Note 13. Stock Award Plans and Stock Based Compensation

(a) Equity Incentive Plans

We maintain the Axcelis Technologies, Inc. 2012 Equity Incentive Plan (the “2012 Equity Plan”), which became effective on May 2, 2012. Our 2000 Stock Plan (the “2000 Stock Plan”) expired on May 1, 2012 and no new grants may be made under that plan after that date. However, awards granted under the 2000 Stock Plan prior to the expiration remain outstanding and subject to the terms of the 2000 Stock Plan.

The 2012 Equity Plan, as amended, reserves 6.5 million shares of common stock, $0.001 par value, for grant and permits the issuance of options, stock appreciation rights, restricted stock, restricted stock units, stock equivalents and awards of shares of common stock that are not subject to restrictions or forfeiture to selected employees, directors and consultants of the Company. The 2012 Equity Plan includes shares specifically approved by the stockholders of the Company. Shares that are not issued under an award (because such award expires, is terminated unexercised or is forfeited) revert back to the Plan. The reserve under the Plan is also increased by expirations and forfeitures of awards outstanding under the 2000 Stock Plan as of May 2, 2012.

The term of stock options granted under these plans is specified in the award agreements. Unless a lesser term is otherwise specified by the Compensation Committee of the Company’s Board of Directors, awards under the 2012 Equity Plan will expire seven years from the date of grant. In general, all awards issued under the 2000 Stock Plan expire ten years from the date of grant. Under the terms of these stock plans, the exercise price of a stock option may not be less than the fair market value of a share of the Company’s common stock on the date of grant. Under the 2012 Equity Plan, fair market value is defined as the last reported sale price of a share of the common stock on a national securities exchange as of any applicable date, as long as the Company’s shares are traded on such exchange.

Stock options granted to employees generally vest over a period of four years, while stock options granted to non‑employee members of the Company’s Board of Directors generally vest over a period of six months and, once vested, are not affected by the director’s termination of service to the Company. In limited circumstances, the Company may grant stock option awards with market-based vesting conditions, such as the Company’s common stock price, or other performance conditions. Termination of service by an employee will cause options to cease vesting as of the date of termination, and in most cases, employees will have 90 days after termination to exercise options that were vested as of the termination of employment. In general, retiring employees will have one year after termination of employment to exercise vested options. The Company settles stock option exercises with newly issued common shares.

Restricted stock units granted to employees during 2018 had both service-based vesting provisions and performance-based vesting provisions. Restricted stock units granted to employees generally vest over a service period of four years, while restricted stock units granted to non‑employee members of the Company’s Board of Directors generally vest over a service period of six months. We have granted restricted stock units to executive officers and other senior employees with performance vesting conditions, which may be subject to further service-based vesting terms. Unvested restricted stock unit awards expire upon termination of service to the Company. We settle restricted stock units upon vesting with newly issued common shares. No restricted stock was granted under either stock plan during the three year period ended December 31, 2018.

As of December 31, 2018, there were 0.6 million shares available for grant under the 2012 Equity Plan. No shares are available for grant under the 2000 Stock Plan.

As of December 31, 2018, there were 2.3 million options outstanding under the 2012 Equity Plan and the 2000 Stock Plan, collectively, and 0.8 million unvested restricted stock units outstanding under the 2012 Stock Plan.

(b) Employee Stock Purchase Plan

The Employee Stock Purchase Plan (the “Purchase Plan”) provides effectively all of our employees the opportunity to purchase common stock of the Company at less than market prices. Purchases are made through payroll deductions of up to 10% of the employee’s salary as elected by the participant, subject to certain caps set forth in the Purchase Plan. Employees may purchase the Company’s common stock at 85% of its market price on the day the stock is purchased.

The Purchase Plan is considered compensatory and as such, compensation expense has been recognized based on the benefit of the discounted stock price, amortized to compensation expense over each offering period of six months. Compensation expense relating to the Purchase Plan was approximately $0.2 million for the year ended December 31, 2018 and approximately $0.1 million for each of the years ended December 31, 2017 and 2016.

As of December 31, 2018, there were a total of 0.2 million shares reserved for issuance and available for purchase under the Purchase Plan. Less than 0.1 million shares were purchased under the Purchase Plan in each of the years ended December 31, 2018, 2017 and 2016. The Purchase Plan will expire in June 2020, unless re-approved by the Board of Directors, with approval of stockholders within twelve months thereafter.

For the purpose of valuing stock options with service conditions, we use the Black‑Scholes option pricing model to calculate the grant‑date fair value of an award. The fair values of options granted were calculated using the following estimated weighted‑average assumptions:


	Year ended December 31,
	2018*	2017*	2016
Weighted-average expected volatility	N/A	N/A	49.3% — 56.7%
Weighted-average expected term	N/A	N/A	4.7 years
Risk-free interest rate	N/A	N/A	1.1% — 2.0%
Expected dividend yield	N/A	N/A	0%

*No stock option awards were granted in 2018 and 2017.

Expected volatility—We consider a number of factors when estimating volatility for stock options granted. Our method of estimating expected volatility relies on a combination of historical and implied volatility. We believe that this blended volatility results in an accurate estimate of the grant‑date fair value of employee stock options because it appropriately reflects the market’s current expectations of future volatility.

Expected term—We calculated the weighted average expected term for stock options granted prior to July 1, 2012, using a forward looking lattice model of the Company’s stock price incorporating a suboptimal exercise factor and a projected post‑vest forfeiture rate. For stock options granted after July 1, 2012 to employees and to non‑employee members of the Company’s Board of Directors, we used the simplified method for estimating the expected life of “plain vanilla” options because we did not have sufficient exercise history to use a lattice model. We expect that we will use a lattice model once sufficient exercise history has been established. A change in the contractual life from 10 years to 7 years was made to reflect the fact that options granted after May 1, 2012 were granted under the 2012 Equity Incentive Plan, which limits option terms to seven years.

Risk‑free interest rate - The yield on zero‑coupon U.S. Treasury securities for a period that is commensurate with the expected term assumption is used as the risk‑free interest rate.

Expected dividend yield—Expected dividend yield was not considered in the option pricing formula since we do not pay dividends and have no current plans to do so in the future.

In limited circumstances, we also issue stock option grants with vesting based on market conditions, such as the Company’s common stock price, or a combination of time or market or performance conditions. The fair values and derived service periods for all grants that have vesting based on market or performance conditions are estimated using the Monte Carlo valuation method. For each stock option grant with vesting based on a combination of time and performance or market conditions, where vesting will occur if either condition is met, the related compensation costs are recognized over the shorter of the explicit service period or the derived service period.

The fair value of the Company’s restricted stock units is calculated based upon the fair market value of the Company’s stock at the date of grant.

(d) Summary of Stock-based Compensation Expense

We use the straight‑line attribution method to recognize expense for stock‑based awards such that the expense associated with awards is evenly recognized throughout the period.

The amount of stock‑based compensation recognized is based on the value of the portion of the awards that are ultimately expected to vest. We estimate forfeitures at the time of grant and revises them, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The term “forfeitures” is distinct from “cancellations” or “expirations” and represents only the unvested portion of the surrendered stock‑based award. Based on a historical analysis, a forfeiture rate of 5% per year was applied to stock‑based awards, including executive officer awards, for the years ended December 31, 2018, 2017 and 2016.

For the year ended December 31, 2018, we recognized stock-based compensation expense of $7.8 million. Stock-based compensation expense was $5.7 million and $5.2 million for the years ended December 31, 2017 and 2016, respectively. We present the expenses related to stock-based compensation in the same expense line items as cash compensation paid to our employees. For the years ended December 31, 2018, 2017 and 2016, we used restricted stock units in our annual equity compensation program.

The benefit of tax deductions in excess of recognized compensation cost is reported as a financing cash flow, rather than as an operating cash flow. Axcelis had tax deductions in excess of recognized compensation cost of $4.1 million for the year ended December 31, 2018 which resulted in a tax benefit of $0.9 million. Because we did not recognize the benefit of tax deductions in excess of recognized compensation cost due to our cumulative net operating loss position, this had no impact on our consolidated statement of cash flows as of and for the years ended December 31, 2018, 2017 and 2016.

(e) Stock Option Awards

The following table summarizes the stock option activity for the year ended December 31, 2018:


				Weighted
		Weighted		Average
		Average		Remaining	Aggregate
		Exercise		Contractual	Intrinsic
	Options	Price		Term	Value
	(in thousands)			(years)	(in thousands)
Outstanding at December 31, 2017	2,576	$	7.91
Granted	—		—
Exercised	(273)		6.34
Canceled	(5)		10.04
Expired	(13)		2.46
Outstanding at December 31, 2018	2,285	$	8.12	2.32	$	22,128
Exercisable at December 31, 2018	2,116	$	7.79	2.21	$	21,174
Options Vested or Expected to Vest at December 31, 2018(1)	2,282	$	8.11	2.35	$	22,109

(1) In addition to the vested options, we expect a portion of the unvested options to vest at some point in the future. Options expected to vest is calculated by applying an estimated forfeiture rate to the unvested options.

The total intrinsic value, which is defined as the difference between the market price at exercise and the price paid by the employee to exercise the options, for options exercised during the years ended December 31, 2018, 2017 and 2016 was $4.1 million, $39.7 million and $2.5 million, respectively.

The total fair value of stock options vested during the years ended December 31, 2018, 2017 and 2016 was $1.9 million, $3.1 million and $3.9 million respectively. The weighted average grant-date fair value of options granted for the year ended December 31, 2016 was $5.75. As of December 31, 2018, there was $0.7 million of total forfeiture‑adjusted unrecognized compensation cost related to non‑vested stock options granted under the 2012 Equity Incentive Plan and the 2000 Stock Plan. That cost is expected to be recognized over a weighted‑average period of 0.7 years.

(f) Restricted Stock Units and Restricted Stock

Restricted stock units represent the Company’s unfunded and unsecured promise to issue shares of the common stock at a future date, subject to the terms of the Award Agreement issued under the 2012 Equity Incentive Plan. Restricted stock unit awards granted in 2018 included time vested share awards and awards with performance vesting conditions. No restricted stock was granted, or vested, during the years ended December 31, 2018, 2017 and 2016. The fair value of a restricted stock unit and restricted stock award is charged to expense ratably over the applicable service period. The purpose of these awards is to assist in attracting and retaining highly competent employees and directors and to act as an incentive in motivating selected employees and directors to achieve long-term corporate objectives.

Changes in the Company’s non‑vested restricted stock units for the year ended December 31, 2018 is as follows:


		Weighted-Average
		Grant Date Fair
	Shares/units	Value per Share
	(in thousands)
Outstanding at December 31, 2017	617	$	14.93
Granted	459		22.41
Vested	(245)		15.90
Forfeited	(11)		17.78
Outstanding at December 31, 2018	820	$	18.76

The weighted average grant-date fair value of restricted stock units granted for the years ended December 31, 2018, 2017 and 2016 was $22.41, $20.72 and $9.73, respectively. Most restricted stock units provide for net share settlement to cover the employee’s personal income tax withholding obligations on vesting of the employee’s restricted stock units. Vesting activity above reflects shares vested before net share settlement. As of December 31, 2018, there was $11.7 million of total forfeiture‑adjusted unrecognized compensation cost related to non‑vested restricted stock units granted under the 2012 Equity Incentive Plan. That cost is expected to be recognized over a weighted‑average period of 2.7 years.