[Object]

It is an object of the present invention to provide a lithium tantalate single crystal substrate which undergoes only small warpage, is free from cracks and scratches, has better temperature non-dependence characteristics and a larger electromechanical coupling coefficient than a conventional Y-cut LiTaO.sub.3 substrate.

[Means to Solve the Problems]

The lithium tantalate single crystal substrate of the present invention is a rotated Y-cut LiTaO.sub.3 single crystal substrate having a crystal orientation of 36 Y-49 Y cut characterized in that: the substrate is diffused with Li from its surface into its depth such that it has a Li concentration profile showing a difference in the Li concentration between the substrate surface and the depth of the substrate; and the substrate is treated with single polarization treatment so that the Li concentration is substantially uniform from the substrate surface to a depth which is equivalent to 5-15 times the wavelength of either a surface acoustic wave or a leaky surface acoustic wave propagating in the LiTaO.sub.3 substrate surface.

A method of manufacturing surface acoustic wave device chips includes grinding a reverse side of a wafer with a surface acoustic wave device formed in each area demarcated by a plurality of crossing projected dicing lines on a face side of the wafer; before or after grinding, applying a laser beam to the reverse side of the wafer such that the laser beam is focused at a position within the wafer, the position being closer to the face side of the wafer than a position corresponding to a reverse side of each of the surface acoustic wave device chips to be produced from the wafer, thereby forming a modified layer for diffusing an acoustic wave; and after grinding and applying the laser beam, dividing the wafer along the projected dicing lines into a plurality of the surface acoustic wave device chips.

A composite substrate production method of the invention includes (a) a step of mirror polishing a substrate stack having a diameter of 4 inch or more, the substrate stack including a piezoelectric substrate and a support substrate bonded to each other, the mirror polishing being performed on the piezoelectric substrate side until the thickness of the piezoelectric substrate reaches 3 m or less; (b) a step of creating data of the distribution of the thickness of the mirror-polished piezoelectric substrate; and (c) a step of performing machining with an ion beam machine based on the data of the thickness distribution so as to produce a composite substrate have some special technical features.

A method and structure for a transfer process for an acoustic resonator device. In an example, a bulk acoustic wave resonator (BAWR) with an air reflection cavity is formed. A piezoelectric thin film is grown on a crystalline substrate. A first patterned electrode is deposited on the surface of the piezoelectric film. An etched sacrificial layer is deposited over the first electrode and a planarized support layer is deposited over the sacrificial layer, which is then bonded to a substrate wafer. The crystalline substrate is removed and a second patterned electrode is deposited over a second surface of the film. The sacrificial layer is etched to release the air reflection cavity. Also, a cavity can instead be etched into the support layer prior to bonding with the substrate wafer. Alternatively, a reflector structure can be deposited on the first electrode, replacing the cavity.

The lithium tantalate single crystal substrate is a rotated Y-cut LiTaO.sub.3 single crystal substrate having a crystal orientation of 36 Y-49 Y cut characterized in that: the substrate is diffused with Li from its surface into its depth such that it has a Li concentration profile showing a difference in the Li concentration between the substrate surface and the depth of the substrate; and the substrate is treated with single polarization treatment so that the Li concentration is substantially uniform from the substrate surface to a depth which is equivalent to 5-15 times the wavelength of either a surface acoustic wave or a leaky surface acoustic wave propagating in the LiTaO.sub.3 substrate surface.

A production method for a composite substrate according to the present invention comprises (a) a step of mirror-polishing a piezoelectric-substrate side of a laminated substrate formed by bonding a piezoelectric substrate and a support substrate; (b) a step of performing machining using an ion beam or a neutral atom beam so that a thickness of an outer peripheral portion of the piezoelectric substrate is larger than a thickness of an inner peripheral portion and a difference between a largest thickness and a smallest thickness of the inner peripheral portion of the piezoelectric substrate is 100 nm or less over an entire surface; and (c) a step of flattening the entire surface of the piezoelectric substrate to remove at least a part of an altered layer formed by the machining using the ion beam or the neutral atom beam in the step (b).

A composite substrate according to the present invention includes a support substrate having a diameter of 2 inches or more, and a piezoelectric substrate having a thickness of 20 m or less and bonded to the support substrate to transmit light. The piezoelectric substrate has a thickness distribution shaped like a fringe. A waveform having an amplitude within a range of 5 to 100 nm in a thickness direction and a pitch within a range of 0.5 to 20 mm in a width direction appears in the thickness distribution of the piezoelectric substrate in a cross section of the composite substrate taken along a line orthogonal to the fringe, and the pitch of the waveform correlates with a width of the fringe. In the piezoelectric substrate, the fringe may include either parallel fringes or spiral or concentric fringes.

A bonded body includes a supporting substrate, a silicon oxide layer provided on the supporting substrate, and a piezoelectric material substrate provided on the silicon oxide layer and composed of a material selected from the group consisting of lithium niobate, lithium tantalate and lithium niobate-lithium tantalate. The surface resistivity of the piezoelectric material substrate on the side of the silicon oxide layer is 1.710.sup.15/ or higher.

A bonded body includes a supporting substrate, a silicon oxide layer provided on the supporting substrate, and a piezoelectric material substrate provided on the silicon oxide layer and composed of a material selected from the group consisting of lithium niobate, lithium tantalate and lithium niobate-lithium tantalate. The surface resistivity of the piezoelectric material substrate on the side of the silicon oxide layer is 1.710.sup.15/ or higher.

Disclosed is a processing method of a bonded wafer, the bonded wafer including a first wafer having a chamfered portion formed on an outer periphery thereof and a second wafer bonded with the first wafer, by grinding and thinning the first wafer. The processing method includes the following steps: arranging a protective film on a side of the second wafer; holding the bonded wafer on a side of the protective film on a chuck table of a processing machine configured to remove the chamfered portion and removing the chamfered portion formed on the outer periphery of the first wafer; rinsing the bonded wafer from which the chamfered portion has been removed; peeling off the protective film from the second wafer; and holding the bonded wafer on the side of the second wafer on a chuck table of a grinding machine, and grinding the first wafer.