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It's not essentially possible to reduce substrate intrinsic resistance but connection and via resistances.
Second, to reduce substarte noises (many type of noise I mean ) it's possible to use BNTAP that is inserted buried layers in substarte and to use BN rings around noisy circuits and also TRENCH layers to isolate the circuits. In fact all depends on your technolgy because some of them may not be available in your technolgy.
So, every specific problem has specific solution, so there is no universal solution here..