Device and Method for Moistening a Polishing Pad

The present invention relates to a device and a method for moistening a polishing pad according to the preambles of the appended independent claims. The invention also relates to a device for polishing a specimen.

Various polishing devices are known in the prior art for polishing rock, metallo-graphic and other specimens of solid materials for different applications. The polishing devices enable to polish specimens with minimal manual work.

An exemplary polishing device comprises a rotatable polishing platen and a polishing pad that is attached to the surface of the polishing platen. The polishing device also comprises a specimen holder for holding one or more specimens against the polishing pad. As the polishing platen is rotated, the polishing pad polishes the specimen(s).

A polishing suspension is used in the polishing device to enhance the polishing action and to prevent overheating during the polishing process. The polishing suspension contains water and/or other suitable liquids, such as ethanol or glycol for moistening, cooling and lubricating the polishing pad and abrasive particles, such as diamond, aluminium oxide or colloidal silica for polishing of the surface of the specimen. The polishing device comprises a dispenser for dispensing the polishing suspension, typically at a predefined rate, on the polishing pad. The dispenser can, for example, be configured to dispense a certain amount of the polishing suspension at regular time intervals on the polishing pad.

A problem associated with the known polishing devices is that, during the polishing, the moisture in the polishing pad can vary considerably as a function of time and as a function of the position on the polishing pad. This has a negative effect on the polishing result. If the polishing pad is too wet, the friction between the specimen and the polishing pad is small, which makes the polishing ineffective and increases the polishing time. If, on the other hand, the polishing pad is too dry, there is a risk that the polishing of the specimen fails due to the large friction between the specimen and the polishing pad.

It is the main objective of the present invention to reduce or even eliminate the prior art problems presented above.

It is an objective of the present invention to provide a device and a method for moistening a polishing pad. In more detail, it is an objective of the invention to provide a device and a method enabling to provide and maintain a substantially constant and uniform moisture content in the polishing pad during the polishing process.

It is also an objective of the invention to provide a device for polishing a specimen. In more detail, it is an objective of the invention to provide a device enabling to polish a specimen with a uniform and high-quality polishing result.

In order to realise the above-mentioned objectives, the device and the method according to the invention are characterised by what is presented in the characterising portions of the appended independent claims. Advantageous embodiments of the invention are described in the dependent claims.

A device according to the invention for moistening a polishing pad comprises measuring means for measuring a physical quantity that is indicative of the moisture in the polishing pad, dispensing means for dispensing a polishing suspension, based on a value of the measured physical quantity, on a surface of the polishing pad, and a housing that encloses the measuring means and the dispensing means, the housing having a contact surface for contacting the surface of the polishing pad.

The moistening device according to the invention can be used for moistening a polishing pad that is used for polishing a specimen. The moistening device can measure a physical quantity that is indicative of the moisture in the polishing pad and then, based on the value of the measured physical quantity, dispense the polishing suspension on the surface of the polishing pad.

The measuring means and the dispensing means are arranged in the housing that is preferably essentially cylindrical. The housing is preferably dimensioned so that the moistening device can be inserted into a specimen cavity of a specimen holder.

The contact surface of the housing is meant to be arranged in contact with a surface of a polishing pad. The measuring of the physical quantity and the dispensing of the polishing suspension are performed through the contact surface. The housing can be made of a wear and corrosion resistant ceramic or metal, or other suitable material. The housing can be a hollow cylinder, one end of which functions as the contact surface. The contact surface is preferably planar.

The measuring means may comprise one or more electrical contact elements (electrodes), which are arranged at the contact surface of the housing. For the measurement, the contact surface and the electrical contact element(s) therein are arranged in contact with the surface of the polishing pad. The measurement is based on measuring a physical quantity that varies as a function of the moisture in the polishing pad. Such a physical quantity is, for example, the capacitance between one electrical contact element and a polishing platen to which the polishing pad is attached, i.e. the capacitance between the opposite sides of the polishing pad. Another such physical quantity is the (electrical) resistance between two electrical contact elements when they are arranged in contact with the surface of the polishing pad.

The electrical contact elements provide an electrical path through which electrical properties of the polishing pad can be measured. The electrical contact elements can have different shapes and sizes. The electrical contact elements are made of an electrically conductive material, which is preferably also wear and corrosion resistant. Preferable materials for the electrical contact elements are, for example, steel and gold-platinum alloy. The electrical contact elements are electrically isolated from each other to prevent short circuits.

The measuring means may comprise a measuring instrument that is electrically connected with electrical connections such as wires, cables and/or carbon brushes to the electrical contact elements and the polishing platen. The measuring instrument can be configured to measure the capacitance between one electrical contact element and the polishing platen, and/or the resistance between two electrical contact elements when they are in contact with the surface of the polishing pad. The values of the capacitance and the resistance depend on the moisture in the polishing pad. The wetter the polishing pad is, the larger the capacitance and the smaller the resistance are.

The dispensing means may comprise a container for the polishing suspension and a nozzle arranged at the contact surface. The nozzle can be connected by a hose to the container. The dispensing means may comprise a valve or a (piezoelectric) micropump arranged in connection with the container, the hose or the nozzle, and a control unit for controlling the operation of the valve or the micropump. The control unit may comprise a processor and a memory including computer program code, the memory and the computer program code being configured to, with the processor, cause the valve or the micropump to dispense suitable amounts of the polishing suspension on the surface of the polishing pad. The amount of the polishing suspension to be dispensed is determined based on the value of the measured physical quantity. The value of the measured physical quantity can be compared to a predefined reference value or profile in order to determine the amount of the polishing suspension to be dispensed. The predefined reference value or profile corresponds to the desired moisture content in the polishing pad. The amount of the polishing suspension to be dispensed on the polishing pad can be, for example, less than 5 μl/cm, less than 2 μl/cmor 0.5-2 μl/cm.

The polishing suspension enhances the polishing action and prevents overheating during the polishing process. The polishing suspension contains water and/or other suitable liquids, such as alcohols (e.g. ethanol, glycol or isopropyl alcohol) for moistening, cooling and lubricating the polishing pad. The polishing suspension may also contain abrasive particles, such as diamonds, aluminium oxide or colloidal silica for polishing of the surface of the specimen. Typically, the polishing suspension (i.e. slurry or fluid) is a mixture of liquid(s) and abrasive(s).

The moistening device may comprise communicating means for communicating with a remote device such as a mobile phone. The communicating means may comprise a transmitter and a receiver for bidirectional wireless communications with the remote device.

An advantage of the moistening device according to the invention is that it can provide and maintain a substantially constant and uniform moisture content in the polishing pad during the polishing process. Another advantage of the moistening device according to the invention is that it enables to achieve a uniform and high-quality polishing result of the specimen. Still another advantage of the moistening device according to the invention is that it enables to optimize (minimize) the consumption of the polishing suspension in the polishing process. Yet another advantage of the moistening device according to the invention is that it can be inserted into a specimen cavity of a specimen holder and thus it can be retrofitted to existing polishing devices. Yet another advantage of the moistening device according to the invention is that it has a compact design wherein the measuring means and the dispensing means are arranged within the same housing.

According to an embodiment of the invention the housing is essentially cylindrical. The cylindrical housing is preferably dimensioned so that the moistening device fits into a specimen cavity of a specimen holder of a polishing device.

According to an embodiment of the invention the housing has a diameter of 10 mm to 100 mm. The diameter of the housing can be 25-60 mm, or 25 mm, 30 mm, 40 mm, 50 mm, or 60 mm. The height of the housing can be, for example, 10-50 mm, 10-30 mm or 20-40 mm.

According to an embodiment of the invention the physical quantity is the resistance on the polishing pad. The resistance on the polishing pad varies as a function of the moisture in the polishing pad. The wetter the polishing pad is, the smaller the resistance is.

According to an embodiment of the invention the measuring means comprises two electrical contact elements arranged on the contact surface and a measuring instrument that is configured to measure the resistance between the two electrical contact elements. The electrical contact elements can have different shapes and sizes. The electrical contact elements are made of an electrically conductive material, which is preferably also wear and corrosion resistant. Preferable materials for the electrical contact elements are, for example, stainless steel and tool steel. For the measurement, the contact surface and the electrical contact elements therein are arranged in contact with a surface of a polishing pad. The electrical contact elements provide an electrical path through which electrical properties of the polishing pad can be measured. The measuring instrument is electrically connected with electrical connections to the electrical contact elements. The measuring instrument is configured to measure the resistance between the electrical contact elements when the contact surface is in contact with the surface of the polishing pad.

According to an embodiment of the invention the dispensing means is configured to dispense the polishing suspension on the surface of the polishing pad if the value of the resistance is larger than a first threshold value. The first threshold value can be set on a case-by-case basis in the light of the characteristics of a specimen to be polished.

According to an embodiment of the invention the physical quantity is the capacitance between opposite sides of the polishing pad. The capacitance between the opposite sides of the polishing pad varies as a function of the moisture in the polishing pad. The wetter the polishing pad is, the larger the capacitance is.

According to an embodiment of the invention the measuring means comprises an electrical contact element arranged on the contact surface and a measuring instrument that is configured to measure the capacitance between the electrical contact element and a polishing platen on which the polishing pad is placed. The electrical contact element can have different shapes and sizes. The electrical contact element is made of an electrically conductive material, which is preferably also wear and corrosion resistant. Preferable materials for the electrical contact element are, for example, stainless steel and tool steel. For the measurement, the contact surface and the electrical contact element therein are arranged in contact with a surface of a polishing pad. The measuring instrument is electrically connected with electrical connections to the electrical contact element and the polishing platen. The measuring instrument is configured to measure the capacitance between the electrical contact element and the polishing platen when the contact surface is in contact with the surface of the polishing pad. A resistor can be used between the measuring instrument and the polishing platen to reduce interference.

According to an embodiment of the invention the dispensing means is configured to dispense the polishing suspension on the surface of the polishing pad if the value of the capacitance is smaller than a second threshold value. The second threshold value can be set on a case-by-case basis in the light of the characteristics of a specimen to be polished.

According to an embodiment of the invention the dispensing means comprises a container for holding the polishing suspension and a hose having a first end connected to the container and a second end arranged in connection with the contact surface. The polishing suspension is dispensed on the surface of the polishing pad through the contact surface. The container can be disposable or refillable. The housing may comprise a hole for filling the container. The volume of the container can be, for example, 1-100 ml, 1-20 ml, 10-50 ml or 50-100 ml.

According to an embodiment of the invention the dispensing means comprises a nozzle connected to the second end of the hose. The nozzle is connected to the contact surface.

According to an embodiment of the invention the dispensing means comprises a valve or a micropump arranged in connection with the container, the hose or the nozzle, and a control unit that is configured to control the operation of the valve or the micropump. The control unit may comprise a processor and a memory including computer program code, the memory and the computer program code being configured to, with the processor, cause the valve or the micropump to dispense suitable amounts of the polishing suspension on the surface of the polishing pad. The amount of the polishing suspension to be dispensed is determined based on the value of the measured physical quantity. The value of the measured physical quantity can be compared to a predefined reference value or profile in order to determine the amount of the polishing suspension to be dispensed. The predefined reference value or profile corresponds to the desired moisture content in the polishing pad. The amount of the polishing suspension to be dispensed on the polishing pad can be, for example, less than 5 μl/cm, less than 2 μl/cmor 0.5-2 μl/cm.

According to an embodiment of the invention the moistening device comprises a power source for supplying electrical power to the measuring means and the dispensing means. The power source is arranged inside the housing. The power source is preferably a rechargeable battery. The housing may comprise a charging socket for wired charging or an inductive receiver for wireless charging.

The present invention also relates to a device for polishing a specimen. The polishing device according to the invention comprises a polishing platen rotatable about an axis, a polishing pad attached to the polishing platen, a specimen holder comprising a plurality of specimen cavities for holding one or more specimens against a surface of the polishing pad, and a moistening device according to the invention inserted into one of the specimen cavities so that the contact surface is in contact with the surface of the polishing pad.

The polishing device according to the invention can be used to polish one or more specimens (i.e. objects) of a solid material, such as a piece of a natural (e.g. rock, mineral, ore or meteorite) or artificial (e.g. metal, concrete, ceramic, composite or semiconductor) material. The specimen to be polished may comprise a substrate on which a semiconductor material, such as silicon or germanium, various III-V compound semiconductor materials, or the like, have been deposited. In this text, the term polishing means polishing, fine-grinding and grinding processes with a polishing pad and a polishing suspension.

The specimen to be polished is inserted into one of the specimen cavities of the specimen holder and held against the surface of the polishing pad with the specimen holder. The specimen holder can be configured to hold one or more specimens against the polishing pad. The number of specimen cavities in the specimen holder can be, for example, 2-5, 6-10, or more than 10. The specimen can be secured in the specimen cavity by clamping. The specimen holder can be attached to a polishing head that presses the specimen(s) with an adjustable pressing force against the polishing pad. The pressing force can be adjusted, for example, based on the value of the measured physical quantity.

The moistening device is inserted into one of the specimen cavities of the specimen holder. The contact surface of the moistening device is arranged in contact with the surface of the polishing pad.

The polishing pad can be made of different materials, such as a fibrous cloth (e.g. real silk, polyester or acetate) or synthetic non-fibrous (e.g. neoprene, polyurethane or composite) material. The polishing pad is preferably disc-shaped, i.e. it has a flat circular shape. The polishing pad is preferably porous, enabling it to absorb the polishing suspension. The diameter of the polishing pad can be, for example, less than 500 mm, preferably 200-400 mm. The thickness of the polishing pad can be, for example, less than 3 mm, preferably less than 2 mm, and more preferably less than 1 mm.

The polishing pad is attached, preferably releasably, to the surface of the rotatable polishing platen. As the polishing platen is rotated, the polishing pad polishes the specimen(s). The polishing platen can be made of a heat conductive and corrosion resistant material, such as aluminium, bronze or stainless steel, or of a plastic, polymer or composite material. The polishing platen may comprise an electrically insulated electrical contact element (for example a sheet made of austenitic stainless steel and having a thickness of about 0.5 mm) on its surface, to which an electrical contact element (for example a carbon brush) can be electrically connected. The electrical contact element can be electrically connected to a measuring instrument of the moistening device. The polishing platen is preferably disc-shaped and heat conductive. The diameter of the polishing platen can be, for example, less than 500 mm, preferably 200-400 mm. Preferably, the diameters of the polishing platen and the polishing pad are essentially the same. The thickness of the polishing platen can be, for example, 20-50 mm. The optimal thickness of the polishing platen depends on the diameter and the material of the polishing platen.

The polishing device may comprise an actuator, such as an electric motor, for rotating the polishing platen. The actuator can be configured to rotate the polishing platen, for example, at a rotational speed of 0-600 rpm. The actuator can be configured to adjust the rotational speed of the polishing platen based on the values of the measured physical quantity. For example, in a case where the moisture falls below a predetermined threshold value, the actuator can be configured to reduce the rotational speed of the polishing platen. To reduce possible interferences caused by the actuator, it may be beneficial to add an electrical insulation layer between the polishing platen and the actuator.

In addition to the polishing platen, also the specimen holder can be rotatable. The specimen holder can be rotatable about an axis, which is parallel to the rotation axis of the polishing platen. The polishing device may comprise an actuator, such as an electric motor, for rotating the specimen holder. The actuator can be configured to rotate the specimen holder, for example, at a rotational speed of 0-150 rpm. The actuator can be configured to adjust the rotational speed of the specimen holder based on the values of the measured physical quantity. For example, in a case where the moisture falls below a predetermined threshold value, the actuator can be configured to reduce the rotational speed of the specimen holder.

An advantage of the polishing device according to the invention is that it can provide and maintain a substantially constant and uniform moisture content in the polishing pad during the polishing process. Another advantage of the polishing device according to the invention is that it enables to achieve a uniform and high-quality polishing result of the specimen. Still another advantage of the polishing device according to the invention is that it enables to optimize (minimize) the consumption of the polishing suspension in the polishing process. Yet another advantage of the polishing device according to the invention is that the moistening device is easy to replace if it breaks.

According to an embodiment of the invention the specimen holder comprises pressing means for pressing the contact surface against the surface of the polishing pad. The pressing means enables to keep the contact surface of the moistening device in contact with the surface of the polishing pad with a suitable pressing force. The pressing force of the pressing means can be adjustable. The pressing means can utilize mechanical force, air pressure, gravity, or magnetic or electromagnetic force in producing the suitable pressing force.

The present invention also relates to a method for moistening a polishing pad. The moistening method according to the invention comprises arranging a moistening device according to the invention in a specimen cavity of a specimen holder, arranging the contact surface of the moistening device in contact with a surface of a polishing pad that is attached to a polishing platen, rotating the polishing platen about an axis, measuring with the moistening device a physical quantity that is indicative of the moisture in the polishing pad, and dispensing with the moistening device a polishing suspension, based on a value of the measured physical quantity, on the surface of the polishing pad.

An advantage of the moistening method according to the invention is that it can provide and maintain a substantially constant and uniform moisture content in the polishing pad during the polishing process. Another advantage of the moistening method according to the invention is that it enables to achieve a uniform and highquality polishing result of the specimen. Still another advantage of the moistening method according to the invention is that it enables to consume less polishing suspension during the polishing process.

The exemplary embodiments of the invention presented in this text are not interpreted to pose limitations to the applicability of the appended claims. The verb “to comprise” is used in this text as an open limitation that does not exclude the existence of also unrecited features. The features recited in the dependent claims are mutually freely combinable unless otherwise explicitly stated.

The exemplary embodiments presented in this text and their advantages relate by applicable parts to the moistening device, the moistening method as well as the polishing device according to the invention, even though this is not always separately mentioned.

illustrates a schematic cross-sectional view of a moistening device according to an embodiment of the invention. The moistening devicecan be used for moistening a polishing pad (not shown in).

The moistening devicecomprises a cylindrical housingthat is dimensioned in such a manner that the moistening devicefits into a specimen cavity of a specimen holder (not shown in). The housingcomprises a contact surfacethat is meant to be arranged in contact with a surface of the polishing pad.

The moistening devicecomprises electrical contact elements,and, which are arranged at the contact surface. The electrical contact elements,andare electrically connected with wires,andto a measuring instrument. The measuring instrumentcan measure the resistance between the electrical contact elementsand, and the capacitance between the electrical contact elementand a polishing platen (not shown in) on which the polishing pad is placed. The resistance between the electrical contact elementsand, and the capacitance between the electrical contact elementand the polishing platen are indicative of the moisture in the polishing pad. A wireis used to electrically connect the measuring instrumentto the polishing platen. For the measurement of the resistance and/or the capacitance, the contact surfaceis arranged in contact with the surface of the polishing pad.

The moistening devicecomprises a containerfor holding a polishing suspension and a hosehaving its first end connected to the container. A second end of the hoseis connected to a nozzlethat is arranged at the contact surface. The hoseis provided with a valvethat controls the flow of the polishing suspension from the containerto the surface of the polishing pad. The moistening devicecomprises a control unitthat controls the operation of the valve. The control unitcontrols the valveto dispense a suitable amount of the polishing suspension on the surface of the polishing pad. The amount of the polishing suspension to be dispensed is determined based on the value of the measured resistance or the capacitance. The control unitreceives the value of the measured resistance or the capacitance from the measuring instrument.