NL8820330A - MASK REPAIR USING AN OPTIMIZED FOCUSED ION BUNDLE SYSTEM. - Google Patents

Abstract

Apparatus and method for repairing semiconductor masks (32) and reticles is disclosed, utilizing a focused ion beam system (8) capable of delivering, from a single ion column, several different species of focused ion beams (12), each of which is individually optimized to meet the differing requirements of the major functions to be performed in mask repair. This method allows the mask (32) to be imaged with high resolution and minimum mask damage. Opaque defects are removed by sputter etching at high rates with minimum damage to the mask substrate (32), with the optional use of a sputter rate enhancing gas such as chlorine, and clear defects are filled in at high rates by deposition of a metallic or other substance compatible with the mask materials by condensation of metal-containing vapor such as chromium hexacarbonyl using a focused ion beam. A focused ion beam column able to produce precisely focused ion beams (12) is employed and is operated at high energies for imaging and sputter etching, and at low energies for imaging and deposition. A liquid metal alloy source (10) containing a plurality of suitable atomic species is employed.

Description

E 6846-1 Ned.PCT iG / EvF P & C

Short designation: Mask repair, using an optimized focused ion beam system.

The present invention relates to focused ion beam systems. In addition, the present invention relates to chemical vapor deposition and uses focused ion beams to increase chemical vapor deposition rates and sputter etching rates of substrate material. More particularly, the present invention relates to the use of the above techniques for repairing photomasks and crosshairs.

The state of the art is the KLA / micrion 808,

Seiko SIR1000, and Ion Beam Systems' MicroTrim. These three systems provide only one type of focused ion beam to the repairable mask, namely a Gallium ion beam of energy between 20 and 50 keV. Such a beam produces significant damage to the mask during imaging due to the high sputtering speed of the Gallium ion beam. In addition, significant amounts of Gallium are expanded into the mask substrate during imaging and repair of an opaque defeat, resulting in an effect called "Gallium contamination," which causes local reductions in substrate transparency, which are susceptible to later identification as opaque -Appearance defects through standard industrial mask-20 inspection devices. Although these systems approach purity defect repair differently, neither of these systems introduces a material in the purity defect which is compatible with the pre-existing usually masked metal film parts, usually chromium, The invention involves a new technique the repair of semiconductor masks and crosshairs, using a focused ion beam system capable of supplying, through a single ion beam column, various types of ion beams, each of which is individually optimized to meet the different requirements of the main functions to be performed during the mask repair. These 30 main functions are: mask image (the formation of an image of the microscopic structure of an area of the surface of a mask); opaque defeat repair (removing optically opaque material from areas on the surface of the mask substrate where such material should not be present); and purity defect repair (the use of the focused ion beam to catalyze the deposition of a chromium alloy material at undesirable locations on the surface of the mask substrate).

8820330 -2-

Features of the invention include: use in mask repair of multiple ion beam column produced, mask image with greatly reduced levels of damage and contamination, repair of opacity defects by either 5 sputter etching or chemically enhanced sputter etching, and repair of purity defects by the deposition of metal materials, which in optical properties strongly correspond to the metal materials normally used for the opaque surfaces of the mask.

The invention allows the mask to be formed with a high resolution and reduced damage rate, allows for opacity defects to be removed more efficiently with a reduced damage rate of the mask substrate, and ensures that purity defects are filled at high speeds using the beam for directly catalyzing the deposition of metal material, compatible with the natural mask materials.

The present invention has five major components. An ion beam column is used, which can produce an accurately focused ion beam, with a beam diameter at the target site, typically less than 0.5 microns, and can operate at a voltage in the range of 2 20 4 to 120 kV with a current density from 1 to 5 A / cm. A liquid metal alloy source for the ion beam column contains suitable atomic species comprising: a low atomic weight element which is compatible with the mask substrate material (for example: silicon); a high atomic weight element which will produce a high sputter etching rate of the optically opaque metal film for rapid repair of opaque defects (eg: gold); an element to be used for the ion-amplified deposition of a metal material, compatible with the metal material normally to be used for covering opaque surfaces of the mask (for example: gold, chromium, or silicon, used to enhance chromium deposition from chromium hexacarbonyl vapor or other compositions).

A mass filter provides rapid selection of the ions desired for the beam at the mask. Either the low atomic weight element or the high atomic weight element can be selected depending on whether the sputter etching or the precipitate is chosen.

A gas supply system is used in the present invention.

It provides a flow of metal-containing vapor in the vicinity of the intersection of the primary ion beam and the target surface during purity defect repair.

882.0330.

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The gas feed system can also provide a flow of etch-rate increasing gas in the vicinity of the intersection of the primary ion beam and the target surface during opaque defect repair. This system is optional, and may consist in part of the same gas feed system used to supply metal-containing vapor as described above.

Fig. 1 shows the focused ion beam system for mask repair.

Fig. 2 shows the mask image.

Fig. 3 shows the repair of opaque defects.

FIG. 4 shows the purity defects repair.

Fig. 5 shows a flow chart for the purity defect repair process.

Fig. 6 shows a flow chart for the opacity defects repair process.

Before imaging the photomask or reticle to be repaired, the mass filter is set to select a beam of the low atomic weight element, the ion column is set to produce a precisely focused beam of the ions on the target surface, and the beam is scanned in a grid pattern to produce an image of the mask structure. The low atomic weight element may be silicon, compatible with the mask substrate material. In this mode of operation, the ion beam causes minimal damage to the mask surface (translucent and opaque surfaces) due to its low sputter erosion rate of the mask surface. In addition, because the ion-25 type is chosen to be compatible with the mask substrate, it causes minimal "contamination" of the translucent surfaces of the mask.

To repair an opaque defect, a first beam of a high atomic weight element is produced, which efficiently removes most of the unwanted optically opaque material. This first beam is produced by adjusting the mass filter to select a beam of the high atomic weight element, adjusting the ion column to produce a precisely focused ion beam, and scanning only the ion beam by unwanted optical opaque material covered areas. The first ion beam quickly removes this unwanted material by a sputter etching process, which can optionally be accelerated by using an etch rate increasing gas, such as chlorine.

8820330.! -4-

When this unwanted material has been largely removed, the system can optionally switch to a second beam using the low atomic weight element. This second ion beam has a sputter etching rate which is significantly less than that of the first ion beam, but still large enough to remove a very thin layer (about 0.01 micrometers) of material which is contaminated in an acceptable time by implanted atoms of the first (high atomic weight) ion beam, which previously scanned the surface with the opaque defect. Implanted atoms of this second ion beam will not contaminate or "contaminate" the mask substrate, since the second ion beam type is compatible with the mask substrate material.

To repair a pure hero defect, the mass filter is set to select an ion type capable of stimulating ion beam enhanced deposition of a metal material from a metal containing vapor. This requires the ion beam to have enough energy to enhance the dissolution of the vapor only in those areas of the mask surface that are scanned by the ion beam to leave an optically opaque metal deposit. At the same time, the ion beam cannot have a sputter etching rate which exceeds the deposition rate. The mass filter is adjusted to select this desired ion type for the beam, the ion column is adjusted to produce an accurately focused ion beam on the target surface, and the beam scans the purity defect region.

The metal element in the metal-containing vapor is chosen to be compatible with the conventional metal film partially covering the mask.

Fig. 1 shows an apparatus 8 for producing focused ion beams according to the present invention. Ion source 10 can be the source of composite ion beam 12, which is a composition of various ion species in the present invention. Composite ion beam 12 first passes through extraction port 14. A voltage is supplied between ion source 10 and this extraction port 14, to induce a strong electric field at the location of the emission point of ion source 10. This electric field emits ions along the optical column for Forming composite ion beam 12. Composite ion beam 12 then meets beam limiting aperture 16 which contains a hole defining the half-angle of the ion beam 12 passing to the remainder of the optical column. That portion of the composite ion beam 12 which passes through the beam limiting opening 16 is focused 8820330.

-5- in the plane of mass separation aperture 24 by means of the upper electrostatic lens 18. After passing the upper electrostatic lens 18, the composite ion beam 12 passes through the mass filter 20, which converts the various ion beams into the composite ion beam 12 separates. In the figure, two separate ion beams are shown, mass-separated beam 26 and ion beam 39. Mass-separated beam 26 represents an ion species contained in the composite ion beam 12, which is not desired in ion beam 39. For example, ion beam 39 would consist of a light ion species, e.g.

Silicon, while mass separated beam 26 would consist of the high atomic weight ion species not desired for imaging. After passing mass filter 20, ion beam 12 (which, as shown, is split into a mass separated beam 26 and ion beam 39) passes through beam extractor 22. The function of beam extractor 22 is to "extract" ion beam 39 from the target surface, ie switch it on and off. Beam extractor 22 turns off the ion beam 39 by deflecting it from the column axis so that it can no longer pass through mass separation opening 24. Ion beam 39 is then turned on again by deactivating beam extractor 22. After passing mass separation aperture 24, ion beam 39 passes through the upper reflector 28, which is used to align ion beam 29 with respect to the lower electrostatic lens 30. The beam then passes through the lower electrostatic lens 30, which lens directs the ion beam 39 onto the surface of the mask 32. Main reflector 34 is an electrostatic octagon, which has variable electrostatic dipole voltages in X and Y directions, for deflecting the ion beam 39 across the surface of mask 32. A channel electron multiplier 36 (CEM or channeltron) is known as a means for capturing secondary electrons or ions from the mask surface for imaging.

Ion source 10 is a standard liquid metal type, such as those from FEI Co., Hillsboro, Oregon; V.G. Instruments, Ine., Stamford, Connecticut; or MicroBeam, Inc., Newbury Park, California.

Ionenborn 10 is mounted in an ion gun structure, which also carries the extraction port 14. This cannon structure is also of one of the above-mentioned standard source types. The diameter of the beam limiting opening 16 determines the total current in the beam 12 as it enters the top lens 18 and the mass filter 20. This aperture will generally have a half-angle beam of 1 to 4 millirads, yielding beam currents of 100 to 1000 pA. These openings are standard 8820330.

-6- products from Advanced Laser Systems, Waltham, Massachusetts and National Aperture, Lantana, Florida. The upper lens 18 forms an image of ion source 10 on mass separation opening 24. When mass filter 20 is activated, ion beam 12 is separated into different beams at the location of mass separation opening 24. Mass separated beam 26 shows one of these beams.

With a suitable choice of the mass filter setting, the desired species in the composite ion beam 12 will pass through the mass separation opening 24 to form ion beam 39. It will be apparent to those skilled in the art that one preferred embodiment for mass filter 20 is a Wien (ExB) filter, which uses crossed electric and magnetic fields to separate beams of different speeds. The correct balancing of the electrical and magnetic field strengths in this ExB mass filter for selecting the desired 15 ion types for ion beam 39 is easy for experts to understand.

In general, the lenses, mass filters, deflectors and extractors are not standard products. However, they are integral components of commercially available ion columns, such as those manufactured by MicroBeam Inc., Newbury Park, California; JEOL, 20 Boston, Massachusetts; and Ion Beam Systems, Beverly, Massachusetts.

When ion beam 39 is not required for any of the mask repair processes described in Figs. 2-4, it is turned off by beam extractor 22. This prevents unwanted exposure of the mask to ion beam 39. The bottom lens 28 is used for depositing on the surface. 25 depicting plane of mask 32 the beam junction formed at the location of the mass separation opening 24. Using main deflector 34, the ion beam generally scans according to a grating pattern for imaging as is known in the art. To repair a defect, the main deflector 34 scans the beam only in the defect 30 areas within the image raster pattern. Channel electron multiplier 36 of either secondary electrons or secondary ions, emitted by the mask 32 due to impact of the focused ion beam 39. It may be one produced by Galileo Electo-Optics of Sturbridge, Massachusetts; or Detector Technology, Brookfield, Massachusetts are standard products.

Mask 32 is mounted on a movable object table 38, which provides accurate positioning of mask 32 under the ion beam 12. Fig. 1 shows one means known in the art for performing this mask positioning position, an X-Y obticle table, BSZÖ530.

-7- sufficient for positioning the mask with an accuracy within 1 micron in X and Y relative to the known defect location.

The center of the field of view for the imaging process described in Figure 2 is the optical axis of the ion column, while its magnitude 5 is determined by the total acceleration voltage of ion beam 39 (voltage difference between ion source 10 and mask 32), and the field strength and length of main deflector 34, as is apparent to experts.

In a preferred embodiment, ion source 10 may be a conventional ion source containing an alloy of gold and silicon. An alloy 10 of chromium, gold and silicon containing ion source can also be used. Such ion sources will produce a composite ion beam from which a single species can be selected using a known mass filter 20.

In a preferred embodiment, the ratio of the alloy-15 components of the gold / silicon ion source may be 15 to 25% silicon, and the remainder gold. A typical alloy for the source could be a gold-silicon eutectic alloy consisting of 18.6 atomic% silicon and 81.4 atomic% gold (melting point about 363 ° C). When a triple chromium-gold-silicon alloy is used for ion source 10, the 20 preferred components may be 20 to 45% chromium, 1 to 55% gold, and the remainder silicon. Manufacture of such alloys is known to experts. Experts will also readily recognize that two dual alloy ion sources can be used. A first dual alloy ion source for use in imaging (Fig. 2) and opaque defect repair (Fig. 3) can be used in combination with a second dual alloy ion source for use in Fig. (Fig. 2) and purity defect repair (fig. 4). Selection of suitable dual alloys for the first and second ion sources is easy for experts.

The function of mass filter 20 is to select between the image (Fig. 2) and repair (Fig. 3, 4) ion beam types, as can be judged by experts. Imaging the defect area before performing a defect repair is necessary to ensure that the purity defect or opaque defect repair will only scan the actual areas of the defect.

The device of the present invention can be used to repair opaque defects in masks using a sputtering process. The sputtering rate can optionally be increased by using a gas which is on the mask surface 882.0930.

-8- reacts with the ions in the primary ion beam 39. A focused ion beam of the sputtering ion type is used at an energy greater than 10 keV with a current density in the range of 1-5 K / cm. Gas feed tube 13 conducts an etch rate increasing gas, such as chlorine, 5 near the target surface. The design of this gas feed tube will be known to experts. Pre-repair mapping (Fig. 2) is also performed at the same voltage level for accurate mapping.

For purity defect repair, the device of the present invention applies material to the mask 32 (Fig. 4), a focused ion beam is used at an energy greater than 2 10 keV with a current density in the range of 1-5 K / cm. Gas feed tube 13 conducts a metal-containing vapor, such as chromium hexacarbonyl, near the target surface. Pre-repair mapping (Fig. 2) is also performed at the same voltage, again to ensure accuracy.

It will be apparent to those skilled in the art that it is preferable to neutralize the accumulated charge on the surface of mask 32 before it reaches a level affecting the optical action of the beam (position, size, current density, energy). A presently preferred method of neutralizing the ion beam is by using a flood gun 37 known in the art to flood the surface of mask 32 with electrons. This flooding process can take place simultaneously with the imaging (Fig. 2) or repair (Fig. 3, 4) processes, or alternately with them.

Imaging is performed using a type of scanning microscopy, which uses either secondary electrons or secondary ions. A collector 36 captures secondary particles of any type for use in imaging as is known in the art. Imaging techniques are known and are outside the scope of the invention.

FIG. 2a shows the mask image as typically performed in the art. Mask substrate 40 consists of atoms 42 of a first atomic type, usually silicon. Opaque regions 44 consist of atoms 46 of a second atomic type, typically chromium. Imaging type ions 48 are used, which implant 35 into the pure regions of the mask, resulting in contamination or "contamination" of the mask substrate 40, as shown. Moreover, the impact of primary ions 48 results in the sputter removal of substrate atoms 40 and opaque region atoms 46 from the mask, as shown. The "pollution" and the sputtering

mO330.J

Etching both result in unwanted damage to the mask.

Fig. 2b shows the mask image as performed according to the present invention. The details of the mask substrate 40, substrate atomic species 42, opaque regions 44, atomic species 46 of the opaque regions are the same as for Fig. 2a.

The present invention differs from the prior art in the use of imaging atoms 40a, which when implanted in the mask substrate cause very little "fouling". The impact of primary ions 40a results in much less sputter removal from the substrate of substrate atoms 40 and 46 in the opaque region. The net result is significantly reduced damage to the translucent and opaque areas of the mask.

Fig. 3a shows the repair of opacity defects, as typically performed in the prior art. Mask substrate 40 consists of atoms of a first atomic type 42, typically silicon. Opaque region 44 consists of atoms of a second atomic type 46, typically chromium. Adjacent to the desired opaque region 44 is opacity defect region 50, consisting of the atomic species 52. Atomic species 52 is shown here as being identical to the atomic species 46 of the opaque region. It is possible that the opacity defect region 50 may consist, in whole or in part, of a third atomic species. In addition, it is also possible that opacity defect region 50 may be isolated and not in contact with a desired opaque region. Gallium ions 48 are used for sputter etching of region 50, resulting in the implantation of Gallium atoms into the substrate 40, causing "fouling" and thus reduced light transmission through the mask substrate 40 into the regions of Gallium implantation.

FIG. 3b shows the repair of opaque defects as performed according to the present invention. The details of the substrate 40, substrate atomic type 42, opaque region 44, atomic type 46 of the opaque region, discord defect region 50, and atomic type 52 of the opaque defect region are the same as for Fig. 3a. The present invention differs from the prior art by using high atomic weight ion species 54, which are shown here in sputter etching of opaque region 50. Atomic species 54 is chosen to maximize the efficiency of the sputter etching process. Optionally, the speed of sputter etching can be further increased 082 0330.

-10- using an etch rate-increasing gas 56. This system is optional and may consist in part of the same gas feeding system used to provide the metal-containing vapor for the precipitate. The pressure of the etching rate-increasing gas is in the range of 1 to 100 microTorr. This range is chosen to provide sufficient gas to significantly increase the etch rate while still maintaining the target ion beam focused on the target.

Fig. 4a shows the repair of purity defects, as typically performed in the art. Two alternative procedures are commonly used. In the top figure, a process of beam-increased carbon deposition is shown. Gallium ions 80 cause the decomposition of carbonaceous gas molecules 82 at the site of the surface of the mask substrate 40, consisting of atomic type 42, typically silicon. Although this process applies an opaque piece over the brightness defect, this piece differs greatly from the optical properties of the original opaque mask material 44, which contains atomic type 46, typically chromium. For example, the opaque piece is black in reflected light, compared to the relatively shiny chrome under-shine areas of the mask. It also has different behavior during the opacity defect repair process discussed in Fig. 3.

In the bottom figure of Figure 4a, an alternative procedure used in the brightness defect repair technique is shown. Gallium ions 80 are used to apply special shapes 82 to the surface of the mask substrate 40 consisting of the atomic species 42, typically silicon, by the sputtering technique 25. These shapes are designed to deflect light away from the brightness defect area, thus making this area appear dark. This process has the drawback of being very slow, non-reversible and limited to the particular wavelength of light for which the special shapes 82 are designed.

Fig. 4b shows the repair of purity defects as performed according to the present invention. Primary ions 100 scan the region of the purity defect 102, typically an undesired hole in the opaque region 44, consisting of the atomic species 46, typical chromium.

While primary ions 100 scan the purity defect region, a flow of metal-containing gas molecules 104 is directed to the surface of the mask in the vicinity of the region where primary ions 100 collide with the surface of the mask substrate 40, consisting of the atomic species 8820330.

-11- 42, typical silicon. Primary ions 100 induce the decomposition of metal-containing molecules 104 only in the region directly scanned by the beam, thus causing a deposition of metal atoms 106 within the defect region. The mass flow rate of the metal-containing vapor is adjusted to provide a pressure near the target surface in the range of 1 to 100 microTorr. This range is chosen to provide sufficient vapor for efficient beam deposition while still ensuring that the primary ion beam remains focused on the target. Since the deposited metal atoms are compatible with the original opaque region 44, the repair recovery is almost indistinguishable from these original opaque regions in appearance and behavior during the opaque defect repair process of FIG. 3. In the lower figure of FIG. 4b, the completed purity defect repair of the present invention is shown schematically.

Fig. 5 shows a preferred embodiment for the purity defect repair process. First of all, in block 200, the area on the mask containing the defect is depicted as described in Fig. 2b. After the defect area is imaged, the beam is extracted (removed from the mask). In block 202, the exact area of the purity defect is then determined within the total image area. In block 204, the flow of metal-containing gas is activated. During the flow of this metallic gas on the mask surface in the vicinity of the intersection of the ion beam and the mask substrate, in block 206 the ion beam is turned on and only the exact region of the purity defect is scanned. In the process shown in Fig. 4b, a deposit of metal material compatible with the original opaque mask material is formed. After a time determined for applying a sufficient material thickness, block 108 is reached, in which the ion beam 30 is again extracted and the metal-containing gas supply is then stopped. Block 210 then depicts the defect area, as was done in block 200, using the procedure described in Fig. 2b. Using the image shown in block 210, the operator (or system computer) makes a decision in block 212 whether the purity defect 35 is fully repaired. If the mask image indicates that the defect has not yet been fully repaired, a branch 214 from block 212 leads back to block 202. In block 202, the remaining defect area is redefined as described above. If the image resulting from block 210 indicates that the defect has been fully repaired, one results in 8 * 20530.

Block 212 coming branch 216 to process completion block 218.

Fig. 6 shows a preferred embodiment for the opaque defect repair process. First, in block 250, the area on the mask containing the defect is depicted as described in Fig. 2b.

5 After the defect area is imaged, the beam is withdrawn (removed from the mask). In block 252, the exact area of the opacity defect is then determined within the total image area.

Optionally, in block 254, an etching rate-increasing gas supply can be activated. In block 256, the desired ion species for sputter etching the opacity defect is then selected, using the mass filter and the beam is turned on and only the defect area is scanned. After the opacity defect is removed, block 258 is reached, in which the beam is again extracted and the etching rate-increasing gas feed is inactivated, if it was activated in block 254. Block 256 then displays the mask again, as was done in block 250, using the procedure described in Fig. 2b. Using the image shown in block 260, the operator (or system computer) makes a decision in block 262 whether the opaque defect has been fully repaired. If the mask image indicates that the defect has not yet been fully repaired, a branch 264 coming from block 262 leads back to block 252. In block 252, the remaining defect area is redefined, as described above. If the image resulting from block 260 indicates that the defect has been completely repaired, a branch 266 from block 262 leads to block 268.

After the defect is removed, some residual contamination of the mask substrate may remain. In block 268, an optional scan using an ion species compatible with the substrate can be used to clean the mask. After completion of block 268, process completion block 270 is reached.

8810330.

Claims (1)

-13 * Device for repairing semiconductor masks and cross-wires by using focused ion beams, containing - an ion source consisting of a large number of ion types, wherein a first type of the large number of ion types is compatible with the material from which the mask or the crosshair is constructed, and wherein a second type of the large number of ion types has a relatively high atomic weight compared to the first type, - means for selecting an ion beam composed of one of the first and second ion types and for directing of a focused ion beam on a target containing a semiconductor mask or cross wire to be repaired, - means for supplying a metal-containing vapor to the target surface, 15. means for selectively applying a low voltage or a high voltage between the ion source and the target, and means for forming an image v the target by means of secondary ion emission. 8810330.