It's case-insensitive by default.

From the `Force.com SOQL and SOSL Reference` on [WHERE conditionExpression](https://developer.salesforce.com/docs/atlas.en-us.soql_sosl.meta/soql_sosl/sforce_api_calls_sosl_where.htm):

> *comparisonOperator*    Case-insensitive operators that compare values.

> **Operator** =  
> **Name** Equals  
> **Description** Expression is true if the value in the specified fieldName equals the specified value in the expression. String comparisons using the equals operator are case-sensitive for unique case-sensitive fields and case-insensitive for all other fields.