated circuit preferably with a halftone phase mask transmitted high transmission become. At the same time, the circuit pattern includes ter in the area of Support logic outside the Memory cell array also isolated and semi-isolated structures, their mapping should be done with low transmission. The halftone phase mask according to this embodiment Provides different transmittances for simultaneous optimization both structural shares available.

According to one another preferred embodiment For example, the halftone phase mask in the mask substrate has a multilayered one Construction with at least one parallel and at the top Layer on, wherein the thickness of the layer on top of the mask substrate corresponds to the depth of the trenches.

The Halftone phase mask leaves very easy to manufacture, as compared to the mask substrate selective etching step the layer can expose, due to the multilayer structure a high reproducibility of the desired transmissions the mask is reached.

According to one another preferred embodiment points beyond the halftone phase mask a third portion of the pattern, wherein the third structural elements as raised webs with a third height from the semitransparent phase shifting material lying on the flat surface of the transparent mask substrate, wherein the mask substrate more trenches having another depth adjacent to the third Structural elements is arranged, are formed such that a the mask substrate penetrating within the third structural elements Light beam a phase jump in the range of 160 ° to 200 °, preferably 180 °, opposite one the mask substrate outside the third structural elements in the area of the other trenches in the surface the mask substrate penetrates the light beam, wherein the further depth of the further trenches is greater than the depth of the trenches.

These embodiment is suitable for the simultaneous projection of several parts of the pattern, where the achievable transmittances are individually optimized. So For example, shares with low transmission, with medium transmission and high transmission to a mask substrate arrange, where for each share a 180 ° phase shift is provided.

According to one another preferred embodiment points beyond the halftone phase mask a third portion of the pattern, wherein the third structural elements as raised ridges on the flat surface of the semitransparent phase-shifting Materials are arranged.

These embodiment advantageously combines a mask with two transmissions with a simple chrome-on-glass Mask. This allows further optimization of the process window.

According to one another preferred embodiment In the halftone phase mask, the third features comprise the third features a structured chrome layer.

The Use of a chromium layer as the absorbing element is included commercially available Masks usual. This can be cost-effective Manufacture masks based on commercially available mask blanks, the advantages of halftone phase masks with two transmissions and a CoG layer exhibit.

The The object of the invention is also achieved by a process for the preparation a halftone phase mask solved.

• – Bereitstellen eines Musters von Strukturelementen mit einem ersten Anteil und einem zweiten Anteil;
• – Bereitstellen eines Maskenrohlings, umfassend ein Maskensubstrat mit einer ebenen Oberfläche, eine darüber liegende Absorberschicht aus einem semitransparenten phasenschiebenden Material mit einer ersten Höhe, eine über der Absorberschicht liegende Metallschicht und eine über der Metallschicht liegende Resistschicht;
• – maskenlithographisches Strukturieren der Resistschicht, um eine Resiststruktur zu bilden, die dem ersten Anteil des Musters und dem zweiten Anteil des Musters entspricht;
• – Übertragen der Resiststruktur in die Metallschicht und in die Absorberschicht durch Ätzen, um eine Metallstruktur und Strukturelemente der Absorberschicht zu bilden;
• – Entfernen der Resiststruktur;
• – vollflächiges Abscheiden einer weiteren Resistschicht;
• – Bestrahlen der weiteren Resistschicht;
• – Ätzen oder Entwickeln der weiteren Resistschicht, um den zweiten Anteil des Musters freizulegen;
• – Ätzen von Gräben in der ebenen Oberseite des Maskensubstrats unmittelbar benachbart zu den zweiten Strukturelementen;
• – Entfernen der Metallstruktur im Bereich des zweiten Anteils des Musters, um Strukturelemente der Absorberschicht freizulegen;
• – Dünnen der Strukturelemente der Absorberschicht im Bereich des zweiten Anteils des Musters, um zweite Strukturelemente des Musters als erhabene Stege auf der ebenen Oberseite des Maskensubstrats mit einer zweiten Höhe zu bilden;
• – Entfernen der weiteren Resistschicht; und
• – Entfernen der Metallstruktur im Bereich des ersten Anteils des Musters, um erste Strukturelemente des Musters als erhabene Stege auf der ebenen Oberseite des Maskensubstrats mit der ersten Höhe freizulegen.

According to a first aspect of the invention, there is provided a method of forming a halftone phase mask, comprising the steps of:

• Providing a pattern of structure elements having a first portion and a second portion;
• Providing a mask blank comprising a mask substrate having a planar surface, an overlying absorber layer of a semitransparent phase-shifting material having a first height, a metal layer overlying the absorber layer, and a resist layer overlying the metal layer;
• Masking lithographic patterning of the resist layer to form a resist pattern corresponding to the first portion of the pattern and the second portion of the pattern;
• - transferring the resist pattern into the metal layer and into the absorber layer by etching to form a metal structure and structural elements of the absorber layer;
• - removing the resist structure;
• - Full-surface deposition of a further resist layer;
• - irradiating the further resist layer;
• Etching or developing the further resist layer to expose the second portion of the pattern;
• - etching trenches in the planar top surface of the mask substrate immediately adjacent to the second features;
• Removing the metal structure in the region of the second portion of the pattern in order to expose structural elements of the absorber layer;
• - thinning the structural elements of the absorber layer in the region of the second portion of the pattern to form second structural elements of the pattern as raised ridges on the planar top surface of the mask substrate with a second height;
• - removing the further resist layer; and
• Removing the metal structure in the region of the first portion of the pattern to expose first structural elements of the pattern as raised ridges on the planar top of the mask substrate with the first height.

• – Bereitstellen eines Musters mit einem ersten Anteil und einem zweiten Anteil;
• – Bereitstellen eines Maskenrohlings, umfassend ein Maskensubstrat mit einer ebenen Oberfläche, eine darüber liegende Absorberschicht aus einem semitransparenten phasenschiebenden Material mit einer ersten Höhe und eine über der Absorberschicht liegende Resistschicht;
• – maskenlithographisches Strukturieren der Resistschicht, um eine Resiststruktur zu bilden, die dem ersten Anteil des Musters und dem zweiten Anteil des Musters entspricht;
• – Übertragen der Resiststruktur in die Absorberschicht durch Ätzen, um Strukturelemente der Absorberschicht zu bilden;
• – Entfernen der Resiststruktur;
• – vollflächiges Abscheiden einer weiteren Resistschicht;
• – Belichten der weiteren Resistschicht;
• – Ätzen oder Entwickeln der weiteren Resistschicht, um im Bereich des zweiten Anteils des Musters die Strukturelemente der Absorberschicht freizulegen;
• – Dünnen der Strukturelemente der Absorberschicht im Bereich des zweiten Anteils des Musters, so dass zweite Strukturelemente des Musters als erhabene Stege auf der ebenen Oberseite des Maskensubstrats mit einer zweiten Höhe gebildet werden;
• – Bilden von Gräben in der ebenen Oberseite des Maskensubstrats unmittelbar benachbart zu den zweiten Strukturelementen des Musters;
• – Entfernen der weiteren Resistschicht im Bereich des ersten Anteils des Musters, so dass die ersten Strukturelemente des Musters als erhabene Stege auf der ebenen Oberseite des Maskensubstrats mit der ersten Höhe freigelegt werden.

According to a second aspect, there is provided a method of forming a halftone phase mask, comprising the steps of:

• - providing a pattern with a first portion and a second portion;
• Providing a mask blank comprising a mask substrate having a planar surface, an overlying absorber layer of a semi-transparent phase shift material having a first height, and a resist layer overlying the absorber layer;
• Masking lithographic patterning of the resist layer to form a resist pattern corresponding to the first portion of the pattern and the second portion of the pattern;
• - transferring the resist structure into the absorber layer by etching to form structural elements of the absorber layer;
• - removing the resist structure;
• - Full-surface deposition of a further resist layer;
• - exposing the further resist layer;
• - etching or developing the further resist layer in order to expose the structural elements of the absorber layer in the region of the second portion of the pattern;
• Thinning the structural elements of the absorber layer in the region of the second portion of the pattern so that second structural elements of the pattern are formed as raised ridges on the planar upper side of the mask substrate with a second height;
• - forming trenches in the planar top surface of the mask substrate immediately adjacent to the second structural elements of the pattern;
• Removing the further resist layer in the region of the first portion of the pattern, so that the first structural elements of the pattern are exposed as raised ridges on the planar top of the mask substrate with the first height.

The Method according to the first Aspect of the invention allows the simple production of a halftone phase mask with two different degrees of transmission of a first and a second part of a sample. Here are only commercial mask blanks used, the use of expensive hybrid masks is according to the invention unnecessary.

The method according to the second aspect of the invention moreover allows the simple production of a halftone phase mask with two different degrees of transmission of a first and a second portion of a pattern, whereby a mask blank without a metal layer is used can. This allows a particularly cost-effective production of the mask.

advantageous Further developments of the invention are specified in the subclaims.

The The present invention will now be described with reference to several embodiments with the help of a drawing closer explained become. Show:

1 in a schematic cross-sectional view of an embodiment of the invention halftone phase mask;

2 in a schematic cross-sectional view of another embodiment of the halftone phase mask according to the invention;

3 in a schematic cross-sectional view of another embodiment of the halftone phase mask according to the invention;

4A in a schematic cross-sectional view of another embodiment of the halftone phase mask according to the invention;

4B in a schematic cross-sectional view of another embodiment of the halftone phase mask according to the invention;

5A to 5D in schematic cross-sectional views of the components resulting from the application of the method according to a first aspect of the invention;

6A to 6D in schematic cross-sectional views of the resulting from the application of the method according to a second aspect of the invention components;

7A to 7C in schematic cross-sectional views of the resulting in the application of further process steps of the process according to the invention components; and

8th schematically in a cross-sectional view the use of the halftone phase mask according to the invention.

The The invention will now be described with reference to a first embodiment of a halftone phase mask explains the photolithographic projection during structuring a photosensitive layer, for example a semiconductor wafer in the manufacture of an integrated circuit can be used. The numerous further developments of the halftone phase mask, as well as procedures for producing halftone phase masks are presented below.

In 1 is schematically a halftone phase mask 5 shown in a cross-sectional view. The halftone phase mask comprises a mask substrate 10 , The mask substrate 10 consists for example of a quartz disk, ie of silicon dioxide, which has a flat surface on the top 11 having. Other materials known to those skilled in the art, such as calcium fluoride, are not excluded. The mask substrate 10 should generally be made of a material which has a high transmittance for transmitted light of the wavelength provided by projection, for example in the UV region at 248 nm or 193 nm.

On the mask substrate 10 is a first share 12 a pattern of structural elements attached. At the first share 12 are first structural elements 14 as raised webs with a first height 16 on the flat surface of the transparent mask substrate 10 arranged.

The first structural elements 14 are formed of a semi-transparent phase-shifting material. In halftone phase mask usually molybdenum silicide is used.

On the mask substrate 10 is also a second share 18 of the pattern of structural elements attached. At the second share 18 of the pattern are second structural elements 20 also as raised webs with a second height 22 that is less than the first height 16 has arranged. The second structural elements 20 consist of the same semi-transparent phase-shifting material and are also formed on the planar surface of the transparent mask substrate.

The transparent mask substrate 10 points between the second structural elements 20 trenches 26 with a predetermined depth 24 on, immediately adjacent to the second structural elements 20 are arranged.

In 1 are only a few first structural elements 14 and second structural elements 20 the halftone phase mask shown; however, it is known in the art that a pattern of, for example, a semiconductor circuit comprises a large number of first structural elements or second structural elements. In addition to the circuit pattern to be imaged, the first and second structural elements frequently also contain further elements which improve the resolution of a projection apparatus. In addition to the elements known in the art for an Optical Proximity Correction (OPC), the use of sublithographic structural elements in the environment of structural elements to be imaged is provided, or also the mixture with other types of mask like Chrome-on-glass (3tone-masks).

By choosing the first height 16 the first structural elements 14 can the transmittance of the mask substrate 10 within the first structural elements 14 penetrating light beam 28 choose. Halftone phase masks become the first height 16 the first structural elements 14 is selected such that between the light beam penetrating the mask substrate within the first structural elements 28 and one the mask substrate outside the first features 14 in the area of the flat surface 11 the mask substrate penetrating light beam 30 results in a phase jump of about 180 °. This leads to the destructive interference known in the art in the region of the edges of the first structural elements 14 , which thereby obtain a sharper contour.

The same way can be done by choosing the second height 22 the second structural elements 20 the transmittance of the mask substrate 10 within the second structural elements 20 along the way 32 choose penetrating light beam. To achieve the function of a halftone phase mask, the second height becomes 22 the second structural elements 20 and the depth 24 the trenches 26 chosen so that between the mask substrate within the second structural elements 20 along the way 32 penetrating light beam 32 and one the mask substrate outside the second structural elements 20 in the area of the trenches 26 of the mask substrate 10 along the way 34 penetrating light beam results in a phase jump of approximately 180 °. This in turn leads to the destructive interference known in the art in the region of the edges of the second structural elements 20 ,

This will be explained below with reference to two concrete numerical examples. Here, the first structural elements 14 of the first share 12 of the pattern have a transmittance for a light beam of less than 10%, eg about 6%. This corresponds to the transmission level typical in the art for medium transmission imaging. For the second structural elements 20 of the second share 18 of the pattern, a transmittance of about 25% and in another example about 50% is chosen. This is referred to as a transmittance for a high transmission image.

The complex refractive index is used to calculate the absorption or the phase difference. When passing a light beam with the wavelength λ along the route 28 the phase of light changes: Δφ A = (2π / λ) · (n a · d a ).

On the way 30 is the change: Δφ B = (2π / λ) · n U · (D a ) where n _{U is} the real part of the refractive index of the surrounding medium (for example air or nitrogen), n _a of the absorber and d _a the first height 16 the first structural elements 14 is. The path difference between the paths 28 and 30 is: Δφ A, B = (2π / λ) · ((n a - n U ) · D a ).

By choosing the first height 16 the first structural elements 14 (ie the thickness d _a ) and the phase-shifting semitransparent material of the first structural elements 14 (With n _a + ik _a ), the desired transmittance of less than 10% (eg 6%), and the phase difference is set to about 180 °.

The same applies to the passage of a light beam having the wavelength λ along the path 32 , At the same time the phase of the light changes: Δφ C = (2π / λ) · (n a · d c + n s · d s ).

On the way 34 is the change: Δφ D = (2π / λ) · n U · (D c + d G ).

The thickness d _c in this case corresponds to the second height 22 the second structural elements 20 and the size d _s corresponds to the depth 24 the trenches 26 , The path difference between the routes 32 and 34 is: Δφ C, D = (2π / λ) · ((n a - n U ) · D c + (n s - n U ) · Ds).

The same applies if the imaginary parts of the refractive indices are taken into account, which determine the differences in the absorption constants: Δα C, D = i · Δφ C, D = i · (2π / λ) · ((ik a - ik U ) · D c + (ik s - ik U ) · D s ) = - (2π / λ) · ((k a - k U ) · D c + (k s - k U ) · D s ).

By choosing the second height 22 the second structural elements 20 (ie the thickness d _c ) sets the desired transmittance (eg 25% or 50%). The depth 24 the trenches then causes the phase difference of about 180 ° between a light beam along the track 32 and 34 ,

For a construction comprising a mask substrate made of quartz and a phase-shifting semitransparent layer of molybdenum silicide (n _a = 2.52, k _a = 0.67), the following numerical values are obtained, for example at a wavelength of 193 nm: at the first height 16 the first structural elements 14 of 64 nm results in a transmittance of 6%. A height of 32 nm or 16 nm of the second structural elements 20 corresponds to a transmittance of 25% or 50%, in order to achieve a 180 ° phase jump, the depth must be 24 the trenches 26 have a value of 86 nm or 130 nm.

The mask substrate 10 In the previous example, it consists of quartz, but other mask materials known to those skilled in the art are not excluded. It is also provided in the context of the invention, the mask substrate 10 in the form of a multi-layered structure, in which a further layer 36 parallel and immediately at the top 11 of the mask substrate 10 is appropriate. The thickness of the further layer 36 corresponds to the depth of the trenches 26 , A halftone phase mask according to this embodiment is shown in FIG 2 shown.

In addition, it is also provided that the pattern on the halftone phase mask 5 another, third share 38 of the pattern of structural elements. The third share 38 of the pattern of features is to be transferred in a projection onto a photosensitive layer of a semiconductor wafer with a high transmission. As in 3 are shown at the third portion 38 of the pattern third structural elements 40 also as raised bars with a third height 44 arranged. The third structural elements 40 consist of the same semi-transparent phase-shifting material and are also on the flat surface 11 the transparent mask substrate 10 educated. To achieve the desired high transmission, points the third height 44 a lower value than the second height 22 on.

The transparent mask substrate 10 points between the third structural elements 40 more trenches 44 with a predetermined depth 44 on, immediately adjacent to the third structural elements 40 are arranged. The other trenches 44 in turn serve the phase shift analogous to the trenches 26 in the range of the second share 18 to set the pattern.

This results in a halftone phase mask 5 that for the first share 12 , the second share 18 and the third share 38 each of the pattern has different transmittances.

Another possibility of a multi-transmission halftone phase mask is in FIG 4A shown. The pattern on the halftone phase mask 5 again comprises another, third share 38 the pattern of structural elements. The third structural elements 48 However, in this example, they are designed as raised metal structures, for example made of chromium, which are above a semitransparent layer 50 are arranged. The semitransparent layer 50 preferably consists of the same material as the structural elements of the first portion 12 of the pattern. The semitransparent layer 50 is in this example with the same height as the first structural elements 14 shown, other heights are not excluded. The third structural elements 48 show a vanishingly low level of transmittance. In the 4 shown halftone phase mask thus combines the function of a halftone phase mask with two different transmissions for the first and second portion of the pattern with a conventional tri-tone mask for the third portion of the pattern. The chromium is usually used to suppress unwanted interference, which would be imaged as a side-lobe intensities in photoresist.

The chrome can also be in the range of the second part 18 of the pattern on the second structural elements 20 be suppressed to oppress side-praise. This is in 4B shown. The structural element 48 ' is above the structural element 20 appropriate. In addition, it is also provided, third structural elements 48 '' as raised webs of metal on an underlying non-thinned partially transparent phase-shifting absorber layer in the region of the second portion 18 of the pattern comprising the thinned semitransparent phase shifting absorber layer, as in 4B shown.

In the transition region between the first structural elements 14 and the second structural elements 20 If there is a jump in the thickness of the semitransparent material. However, this leads to no unwanted aberrations, since this area is already dark and thus does not cause interference.

The following is with reference to 5 a method for producing a halftone phase mask is described. In a first step, a pattern of structure elements having a first portion and a second portion is provided. This pattern is used in a photomask prepared by the process according to the invention for the lithographic patterning of a photosensitive layer, for example, a semiconductor wafer.

Starting point of the method according to the invention is a mask blank (also called mask blank), as in 5A shown. The mask blank 60 includes a mask substrate 10 with a flat surface 11 , The mask substrate 10 is made, for example, of quartz, ie of silicon dioxide. Above the level surface 11 of the mask substrate 10 becomes an absorber layer 62 of a semitransparent phase shifting material having a first height 16 applied. As semitranspa For example, molybdenum silicide is used as a costly phase shifting material, but other materials known to those skilled in the art are not excluded. Above the absorber layer 62 becomes a metal layer 64 applied, such as chrome / black chrome layers as they are commonly used for Chrome-on-glass masks. Over it becomes a resist layer 66 applied, for example by full-surface deposition.

The next step is the resist layer 66 structured in a mask-lithographically manner. For this purpose, for example, a mask writer is used, which irradiates the resist layer corresponding to the first portion of the pattern and the second portion of the pattern, for example with a light beam or with an electron beam. It is likewise possible with known methods to photolithographically pattern the resist layer 66 by means of a mask in projection exposure. As a result, by developing the irradiated resist layer 66 over the metal layer 64 a resist pattern corresponding to the first portion of the pattern and the second portion of the pattern of features is formed.

In the next step, the resist pattern becomes the metal layer 64 and in the absorber layer 62 for example, transferred by etching. The etchant is chosen so that the mask substrate 10 not attacked. You then get structural elements 68 the metal layer and structural elements 70 the absorber layer, which also correspond to the first portion of the pattern and the second portion of the pattern.

In the next step, the resist pattern is completely removed, resulting in an arrangement as shown in FIG 5B is shown.

Thereafter, a further resist layer 72 For example, by spin coating deposited over the entire surface and then by irradiation and etching (or developing) so structured that the area of the second portion 18 of the pattern is exposed. The resulting structure is in 5C shown.

Subsequently, trenches 26 in the flat top 11 of the mask substrate 10 immediately adjacent to the second structural elements 20 with a certain depth 24 etched. The metal serves as an etching mask.

The structured further resist layer serves in the following as a mask to the metal structure 68 in the range of the second share 18 of the pattern by means of etching.

The next step will be the structural elements 70 the absorber layer 62 in the range of the second share 18 the pattern thinned, ie reduced in height. This is again done with an etching step, wherein also the structured further resist layer 72 is used as a mask. This will be the second structural elements 20 of the pattern as raised webs on the flat top 11 of the mask substrate 10 with a second height 22 educated.

Subsequently, the further resist layer 72 completely removed, eg by etching.

In the next step, the metal layer is in the range of the first part 12 of the pattern to remove first features of the pattern as raised lands on the planar top of the mask substrate at the first height 16 expose. The halftone phase mask 5 after this process step is in 5D shown.

As a variant of the described method, it may be useful to depth the substrate etching 24 at least partially after the thinning of the absorber 62 on the thickness 22 perform and etch the metal layer 64 right after the structuring of the further resist layer, or the first partial etching to a part of the depth 24 perform.

In the 6A to 6D an alternative process control is shown, which allows use of a mask blank without metal layer. These so-called chromium-free mask blanks are widely used in the art and allow a cost-effective production of a halftone phase mask according to the inventive method.

According to 6A is again a mask blank 60 Starting point of the procedure. The mask blank comprises a mask substrate 10 with a flat surface 11 , an overlying absorber layer 62 and a resist layer 66 , The layers used are as related to 5 explained on the mask substrate 10 applied.

The next step is the resist layer 66 structured in a mask-lithographically manner. As a result, a resist pattern corresponding to the first portion of the pattern and the second portion of the pattern of features is formed.

In the next step, the resist structure becomes the absorber layer 62 for example, transferred by etching. The etchant is chosen so that the mask substrate 10 not attacked. You then get structural elements 70 the absorber layer, which also correspond to the first portion of the pattern and the second portion of the pattern.

In the next step, the resist pattern is completely removed, resulting in an arrangement as shown in FIG 6B is shown.

Thereafter, a further resist layer 72 For example, by spin coating deposited over the entire surface and then by irradiation and etching (or developing) so structured that the area of the second portion 18 of the pattern is exposed. The resulting structure is in 6C shown.

The next step will be the structural elements 70 the absorber layer in the region of the second portion of the pattern thinned, ie reduced in height. This is again done with an etching step, wherein the structured further resist layer 72 is used as a mask. As a result, the second structural elements 20 of the pattern are formed as raised ridges on the flat top of the mask substrate with a second height.

Subsequently, as already related to 5 explained, trenches 26 etched in the planar top surface of the mask substrate immediately adjacent to the second features having a certain depth. For this purpose, an etchant is used which has a high selectivity to the mask substrate and the absorber layer.

Subsequently, the further resist layer 72 completely removed, eg by etching, around first features of the pattern as raised lands on the planar top of the mask substrate 10 to expose at the first height. The halftone phase mask after this process step is in 6D shown.

The procedure, as related to the 5 In another embodiment, the invention may be modified to produce a halftone phase mask in which a third portion of the pattern is provided as a COG tri-tone mask. This type of mask has already been discussed in the discussion of 4 explained. The following are with reference to 7 the necessary additional steps in a process for producing a halftone phase mask according to 5 described.

After removing the further resist layer 72 (please refer 7A ) becomes an additional resist layer 74 applied, which is subsequently structured according to the third portion of the pattern. The resulting structure is in 7B shown.

In the subsequent etching, the metal layer is in the region of the first portion 12 the pattern removed to the first structural elements of the pattern as raised ridges on the planar top of the mask substrate 10 to expose at the first height. In addition, third structural elements 78 the metal layer on the flat surface of the semitransparent phase-shifting material 76 applied. This results in a halftone phase mask, as in 7C is shown.

In the described methods, the depth of the trenches and the height of the second structural elements are selected such that a light beam penetrating the mask substrate within the second structural elements has a phase jump in the range of 160 ° to 200 °, preferably 180 °, relative to the mask substrate outside the second Structural elements in the region of the trenches in the surface of the mask substrate penetrating light beam undergoes. The height of the first structural elements is chosen so that the mask substrate 10 within the first structural elements penetrating light beam, a phase jump in the range of 160 ° to 200 °, preferably 180 °, with respect to a mask substrate 10 experiences light beam penetrating outside the first structural elements in the region of the planar surface of the mask substrate.

At the The step of providing the mask blank becomes the height of the absorber layer chosen so that the transmittance of a mask substrate within the first structural elements penetrating light beam less than 10%, preferably about 6%, is and the step of thinning the second structural elements is performed so that the transmittance one the mask substrate within the second structural elements penetrating light beam between 10% and 70%, preferably between 20% and 60%.

The use of the halftone phase mask according to the invention for structuring a light-sensitive layer applied to a semiconductor wafer is particularly advantageous. A construction used for this purpose is in 8th shown.

A semiconductor wafer 82 gets on a moving substrate holder 80 stored. The substrate holder 80 is inside a projector 84 appropriate. The projection apparatus 84 includes a projection optics 86 , a light source 88 and a mask holder 90 that is between the projection optics 86 and the mask holder 90 is attached. After introducing the halftone phase mask 5 in the mask holder 90 becomes a photosensitive layer 92 , For example, a resist layer, on the top of the semiconductor wafer 82 with that on the halftone phase mask 5 exposed patterns exposed.

The Halbtonphasenmas invention Ke or a halftone phase mask produced by the method according to the invention proves to be particularly advantageous when the first portion of the pattern and the second portion of the pattern correspond to a plane of a dynamic random access memory (DRAM) circuit pattern. The dynamic memory comprises a dense line-column pattern in the region of the memory cell array and contains isolated or semi-isolated structures in the area of the support logic outside the memory cell array. In a halftone phase mask for dynamic random access memory, the second portion of the pattern in the region of the memory cells has dense structures (eg, line-column patterns) which are preferably transmitted with high transmission in the manufacture of the integrated circuit. At the same time, the first part of the pattern in the area of the support logic outside of the memory cell array also comprises isolated and semi-isolated structures whose imaging should take place with low transmission. The halftone phase mask provides different transmittances for the simultaneous optimization of both structural components, resulting in a large process window in the manufacture of the integrated circuit.

5

Halbtonphasenmaske

10

transparent mask substrate

11

level surface

12

first proportion of

14

first structural elements

16

first height

18

second proportion of

20

second structural elements

22

second height

24

depth

26

trenches

28

route a ray of light

30

route a ray of light

32

route a ray of light

34

route a ray of light

36

layer

38

third proportion of

40

third structural elements

42

Further trenches

44

depth the other trenches

46

third height

48

metal structure

48 '

structural element made of metal

48 ''

structural element made of metal

50

semi-transparent material

60

mask blank

62

absorber layer

64

metal layer

66

resist layer

68

metal structure

70

structural elements

72

Further resist layer

74

Further resist structure

76

semi-transparent material

78

metal structure

80

substrate holder

82

Semiconductor wafer

84

projector

86

projection optics

88

light source

90

mask holder

92

photosensitive layer

Claims (26)

Halftone phase mask for projecting a pattern of structural elements formed on the mask onto a photosensitive layer in the manufacture of integrated circuits on a semiconductor wafer, comprising: a transparent mask substrate ( 10 ); - a first share ( 12 ) of a pattern in which first structural elements ( 14 ) as raised ridges with a first height ( 16 ) of a semi-transparent phase-shifting material deposited on the flat surface ( 11 ) of the transparent mask substrate ( 10 ) is arranged, are formed such that a the mask substrate ( 10 ) within the first structural elements ( 14 ) penetrating light beam a phase jump in the range of 160 ° to 200 ° relative to a mask substrate ( 10 ) outside the first structural elements ( 14 ) in the area of the flat surface ( 11 ) of the mask substrate ( 10 ) undergoes penetrating light beam; and - a second share ( 18 ) of the pattern in which second structural elements ( 20 ) as raised webs with a second height ( 22 ) from the same semitransparent phase-shifting material of the first structural elements ( 14 ) placed on the flat surface ( 11 ) of the transparent mask substrate ( 10 ) and adjacent to the second structural elements ( 20 ) arranged trenches ( 26 ) in the surface of the mask substrate ( 10 ) with a depth ( 24 ) are formed such that the mask substrate ( 10 ) within the second structural elements ( 20 ) penetrating light beam a phase jump in the range of 160 ° to 200 ° relative to a mask substrate ( 10 ) outside the second structural elements ( 20 ) in the area of the trenches ( 26 ) in the surface of the mask substrate ( 10 ) penetrating light beam, the first height ( 16 ) greater than the second height ( 22 ), so that in the first share ( 12 ) of the pattern, the mask substrate ( 10 ) within the first structural elements ( 14 ) penetrating light beam has a lower transmittance than a mask substrate ( 10 ) within the second structural elements ( 20 ) penetrating light beam. Halftone phase mask according to claim 1, wherein the transmittance of a mask Subst advice ( 10 ) within the first structural elements ( 14 ) penetrating light beam is less than 10% and at which the transmittance of the mask substrate ( 10 ) within the second structural elements ( 20 ) penetrating light beam is between 10% and 70%. Halftone phase mask according to Claim 1 or 2, in which the mask substrate ( 10 ) consists of quartz. Halftone phase mask according to one of claims 1 to 3, in which the semitransparent phase-shifting material molybdenum silicide includes. Halftone phase mask according to one of Claims 1 to 4, in which the second component ( 18 ) of the pattern comprises a line-column pattern. Halftone phase mask according to one of Claims 1 to 5, in which the first component ( 12 ) of the pattern has larger center-center distances of the structures than the second portion ( 18 ) of the pattern. Halftone phase mask according to claims 5 and 6, in which the pattern of a plane of a circuit pattern of a dynamic Memory with random access corresponds. Halftone phase mask according to one of Claims 1 to 7, in which the mask substrate ( 10 ) a multilayer construction with at least one parallel to and at the top layer ( 36 ), wherein the thickness of the layer ( 36 ) on top of the mask substrate ( 10 ) the depth ( 24 ) of the trenches ( 26 ) corresponds. A halftone phase mask according to any one of claims 1 to 7, further comprising a third portion ( 38 ) of the pattern, in which third structural elements ( 40 ) as raised webs with a third height ( 46 ) from the semitransparent phase-shifting material deposited on the flat surface ( 11 ) of the transparent mask substrate ( 10 ) and in the surface of the mask substrate ( 10 ) adjacent to the third structural elements ( 40 ) further trenches ( 42 ) with a further depth ( 44 ) are formed such that the mask substrate within the third structural elements ( 40 ) penetrating light beam a phase jump in the range of 160 ° to 200 ° relative to a mask substrate ( 10 ) outside the third structural elements ( 40 ) in the area of the further trenches ( 42 ) in the surface of the mask substrate ( 10 ) penetrating light beam, whereby the further depth ( 44 ) of the further trenches ( 42 ) greater than the depth ( 24 ) of the trenches ( 26 ). Halftone phase mask according to one of Claims 1 to 8, which furthermore has a third portion of the pattern, in which third structural elements ( 48 ) are arranged as raised ridges on a flat surface of the semitransparent phase-shifting material. Halftone phase mask according to one of Claims 1 to 8, which furthermore has a third portion of the pattern, in which third structural elements ( 48 '; 48 '' ) as raised webs of metal over the underlying thinned or undiluted semi-transparent phase-shifting absorber layer in regions of the second portion ( 18 ) of the pattern with thinned semitransparent phase-shifting material and its openings are arranged. Halftone phase mask according to Claims 10 and 11, in which the third structural elements ( 48 ) comprise a patterned chromium layer. Method for producing a halftone phase mask comprising the following steps: - providing a pattern of structural elements with a first fraction ( 12 ) and a second share ( 18 ); - providing a mask blank ( 60 ) comprising a mask substrate ( 10 ) with a flat surface ( 11 ), an overlying absorber layer ( 62 ) of a semitransparent phase shifting material having a first height ( 16 ), one above the absorber layer ( 62 ) lying metal layer ( 64 ) and one above the metal layer ( 64 ) Resist layer ( 66 ); Mask-lithographic structuring of the resist layer ( 66 ) to form a resist pattern corresponding to the first fraction ( 12 ) of the sample and the second component ( 18 ) of the pattern corresponds; Transferring the resist structure into the metal layer ( 64 ) and in the absorber layer ( 62 ) by etching to form a metal structure ( 68 ) and structural elements ( 70 ) of the absorber layer; - removing the resist structure; - full-surface deposition of another resist layer ( 72 ); Irradiating the further resist layer ( 72 ); Etching or developing the further resist layer ( 72 ), the second share ( 18 ) of the pattern; - etching of trenches ( 26 ) in the flat top ( 11 ) of the mask substrate ( 10 ) immediately adjacent to the second structural elements ( 20 ); Removing the metal structure ( 68 ) in the range of the second part of the sample, structural elements ( 70 ) to expose the absorber layer; - thinning of the structural elements ( 70 ) of the absorber layer in the region of the second portion of the pattern to form second structural elements ( 20 ) of the pattern as raised ridges on the planar top surface of the mask substrate having a second height ( 22 ) to build; Removing the further resist layer ( 72 ); and - removing the metal structure ( 68 ) in the area of first share ( 12 ) of the pattern to first structural elements ( 14 ) of the pattern as raised ridges on the flat top ( 11 ) of the mask substrate ( 10 ) with the first height ( 16 ). A method of producing a halftone phase mask comprising the steps of: - providing a pattern with a first portion ( 12 ) and a second share ( 18 ); - providing a mask blank ( 60 ) comprising a mask substrate ( 10 ) with a flat surface, an overlying absorber layer ( 62 ) of a semi-transparent phase-shifting material having a first height ( 16 ) and one above the absorber layer ( 62 ) Resist layer ( 66 ); Mask-lithographic structuring of the resist layer ( 66 ) to form a resist pattern corresponding to the first fraction ( 12 ) of the sample and the second component ( 18 ) of the pattern corresponds; Transferring the resist structure into the absorber layer ( 62 ) by etching to structural elements ( 70 ) of the absorber layer ( 62 ) to build; - removing the resist structure; - full-surface deposition of another resist layer ( 72) ; - exposing the further resist layer ( 72 ); Etching or developing the further resist layer in order to obtain in the region of the second component ( 18 ) of the pattern, the structural elements ( 70 ) to expose the absorber layer; - thinning of the structural elements ( 70 ) of the absorber layer in the region of the second portion ( 18 ) of the pattern, so that second structural elements ( 20 ) of the pattern as raised lands on the planar top surface of the mask substrate ( 10 ) with a second height ( 22 ) are formed; - forming trenches ( 26 ) in the flat top ( 11 ) of the mask substrate ( 10 ) immediately adjacent to the second structural elements ( 20 ) of the pattern; Removing the further resist layer ( 72 ) in the region of the first portion of the pattern, so that the first structural elements ( 14 ) of the pattern as raised lands on the planar top surface of the mask substrate ( 10 ) with the first height ( 16 ) are exposed. Method according to Claim 13 or 14, in which the depth of the trenches and the height of the second structural elements ( 20 ) are selected so that the mask substrate ( 10 ) within the second structural elements ( 20 ) penetrating a phase jump in the range of 160 ° to 200 ° with respect to a mask substrate outside the second structural elements ( 20 ) in the area of the trenches ( 26 ) in the surface of the mask substrate ( 10 ) experiences penetrating light beam. Method according to Claim 15, in which the height of the first structural elements is selected so that the mask substrate ( 10 ) within the first structural elements ( 14 ) penetrating light beam a phase jump in the range of 160 ° to 200 ° relative to a mask substrate ( 10 ) outside the first structural elements ( 14 ) in the region of the planar surface of the mask substrate ( 10 ) experiences penetrating light beam. Method according to one of claims 13 to 16, wherein in the step of providing the mask blank ( 60 ) the height ( 16 ) of the absorber layer ( 62 ) is selected so that the transmittance of the mask substrate ( 10 ) within the first structural elements ( 14 ) penetrating light beam is less than 10%, and in which the step of thinning the second structural elements ( 20 ) is performed so that the transmittance of the mask substrate ( 10 ) within the second structural elements ( 20 ) penetrating light beam is between 10% and 70%. Method according to one of claims 13 to 17, wherein in the step of providing the mask blank ( 60 ) a mask substrate ( 10 ) is used, which consists of quartz. Method according to one of claims 13 to 18, wherein in the step of providing the mask blank ( 60 ) is used as a semitransparent phase-shifting material molybdenum silicide. A method according to any one of claims 13 to 19, wherein Step of providing the pattern as a second portion a line-column pattern is used. Method according to one of claims 13 to 20, wherein in the step of providing the pattern the first portion ( 12 ) of the pattern have larger center-center distances of the structures than the second portions ( 18 ) of the pattern. The method of claim 20 and 21, wherein at Step of providing the pattern the pattern to the circuit pattern a dynamic random access memory accordingly selected becomes. Method according to one of claims 13 to 22, wherein in the step of providing the mask blank ( 60 ) a mask substrate is used, which has a multilayer structure with at least one on the planar upper side of the mask substrate ( 10 ), wherein the thickness of the layer on top of the mask substrate is the depth of the trenches ( 26 ) is carried out accordingly. Method according to Claim 23, in which the trenches ( 26 ) through a to the mask substrate ( 10 ) selective etching of the layer are formed. The method of claim 13, wherein the step of providing further comprises a third portion ( 38 ) of the pattern of structural elements is provided and in which, after removal of the further resist layer ( 72 ) is additionally applied an additional resist layer, which is subsequently structured in accordance with the third portion of the pattern, so that in the step of removing the metal layer, the metal layer in the region of the first portion ( 12 ) of the pattern is removed to form first structural elements ( 14 ) of the pattern as raised lands on the planar top surface of the mask substrate of the first height (FIG. 16 ) and, in addition, third structural elements ( 78 ) as metal structures on a flat surface of the semitransparent phase-shifting material ( 76 ). Method according to Claim 25, in which the third structural elements ( 78 ) are formed as a structured chromium layer.