HK1030833A - An improved system and method for automated defect inspection of photomasks - Google Patents

Description

Improved system and method for automatic fault detection of photomasks

The present invention relates to semiconductor manufacturing equipment, and more particularly to an improved system and method for automated fault detection of photomasks.

Semiconductor manufacturing processes typically include lithographic processes for forming patterned areas on the surface of a semiconductor device. The semiconductor manufacturing process generally involves overlaying a photoresist material on the surface of the semiconductor device and patterning the photoresist material by exposing the photoresist material to light, particularly violet infrared light, to crosslink the photoresist material, which crosslinks the photoresist material and prevents reaction with a developer because the photoresist material, if developed, can no longer crosslink by exposure to violet infrared light. Other types of photoresists are prevented from cross-coupling when exposed to ultraviolet infrared light.

A photomask is used to form a pattern on a photoresist and functions as a mask to block light from passing through predetermined areas of the photomask during photolithography, and typically has a black or highly absorbing material layer, such as chrome or chrome alloy, that is patterned according to the pattern design to be raised on the photoresist. The absorber layer is formed on a substrate, which may comprise glass or quartz material.

As the size of semiconductor devices becomes smaller, the fabrication of photomasks becomes more difficult and it is required that the inspection reliability of photomasks should be secured. The failure detection capability of these photomasks is related to a certain minimum feature size, which generally refers to the basic specification (GROUNDRULE) of the features used to manufacture the photomask, i.e., the minimum feature size is 150NM for 1 mask magnification and 600NM for 4 mask magnification.

Because photomasks include features that are less than one micron in size, inspection of photomasks is typically performed by a microprocessor using automated inspection equipment. Referring to FIG. 1, a measurement device 10 includes a stage 14 for positioning a photomask 16 to be measured, an energy source 18 for emitting light of a predetermined intensity toward the photomask, a photosensitive device or sensor 20 for correcting the reflected and/or transmitted light intensity, and storing the data in a memory 22. Based on the transmitted and reflected light intensities, a processor 24 performs calculations to determine the corrected feature size. The processor 24 includes a data set for comparing the light intensity distribution of the photomask to be inspected. Two inspection systems are used to inspect the photomask, one of which is a stamp-to-stamp approximation method that compares features of the photomask to similar features of the same photomask to determine if a defect is present. Generally, ultraviolet light is irradiated onto a photomask to be inspected and a main photomask, the intensity of the emitted laser light and/or reflected light is measured, and the patterns of the two photomasks are compared. The second approximation is a die-database measurement system that includes a Reference Database Computer (RDC) in processor 24 that provides a digital image for comparing the photomask to be inspected, which is the most accurate manufacturing process, that demonstrates that the original circuit has been properly replicated on the photomask, that the laser beam has propagated through, or reflected from, the photomask to be inspected, and that the light intensity at a particular location is compared to the digital image.

Both of these methods are capable of detecting complex reticle patterns, including those of narrow size, compact Optical Proximity Correction (OPC) and Phase Shift Masks (PSM). OPC helps compensate for lost light and ensures that an accurate pattern can be formed on a semiconductor wafer, for example, if there is no OPC, a rectangle can look like an ellipse from the end because the edges have a corner rounding effect, OPC corrects the corner rounding problem by adding small serifs (lines) towards the corners to ensure that the corners are not rounded or to move one feature edge so that the size of the wafer feature is more accurate. The phase shift mask changes the phase of a light beam passing through the photomask and allows improvement of the depth of focus and resolution of wafer surface non-uniformity.

In conventional automated systems, a certain number of sub-primitive specification features may lead to failure to detect the photomask. To successfully form sub-micron features on a silicon wafer, sub-primitive specification features on the photomask appear to become more and more abundant.

In one example, an active area mask (photomask) is used to form the Active Area (AA) of a trench type Dynamic Random Access Memory (DRAM) design. To equate to this reduction in feature length, the features to be designed on the photomask are asymmetrically offset due to the corner rounding effect. Such biasing includes shrinking or increasing in size, which may be accomplished through database manipulation (database biasing), or through process control (process biasing). This bias will be larger and larger as the base specification decreases. An example of an offset is shown in fig. 2. One 40-line design has a basic specification of 175NM, with a length of 1050NM, spaced from another 42-line design by 350NM, which is also 1050 NM. For 40 'lines and 42' lines, one photomask datum is biased by 200NM, and the design lengths of 40 lines and 42 lines can be obtained. However, a length of 1250NM forms a 150NM void 44, i.e., a sub-baseline specification feature.

The bias often produces sub-standard feature sizes on the photomask of interest for imaging processes based on an unused cell design, e.g., for a 150NM basic standard, the spacing between adjacent AA features along one axis is about 300NM, which data is saved as design size. Offset lengths of each shape greater than 75NM produce a sub-base specification feature on the mask (see fig. 2). A similar situation may occur if a serif is created by writing an optically approximately corrected data set on the mask, and if an assist feature is present in a Chrome On Glass (COG) or phase shift mask.

As shown in fig. 3, serifs 50 and 52 of the mask are shown in the figure, serifs 50, 52 and line 53 are used to produce lines 54 and 56, respectively. Other assist features may also be used, for example assist features 58, 60 and 62 may be used to generate structures 64 and 66, respectively, as shown in FIG. 4, where serifs and assist features often generate sub-primitive specification features on a photomask.

Because photomasks enable defect-free inspection due to the generation of these sub-basic specification features when they are fabricated, it is desirable to provide a system and method for eliminating defect defects in photomasks at the beginning of the generation of the sub-basic specification features on the photomasks.

A method for inspecting a photomask according to the present invention includes the steps of providing a design data set for manufacturing a photomask, searching the design data set for sub-basic specification features, eliminating the sub-basic specification features based on the design data set to form an inspection data set, and inspecting the manufactured photomask based on the design data using the inspection data set.

Another method of inspecting a photomask comprising the steps of providing a design data set for manufacturing a photomask, identifying sub-basic specification features in said design data set that meet a predetermined dimensional criteria, eliminating the identified sub-basic specification features from said design data set to form inspection data, providing an inspection tool, inspecting the manufactured photomask according to the design data against data in the inspection data set, adjusting said inspection tool, scanning the identified sub-basic specification features, and inspecting the manufactured photomask using said inspection data set. A program storage device readable by a computer, wherein program instructions are executable by the computer to perform method steps for detecting a photomask, the method steps comprising: providing a design data set for manufacturing the photomask, searching the design data set, finding out the sub-basic specification features, eliminating the sub-basic specification features according to the data set to form a detection data set, and detecting the manufactured photomask according to the design data by using the detection data set.

In other methods, the method step of detecting a photomask can be performed by a computer, the sub-specification features can include sub-specification gaps, and the step of eliminating the sub-specification features can further include the step of merging features of the design dataset located near the gaps, thereby eliminating the gaps in the test design set. The step of merging features may merge features using a biasing process. The photomask may further include sub-standard lines, and the step of removing sub-standard features may further include the step of removing sub-standard lines from the design data set for providing the inspection data set. The step of searching the design data set for the sub-base specification features is searching the design data set according to a predetermined feature size standard to determine the sub-base specification features. The step of inspecting the photomask according to the design dataset using the inspection dataset may include adjusting a sensitivity of an inspection tool to scan sub-specification features. The step of providing said set of design data for manufacturing a photomask may comprise providing a digital image of a computer drawing for manufacturing a photomask.

In yet another method, the step of forming a set of test data can further include the step of merging features of the design data set located near the gap, thereby eliminating the gap in the test design set, and/or the step of removing a sub-standard line from the design data set for providing said test data set. The step of searching the design data set for sub-base specification features may include searching the design data set for sub-base specification features based on predetermined feature size criteria.

The above and other objects, features and advantages of the present invention will become more apparent and readily appreciated from the following detailed description of the embodiments taken in conjunction with the accompanying drawings.

Preferred embodiments of the present invention will now be described in further detail with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating a conventional photomask inspection system;

FIG. 2 is an example of offsetting according to the prior art;

FIG. 3 is a case where a serif is used according to the prior art;

FIG. 4 is a case where assist features are used according to the prior art;

FIG. 5 is a block diagram of a photomask inspection system implemented in accordance with the present invention;

FIG. 6 is a top plan view of an enlarged photomask feature provided as a set of design data sets representing a subroutine gap to be detected, implemented in accordance with the present invention;

FIG. 7 is a top plan view of the enlarged photomask feature modulation of FIG. 6 resulting in a set of inspection data sets utilizing data merge features to eliminate the above-described gaps, implemented in accordance with the present invention;

FIG. 8 is a top plan view of an enlarged photomask feature provided as a set of design data sets representing a subroutine line segment to be inspected, implemented in accordance with the present invention;

FIG. 9 is a top plan view of the enlarged photomask feature modulation of FIG. 8 resulting in a set of inspection data sets with the line segments eliminated by the data merge feature implemented in accordance with the present invention; and

FIG. 10 is a block diagram/flow diagram illustrating a photomask inspection system/method of the present invention.

The present invention relates to semiconductor manufacturing equipment, and more particularly to an improved system and method for automatically detecting defects in a photomask. The method of the invention comprises a method for eliminating sub-routine features after comparison with actual features of a photomask on the basis of a reference data set, and a system for implementing said method, in one embodiment of the invention the detection sensitivity is attenuated, so that features smaller than a predetermined size will not be detected, in such a way that the resolution of the mask detection becomes higher, since those sub-routine features will be weakened, which no longer cause detection to be invalid. One advantage of the inventive arrangements is that a set of test or design data sets is created that is used as reference data for comparing photomask features, and the merged features are used to control the data sets, eliminating subroutine gaps and removing subroutine print patterns.

Referring now in detail to the drawings in which like reference numerals represent the same or similar elements throughout the several views, there is shown in FIG. 5 a block diagram of a system 100 implemented in accordance with the present invention, the system 100 including a light source 102 for directing a beam of light onto a photomask 104 to be inspected, the photomask 104 having a pattern having a shape or characteristic lithographically generated for a semiconductor device.

A sensor 106 is used to measure the intensity of light striking the photomask 104 and reflected and transmitted by the photomask, respectively. A processor 108 is used to calculate the reflected and transmitted optical densities to identify the mask pattern on the mask 104. The processor 108 includes a memory 110 for storing density data and the like, the memory 110 further including a set of inspection data sets 112 forming an inspection pattern for comparison with the pattern to be formed on the photomask 104, the inspection data sets 112 preferably being created using a set of design data sets 113 in accordance with the present invention, and an application software 114 in the memory for execution by the processor 108 to perform the inspection. A stage or robot 116 is controlled by the processor 108 to move the photomask 104 under the beam of the light source 102, which is preferably a laser light source, particularly an infrared light source such as an excimer laser. However, the laser source may be moved and the mask 104 may be stationary. Application software 114 performs a comparison calculation of optical density between data set 112 containing the digital image of photomask 104 and photomask 104.

If the process is small, such as less than 1 micron, the photomask 104 includes sub-process features for improving the fabrication of the photomask 104, such as serifs, line segments, voids, and the like. In addition, the rounded corner feature of the photomask may be calculated, and may also include the shape of a subroutine or the shape described above.

In accordance with the present invention, sub-routine features, such as shape features, are eliminated from the data set 112 by offsetting adjacent features to eliminate gaps, merging the gaps, and eliminating the gaps based on the detected conditions.

Referring now to fig. 6 and 7, showing the subroutine features of the present invention for designing patterns and detecting patterns, respectively, two segments 150 in fig. 6 are separated by a gap 152 in the photomask 104, the gap 152 having a dimension "a" which is a subroutine feature, and in a preferred embodiment of the present invention, the segment numbers 150 and 152 represent a set of digital design data sets created using computer aided design tools or a density profile of an actual photomask which, when digitized, may be manipulated in accordance with the present invention, the design data representing the subroutine features of fig. 6 preferably being used as reference data or data set 112 (fig. 5). In FIG. 7, segments 150 are offset along their length, eliminating gaps 152 between the stages, and after merging segments 150, the data is stored in data set 112 to be used to inspect photomask 104. In this manner, if a void 152 is found during inspection of the photomask, the inspection device will not confirm that this is a defect because the void 152 has been eliminated from the dataset 112, and if a set of design datasets is provided, it is recommended to run a search algorithm that activates the application software 114 (FIG. 5) to retrieve subroutine features such as assist feature serifs, etc., based on the size or area of the features, and the same features are automatically deleted from the dataset 112.

Referring to fig. 8 and 9, the subroutine features of the design pattern and the test pattern of the present invention are shown, respectively. As can be seen in FIG. 8, the two segments 154 are separated by a gap 156 and a subroutine line segment 158 on the photomask 104. The size of the line segment 158 is "B", which is a subroutine feature. In the preferred embodiment, segments 154, line segments 158, and spaces 156 are included in a set of digitized design data sets created using computer aided design tools or by creating a density map of the actual photomask. According to the invention, the set of configuration data sets is processed after the digitization has been achieved. The design data representing the subroutine features of fig. 8 is preferably used as reference data for the data set 112 (fig. 5). In fig. 9, segment 154 is located for processing while segment 158 is removed, and after segment 158 is removed, the set of data becomes data set 112. In this manner, if line segment 158 is encountered during inspection of photomask 104, it will not be considered a defect because void 152 is eliminated from the data set 112 for inspection, and when a set of design data sets is provided, subroutine features, such as assist features, serifs, etc., are preferably retrieved using a search algorithm (FIG. 5) in application software 114. Such retrieval may be based on the size or area of the feature, whereupon the identified feature is automatically eliminated from the data set 112. If the features stored in the data set 112 have changed as described above, then inspection of the photomask is performed.

It should be noted that the components shown in fig. 10 may be implemented by using various forms of hardware, software or their combination. For example, these components may be implemented in software executable on one or more appropriately programmed general-purpose digital computers including a processor, memory and input/output interfaces. Referring now to the drawings, wherein like reference numerals designate identical or similar parts throughout the several views, fig. 1-10 illustrate a system/method for inspecting a photomask, with subroutine features, implemented in accordance with the present invention. In block 202, an inspection system, such as system 100 (FIG. 5), is provided for inspecting the photomask. In block 204, a set of design data sets for the photomask is provided or generated and stored in a memory. In block 206, a search algorithm is executed that identifies the characteristics of the subroutine, preferably using the application software of a general purpose computer. The search algorithm searches for design data, other things, assist features, or shift measurements of the sub-program features contained in the photomask to prevent the fillet effect from occurring. Such a search may be performed using predetermined criteria such as the area of a feature, the minimum length of the feature, or the spacing (spacing) between features. In block 208, the lines or areas are eliminated by moving the gaps and merging the identified features, and/or using the processor. In block 210, a set of test data sets is created based on the revised design data. In block 212, the detection criteria are adjusted so that the sub-program features present on the photomask, generated from said design data, will not be recognized by the detection device (system 100), and in this way the photomask will become particularly suitable for detecting a criteria that closely approximates the size of said sub-program features. In block 214, the system 100 of the present invention removes the subroutine features from the corrected inspection data and uses the inspected design data to create the actual photomask.

While the improved automatic photomask defect inspection system and method of the present invention have been described in terms of preferred embodiments (which are intended to be illustrative and not limiting), it is noted that numerous variations and modifications can be made by those skilled in the art in light of the teachings of the present invention, which are set forth herein in the examples without departing from the principles of the invention and the scope of the appended claims. The above detailed description of the invention is written in order to satisfy the requirements of patent law, and the literal language of the invention claimed is briefly summarized in the appended claims.

Claims (20)

1. A method of inspecting a photomask comprising the steps of:

providing a set of design data for manufacturing a photomask;

searching the design data set to find out the sub-basic specification characteristics;

removing the sub-primitive specification features from said data set to form a test data set, and

the manufactured photomask is inspected based on the set of design data using the set of inspection data.

2. The method of claim 1, wherein a sub-basic specification feature comprises a sub-basic specification gap, and wherein the step of eliminating a sub-basic specification feature further comprises the step of merging features of a design data set located in the vicinity of the gap, thereby eliminating the gap in the test data set.

3. The method of claim 2, wherein the step of merging the features comprises using a migration process to achieve the merged features.

4. The method of claim 1, wherein the photomask includes sub-baseline specification lines, and wherein the step of removing the sub-baseline specification features further comprises the step of removing the sub-baseline specification features from the design dataset to provide the test dataset.

5. The method of claim 1, wherein the step of searching the design data set for sub-base specification features comprises the step of searching the design data set for sub-base specification features based on predetermined feature size criteria.

6. The method of claim 1, wherein said step of using said test data set to test the photomask being fabricated based on said design data set includes the step of adjusting the sensitivity of a test tool to scan said sub-basic specification features.

7. The method of claim 1, wherein the step of providing a design data set for manufacturing a photomask comprises the step of generating said photomask using a computer-aided digital image.

8. A method of inspecting a photomask comprising the steps of:

providing a set of design data for manufacturing a photomask;

identifying sub-basic specification features in said design data set that meet a predetermined dimensional criterion;

removing the identified sub-primitive specification features from the design dataset to form a test dataset;

providing a detection tool for comparing the data of the photomask and the detection data set which are manufactured according to the design data detection;

adjusting the detection tool to scan the identified sub-basic specification features; and

the manufactured photomask is inspected using the set of inspection data.

9. The method of claim 8, wherein said sub-basic specification features comprise sub-basic specification gaps, and said step of eliminating sub-basic specification features further comprises the step of merging features of design data sets located adjacent to said gaps, thereby eliminating said gaps in said test data sets.

10. The method of claim 9 wherein the step of merging the features includes using a migration process to achieve the merged features.

11. The method of claim 8, wherein the photomask includes sub-baseline specification lines, and wherein the step of forming the test data set further comprises the step of removing the sub-baseline specification features from the design data set to provide the test data set.

12. The method of claim 8, wherein the step of searching the design data set for sub-base specification features comprises the step of searching the design data set for sub-base specification features based on predetermined feature size criteria.

13. The method of claim 8, wherein the step of providing a design data set for manufacturing a photomask comprises generating the photomask using a computer-aided digital image.

14. A program storage device readable by a computer, wherein program instructions are executable by the computer to perform method steps for detecting a photomask, the method steps comprising:

providing a set of design data for manufacturing a photomask;

searching the design data set to find out the sub-basic specification characteristics;

removing the sub-basic features from said data set to form a test data set;

and detecting the manufactured photomask according to the design data by using the detection data group.

15. The program storage device of claim 14, wherein said sub-basic specification features comprise sub-basic specification gaps, and said step of eliminating sub-basic specification features further comprises the step of merging features of design data sets located adjacent to said gaps, thereby eliminating said gaps in said test data sets.

16. The program storage device of claim 15, wherein the step of merging features comprises the step of implementing the merging features using a migration process.

17. The program storage device of claim 14, wherein the photomask includes sub-base specification lines, and wherein the step of forming the test data set further comprises the step of removing the sub-base specification features from the design data set to provide the test data set.

18. The program storage device of claim 14, wherein said step of searching the design data set for sub-base specification features comprises the step of searching the design data set for sub-base specification features based on predetermined feature size criteria.

19. The program storage device of claim 14, wherein said step of using said inspection dataset to inspect a fabricated photomask in accordance with said design dataset comprises the step of scanning said sub-basic specification features by adjusting the sensitivity of an inspection tool.

20. The program storage device of claim 14, wherein the step of providing a design data set for manufacturing a photomask comprises generating the photomask using a computer-aided digital image.