Patent Grant
7156720
1. Field of the Invention
The present invention relates to a substrate holding apparatus, and more particularly to a substrate holding apparatus in a chemical mechanical polishing apparatus for polishing a substrate such as a semiconductor wafer to a flat mirror finish.
2. Description of the Related Art
As semiconductor devices have become more highly integrated in recent years, circuit interconnections have become finer and distances between those circuit interconnections have become smaller. In a case of photolithography, which can form interconnections that are at most 0.5 μm wide, it is required that surfaces on which pattern images are to be focused by a stepper should be as flat as possible because depth of focus of an optical system is relatively small. In order to planarize such a semiconductor wafer, there has been used a polishing apparatus for performing chemical mechanical polishing (CMP).
This type of chemical mechanical polishing apparatus comprises a polishing table having a polishing pad (polishing cloth) attached to an upper surface of the polishing table, and a top ring for holding a substrate to be polished, such as a semiconductor wafer. The polishing table and the top ring are rotated at independent rotational speeds, respectively. The top ring presses the substrate against the polishing pad under a predetermined pressure. A polishing liquid (slurry) is supplied from a polishing liquid supply nozzle onto the polishing pad. Thus, a surface of the substrate is polished to a flat mirror finish.
The top ring 104 has an elastic pad 110 attached to a lower surface of the top ring 104. For example, the elastic pad is made of polyurethane. The semiconductor wafer W is held by the top ring 104 in a state such that the semiconductor wafer W is brought into contact with the elastic pad 110. Further, the top ring 104 has a cylindrical guide ring 112 provided at a peripheral portion of the top ring 104. The guide ring 112 serves to prevent the semiconductor wafer W from being separated from the lower surface of the top ring 104 during polishing. The guide ring 112 is fixed to the peripheral portion of the top ring 104. The guide ring 112 has a lower end located at a position lower than a holding surface of the top ring 104, and accordingly, forms a recessed portion at an inward position of the guide ring 112. Thus, a semiconductor wafer W to be polished is held within the recessed portion of the top ring 104 so as not to be ejected from the top ring 104 during polishing.
With the conventional polishing apparatus, the semiconductor wafer W is held on a lower surface of the elastic pad 110 in the top ring 104 and pressed against the polishing pad 100 on the polishing table 102 by the top ring 104. The polishing table 102 and the top ring 104 are rotated so as to move the polishing pad 100 and the semiconductor wafer W from the polishing liquid supply nozzle 106. For example, a suspension of fine abrasive particles in an alkali solution is used as the polishing liquid. Thus, the semiconductor wafer W is polished to a flat mirror finish by a combined effect of a chemical polishing effect attained by the alkali and a mechanical polishing effect attained by the abrasive particles.
In the aforementioned polishing apparatus, various complicated factors which may affect an amount of polishing should be controlled in order to planarize a semiconductor wafer W over an entire surface thereof with high accuracy. Such factors include a relative sliding speed between the semiconductor wafer W and the polishing table 102, an amount (or distribution) of polishing liquid at an interface (polishing interface) between the semiconductor wafer W and the polishing pad 100, a pressing force applied to the semiconductor wafer W to press the semiconductor wafer W against the polishing pad 100 by the top ring 104, a temperature of the polishing interface, and the like.
When an acid or alkali polishing liquid is used to perform a chemical mechanical polishing process (CMP), the temperature of the polishing interface exerts a great influence on a polishing rate. Additionally, if the top ring 104 is increased in temperature, the top ring 104 is deformed so as to exert an adverse influence on a pressing force. Thus, control of the temperature of the polishing interface has two aspects with respect to a level of planarization.
An example of a substrate holding apparatus including a means for controlling a temperature of a polishing interface is disclosed in Japanese laid-open patent publication No. 2000-225559, relevant parts of which are hereby incorporated by reference. Specifically, the substrate holding apparatus includes a holding plate having a substrate holding surface and an elastic pad attached to the holding surface of the holding plate. A substrate is held via the elastic pad on the substrate holding surface, and a surface of the substrate to be polished is pressed against a polishing surface on a polishing table. Grooves are formed in the substrate holding surface of the holding plate. The grooves are supplied with a fluid controlled in terms of temperature. Thus, a temperature of the substrate is controlled via the elastic pad.
Further, no flow regulating valve is provided downstream of the communication grooves 128, but the regulators 125 are provided downstream of the communication grooves 128. Accordingly, the temperature control fluid 129 is supplied to the communication grooves 128 only when pressure of a fluid in the communication grooves 128 is lowered. Thus, the cooling effect is unsatisfactory in the conventional substrate holding apparatus. Furthermore, because the temperature control fluid 129 may leak from a periphery of the elastic pad 110 into the wafer W to cause uneven temperature control and contamination of the wafer W, a liquid cannot be used as the temperature control fluid 129.
Additionally, it is necessary to form a plurality of communication grooves 128 in the top ring 104 and further form a plurality of passages for allowing the temperature control fluid 129 to flow through the communication grooves 128. Thus, many troublesome processes are required to form grooves and holes, and a structure of the top ring 104 becomes complicated. Accordingly, use of the communication grooves 128 is effective rather in applying a back pressure to a rear face of the wafer W.
In order to solve the above drawbacks, there has been proposed a substrate holding apparatus having an air bag as shown in
Although the substrate holding apparatus shown in
The present invention has been made in view of the above drawbacks. It is, therefore, an object of the present invention to provide a substrate holding apparatus which can accurately control temperature of a substrate in a direct manner with a relatively simple arrangement.
According to a first aspect of the present invention, there is provided a substrate holding apparatus which can accurately control temperature of a substrate in a direct manner with a relatively simple arrangement. The substrate holding apparatus has a top ring configured to hold a substrate to be polished and press the substrate against a polishing surface, and an air bag attached to the top ring so as to be brought into contact with a rear face of the substrate. The substrate holding apparatus also has a regulator operable to regulate a temperature control fluid to be supplied into the air bag, and a flow regulating valve operable to regulate a flow rate of the temperature control fluid discharged from the air bag.
According to a second aspect of the present invention, there is provided a substrate holding apparatus which can accurately control temperature of a substrate in a direct manner with a relatively simple arrangement. The substrate holding apparatus has a top ring configured to hold a substrate to be polished and press the substrate against a polishing surface, and an air bag attached to the top ring so as to be brought into contact with a rear face of the substrate. The air bag includes a plurality of chambers. The substrate holding apparatus also has a plurality of regulators operable to regulate temperature control fluids to be supplied into corresponding chambers in the air bag, and a plurality of flow regulating valves operable to regulate flow rates of the temperature control fluids discharged from the corresponding chambers in the air bag. In this case, the substrate can be controlled in terms of temperature at each local area of the substrate.
According to the present invention, a fluid (gas or liquid) controlled in terms of temperature is supplied to the air bag near a rear face of the substrate (wafer) and discharged from the air bag. Thus, heat exchange can efficiently be performed to stabilize a temperature of the substrate for a long term of a chemical mechanical polishing (CMP) process.
The substrate holding apparatus may include a thermometer provided in the top ring or the air bag to measure a temperature of the substrate held by the top ring. The thermometer may monitor the temperature of the substrate held by the top ring. The substrate can be controlled in terms of temperature based on results monitored by the thermometer. The air bag may comprise a close-type air bag or an open-type air bag.
According to a third aspect of the present invention, there is provided a substrate holding apparatus which can accurately control temperature of a substrate in a direct manner with a relatively simple arrangement. The substrate holding apparatus has a top ring configured to hold a substrate to be polished and press the substrate against a polishing surface, and an air bag attached to the top ring so as to be brought into contact with a rear face of the substrate. The substrate holding apparatus also has a regulator operable to regulate a temperature control fluid to be supplied into the air bag, and a thermometer provided in the top ring or the air bag to measure a temperature of the substrate held by the top ring.
According to a fourth aspect of the present invention, there is provided a substrate holding apparatus which can accurately control temperature of a substrate in a direct manner with a relatively simple arrangement. The substrate holding apparatus has a top ring configured to hold a substrate to be polished and press the substrate against a polishing surface, and an air bag attached to the top ring so as to be brought into contact with a rear face of the substrate. The air bag includes a plurality of chambers. The substrate holding apparatus also has a plurality of regulators operable to regulate temperature control fluids to be supplied into corresponding chambers in the air bag, and a thermometer provided in the top ring or the air bag to measure a temperature of the substrate held by the top ring. In this case, the substrate can be controlled in terms of temperature at each local area of the substrate.
The thermometer may monitor the temperature of the substrate held by the top ring. The substrate can be controlled in terms of temperature based on results monitored by the thermometer. The air bag may comprise a close-type air bag or an open-type air bag.
The above and other objects, features, and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.
A substrate holding apparatus according to embodiments of the present invention will be described below with reference to
The air bag 4 presses the wafer W against a polishing table under a uniform pressure. The regulator 5 maintains and regulates a pressure of the air bag 4. The temperature control fluid 9 flows through the regulator 5 into the air bag 4. The temperature control fluid 9 in the air bag 4 is continuously or intermittently discharged by the flow regulating valve 6. Heat exchange is performed between the wafer W and the temperature control fluid 9. Thus, by adjusting the temperature of the temperature control fluid 9, the wafer W can be maintained at a predetermined temperature.
In the present embodiment, there is no elastic pad, which has poor heat conductivity. Heat conduction is performed via a thin film of the air bag 4. As a result, even if a CMP process is performed to polish a thick copper film for a long term, temperature increase is not caused. Accordingly, a high polishing rate can be maintained until completion of a polishing process. Further, even when a polishing process is performed at a high pressing force and a high rotational speed in order to increase a polishing rate, temperature increase can be prevented.
As shown in
As shown in
The regulators 5 and the flow regulating valves 6 are provided so as to correspond to the divided chambers 34a, 34b, and 34c. Temperature control fluids 9 are supplied at different flow rates into the divided chambers 34a, 34b, and 34c, respectively. Thus, the central portion, the intermediate portion, and the peripheral of the wafer W can be cooled separately from each other.
With the air bag having the divided chambers 34a, 34b, and 34c to control a temperature of the wafer W, temperature control can be performed at respective areas of the wafer W. In a case of a copper CMP process, a polishing rate is lowered when the temperature of the wafer becomes larger than a certain value. Particularly, decrease of a polishing rate becomes significant at a central portion of a wafer when the temperature of the wafer is increased. According to the substrate holding apparatus 31 described above, the wafer W can intensively be cooled at the central portion thereof. Thus, it is possible to effectively prevent decrease of a polishing rate.
In the above embodiments, a fluid 9 controlled in temperature is introduced into the air bag to control the temperature of the wafer W. However, in order to perform accurate temperature control, it is necessary to measure the temperature of the wafer W to be polished. In a conventional polishing apparatus, because the surface of the wafer cannot directly be measured, a temperature of a polishing pad is measured at a position through which the wafer has passed to thereby measure the temperature of the wafer. To the contrary, in the substrate holding apparatus employing an air bag without any elastic pads, the temperature of the rear face of the wafer W can directly be measured. Accordingly, a thermometer may be provided in the top ring 2 to measure the temperature of the rear face of the wafer W in the above embodiments. When the temperature of the wafer W is monitored by the thermometer, temperature control of the wafer W can be performed more accurately.
If a thermometer provided in the top ring is brought into direct contact with the wafer, distortion is applied to the wafer W. Accordingly, a non-contact radiation thermometer is suitable for the thermometer to measure the temperature of the wafer W. It is desirable to use an infrared thermometer as a radiation thermometer. In the case of an infrared thermometer, an infrared ray permeates an Si wafer and is thus suitable only for a metal wafer. In the case of a radiation thermometer, when the air bag is made of a material which is permeated by electromagnetic radiation (including light ray), the temperature of the wafer W can sufficiently be measured even if a measurement end of the thermometer is located above the air bag. However, even a thin film of the air bag inhibits permeation of electromagnetic radiation to some extent. Accordingly, when an open-type air bag as shown in
As described above, according to a substrate holding apparatus for a chemical mechanical polishing (CMP) apparatus, a fluid controlled in terms of temperature is brought into contact with a rear face of a substrate to be polished in order to stabilize variation of temperature of the substrate during a CMP process. Accordingly, even if a CMP process is performed for a long term, temperature increase is not caused. Further, even when a polishing process is performed at a high pressing force and a high rotational speed in order to increase a polishing rate, temperature increase can be prevented. Accordingly, a high polishing rate can be maintained until completion of the polishing process. Thus, the present invention is useful for a substrate holding apparatus in a polishing apparatus for polishing highly integrated semiconductor wafers to a flat mirror finish.
Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.
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