Open Photoshop and create a new document (CTRL+N). Make it 4px in width and 4px in height. Make sure to set the "Background Contents" to "Transparent".



Select the Zoom Tool (Z) and zoom all the way in (1600%). Then select the Pencil Tool.



Set the "Master Diameter" to 1px and the "Hardness" to 100%.



Start by drawing a square in the top left corner.



Continue drawing until you have filled one fourth of the canvas.



Do the same thing in the bottom right corner.



When you're done, goto "Edit" and select "Define Pattern..." from the menu.



Find a name for your new pattern and select "OK" to finish.



Done! But how do you use your pattern? It's not very difficult. Create a new document (CTRL+N) and make it 150*50px and set the "Background Contents" to white.



Then press CTRL+A to select your entire work area. Then select "Layer" - "New Fill Layer" and "Pattern".



Set a name if you want and press "OK".



In the next window you can select your pattern by selecting it in the box to the left. You can also set the scale, but I reccomend not to do that. When you're done, select "OK".



You're done! Now you can select the pattern layer and do whatever you want with it. Change the transparency, blending mode etc.