My dog dosent want to stay outside for long.?

Everytime I put my dog outside and im not out there with her she doesnt want to stay, shes been an inside dog since she was a puppy, shes three now. I want to get her used to being in the backyard whenever im not home but she scratches the door like crazy, is there any way I can get her to get used to staying outdoors? or do I just throw her out there and hope she gets used to it.