Document and Entity Information - shares	3 Months Ended
	Dec. 31, 2020	Feb. 05, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Registrant Name	AMTECH SYSTEMS, INC.
Entity Central Index Key	0000720500
Current Fiscal Year End Date	--09-30
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		14,141,122
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	0-11412
Entity Tax Identification Number	86-0411215
Entity Address, Address Line One	131 South Clark Drive
Entity Address, City or Town	Tempe
Entity Address, State or Province	AZ
Entity Address, Postal Zip Code	85281
City Area Code	480
Local Phone Number	967-5146
Entity Interactive Data Current	Yes
Entity Incorporation, State or Country Code	AZ
Document Quarterly Report	true
Document Transition Report	false
Trading Symbol	ASYS
Title of 12(b) Security	Common Stock, par value $0.01 per share
Security Exchange Name	NASDAQ