Elasticsearch exclude bool "term" from getting highlighted

I have the following elastic search query with query string that should match all the fields and term query should match the respective fields given below. I want only the query_string to be part of the highlight. When i use required_field_match it highlights only the term "email" on the channel field. without required_field_match it matches "email" and query_string on all the fields which i dont want. Can you let me know how to exclude "channel" field from highlight ?

 {
   "query":{
      "bool":{
         "must":[
            {
               "term":{
                  "channel":"email"
               }
            },
            {
               "query_string":{
                  "query":"\"payment type\"",
                  "default_operator":"AND"
               }
            }
         ]
      }
   },
   "highlight":{
      "pre_tags":[
         "<span class='highlight'>"
      ],
      "post_tags":[
         "</span>"
      ],
      "require_field_match":false,
      "fields":{
         "requestSummary":{
            "number_of_fragments":0
         },
         "emails.emailBody":{
            "number_of_fragments":0
         },
         "chatTextArray.text":{
            "number_of_fragments":0
         },
         "chatTextArray.name":{
            "number_of_fragments":0
         }
      }
   },
   "facets":{
      "channel":{
         "terms":{
            "field":"channel"
         }
      },
      "siteId":{
         "terms":{
            "field":"siteId"
         }
      },
      "closeDt":{
         "terms":{
            "field":"closeDt"
         }
      },
      "srId":{
         "terms":{
            "field":"srId"
         }
      }
   }
}

Search results:

    {
       "highlight":{
          "emails.emailBody":[
             "helps keep your information safe, visit:  http://pages.half.ebay.com/help/policy/privacy.html#toc-02 
In this <span class='highlight'>email</span>"
          ],
          "requestSummary":[
             "Change <span class='highlight'>payment</span> <span class='highlight'>type</span>"
          ]
       }
    }