I know that CMOS sensors appeared in the beginning of 90s, and evolved up to 2000s. I'm mainly talking about high ISO photos quality. For example, Canon 5D mark 3 has better results in high ISO tests than Canon 5D mark 1, and both of them has the same FF CMOS sensors.
Have CMOS sensors changed at all since 2000s? Do sensors continue to evolve nowadays? Why new DSLR cameras with the same sensor have better results than old one?
The Canon 5D Mk 3 and Mk 1 does not have the same sensor. They both have sensor based on a CMOS production technique, but that does not mean the sensors are identical.
CMOS is also the same technique used to produce the electronic chips in your computer and mobile phone, and we know those have changed (improved) since 2000. Some of these improvements have also affected sensors used in cameras, but can not explain all the improvement.
There are other improvements with CMOS sensors that have resulted in higher dynamic range, much better ISO performance, new focusing techniques (Canon's dual pixel system) and a whole lot of smaller changes.
Saying all CMOS sensors is the same is like saying all Intel CPUs are the same. Modern instances of CMOS sensors have lower noise and higher resolution than previous generations. The sensors are fairly regularly (every year or two) being changed in the newer models of cameras. The basic technique for sampling light may stay the same, but the actual sensors have improved greatly and are not the same as they were 10, or even 2 years ago.
CMOS sensors have greatly improved over the last 13 years. Backside illumination (more used on small sensors), gapless photo sites with micro lenses capture more photons, smaller and more improved electronics, and even the algorithms used on the data read by the sensors have all added to the big increase in the quality of CMOS sensor technology.
There have been some advancements in CMOS sensors.
Reductions in process size mean that the electrical components required for every pixel can be made smaller, allowing more light to hit the light sensitive area of the pixel. Lately this has been an improvement of diminishing returns.
Back side illumination allows for greater light sensitivity, particularly for very small pixels such as those found in a compact camera or cellphone.
The name may be slightly confusing - basically all it means is that the electrical components are located on the rear of the sensor rather than the front, allowing more light to hit the sensor. As you might imagine though, it is not as easy to produce.
Various improvements in CMOS production make production cheaper and faster, though without necessarily improving image quality.
There are other improvements in camera imaging that are unrelated to the sensor but that make up for deficiencies in the sensor such as improved demosaicing and noise reduction algorithms. Other improvements may include the ability to read more pixels, or to read pixels at a greater rate, which only indirectly affect the sensor as it allows for sensors with greater pixel counts to be used.
