Electricity: electrical systems and devices – Electric charge generating or conducting means – Use of forces of electric charge or field
Utility Patent
1999-03-12
2001-01-02
Sherry, Michael J. (Department: 2836)
Electricity: electrical systems and devices
Electric charge generating or conducting means
Use of forces of electric charge or field
Utility Patent
active
06169652
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the design of electrostatic chucks that are particularly suited for use in projection lithography employing either soft x-rays or electrons and in particular for use in a lithographic system that includes a multi-chamber housing the reticle, optics, e.g., camera and condenser, and wafer.
BACKGROUND OF THE INVENTION
A number of different chucks are widely used to hold semiconductor wafers during processing. Mechanical chucks can secure the wafer by using arms or clamps to press the wafer against a supporting surface. The clamping force is inherently non-uniform, resulting in uneven stresses in the wafer which can cause deformation, and uneven thermal contact between the wafer and the support. Vacuum chucks secure the wafer by creating a vacuum beneath the wafer backside, thereby generating a clamping force due to the pressure differential between the processing chamber which is at higher pressure and the wafer backside. Vacuum chucks can provide a more uniform clamping force than can mechanical chucks, but in the low pressure environments required for many semiconductor processing applications, the pressure differential is insufficient to generate an adequate clamping force. For example, advanced lithography systems such as Extreme Ultraviolet Lithography (EUV) and Scattering with Angular Limitation Projection Electron Lithography (SCALPEL) operate at subatmospheric pressures.
With projection photolithography, a reticle (or mask) is imaged through a reduction-projection lens onto a wafer below. Reticles for EUV projection lithography typically comprise a silicon substrate coated with an EUV reflective material and an optical pattern fabricated from an EUV absorbing material that is formed on the reflective material. In operation, EUV radiation from the condenser is projected toward the surface of the reticle and radiation is reflected from those areas of the reticle reflective surface which are exposed, i.e., not covered by the x-ray absorbing material. The reflected radiation effectively transcribes the pattern from the reticle to the wafer positioned downstream from the reticle. A scanning exposure device uses simultaneous motion of the reticle and wafer (each mounted on its own X-Y stage platen) to continuously image a portion of the reticle onto the wafer through a projection optics. Scanning, as opposed to exposure of the entire reticle at once, allows for the projection of reticle patterns that exceed in size that of the image field of the projection lens. The stage platen includes mirrors that are mounted along its sides. Interferometer heads that direct laser beams onto the associated mirrors and detect the beam reflection therefrom are employed for position measurements.
Electrostatic chucks combine the advantages of the more uniform clamping ability of vacuum chucks and the usability in vacuum environments of mechanical chucks. In an electrostatic chuck (ESC), a voltage difference is applied between the wafer and a metallic electrode or pair of electrodes, the wafer and electrode(s) being separated by an interposed dielectric layer. The magnitude of the electrostatic clamping force thus generated depends on the applied voltage, the separation between the wafer and the electrode (s), and the dielectric constant of the interposed layer. As a result of their advantages over other chucking devices, ESCs have gained wide usage in the semiconductor processing industry.
Wafer and mask substrates used in semiconductor fabrication must be protected from particulate contamination. However, existing electrostatic chucks can produce sizable electric fields above the surface of the substrate which lead to electrostatic deposition of charged contaminant particles onto the substrate. These electric fields arise in the form of stray electric fields from the chuck electrodes, or results from the loss of electrical control of the substrate itself. Furthermore, the high voltages (e.g., 500 V or greater) produced in such chucks can cause electrical arcing from the leads and chuck electrodes to surrounding surfaces. Arcing can also contribute to contamination and substrate damage.
Aside from the quality of the optics that are employed in EUVL systems, factors that influence the quality of the printed wafers fabricated include the ability to prevent contamination of the substrate (i.e., mask and wafer) surfaces. Current electrostatic chucks used for gripping these lithographic components do not exclude electric field gradients and therefore do not prevent the associated electrostatic deposition of particles. Furthermore, existing chucks do not provide for voltage control of the lithographic component to prevent electric fields from developing between the lithographic component and a nearby structure that is at a different potential.
SUMMARY OF THE INVENTION
The present invention is directed to an electrostatically screened, voltage-controlled electrostatic chuck that will significantly reduce the likelihood of contaminant deposition on substrates during photolithography.
In one embodiment, the invention is directed to an electrostatic chuck for holding a substrate that includes:
an insulator block having an outer perimeter and a planar surface adapted to support the substrate and comprising at least one electrode;
a source of voltage that is connected to the at least one electrode;
a support base to which the insulator block is attached; and
a primary electrostatic shield ring member that is positioned around the outer perimeter of the insulator block.
In a preferred embodiment, (1) a pair of electrodes are embedded in the insulator block; (2) the primary electrostatic shield ring defines a planar surface that is flush with the planar surface of the insulator block; (3) the primary electrostatic shielding ring is grounded; and/or (4) the electrostatic chuck includes a secondary electrostatic shield ring positioned around and spaced apart from an outer surface of the primary electrostatic shield ring.
The electrostatic chuck permits control of the voltage of the lithographic substrate typically by grounding it; in addition, it provides electrostatic shielding of the stray electric fields issuing from the sides of the electrostatic chuck. The shielding effectively prevents electric fields from wrapping around to the upper or front surface of the substrate. By “upper or front surface” is meant the surface of the substrate which faces approaching radiation, e.g., EUV radiation.
REFERENCES:
patent: 5221403 (1993-06-01), Nozawa et al.
patent: 5486975 (1996-01-01), Shamouilian et al.
patent: 5606485 (1997-02-01), Shamouilian et al.
patent: 5748434 (1998-05-01), Rossman et al.
patent: 5815366 (1998-09-01), Morita et al.
patent: 5822171 (1998-10-01), Shamouilian et al.
patent: 5835333 (1998-11-01), Castro et al.
patent: 5835334 (1998-11-01), McMillin et al.
patent: 5996218 (1999-12-01), Shamouilian et al.
Burns Doane Swecker & Mathis L.L.P.
EUV, L.L.C.
Sherry Michael J.
LandOfFree
Electrostatically screened, voltage-controlled electrostatic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrostatically screened, voltage-controlled electrostatic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrostatically screened, voltage-controlled electrostatic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2521560