Note that with devices like that which are reliant on the negative bias, the -5V supply should be the first thing to switch on and the last thing to switch off, if they are being separately controlled. Without the negative supply the chip may draw excess current.
Also be sure all pins other than power are either floating, have pullups to the chip 5V pin or are grounded (as appropriate), until all power rails are correct and stable. Applying a higher voltage to a pin than whatever power supply voltage is present at any instant can damage or destroy the device.
For your testing sequence - the data sheet says the DRAM may not operate correctly until at least eight full refresh cycles have been completed.
Also be sure all pins other than power are either floating, have pullups to the chip 5V pin or are grounded (as appropriate), until all power rails are correct and stable. Applying a higher voltage to a pin than whatever power supply voltage is present at any instant can damage or destroy the device.
For your testing sequence - the data sheet says the DRAM may not operate correctly until at least eight full refresh cycles have been completed.