A method and apparatus to modify the surface structure of a silicon substrate or deposited silicon layer in a controllable manner using gas only in an atmospheric environment, suitable for making photovoltaic (PV) wafer based devices. The method and apparatus comprising the steps of disposing the substrate or deposited layer on a moveable carrier; pre-heating the substrate or deposited layer; and moving the substrate or deposited layer for etching through an atmospheric reactor; under an etchant delivering module inside the reactor and applying at least one etchant in gas form at a controlled flow rate and angle to the substrate or deposited layer in the reactor, wherein the at least one etchant gas is selected from the group comprising fluoride-containing gases and chlorine-based compounds. The technical problem that has been solved is the provision of a high throughput dry etching method at atmospheric pressure. This apparatus does not require plasma to aid the etching process using fluoride-containing gases and chlorine-based compounds and is performed at open atmospheric pressure. The use of elemental fluorine, which has a significantly lower bonding energy than any of the other etchants used to date, allows for the use of much lower power energy source to crack the elemental fluorine in to its etching radicals. The apparatus enables the delivery of a predetermined texture finish by controlling the flow rate of the gasses which are bombarded on the surface of the substrate.