International Business Machines Corporation

Peter Nehmiz

Harald Bohlen

Johann Greschner

Helmut Engelke

Werner Kulcke

Uwe Behringer

Peter Vettiger

Werner Zapka

Reinhold Muhl

Hans J Trumpp

Erwin Bretscher

According to this process two partial patterns which, if superimposed upon each other in a predetermined alignment relative to each other yield the desired pattern, with elements of both partial patterns combining to form elements of the pattern, and these partial pattern elements overlapping sectionally, are projected with a suitable radiation onto the radiation-sensitive layers. Overlapping is achieved in that when designing the two partial patterns a pattern corresponding to the desired pattern is used as a basis in that the elements of this pattern are exposed to a negative windage, the negative windage pattern is subsequently partitioned into two negative windage patterns corresponding to the partial patterns, and finally the negative windage partial pattern elements are exposed to a positive windage to the desired size of the partial pattern elements. The method is used in particular when a pattern is to be transferred by means of hole masks, and if it is necessary, e.g. because the pattern shows annular elements, to use instead of one mask only two complementary masks each comprising at least one part of the pattern.

Method of transferring a pattern into a radiation-sensitive layer

An apparatus and method for testing transmission masks for corpuscular lithography, in which an image of a portion of mask is guided across a pinhole diaphragm, comprising at least one aperture with submicron dimensions, by inclining the corpuscular beam. The relative spacing of two measuring points is derived from the interferometrically measured table displacement and the beam inclination. This test for geometrical errors is effected by placing below the single hold in the diaphragm a scintillator followed by a photomultiplier coupled to an output circuit. For testing the entire mask area for errors and impurity particles, a multihole diaphragm, having submicron apertures arranged in matrix fashion, can be used above an integrated circuit of the charge transfer type which provides a MOS capacitor as a particle detector underneath each diaphragm opening. The exposure mask is scanned in steps, effecting several single exposures at each position by inclining the beam.

Error-corrected corpuscular beam lithography

The photoresist film 12 on the surface of a wafer 11 is exposed through the shadow pattern which is generated by a transmission mask 13 arranged a short distance therefrom when the mask is subjected to a large-area electron beam. The source of the electron beam is an unstructured photocathode 16 on an ultraviolet transparent carrier such as, quartz glass 17 which is subjected to UV radiation from the backside. The electrons exiting from layer 16 are accelerated by a homogeneous electric field 14 towards the mask 13 and shaped to form a homogeneous collimated electron beam. By means of laterally positioned electrostatic deflecting electrodes 19a, 19b, the entire electron beam can be tilted relative to the wafer for adjusting the mask pattern.

Electron beam projection lithography

For mutually aligning (registering) mask and substrate in X- or corpuscular ray lithography, an electron beam (16) is used which extends collaterally to the exposure beam (ion beam or X-ray) and which is suppressed during the actual exposure process. For coupling the electron beam to the exposure beam path, a magnetic field (7) is used. The accurate relative position of mask and substrate is determined during alignment by tilting the electron beam. Fine alignment during exposure is effected by suitably tilting the ion beam or shifting the substrate relative to the X-ray. The mask (10) used for exposure consists of a very thin silicon layer with a pattern area (M) and a registration area (R) spatially separated therefrom. The registration area consists of a plurality of openings, the pattern area of blind holes.

Mask and system for mutually aligning objects in ray exposure systems

For compensating scattering losses of electrons in photoresists (proximity effect) which influence electron beam lithography by altering the pattern geometry it is suggested to expose selected partial areas of a pattern to an additional irradiation dosage in a second exposure step. For that purpose, a specific mask with corresponding correction openings can be used which is applied with the same, or with a different electron beam intensity. In a particularly advantageous manner the correction of the proximity effect can be achieved when complementary masks are used; the correction openings for the partial areas of the one complementary mask are arranged in the other complementary mask. The proximity effect is then corrected without an additional exposure step. For measuring the proximity effect a photo-optical process is suggested where line patterns with decreasing ridge width in the photoresist are defined through electron beam projection, and where the developing process of the photoresist is discontinued prematurely. The ridge edges which in the presence of the proximity effect are asymmetrical can be easily detected under the microscope.

Method of compensating the proximity effect in electron beam projection

A projection mask comprises a thin P.sup.+ -doped silicon layer with through holes adapted to the mask pattern, a grid supporting this layer having silicon ribs. On at least on its side facing away from the grid, the layer has a layer, which is at least as thick as to prevent the implanting of ions in the silicon layer. At least the mask surface exposed to ion irradiation is electrically and thermally conductive, and mechanically resistant. The coating of the silicon frame of the mask is such that it does not cause any mask deformation caused by temperature and/or through inherent tensions of the coating. Preferred absorbing materials are gold, silver, platinum, tungsten, and tantalum, and mechanically resistant materials are preferably carbon, molybdenum, titanium, tungsten, and tantalum. In operation, the mask with grid is placed onto the substrate to be irradiated, and subsequently blanket-illuminated with an ion beam, or scanned line-by-line until each point on the mask has been covered by the beam path.

Shadow projection mask for ion implantation and ion beam lithography

A mask for structuring surface areas and a method for manufacture thereof. The mask includes at least one metal layer with throughgoing apertures which define the mask pattern and a semiconductor substrate for carrying the metal layer. The semiconductor substrate has throughholes that correspond to the mask pattern. The throughholes in the semiconductor substrate extend from the metal layer-covered surface on the front to at least one tubshaped recess which extends from the other back surface into the semiconductor substrate. Holes are provided in a surface layer in the semiconductor substrate. The surface layer differs in its doping from the rest of the substrate and the holes which are provided in the surface layer have lateral dimensions larger than the apertures in the metal layer so that the metal layer protrudes over the surface layer.

Method of making mask for structuring surface areas

The mutual alignment of mask and substrate patterns of a specific semiconductor structure are attained by use of a plurality of individual marks in a specific geometric position with respect to each other. By the arrangement of openings in the alignment pattern of the mask, the broad electron beam is split into a multitude of individual beams which interact with alignment marks on the substrate. The interaction is used to generate a coincidence signal. The signal to noise ratio of this arrangement is determined by the overall current and is comparable to that of a thin concentrated electron beam. Registration is effected in a small amount of time and the disadvantageous effects of the high current density used in the raster process are not a factor. In a preferred embodiment, the alignment pattern of the mask is a matrix with center spacings of openings increasing upon advance in two directions perpendicular to each other such that no distance can be represented by the sum of smaller distances. Alignment signals are provided by detecting either absorbed or reflected electrons. A plurality of detectors in the mask are used to detect the reflected electrons.

Alignment system for particle beam lithography

A mask for structuring surface areas and a method for manufacture thereof. The mask includes at least one metal layer with throughgoing apertures which define the mask pattern and a semiconductor substrate for carrying the metal layer. The semiconductor substrate has throughholes that correspond to the mask pattern. The throughholes in the semiconductor substrate extend from the metal layer-covered surface on the front to at least one tub-shaped recess which extends from the other back surface into the semiconductor substrate. Holes are provided in a surface layer in the semiconductor substrate. The surface layer differs in its doping from the rest of the substrate and the holes which are provided in the surface layer have lateral dimensions larger than the apertures in the metal layer so that the metal layer protrudes over the surface layer.

Mask for structuring surface areas, and method of making it

A method of pattern exposing an energy beam sensitive target surface to a particle beam by proximity printing, wherein mask alignment errors such as lateral deviations, skew and linear distortions are determined and are effectively corrected by scanning the mask area being transferred with a controllably tilted particle beam, the particle beam having a diameter which is small compared to the area of the mask being scanned. At each scan point the particle beam is controllably tilted in the same azimuth direction as the alignment error for that point and by a tilt angle (taken with respect to the normal direction of the target surface) which has a tangent equal to the product of the magnitude of the alignment error and the separation between the mask and target surface at that point.

Method of shadow printing exposure

Radiation sensitive layers are x-ray exposed by providing a metal mask pattern on the layer through which the layer is exposed. The metal mask pattern is formed by applying a blanket metal layer to the radiation sensitive layer followed by an electron beam sensitive resist layer which is patterned by an electron beam exposure process. The exposed portions of the metal layer are then etched away to form the metal mask pattern.

Exposure process

A method of exposure of a target object by means of corpuscular beam shadow printing through a mask with several complementary zones wherein the beam, shiftable and tiltable about a point in the mask plane and arranged in parallel at a small distance from the target object, is first impinged upon a first of the complementary zones, then the object is shifted under a second of the complementary zones, and the positioning of the beam is changed so that any deviation of the actual position of the second area of the target object to be exposed from its nominal position is determined and compensated for by tilting the beam about a point substantially in the mask plane.

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Stuttgart, Germany

Peter Nehmiz