Abstract: A method for making a groove of a precise width in a substrate material. The groove may have any cross-sectional shape. The groove is formed by initially etching the substrate material. The groove width is then measured. The measured groove width is compared to the desired groove width. Oxide is grown on the substrate in the region of the groove to adjust the width of the groove. The oxide may or may not be grown with the original etchant mask left on the substrate. Depending on whether it is desired to increase or decrease the groove width, the oxide is or is not removed. The process for increasing or decreasing groove width may be repeated any number of times as necessary to achieve a proper groove width. A number of grooves may be formed using these processes. For many applications, the groove will be covered with a plate or other type of cap to define a channel as used in flow restrictors.