In the field of semiconductor manufacture, widespread use is made of a plasma processing apparatus that performs etching and film-forming by applying a plasma to a target substrate such as a silicon wafer or the like (which will be referred to as a “substrate” hereinafter). Such plasma processing is carried out under a depressurized pressure, which makes it impossible to use a vacuum chuck in holding the substrate in place. Thus, substrate mounting devices such as a mechanical clamp and an electrostatic chuck using an electrostatic force are put into general use.
The electrostatic chuck includes a substrate mounting surface formed of an insulating body having a sheet electrode embedded therein. A high potential is applied to the sheet electrode so that a Coulomb force or a Johnsen-Rahbek force can be generated by the static electricity distributed in the dielectric body and the polarized and electrified charges of the substrate. This force is used for the electrostatic chuck to fix the substrate to the substrate mounting surface.
Although the basic function of the electrostatic chuck is to attract and hold the substrate, it is recently the general case that the electrostatic chuck is used for the purpose of controlling a silicon wafer temperature in a wafer machining process, e.g., for the purpose of cooling a silicon wafer with the stream of an inert gas such as helium or the like flowing between the silicon wafer and the electrostatic chuck or for the purpose of heating the silicon wafer through the combined use with a heater. This is because a film-forming temperature has an extremely close relationship with a film-forming speed, a film-forming quality and the like.
For this reason, in addition to mechanical properties, particle reduction, purity improvement, a plasma resistance and a chemical resistance, the silicon wafer temperature control function and the temperature distribution uniformity when the silicon wafer is subjected to film-forming and etching become the evaluation items of paramount importance in evaluating the electrostatic chuck.
In general, the temperature control function depends on the heat applied to a substrate and a mounting table from the outside. The characteristics involved in a attracting and holding function, such as an adsorptive force, a leak current and attachment-detachment responsiveness, have an influence on the temperature of a target substrate.
Therefore, the performance evaluation of an electrostatic chuck used in a plasma processing apparatus needs to be conducted under a condition that takes into account the heat inflow from plasma to a substrate and a mounting table. If a wrong heat inflow condition is used in the performance evaluation, the results of evaluation will differ greatly from the evaluation results obtained under an actual condition to be applied.
If the plasma processing apparatus is used to measure the characteristics of the electrostatic chuck under the same condition as that of an actual etching process or other actual processes, it would be possible to correctly evaluate the performance of the electrostatic chuck. However, use of the plasma processing apparatus only for the evaluation purpose costs much because the plasma processing apparatus is expensive and complex-to-operate. Another problem lies in that the time and effort required in the evaluation becomes too great.
In view of these circumstances, JP2006-86301A discloses an electrostatic chuck evaluating apparatus and method in which an electrostatic chuck is evaluated by installing the electrostatic chuck within a vacuum-evacuatable sealed chamber, heating a substrate with a lamp heater arranged above the electrostatic chuck and simulating a thermal condition available within a plasma processing apparatus.
As disclosed in JP2006-86301A, the electrostatic chuck evaluating method performed by an evaluation apparatus that simulates heat inflow from a plasma using a lamp heater (halogen lamp) as an external heat source is preferable in that the method makes it possible to evaluate the performance of an electrostatic chuck in a quite easy manner.
However, an investigation conducted by the present inventors reveals that the electrostatic chuck evaluating method disclosed in JP2006-86301A encounters a difficulty in simulating the heat inflow from a plasma.
The reason is that there is a difference in the heat transfer mechanism between the heat transfer from a plasma and the heat transfer from a conventional heating lamp or heater. In general, it is thought that the heat transfer from high temperature plasma is predominantly the contact heat transfer of molecules turned to a plasma.
In contrast, the heat transfer from a heating lamp occurs in such a way that infrared rays irradiated from a heating lamp is resonantly absorbed in a substrate, the energy of which imparts motion (vibration) to molecules so that the vibrating molecules can be rubbed with each other to generate heat.
In this regard, the infrared rays irradiated from the heating lamp mainly includes near infrared rays (with a wavelength from about 0.78 μm to 2 μm) and infrared rays (with a wavelength from about 2 μm to 4 μm). Referring to FIG. 6, a silicon wafer as a target substrate allows most of the infrared rays (infrared light) belonging to a wavelength region from about 1 μm to 5 μm to pass therethrough. For this reason, even if an attempt is made to heat the silicon wafer as a target substrate with an infrared lamp, the silicon wafer is scarcely heated and, instead, the infrared light penetrates the silicon wafer to heat only a surface (mounting surface) of an electrostatic chuck lying below the silicon wafer.
FIGS. 5A and 5B show a silicon wafer heating situation in the event that a silicon wafer (target substrate) is suction-fixed to an electrostatic chuck and then infrared rays are irradiated on the silicon wafer by an infrared lamp. When microscopically viewed, both the electrostatic chuck and the silicon wafer have irregularities on their surfaces. Therefore, as illustrated in FIG. 5A, close contact sites and spaced-apart sites exist in the contact surfaces of the electrostatic chuck and the silicon wafer.
Under this state, the light (infrared light) irradiated from the infrared lamp almost penetrates the silicon wafer as set forth earlier. Thus, as shown in FIG. 5B, the surface of the electrostatic chuck is heated in the spaced-apart sites but the contact surfaces are heated in the close contact sites. As a result, there occurs a situation that the heat of the electrostatic chuck (the heat of the substrate mounted in place) is sufficiently transferred in the close contact sites but no sufficient heat transfer occurs in the spaced-apart sites.
On the other hand, contact heat transfer is predominant in an actual process using a plasma. According to the contact heat transfer, the molecules turned to high temperature plasma make contact with a silicon wafer to generate heat. This means that the silicon wafer is uniformly heated over the entire surface thereof.
Thus, the thermal state of the electrostatic chuck and the silicon wafer in case of using an evaluation apparatus that performs simulation with the infrared light is thought to greatly differ from the thermal state in an actual plasma processing apparatus.
For the above-noted purpose, it is usually most preferable to use an infrared heater, which is inexpensive and exhibits an improved heating efficiency. However, in order for an evaluation apparatus using the infrared heater to simulate the thermal state of a plasma processing apparatus, the evaluation apparatus needs to be designed to ensure that the thermal state within the apparatus corresponds to the thermal state of an actual plasma processing apparatus.