The best way to make sure your players invest in character backgrounds is, in my experience, to actually use those backgrounds, and reward players that provide them. Players will not do something they don't consider worth doing.
The rewards vary from group to group. If you haven't done so already, I suggest taking notes of what kind of thing is the most interesting for each of your players: some look for a cool story, some look for roleplaying experiences and personal drama, some look for power-ups, some look for ways to do cool stuff with their characters they can brag about later, some look for some fun while not being at the center of attention. Remember, each of these is perfectly fine and everyone has a different way of having fun. It's alright if someone only cares about his kill count, as long as he's happy playing and the rest of the group is cool with him; and for the love of everything, don't "reward" such a player with a deep intricate story arc centering on him. Give him a bigger axe instead.
The next step is to actually use that information during the game. If your character values the story, have his background be a central part of a story arc. If he values his shiny magical items, make sure a powerful magic item comes up from his background and that he needs to investigate and make use of his personal story to gain it. And so on, and so forth.
This can, of course, be kind of like a dog that eats his own tail, with the DM not being able to use backgrounds for his story since his players do not have any background, and the PCs not providing background info since the DM does not reward them. However, there are three tricks to avoid that situation. First, you can talk to your players. Seriously, mature players will easily abide to your request. Second, if your players have similar interests (not that uncommon), even just one character's background "paying off" will entice the others to follow in the next campaign. And thirdly, you can offer actual, practical advantages for backgrounds in the first few adventures / campaigns you have with your group: for instance, you could give extra starting money, or a clue to an enigma, a powerful NPC's help, or even just a Good Player Cookie to "bank in" later in the adventure for some extra benefit in a certain situation. Heck, depending on your players even actual cookies could be good.
Remember, you don't need a GOOD background to start: if you have even just a vague short background story, like "I was hit and have amnesia, but I have a strange feeling I might be the son of the emperor" is enough to start providing those rewards that will make sure the rest of the players will put more effort in their backgrounds. Just make sure to reward better backgrounds with better rewards - even when the rewards themselves are incomparable, the amount of time a smile stays on the player's face afterwards is a good indicator of how "good" a reward is.