QuickLinks -- Click here to rapidly navigate through this document

EXHIBIT 5.1

Gadsby Hannah LLP
225 Franklin Street
Boston, MA 02110

September 2, 2003                        

Ibis Technology Corporation
32 Cherry Hill Drive
Danvers, Massachusetts 01923

Re:

Registration Statement on Form S-3

Ladies and Gentlemen:

        This opinion is furnished to you in connection with the legality of up to 2,000,000 shares of common stock, $.008 par value (the "Common Stock"), to be issued pursuant to the Registration Statement on Form S-3 (the "Registration Statement") being filed today by Ibis Technology Corporation, Inc., a Delaware corporation (the "Company"), with the Securities and Exchange Commission (the "Commission") under the Securities Act of 1933, as amended (the "Securities Act").

        We have examined the Registration Statement, including the exhibits thereto, and such other documents, corporate records and instruments, and have examined such laws and regulations as we have deemed necessary for purposes of rendering the opinions set forth herein.

        In our examination of such legal documents, we have assumed the genuineness of all signatures, the legal capacity of all signatories who are natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as copies and the authenticity of the originals of such latter documents. Insofar as this opinion relates to factual matters, we have assumed with your permission and without independent investigation that the statements of the Company contained in the Registration Statement are true and correct as to all factual matters stated therein.

        We have relied as to certain matters on information obtained from public officials, officers of the Company, and other sources believed by us to be reliable, assumptions which we have not independently verified. We are expressing no opinion herein as to the application of or compliance with any federal or state law or regulation to the power, authority or competence of any party other than the Company.

        We are opining herein solely with respect to the federal laws of the United States and the state laws of the Commonwealth of Massachusetts. To the extent that the laws of any other jurisdiction govern any of the matters as to which we are opining herein, we have assumed that such laws are identical to the state laws of the Commonwealth of Massachusetts, and we are expressing no opinion herein as to whether such assumptions are reasonable or correct.

        Our opinions below are qualified to the extent that they may be subject or affected by (i) applicable bankruptcy, insolvency, reorganization, moratorium, usury, fraudulent conveyance or similar laws affecting the rights of creditors generally, (ii) statutory or decisional law concerning recourse by creditors to security in the absence of notice or hearing, (iii) duties and standards imposed on creditors and parties to contracts, including, without limitation, requirements of good faith, reasonableness and fair dealing, and (iv) general equitable principles. Furthermore, we express no opinion as to the availability of any equitable or specific remedy, or as to the successful assertion of any equitable defense, upon any breach of any agreements or documents or obligations referred to therein, or any other matters, inasmuch as the availability of such remedies or defenses may be subject to the discretion of a court. We express no opinion as to the enforceability of any provision (a) to the

effect that rights and remedies are not exclusive, that any right or remedy is cumulative and may be exercised in addition to any other right or remedy and does not preclude recourse to one or more other rights or remedies, (b) requiring the payment of penalties, consequential damages or liquidated damages, (c) relating to the effect of invalidity or unenforceability of any provision on the validity or enforceability of any other provision, or (d) that indemnifies any person against damages arising from its own negligence or misconduct.

        Based upon and subject to the foregoing, we are of the opinion that:

        1.     With respect to the Common Stock, when (i) specifically authorized for issuance by the Company's Board of Directors or an authorized committee thereof (the "Authorizing Votes"), (ii) the Registration Statement has become effective under the Securities Act, (iii) the terms of the sale of the Common Stock have been duly established in conformity with the Company's Articles of Organization and By-laws and assuming such terms and sale do not violate any applicable law or result in a default under or breach of any agreement or instrument binding on the Company and comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company, (iv) the Common Stock has been issued and sold as contemplated by the Registration Statement, and (v) the Company has received the consideration provided for in the Authorizing Votes and such consideration per share is not less than the par value per share of the Common Stock, the Common Stock will be validly issued, fully paid and non-assessable.

        This opinion is to be used only in connection with the offer and sale of the Common Stock while the Registration Statement is in effect and may not be used, quoted or relied upon for any other purpose nor may this opinion be furnished to, quoted to or relied upon by any other person or entity, for any purpose, without our prior written consent.

        Please note that we are opining only as to the matters expressly set forth herein, and no opinion should be inferred as to any other matters. This opinion is based upon currently existing statutes, rules, regulations and judicial decisions as of the date hereof, and we disclaim any obligation to advise you of any change in any of these sources of law or subsequent legal or factual developments which might affect any matters or opinions set forth herein.

        We hereby consent to the filing of this opinion with the Commission as an exhibit to the Registration Statement in accordance with the requirements of Item 601(b)(5) of Regulation S-K under the Securities Act and to the use of this Firm's name therein and in the related Prospectus under the caption "Validity of Securities." In giving such consent, we do not hereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission.

Very truly yours,

/s/ Gadsby Hannah LLP

GADSBY HANNAH LLP

2

QuickLinks

EXHIBIT 5.1