JP5048300B2 - Evaluation apparatus for substrate mounting apparatus and evaluation method therefor - Google Patents

Description

  The present invention relates to an evaluation apparatus and an evaluation method for a substrate mounting apparatus used for fixing and temperature control of a substrate to be processed such as a silicon wafer in a semiconductor process. The present invention relates to an apparatus and a method for simply evaluating the function of a substrate mounting apparatus when receiving a signal.

  2. Description of the Related Art In the field of semiconductor manufacturing, plasma processing apparatuses that perform etching and film formation by applying plasma to a substrate to be processed (hereinafter referred to as a substrate) such as a silicon wafer are frequently used. Since such plasma treatment is performed under reduced pressure, a vacuum chuck cannot be used for holding the substrate, and a substrate mounting apparatus such as a mechanical clamp or an electrostatic chuck using electrostatic force is generally used.

  In an electrostatic chuck, the substrate mounting surface is made of an insulator, and a high potential is applied to the planar electrode embedded in the insulator, so that static electricity distributed by the insulator and electrostatic charge caused by polarization charge on the substrate can be prevented. In this method, the substrate is fixed to the substrate mounting surface by Coulomb force or Johnson Rabeck force.

  The basic function of this electrostatic chuck is to fix the substrate by adsorption. In recent years, an inert gas such as helium is allowed to flow between the silicon wafer and the electrostatic chuck to cool the silicon wafer or a heater. In general, cases are used in combination with the purpose of controlling the temperature of the silicon wafer during the processing process, such as heating the silicon wafer in combination. This is because the film forming speed, the quality of the film forming, and the like and the film forming temperature are very closely related.

  For this reason, in the evaluation of the electrostatic chuck, in addition to the mechanical characteristics, particle reduction, purity improvement, plasma resistance, chemical resistance, the temperature adjustment function of the silicon wafer during film formation and etching of the silicon wafer, and Uniformity of temperature distribution has become an extremely important evaluation item.

  In general, the temperature adjustment function depends on heat input from the outside to the substrate and the mounting table, and characteristics such as adsorption force, leakage current, and desorption responsiveness related to the adsorption fixing function affect the temperature of the substrate to be processed.

  Therefore, the performance evaluation of the electrostatic chuck used in the plasma processing apparatus must be performed under conditions that take into account the heat input from the plasma to the substrate or mounting table. This is far from the results below.

  If the characteristics of the electrostatic chuck are measured under the same conditions as in an actual etching process using a plasma processing apparatus, an accurate performance evaluation can be performed. However, only for this evaluation, it is costly to use an expensive and complicated plasma processing apparatus. Moreover, there is a problem that labor and time required for evaluation become excessive.

  For this reason, in Patent Document 1 below, an electrostatic chuck is installed in a sealed chamber that can be evacuated, the substrate is heated by lamp heating means disposed above the electrostatic chuck, and the thermal conditions in the plasma processing apparatus are simulated. An “electrostatic chuck evaluation apparatus and electrostatic chuck evaluation method” for evaluating an electrostatic chuck is disclosed.

JP 2006-86301 A

  As disclosed in Patent Document 1, an electrostatic chuck evaluation method that uses a lamp heating means (halogen lamp) as an external heat source and simulates heat input from plasma to perform an electrostatic chuck is very simple. This is a preferred method in that it can be evaluated.

  However, according to the results studied by the present inventors, it has been found that it is difficult to simulate heat input from plasma in the electrostatic chuck evaluation method disclosed in Document 1.

  The reason is the difference in heat transfer mechanism between heat transfer from plasma and heat transfer from a normal heating lamp or heater. In general, heat transfer from high-temperature plasma is considered to be mainly due to contact heat transfer of plasma-ized molecules.

  On the other hand, the heat transfer from the heating lamp is caused by the infrared rays irradiated from the heat source being absorbed and absorbed by the substrate, and the energy induces the movement (vibration) of the molecules, which is heated by the friction between the vibrated materials. It is what is done.

  Here, the infrared rays irradiated from the heating lamp are mainly near infrared rays (0.78 μm to 2 μm) and infrared rays (2 μm to 4 μm). On the other hand, as shown in FIG. 6, the silicon wafer as the substrate to be processed almost transmits infrared rays (infrared light) in a wavelength region of about 1 μm to 5 μm. For this reason, even if the silicon wafer which is the substrate to be processed is heated by the infrared lamp, the silicon wafer is hardly heated, and the infrared light is transmitted through the silicon wafer, and the surface of the electrostatic chuck (the mounting surface) below the silicon wafer. Surface) will be heated exclusively.

  FIG. 5 is a view showing a heating state of the silicon wafer when a silicon wafer (substrate to be processed) is sucked and fixed by an electrostatic chuck and irradiated with infrared rays by an infrared lamp. If both the electrostatic chuck and the silicon wafer are viewed microscopically, there are flickers on the surface. For this reason, as shown in FIG. 5 (a), the contact surface between the electrostatic chuck and the silicon wafer has a close contact portion and a space generating space.

  In such a state, the irradiation light (infrared light) from the infrared lamp is almost transmitted through the silicon wafer as described above. Therefore, as shown in FIG. Thus, the contact surface is heated at the close contact portion. As a result, the temperature of the electrostatic chuck (the temperature of the mounting substrate) is sufficiently thermally conducted in the close contact portion, but the heat is not sufficiently conducted in the non-contact portion.

  On the other hand, in an actual process using plasma, it is considered that contact heat transfer is mainly performed when molecules converted into plasma at a high temperature come into contact with a silicon wafer. For this reason, the silicon wafer is uniformly heated on the entire surface thereof.

  Therefore, it is considered that the thermal state of the electrostatic chuck and the silicon wafer is far from the case of using the simulation evaluation apparatus that simulates using infrared light and the actual plasma processing apparatus.

  In general, as a heater used for the above-mentioned purpose, an infrared heater is most desirable because it is inexpensive and has high heating efficiency. However, in order to simulate the thermal state of the plasma processing apparatus with a simulated evaluation apparatus using an infrared heater as a heat source, the device is designed so that the thermal state in the simulated evaluation apparatus corresponds to the state in the actual plasma processing apparatus. There is a need to.

  Therefore, the present invention makes it possible to create a thermal state corresponding to an actual plasma processing apparatus in a simulation evaluation apparatus that evaluates the performance of a substrate mounting apparatus using an infrared heater as a heat source. It is an object of the present invention to provide means capable of simply simulating a thermal state and performing performance evaluation of a substrate mounting apparatus.

  As a means for simply evaluating the performance of the substrate mounting apparatus, it is generally performed to measure the temperature or temperature distribution of the substrate to be processed fixed by the substrate mounting apparatus. As such temperature measurement means, an embedded or affixed thermocouple method is usually employed, in which measurement values can be obtained accurately and reliably, and an evaluation-dedicated board preliminarily fitted with a thermocouple is often used.

  The present inventors use not a silicon wafer that transmits infrared light but a material having a low infrared light transmittance and a large absorption coefficient as a material for an evaluation-dedicated substrate (hereinafter referred to as an evaluation substrate). We focused on solving the above problems.

  In general, ceramic materials are difficult to transmit infrared light. However, the material used for the evaluation substrate is required not only to have low infrared light transmission but also to have various other requirements. One is to prevent the substrate mounting device from being contaminated by the evaluation substrate, and the other is that the thermal characteristics of the material such as thermal conductivity and specific heat are similar to those of silicon wafers. Is. The present inventor has made various studies on ceramic materials satisfying such requirements, and has found that all of the above problems can be solved by using silicon carbide (SiC) as the material of the evaluation substrate, thereby completing the present invention. I came to let you.

  The present invention based on this knowledge is an evaluation apparatus for a substrate mounting apparatus for fixing and controlling the temperature of a substrate to be processed placed on a mounting surface, and an airtight chamber capable of depressurization in which the substrate mounting apparatus is installed. And a heat source disposed opposite to the mounting surface and irradiating infrared light, and placed on the mounting surface in place of the substrate to be processed, formed of a material that absorbs the infrared light, And an evaluation substrate having means for measuring temperatures at a plurality of locations on the surface or inside.

  It is particularly preferable that the substrate mounting device is an electrostatic chuck, and the evaluation substrate is made of silicon carbide. The first reason why silicon carbide is preferable is that silicon carbide is formed only from Si and C, and there is no possibility of causing metal contamination to the silicon wafer. In contrast, ceramics such as Al-based and Ti-based oxides, carbides, and nitrides can be used because of their low infrared transmittance, but in processes that require a higher degree of cleanliness, the cause of contamination It is more preferable to use SiC that is less likely to become.

  The second reason why silicon carbide is preferable is that its thermal conductivity is remarkably large among ceramics, and shows a value almost similar to that of silicon. Also, the specific heat shows a value almost the same as that of silicon. For this reason, it is expected that the heat transfer phenomenon between the electrostatic chuck and the substrate shows a similar tendency between the silicon wafer and the silicon carbide evaluation substrate. This is because it is a great advantage in the evaluation of the above.

  The present invention provides a substrate mounting device for fixing and controlling the temperature of a substrate to be processed placed on a mounting surface in an airtight chamber that can be decompressed, and a material that absorbs infrared light on the substrate mounting device. An evaluation substrate having a means for measuring the temperature of a plurality of locations on the surface or inside is placed, the evaluation substrate is heated by a heat source that irradiates infrared light on the placement surface, and the temperature is set. The characteristics of the substrate mounting apparatus are evaluated including the temperature distribution of the evaluation substrate obtained by the measuring means. It is preferable to measure and evaluate the temperature at a plurality of locations on the evaluation substrate, and it is particularly preferable that the substrate mounting device is an electrostatic chuck and that the material of the evaluation substrate is silicon carbide.

  According to the present invention, for example, when an electrostatic chuck is used in a plasma processing apparatus, a heat input condition that approximates heat input from plasma to a substrate attracted and fixed to the substrate mounting apparatus is simulated by simple means. It became possible. Thereby, it becomes possible to easily perform a more accurate evaluation of the thermal characteristics of the substrate mounting apparatus according to the actual use conditions in the plasma processing apparatus.

  Preferred embodiments of the present invention will be described with reference to the drawings of the examples, but the present invention is not limited thereto. FIG. 1 is a cross-sectional view of an evaluation apparatus which is an embodiment of an evaluation apparatus for an electrostatic chuck according to the present invention. This apparatus is arranged to face the airtight chamber 1, the electrostatic chuck 2 attached to the inside thereof, the evaluation substrate 4 placed on the placement surface 3 of the electrostatic chuck, the placement surface 3, An infrared heater 5 for heating the evaluation substrate 4, a vacuum pump 6 for sucking the inside of the chamber 1 to a vacuum, and the like are included.

  The electrostatic chuck 2 has a structure in which an electrode 8 is embedded in an insulating base 7 constituting the mounting surface 3, and the insulating base 7 is fixed on a cooling board 9. A refrigerant flow path is formed in the cooling plate 9, and the refrigerant flows through the refrigerant inflow / outflow pipes. Further, a higher voltage than the DC power supply 10 is applied to the electrode 8.

  The infrared heater 5 is attached to the ceiling of the chamber 1 via a heat insulating column 11, and a heat insulating plate 12 is disposed on the back surface of the heater 5 to prevent overheating of the ceiling. The heater 5 is supplied with electric power from an AC power supply 13 outside the chamber 1. The supplied power is controlled to an appropriate value by a control device (not shown).

  Thermocouples 14 are attached to the surface or inside of the evaluation substrate 4 at a plurality of locations (two locations in the example in the figure), and the electromotive force thereof is connected to an external thermometer 15 via connection terminals provided on the inner wall of the chamber 1. The temperature of each part of the evaluation substrate 4 is measured.

  In the present invention, the type of the electrostatic chuck 2 to be evaluated is not particularly limited. For example, the insulating substrate 7 may be either a ceramic substrate formed by thermal spraying or sintering, or an insulating resin substrate such as a polyimide film. The electrode 8 only needs to be able to apply a voltage almost uniformly to the entire surface of the substrate to be processed, and may have any structure such as a film shape, a plate shape, or a spiral winding shape.

  The cooling plate 9 and the insulating base 7 are preferably bonded together to improve heat conduction, and the cooling plate 9 is preferably made of a material having high heat conductivity.

  Further, a system in which a cooling medium such as He gas is allowed to flow between the evaluation substrate 4 and the insulating base 7 and thereby the evaluation substrate 4 is directly cooled may be used. Furthermore, a heater may be provided in the cooling plate 9, and the cooling plate 9 may be used as a heat source instead of a heat sink.

  The chamber 1 is preferably one that can be vacuumed by a vacuum pump 6 and can maintain a vacuum of several Torr or less, specifically the same level as various plasma processing furnaces. Further, the type of the infrared heater 5 used in the present invention is not particularly limited. There are a great many types of infrared heaters 5. Generally, a metal heating wire, graphite, conductive ceramics, etc. are heated, and this heat is transmitted to an infrared irradiation body (usually ceramics or carbon) from the irradiation body. However, it is preferable that the shape and structure be such that the entire surface of the substrate can be heated almost uniformly.

  Furthermore, it is also a particularly preferable reason that silicon carbide is composed only of Si and C. This is because a very clean process is required in the manufacturing process of the semiconductor device, and it is necessary to strictly prevent the contaminants from adhering to the electrostatic chuck. This is because silicon carbide consists only of Si and C, and Si is a constituent element itself of the silicon wafer. In addition, at the substrate temperature at the time of electrostatic chuck evaluation, there is no possibility that SiC of SiC is decomposed to cause contamination. That is, by using SiC as the material of the evaluation substrate, it can be said that there is almost no possibility that the silicon wafer is contaminated with other elements through the electrostatic chuck.

  Examples of Si-based ceramics that do not contain a metal element other than Si include oxides (SiO 2) and nitrides (Si 3 N 4) in addition to Si carbides. However, among these, SiC is particularly preferable. This is because SiC is cheaper and easier to obtain than other Si-based ceramics and is relatively easy to machine, and also has excellent thermal characteristics.

  The heat received from the plasma (or infrared heater) on the substrate is transferred to the electrostatic chuck through the silicon wafer (or evaluation substrate), and this heat conduction is governed by the thermal conductivity and specific heat of the substrate. Therefore, it is preferable that these thermal characteristics are substantially similar between the evaluation substrate and the silicon wafer.

  The thermal conductivity k of silicon is high, about 150 W / m · K. However, k of ordinary ceramics is remarkably low. For example, k of alumina or silicon nitride is about 20 to 30 W / m · K, and k of silica is even lower than these. Therefore, when these materials are used for the evaluation substrate, the heat from the upper part is not smoothly transferred to the electrostatic chuck side, and the temperature of the substrate may be different from that of the silicon wafer.

  On the other hand, k of silicon carbide is remarkably higher than k of ordinary ceramics, and its value is about 60 to 200 W / m · K, although it depends on the degree of crystallization of the material. Therefore, if SiC is used for the evaluation substrate, a heat conduction condition similar to that of a silicon wafer can be ensured. The specific heat of silicon wafer, silicon carbide, silica, silicon nitride, alumina, etc. is not so different and is usually about 0.6 to 0.9 J / g · K.

  Next, the work procedure in the evaluation apparatus of the present embodiment will be described. FIG. 2 is a flowchart showing this procedure. First, an electrostatic chuck (abbreviated as ESC) to be evaluated is set at a predetermined position in an airtight chamber and fixed by bolting or the like (S1). At the same time, the refrigerant inflow and outflow pipes are installed. Next, an evaluation substrate with a predetermined number of thermocouples attached in advance is set on the ESC mounting surface, a high potential is applied to the ESC electrode, and the evaluation substrate is adsorbed and fixed by electrostatic force. (S2). The thermocouple wiring can be taken out of the chamber through a terminal box provided on the inner wall surface of the hermetic chamber. In a state where the chamber is kept airtight, it is sucked and exhausted by a vacuum pump, and the inside of the chamber is set to a vacuum degree of about 0.1 Pa (S3).

  Next, the infrared heater is turned on (S4). The power of the infrared heater is set to a level that simulates heat input from plasma in the plasma processing furnace in advance by a blank test. At the same time, a predetermined flow rate of coolant is passed through the cooling plate to cool the ESC and the evaluation substrate. After heating the evaluation substrate for a predetermined time under these conditions, the temperature distribution of the substrate is measured with a thermocouple attached to the evaluation substrate (S5). Based on the temperature measurement data, not only the temperature adjustment function of the ESC but also the performance evaluation of the adsorption fixing function can be performed.

  That is, the heat transfer between the ESC mounting surface and the evaluation substrate is strongly dependent on the adhesion between the two, so that if the ESC adsorption force is low, the substrate will be cooled insufficiently. Further, the uniformity of the temperature of the evaluation substrate is an important requirement, and if the ESC adsorption force is low and the entire substrate is not uniformly adsorbed, the substrate temperature is not uniform. Therefore, various information for ESC function evaluation can be obtained by measuring the substrate temperature. In addition to temperature measurement, ESC leakage current and the like may be measured simultaneously.

  After the measurement is completed, the infrared heater is turned off (S6), the airtight chamber is opened to the atmosphere, and the ESC is removed, thereby completing a series of measurement operations (S7, S8).

  Using five electrostatic chucks of the same type, the temperature of the evaluation substrate was measured by the evaluation apparatus of the present invention (evaluation apparatus as shown in FIG. 1) according to the procedure shown in FIG. As a comparison object, a thermocouple is attached to a silicon wafer for actual processing in the same manner as the evaluation substrate using the same five electrostatic chucks, and this ESC and the silicon wafer are connected to an actual plasma processing apparatus (plasma etching apparatus, hereinafter referred to as an actual apparatus). The temperature of the thermocouple of the silicon wafer was measured in the plasma generation state.

  FIG. 3 shows the results of temperature measurement. The “real machine” is the case where the temperature of the silicon wafer is measured with an actual plasma processing apparatus, and the “simulated evaluation apparatus” is the case where the temperature of the evaluation substrate is measured with the apparatus of the present invention. In all cases, the notch (wafer cutout) is 0 degree, the circle with a radius of 35 mm is divided into 90 degrees, and the average of the thermocouple temperatures at four locations (the intersection of the X axis, Y axis and the circle with a radius of 35 mm) Value. In an actual machine, the temperature fluctuates in the range of 40 to 46 ° C., and it seems that the temperature fluctuation between the electrostatic chucks is large. On the other hand, in the simulation evaluation apparatus, the temperature fluctuates in the range of 43 to 45 ° C., and the temperature fluctuation between the electrostatic chucks seems to be small. However, the tendency of fluctuations corresponds well between the actual machine and the simulation evaluation device.

In order to make this correspondence clearer, the average value of the temperature measurement values of the five electrostatic chucks was determined for each of the actual machine and the simulation evaluation apparatus, and the temperature difference from the average temperature was calculated as follows.
Temperature difference ΔT (actual machine) = actual machine temperature at each chuck T-average temperature (actual machine)
Temperature difference ΔT (simulation evaluation device) = simulation evaluation device temperature T at each chuck−average temperature (simulation evaluation device)

  In addition, a value three times ΔT of the simulation evaluation apparatus was calculated and compared with ΔT of the actual machine. A comparison of the values of the temperature difference ΔT is shown in FIG. As can be seen in the figure, 3 × ΔT (simulated evaluation device) corresponds very well to ΔT (actual device), and the device of the present invention simulates a measured value well corresponding to the temperature measurement value in the actual device. It was confirmed that it was obtained by an evaluation device. Therefore, it is considered that the evaluation of the electrostatic chuck function under the same thermal conditions as the actual machine can be performed by the simulation evaluation apparatus. If the heat input level from the infrared heater in the simulation evaluation apparatus is made higher, it is considered that a result closer to the temperature in the actual machine can be obtained.

It is a cross-sectional schematic diagram of the evaluation apparatus which is an Example of the evaluation apparatus of the electrostatic chuck of this invention. It is a flowchart which shows the example of the work procedure in the evaluation apparatus of the electrostatic chuck of this invention. It is a figure which shows the example of the measurement result of the substrate temperature in a present Example. It is the figure which displayed the data of FIG. 3 by temperature difference (DELTA) T with average temperature. It is the figure which showed the heating condition of the silicon wafer when the to-be-processed substrate (silicon wafer) is adsorbed and fixed by the electrostatic chuck, and this is irradiated with infrared rays by an infrared lamp. It is the figure which showed the silicon (Si) light transmittance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Airtight chamber 2 Electrostatic chuck 3 Board | substrate mounting surface 4 Evaluation board | substrate 5 Infrared heater 6 Vacuum pump 7 Insulation base | substrate 8 Electrode 9 Cooling board 10 DC power supply 11 Heat insulation pillar 12 Heat insulation board 13 AC power supply 14 Thermocouple 15 Thermometer

Claims (6)

An apparatus for evaluating a substrate mounting apparatus that imitates and evaluates heat input from a plasma, which is placed on a mounting surface and fixes and controls the temperature of a substrate to be processed that receives heat input from plasma in a plasma processing process. Because
An airtight chamber capable of depressurization in which the substrate mounting apparatus is installed;
A heat source disposed opposite to the mounting surface and irradiating infrared light;
Instead of the substrate to be processed, the substrate is placed on the mounting surface, absorbs the infrared light, and is formed entirely of a material having a thermal conductivity and specific heat similar to silicon, and has a plurality of temperatures on the surface or inside. An evaluation apparatus for a substrate mounting apparatus, comprising: an evaluation substrate having means for measuring the above. The apparatus for evaluating a substrate mounting apparatus according to claim 1, wherein the substrate mounting apparatus is an electrostatic chuck. The evaluation apparatus for a substrate mounting apparatus according to claim 1, wherein the evaluation substrate is made of silicon carbide. A substrate mounting device that fixes and controls the temperature of the substrate to be processed that receives heat input from the plasma in the plasma processing process placed on the mounting surface is installed in a depressurized airtight chamber to simulate the heat input from the plasma. An evaluation method for a substrate mounting apparatus to be evaluated,
An evaluation substrate having means for measuring the temperature of a plurality of locations on the surface or inside thereof, which is formed entirely of a material that absorbs infrared light and has a thermal conductivity and specific heat similar to silicon, on the substrate mounting device. Placed
The evaluation substrate is heated by a heat source that irradiates the placement surface with infrared light,
The measured value is corrected by a correspondence relationship between the temperature distribution of the measured value of the evaluation substrate obtained by the means for measuring the temperature and the temperature distribution in the actual plasma processing process prepared in advance,
A method for evaluating a substrate mounting apparatus, comprising: evaluating characteristics of the substrate mounting apparatus. 5. The substrate mounting apparatus evaluation method according to claim 4, wherein the substrate mounting apparatus is an electrostatic chuck. 6. The method for evaluating a substrate mounting apparatus according to claim 4, wherein a material of the evaluation substrate is silicon carbide.

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