(JP10303443-A)      A solar cell production process involves immersing a silicon substrate either (a) in an aqueous etching solution of hydrofluoric acid, nitric acid and an etching rate adjuster containing phosphoric acid or a water soluble lower carboxylic acid to form tiny projections and recesses in the substrate surface; or (b) in an aqueous etching solution of hydrofluoric acid, nitric acid and an etching rate adjuster containing phosphoric acid or a water soluble 3-6C carboxylic acid and then in an aqueous solution of alkali metal hydroxide and isopropyl alcohol. Also claimed are (i) a solar cell with a single crystal or polycrystalline substrate having a continuous spherical surface recess with a depth to diameter ratio of 0.2-0.45; and (ii) a solar cell as in (i) in which the substrate surface also has tiny pyramidal projections and recesses. Further claimed are semiconductor production units including an etching device which contains the etching solution described in (b), the units having a detector for detecting the nitric acid concentration in the solution or a substrate holder for holding one or more silicon substrates in the upright position during etching.    ADVANTAGE -   The process employs a wet etching method for high productivity manufacture of silicon solar cells with tiny projections and recesses which provide a high light-confining effect.    (US6156968-A)      A solar cell production process involves immersing a silicon substrate either (a) in an aqueous etching solution of hydrofluoric acid, nitric acid and an etching rate adjuster containing phosphoric acid or a water soluble lower carboxylic acid to form tiny projections and recesses in the substrate surface; or (b) in an aqueous etching solution of hydrofluoric acid, nitric acid and an etching rate adjuster containing phosphoric acid or a water soluble 3-6C carboxylic acid and then in an aqueous solution of alkali metal hydroxide and isopropyl alcohol. Also claimed are (i) a solar cell with a single crystal or polycrystalline substrate having a continuous spherical surface recess with a depth to diameter ratio of 0.2-0.45; and (ii) a solar cell as in (i) in which the substrate surface also has tiny pyramidal projections and recesses. Further claimed are semiconductor production units including an etching device which contains the etching solution described in (b), the units having a detector for detecting the nitric acid concentration in the solution or a substrate holder for holding one or more silicon substrates in the upright position during etching.    ADVANTAGE -   The process employs a wet etching method for high productivity manufacture of silicon solar cells with tiny projections and recesses which provide a high light-confining effect.