JP3244501B2 - Hydrogen plasma processing method - Google Patents

Description

The present invention relates to a method for processing a TFT or the like formed of a non-single-crystal semiconductor formed in advance on an insulating film such as an insulating transparent substrate.

[Conventional technology]

A non-single-crystal semiconductor thin film such as an amorphous silicon thin film or a polycrystalline silicon thin film has many dangling bonds. For example, in the case of a polycrystalline silicon thin film, defects such as dangling bonds existing at crystal grain boundaries become trap levels for carriers and function as barriers for carrier conduction. (JYWSet, J. Appl. Phys., 46, p5
247 (1975)). Therefore, in order to improve the performance of the polycrystalline silicon thin film transistor, it is necessary to reduce the defects. (J. Appl. Phys., 53 (2), p1193 (198
2)). As the method, a hydrogen plasma processing method is best known. And as a device to do that
2. Description of the Related Art Generally, a system for generating a plasma by applying a high frequency to a counter electrode arranged in parallel with a substrate, such as a PCVD apparatus.

[Problems to be solved by the invention]

However, in the conventional plasma treatment using hydrogen gas, TF
Failures due to plasma damage, such as a shift in the Vth (threshold voltage) of T and a failure in gate withstand voltage, occurred frequently, making practical use difficult.

Although the cause of this plasma damage is not yet clear, experiments by the present inventors have shown that the potential on the substrate surface is directly and indirectly affected. In the case of a normal PCVD apparatus, the substrate surface potential is uniquely determined by the processing conditions such as the high-frequency power applied to the counter electrode or the gas pressure and the structure of the apparatus.

Therefore, the present invention secures the effect of improving the TFT characteristics,
An object of the present invention is to provide a processing method which does not receive the above-mentioned plasma damage.

[Means for solving the problem]

According to the hydrogen plasma processing method of the present invention, an electrode for generating plasma in a vacuum vessel, a holder for holding an insulating material to be processed, and a high-frequency application for applying different high-frequency power to the electrode and the holder, respectively. When a high-frequency power is applied to the holder by the high-frequency application system using a hydrogen plasma processing apparatus having a system, a floating potential generated in the insulating workpiece is measured, and the measured floating potential is positive. It is characterized in that the increase / decrease of the high frequency power is controlled so as to make the value low or a slightly negative value.

〔Example〕

One embodiment of the hydrogen plasma processing method of the present invention is shown in FIG.

An electrode 2 for applying a high frequency to generate a plasma is placed in a vacuum vessel 1 via an insulator 3. In this embodiment, high-frequency discharge is used, but ECR may be used as a means for generating plasma. A substrate holder 5 on which an insulative material 4 is set facing the electrode 2 is placed via an insulator 6. Hydrogen gas is introduced into the vacuum vessel 1 from the gas nozzle 8 of the electrode 2 through the mass flow controller 7. Plasma is generated by applying high frequency power to the electrode 2. At this time, a potential, which is a floating potential, is induced on the surface of the insulating material 4. This value differs between when the substrate holder 5 is grounded and when it is not, but as described above, it is uniquely determined by the processing conditions or the device structure. This floating potential should theoretically show a negative value, but many devices showed a positive value as measured by the inventors. Although it depends on the processing conditions, it is considered that the area of the electrically floating substrate holder 5 is large and is different from an ideal plasma to be theoretically handled. It has been confirmed that the greater the positive value of the floating potential, the greater the plasma damage to the TFT characteristics. Therefore, plasma damage can be reduced by lowering the positive floating potential or setting it to a somewhat negative potential.
As such means, it is conceivable to connect a coil and a capacitor in series between the substrate holder 5 and the ground, for example, to change the capacitance of the capacitor. In the present embodiment, this is made possible by applying a high frequency to the substrate holder 5. The floating potential (more precisely, the surface potential of the insulated material) can be arbitrarily controlled from a positive potential to a negative potential by the applied high-frequency power.

FIG. 2 is a schematic diagram of a high-frequency application system. On the other hand, power is applied to the electrode 2 from one crystal resonator 11 via the phase controller 12 through the high frequency amplifier 13 and the matching circuit 14. Similarly, power is applied to the substrate holder 5 through the high-frequency amplifier 15 and the matching circuit 16.

First, high-frequency power is applied only to the electrode 2, and then the floating potential is measured while the substrate holder 5 is applied.
Also applies high frequency power. Then, the insulating material 4
Generates a negative self-bias. The negative self-bias increases toward the negative side as the high-frequency power increases. The surface potential of the insulative workpiece 4 becomes a floating potential + a self-bias, and can be arbitrarily controlled by high-frequency power applied to the substrate holder 5.

Using the hydrogen plasma processing method of the present invention, the surface potential of the insulating material 4 is positively low or slightly negative, and the TFT characteristics of the hydrogen plasma-treated insulating material 4 are good. The plasma damage was endless.

〔The invention's effect〕

As described above, according to the present invention, high performance of an insulated gate field effect transistor in which at least a part of a channel region of a TFT or the like is made of a non-single-crystal semiconductor can be realized without failure due to plasma damage. Further, the present invention can be widely applied to semiconductor processes in general, and the effect thereof is extremely large.

[Brief description of the drawings]

 FIG. 1 is a structural view of an apparatus according to an embodiment of the present invention. FIG. 2 is a high-frequency system diagram of the embodiment. DESCRIPTION OF SYMBOLS 1 ... Vacuum container 2 ... Electrode 3, 6 ... Insulator 4 ... Insulated workpiece 5 ... Substrate holder 7 ... Mass flow controller 8 ... Gas nozzle 11 ... Crystal oscillator 12 ... Phase controller 13,15 High frequency amplifier 14,16 Matching circuit

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-15219 (JP, A) JP-A-1-214123 (JP, A)

Claims (1)

(57) [Claims] 1. Hydrogen having an electrode for generating plasma in a vacuum vessel, a holder for holding an insulating material to be processed, and a high-frequency application system for applying different high-frequency powers to the electrode and the holder, respectively. Using a plasma processing apparatus, when applying high-frequency power to the holder by the high-frequency application system, measure the floating potential generated in the insulating material to be processed, the measured floating potential is low at a positive value, Alternatively, an increase or decrease in the high-frequency power is controlled so as to have a slightly negative value.