Hello @QuocHuyUT
After programming flash, the IDE will by default reset the device - which causes the ROM bootrom code to run and call into a"valid image" in flash at 0x0. Thus if you have no valid image in flash at 0x0 this is not going to work.
One allow you to debug your application at 0x6000 via a LinkServer / CMSIS-DAP debug connection (assuming you have your boot loader or a "dummy application" at address 0x0) would probably be to change the way that the IDE resets the target after programming flash. To do this, edit the launch configuration (by double clicking on the .launch file that will have been created in your project) and change the "reset handling" option to "SOFT".
BR
Alice
