DE102006033450B4 - Substrate and method for producing a photomask - Google Patents

Abstract

A substrate (1) comprising: - a patterned conductive layer (3) disposed over a substrate surface (10) such that one or more intermediate layers may be interposed between the conductive layer (3) and the substrate surface (10); a first region (91) within the patterned conductive layer (3) comprising first structures of the material of the patterned conductive layer (3), and a second region (92) within the patterned conductive layer (3) of alignment marks (3) 7) provided for determining the relative position of the patterned layer disposed on the substrate (1) with respect to a reference position, wherein the alignment marks (7) are formed from the material of the patterned conductive layer, the substrate further comprising one comprising connecting line (93a-d) formed of the conductive material of the patterned conductive layer (3) and connected to at least one of Alignment marks (7) is connected, wherein the connecting line (93a-d) is also connected to a second structure (94) on the substrate (1), which is held at a predetermined potential, so that the alignment mark (7) on the given Potential is held.

Description

The present invention relates to a substrate having alignment marks capable of determining the relative position of a pattern formed on a substrate or a structure formed on a substrate with respect to a reference position using an electron beam, and a method of manufacturing the same a photomask.

In the manufacture of a semiconductor device, such as an integrated circuit or the like, the device components are usually formed by patterning layers deposited on a silicon wafer. The patterning of these layers is usually achieved by applying a resist material to the layer to be patterned and subsequently exposing predetermined areas of the resist layer that are sensitive to the exposure wavelength. Thereafter, the resist material is developed and the irradiated or unirradiated areas are removed. As a result, portions of the layer to be patterned are masked by the photoresist pattern produced during a subsequent processing step, such as an etching step or an implantation step. After performing the processing step on the exposed areas of the layer to be structured, the resist mask is removed.

For patterning the resist layer, photolithographic masks (photomasks) are usually used to transfer a predetermined pattern to the layer to be patterned.

Standard chromium-on-glass (COG) glasses each comprise a substrate made of a transparent material, such as quartz glass, and a structured layer of opaque material, such as a metal, such as chromium. Phase masks (PSM) differ from standard chrome masks in that they contain two types of transparent regions. The optical path length of the light waves in the two areas is different by λ / 2, which corresponds to a phase shift of 180 °. In a halftone phase mask, a phase-shifting semitransparent material such as MoSi (molybdenum silicide) is deposited on a transparent substrate such as a quartz substrate. The MoSi layer is structured. In addition, sections of a structured, opaque layer, for example of chromium, are applied to the structured regions of the MoSi layer. In other words, a halftone phase mask is composed of an unstructured quartz substrate and two differently structured layers, a phase-shifting, semitransparent layer and an opaque layer.

In contrast, an alternating-phase mask of a transparent substrate, for example, a quartz substrate, which is itself structured, and a structured opaque layer applied thereto, for example a structured chromium layer, constructed.

When producing a halftone phase mask and also an alternating phase mask, the problem arises that two different layers have to be structured independently of one another with different patterns. For example, in a first step, the (semitransparent) phase-shifting layer can be patterned, while in a second step the opaque chromium layer is patterned or vice versa. Usually, in a first step, two superimposed layers are structured together, while in a second step, the upper of the two layers is patterned with a different pattern. For this purpose, in each case two different exposure steps are carried out with a respective suitable resist layer.

Conventionally, the first layer to be patterned has been patterned using electron beam lithography, while in the second layer to be patterned, the corresponding photoresist material has been exposed by laser lithography. The alignment of the pattern to be transferred to the second layer with respect to the pattern transferred to the first layer is accomplished by using alignment marks patterned in the first layer and detected by the laser beam.

1A shows an exemplary mask 9 with a sensitive area 91 which contains the pattern to be patterned later on the wafer and a peripheral area 92 which is outside the sensitive area. The alignment marks 7 are within the border area 92 arranged.

As in 1B 2, the laser beam used in the second exposure step, which is from a laser source, is scanned 8th has been generated, the area of the registration mark 7 and indicates the position of the alignment marks. From the position of alignment marks 7 lets the relative position of the on the surface 10 of the mask substrate 1 generated pattern with respect to a reference position such as the zero position of the scanning laser source 8th determine so that the exposure of the second layer can be done with the required overlay accuracy.

As in 1B is shown is the alignment mark 7 on the surface 10 of the quartz substrate 1 arranged. The alignment mark 7 is completely from the photoresist layer 6 covered.

To produce ever-smaller structures in semiconductor device fabrication, it is necessary that the structures of the masks contain dimensions of ever smaller size. However, these are no longer achievable with the conventional structuring using a laser beam. For this reason, structuring of the second layer using an electron beam is increasingly employed. It is assumed that for structure sizes of less than 65 nm to be generated, the second lithography stage must also be exposed using electron beam lithography.

When adjusting the already processed mask substrate, however, using the conventional alignment mark, there is the problem that the alignment marks are isolated on an insulating quartz material and, moreover, are covered with an insulating resist layer. Usually, the secondary electrons reflected by the substrate are detected for adjustment with an electrode detector. This method works very well to study surfaces because the generated secondary electrons are virtually unadulterated into the detector. Obtaining information from the volume is much more difficult with this method, since the secondary electrons are exposed to matter interactions as they pass through the volume. The state of the electrons is thus always subject to a certain energy and momentum distribution. In the image thus generated, this effect is reflected as a blur. The blurrier the image becomes, the more difficult it is to determine the position of the alignment marks.

Since the alignment marks charge upon irradiation with electron beams and thus have a similar potential as the surrounding resist, a distorted image of the alignment mark is produced at the electron detector. For this reason, accurate detection of the position of the alignment marks has not been possible. As a result, an overlay error occurs in the second patterning step. Furthermore, distortion of the generated pattern occurs.

To solve the problem, it has been proposed to apply a conductive layer on the upper resist layer. As a result, a reduction of the overlay error induced by surface charges has been achieved. Volume effects can not be compensated or minimized with this method.

US Pat. No. 6,531,786 B1 For example, an alignment mark having a pattern of marking elements disposed on a conductive layer is described. The US 2002/0081815 A1 as well as the US 2002/0158348 A1 also deal with structures that are useful in processing substrates with charged particles.

In the DE 101 42 593 A1 and the associated subsequent application US 2003/0044698 A1 In addition, a method for adjusting a phase-shifting mask having a multilayer structure will be described.

In addition, are from the US Pat. No. 6,180,291 B1 Photo masks are known in which a conductive layer is disposed above or below the mask structures to avoid electrostatic charging.

It is an object of the present invention to provide alignment markings which enable an exact relative positioning of the electron beam relative to a structure previously formed on the substrate for structuring the second layer to be patterned. The present invention is also based on the object to provide an improved method for producing a photomask.

According to the present invention, the object is achieved by the substrate according to claim 1 and the method according to claim 5. The preferred embodiments are subject of the dependent claims.

According to the present invention, the object is provided by a substrate having a region of a patterned conductive layer disposed on a substrate surface and alignment marks disposed on the substrate surface for determining the relative position of the patterned layer disposed on the substrate with respect to a reference position wherein the alignment marks are formed of the material of the patterned conductive layer, the substrate further comprising a connection line formed of a conductive material connected to the alignment mark and adapted to hold the alignment mark at a predetermined potential ,

As a result, secondary electrons, which come from the alignment marks, have a significantly different energy and momentum distribution than the secondary electrons generated in the volume. The electrons from the alignment marks can thus be easily distinguished from the other electrons, which significantly improves the imaging quality. The more precise the Alignment mark is reproduced, the more accurate the position of this structure can be determined. This enhancement of the positioning of the alignment mark directly contributes to an improvement in the position determination of the sensitive area.

The present invention thus provides a substrate with alignment marks, with which the relative position of a substrate with respect to a reference position, for example an internal position (0, 0 coordinate) of the electron beam device can be determined. Specifically, it is possible to make an accurate alignment with respect to the patterned conductive layer using a charged particle beam.

The substrate may be any substrate, but in particular an insulating or semiconducting substrate. The substrate may in particular be a mask substrate on which a photolithographically usable mask will be produced in the subsequent process steps. In particular, the substrate may be an insulating substrate having a plurality of layers deposited thereon. However, the substrate can also be constructed from a conductive material and comprise at least one insulating layer applied to the substrate surface. The alignment mark is made of the material of the patterned conductive layer. Accordingly, the manufacture is particularly simple, and a local reference to the pattern generated in the structured conductive layer is established. The alignment mark is made of a conductive material and further includes a connection lead, which is also formed of a conductive material and connected to the alignment mark. The connection line is suitable for keeping the alignment mark at a predetermined potential. Preferably, the connecting line is made of the material of the structured conductive layer. For example, the connection line allows a connection of the alignment mark with another structure, which is kept at a predetermined potential. This structure may in particular be arranged on the mask itself and, for example, grounded.

Alternatively, however, the structure can also be arranged outside the mask. Preferably, the alignment mark is made of the same material as the connection line, so that the connection line can be easily produced simultaneously with the structuring of the alignment mark.

For example, where the substrate is a mask substrate, the area of the structured conductive layer comprises the pattern to be transferred through the mask.

According to the present invention, it is preferred that at least one connecting line is suitable for connecting two alignment markings with one another. Thereby, the number of connection lines can be reduced.

Preferably, the substrate further comprises a portion of another patterned layer disposed between the substrate surface and the patterned conductive layer. This means that the structured conductive layer does not necessarily rest directly on the substrate surface, but one or more intermediate layers may still be arranged between the conductive layer and the substrate surface.

The present invention further provides a method of making a photomask, comprising the steps of providing a mask substrate, providing a first layer to be patterned, providing a second layer of conductive material to be patterned on the first layer to be patterned, and providing a first resist layer on the second layer to be patterned, patterning the first resist layer, transferring the pattern formed in the first resist layer into the second and first layers to be patterned, depositing a second resist layer, patterning the second resist layer, and transferring the generated resist pattern to the second pattern to be patterned A layer, wherein, by the step of patterning the first resist layer, alignment marks for determining the relative position of the patterned area formed in the first patterning step with respect to a reference position d and the alignment marks are etched in the step of transferring the pattern formed in the first resist layer to the second layer to be patterned, further comprising the step of providing connection lines connected to the alignment marks and adapted to align the alignment marks on a predetermined one To hold potential.

In the method according to the invention, patterns are thus produced in two different layers. This is done by transferring a first pattern into the first and the second layer to be structured in a first step. In a second step, a second pattern is transferred only to the second layer to be structured. In the first step, registration marks are simultaneously transferred to the second layer to be patterned. Thereby, a positional relationship between the first pattern and the alignment marks is set and is not subject to any adjustment-related fluctuations. By adjusting the second pattern on the alignment marks thus also the positional relationship of the second pattern is clearly defined with respect to the first pattern. Furthermore, the method according to the invention is less complex if alignment marks are simultaneously transferred to the second layer to be structured in the first step.

Preferably, the connecting lines will be defined in the step of patterning the first rice layer. As a result, further processing steps can be saved.

Furthermore, it is preferred that the connection line is connected to a structure on the substrate, wherein the structure is kept at the predetermined potential.

The present invention will be further described below with reference to the accompanying drawings. Show it:

1A a conventional mask after performing the first structuring step;

1B a schematic arrangement for determining the position of the alignment mark;

2 - 6 Steps in generating a halftone phase mask;

7A a plan view of a mask with alignment marks according to the invention;

7B a schematic arrangement for determining the position of the alignment marks;

7C an exemplary measurement result;

8th - 10 further steps for producing the halftone phase mask; and

11 a plan view of a substrate with four alignment marks according to an embodiment of the present invention.

In 2 are on a transparent mask substrate, such as synthetic quartz 1 , on the surface 10 a semitransparent MoSi layer 2 with a layer thickness of about 300 nm, a chromium layer 3 with a layer thickness of about 70 nm and a resist layer 4 from an electron beam sensitive material such as FEP 171 Fujifilm applied with a layer thickness of about 300 nm. The MoSi layer corresponds to this 2 the first layer to be structured, while the chromium layer 3 corresponds to the second layer to be structured. First, the resist layer 4 structured using electron beam lithography. More specifically, predetermined areas of the resist layer 4 according to a predetermined pattern the electron beam 5 exposed.

In this case, in particular, the electron resist layer for structuring the alignment marks 7 with the associated connection lines 93a , b, c, d exposed.

After the exposure step, the resist material becomes 4 depending on whether a positive or negative electron resist is used, the exposed or unexposed areas are dissolved in a suitable developer. Subsequently, using a plasma etching method with a conventional etching gas mixture such as He, Cl ₂ , O ₂ as an etching gas, the exposed portions of the chromium layer 3 etched. The resulting structure is in 3 shown. In this etching step, the alignment marks also become 7 with the associated connection lines 93a etched, b, c, d.

The following is the electron resist material 4 removed, as in 4 is shown.

Subsequently, using a plasma etching process with, for example, He, Cl ₂ , O ₂ as the etching gas mixture, the now exposed areas of the MoSi layer 2 etched.

The resulting structure is in 5 shown.

To carry out the second stage of the mask production, the in 5 shown substrate with another electron resist layer 6 covered. The second electron resist layer 6 may be of the same material as the first electron resist layer 4 be built or also from a different material.

7A shows a plan view of the previously processed substrate with the associated alignment marks 7 , In 7A includes the previously processed mask substrate 9 a sensitive area 91 which contains the circuit pattern to be transferred later to the wafer, and a peripheral area 92 , Within the border area 92 are the alignment marks 7 arranged. The alignment marks are designed, for example, as crosses with a length of intersecting beams of 20 to 40 μm. Furthermore, connection lines 93a provided to d, which are suitable, the alignment marks 7 to hold on to a given potential.

As in 7A shown are the connecting lines 93a to 93d with a grounded one structure 94 connected. As in 7A shown, run the connecting lines 93a to 93d within the periphery of the mask substrate 9 , Because of the connecting lines 93a to d the alignment marks 7 with the grounded structure 94 The alignment marks do not load when covered with an electron resist material and exposed to an electron beam, so that detection with high accuracy is possible.

Usually, after application of the second electron resist material, metallic, knife-like structures are thus applied to the second electron resist layer 6 placed in contact with an underlying conductive layer, such as the chrome layer 2 will be produced. These knife-like structures are grounded so that eventually the contacted conductive layer is grounded. For example, the connecting lines 93a -D be associated with these knife-like structures.

Then, using the electron beam writer, the second electron resist layer 6 exposed. In order for the second exposure step to have a correct alignment with respect to the first structured layer, the mask must be exactly aligned before the start of the second exposure step. Satisfactory quality of the phase-shifting pattern can only be achieved if this alignment is done with high accuracy. For this reason, before starting the exposure, a step of determining the position of the alignment marks 7 carried out.

7B shows a structure for determining the position of the alignment marks 7 , reference numeral 5 denotes the electron beam generated by an electron beam writer which scans the substrate surface. The electron beam is generated to produce a secondary electron beam 51 from the substrate surface or alignment mark 7 reflected and from an electron detector 52 demonstrated.

As in 7C is shown, the electron beam scans the flanks of the alignment mark, and the reflected electrons are determined. The reflectance of the surface depends on whether the surface is covered with a conductive or insulating material. It results in the lower part of 8C shown distribution of secondary electrons. reference numeral 55 indicates the center of gravity of the distribution shown 54 , Finally, the shape of the alignment mark can be determined from the center of gravity positions. From the positions of the alignment mark, the relative position of the on the mask substrate 1 formed pattern with respect to a reference position, in particular the reference or (0, 0) position of the electron beam writer determine. As a result, the electron beam generated by the electron beam writer is properly positioned to achieve an accurate superposition of the patterns to be written.

Because, as with reference to 7A has been described, the alignment marks 7 with the connecting lines 93a -D are connected, the detection of the alignment marks with an electron beam, an electrical charge of the alignment marks is avoided. As a result, the positions of the alignment marks 7 be determined more accurately, resulting in a reduction of the overlay error of the second structuring step.

8th schematically shows the subsequent second exposure step for exposing the second electron resist layer 6 , Here is the electron beam 5 as described above, appropriately positioned to ensure exact alignment of the patterns to be written. Subsequently, as in 9 again, the electron resist material is developed, wherein, depending on whether a positive or negative resist is present, the exposed or unexposed areas are dissolved in the developer, and the underlying exposed areas of the chromium layer 3 are etched by a plasma etching method using an etching gas mixture of, for example, He, Cl ₂ , O ₂ . Finally, after removal of the electron resist layer, the in 10 shown in cross-section structure. Here is the sensitive area 91 arranged in the middle, while the edge area 92 located outside the middle range.

11 shows a further embodiment of the substrate according to the invention with a plurality of alignment marks 7 and the associated connection lines 93a to d. As in 11 is shown, the connection lines are arranged so that they adjacent registration marks 7 connect with each other. As a result, the connecting lines can be arranged in a particularly space-saving manner.

Although, as stated above, the alignment marks according to the invention are particularly advantageous in the production of photomasks, it is obvious that they can equally be applied whenever two different electron beam exposure steps are carried out on an arbitrary substrate.

LIST OF REFERENCE NUMBERS

1

quartz substrate

10

substrate surface

2

MoSiON film

3

chromium layer

4

first electron resist layer

5

electron beam

51

secondary electron

52

electron detector

53

Scanning direction of the electron beam

54

detected secondary electron signal

55

Center of gravity of the secondary electron signal

6

second electron resist layer

7

alignment

8th

laser source

9

photomask

91

sensitive area

92

border area

93a

connecting line

93b

connecting line

93c

connecting line

93d

connecting line

94

grounded structure

Claims (7)

Substrate ( 1 ) comprising: - a structured conductive layer ( 3 ) over a substrate surface ( 10 ) is arranged so that still one or more intermediate layers between the conductive layer ( 3 ) and the substrate surface ( 10 ), - a first area ( 91 ) within the structured conductive layer ( 3 ), the first structures of the material of the structured conductive layer ( 3 ), and - a second area ( 92 ) within the structured conductive layer ( 3 ), the alignment marks ( 7 ), which is used to determine the relative position of the material on the substrate ( 1 ) are provided with respect to a reference position, wherein the alignment marks ( 7 ) are formed from the material of the structured conductive layer, wherein the substrate further comprises one of the conductive material of the structured conductive layer ( 3 ) formed connecting line ( 93a to d) associated with at least one of the alignment marks ( 7 ), the connecting line ( 93a -D) also with a second structure ( 94 ) on the substrate ( 1 ), which is held at a predetermined potential, so that the alignment mark ( 7 ) is maintained at the predetermined potential. Substrate ( 1 ) according to claim 1, characterized in that at least one connecting line ( 93a to d) two alignment marks ( 7 ) connects to each other. Substrate ( 1 ) according to claim 1 or 2, characterized in that the substrate is a mask substrate. Substrate ( 1 ) according to claim 1, characterized in that the structure ( 94 ) is grounded. A process for producing a photomask, comprising the steps of: - providing a mask substrate ( 1 ), - providing at least one first layer to be structured ( 2 ), - providing a second layer to be structured ( 3 ) of a conductive material on the first layer to be patterned ( 2 ) and - providing a first resist layer ( 4 ) on the second layer to be structured ( 3 ), - structuring of the first resist layer ( 4 ), - transmitting in the first resist layer ( 4 ) in the second ( 3 ) and in the first ( 2 ) layer to be structured, - application of a second resist layer ( 6 ), - structuring of the second resist layer ( 6 ) and - transferring the generated resist pattern into the second layer to be structured ( 3 ), wherein the step of structuring the first resist layer comprises first structures and alignment marks ( 7 ) for determining the relative position of the structured region formed in the first structuring step with respect to a reference position, and the first structures and the alignment marks ( 7 ) in the step of transferring the in the first resist layer ( 4 ) generated pattern in the second layer to be structured ( 3 ), further comprising the step of providing connection lines ( 93a to d) with a second structure ( 94 ) on the substrate ( 1 ), the second structure ( 94 ) is maintained at a predetermined potential, and with the alignment marks ( 7 ), so that the alignment marks ( 7 ) are kept at the predetermined potential, wherein the connecting lines ( 93a to d) from the material of the second layer to be structured ( 3 ) consist. The method of claim 5, wherein the interconnection lines in the step of patterning the first resist layer (16). 4 ) To be defined. Method according to claim 5 or 6, characterized in that the second structure ( 94 ) is grounded.

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