JPS627263B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a metal nitride thin film with low internal stress and low specific resistance.

In general, nitrides of high-melting point metals such as titanium, molybdenum, and tantalum have extremely high melting points and high mechanical hardness, and are thermally and chemically stable, providing mechanical and thermal protection for various devices and parts. It is used as a film, and has recently been put into practical use as a highly heat-resistant electrode material for semiconductor integrated circuits.

When using a metal nitride thin film as an electrode material for a semiconductor integrated circuit, the first condition is that the specific resistance is low.

Generally, it is known that nitrides such as titanium and zirconium have a lower resistivity than the original metal element when compared in bulk. However, thin films used as electrode materials with a thickness of several hundred to several thousand angstroms generally tend to have a high specific resistance due to various scattering mechanisms, and reducing this resistance is an important technique.

For example, when a titanium nitride thin film is obtained by reactive sputtering in a nitrogen/argon mixed gas, when the nitrogen partial pressure and the nitrogen/argon mixed gas pressure are increased, the elemental composition of the titanium nitride thin film is affected by impurities in the film, resulting in specific resistance. increases, so it is usually set to the lowest pressure that can sustain a discharge. Also,
It is effective to apply a negative DC bias voltage to the substrate in order to further lower the resistivity.

FIG. 1 shows a schematic diagram of a sputtering apparatus in which a negative bias voltage is applied to a substrate. In the figure, 1 is a vacuum chamber, 2 is an exhaust system, 3 is a metal target such as titanium, molybdenum, tantalum, etc.
4 is a shield plate, 5 is a high frequency power supply circuit, 6 is a substrate, 7 is a bias power supply, 8 is a gas inlet, and 9 is a flow rate control valve. FIGS. 2 and 3 are graphs showing the effect of substrate bias on the specific resistance of a titanium nitride thin film and the internal stress generated within the film, respectively. ρ indicates specific resistance, and σ indicates internal stress (shown as a solid line). This data is based on nitrogen partial pressure
2.8mTorr, nitrogen/argon mixed gas pressure 16.8m
This is the case with Torr and high frequency power of 400W.

In this way, applying a substrate bias is extremely effective in reducing the resistivity ρ of a titanium nitride thin film, but on the other hand, it generates significant internal stress σ in the film, so it is difficult to apply a wafer bias when manufacturing semiconductor integrated circuits. The warping of the film makes it difficult to form fine patterns, and when the film is thick, it causes serious problems such as cracking and peeling.

One way to solve this problem is to set the bias voltage in the transition region shown in Figure 2, that is, the point where the specific resistance and internal stress suddenly change, to obtain a film with intermediate specific resistance and internal stress. However, the range of bias voltage that determines the transition region is extremely narrow.
It was extremely difficult to obtain reproducibility.

In order to solve the above problems, the present invention applies a bias voltage in which a zero bias voltage state and a negative bias voltage state are alternately repeated as a substrate bias, thereby reducing the internal stress and specific resistance of a metal nitride thin film. The purpose is to reduce the amount of water to a level that poses no practical problems.

To achieve the above object, the present invention provides a method for producing a metal nitride thin film having conductivity by a reactive sputtering method, in which a metal nitride is deposited to a thickness of several angstroms within a time. Invention of a method for manufacturing a metal nitride thin film, characterized in that the metal nitride thin film is deposited by applying a substrate bias in which the voltage is alternately in a zero state and a negative state over time to a substrate on which the thin film is to be deposited. This is the gist of the report.

Next, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements can be made without departing from the spirit of the present invention.

The apparatus used to carry out the present invention is shown in FIG. 1, and the procedure is to first exhaust the chamber 1, then
Nitrogen is introduced by adjusting a flow rate control valve 9 provided at the gas inlet 8 until a predetermined partial pressure is reached. Subsequently, argon is introduced until the total pressure reaches a predetermined pressure, and then discharge is started to deposit a metal nitride thin film. A voltage having a waveform in which the bias voltage alternates between a zero state and a negative state is applied to the substrate bias power supply 7. FIG. 4 shows an example of the bias voltage waveform, which is a rectangular wave with a duty of 1/2. The voltage magnitude -V is, for example, -50V, and the period T is, for example, 100 _nS . FIG. 5 shows another example of the bias voltage waveform, which is a pulsating bias voltage waveform that can be easily obtained by half-wave rectifying the commercial power supply. The magnitude of the voltage -V is given by V=√2V _rnS , where V _rnS is the effective value of the AC voltage before rectification. The period T is 20 _nS when the commercial frequency is 50 Hz.

As an example, a titanium nitride thin film with a nitrogen partial pressure of 2.8 m
Torr, nitrogen/argon mixed gas pressure 16.8m
Torr, high-frequency power of 400 W, and negative pulsating bias voltage obtained by half-wave rectification of AC voltage with effective values of 30 V, 40 V, and 50 V as substrate bias voltage. Internal stresses are shown in dashed lines in FIGS. 2 and 3. However, the horizontal axis represents the effective value of the bias voltage. From the data shown by the broken lines in Figures 2 and 3, it is clear that the rapid change in resistivity observed when DC bias voltage is applied is alleviated, and the region where internal stress begins to occur is It can be seen that it is possible to easily obtain a film in which the internal stress is small and the specific resistance is so low that it does not pose a practical problem.

As mentioned above, when considering the mechanism of growth of titanium nitride thin film when applying a bias voltage that alternates between zero and negative values, we find that the specific resistance obtained when the substrate bias is zero is large, but the internal By growing a film with low stress and a film with high internal stress but low resistivity obtained when the substrate bias is a negative value, an intermediate film between the two is formed. As a result, it can be considered as a film that combines the advantages of both.

The period of the AC bias applied in the present invention is short considering that the film deposition rate in this type of sputtering method is several tens of angstroms per second, and the period of the alternating current bias applied is short, considering that the film deposition rate in this type of sputtering method is several tens of angstroms per second. It is a cycle. In this type of sputtering method, a film with a thickness of several angstroms is not deposited on the substrate as a clean monolayer, but is mixed with the sputtered layer under the bias conditions of the next half cycle. , a uniform film will be deposited. This uniform film is shown in Figures 2 and 3.
This is thought to cause the characteristics shown by the broken line in the figure.

As explained above, according to the present invention, internal stress is small and specific resistance is reduced by applying a waveform bias voltage in which the voltage is alternately zero and negative as the substrate bias voltage in reactive sputtering. A metal nitride thin film with a small amount of nitride can be easily obtained, and if this thin film is used as a part of the electrode of a semiconductor integrated circuit, for example as a diffusion barrier layer, a semiconductor integrated circuit with excellent heat resistance and reliability can be produced at a high yield. , which has effects that can be realized economically.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the sputtering apparatus, and Figures 2 and 3 show the substrate DC bias effect (solid line) and the substrate DC bias effect (solid line) and the internal stress of the titanium nitride thin film formed by high-frequency reactive sputtering. A graph showing the effect (dashed line) of applying a bias voltage with a waveform in which the voltage alternately repeats zero and negative values as a bias, and FIGS. 4 and 5 show the bias voltage waveform that is a feature of the present invention. An example is shown for rectangular and pulsating bias voltages, respectively. 1... Vacuum chamber, 2... Exhaust system, 3... Metal target, 4... Shrink plate, 5... High frequency power supply circuit, 6... Substrate, 7... Bias power supply, 8
...Gas inlet, 9...Flow control valve.

Claims (1)

[Claims] 1 In a metal nitride thin film manufacturing method in which a conductive metal nitride thin film is formed by a reactive sputtering method, the voltage is zero and negative within the time it takes for the metal nitride to be deposited to a thickness of several angstroms. A method for producing a metal nitride thin film, characterized in that the metal nitride thin film is deposited by applying a substrate bias having alternating conditions to a substrate on which the thin film is deposited.