Patent Application
20230321758
A robotic device can be used to handle wafers within a processing system where human handling would be inefficient or otherwise undesirable, such as in a system for performing wafer loading and removal, chemical mechanical planarization (CMP), etching, deposition, passivation, and other processes. The robotic device may have an end effector for, among other things, loading wafers from a stack into one or more processing ports. The end effector can hold a wafer by suction applied through one or more vacuum draw eyelets. The end effector can have a forked shape, a spatula shape, or another suitable configuration. The wafer contact eyelets may be located at one or more end portions of the end effector. In operation, the vacuum draw eyelets seize and hold individual wafers for transfer and handling. The wafers can be made of silicon, semiconductor materials, or other materials.
Examples of end effectors are mentioned in U.S. Pat. Publications Nos. 2022/0051928 (published Feb. 17, 2022) (Transfer Device, Transfer System, and End Effector), 2020/0206954 (published Jul. 2, 2020) (Apparatus, System and Method for Providing a Conformable Cup for an End Effector), and 2018/0215049 (published Aug. 2, 2018) (Suction Apparatus for an End Effector, End Effector for Holding Substrates and Method of Producing an End Effector).
The present disclosure relates to a method of making a ceramic device with a controlled roughness. The method includes using a defocused laser beam to roughen a surface of a ceramic substrate, and removing one or more portions of the roughened surface without removing another portion of the roughened surface. If desired, the ceramic device may include reaction-bonded silicon carbide. If desired, an opening may be formed so that the ceramic device can be used to apply a clamping suction to a wafer surface.
The present disclosure also relates to a ceramic device including a surface having a controlled roughness produced by a defocused laser beam, and a second surface having a second roughness. The first surface may be used to form an interface with a mating element, such as a wafer. The first surface may have one or more properties for achieving a desired interface with the mating element, such as suitable roughness and adequate wear resistance. If desired, the ceramic device may include reaction-bonded silicon carbide, and may include an opening for establishing a clamping suction to the mating element, which may be, for example, the back side of a semiconductor wafer.
Throughout the drawings, like elements are designated by like reference numerals and other characters. The drawings show non-limiting examples for purposes of illustration and explanation of the present disclosure, and are not drawn to scale.
Reaction-bonded silicon carbide (RB—SiC, or Si/SiC) (an example of a ceramic material) may be used in a variety of products and systems, including semiconductor equipment, industrial wear, thermal management, furnace components, armor, etc. Attractive properties of reaction-bonded silicon carbide include low thermal-expansion, high thermal-conductivity, high hardness, high wear-resistance, high stiffness, and chemical inertness.
Reaction-bonded silicon carbide is a multi-phase material formed by reactive infiltration in which molten elemental silicon (Si) is brought into contact with a porous mass of interconnected silicon-carbide (SiC) particles plus carbon (C) in a vacuum or inert atmosphere. A wetting condition is created such that the molten silicon is pulled by capillary action into the mass of interconnected silicon-carbide particles and carbon, and the silicon reacts with the carbon in the mass to form additional silicon carbide. The resulting reaction-bonded silicon-carbide material contains primarily silicon carbide, but also unreacted, interconnected silicon.
The infiltration process is illustrated in
In the illustrated process, the molten silicon reactively infiltrates into the preform 20 (
Thus, as the term is used herein, reaction-bonded silicon carbide is a fully dense, two-phase composite of silicon-carbide particles in a continuous silicon matrix. Reaction-bonded silicon carbide is mentioned in U.S. Pat. Application No. 17/248,309 (filed Jan. 19, 2021) and U.S. Pat Publications Nos. 2021/0331985 (published Oct. 28, 2021), 2018/0099379 (published Apr. 12, 2018), and 2017/0291279 (published Oct. 12, 2017). The entire disclosures of U.S. Pat Application No. 17/248,309 and U. S. Pat Publications Nos. 2021/0331985, 2018/0099379, and 2017/0291279 are incorporated herein, in their entireties, by reference.
Referring now to
If desired, the top surfaces 50, 52 of the main and inner sections 42, 46 may be formed by a suitable machining process, as described in more detail below. In the illustrated configuration, the top surface 54 of the wafer-contact portion 44 is roughened by a defocused laser, and is not subsequently machined, as described in more detail below. In
Each vacuum draw eyelet 36, 38, including in each case the main, wafer-contact, and inner sections 42, 44, 46, may be formed in one integral piece of a reaction-bonded silicon-carbide material. As illustrated in
Each one of the vacuum draw eyelets 36, 38 may have essentially the same structure and configuration, may be produced (manufactured) in essentially the same way, may be connected to the same vacuum source 56, and may operate in essentially the same way. The vacuum draw eyelets 36, 38 (examples of wafer-contact devices) are connected to the end-effector arm 34 by suitable adhering agents or connecting devices (not illustrated in the drawings). The present disclosure is not limited, however, to the specific configurations and processes illustrated in the drawings and described herein except to the extent such features are mentioned in the accompanying claims.
In operation, the entire top surface 54 of the wafer-contact portion 44 may come into contact with the back side of a semiconductor wafer (not illustrated). When such contact occurs, a plane which contains essentially all of the top surface 54 of the wafer-contact portion 44 is coincident with a plane which contains the back side of the wafer, at least in the vicinity of the wafer-contact portion 44. The top surface 52 of the inner section 46, the back side of the wafer, and inwardly-facing surfaces 58 of the wafer-contact portion 44 form a suction chamber 60 (
As described in more detail below, the desired defocused laser roughening causes the top surface 54 of the wafer-contact portion 44 to be sufficiently rough to prevent the top surface 54 from sticking to the back side of the wafer. The top surface 54 may not be so rough, however, as to permit air (or another gas) to leak into the suction chamber 60, through the contact interface between the top surface 54 and the back side of the wafer, and prevent the wafer from adhering to the end effector 32.
In operation, a suitable robotic system connected to the end effector 32 moves the end-effector arm 34 such that the eyelets 36, 38 come into contact with the bottom surface of a wafer (not illustrated). A vacuum is then drawn through the end effector 32 and applied through the vacuum eyelets (or pads) 36, 38 to securely attach the wafer to the end effector 32. The robotic system then moves the wafer to another desired location. Subsequently, the application of vacuum from the vacuum source 56 may be discontinued such that the wafer is released from the vacuum pads 36, 38 and the end effector 32 can be moved away from the wafer.
Referring now to
The defocused laser may pass across the surface 64 a desired number of times to achieve a desired, customer-requested, surface roughness. If desired, the thickness of the roughened ceramic substrate 68 may be the same as the greater thickness t2 of the wafer-contact portion 44 (
After the ceramic substrate 62 illustrated in
If desired, instead of or in addition to the eyelets 36, 38, an end effector may have rings for establishing a vacuum chamber for clamping the back side of a wafer to an arm of the end effector. The rings may have a suitable roughness established by defocused laser roughening on surfaces where the rings come into contact with the wafer, to obtain the desired clamping without sticking.
Thus, according to the present disclosure, a reaction-bonded silicon-carbide material has a surface that has a suitable roughness created by defocused laser roughening to prevent back side wafer contamination and permit the roughened device to have a long useful life (with low wear). The wafer contact surface 54 should be sufficiently rough to prevent it from sticking to the wafer. If the wafer contact surface 54 were too flat and smooth, it would tend to undesirably stick to the back side of the wafer by a phenomenon referred to as “optical contacting” or “contact bonding.” The phenomenon is mentioned in A Study of Glass Surfaces in Optical Contact, Lord Rayleigh, Proc. Phys. Soc., A156, 326 (1936), and Optical Contacting Grows More Robust, Chris Myatt, Nick Traggis, and Kathy Li Dessau, Laser Focus World, Jan. 1, 2006. A “sticky” interface with the wafer may not be acceptable, especially in connection with a semiconductor fabrication system which requires the end effector 32 to efficiently and rapidly clamp and un-clamp (release) wafers.
On the other hand, the roughness of the wafer-contact surface 54 should not be so rough as to permit a vacuum leak through its interface with the back side of the wafer, or to permit undesirable, premature wear. If the contact surface is too rough, adequate vacuum clamping may not be achievable. That is, air (or another gas) could leak between the wafer and the reaction-bonded silicon-carbide material between the peaks and valleys of the too-rough surface. Moreover, a too-rough (spikey) surface could wear quickly due to a low bearing ratio.
The present disclosure advantageously employs reaction-bonded silicon-carbide material for wafer contact surfaces of vacuum end effectors (vacuum EEs) that can be used to robotically move wafers through a semiconductor manufacturing facility. Compared to other possible wafer contact materials, such as polymer, metal, and oxide ceramic, reaction-bonded silicon carbide provides high purity, high hardness, and a consistent tribological interface. For applications where reaction-bonded silicon carbide touches a wafer surface, a well-controlled surface roughness may be required. If the wafer-contact surface is too smooth, the wafer may stick via optical contact bonding, and if the surface is too rough, a vacuum leak may occur and prevent robust clamping.
Thus, the present disclosure describes a laser roughening method for generating a desired controlled roughness of a wafer contact component formed of reaction-bonded silicon carbide and located on an end effector assembly. As indicated above, reaction-bonded silicon carbide may be particularly well suited to roughening because it is a two-phase composite material of silicon carbide (SiC) and elemental silicon (Si), and the two phases are machined at different rates.
The roughening process may be performed by a laser beam applied to the surface 64 of the substrate 62. If desired, the laser beam may be generated by a DMG Mori LaserTech 45 shape machine tool which is a fiber-laser tool configured for producing a 100 watt (W) laser beam, with a beam wavelength (λ) of 1,064 nanometers (nm). The laser beam should be defocused, that is, the ideal focus of the beam should be displaced from the surface 64 of the ceramic substrate 62. The substrate surface 64 should be roughened but not cut. According to one aspect of the present disclosure, the roughened surface should have an average roughness (Ra) in the range of from 0.3 to 1.1 µm. According to another aspect of the present disclosure, the roughened surface may have an average roughness (Ra) in the range of from 0.36 to 0.44 µm. If desired, the average surface roughness may be measured by a Mitutoyo SJ-210 surface profilometer.
In operation, the laser beam may be defocused by displacing the ideal focus of the laser beam away from the substrate surface 64, in a direction orthogonal to the substrate surface 64, by a distance in the range of from 0.9 to 1.1 millimeters (mm). The intensity of the laser beam at the point where its defocused portion is incident on the wafer surface may be in the range of from 7.2 to 8.8 W. The laser beam may be pulsed with a pulse frequency (f) in the range of from 90 to 110 kilohertz (kHz). The pulse duration (t) of the laser beam may be in the range of from 109 to 132 nanoseconds (ns). The tracking velocity (v) of the laser beam, that is, the velocity at which an incident portion of the beam moves across the substrate surface 64, in the plane of the substrate surface 64, may be in the range of from 2,250 to 2,750 millimeters per second (mm/s).
If desired, components with a roughness gradient can be made by using a different number of laser passes at different surface locations.
The present disclosure is not limited to the fabrication or use of the eyelets 36, 38 described herein. The laser-roughening process may also be used to produce a variety of other devices with ceramic, especially reaction-bonded silicon carbide, surfaces, including end-effector pads, rings, and cups. The laser-roughening process described herein may also be used to produce a variety of other devices that may be used in a semiconductor fabrication plant, especially devices which contact wafers, and where controlled surface roughness is desired, such as vacuum wafer pin chucks, vacuum wafer through-hole chucks, and electrostatic chucks. The laser-roughening process described herein may also be used to produce a variety of other devices, especially ceramic devices, where it is desirable for one or more surfaces of the device to have a controlled roughness, such as bearing seals, cylinder liners, human artificial joints (hips, knees, etc.), bonding surfaces, and air-bearing surfaces.
Turning now to
