2. Factors affecting ITO square resistance
R □ = ρ / D (1) from formula (1), it can be seen that in order to obtain ITO films with different surface resistance (R □), it is actually to obtain different film thickness and resistivity. Generally speaking, it is easy to get different film thickness when preparing ITO thin films. The thickness of the required film can be obtained by adjusting the deposition rate and deposition time, and the thickness and uniformity of the film can be accurately controlled by corresponding process methods and means.
The resistivity (ρ) of ITO film is the key to the preparation of ITO film, and it is also an important index to measure the properties of ITO film. In formula (2), N and τ represent carrier concentration and carrier mobility respectively. When n and τ are larger, the resistivity (ρ) of the film is smaller, and vice versa. The carrier concentration (n) is related to the composition of ITO film, that is, the tin content and oxygen content of ITO film itself. In order to get a higher carrier concentration (n), the tin content and oxygen content of ITO deposition material can be adjusted; while the carrier mobility (τ) is related to the crystal state, crystal structure and defect density of ITO film, in order to get a higher carrier concentration (n) Higher carrier mobility (τ) can reasonably adjust the deposition temperature, sputtering voltage and film forming conditions.
In the production process, the raw material properties and process control of each process may affect the ITO resistance value due to the following factors:
a. The film thickness uniformity and adhesion of photoresist coating will affect the blocking performance of the adhesive, resulting in the adhesive being soaked, over developed, side etched and over etched, making the pattern irregular and the resistance larger. Therefore, the substrate should be cleaned, the photoresist with good barrier and adhesion should be selected, and the film thickness (about 1.5 μ m) and uniformity should be strictly controlled.
b. The selection of appropriate exposure method and exposure amount is the premise of forming high-quality graphics. The improper selection of developer and etching solution and their temperature, concentration and time will also cause graphics distortion and can not get the resistance value required by the design. According to the properties of the positive adhesive, the proper pre curing, the temperature and time of the solid film should be selected, which has a great influence on the figure and resistance.
C. influence of other process: if high temperature baking and cleaning of various lye are used in the production process, generally staying at 300 ℃ for more than 30 minutes will make R □ grow 2-3 times, which is the biggest factor affecting R (.  However, ITO is prone to aging and corrosion in alkaline environment. If the cleaning time is too long and the cleaning is not clean, R □ will increase. Therefore, high temperature production and repeated cleaning with alkaline solution are not suitable in the production process.
2、 The relationship between choosing suitable power supply and coating quality
Smart choice of coating power supply can help achieve specific goals in terms of sputtering rate, film quality and setting cost and complexity. Each power solution has its own specific advantages and disadvantages. Therefore, there is no absolutely correct answer. The selection must be based on the recommendations provided in this article and the individual's process priorities.
Power selection overview

Table 1 lists the main factors to be considered in the selection of power supply, rating each power supply solution. Find the most important factors for the process in the leftmost column, and then select the power scheme with the highest rating for these parameters. Further refer to this table for information on the performance performance of the selected power scheme's important requirements. Then, read on to learn more about what needs to be considered before making the final decision.
Table 1. Power selection matrix

Process setting details

This part solves the common problems in the setup of sputtering process. It solves the problems that are not solved in the above reference table, and also provides suggestions on power settings.
Choose RF power supply to achieve the highest film quality
If film quality is the only factor to be considered, RF power supply is the best choice for process power supply. RF energy can make the electrons in the plasma become very active. This creates a "thump effect" in which electrons can hit the substrate with more energy. This makes them compact, producing even and flat films with few holes.
The main disadvantage of RF power supply is its very low speed. Its sputtering rate is only 20%, while that of all other power schemes is 70% or higher, reaching 100%. However, for some important applications, such as antenna arrays and solar panels used in outer space, this low speed is also acceptable. It depends on what you think is most important.

RF settings

For processes using relatively small cathodes (1 to 1.5m, 3.3 to 4.9 '), network matching deployment is the key to setting up RF correctly. To maximize the power delivered by the load, place the matching network as close to the cathode as possible. This shortens the length of the output cable from the matching network, which is also part of the load. Therefore, the shorter cable can improve the power transmission and process repeatability.
Grounding is another important factor in RF setting of small cathode. The ground strap must be short and wide to maximize the surface area, and all connections must be very clean to avoid resistance.
Unfortunately, there is no simple way to use a larger cathode process using wavelength mode. Compared with the process of small cathode RF, it is more complex to set them up, and more tests are needed, so the probability of error is very high.
The rotating cathode is not compatible with the RF power supply. Generally speaking, they are most suitable for AC, DC or pulse DC power supply processes, in which they can increase target utilization by 80% to 90%.
Select AC and pulse DC power supply

The choice of AC power or pulse DC power depends on the number of cathodes in the system. For any off-line batch system, pulse DC power supply should be a better choice. For a new on-line system with more than one cathode, AC is better than pulse DC. With a small amount of money, the process can be cleaner and more durable, and the film quality is better.
1. The film quality produced by ordinary DC power supply (above figure) is relative to that produced by AC power supply (below figure)
Select DC and pulse DC

It is usually better to choose the pulse DC power supply than the DC power supply, because the film quality produced by the pulse DC power supply is better and the normal production period is longer. Many systems use DC power because they are installed without a pulse technology power supply.
In addition, the low frequency pulse can make the electron more active and produce the "thumping effect". In this way, the flatness, aggregation density and transmission of the film can be improved, and the generation of holes can be reduced. The process using pulse DC power also needs shorter time and less frequent cleaning steps than that of common DC power. This can greatly improve the production efficiency of the process and the output of finished products.

1. Film quality produced by ordinary DC power supply (above figure) vs. film quality produced by pulse DC power supply (below figure)
Source: University of Salford, Centre for advanced materials and surface engineering
Cost is not an important decisive factor in choosing normal DC or pulse DC power supply. Compared with ordinary DC, pulse DC can use much cheaper target. Generally speaking, the quality of the films produced by AC and pulse DC is better than that by DC. It can also save a lot of cost by using lower target materials in the process of AC or pulse DC. Any kind of DC sputtering process will produce "bumps", which will protrude and pierce the adjacent material layer. Therefore, the high-grade aluminum target must be used in the process of DC power supply, while the target with acceptable price can be used in the AC and pulse DC processes, and there is no negative impact on the quality of the film.
The pulsed DC power supply reduces the possibility of nodulation and helps to maintain the target quality for a long time, so that the target can be better utilized. The process power supply method can reduce the formation of electrolyte and arc discharge by periodically reversing polarity to discharge the target surface. With the increase of frequency, the discharge frequency of electrolyte surface also increased, which reduced the possibility of nodulation. This can not only prolong the target life, but also reduce the damage to the substrate.
Figure 3 in a typical magnetic control process using a planar target, a small explosion in the low splash rate area of the target surface will release particles, so you have to replace the target before it is fully utilized.

High efficiency arc management and low energy storage can reduce the damage when the power supply to the arc is limited to cause the nodule explosion. These features allow the operation of an old target that may contain nodules, while reducing the arc energy to a level that maintains film quality. Without these features, when nodulation increases, the process must be stopped, and the target discarded and replaced, even if only a part of the target may be utilized. This requires the use of new targets, thus increasing costs, even if the old targets may only be used in part. It also reduces production by requiring the system to shut down completely
Select RF DC and RF pulse DC power supply
  Report errors

Generally speaking, it is better to choose RF pulse DC power supply than ordinary RF DC power supply. The differences in film quality, production rate and cost can be applied in the same way as the description of DC and pulse DC power supply.
Set the process of RF DC power supply or RF pulse DC power supply

The combination of RF and DC or RF and pulse DC will add some complexity and cost to the process setting. When these two different types of power supply operate at the same time, especially in the arc control will bring challenges.
In these configurations, DC or pulse DC power supply can detect and respond to arc more accurately than RF power supply. Therefore, the DC power supply must be able to control the RF device and turn off the DC and RF power supply in case of arc. It must also be able to restore power supply quickly after the arc disappears. The DC power supply in today's market is quite different in this respect. Some do not provide built-in DC / RF control methods, while others provide strong control.
The choice of power supply is not only an art, but also a science.  Many factors, including target material, process chemistry and cathode design, must be considered in determining the ideal power supply for application. It must also meet the special performance standards set for sputtering rate and film characteristics.
For some processes and / or materials, the selection is very limited, so the selection of power supply is relatively simple.  However, for materials such as tin dioxide and silicon dioxide, there are many choices of process power supply. In the case of silica, options include pulsed DC, AC and RF. How to choose among them depends on the first consideration. Generally speaking, pulse direct current can make the deposition rate of silica the fastest, but compared with other power methods, it may also lead to process instability. It will also face the problem of anode disappearance. If we choose to use alternating current to deposit silica, the sputtering rate may be slightly lower, but the problem of anode disappearance can be avoided. Finally, RF not only does not cause the anode to disappear, but also produces the highest quality film of all options. The main disadvantage of RF is the lowest sputtering rate. However, if film quality is important for applications, RF may still be the best choice.
As mentioned before, special requirements for sputtering rate, film characteristics and other factors must be considered when selecting power supply. In addition, cathode design, (rotatable / planar, single / dual), process chemistry and target materials should be considered. Generally speaking, with the decrease of target conductivity, the frequency of recommended process power supply type should be higher. That is to say, the process of using the target with strong insulation often needs RF and other high-frequency power supply to complete smoothly, while the target with strong conductivity usually needs DC and pulse DC. Please note that in some reactive applications, even if the target you are using can conduct electricity, the resulting film may be electrically insulated, so that the anode may be covered by the insulating material. In this case, if it is very important to avoid anode disappearance for successful production, the double cathode process with AC power supply will be the best choice.
3、 Power quality assessment

Test 1

Operate your power supply at full rated output. Shut off the gas supply suddenly. This is to imitate the reality that someone fails to replenish or replace the gas bottle. What happens to the power supply? Does it continue to operate normally, or does it just switch to high voltage, open circuit, or fails (the failure may involve smoke, fire or other obvious fault indications)?
If your power supply is still fully functional, continue with the following tests.
Test 2

Supply gas again. Even if you pass test 1, is your power supply broken now, or is it back to normal operation?
If your power supply is still fully functional, continue with the following tests.
Test 3

After test 1 and test 2, run your power supply in all metal mode (high voltage, low current).
If your power supply is still fully functional, continue with the following tests.
Test 4

Slowly reduce the air pressure to the middle of 4 Torr. Your power supply should be able to withstand insufficient gas.
If your power supply is still fully functional, continue with the following tests.
Test 5

In order to test your power supply's fast processing ability and the ability of large impedance value change (see the following lag curve), please run the power supply in argon charging and all metal mode (high voltage and low current), then quickly switch to argon charging, full rated power and full reaction mode, and finally to argon charging and full rated power.
Hysteresis curve
If your power supply is still fully functional, continue with the following tests.

Test 6

If your power supply passes 1-5 tests, observe it under severe arc discharge conditions. Can the power supply detect and conduct arc suppression before the arc damages the film quality?
conclusion

If you can't pass all the tests, the quality of the power supply is not enough to ensure your process output and investment capital. In addition, if necessary, advanced protective circuits can shut down the device to prevent damage to the power supply.
4、 Splash rate (rate, efficiency)
1. Factors determining the sputtering rate
The splash rate depends on each different configuration - the configuration can be dynamic. The following factors determine the sputtering rate:
Geometry and cathode / anode design of sputtering chamber
Operating air pressure
Gas mixing
Target thickness
Magnetic field intensity
Running power
Distance from target to substrate
It is possible to see a splash rate of 2 to 10 μ / s. In order to optimize the sputtering system, we must balance the cost, the sputtering rate and the film quality. The key is to really understand the sputtering chamber and the sputtering process. The initial rate of operation should be longer than the actual process to understand the characteristics of the sputtering chamber and process. To understand what will happen in the actual process, we can try these initial rates under the condition of low power, and slowly adjust the power, as a system evaluation method.
2. Optimization of sputtering rate
The general rule is that the lower the pressure, the higher the sputtering rate and the film quality, because in this case, the molecular collision in the plasma area is less, and the plasma projection distance (the ability of splashed particles to reach the substrate from the target) is longer. Therefore, try to splash at low pressure as much as possible. Of course, avoid falling into gas shortage, which will cause problems in your power supply.
The second thing you can do is use a magnetometer to check the balance of the magnetron. Unbalanced magnetron will increase the distance of plasma projection and produce extra electrons, which will affect the substrate temperature and film quality. The balanced magnetron can concentrate the projection distance, which will help to improve the sputtering rate, especially when the distance between cathode and substrate is large.
Unbalanced magnetron (above) vs. balanced magnetron (below)
Third, check the strength of the magnet. With the increase of magnetic force, the distance of plasma projection increases. One thing to note is that although this can lead to higher sputtering rate and film accumulation density, a stronger magnetic force will deepen the depth of the target groove, which will reduce the utilization rate. In the typical magnetron sputtering process using planar targets, the sputtering focuses on the "racetrack", that is, the target surface area with the strongest tangent magnetic field. (Figures 1 and 2)

Figure 1 plane target showing runway erosion pattern
The sputtering rate outside the runway is much lower and oxides may form (Figure 3). In the sputtering process of ITO and other ceramic targets, oxides can be easily formed because the target materials contain oxygen and are usually introduced into the cavity. In metal splashing, the existence of oxygen can be attributed to the leakage of cavity or water vapor caused by degassing of substrate and carrier. The area where oxides form is often referred to as "nodulation.". These oxide areas are insulated and allow charge accumulation. Because the film is very thin, the electric field is very strong even at low voltage. Once the electric field is strong enough, the target surface will break down (ARC).  These arc generated particles can damage the substrate. In serious cases, when the arc is not eliminated, or the arc continues to burn due to lack of power or lack of power, the target material will also be damaged.
All of these show that the sputtering rate is a complex and multifaceted problem.