Android : Background process in Async Task

The problem in async task when i open my Application i want to copy my all data from internal card to external mmc. the files & folder copy task is running properly but i want it to run in background which may not stuck the screen. but when i open app it runs and copy data but the screen gets stuck. Please help me out in this.

i coded following function under async task.

public class BackGroundProcess extends AsyncTask<String, String, String>  // inner class to perform all background process i.e. invisible
 {

        public BackGroundProcess() {
            doInBackground(intPath,extPath);
            // TODO Auto-generated constructor stub
        }
    @Override
    public String doInBackground(String... params) {
        // TODO Auto-generated method stub
        CommonMethods.copyRecursive(intPath, extPath);
        return null;
    }

and on onCreate() method i am creating the object of class like :-

BackGroundProcess bg = new BackGroundProcess();

but the screen stucks while it copies the data.

Please help me out in this how to get rid of this i want it to run in the back ground with no screen stuck. one more question: using threads is a good idea? if yes kindly guide me thru coz i am new to android.

thanx in advance.