Birkat Yotzer Or is praise to Hashem, “Who constantly renews the acts of creation daily.” Over time, liturgy was added to this berachah; there is a special poem for weekdays and a special poem for Shabbat. Not only do we praise Hashem, but even angels and Seraphim, which are sublime spiritual creations, bless, praise, glorify, sanctify, revere, and proclaim the sovereignty of His Name, Blessed Be He, and say, “Kadosh, kadosh, kadosh, Hashem Tzevakot, melo kol ha’aretz kevodo” (“Holy, holy, holy, is Hashem, Master of Hosts, the whole world is filled with His glory”), and “Baruch kevod Hashem mimekomo” (“Blessed is the glory of Hashem from His place”). Their praise is included in Birkat Yotzer HaMe’orot.
The Rishonim disagree as to whether an individual may say Kedushat HaMalachim (“Kadosh, kadosh, kadosh…”) in Birkat Yotzer. There are those who say that these verses are matters of sanctity, just like Kedushah in Chazarat HaShatz, and therefore, whoever prays individually is prohibited from reciting them (Ran, Rabbeinu Yerucham). On the other hand, others say that this is not an ordinary Kedushah, but rather a description of how angels sanctify Hashem’s Name, and therefore, even an individual can say the verses (Talmidei Rabbeinu Yonah, Rosh). In order to avoid uncertainty, it is best for a person praying individually to recite the verses of Kedushah as if reading from the Torah, in the melody of cantillation signs, because according to all opinions, an individual is allowed to learn them, and in that way he also fulfills his obligation (Terumat HaDeshen, Shulchan Aruch 59:3). It is not necessary to know the exact cantillation signs (ta’amei hamikra); rather, the main idea is that he tries to recite the words somewhat in cantillation to appear as if he is reading from the Prophets (Nevi’im).
Some poskim rule that the congregation must respond Amen upon hearing the chazan recite Birkot Keriat Shema (Rosh), whereas others maintain that Amen may not be answered, so as not to interrupt between the berachot and Keriat Shema (Talmidei Rabbeinu Yonah, based on the Rambam).
In practice, the minhag of the Sephardim is that one who is reciting Birkot Keriat Shema does not answer Amen after the chazan, for that is considered to be an interruption (hefsek). In order not to encounter uncertainty, l’chatchilah it is proper to conclude the berachah along with the chazan or slightly afterwards, and in that way, according to all opinions, it is unnecessary to respond Amen. In any case, even one who finishes before the chazan does not respond Amen.
The minhag of the Ashkenazim is to answer Amen after Birkat Yotzer HaMe’orot in Shacharit, and after both Birkot HaMa’ariv Aravim and Ga’al Yisrael in Ma’ariv. However, regarding the berachah immediately before Keriat Shema, one should try to conclude it with the chazan or slightly after him, so that it will not be necessary to answer Amen and cause an interruption between the berachah and Keriat Shema. Nevertheless, one who already finished reciting the berachah and heard the chazan say it must answer Amen (Mishnah Berurah 59:24-25; Kaf HaChaim 26:28).