Try this
XmlDocument xmlDoc = new XmlDocument();
XmlElement rootElem = xmlDoc.CreateElement("xml");
XmlElement field = xmlDoc.CreateElement("field");
field.SetAttribute("value", "95010");
field.SetAttribute("name", "ORDERNUMBER");
rootElem.AppendChild(field);
xmlDoc.AppendChild(rootElem);
xmlDoc.Save("output.xml");
it results
<field value="95010" name="ORDERNUMBER" />