... or your gate resistor could be too low. If you are going to put a resistor in series make sure it is no more than 10 Ohms. You want good gate drive, but sometimes the 10 Ohms will dampen any such oscillations
It's true that having a larger Rg can dampen transients by slowing the switching action, but this that's not the proper way to deal with the transients, since the slower switching degrades efficiency. The primary function of a gate resistor should be to dampen ringing on the gate (caused by stray inductance on the gate driver current loop), not to dampen ringing on Vds. That should be dealt with by using proper layout techniques, and snubber networks.
Unless he has a large amount of stray inductance on his gate leads, I doubt, 5/10 ohms is not enough to dampen it.
I am using 10 ohms for turn on and 5 ohms(one is bypassed by diode) for turn off.
Okay, let's do some calculations. The Cgd of your FET is given as 490pF in the datasheet. From your waveforms, it looks like you have a Vds of 100V and a fall time around 100ns. So you have current flowing into your gate resistor equal to i=490pF * 100V/100ns, or 0.49A. That will induce 4.9V across your 10 ohm gate resistor. Also there will be a bit more than that, due to resistance in the gate driver IC and the FET itself, along with stray inductance. So during "turn on" you're losing 5V on your gate drive voltage, which may be enough to cause parasitic turn off. And a similar thing will happen on the upper FET in the leg possibly leading to parasitic turn-on at the same time. The two can work together to create nasty oscillations.
I would try decreasing the gate resistors, by half. If your gate driver circuit layout is good, you shouldn't need more than an ohm or two anyways to damped out ringing on the gate.
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yeah, dick_freebird,..I am also doubting whether its due to probe ..Ground loop is unlikely as i have made ground trace as wide as possible..
The importance of proper ground referencing can't be overstated enough. Just a few tens of nanohenries in the switching path can cause gross waveforms to appear. You should put the ground clip directly on the source terminal of the FET, and the probe tip directly on the gate terminal. Make sure to be cautious when using non isolated probes. Is your inverter isolated?