I do hope that you have met in person because HUGE amount of romance fraud comes out of Ghana. Believe me, this is why I asked because the majority of the romance fraud that I see here comes from Ghana.
Normally the scam starts with trying to establish a romantic relationship, perhaps just a friendship at first. They also may claim to be a citizen of the UK or US or wherever so that you would not suspect they have any ulterior motive. They pull at your heartstrings by telling stories of hardship or tragedy that they have suffered in their life. At some point they want to come visit. They may ask you to send money for a passport and/or plane ticket. They may tell you that they have money, perhaps even that they are wealthy, but their money is tied up or something like that, perhaps they tie it into a tragedy or something. Then the next step is when they supposedly have the passport and plane ticket, they suddenly come up with this Basic Travel Allowance or (BTA) which is supposedly to show authorities that they have enough money to fund their trip. This is a lie. There is no such thing. They ask you to send that money so they can put it into a bank account to show the authorities. This is just another method to steal money from you. Then the next part of the scam would be when they are supposed to arrive. You wait for them at the airport and they never show up. A few days go by, you get extremely worried, none of your methods of communication work, and then suddenly a "friend" or "relative" of the scammer contacts you to let you know that she has been detained/arrested by authorities for carrying something illegal, I have heard of unregistered gold and they say it would have been a gift for you (perhaps to pay you back for the money you sent). The friend or relative of the scammer then asks for you to send money to bribe or pay fines in order to have the scammer released. From there, I have not heard of how else they are able to get money out of people. Of course there are variations to the scheme, but that's pretty much how it goes.
Here is a link that you can go to for more information:
And here is another link from the government of Ghana:
Whatever you do, DO NOT send money.
If this turns out not to be a scam, you can look at the link below for all the information that you need on the visitor visa:
Essentially, he must have a valid reason for visiting, must have a way to support themselves without working illegally, must have significant ties to his home country, and must have the intent to return home.
A letter of invitation helps with some of this as it will help to show why he is coming to the U.S., how much time he will need and that perhaps he will have a place to stay so that he doesn't have to spend money. Usually you want to show that he is going just for a few weeks or so. If it is longer than that, immigration will wonder why and will become suspicious. They are almost sure to deny someone that says they want to visit for 5 or 6 months unless they have very strong evidences of everything else I listed above. But keep in mind that a letter of invitation is a small part of the process and isn't even a requirement (people mistakenly believe it is the most important) and it can sometimes be used against the applicant. For example, if the consular officer believes that the applicant will have too much support meaning that they could stay illegally in the U.S. or if there is a romantic connection, the officer would deny the visa. Sometimes it is better to not even have a letter of invitation. The most important part of a case is to have strong ties to the home country.
So your letter should state why you are inviting him and that you will provide room and board while he is here visiting.
Now as to some of the ties, he will need to show that he has significant close family at home, property not easily sold, and a good job for a good company that he has had for awhile that he would not normally abandon.
So if he is young, and without much money or any property or a good job, he would probably be denied. They would see him as a risk for staying illegal. Also, persons that are planning to travel with their spouse and children are a risk as well because some of their significant ties are actually going with them.
I mean some people have been approved with less, but I am trying to give you the idea for the best chance.
And if that fails, there are essentially three ways for him to come and none are really fast, unfortunately:
1) The K-1 fiance visa takes 6 to 9 months, but you must have met before during the last two years in order to process it. The I-129F will cost $340 plus a $350 fee for the visa processing fee. After he enters the U.S., then you have to marry and then you have to pay $1070 for the I-485 and he will have to wait about 5 to 7 months and gets another interview that you attend with him so that he can get Residency.
2) The K-3 spouse visa takes 6 to 9 months, you must be married. The I-129F will cost $340 plus $420 for the I-130, and $350 for the visa processing fee. Then after he enters the U.S., you must still file the I-485 for $1070 and wait for the marriage interview about 5 to 7 months later.
3) The CR-1 visa (or IR-1 if your marriage is more than 2 years old) takes about 1 year or so. You must be married. The fees are $420 for the I-130, $330 for the visa processing fee, $88 for an Affidavit of Support fee. But once he enters the U.S., he enters as a Resident and he does not have to file (or pay for) an I-485 nor does he have to attend an additional interview. He just gets his green card in the mail a few weeks later.
So the K-1 and K-3 are faster but generally more expensive. The CR-1 (and IR-1) are slower, but generally cheaper. And no, there is no middle-visa that he can use to enter the U.S. while that process is pending. He will most likely have to wait outside.
Here is a link to all three:
Please let me know if you have any additional questions.