Showerhead and method for manufacturing the same

A method for manufacturing a showerhead, comprising:

• forming a hole in a disk-shaped member, which has a high-frequency conductor embedded therein, in a direction of a thickness of the disk-shaped member to expose a portion of the conductor;
• connecting an electrode terminal portion to the conductor exposed at a bottom of the hole;
• fitting a glass preform in a form of a doughnut to the electrode terminal portion;
• fitting to the electrode terminal portion a cylindrical member having a first end portion facing the conductor and a second end portion facing away from the first end portion, the second end portion's outer diameter being smaller than the first end portion's outer diameter, the second end portion's inner diameter being larger than the first end portion's inner diameter;
• fusing the glass preform;
• pressing the cylindrical member toward the conductor until the fused glass preform protrudes into a gap between the second end portion's outer diameter and an inner wall of the hole and a gap between the diameter-increased portion and an outer peripheral surface of the electrode terminal portion;
• and solidifying the fused glass preform to seal the cylindrical member.