Method and apparatus for depositing a material layer originating from process gas on a substrate wafer

An apparatus for depositing a material layer originating from process gas on a substrate wafer, comprising

• a reactor chamber, which is delimited by an upper dome and a lower dome and a side wall;
• a rotatable susceptor for holding the substrate wafer during deposition of the material layer;
• a preheating ring surrounding the susceptor, the preheating ring having a circular central opening within which the rotatable susceptor rotates;
• a liner, on which the preheating ring is supported in a centered position wherein a gap D having a uniform width is present between the preheating ring and the susceptor;
• and
• a spacer between the liner and the preheating ring, the spacer keeping the preheating ring in a centered position and providing a vertical distance Δ between the preheating ring and the liner, the spacer comprising balls embedded partly in recesses in the preheating ring and partly in the liner, which enable a relative radial movement between the preheating ring and the liner due to thermal expansion, each ball lying in a elongated recess extending in a radial direction.