Method of manufacturing window, window manufactured by the method of manufacturing window, and display device including the window

A method of manufacturing a window, the method comprising:

• preparing a first preliminary glass substrate that does not contain Li+ ions and contains Na+ ions;
• providing a first strengthening molten salt to the first preliminary glass substrate to form a second preliminary glass substrate, wherein the first strengthening molten salt comprises NaNO3 and at least one of KNO3, KCl, or K2SO4, wherein with respect to a total weight of the first strengthening molten salt, NaNO3 is provided in an amount of about 20 to 40 percentages by weight (wt %), and the at least one of KNO3, KCl, or K2SO4 is provided in an amount of about 60 to 80 wt %, and wherein the first strengthening molten salt is provided at a temperature of about 450 to 500° C. for a period of about 3 to 9 hours;
• providing heat to the second preliminary glass substrate at a temperature of about 400 to 500 degrees in Celsius (° C.) for a period of about 3 to 7 hours to form a third preliminary glass substrate;
• and
• providing a second strengthening molten salt to the third preliminary glass substrate to form a window comprising a glass substrate, wherein the second strengthening molten salt does not contain NaNO3 and contains at least one of KNO3, KCl, or K2SO4, and is provided at a temperature of about 380 to 420° C. for a period of about 1 hour to 2 hours,
• wherein the window comprises a compressive stress layer having a compressive stress of about 742 megapascals (MPa) or less as measured through a method of ASTM C770-16, and the compressive stress layer has a thickness of about 80 to 100 micrometers (μm) and wherein with respect to 100% of a total thickness of the glass substrate, the thickness of the compressive stress layer is about 13 to 21%.