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Publication numberUS3849659 A
Publication typeGrant
Publication dateNov 19, 1974
Filing dateSep 10, 1973
Priority dateSep 10, 1973
Also published asDE2443121A1
Publication numberUS 3849659 A, US 3849659A, US-A-3849659, US3849659 A, US3849659A
InventorsKeeffe T O
Original AssigneeWestinghouse Electric Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Alignment of a patterned electron beam with a member by electron backscatter
US 3849659 A
Abstract
A patterned electron beam from a photocathode source is aligned with precisely located areas of a major surface of a member. At least one and preferably two detector marks of predetermined shape are located, preferably widely spaced away, adjacent the major surface of the member, and corresponding detector means are positioned adjacent periphery portions of the member. Each detector mark is capable of producing backscattered electrons on irradiation by an electron beam, and each detector means is capable of detecting backscattered electrons from the corresponding detector mark and producing an electrical signal corresponding to the area of the corresponding mark irradiated by an electron beam. The patterned electron beam to be aligned has at least one alignment beam portion of predetermined cross-sectional shape and corresponds to a detector mark. The backscattered electrons produced by impingement of the alignment beam portions on the corresponding detector marks are detected by the detector means. The position of the electron beam is moved relative to the member until the backscattering detected by the detector means indicates alignment of the alignment beam portions with the corresponding detector marks.
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Description  (OCR text may contain errors)

ll-l9-7 Nov. 19, 1974 ALIGNMENT OF A PATTERNED ELECTRON BEAM WITH A MEMBER BY ELECTRON BACKSCATTER OKeeffe et a1. 250/492 A Ferty 2501492 A Primary Examiner-James W. Lawrence Assistant Examiner-C. E. Church Attorney, Agent, or FirmC. L. Menzemer [5 7] ABSTRACT A patterned electron beam from a photocathode source is aligned with precisely located areas of a major surface of a member. At least one and preferably two detector marks of predetermined shape are located, preferably widely spaced away, adjacent the major surface of the member, and corresponding detector means are positioned adjacent periphery portions of the member. Each detector mark is capable of producing backscattered electrons on irradiation by an electron beam, and each detector means is capable of detecting backscattered electrons from the corresponding detector mark and producing an electrical signal corresponding to the area of the corresponding mark irradiated by an electron beam. The patterned electron beam to be aligned has at least one alignment beam portion of predetermined cross-sectional shape and corresponds to a detector mark. The backseattered electrons produced by impingement of the alignment beam portions on the corresponding detector marks are detected by the detector means. The position of the electron beam is moved relative to the member until the backscattering detected by the detector means indicates alignment of the alignment beam portions with the corresponding detector marks.

13 Claims, 6 Drawing Figures PATENTE HUV I 91974 SHEET 1 0F 3 Y- ERROR MAGNIFICATION ERROR PATENTEL, rm 1 91914 3'. 849.659

- SHEH 2 0F 3 SCATTERING a RANGE 502.5kev

?5- lOkev I I i I 4.2----- I I RANGE m 1 I MILLIMETERS I i I I E O l l l l l l l I I l 0 IO 20 3O 4O 5O 6O 7O 8O 90 I00 TRAJECTOR-Y ANGLE OF BACKSCATTER IN DEGREES ALIGNMENT OF A PA'ITERNED ELECTRON BEAM WITH A MEMBER BY ELECTRON BACKSCATTER GOVERNMENT CONTRACT This invention is made in the course of or under Government Contract F 336l5-67-C-1335.

FIELD OF THE INVENTION The invention relates to the making of integrated circuits and other micro-miniature electronic components with submicron accuracy.

BACKGROUND OF THE INVENTION The present invention is an improvement on the electron beam fabrication system described in U.S. Pat. No. 3,679,497, granted July 25, 1972, and the alignment system therefor described in U.S. Pat. No. 3,710,101, granted Jan. 9, 1973, both of which are assigned to the same assignee as the assignee of the present application.

In said fabrication system, a planar photocathode source (called an electromask) produces a patterned beam of electron radiation which is directed onto an electron sensitive layer (called an electroresist) on a major surface of a member spaced from the photocathode. The patterned beam causes a precisely patterned differential in solubility between irradiated and unirradiated areas of the sensitive layer corresponding to the patterned electron beam. The pattern in differential solubility is transferred to a pattern in a component layer or body by removing the less soluble portion of the electroresist layer (i.e. either the irradiated or unirradiated portion) to form a window pattern therein, and subsequently selectively etching and doping the component layer or body through the window pattern developed in the resist layer, or depositing a component layer by evaporation, sputtering, oxidizing or epitaxially growing through the window pattern in the electroresist layer.

The resolution of the electron image projection system, e.g. less than 0.5 micron, is, however, lost in the juxtaposition of component patterns unless the same resolution can be maintained in the alignment of successive electromasks with the same member. Making of an integrated circuit device requires, for example, registration and irradiation of at least 2 to different component patterns in electroresist layers that are subsequently developed and transferred to a component layer by etching, doping or deposition. The electron radiation for each pattern must be aligned with precisely located areas of the major surface each time with a precision of 0.5 micron or less with respect to the first pattern. Otherwise, the precision and economies of the electron image projection system will not beobtained in the finished integrated circuit device.

Apparatus has been developed for precision juxtapositioning of multiple component patterns by electron beam induced conductivity marks (EBIC). See U.S. Pat. No. 3,710,101 issued Jan. 9, 1973 and U.S. Pat. application Ser. No. 264,699, filed June 20, 1972, and assigned to the same assignee asthe present application. A small indexing electron beam pattern or mark of predetermined shape is provided on the photocathode source to produce an alignment beam portion, and a detector mark of predetermined shape is formed on an oxide layer on the member and overlaid with a metal layer. A DC potential is applied across the oxide layer between the metal layer and the member. The current flow between the potential and the terminals will vary in proportion to the portion or area of the detector mark irradiated by the alignment beam portion. Thus, the alignment beam portion can be precisely aligned with the detector mark by reading the electron induced current corresponding to the area of the detector mark irradiated. The electrical current flow may be processed through an amplifier to actuate a servomechanism to move the photocathode source or the member, or change the magnetic field formed by focusing and deflecting electromagnets surrounding the photocathode source and member to align and direct the electron beam pattern, and in turn provide automatic alignment of the alignment beam portion and the detector mark.

One of the difficulties with this alignment system is that it requires fabrication of the detector mark on the member itself. Moreover, it usually requires one or more extra fabrication steps to form the detector marks. The present invention overcomes these difficulties and disadvantages and provides an alternative method and apparatus for precision alignment of an electron beam with selected areas of a major surface of a member. Specifically, the present invention provides an alignment system which can be utilized with negligible interference with the usual fabrication sequence.

Backscattering detection has been previously used to align a scanning electron microscope. In the electron microscope, a single beam of fine dimension, e.g. 0.2 micron in diameter, is projected onto the surface of a member and selectively irradiates portions of the surface by moving through a matrix on command from a computer. The detector means for detection of the backscattered electrons were placed opposite each other adjacent the electron beam source. Such an alignment system is, however, not operative in the electron image projection system because of the electric and magnetic fields present. Indeed, it would logically be considered impossible to adapt the backscattering technique to align the electron image projection system because of the need for high intensity electric and magnetic fields in the space between the photocathode source and the selectively irradiated member.

However, it has been found, surprisingly contrary to previous considerations, that the backscattering technique can be adapted to precision align a patterned electron beam from a photocathode source with selected areas of a major surface of a member. Moreover, the adaption as hereinafter described provides an alignment system with greater responsiveness and in turn greater alignment accuracy than previously described alignment systems, see, e.g. U.S. Pat. No. 3,710,101, granted Jan. 9, 1973, U.S. Pat. application Ser. No. 370,489, filed June 15, 1973, U.S. Pat. application Ser. No. 370,558, filed June 15, 1973, U.S. Pat. application Ser. No. 371,447, filed June 19, 1973, and U.S. Pat. application Ser. No. 370,115, filed June 13, 1973 all now abandoned.

SUMMARY OF THE INVENTION A method and apparatus are provided for the alignment of a patterned electron beam projected by a photocathode source with selected areas'of a major surface of a member with a desired degree of accuracy such as 0.5 micron or less. The invention provides an alternative alignment technique to previously described methods and apparatus and extends the application of the electron image projection system in the making of precision integrated circuits.

A member such as a single-crystal silicon wafer is provided with at least one and preferably two widely spaced apart detector marks of predetermined shape or shapes adjacent a major surface thereof. Each detector mark is capable of producing electron backscatter on irradiation by an electron beam. The predetermined shapes of the detector marks are preferably all the same and are preferably of regular geometric shape such as a circle, rectangle, square or triangle. The detector means corresponding to the detector marks are positioned adjacent periphery portions of the member, and are capable of detecting backscattered electrons from the detector marks and producing an electrical signal corresponding to the area of the detector mark irradiated by an electron beam.

The photocathode source from which the patterned electron beam is projected is positioned in spaced relation from the major surface of the member. The patterned electron beam to be aligned has alignment beam portions corresponding to the detector marks and of predetermined cross-sectional shape. The photocathode source is so disposed relative to the member that the alignment portions of the patterned electron beam irradiate the major surface close to the detector marks. The position of the member relative to the electron beam is varied either manually or automatically so that the alignment portions impinge on and overlap the detector marks. Electrical signals are thereupon produced by each detector means corresponding to the area of the corresponding detector mark that is irradiated by virtue of the backscattered electrons emitted by the detector marks and detected by the detector means. The electron beam is moved relative to the member causing the electrical signal produced by the detector means to be varied until the electrical signal indicates optimum alignment of the alignment beam portions with the corresponding detector marks.

The alignment beam portions and the detector marks may be of any suitable relative size within practical limits provided the shapes of both are predetermined. Preferably, however, each alignment beam portion is of the same cross-sectional shape as the predetermined shape of the corresponding detector mark so that alignment can be determined simply by reading a maximum or a minimum in the electrical signal from the detector means. Otherwise, electrical processing of the electri-. cal signals are needed, while the alignment beam portions are oscillated over the corresponding detector marks, to determine optimum alignment of the alignment beam portions with the corresponding detector marks.

The detector marks can be of any desired shape to be capable of backscattering electrons to the detector means. In this connection, it should be noted that the detector marks can be defined by either an abundance of backscattered electrons or a lack of backscattered electrons. In either instance, the detector marks are preferably formed of a plurality of narrow, elongated angular planes which are closely spaced in a substantially parallel arrayand which are elongated generally in the direction of the corresponding detector means. It is further preferred that the detector marksbe formed in closely spaced pairs with the elongated angular planes of one detector mark substantially perpendicular to the elongated angular planes of the other detector marks of said pair. By these preferred features, the backscattering of electrons from the detector marks in the direction of the corresponding detector means is maximized and correction of the alignment beam portions to optimum alignment with the detector marks is more rapidly and more accurately attained.

Further, it is preferred that the alignment sequence is done automatically by an electrical means which moves the patterned electron beam relative to the member responsive to electrical signals from the detector means. The electrical means preferably include for this purpose a modulation means for oscillating the movement of the alignment beam portions over the corresponding detector marks; phase detection means, preferably synchronized with the modulation means, for detecting along orthogonal axis the errors from alignment of alignment beam portions and the corresponding detector marks, and outputting electrical signals corresponding thereto; and actuating means for changing the electrical input to the electromagnetic means directing the patterned electron beam from the photocathode source onto the major surface of the member responsive to the electrical signals from the phase detector means. Preferably, the electrical means also includes termination means for terminating the oscillation by the modulation means at optimum alignment of the alignment beam portions and the corresponding detector marks.

Other details, objects and advantages of the invention will become apparent as the following description of the presently preferred embodiments and presently preferred methods of practicing the same proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, the present preferred embodiments of the invention and the present preferred methods of practicing the invention are illustrated in which:

FIG. 1 is a cross-sectional view in elevation of an electron image projection device employing the present invention;

FIG. 2 is a fragmentary cross-sectional view in elevation taken along line II-II of FIG. 1;

FIG. 3 is a fragmentary cross-sectional view in perspective taken along line III-III of FIG. 2;

FIG. 4 is a fragmentary enlarged view of a portion of the cross-sectional view shown in FIG. 2 showing the plane path of backscattered electrons from the detector marks to the detector means;

FIG. 5 is a graph showing the relation of backscatter emissions of electrons from the detector marks as shown in FIG. 4 to range of travel along the plane in which the major surface of the member is located; and

FIG. 6 is a block diagram of an electrical circuit for the electron image projection device shown in FIG. 1 to automatically align the electron beam pattern.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An electron image projection device suitable to practice the present invention is described in US. Pat. Nos. 3,679,497 and 3,710,101 except for the alignment technique and apparatus therefor. For convenience and clarity of description the device is redescribed in part here.

Referring to FIG. 1, an electron image projection device is shown. A hermetically sealed chamber of nonmagnetic material has removable end caps 11 and 12 to allow for disposition of apparatus into and removal of apparatus from the chamber. A vacuum port 13 is also provided in the sidewall of chamber 10 to enable a partial vacuum to be established in the chamber after it is hermetically sealed.

Disposed within chamber l0 is cylindrical photocathode source or electromask 14 and alignable member 15 (e.g. a semiconductor wafer) in substantially parallel, spaced relation. Member 15 is supported in specimen holder 16 as more fully described later. Photocathode 14 and holder 16 are in turn positioned in substantially parallel array by annular disk-shaped supports 17 and 18, respectively. Photocathode 14 and holder 16 are spaced apart with precision by tubular spacer 19 which engages grooved flanges 20 and 21 via gaskets 22 and 23 around the periphery of supports 17 and 18. The entire assembly is supported from end cap 11 of chamber 10 at support 17 to allow for ease of disposition of the photocathode source and the alignable member within the chamber.

Photocathode source 14 is made cathodic and member 15 is made anodic to direct and accelerate a patterned electron beam emitted from photocathode 14 to member 15. To accomplish this, holder 16 and supports 17 and 18 are of highly conductive material and spacer 19 is of highly insulating material. A potential 19A of, for example, 10Kv, is applied between supports 17 and 18. The difference in potential is conducted to and impressed on photocathode source 14 and member 15 via supports 17 and 18 and holder 16.

Surrounding chamber 10 are three series of electromagnetic coils, positioned perpendicular to each other, to control the impingement of the patterned electron beam on member 15. Cylindrical electromagnets 24,, 24 and 24 are positioned axially along the path of the electron beam from photocathode 14 to member 15 to cause electrons to spiral and move radially as they travel the distance from the photocathode source to the substrate and in turn focus the electron beam pattern. These electromagnetic coils permit also control of the rotation (6) and the magnification (M) of a patterned electron beam emitted from the photocathode source. Rectangular electromagnets 25 and 25 and 26 and 26 are symmetrically positioned in Helmholtz pairs perpendicular to each other, and to electromagnetic coils 24 -24 to cause electrons to transversely deflect as they travel the distance from the photocathode to the member. These electromagnetic coils permit control of the direction (in X and Y coordinates) of a patterned electron beam emitted from the photocathode source.

In operation, light source 27 such as a mercury vapor lamp backed by reflector 27A irradiates a photocathode layer 28 (e.g. gold or palladium) in the photocathode source 14. The photocathode layer is irradiated through a substantially transparent substrate 29 such as quartz overlaid with a layer 30 containing the negative of a desired component pattern. The layer 30 is of material (e.g. titanium dioxide) which is opaque to the light radiation. The photocathode material is thus made electron emissive in a patterned electron beam corresponding to the desired component pattern. A part of the patterned electron beam emitted from the photocathode source 14 is preferably at least two and most desirably four alignmentbeam portions 43 preferably of the same predetermined cross-sectional shape (e.g. squares of 300 X 300 microns). The alignment beam portions are positioned in widely spaced away pairs, with each pair preferably positioned opposite the other pair along the periphery of the alignment beam portions of each pair closely spaced.

Referring particularly to FIG. 2, member 15 is precision mounted within physically permissible limits in holder 16 and in turn with respect to photocathode source 14. Member 15 has a flat peripheral portion 31; and holder 16 has depression 32 into which member 15 fits. Holder 16 has pins 33, 34, 35 and 36 positioned in respective quadrants around the periphery of depression 32. Member 15 is positioned by resting flat peripheral portion 31 of member 15 against pins 33 and 34 and curvilinear peripheral portion 37 of member 15 against pin 35. The member is thereby located with an accuracy of about 25 microns or less. Movable pin 36, which is fitted with a compression spring 38, is positioned and pushed against the curvilinear portion of member 15 to firmly retain member 15 and in turn, maintain member 15 precisely located.

On member 15 at widely spaced apart positions preferably at opposite peripheral portions are pairs of detector marks 39 and 40, and 41 and 42. Each detector mark corresponds to an alignment beam portion 43 and has a predetermined shape preferably the same as the predetermined cross-sectional shape of the corresponding alignment beam portions 43. Further, each detector mark is capable of backscattering electrons on irradiation by an electron beam. Positioned adjacent the periphery portions of member 15 at each detector mark, preferably substantially in the plane of the major surface of the member 15 in holder 16, is corresponding detector means 44, 45, 46 and 47, respectively. Each detector means, which is, for example, a scintillator-photomultiplier circuit, is capable of detecting backscattered electrons from the corresponding detector mark and producing an electrical signal corresponding to the area of the corresponding detector mark irradiated by an impinging electron beam as hereinafter described.

Referring to FIG. 3, the details are shown of a preferred embodiment of the detector marks. Each detector mark is comprised of a plurality of narrow, elongated holes 48 etched in a spaced, substantially parallel array. Each hole is typically about 1.0 micron in width, and the holes are spaced 3.0 microns apart to form in effect a grating of a large number of lines, e.g. 75. The width of the holes and the spacing between holes is, however, adjusted to the desired resolution of alignment. Additionally, each hole 48 has an elongated angular plane (i.e. curvilinear surface) 48A extending the length of the detector mark in the general direction of the corresponding detector means, and being very narrow, e.g. 0.5 micron in width. Said angular plane 48A is capable of backscattering electrons to the corresponding detector means, as shown in FIGS. 2 and 4, with the effect of the electric and magnetic fields present between the photocathode l4 and the member 15. The angular planes 48A induce the electrons to preferentially emit from the detector marks at a relatively low trajectory (e.g. to the axis of incidence) producing large linear ranges over the plane of the major surface of the member under the influence of the electric and magnetic fields.

Referring to FIG. 4, the relation of linear range of backscattered electrons as a function of the initial trajectory angle is shown. Electrons are backscattered at angles of 40, 50 and 75 to the axis of incidence which in this embodiment is presumed to be perpendicular to the major surface of the member. As shown, the range is not directly proportional to the trajectory angle. The 75 and 40 trajectory 1O Kev electrons traveled 6.4 and 4.2 millimeters, respectively, while the 50 trajectory 2.5 Kev electrons traveled only 3 millimeters along the plane of the major surface.

The reason for this seemingly erratic behavior can best be explained by reference to FIG. 5. FIG. 5 shows the distribution range of Kev backscattered electrons as a function of the initial angle of trajectory. As seen, there are maximums at 40 and 75 and minimums at 60 and 90. This distrubution curve is caused by the fact that the electrons backscattered at 60 com- .plete approximately one full orbit in the electric and magnetic fields before they again return to the plane of the major surface, while electrons backscattered at 75 and 40 complete about onehalf and one and one-half orbits, respectively, before they return to the plane of the major surface. Electrons backscattered at 90, of course, have zero range as they do not leave the plane of the major surface. Thus, the maximum range of 6.4 mm is achieved at a trajectory of 75 and a secondary maximum range of 4.2 mm is achieved at a trajectory of 40 to the incidental axis.

Similarly, electrons backscattered with 2.5 Kev energy have a single maximum range of 3 millimeters at a trajectory angle of 50 to the axis of incidence.

The ranges above show the operability of the present invention. Further analysis shows that a detector means extending from 1.5 mm to 6.5 mm from the backscattering point on the detector mark will collect about one-half of the electrons backscattered with greater than 2.0 Kev energy from a surface inclined at 48 to the axis of incidence of the irradiating electrons.

Further it should be observed that, although the efficiency of detection is lower, the present invention is more sensitive then previously described alignment systems and thus provides a more accurate alignment system. The lack of efficiency results from the small percentage of the surface of the detector mark being inclined at the correct angular 'plane(s) or curvilinear surfaces 48A and the small percentage of backscattered electrons above the threshold energy to reach the detector means. For example, assuming a detector mark of 0.3 mm X 0.3 mm having 75 lines or holes, each hole of which contributes an angular plane at approximately 45 of about 0.5 micron in width, only approximately lO percent of the surface is properly inclined to backscatter detectible electrons. The yield of detectible backscattered electrons is further reduced by the fact that only about 5 percent of the backscattered electrons of a 10 Kev electron beam are above 2.5 Kev. Yet the present alignment system is more sensitive because of the availability of high quality backscatter electron detectors which more than compensate for the reduction in efficiency.

Further, it should be noted that the alignment beam portions may also be made-up of narrow, elongated portions in a spaced, substantially parallel array. This embodiment is caused by the desire, in making matched sets of photocathode sources or electromasks and members, that the alignment beam portions be used to irradiate electroresist layers in the fabrication of the detector marks for said sets. The elongated portions of the alignment beam portions thus are the same in dimensions to the holes 48 of the detector marks.

This embodiment is very practical in fabrication. However, it causes the electrical signal produced by the detector means to contain high frequency modulation superimposed on the low frequency signal corresponding to the area of the detector mark irradiated. Thus, the electrical signal must be processed through a highfrequency detector to obtain a low frequency AC signal corresponding to the oscillations in the areas of the detector marks irradiated by the corresponding alignment beam portions.

in operation, the alignment beam portions 43 of predetermined cross-section impinge on and overlap the corresponding detector marks 39, 40, 41 and 42, respectively. The electron beams induce the emission of backscattered electrons corresponding to the area of overlap between the electron beams 43 and their corresponding detector marks. Alignment can, therefore, be accurately made simply by observing the maximum current reading from electrical signals from the detector means 44, 45, 46 and 47, respectively, as the electron beam from photocathode source 14 is moved relative to member 115.

Where the predetermined cross-sectional shape of the alignment beam portion is different from the predetermined shape of the corresponding detector mark, the reading of electrical signal from the corresponding detector means to determine optimum alignment is somewhat different than above described. Optimum alignment is no longer indicated by the maximum or minimum in the signal readings from the detector means. Rather, a plateau is reached in the signal reading, and optimum alignment is achieved by either selecting the mean point on the plateau taking into consideration any differences in the geometric shapes of the alignment beam portions and detector marks, or selecting the mean point on the signal rise from the detector means as the alignment beam portions move into or out of the areas of the corresponding detector marks. The latter alignment sequence permits alignment with the edge of the detector mark. Any of these embodiments may be readily used in either a manual or automatic alignment system with electrical signal processing apparatus such as that hereinafter described.

Further, manual aligning of the electron beam pattern with selected areas of the major surface of the member may be employed irrespective of the embodiment of the detector marks utilized. Manual operation is, however, not preferred in commercial applications because it is time consuming and subject to human errors in observing the current reading in the electrical signals from the detector means. For these reasons, it is preferred that the electrical signals from the detector means be electronically processed to control and operate alignment means such as the electromagnetic coils 24 24 24 25 25 26, and 26 and automatically position the alignment beam portions where the electrical signals indicate optimum alignment of the alignment beam portions and the detector marks. Not only can the optimum response position be obtained more rapidly, but the human error is eliminated with the same response point indicated each time alignment is performed.

Referring to FIG. 10, a block diagram of electrical means is shown to automatically align alignment beam portions 43 with detector marks 39, 40, 41 and 42 and in turn precision align the patterned electron beam from photocathode source 14 with selected areas of the major surface of the member 15. The electircal signal from detector means 44 is conveyed via lead to preamplifier 51, which amplified signal is then conveyed via lead 52 to high-frequency detector 53. In detector 53 the high frequency modulation, caused by the elongated portions or lines of the alignment beam portion, is removed from the signal so that only the low frequency signal corresponding to the area of detector mark 39 irradiated is outputted. The output from highfrequency detector 53 passes by lead 54 to tuned amplifier 55. The output of amplifier 55 passes through lead 56 to a phase adjustor 57 and then through lead 58 to a phase detector 59. A gated oscillator 60 impresses a reference signal through conductors 61 and 62 on the phase detector 59. The output of phase detector 56 thus comprise the X-error signal which passes via lead 63, gate 64 and lead 65 to integrator 66. The

integrator 66 has a direct-current output to adder 67,

where the output is superimposed on the alternating current, corresponding to the reference signal, from the oscillator 60 via lead 68. The alternating current provides the X-component of the primary oscillation of the alignment beam portions over the detector marks. The added actuating signal is passed to power and control the electromagnetic coils 25 25,, 26 and 26 Similarly, the electrical signal from detector means 45 is conveyed via lead 69 to preamplifier 70, which amplifies the signal and the amplified signal is conveyed via lead 71 to high-frequency detector 72. In detector 72 the high frequency modulation is removed from the signal so that only the low frequency signal is outputted that corresponds to the varying area of detector mark 40 irradiated by the corresponding alignment beam portion 43. The output from highfrequency detector 72 passes by lead 73 to tuned amplifier 74. The output of amplifier 74 passes through lead 75 to phase adjustor 76 and then through lead 77 to phase detector 78. Oscillator 60 impresses a reference signal, which is at 90 phase angle to the signal to phase detector 59, through conductors 79 and 80 on phase detector 78. The output of phase detector 78 thus comprises the Y-error signal which passes via lead 79, gate 80 and lead 81 to integrator 82. Integrator 82 has a direct-current output to adder 83, where the output is superimposed on the alternating current from oscillator 60 via lead 84. The alternating current provides a the Y-component of the primary oscillation of the alignment beam portions over the detector marks by powering the electromagnetic coils 25,, 25 26, and 26 Similarly, the signal from detector means 46 is conducted via lead 85 to preamplifier 86, and passed thereafter via lead 87 to high frequency detector 88. In detector 88, the high frequency modulation is removed from the signal so that only the low frequency signal, which corresponds to the oscillation in the areas of detector mark 41 irradiated, is outputted from the detector 88. The output from detector 88 passes via lead 89 to tuned amplifier 90 and then via lead 91 through phase adjustor 92 and lead 93 to phase detector 94. Os-

cillator 60 impresses a reference signal through lead 95 on phase detector 94. The output from phase detector 94 through lead 96 thus corresponds to a error signal, passes through gate 97 and lead 98 to control a motordriven precision potentiometer 99 to efi'ect the rotational control of the electron beam pattern by increasing or decreasing the current to the electromagnetic coils 24,, 24 and 24 The signal from detector means 47 is conducted via lead 100 to preamplifier 101 and passes thereafter via lead 102 to high frequency detector 103. In detector 103, the high frequency modulation caused by the movement of the elongated portions of the corresponding alignment beam portions over detector mark 42 is removed from the signal so that only the low frequency signal, which corresponds to the oscillation in the area of detector mark 42 irradiated, is outputted from the detector 103. The output from detector 103 passes via lead 104 to tuned amplifier 105 and thence via lead 106 through phase adjustor 107 and lead 108 to phase detector 109. Oscillator 60 impresses a signal, at 90 phase angle to the signal to phase detector 94, through lead 1 10 to phase detector 109. The output from phase detector 109 through lead 111 in turn corresponds to a magnification (M) error signal, which passes through gate 112 and lead 113 to control a motor-driven precision potentiometer 114. Said output signal controls the size of the patterned electron beam through a motor driven gang potentiometer 114 which adjusts the main focus field.

The error signals in conductors 63, 79, 96 and 111 are cross-fed electronically via leads 115, 1 l6, 1 17 and 118, respectively, into a four input delayed null detector 119 whose output is conveyed by lead 120 to a setreset flip-flop 121. The operation of the flip-flop is initiated by actuation of a start sequence switch, whereupon current begins to flow via leads 122 and 123 to energize the ultraviolet source 27 to cause a patterned electron beam to be emitted from photocathode source 14, including the four alignment beam portions 43. Likewise, current from 122 passes through lead 124 to the gated oscillator 60, which in turn feeds sinusoidal signals in quadrature through leads 68 and 84 to the X and Y controls 67 and 83, respectively. The entire electron beam pattern, including the alignment beam portions 43, are thus caused to oscillate in a circle of, for example, 6 microns diameter at a frequency of 45 Hertz.

Once the aligning electron beam portions 43 are aligned on detector marks 39, 40, 41 and 42, respectively, by operation of integrators 66 and 82, and potentiometers 99 and 114, the error signals passing through leads 115, 116, 117 and 118 reach a zero value which is detected by the null detector 119. The null detector thereupon produces an electrical signal which passes through lead 120 to the flip-flop 121, which terminates the operation of the gated oscillator 60 and closes gates 64, 80, 97 and 1 12 by signals through leads 125, 126, 127 and 128, respectively. The time sequence of the selective electron beam exposure of an electroresist layer on the major surface of member 15 is then begun and continued until the resist is fully exposed. A period of from 3 to 10 seconds is usually adequate to produce a sufficient electron beam treatment of the electroresist to cause it to be properly differentially soluble in selected solvents. The photocathode source 14 generates a patterned electron beam from all ill the emissive areas during the alignment period; however, the alignment period is so brief that the electroresist on member has not been significantly exposed.

While the present invention is particularly suited and has been specifically described to align an electron image projection system, it is distinctly understood that the invention may be otherwise variously embodied and used. For example, it should be observed that, as an alternative, two detector marks could be used with the automatic alignment circuit as shown in abovereferred US. Pat. No. 3,710,101. More broadly, the invention may be used in the procedure for precision etching of selected areas of metal sheets to obtain desired shapes and patterns for various scientific and industrial applications.

What is claimed is:

l. A method of aligning a patterned electron beam generated by a photocathode source with selected areas of a major surface of a member with a high degree of precision comprising the steps of:

A. forming adjacent a major surface of a member at least two widely spaced apart detector marks of predetermined shape capable of producing electron backscatter on irradiation by an electron beam;

B. positioning detector means corresponding to the detector marks adjacent periphery portions of the member;

C. detecting by the detector means backscattered electrons produced by the detector marks and producing electrical signals corresponding to the respective areas of the detector marks irradiated by electron beams;

D. positioning a photocathode source capable of projecting an electron beam spaced from the major surface of the member;

E. causing a patterned electron beam to be projected by the photocathode source onto the major surface of the member, said electron beam having alignment beam portions corresponding to the detector marks, and each said alignment beam portion'having a predetermined cross-sectional shape;

F. moving the patterned electron beam relative to the member while continuing step C so that electrical signals vary; and

G. positioning the patterned electron beam relative to the member where the electrical signals indicate optimum alignment of the alignment beam portions with the corresponding detector marks.

2. A method of aligning a patterned electron beam generated by a photocathode source with selected areas of a major surface of a member with a high degree of precision as set forth in claim 1 wherein:

the detector marks are formed of narrow, elongated planes positioned in closely spaced, substantially parallel array, said planes elongated in a direction generally toward the corresponding detector means.

3. A method of aligning a patterned electron beam generated by a photocathode source with selected areas of a major surface of a member with a high degree of precision as set forth in claim 2 wherein:

said detector marks are formed in widely spaced apart pairs with the detector marks of each pair closely spaced and the narrow, elongated planes of the detector marks of each pair substantially perpendicular to the narrow, elongated planes of the other detector mark of said pair of marks.

4. A method of aligning a patterned electron beam generated by a photocathode source with selected areas of a major surface of a member with a high degree of precision as set forth in claim 1 wherein:

steps F and G are automatically performed by electrically processing said electrical signal on oscillation of movement of the alignment beam portions over the corresponding detector marks, and steps F and G are automatically terminated on optimum alignment of the alignment beam portions and the corresponding detector marks.

5. A method of aligning a patterned electron beam generated by a photocathode source with selected areas of a major surface of a member with a high degree of precision as set forth in claim 1 wherein:

each detector mark is of substantially the same predetermined shape as the predetermined crosssectional shape of the corresponding alignment beam portion of the patterned electron beam.

6. Apparatus for selectively irradiating precisely located areas of the major surface of a member comprismg:

A. a photocathode source for generating a patterned beam of electrons including at least one alignment beam portion of predetermined cross-sectional shape;

B. a member positioned with a major surface thereof in spaced relation with the photocathode source generating the patterned electron beam;

C. at least one detector mark corresponding to said alignment beam portion positioned adjacent said major surface of the member and capable of producing electron backscatter on irradiation by the patterned electron beam, each said detector mark being of a predetermined shape;

D. means for applying a potential between the member and the photocathode source whereby electrons from the photocathode source are directed to and selectively irradiate portions of said major surface of the member;

E. electromagnetic means for directing the patterned beam of electrons from the photocathode source to irradiate selected portions of said major surface of the member close to the selected areas, where each alignment beam portion is directed to irradiate se lected portions of said major surface close to the corresponding detector mark;

F. detector means corresponding to the detector marks positioned adjacent periphery portion of the member and capable of detecting backscattered electrons produced by the detector mark and producing electrical signals corresponding to the areas of the corresponding detector marks irradiated by the alignment beam portions; and

G. electrical means for moving the patterned beam of electrons relative to the member responsive to said electrical signals from said detector means to cause the alignment beam portions to substantially align with the respective detector marks, whereby the patterned beam of electrons from the photocathode is located and oriented relative to the member so that precisely located areas of the major surface of the member can be selectively irradiated with the patterned electron beam.

7. Apparatus for selectively irradiating precisely located areas of a major surface of a substrate as set forth in claim 6 wherein:

said detector means are substantially planarly aligned with the said major surface of the member.

8. Apparatus for selectively irradiating precisely located areas of a major surface of a member as set forth in claim 6 wherein:

each detector mark is of substantially the same predetermined shape as the predetermined crosssectional shape of a corresponding alignment beam portion.

9. Apparatus for selectively irradiating precisely located areas of a major surface of a member as set forth in claim 6 wherein:

each detector mark comprises a plurality of narrow elongated angular planes in a closely spaced, substantially parallel array with the angular planes elongated in a direction generally toward a detector means.

10. Apparatus for selectively irradiating precisely .located areas of a major surface of a member as set forth in claim 9 wherein:

said detector marks are positioned in widely spaced pairs with the detector marks of each pair closely spaced and the angular planes of each detector mark of each pair substantially perpendicular to the planes of the other detector mark of said pair.

11. Apparatus for selectively irradiating precisely located areas of a major surface of a member as set forth in claim 9 wherein:

each alignment beam portion of the patterned electron beam consists of "a plurality of closely spaced, substantially parallel and narrow beam portions oriented in the same direction as the angular planes of the corresponding detector marks.

12. Apparatus for selectively irradiating precisely located areas of a major surface of a member as set forth in claim 9 wherein:

the patterned beam of electrons generated by the photocathode source includes at least two relatively widely spaced apart alignment beam portions of predetermined cross-sectional shape.

13. Apparatus for selectively irradiating precisely located areas of a major surface of a member as set forth in claim 9 wherein:

the electrical means includes modulation means for oscillating movement of each alignment beam portion over the corresponding detector mark. phase detection means for detecting along orthogonal axis the error from alignment of the alignment beam portions and the corresponding detector marks and outputting an electrical signal corresponding thereto, and actuating means for changing the electrical input to the electromagnetic means responsive to the electrical signals from the phase detector means to bring the alignment beam portions and the detector marks into alignment. v

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
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US4327292 *May 13, 1980Apr 27, 1982Hughes Aircraft CompanyAlignment process using serial detection of repetitively patterned alignment marks
US4385238 *Mar 3, 1981May 24, 1983Veeco Instruments IncorporatedReregistration system for a charged particle beam exposure system
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Classifications
U.S. Classification250/492.1, 250/491.1, 219/121.12, 219/121.3
International ClassificationH01L21/027, H01J31/50, H01J37/304
Cooperative ClassificationH01J37/3174, H01J37/3045, B82Y10/00, B82Y40/00
European ClassificationB82Y10/00, B82Y40/00, H01J37/304B, H01J37/317B