Billerica-based Entegris Inc. has a deal to buy ATMI Inc. for $1.15 billion. That would combine two key semiconductor industry suppliers to create a leader in advanced process materials, contamination control, and wafer handling, Entegris said. It expects to save about $30 million a year and immediately boost its adjusted earnings per share. The deal is subject to regulatory and shareholder approvals. Entegris would pay $34 in cash per ATMI share — a 26 percent premium over the company’s Monday closing stock price. Shares of Danbury, Conn.-based ATMI rose 25.5 percent to $33.79 on Tuesday.