Interviewers want to be assured that you will be happy and content with the role. A growing pay package may motivate you, but explaining that what drives you is not an external factor. Determine what you are looking for in a job, and explain that. Since this would be your first job, you can rely on a good story from your internships or volunteer experiences.
Example: “In my internship with Better Firm, I assisted several executives coming from mixed cultures. Working in a team and brainstorming a confluence of ideas to arrive at the optimal solution made my day. As an avid learner, I take pride in doing tasks of all sizes. Whether it was ordering tea-time snacks for breaks between presentations or scheduling client meetings, I was proactive in my approach. I get a boost of energy simply by knowing that I have given any assignment the best shot and have not let anything slip through the cracks.”